Is time real?

[Mu naught]

This is a troubling question for me. Certainly there exists in our universe sequences of events which may or may not be undone easily. For example, I can walk 31 steps forward, then walk 31 steps backward and return to where I was. However, I can not easily unmix milk from my coffee after I have poured it in, though I shouldn't think it is impossible.

This isn't really what we mean when we think of the concept of "time". A simple sequence of events is something we can do or undo, but no one here thinks they can return to yesterday, or last year. When we think of time, we think of us somehow floating along in a bubble that we call the present, and behind us is the past and before us the future. We can not look forward into the future, but we can look behind us into the past and around us inside the bubble at the present. I personally suspect that this is really an illusion, and that the concepts of "past' and "future" have no physical meaning, but trying to prove it in any concrete way I think is beyond my scope for now. Any thoughts on this topic?

[ConradDJ]

I think the problem we run into in trying to understand time is that both in the physical world and in everyday life we're dealing with two very different notions of time. And to me it's nonsense to call either aspect of time an "illusion"... since if something so basic to all our experience of the world is illusory, what basis do we have left for deciding whether anything is "real"?

The problem is made very difficult by the fact that one of the two aspects of time -- call it clock-time or calendar-time -- is very well conceptualized, again both in physics and in everyday life. The other aspect -- the time we actually experience in this ongoing present moment we call "now" -- is almost unconceptualized, even though it's the most familiar thing in the world to us.

To me, what's illusory in this situation is that "time" refers to something simple. On the one hand we're very much at ease with clock-time as a conceptual structure. We picture time laid out in front of us, from the beginning of the universe on into the future, and mark off the points when certain things happen, and measure the distance between them. (It turns out that in Relativity, time is connected with space in a very counter-intuitive way, but we're still dealing with a classical continuum, so we tend to overlook that complication.)

On the other hand, we're so familiar with the way things happen in the present moment that we tend to assume this fits nicely into our picture of clock-time. But the "present" we experience is nothing like a "point in time" -- like the frozen instant captured in a snapshot. Of course "now" has something to do with the time I see on the clock, but to try to conceptualize it as a "moving point" on the time-line doesn't do it justice at all. It's more like a continuously evolving event in which a factual situation we inherit from the past opens up certain possibilities, such that present interaction with things can "choose" certain of these possibilities and reject the rest, and so change the possibility-structure inherent in the situation. This aspect of time as an ongoing interactive selection process that evolves possibilities seems to me to have a strong resemblance to aspects of Quantum theory. But we have yet to work out what's involved in this aspect of time, so it seems mysterious and maybe unapproachable.

Heidegger made some real progress with this issue in his unfinished Being and Time. And Bergson at least pointed out the radical difference between these two aspects of time. But the issue hasn't even been approached in physics -- even though I think there are strong indications both in the Quantum theory and in Relativity that it's important. I agree with Lee Smolin's guess that the key to fundamental physics will be a better understanding of time, specifically the aspect that's essentially different from space. But many other physicists are willing to accept the traditional time-continuum picture and treat the actual happening of the present moment as an "illusion" produced by human consciousness. And many philosophers have misread Relativity as "proving" that time and space are essentially the same.

[Jack21222]

It's a dimension, just as real as "up."

[ConradDJ]

It's a dimension, just as real as "up."

That's definitely one of the things it is.

Up and down are different, because of gravity. Past and future are different in a different way, because something definite has happened in the past, that's brought us to where we are now, and the future is only possible. To some extent it's predictable, but it hasn't happened yet.

The easy aspect of time is laying this out like a map, with the past "back there" and the future "in front of us". We can refer to last Wednesday or next Wednesday with equal clarity.

The hard part about time is understanding what it means "to happen"... how this "present moment" (which is all we've ever experienced) actually works, to make new facts out of possibilities. As always, we're dealing both with a subjective experience and with something physically real. We have a lot of research to work with both in psychology and in Quantum physics. But I don't think we yet have adequate concepts for describing this "process"... largely because it's very foreign to the orientation of the philosophical tradition. And because happening is so familiar to us that we tend just to take it for granted.

[GeorgCantor]

This is a troubling question for me. Certainly there exists in our universe sequences of events which may or may not be undone easily. For example, I can walk 31 steps forward, then walk 31 steps backward and return to where I was. However, I can not easily unmix milk from my coffee after I have poured it in, though I shouldn't think it is impossible.

This isn't really what we mean when we think of the concept of "time". A simple sequence of events is something we can do or undo, but no one here thinks they can return to yesterday, or last year. When we think of time, we think of us somehow floating along in a bubble that we call the present, and behind us is the past and before us the future. We can not look forward into the future, but we can look behind us into the past and around us inside the bubble at the present. I personally suspect that this is really an illusion, and that the concepts of "past' and "future" have no physical meaning, but trying to prove it in any concrete way I think is beyond my scope for now. Any thoughts on this topic?



I agree with Rovelli that time is a semi-classical concept. What would that mean for space? Well, the same. Both are not fundamental constituents of reality(and not real in the ordinary sense) but emergent manifestation of the way underlying fundamental constituents(strongs, loops, ???) interact.


http://discovermagazine.com/2007/jun/in-no-time/article_view?b_start:int=0&-C=

[apeiron]

Up and down are different, because of gravity. Past and future are different in a different way, because something definite has happened in the past, that's brought us to where we are now, and the future is only possible.

Good points Conrad. Space is our way of modelling/measuring stasis or the location of things, time is our way of modelling/measuring flux or change. Space is thus defined by its available physical symmetries (you can go one direction and then return the other way) while time is defined instead by its asymmetry - the changes that make a lasting change.

It all gets confused in physics models because both Newton's mechanics and Einstein's relativity treat change as a symmetric operation (the equations allow the world to be run in either direction). It is only thermodynamics that has the extra constraints to give time an arrow in physical theory. Thermodynamics introduces the notion of a thermodynamic gradient of entropy down which a system must slip, and cannot return. Although the Boltzmann ensemble interpretation of thermodynamics then re-introduces locally symmetric processes and once again time becomes a dimension that seems reversible (the ergodic hypothesis).

[binbots]

Is it safe to say that only the past exist. The present is never present, always in the past. The future does not exist until it becomes past. But then again wouldn't the past just be what we beleive has happened. WOW, someone has got to figure out this whole time business.

[Mu naught]

I've thought of time in the following way in the past. To simplify things a bit, imagine a two dimensional universe as simply a flat plane, you can call it the standard (x,y) plane.

Imagining time as a dimension, then time would constitute the z axis, or we could label it the 't' axis for simplicity. Now, if you think of this (x,y) plane as representing space, and the t axis representing time, then the flow of time, or arrow of time, is represented by this plane moving along the t axis in one direction. In this sense, your ultimate position in "spacetime" is always changing. Your (x,y) position may remain constant, but your position given by (x,y,t) is always changing because your position on the 't' axis is always changing.

I can instantly recognize flaws in this analogy though, which tie into flaws in the way we define time in the real world. The major flaw being, that the "rate of time" in such a scenario is given by the velocity the (x,y) plane is traveling along the 't' axis, and velocity is given as a function of time... therefore, the definition of time in such a universe is cyclical!

I find the same problem to be true in the real world. We always measure time by the motion of things. Either the motion of gears in a clock, the oscillation of a cesium atom, or a number of other ways - we can not measure time except by measuring motion. An the measure of motion is really the measure of the rate of change of a position - or a velocity. So even in the real world, the definition of time is cyclical, at least the way we measure it!

The fact that, I for one, can not think of a non-cyclical way of defining time leads me to the idea that time is not a real thing, but some sort of abstraction we humans have invented. I hope I have made my idea clear, if not I will try to explain it in another way.

[apeiron]

The fact that, I for one, can not think of a non-cyclical way of defining time leads me to the idea that time is not a real thing, but some sort of abstraction we humans have invented. I hope I have made my idea clear, if not I will try to explain it in another way.

If you take the thermodynamic view, then you can measure the average temperature of the universe - the cosmic background radiation - and use this as your clock. Looking around at different point's of the universe's history, this is one thing that will change for observers "at rest" and so can define the current "now" as different from previous or future "nows".

[Galteeth]

Either action still respects the arrow of time. Your backward steps that have "undone" your actions don't undue the loss of free energy that came from your forward steps, and in fact created their own loss of free energy.

[Mu naught]

If you take the thermodynamic view, then you can measure the average temperature of the universe - the cosmic background radiation - and use this as your clock. Looking around at different point's of the universe's history, this is one thing that will change for observers "at rest" and so can define the current "now" as different from previous or future "nows".

I really like this idea, but I think it only works in an open universe. In a flat or closed universe, there should be points in "time" where the average temperatures are equal... it's definitely a fascinating way of thinking about time though, or at least a way of defining or measuring it.

[pallidin]

Time only exists with change. Without change, time can not exist.

[apeiron]

I really like this idea, but I think it only works in an open universe. In a flat or closed universe, there should be points in "time" where the average temperatures are equal....

By the thermodynamic view, if gradients don't exist, then yes, time also ceases effectively.

An equilibrium state such as an ideal gas or the heat death universe is an example of a realm where change becomes no change. There is no gradient even though there is still dynamism. So no change despite still continual change. And thus no real time in the sense of a still developing history. Development has halted.

[madness]

By the thermodynamic view, if gradients don't exist, then yes, time also ceases effectively.

An equilibrium state such as an ideal gas or the heat death universe is an example of a realm where change becomes no change. There is no gradient even though there is still dynamism. So no change despite still continual change. And thus no real time in the sense of a still developing history. Development has halted.

Are you implying that time does not physically exist without a thermodynamic gradient? I would prefer the view that time is something mentally constructed, that needs a thermodynamic gradient in order to function the way it does.

[ConradDJ]

Are you implying that time does not physically exist without a thermodynamic gradient? I would prefer the view that time is something mentally constructed, that needs a thermodynamic gradient in order to function the way it does.

When you speak of time as a mental construct, I think you’re referring to our moment-by-moment experience of things happening. As distinct from the time-continuum pictured in physics, on which one would map a thermodynamic gradient.

Because the time-continuum is so fundamental in physics, there’s a strong tendency to assume that’s the only aspect of time that’s relevant. In order to push the “happening” aspect of time out of physics, it’s often treated as something our minds do, somehow, independently of the physical world. Looked at in a broader scientific context I think this makes no sense at all – but it serves the purpose of letting physicists treat time as something simple.

But the “happening” aspect of time is hard to dismiss in Quantum theory. And even in Relativity, there’s an important difference between the time-continuum and the proper time of any observer. To illustrate:
I've thought of time in the following way in the past. To simplify things a bit, imagine a two dimensional universe as simply a flat plane, you can call it the standard (x,y) plane.

Imagining time as a dimension, then time would constitute the z axis, or we could label it the 't' axis for simplicity. Now, if you think of this (x,y) plane as representing space, and the t axis representing time, then the flow of time, or arrow of time, is represented by this plane moving along the t axis in one direction.


Here we’re looking at the universe as if we could stand outside of space and time and observe it globally, like an object we can set on our desks and observe from all angles. Time is then pictured as another dimension of space – and as our calendars and historical time-lines attest, the is a very useful way to think about time.

However, this familiar picture misrepresents the way space and time are combined to make spacetime in Relativity. In this picture – assuming a “flat” spacetime – the “distance” between two events in spacetime would be the square root of x2+y2+t2, whereas in Relativity the invariant interval is the square root of x2+y2 minus t2. That is, we’re in Minkowski’s spacetime, not Newton’s.

The structure of Relativistic spacetime is very difficult to picture “from the outside”... but it’s not hard to see “from inside” – i.e. from my own point of view as an observer. What the minus-sign means is just that my present moment now contains events that are happening right around me, as well as distant events that happened some time ago. When I look at a star, my “now” includes an event on the surface of that star that's as distant from me in time as it is in space. Because of the minus-sign, the space-distance and time-distance offset each other.

There’s nothing “subjective” about this situation – we’re talking about the physical structure of spacetime, not a “mental construction”. But Relativity tells us that distant observers do not share the same “now” – the present moment each of us lives in is an essentially local aspect of the structure of time. So even though for some purposes it makes sense to map the universe on a time-line, as if it were all “moving forward in time” as a single entity, that’s not how physical time actually operates. The physical context of my “now” is made up of events that just happened right around me, and the events “on my past light-cone” that are equidistant in space and time. Likewise what happens here and now is relevant only to what can happen close by and to possible events “on my future light-cone.”

So the physical structure of happening, in our world, is not at all like an x,y plane “moving” along the z-axis. It’s more like a complex web of events influencing other events nearby and far away. There is definitely still a “direction” of time, in a Relativistic universe – no event ever influences an event in the past. But the time of each observer is physically distinct from that of other observers.

My point is that even in Relativity – where we can still imagine what happens in the world in a classically deterministic way – the temporal structure of happening is complex. The global time-continuum is only one aspect of the physical structure of time. What we observe in our own local present moments reflects a different aspect of physical time, not something mysteriously created by our minds.

[madness]

What I really meant is that dynamic time rather than the "frozen river" time is a mental construction. And physical theories modelling spacetime as manifolds etc. are also mental constructions in a sense - they are abstract models designed to generalise our direct experience (observations). I do not really believe space or time exist except as a way to categorise and understand objects and events.

[octelcogopod]

I think that there are two notions of time.
One is the mental one, which is a side effect of consciousness and memories, and the other one is physical time.

I believe physical time is a side effect of the inner workings of quantum physics, and in general how the universe is built.
The universe can only have one state, and that is the current state it is in.
This state just is, it doesn't have a time property except the inner workings that define why and how things can move, and events can happen over a period.

So I guess if we want to know why the universe is changing, and why things move around, we will have to create the math and physical models that describe this based on observation of quantum particles, and whatever else is out there.

Also, since the universe is in a constant single state, the past and the future do not exist physically.

Or at least, that's my take on it.

[apeiron]

What the minus-sign means is just that my present moment now contains events that are happening right around me, as well as distant events that happened some time ago. When I look at a star, my “now” includes an event on the surface of that star that's as distant from me in time as it is in space. Because of the minus-sign, the space-distance and time-distance offset each other.

There’s nothing “subjective” about this situation....

Good explanation. The interesting thing to me is that really relativity means we should be taking the relativistic story as the baseline, no time, equilibrium state. So in some important sense, time was in a different state during the early big bang, before the Higgs transition that created located massive particles moving slower than light.

Before the Higgs mechanism kicked in with sufficient expansion/cooling, all particles existed only relativistically, moving at the speed of light. What it actually means to say electrons or quarks even "existed" in that environment seems debateable. There would be no locality as such. The time-like separation between locations would shrink to zero - which is why a particle going at the speed of light like a photon is said to experience no time.

In a hot relativistic realm, the entire system would be in communication at the same rate, and so there would be no gradient to define an arrow of time locally.

However once mass condenses out of the quark-gluon soup, suddenly you have lumps of mass travelling slower than light speed. These lumps can slow all the way down to be "at rest" even. And lumps at rest would thus maximise a local potential for temporality. They would create a new kind of gradient, a gap that exists between their inertial position and their potential to interact at lightspeed via EM and gravity in particular.

So we can see that once time is broken down into the notion of changes that are changes (rather than merely the milling non-change of a dynamic equilibrium), and then further broken down to a model based on entropic gradients, time becomes an emergent property of systems. And it can come in a variety of grades.

In a relativistic realm, all actions between locations are happening at the same rate - lightspeed - so it is a rather vanilla notion of "time passing".

Then when mass condenses out, suddenly there are lumps of matter going slower than light, and so introducing a time lag between their physical actions (mechanically bumping about) and their energetic exchanges (radiating photons, communicating slow shifts in position as lightspeed changes in the gravity fields associated with their mass).

Time immediately becomes richer because there is a gradient, a game of catch-up to be played. A local component is introduced and there is no longer just a vanilla relativistic equilibrium realm.

It could be that following this approach, we could argue for a hierarchy of temporal richness. So first the step up in complexity that comes with the condensation of massive particles. Then further steps up with the more complicated dissipative structures we are talking about when we deal with life and mind.

But anyway, the key thing here is that there is already in the cosmological story a clear phase transition in the nature of "time". At the point mass condensed out, a new kind of locality was invented. Time visibly passes for objects able to move slower than light because of the gap between their motions "in space" and their energetic exchanges.

Newton's model of time arose from the wrong assumption - that the natural baseline for measuring time was from the point of view of an observer at rest. Relativity fixed that by making the baseline dynamic - the lightspeed realm - and we can instead measure time in terms of deviations from that natural rate (with "at rest" being the greatest possible deviation, the one that creates the largest out-of-equilbrium gradient to drive change, locally).

[apeiron]

Are you implying that time does not physically exist without a thermodynamic gradient? I would prefer the view that time is something mentally constructed, that needs a thermodynamic gradient in order to function the way it does.

It is always a matter of modelling, and the map is not the territory, just the map. So we could have various views of what time or space are, chosing the ones most suited to our current purposes.

Having said that, the Newtonian notion of time is very simple and unrealistic. The thermodynamic view seems richer because it is based on a self-organising systems model of reality.

So what I was saying is that time is generally agreed to be our way of measuring change. And change in turn must depend on the existence of a gradient. So with no gradient, a system would be at equilibrium and this indeed seems a pretty timeless place.

The way this changes the notion of time is that we no longer need to worry about the fact it has an asymmetric arrow (that comes with the idea of the gradient). And it also makes time not a single thing (so time always flows the same even before universes exist). Instead it becomes a systems property and so something that can be found in various grades of being.

The universe becomes a nested hierarchy of gradients. So you have the basic gradient set up by the big bang - the one that runs from a hot point to a cold void. This is the naked spreading radiation story. Then a second more complex gradient was created on top of this basic entropic story by the appearance of located mass able to go slower than light speed. Time was now a richer, more complex thing, in our universe as more kinds of change became possible.

Life and minds exist in an even richer variety of time. Organisms have memories and expectations. By harnessing natural entropic gradients like sunshine - by steepening those gradients locally by accelerating the production of entropy - an even more complex kind of time passing is created.

It could be said that this is now stretching the physical definition of time. And I would agree. The really major transition in the nature of time was the one where mass condensed out. Yet I can still relate organismic time to physical theory. As I said, life pays for its existence by steepening entropic gradients. It literally changes the universe faster, and that does mean more is happening.

[ConradDJ]

So in some important sense, time was in a different state during the early big bang, before the Higgs transition that created located massive particles moving slower than light... In a hot relativistic realm, the entire system would be in communication at the same rate, and so there would be no gradient to define an arrow of time locally...

But anyway, the key thing here is that there is already in the cosmological story a clear phase transition in the nature of "time". At the point mass condensed out, a new kind of locality was invented. Time visibly passes for objects able to move slower than light because of the gap between their motions "in space" and their energetic exchanges.


Yes, this begins to sketch out some of the complexity that belongs to the physical structure of time. I think eventually it will be clear that the concept of "time" in physics is a lot like the concept of "life" in biology – a complex notion with many important facets, all of which play a role in an evolutionary process.

The example you point out – Relativity makes an absolute distinction that had never before been suspected, between light-speed and speed in general, which is equivalent to being at rest. Instead of just “motion” we have a radical difference between the way masses and massless particles relate to space and time. It’s almost as though the physical world has two completely distinct spacetime structures superimposed on each other.

There’s the more “primitive” structure of light-speed connections – in this regime, the early universe is still happening right now, in my present moment – though it’s 13.7 billion miles away. And there’s the completely distinct structure of dynamics between masses, that approximates Newtonian dynamics except when things are moving very fast, relative to each other, or where there are high concentrations of mass.


So as to the philosophical question – “Is time real?” – Yes, certainly, but how it works is not so simple as we tend to think. Our notions about time today are like the way some people thought about “life” in the 18th century – as a simple, elemental force that animated things.

Discussions of time still tend to get caught in the same dichotomy that the ancient Greek philosophers invented – “everything is in flux” / “change is really just an illusion.” But time in modern physics is not just an empty background against which things change or stay the same.

To me, this is where philosophy can play a significant role, as distinct from science. The task of science is to look at the available hypotheses and figure out which best fit the facts. The task of philosophy is to invent new ways of imagining the world and what’s going on in it. Because if there’s one thing that’s clear in physics today, it’s that our knowledge of the world has gone far beyond what we know how to imagine.

Nearly all observable physical phenomena are theoretically “well understood” today. But we don’t have any hypotheses that begin to explain why the world should be built the way it is. Why Relativity, why Quantum theory – and why does so much of the world behave just like classical, Newtonian physics? There are several profoundly different kinds of structure involved in fundamental physics – each with its own “temporality”, to borrow Heidegger’s term... its own way of “doing time.” The ancient arguments about flux vs stasis don’t shed any light on what’s going on here.

[petm1]

I see time as a dilating area from every massive point within our visible universe, think light waves. We see time by putting the billions of photons from all the different light waves together as our individual presents. We may be able to map our world lines through space but it is our center connection that we map through time.

[imiyakawa]

If quantum events do not play a direct causal role in the generation of consciousness, I'd say that our perception time is illusory. (Of course by saying this I'm endearing all the confounding issues of entropy, etc). Think about it. What we experience as now is just because the particles in our brain are in a certain configuration, that state causing consciousness to think the thought "why am I in the now?". That thought does not exist any-when, it was just a particular ensemble of particles that exist(ed)(s).

[apeiron]

The ancient arguments about flux vs stasis don’t shed any light on what’s going on here.

What I do think they show is that it has always been logical to look at a system and separate its description, its measurements, in these two contrasting directions. So there is always the something that stays the same, and always the something that changes. In physics, this became identified as the space, a collection of locations that allows things to be static, and as time, the further dimension in which flux happens.

So a metaphysical separation (what seemed most obvious and sensible back then) is still the essential separation of physical modelling.

The same is true of the other ancient greek dichotomies like the one and the many (the local and global). Or particulars and universals, substance and form, discrete and continuous, etc.

What I don't think the greeks had was our modern notion of equilibrium. Which is a neat reversal in view. Instead of stasis being the local measurement (the microstate) and flux the global measurement (the macrostate), the notion if equilibrium switches it round so all is flux locally (particles in random motion) and stasis at the global scale (overall, nothing is changing).

Now an observer armed with a clock would see two different regimes dependent on scale. Shrunk to the local level, there would be flux and change to measure. Expanded to the global scale, it would all go quiet. No change so ticking time becomes meaningless.

However neither of these two views - the ones that put flux as a global emergent property or a local equilibrium property - really are right to describe our universe which expands and cools. This is the great subtlety.

A global scale observer would see a universe which is still expanding, still getting bigger in time. So actually, stasis~flux is a fractal or scalefree property of such a system. There is an equilibrium balance, but it is evenly spread across all possible scales of observation.

Well, it is even spread in a relativistically thermalising universe - one that is expanding and cooling as a bath of light radiation. But deviations from this lightspeed equilibrium are created by matter particles condensing out and creating localised temporal warpage in the smooth stasis~flux balance.

[apeiron]

If quantum events do not play a direct causal role in the generation of consciousness, I'd say that our perception time is illusory. (Of course by saying this I'm endearing all the confounding issues of entropy, etc). Think about it. What we experience as now is just because the particles in our brain are in a certain configuration, that state causing consciousness to think the thought "why am I in the now?". That thought does not exist any-when, it was just a particular ensemble of particles that exist(ed)(s).

The job of science should be to reduce the world to meaningful descriptions, nor meaning less. And clearly, reducing the description of an aware brain to an ensemble of particles is not meaningful as it does not explain anything about why or how this ensemble also happens to be an intelligent, adaptive, arrangement.

So we can say that brains are shaped into arrangements by past learning and become organised with both specific and general anticipations of the immediate future. A brain has goals and expectations about what will happen, could happen, should happen. So the "now" is a meaningful departure point - a "static" location from which fresh change (fresh learning, experience, adaptation) will arise.

The past becomes psychologically what we cannot changed (it changed us), the now is a located, focused, state of organisation and readiness, the future is the realm of changes yet to happen and which we are poised to have some influence over. Hence the feeling we have some measure of free will.

Psychological time is different from physical time because every "now" is highly located. For an ensemble of particles, one place in the universe is as good as another so far as each particle is concerned. But for an organised brain, every now becomes a unique location. Your now is different from my now - it contains its own unique organised state, its own unique collection of learnings, goals and anticipations.

A physical reductionist model of time (like Newtonian mechanics) cannot capture this kind of located complexity. This is why I am talking about a systems model of time that might perhaps capture both the physical and psychological extremes of change, flux, etc, in the one measurement method. This would be a more general model of temporality.

[pallidin]

Without change, "time" has no meaning, influence or value.

[imiyakawa]

And clearly, reducing the description of an aware brain to an ensemble of particles is not meaningful as it does not explain anything about why or how this ensemble also happens to be an intelligent, adaptive, arrangement.

I don't see how our observations of the brain as intelligent, ordered, etc have anything to do with the discussion of whether our perception of time has some fundamental meaning or is just illusory?

the future is the realm of changes yet to happen and which we are poised to have some influence over.

Doesn't the latter part of that statement presuppose true free will (say the definition is action without possible prediction)?

Psychological time is different from physical time because every "now" is highly located.

How can we be absolutely sure of this? Let's hypothesis for a moment that the entropy arrow doesn't exist. Now let's state that the universe goes back and forth through time for some unidentified reason. t = 1a, 2a, 3a, 4a, 5, 4b, 3b, 2b, 1b ... At t = 2b, for instance, we'd all be absolutely convinced that it was actually t = 2a, simply because the particle state of our brain is identicaly at t = 2a = 2b. But t = 2b is not t = 2a, and thus our perception of "now" is just resultant of the arrangement of particles in our brain at t = x.

A physical reductionist model of time (like Newtonian mechanics) cannot capture this kind of located complexity. This is why I am talking about a systems model of time that might perhaps capture both the physical and psychological extremes of change, flux, etc, in the one measurement method. This would be a more general model of temporality.

Wow, that's a good way to go about this!

[apeiron]

I don't see how our observations of the brain as intelligent, ordered, etc have anything to do with the discussion of whether our perception of time has some fundamental meaning or is just illusory?

Do you mean our actual perceptual experience now, or how we conventionally model it as a linear sequence of moments?

Either way, it would be a model - a construction rather than an illusion - and meaningful as we tend to chuck out models that don't work for us.

And my general argument is that issues arise, as in this OP, because there is taken to be some fundamental conflict between how we naive experience time and what our (broadly Newtonian) scientific models say it "really is". If we can put both the psychological view and the physical view on the same general footing, then there would not be a conflict.

This would be a reason for deconstructing both so as to look for some better shared basis of modelling.

This was the general philosophical approach of philosophers like Bergson, Whitehead and Peirce, and also ties nicely with a modern thermodynamic approach to time.


Doesn't the latter part of that statement presuppose true free will (say the definition is action without possible prediction)?


It is a statement in support of autonomy. To call action "free" is a bigger leap. For example, in my systems approach, humans act according to socially constructed goals largely. But this does not make such socially constrained action "not free" in my view. So what use would I have for "free" here?


How can we be absolutely sure of this? Let's hypothesis for a moment that the entropy arrow doesn't exist. Now let's state that the universe goes back and forth through time for some unidentified reason. t = 1a, 2a, 3a, 4a, 5, 4b, 3b, 2b, 1b ... At t = 2b, for instance, we'd all be absolutely convinced that it was actually t = 2a, simply because the particle state of our brain is identicaly at t = 2a = 2b. But t = 2b is not t = 2a, and thus our perception of "now" is just resultant of the arrangement of particles in our brain at t = x.


Yes, if reality secretly had this bizarre structure, then we would be well and truly fooled wouldn't we. Yet just like the MW interpretation of QM, it is the kind of argument we cannot easily disprove, but nor do we have any reason to believe it. And even if it were true, it makes no practical difference. We would still use thermodynamics as a model to account for our world as we experience it.

[operationsres]

^ Agreed with everything you replied.

"So what use would I have for "free" here?"
Ah the free will definition I was referring to was more a physicists definition - action that is impossible to predict.

My remaining question is, which is more what I wanted to get at before rather than time, "is there a now?". Let's assume that the wavefunction collapse/reduction is not stochastic on the fundamental level. How can we know now is actually a real now and that our perception of it isn't just secondary phenomenon of our brain being in that state experiencing now-ness, as it always does, at that particular time?

What reason do we have to posit that time is flowing from A to B? Why can't time just happen all at once? People just think they're on point x on the timeline because they're thinking it from the brain-state at time x, such thinking is inevitable.

My point is, if collapse is determined somehow, we wouldn't know the difference if time was a flow or a stock. In either model we think time is flowing.

Sorry this is my other account for posting my uni homework questions :p (can't have lecturers catching me!)

(As for the entropic arrow and these two models, I believe the entropic arrow only accounts for the directionality of physical causality, not of the feeling of a flow).

[Boy@n]

Time must be real, or else why would we meassure different change in one atomic clock being stationary on the ground and the other inside a fast traveling airplane?

Also, we are never really stationary, the way we move through space-time even when we sit perfectly still is hard to visualize. Earth rotates around own axis, then around Sun, Sun spiraling towards Milky way centre, our galaxy traveling its own way, clusters of galaxies too, and so on and on, and finaly Universe itself expanding at accelerating speed.

So, even if there wouldn't be any real time, you moving 10 steps ahead and then 10 steps back to the same initial position is never the same position in Universe coordinates, it's more kinda millions miles away from it :)

[apeiron]

My point is, if collapse is determined somehow, we wouldn't know the difference if time was a flow or a stock. In either model we think time is flowing.


Sorry, I just wrote a long reply and the system ate it. I can't be bothered doing it again.

Gist is that yes, QM also needs to contribute to any more general model of time. I see the transactional interpretation as being central here.

And QM also seems to give your argument an even bigger problem as non-locality is precisely about spanning the flow of time. You can't imagine a jumble of topologically disconnected spatial frames and still have non-locality find a way through the maze to connect them. And if you can, then the paths aren't topologically broken in the first place because the connecting paths exist.

Sort of like the many worlds argument. How can that be rendered than other as a topologically branching tree?

[imiyakawa]

And QM also seems to give your argument an even bigger problem as non-locality is precisely about spanning the flow of time. You can't imagine a jumble of topologically disconnected spatial frames and still have non-locality find a way through the maze to connect them. And if you can, then the paths aren't topologically broken in the first place because the connecting paths exist.

YES!!!!!! That's brilliant.

[apeiron]

YES!!!!!! That's brilliant.

...but not original. There is quite a bit of debate around this issue. For example -

http://plato.stanford.edu/archives/spr2002/entries/spacetime-bebecome/

http://www.google.co.nz/url?sa=t&source=web&ct=res&cd=1&ved=0CBQQFjAA&url=http%3A%2F%2Fphilosophy.ucsd.edu%2Ffaculty%2Fc callender%2Findex_files%2Fphysics%2520against%2520 tense.doc&rct=j&q=quantum+topological+foliation+nonlocality&ei=qTjuS9u5JIuStgPzm_zGDw&usg=AFQjCNFSWCR-Yk8paVETToZMQvX3EtW_oQ

[magpies]

What time is it right now anyhow?

[apeiron]

What time is it right now anyhow?

About 2.725 degrees K according to the CMB clock :smile:.

[petm1]

But is temperature real? :redface:

[magpies]

The real test for if something is real or not is if it can be destroyed right??? So why don't we start work on a time bomb that destroys time it's self that way we can at once have the answer to these questions :)

[petm1]

We are all looking forward to our "time bomb", it is called death. Death does not stop time for everyone at once, just each of us in turn. What answers we will find beyond this change is everyone guess.

[ConradDJ]

I see time as a dilating area from every massive point within our visible universe, think light waves. We see time by putting the billions of photons from all the different light waves together as our individual presents. We may be able to map our world lines through space but it is our center connection that we map through time.


I'm not sure I get the picture you have in mind here... but I think it's important to try to envision what's going on in physics in some such way.

This seems to get at two profoundly distinct aspects of space and time -- on the one hand, the web of connections between things along their light-cones, through which we interact with the world at a distance. And on the other hand, the parallel progress each of us (as an entity with mass) makes through time as we stay more or less in the same place.

So much is "well-understood" in physics, theoretically -- that we haven't yet learned how to translate back into the world we actually experience. We still tend to imagine the universe as if it were Newtonian -- a vast, empty space existing over all time, in which things move around according to certain interaction-laws. In that picture, time is just a coordinate-axis.

But obviously no one experiences the world that way -- as if you could stand outside of space and time and see the whole thing at once. It seems that learning to imagine the world as we actually experience it, in real time, is a unique challenge...

[petm1]

the web of connections between things along their light-cones

Light cones dilate at c from every point, they are never static even when we are at rest with our surroundings. Time dilates at c from every point even in the dark the two motions are what I "see" as time

We still tend to imagine the universe as if it were Newtonian

Newton saw the world with gravity as an attractive force, with gr we think of gravity as a warping of space/time, but "if" the flow of time is outward from every point, and it is the same motion started at the big bang (or the little twist, if you think of big bang as an effect from a collapse), then I think of gravity as an outward motion. Each of these views make up gravity which is how I "feel" time.

But obviously no one experiences the world that way -- as if you could stand outside of space and time and see the whole thing at once. It seems that learning to imagine the world as we actually experience it, in real time, is a unique challenge.

Myself I think that time is the orthogonal part of reality, I am standing outside of the time inside of every atom including the ones that makeup myself, it is warping of time that makes up the edges in space.

[apeiron]

About 2.725 degrees K according to the CMB clock :smile:.

Note that if the CMB is taken as the true global clock, then the presence of mass distorts its rate. The void looks slightly cooler than it ought because some small percentage of the universe's total energy remains locked up as matter - quarks, electrons, neutrinos, dark matter. If this had been given up early on as radiation (if there had been no CP violation in matter-antimatter) then the CMB would still look a little warmer, and so the universe a little younger.

Therefore, to be accurate, the CMB is not a perfect clock. The existence of mass distorts its keeping of universal time. However, we could still calculate the contribution that the conversion of all remaining mass to radiation would make, and so get a "true" reading of the time. In terms of a global temperature or macrostate.

[Galteeth]

Scientific American ripped off this thread in their latest issue. Must be a slow news period. You would think the B-muon story would warrant more coverage.

[petm1]

There are no perfect clocks, only local clocks.:surprised

[Kglocc]

If you take the position of everything at in a 1/infinity fraction of "time" you get a map of the universe in a 3 dimensional matrix. Then once you quantify every possible future of every 1/infinity fraction of "space" you can predict the future with math.
Conversely, Time is relative? Time will fly having a good time. Time slows down when adrenaline is pumping and your mind is making more long term memories and connections. So, Time manifests itself as memory in humans? Are memories "real"?
Is "real" "time"?

[magpies]

Have you ever had a day that passed by in about one minute?

[gabrielh]

It's interesting that after stumbling upon this thread Scientific American releases this article (http://www.scientificamerican.com/article.cfm?id=is-time-an-illusion) called Is Time An Illusion? Thought it might be worth sharing here.

[magpies]

Eh... slow news day. The reason physics papers don't use time like we normally do is because when you try to factor in for xyz amount of change the math can start to get insane. It's like trying to keep track of every object in a room vs just one of them.

[petm1]

It's interesting that after stumbling upon this thread Scientific American releases this article called Is Time An Illusion? Thought it might be worth sharing here.


Describing time as physical must count for thinking of time as real, I would think.

[Borg]

Describing time as physical must count for thinking of time as real, I would think.

Have you read the article? It brings up some interesting points about time, whether it really exists and how rethinking our views about the existance of time may be necessary if we are to ever come up with a Unified Field Theory.

[petm1]

Yes I read the article.

[Theriault]

[QUOTE=ConradDJ;2712502]That's definitely one of the things it is.

"Up and down are different, because of gravity."

How does one establish up (or down) as a separate spherical radial from a gravity locus? Is gravity smooth or discrete in terms of directions from a locus? Does the size of a gravity locus ( planet vs ball bearing ) determine or change the spherical radial gravity direction arrays? It seems impossible for an object to have an infinite number of gravity vectors, so up and down are pretty useless generally as terms.

[Descartz2000]

"Is time real?" :
I think asking what 'real' means is confusing. I think it comes down to the following question: if there are no inherent value differences between 'present/now' states, then how can I claim any single 'now' state is more in existence than any other? If 'real' equates to 'existence', then yes, I would argue time is real.

[Descartz2000]

"Is time real?" :
I think asking what 'real' means is confusing. I think it comes down to the following question: if there are no inherent value differences between 'present/now' states, then how can I claim any single 'now' state is more in existence than any other? If 'real' equates to 'existence', then yes, I would argue time is real.

But, 'real' meaning it is all laid out in principle, it is there and valid when I am not experiencing it as a 'now' state. As a 'flow' or as a movement, time is an illusion. But in its entire lay out, it is real and existing.

[loseyourname]

The amount of attention this question commands has always perplexed me. Is distance real? Well, is there a distinction between me and the water bottle sitting on my desk two feet away from me? Sure. Is there a distinction between the difference between me and that water bottle and the difference between me and the grill sitting outside? Sure, one is farther away spatially than the other.

Well, is there a distinction between what I'm doing now and what I did yesterday? Sure. Is there a difference between that distinction and the distinction between what I'm doing now and what I did last week? Sure. One is farther away temporally than the other.

What people really seem to want to ask is whether these measures of magnitude of distinction are fundamental or if they require distinction to exist. Imagine a world in which only one indivisible object exists and it never changes in any way. Since it can't be distinguished from other objects or even from itself, space and time don't really come into play. But in the actual world in which we exist, in which many objects exist and they all change, space and time are as real as any other means of making distinctions, like color and magnetism and criminal backgrounds.

Anyway, the real problem in the OP isn't whether or not time is real, it's whether or not the future and past are real.

[Ivan Seeking]

This is a troubling question for me. Certainly there exists in our universe sequences of events which may or may not be undone easily. For example, I can walk 31 steps forward, then walk 31 steps backward and return to where I was. However, I can not easily unmix milk from my coffee after I have poured it in, though I shouldn't think it is impossible.

This isn't really what we mean when we think of the concept of "time". A simple sequence of events is something we can do or undo, but no one here thinks they can return to yesterday, or last year. When we think of time, we think of us somehow floating along in a bubble that we call the present, and behind us is the past and before us the future. We can not look forward into the future, but we can look behind us into the past and around us inside the bubble at the present. I personally suspect that this is really an illusion, and that the concepts of "past' and "future" have no physical meaning, but trying to prove it in any concrete way I think is beyond my scope for now. Any thoughts on this topic?

The question of whether time travel to the past is possible, has not been answered. Also, what might prevent a practical time machine from being built are practical limitations, such as the energy required. Other scenarios seem to allow that the past is real, but we could be fundamentally prevented from going there. In one scenario, a radiation feedback loop would destroy the entire effort, but that in itself implies that the past is real [actually, it depends on the assumption that the past is real].

[Ivan Seeking]

If the past were not real, would the equations from GR tell us that?

[Pythagorean]

If the past were not real, would the equations from GR tell us that?

It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.

Of course, I wouldn't say it doesn't exist; just that it doesn't exist as we know it.

[Ivan Seeking]

It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.

Of course, I wouldn't say it doesn't exist; just that it doesn't exist as we know it.

The laws of physics are assumed to apply everywhere. I don't understand your point. In the case of a time machine, we are talking about the past wrt the frame of reference of the observer.

[Pythagorean]

The laws of physics are assumed to apply everywhere.

What do you mean by that? It shouldn't contradict what I'm saying.

In the case of a time machine, we are talking about the past wrt the frame of reference of the observer.

GR tells us how matter shapes space and time, SR tells us how motion does. One could argue that such tools would be useful in constructing a model of an observer's past, but naturally, even predictive models don't have the final say on whether something is real or not.

It would be strange indeed, if an observer was able to reduce the entropy of the universe in his frame, while time-traveling (bound to be an entropy-increasing event). I can hardly perceive of how you'd ever travel backwards through time in the first place, or how you'd get the rest of the universe to cooperate with you.

a) either all "pasts" would have to be recorded somewhere physical (if that's even possible) so that you had something to "travel" to.

or

b) you'd have to somehow move all the particles back into the position of a past (but because simultaneity doesn't exist, I'm not sure how you'd ever manage to do that.)

To me, time travel on the same footing as intelligent design: that is, if you want to nitpick, it could be true, but it's highly unlikely.

[ConradDJ]

It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.

I agree it's important to point out that past and future have meaning from some particular standpoint in the world -- not globally. From any physical point of view, though, there is a "past" that was "real" once but isn't any more, and there (presumably) will be a future that isn't "real" yet.

It seems intuitive to expand the notion of reality to include everything that ever actually happened up till now, and maybe everything that ever will happen too. But that doesn't seem to describe the physical world very well, once we get beyond classical physics into quantum theory and /or relativity.

The basic problem with our intuition, I think, is that we want to "step outside" our own point of view and imagine the universe "objectively" -- as if all of space and time could be "seen" in some sense at once, without actually being IN it somewhere. As if we could put the universe and its history on our desks and look at it from all angles. But I think the lesson of recent physics is that "you have to be there." If you abstract from having a particular point of view IN space and time, you can no longer conceptualize the world consistently.

[apeiron]

I agree it's important to point out that past and future have meaning from some particular standpoint in the world -- not globally.

No, I would still suggest that the idea of locally symmetric time is an assumption, a helpful simplification, of Newtonian mechanics, carried over into relativistic mechanics. Backwards and forwards in time have no differentiation only in those kinds of theories.

But a thermodynamic model of reality does give you a basis for a "more realistic" view of time as an asymmetry. I don't mean thermodynamics as in Boltzmann's statistical mechanics - which, mechanically, locally, again defines no arrows - but thermodynamics as in the modelling of the dissipation of entropy gradients.

And regarding the universe, the average temperature, the cosmic background radiation, does give a global reference which can distinguish the past from the future. Everywhere, the universe is warmer towards its past and colder towards its future.

Of course, the local motion of bodies introduces local relativistic effects like the Unruh radiation. But generally speaking, there is a thermal gradient that marks an irreversible process, a one way direction for change, and hence a global arrow of time.

[Ivan Seeking]

What do you mean by that? It shouldn't contradict what I'm saying.



GR tells us how matter shapes space and time, SR tells us how motion does. One could argue that such tools would be useful in constructing a model of an observer's past, but naturally, even predictive models don't have the final say on whether something is real or not.

It would be strange indeed, if an observer was able to reduce the entropy of the universe in his frame, while time-traveling (bound to be an entropy-increasing event). I can hardly perceive of how you'd ever travel backwards through time in the first place, or how you'd get the rest of the universe to cooperate with you.

a) either all "pasts" would have to be recorded somewhere physical (if that's even possible) so that you had something to "travel" to.

or

b) you'd have to somehow move all the particles back into the position of a past (but because simultaneity doesn't exist, I'm not sure how you'd ever manage to do that.)

To me, time travel on the same footing as intelligent design: that is, if you want to nitpick, it could be true, but it's highly unlikely.

Nonetheless, we get real solutions using various schemes, and GR, suggesting that time travel to the past is theoretically possible. Therefore, it would seem that GR predicts that the past is real. Yes, no?

To me, your argument sounds a bit like saying that clocks in SR don't really run slowly as a function of speed, wrt a fixed observer, they just appear to run more slowly.

[Pythagorean]

Nonetheless, we get real solutions using various schemes, and GR, suggesting that time travel to the past is theoretically possible. Therefore, it would seem that GR predicts that the past is real. Yes, no?


I don't know about the formulation that does that. Is it something that is inferred from the model or something that was set out to be proven? If you have the link to the relevant paper, I may have more context.

More as an aside, my intuition is that the past is something that doesn't exist anymore, but that it is real, nonetheless, adhering to that definition.


To me, your argument sounds a bit like saying that clocks in SR don't really run slowly as a function of speed, wrt a fixed observer, they just appear to run more slowly.

No, not really, but that is my understanding of SR. If you were on board with the clock, for instance, you wouldn't observe time speeding up or slowing down in your frame.

[pallidin]

"Time" is an aspect of "change"
If NOTHING CHANGES, time is meaningless and can not exist.

[loseyourname]

No, I would still suggest that the idea of locally symmetric time is an assumption, a helpful simplification, of Newtonian mechanics, carried over into relativistic mechanics. Backwards and forwards in time have no differentiation only in those kinds of theories.

But a thermodynamic model of reality does give you a basis for a "more realistic" view of time as an asymmetry. I don't mean thermodynamics as in Boltzmann's statistical mechanics - which, mechanically, locally, again defines no arrows - but thermodynamics as in the modelling of the dissipation of entropy gradients.

Well, at least on this planet, we have a far simpler indicator of time direction: living creatures and born and then later die. It never happens in the reverse direction. Trees don't shrink into saplings and then seeds.

[apeiron]

Well, at least on this planet, we have a far simpler indicator of time direction: living creatures and born and then later die. It never happens in the reverse direction. Trees don't shrink into saplings and then seeds.

Agreed - but not necessarily that it is a simpler indicator.

I was making the familar argument that entropification is the global arrow of time. It points out the ultimate and irreversible direction of all change.

But as well as a direction, there is the question of rate. Time moves forward (entropy procedes) at some actual speed. For the universe it follows an asymptotic curve set by an expanding/cooling field of radiation - the CMB.

Now life and other kinds of dissipative structure are in fact examples of order or negentropy - an action against this general gradient. But then of course, living systems pay for their back-pedalling against the general flow by at the same time accelerating the local rate of entropification in their immediate environments. They create more waste heat faster than would otherwise exist by simpler processes, such as the redshifting of the CMB.

So you have the CMB cooling at it steady rate. Then you have more complex systems that accelerate that rate - and so pay for their own "deceleration", their own persistent order or lack of change as structured systems doing things like growing and metabolising.

So life exists by slowing time, the natural rate of entropification, you could say. But only by balancing the books by also accelerating it to the same degree. Overall, it balances out in the long run for the universe, confirming its global arrow and global rate.

I would certainly call that a complex indicator (though a simple one perhaps if we are just talking about direction, rather than direction and rate).

[loseyourname]

I meant simpler to observe, in the sense that it requires no knowledge of physics or special tools. There are other types of events that only happen in one direction. Rocks, for instance, don't ever fall from the bottom of a cliff to the top. Rivers never flow uphill. Explosions don't contract and become bombs. Bullets don't fly backwards out of targets and into guns. Abraham Lincoln's skeleton won't crawl out of his grave and grow flesh and then de-age into an infant.

Observation of these types of events would make it justified to say you're traveling into the past.

[Jonnyb42]

I do not know if it is real or not. My thought flow for this is: It is real, because I know of it, it is real. However, if 'real' meant I know of it, then everything would be real, and that word would no longer have meaning, therefore something is not real by simply knowing of it.
Since we can take measurements of time, then I suppose I am leaning towards it being real.

My comments on this matter is the fact that when we look at what has happened, I know that it was the only way things would ever happen. You think you make decisions, and you do, but what you may not realize at first is that that is the same decision you were going to make even a billion years ago. The future is going to be laid down exactly one way, and it will become just a part of the past.
It is like a solid with a 2 dimensional reference frame travelling through it, the solid doesn't change, (with time? uh oh) but yet the observer sees things as changing, it only sees in a 2 dimensional plane. The mechanics that underlie this references frame's movement through the solid, however, is of higher understandings, and mysterious at the moment.

[petm1]

Time is real and space is not or space is real and time is not, sorry for space/time to be real you need both. In my mind time is all that is real, space is how I see the "age" of the different photons creating the dilating image on the retina in the back of my eyes.

[petm1]

If you think of mass as the past and a "real" direction in time, we see it which ever direction we look in space, then where does that leave our future which I see as the "real" illusion of time.

[ThomasT]

But a thermodynamic model of reality does give you a basis for a "more realistic" view of time as an asymmetry. I don't mean thermodynamics as in Boltzmann's statistical mechanics - which, mechanically, locally, again defines no arrows - but thermodynamics as in the modelling of the dissipation of entropy gradients.But isn't thermodynamics a bit problematic, conceptually? Why not just work on modelling the universe in terms of a global wave mechanical view of things based on some fundamental dynamical laws governing it's overall evolution? Is this simply out of the question because it would be, eventually, too complicated?

[pallidin]

If time did not exist it would not be possible for you to respond to these posts AFTER your question.
Else you would have done such simultaneously, which did not happen.

[ThomasT]

I meant simpler to observe, in the sense that it requires no knowledge of physics or special tools. There are other types of events that only happen in one direction. Rocks, for instance, don't ever fall from the bottom of a cliff to the top. Rivers never flow uphill. Explosions don't contract and become bombs. Bullets don't fly backwards out of targets and into guns. Abraham Lincoln's skeleton won't crawl out of his grave and grow flesh and then de-age into an infant.

Observation of these types of events would make it justified to say you're traveling into the past.I like to illustrate time by dropping a pebble into a calm, smooth pool of water. There's no going back in time, because there's no back in time to go back to. The expansion of the disturbance in the pool of water is characteristic of all waves on all scales. Why would the 'universal wavefront' be expected to be any different? If our universe is an evolving disturbance in some unknown medium, then backward time travel is impossible.

[ThomasT]

If time did not exist it would not be possible for you to respond to these posts AFTER your question.
Else you would have done such simultaneously, which did not happen.A timely reply.

[Descartz2000]

It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.

Of course, I wouldn't say it doesn't exist; just that it doesn't exist as we know it.

I agree. It seems the past is only the 'past' (12 pm) because I am viewing it from my present now state (1 pm). It seems that 1pm carries no more value in how 'real' it is, than that of 12pm. There is no past that exists, it is only a previous present state of 'now'. If the past is the past as we intuitively think of it, then what is that past state when I am experiencing it? This points to the conclusion that the past is only an illusion.

[Descartz2000]

I agree it's important to point out that past and future have meaning from some particular standpoint in the world -- not globally. From any physical point of view, though, there is a "past" that was "real" once but isn't any more, and there (presumably) will be a future that isn't "real" yet.

It seems intuitive to expand the notion of reality to include everything that ever actually happened up till now, and maybe everything that ever will happen too. But that doesn't seem to describe the physical world very well, once we get beyond classical physics into quantum theory and /or relativity.

The basic problem with our intuition, I think, is that we want to "step outside" our own point of view and imagine the universe "objectively" -- as if all of space and time could be "seen" in some sense at once, without actually being IN it somewhere. As if we could put the universe and its history on our desks and look at it from all angles. But I think the lesson of recent physics is that "you have to be there." If you abstract from having a particular point of view IN space and time, you can no longer conceptualize the world consistently.

I agree with much of what you wrote, but I think the point is that just because we single out a point in time and then claim the past is the past and the future is out there waiting from this unique view point is incorrect. It seems this appears true from this view point in time, but objectively it is not. So, in other words, there is an objective view point in principle, in the sense that claiming no single viewpoint in time has any more value than any other. So, in this regard, the past and future are really just illusions of my experience. No 'now' state stands out more than any other simply because I claim my 'now' state here as I write this is more valid than the moment I had 5 minutes ago. The value does not change between these states, it is only my view point that changes.

[Pythagorean]

I agree. It seems the past is only the 'past' (12 pm) because I am viewing it from my present now state (1 pm). It seems that 1pm carries no more value in how 'real' it is, than that of 12pm. There is no past that exists, it is only a previous present state of 'now'. If the past is the past as we intuitively think of it, then what is that past state when I am experiencing it? This points to the conclusion that the past is only an illusion.

I wouldn't say the past is only an illusion. The current state of the universe is still dependent on the past state in my mind, so what does exist is the history. The past exists in the sense that history exists, but because there's no simultaneity, constructing that history on an absolute scale seems paradoxical to me.

[apeiron]

So, in this regard, the past and future are really just illusions of my experience. No 'now' state stands out more than any other simply because I claim my 'now' state here as I write this is more valid than the moment I had 5 minutes ago. The value does not change between these states, it is only my view point that changes.

If you view the situation thermodynamically - where time does have an objective direction, there is some entropic gradient to be run down - then there is an objective measure of even psychological state.

For the ordinary material world, things unwind. Entropy increases with time, and so objectively distinguishes past states from now states, and future states.

For complex dissipative structures that arise on entropy gradients, like life and mind, there is instead an opposite process of increasing negentropy - information accumulated in the form of constraints.

This is what memory is. Habits and knowledge that accumulates over time and increasingly constrains our ability to respond to the world. For a child, everything is fresh and new. For the aged, everything is increasingly familiar and stereotyped, a well rehearsed response.

So we can all say that towards our psychological past we were immature (in the entropic sense of being less constrained, less developed). And towards our future, we will become senescent (overloaded with constraints, reduced in our capacity for novel responses). Right now hopefully we are in the mature system phase where habit and creativity are in fruitful balance.

Of course, this is change over a lifetime, not 5 minutes. But we can still say that a different sets of constraints (expectations, goals, anticipations, etc) were ruling us 5 minutes ago. And so that moment can be distinguished from this moment in terms of its particular informational constraints.

You also have to factor in the process of generalisation - memories gradually become less particular, more general, on the whole. That is how habits and routines form. And how detail gets forgotten.

So psychologically - for humans, who have the words to shape the habit of "remembering" prior mental states: ie anticipating or forward modelling what it would be like to be "me back then" - we can compare our now (as a particular state of mental constraint) with memories of other recent different nows (with some different particular collection of ideas and goals).

The illusion lies in thinking we are actually going backwards in time in any way. The ability to recall the past is in fact a feat of forward projection just like any other form of mental imagery. Brains are designed for anticipation (which is why animals have only recognition not autobiographical recall). And humans have just learnt the trick of imagining "backwards" to prior states along a thermal gradient.

So objectively, only a forward orientation in time exists - from being to becoming, from the actual to the potential. But the past increasingly constrains our potential reponses as informational constraints accumulate and our ability to entropify becomes itself limited (the biological definition of senescence, or fragility to environmental perturbation).

[Galteeth]

Agreed - but not necessarily that it is a simpler indicator.

I was making the familar argument that entropification is the global arrow of time. It points out the ultimate and irreversible direction of all change.

But as well as a direction, there is the question of rate. Time moves forward (entropy procedes) at some actual speed. For the universe it follows an asymptotic curve set by an expanding/cooling field of radiation - the CMB.

Now life and other kinds of dissipative structure are in fact examples of order or negentropy - an action against this general gradient. But then of course, living systems pay for their back-pedalling against the general flow by at the same time accelerating the local rate of entropification in their immediate environments. They create more waste heat faster than would otherwise exist by simpler processes, such as the redshifting of the CMB.

So you have the CMB cooling at it steady rate. Then you have more complex systems that accelerate that rate - and so pay for their own "deceleration", their own persistent order or lack of change as structured systems doing things like growing and metabolising.

So life exists by slowing time, the natural rate of entropification, you could say. But only by balancing the books by also accelerating it to the same degree. Overall, it balances out in the long run for the universe, confirming its global arrow and global rate.

I would certainly call that a complex indicator (though a simple one perhaps if we are just talking about direction, rather than direction and rate).

Life does not exist by slowing time per ce, in the sense you're using it, it speeds it up. The thing about global entropy is that while order decreases globally, information is expanding and the complexity of information (or negentropic enclaves if you like) is increasing. By thinking of thermodynamics as an extension of information theory this makes a bit more sense. It's like a book. The more of the story you've read, the less of the story their is. Or--- A book with a lot of blank pages might be highly ordered, but not very interesting. But it has infinite potential. The more you write, the more constrained the possibilities become... but you have to "pick" a story to write if there is going to be anything interesting overall.

The slight problem with this metaphor of course is that no one is "writing" the evolution of the universe... it's just my hunch but I think the tendency towards "high negentropic enclaves" or life is going to turn out to be stronger then people currently think.

[Descartz2000]

I wouldn't say the past is only an illusion. The current state of the universe is still dependent on the past state in my mind, so what does exist is the history. The past exists in the sense that history exists, but because there's no simultaneity, constructing that history on an absolute scale seems paradoxical to me.

But, the crux is not if the two events are simulataneous. They do not exist at the same physical times and locations, but they both exist equally at differing times and locations where one has no objective value or 'realness' over another in principle. If this is true and the 1pm event is as real and existing as much as the 2pm event, then how can I claim that both are not real and true in an objective sense at all times. So, in other words, if no specific time is identified or singled out as my place to view from, as both are equally as valid, then I can't claim at any point that one is true and the other is not. It may appear true from that viewpoint, but why is that viewpoint more or less valid than the other?

The past is an illusion in the sense that there is no true past. There is a 'past' from my current viewpoint, but what is the 'past' from this viewpoint, is the 'future' from another, and since neither is more valid, then the 'past' is just a perspective and it is an illusion. I'm not sure that 'history' plays such a big role here. It seems the 'equally real' events at 1pm and 2pm are key when talking about simultaneously valid states.

[Descartz2000]

If you view the situation thermodynamically - where time does have an objective direction, there is some entropic gradient to be run down - then there is an objective measure of even psychological state.

For the ordinary material world, things unwind. Entropy increases with time, and so objectively distinguishes past states from now states, and future states.

For complex dissipative structures that arise on entropy gradients, like life and mind, there is instead an opposite process of increasing negentropy - information accumulated in the form of constraints.

This is what memory is. Habits and knowledge that accumulates over time and increasingly constrains our ability to respond to the world. For a child, everything is fresh and new. For the aged, everything is increasingly familiar and stereotyped, a well rehearsed response.

So we can all say that towards our psychological past we were immature (in the entropic sense of being less constrained, less developed). And towards our future, we will become senescent (overloaded with constraints, reduced in our capacity for novel responses). Right now hopefully we are in the mature system phase where habit and creativity are in fruitful balance.

Of course, this is change over a lifetime, not 5 minutes. But we can still say that a different sets of constraints (expectations, goals, anticipations, etc) were ruling us 5 minutes ago. And so that moment can be distinguished from this moment in terms of its particular informational constraints.

You also have to factor in the process of generalisation - memories gradually become less particular, more general, on the whole. That is how habits and routines form. And how detail gets forgotten.

So psychologically - for humans, who have the words to shape the habit of "remembering" prior mental states: ie anticipating or forward modelling what it would be like to be "me back then" - we can compare our now (as a particular state of mental constraint) with memories of other recent different nows (with some different particular collection of ideas and goals).

The illusion lies in thinking we are actually going backwards in time in any way. The ability to recall the past is in fact a feat of forward projection just like any other form of mental imagery. Brains are designed for anticipation (which is why animals have only recognition not autobiographical recall). And humans have just learnt the trick of imagining "backwards" to prior states along a thermal gradient.

So objectively, only a forward orientation in time exists - from being to becoming, from the actual to the potential. But the past increasingly constrains our potential reponses as informational constraints accumulate and our ability to entropify becomes itself limited (the biological definition of senescence, or fragility to environmental perturbation).

I'm not sure that because things unfold in linear manner that there is a true and objective distinction between past, present, future states. It seems that to claim past and future states are objectively true is misleading. It seems there is a direction of how things unfold, but you can't pick one state and declare that it is more valid than another. But, if true, then how can you ever claim there is a past, as I must claim a present 'now' state as more valid to view this from. If I can't do this, and I accept that all states are present 'now' states, then what we think of as past, present, and future states have no distinction. They may have an order of unfolding, but they do not have a value difference in terms of being real or valid. So, all states are equally valid and true in principle regardless of my viewpoint.

[Galteeth]

I'm not sure that because things unfold in linear manner that there is a true and objective distinction between past, present, future states. It seems that to claim past and future states are objectively true is misleading. It seems there is a direction of how things unfold, but you can't pick one state and declare that it is more valid than another. But, if true, then how can you ever claim there is a past, as I must claim a present 'now' state as more valid to view this from. If I can't do this, and I accept that all states are present 'now' states, then what we think of as past, present, and future states have no distinction. They may have an order of unfolding, but they do not have a value difference in terms of being real or valid. So, all states are equally valid and true in principle regardless of my viewpoint.

Well, only one "state", that is, the constantly moving into the future "present" exists in the absolute sense. The past and future projections are usefully constructed models, but whether they have any existence independent of the human mind (which exists in that funny moving present state) is suspect.

[apeiron]

I'm not sure that because things unfold in linear manner that there is a true and objective distinction between past, present, future states. It seems that to claim past and future states are objectively true is misleading. It seems there is a direction of how things unfold, but you can't pick one state and declare that it is more valid than another. But, if true, then how can you ever claim there is a past, as I must claim a present 'now' state as more valid to view this from. If I can't do this, and I accept that all states are present 'now' states, then what we think of as past, present, and future states have no distinction. They may have an order of unfolding, but they do not have a value difference in terms of being real or valid. So, all states are equally valid and true in principle regardless of my viewpoint.

If you believe that the state of things has to be crisp and definite - something either is or it isn't - then you indeed face a logical bind. Past and future are either states that are - which ends up in the deterministic block time view where the now is an illusion - or instead only the now is real, which makes past and future the illusion.

So yes, think that way and you are trapped into mutually contradicting positions, neither of which feels right.

Which is why I stressed the further dimension to reality, the dimension of development that runs from the vague to the crisp, from becoming to being, possibility to actuality, etc. This is a traditonal idea in metaphysics even if it has become largely lost in physics.

So the past is definite (it cannot be changed) while the future is indefinite (it is still full of vague potential, a capacity for change, while also of course highly constrained because of a weight of accumulated history).

The best kind of model of this could be a scalefree network or other "edge of chaos" model where the "now" is a mix of past and future - a powerlaw mixture of the changed and the changing, islands of stasis and flux.

Look inside the "now" of the universe - which can be measured in a general way by its current temperature - and you will be able to see that it is in fact an average of local "nows".

This follows from the transactional interpretation of QM, a la Cramer, I believe.

[Max™]

Is this moment, as I am typing this, now?

If so, why does this moment a short time later feel like now?

Is there a wall of change sweeping across the universe, busily sorting things into past states, which my awareness happens to be surfing happily along with?


If so, can I not determine an absolute definition of simultaneous events, and thus destroy the very foundations of relativity?

If relativity is to hold, then I am forced to consider the possibility that my "now" is not unique, and that it is most likely an artifact induced by the manner in which my brain stores information.

The connection between my sense of self, that feeling that I am existing, and the temporal data encoded in my mind, is perhaps the source of all this confusion?


Perhaps I am little more than a bookmark, a misplaced one at that, constantly stating that I am here, while I am actually registering my self being at a different point on the page entirely!

[Descartz2000]

If you believe that the state of things has to be crisp and definite - something either is or it isn't - then you indeed face a logical bind. Past and future are either states that are - which ends up in the deterministic block time view where the now is an illusion - or instead only the now is real, which makes past and future the illusion.

So yes, think that way and you are trapped into mutually contradicting positions, neither of which feels right.

Which is why I stressed the further dimension to reality, the dimension of development that runs from the vague to the crisp, from becoming to being, possibility to actuality, etc. This is a traditonal idea in metaphysics even if it has become largely lost in physics.

So the past is definite (it cannot be changed) while the future is indefinite (it is still full of vague potential, a capacity for change, while also of course highly constrained because of a weight of accumulated history).

The best kind of model of this could be a scalefree network or other "edge of chaos" model where the "now" is a mix of past and future - a powerlaw mixture of the changed and the changing, islands of stasis and flux.

Look inside the "now" of the universe - which can be measured in a general way by its current temperature - and you will be able to see that it is in fact an average of local "nows".

This follows from the transactional interpretation of QM, a la Cramer, I believe.

But, it seems the 'now' is all that is real. I am not agreeing with presentism. However, how can I not claim that every state has its own state of 'now'. If true, and all states are now states at their own unique times, then in principle, when they physically are present, they are real and existing. However, since no now state is more or less preferred to view from, then I can't claim that any one of these now states is not existing in principle regardless of my viewpoint? And I do claim the past and future are illusions simply because they are not objectively true. A future state is not an inherent future from all viewpoints. Some viewpoints might claim it to be a present and past state.

[Descartz2000]

Is this moment, as I am typing this, now?

If so, why does this moment a short time later feel like now?

Is there a wall of change sweeping across the universe, busily sorting things into past states, which my awareness happens to be surfing happily along with?


If so, can I not determine an absolute definition of simultaneous events, and thus destroy the very foundations of relativity?

If relativity is to hold, then I am forced to consider the possibility that my "now" is not unique, and that it is most likely an artifact induced by the manner in which my brain stores information.

The connection between my sense of self, that feeling that I am existing, and the temporal data encoded in my mind, is perhaps the source of all this confusion?


Perhaps I am little more than a bookmark, a misplaced one at that, constantly stating that I am here, while I am actually registering my self being at a different point on the page entirely!

I think it depends on when/where you ask the question. If I ask: "is this moment more real here at 12pm than all other times?". I may respond "yes, it is, because I am asking the question now". But, what if I ask the exact same question tomorrow, and the next day, and the day after that? Is there a 12pm that stands out as more real than the others? If not, then how can I claim in an objective sense that any one of them is more real or valid than any other? I can't. Therefore, every now state is equally real and true. Maybe, all are not physically true at the same times (as the process of changing states is linear), but all are true now states, and in principle they all exist simultaneously.

[ConradDJ]

Is there a wall of change sweeping across the universe, busily sorting things into past states, which my awareness happens to be surfing happily along with?

...If relativity is to hold, then I am forced to consider the possibility that my "now" is not unique, and that it is most likely an artifact induced by the manner in which my brain stores information.

The connection between my sense of self, that feeling that I am existing, and the temporal data encoded in my mind, is perhaps the source of all this confusion?

There is pretty strong evidence that there is no "wall of change sweeping across" the whole universe at once. I think what relativity tells us is that the present moment "now" is local to every point of view. My "now" as I write this is connected to your "now" as you read it, by electronic signals and data-storage units. But they're not the same now. Unless we're face-to-face with each other in more or less the same place, we don't really share the same "now".

I don't see that this makes the "now" any less "real" or "unique" or significant for each one of us. And as to the confusion -- I think we need to distinguish the temporal structure we build in our minds and put on our calendars, and measure with clocks -- the objective "time-line" used in history and physics -- from the "being here" aspect of time, the experience of time "from inside". The latter isn't necessarily something "in our heads" or a figment of consciousness. The "now" I'm living in presumably includes all these things around me -- it's no less "physically real" than the time-line, but it's local to this "here and now."

The two aspects of time are connected in a way that maybe hasn't been well understood, in physics or in philosophy or psychology... but the thing is, they have very different kinds of structure. Objectively the "now" is at best something fleeting and undeterminable -- as soon as you point to one point on the time-line as "now", it's already past. The "now" has no meaning in Newtonian physics. But from a point of view in time, "now" is fundamental. And it doesn't instantly "go away" -- it stays here and changes, all the time. "Now" is the most basic and constant aspect of all our experience.

I think the "confusion" about Time comes mainly from a mistaken assumption that the word must refer to something simple, that we should be able to conceptualize Time as a single "process" or "dimension". But just because time is the most familiar thing in the world, to us, doesn't mean it's uncomplicated.

[pallidin]

Such pondering can lead to insanity.
This is why I prefer to pre-treat my fragile mind with copious amounts of sedation, normally beer. :surprised

[apeiron]

A future state is not an inherent future from all viewpoints. Some viewpoints might claim it to be a present and past state.

There is pretty strong evidence that there is no "wall of change sweeping across" the whole universe at once. I think what relativity tells us is that the present moment "now" is local to every point of view.

Agreed, the basics facts of relativity have to be factored into anything being said here. One observer can judge two events to be simulataneous, which to another observer follow one after the other, etc.

But this is why I like a thermal approach to time - it recognises, as Conrad says, that it is not a simple dimension, but complex. A simple view of time is that it is another geometric dimension - measured in terms of distance covered. But a complex view recognises that time can be ticked off in two kinds of units - thermalisation (cooling, entropification) as well as distance (expansion, motion). There is a duality here as these two physical processes are two sides of the same coin.

So getting back to my argument that the temperature of the universe does act like a universal clock, a global wall of change sweeping through, imagine looking up into the night sky and making a visual reading of its prevailing temperature. Registering photons.

Light cone logic applies of course. So that is a strict locality constraint. But so too does a transactional interpretation of QM, which admits thus an essential nonlocality. Individual events have a "timelessness", or rather, they turn indeterminate spatiotemporal potential into some actual crisply decohered event.

Anyway, looking up at the stars, we are catching energetic photons from all directions. But there is clearly a powerlaw relationship. In general, the stars are all equally bright, but distance makes them dim. And also further away in time, in our "past".

But from a transactional QM point of view, nothing has "happened" until the star has "decided" to emit a photon and my eye has "decided" to accept it. The connection is formed across time in some fundamental (nonlocal) sense. Once it has "happened" of course, it is a fixed part of the universe's history. It is woven into the history of the universe.

Note also that such events are always (excepting a non-zero but vanishing degree QM uncertainty) entropic - they go in the direction of a thermal gradient. My eye may emit photons of its own, but they will be way down in the weak infrared, never climbing back up the gradient to be hot like a star's emissions.

So looking up at the night sky, I am seeing photons over every distance (and hence distance back in time). But every individual event is also timeless in that it required me, as the decohering, wavefunction collapsing, observer to anchor one end of a transaction that is in fact "making time". Creating an act of communication, ie: thermalisation.

Of course, the conventional view is that the star emitted a particle, a photon, and it crossed vast regions of space, red-shifting as it went, before smacking into my retina. This is a realist view based on strict locality. It is a convenient way of modelling the situation perhaps, but contradicted at a fundamental level by QM, and the reason why some more subtle and complex model of time is actually needed.

Anyway, that is the situation. I look out at the stars and make thermalising connections with hot radiation sources over an incredible range of spatiotemporal "distances". The majority are in fact "near to" - the closer stars in the same galaxy. But in powerlaw fashion, photons could reach me from any distance within the visible universe.

So this admits that the "now" here is my now. But it is a complex now because my now is directly (nonlocally) part of some time-distant star's "now". The whole path of that photon exchange was a collapse of a wavefunction that put the star, my eye, and everything along the way, in a strict temporal order (and strict thermalisation order, as part of what happened was the red-shifting as well).

But there is also a global wall of change in this story as well. When I look out at the night sky, in every direction, over every distance and hence timescale, the sky looks pretty black. Stars (located thermal bodies) are the exception. And 98% of what I see is the global coldness, the weak thermal sizzle of the cosmic background radiation. This is a pure measure of the universes thermalisation, or cooling due to expansion and consequent red-shifting.

So mostly, my interactions are ruled by a global clock - the CMB. Just as to one side of me, there is an important heat source, the sun, to the other, there is a vast heat sink. And this is the entropy gradient that even makes it possible for us to exist as located, complex, observers.

What does this all say about the issue of "now"? Well, first up, GR alone is only a partial model. QM and thermodynamics are needed for a more complete story. As well as distance (GR), there is entropy (thermodynamics). And as well as locality (GR), there is nonlocality (QM).

Second, most of our temporal relations are either warm and short-range (the sun is only minutes away), or cold and distant. So our "now" is quite tightly defined in fact by a fairly precise position on an entropic gradient (hot foreground, cold backdrop). We can of course have thermal interactions over incredible distances (and hence times measured in distance). But these become vanishingly weak and do very little to nudge our otherwise quite tightly determined location on a thermal scale (the one locating us at some point between our dominant heat source and our dominant heat sink).

Third, it seems that thermo considerations are in fact a better way of thinking about time as a dimension. Time can be equated with distance (as distance is thermalising in practice - expansion causing red-shifting even without anything else happening). But if we equate time with change, and change with gradients, and gradients with entropification, then "now" can be seen in thermal terms. It becomes a measure of potential action.

My past is the past because that is a gradient already run down (and star light is not in my past until it has become an event registered as part of my now - and that star's now too). My now is where I happen to be on the gradient (the one between my dominant heat source and dominant heat sink). And my future is all the distance yet to slither down that entropy gradient towards the ultimate blah of a universal heat death.

[Max™]

Your now is just the point where your awareness seems to be directed at any given position along your worldline.

I can point to a moment as a "now" without it being in the past, case in point: the moment when you read these words is in the future from my perspective, I am pointing to that moment from the past, which I would claim was briefly a "now" from my point of view.

That "now" was a different event for me than it was for you, I was perhaps in bed, or outside whacking sticks with my bokken, using a general plane of rough simultaneity, mind.

Tomorrow, when I check back on this thread, this moment when I read these words I wrote a day before will seem like "now" to me, but I am aware as I write them that it is off that way *motions vaguely in the downstream direction of time*, or more accurately, I am aware that it can only be off in that direction, towards what I would label the future.

It is possible that I might be killed before I get a chance to fulfill that little bit of prophetic self-interaction, or the computer could crash, these boards could lose the post, or any number of different things could prevent my reading this post tomorrow.

Which raises another interesting question, why can we only recall what we did in the past?

I can not directly observe the moments when I posted in this thread yesterday, though I do hold information about them, and can even relive them to some extent by reading the post again.

I know that tomorrow from my perspective must be further downstream in time from the point I am viewing, yet I do not have information about that event, and can only relive it in my imagination.


Something interesting to think about, when I get around to thinking about it, that is.

[Math Is Hard]

Your now is just the point where your awareness seems to be directed at any given position along your worldline.

I can point to a moment as a "now" without it being in the past, case in point: the moment when you read these words is in the future from my perspective, I am pointing to that moment from the past, which I would claim was briefly a "now" from my point of view.

Actually, you never perceive "now". No one does. It takes a bit of time for all the information from "now" to flow through your sensory systems and be processed by your brain to have the "now" experience, and by then, it's gone. So there's always a bit of lag.


That "now" was a different event for me than it was for you, I was perhaps in bed, or outside whacking sticks with my bokken, using a general plane of rough simultaneity, mind.


Is there anything meaningful in saying one person's experience at moment x was different than another person's experience at moment x?


Tomorrow, when I check back on this thread, this moment when I read these words I wrote a day before will seem like "now" to me, but I am aware as I write them that it is off that way *motions vaguely in the downstream direction of time*, or more accurately, I am aware that it can only be off in that direction, towards what I would label the future.

It is possible that I might be killed before I get a chance to fulfill that little bit of prophetic self-interaction, or the computer could crash, these boards could lose the post, or any number of different things could prevent my reading this post tomorrow.


Why would reading things you wrote in the past seem like "now"? That might be something unique to your perspective.


Which raises another interesting question, why can we only recall what we did in the past?

Why don't purple monkeys fly out of my butt? Who knows. It's just the way things work. Your brain can't make a memory out of events your sensory apparatus hasn't come into contact with yet.


I can not directly observe the moments when I posted in this thread yesterday, though I do hold information about them, and can even relive them to some extent by reading the post again.

I know that tomorrow from my perspective must be further downstream in time from the point I am viewing, yet I do not have information about that event, and can only relive it in my imagination.

Something interesting to think about, when I get around to thinking about it, that is.

OK, but I still don't see where you aren't just restating the obvious.

[inflector]

...[snip]...
And QM also seems to give your argument an even bigger problem as non-locality is precisely about spanning the flow of time. You can't imagine a jumble of topologically disconnected spatial frames and still have non-locality find a way through the maze to connect them. And if you can, then the paths aren't topologically broken in the first place because the connecting paths exist.

Sort of like the many worlds argument. How can that be rendered than other as a topologically branching tree?

I know the above excerpt is from a few months back, however, as I have just for the first time read this quote, I wanted to make sure I understand it correctly.

First, you say:
You can't imagine a jumble of topologically disconnected spatial frames and still have non-locality find a way through the maze to connect them. And if you can, then the paths aren't topologically broken in the first place because the connecting paths exist.

What precisely do you mean by topologically disconnected spatial frames? Do you mean that there is no causal connection between the frames?

Could it not be the case where spacetime is very much like a tree where the connections that are causally constrained at the speed limit of C would be those defined as traversing up, down, and across the branches of the tree itself. But as with an actual tree, branches from one major bough often brush up against branches from another bough thereby bypassing the normal connection/causality speed limit? Is it not possible that non-local interactions are caused by these sorts of temporary connections between otherwise topologically disconnected spatial frames?

[Max™]

Actually, you never perceive "now". No one does. It takes a bit of time for all the information from "now" to flow through your sensory systems and be processed by your brain to have the "now" experience, and by then, it's gone. So there's always a bit of lag.

Well, I do perceive "now", I'm merely aware that I do a few fractions of a second after the moment which I labeled as the present.


Is there anything meaningful in saying one person's experience at moment x was different than another person's experience at moment x?

If I am attempting to define a general plane of simultaneity for earth bound observers, I suppose there is?

We're close enough spatially, and in similar enough states of motion that the discontinuity between what I claim is a set of simultaneous events will differ little from the set you claim, only at the most distant fringes of our observable portions of the universe would we be likely to notice such small variations.

The moment when you read this, is roughly the same instant as a bird landing on a branch outside your window, as a car accident in Calcutta, as me scratching my ear upstairs.



Tomorrow, when I check back on this thread, this moment when I read these words I wrote a day before will seem like "now" to me, but I am aware as I write them that it is off that way *motions vaguely in the downstream direction of time*, or more accurately, I am aware that it can only be off in that direction, towards what I would label the future.

It is possible that I might be killed before I get a chance to fulfill that little bit of prophetic self-interaction, or the computer could crash, these boards could lose the post, or any number of different things could prevent my reading this post tomorrow.Why would reading things you wrote in the past seem like "now"? That might be something unique to your perspective.

When I re-read the bit I quoted inside your quote here, it felt like "now", does that explain what I was saying better?

Which raises another interesting question, why can we only recall what we did in the past?
Why don't purple monkeys fly out of my butt? Who knows. It's just the way things work. Your brain can't make a memory out of events your sensory apparatus hasn't come into contact with yet.

I can't technically observe the past from my perspective either, I'm just aware that it exists due to information which I identify as having been stored in my brain at a prior date.

I am aware that the future exists as well, though I can not observe it from my perspective either.

It isn't as simple as "it's just how things work", maybe that works for you, I've never liked "just because" type answers myself.



I can not directly observe the moments when I posted in this thread yesterday, though I do hold information about them, and can even relive them to some extent by reading the post again.

I know that tomorrow from my perspective must be further downstream in time from the point I am viewing, yet I do not have information about that event, and can only relive it in my imagination.

Something interesting to think about, when I get around to thinking about it, that is.OK, but I still don't see where you aren't just restating the obvious.

Perhaps I didn't make my point as obvious as you thought?

There is no requirement for the three spatial dimensions we observe to have a particular axis of interaction. If I move to the right, that does not require that I was moving from the left at some prior point. If I move further to the right, it does not mean I have to continue going that way. If I wish to stop moving to the right at a given speed, I can do so.

Yet, I am aware of what I find best described as motion through time, but I am unable to stop, or change direction... and even then, describing time as just a different type of spatial direction makes me want to ask silly questions.

What is the speed of left, for example?

[apeiron]

What precisely do you mean by topologically disconnected spatial frames? Do you mean that there is no causal connection between the frames?

I was arguing that if they were disconnected, then it seems by definition there could be no causal linkage. Otherwise - even just with nonlocal effects - there is a link of some kind.


Could it not be the case where spacetime is very much like a tree where the connections that are causally constrained at the speed limit of C would be those defined as traversing up, down, and across the branches of the tree itself. But as with an actual tree, branches from one major bough often brush up against branches from another bough thereby bypassing the normal connection/causality speed limit? Is it not possible that non-local interactions are caused by these sorts of temporary connections between otherwise topologically disconnected spatial frames?

If two branching histories touch, then by this analogy where they touched they would share the same light cone surely?

[inflector]

If two branching histories touch, then by this analogy where they touched they would share the same light cone surely?

Well, I was thinking that they wouldn't share the same light cone. That's why I thought this could be a mechanism for non-local interaction which seems to be present in quantum entanglement, for example.

To me, nonlocal implies non-overlapping light cones, but perhaps I have this wrong.

I've been thinking about weird topologies for spacetime that would make nonlocal correlations possible using a realist perspective. A topology/geometry that would allow a dBB interpretation of quantum mechanics to meld with general relativity. A lost cause perhaps, I know, but hey, I've always liked working on the impossible.

[apeiron]

To me, nonlocal implies non-overlapping light cones, but perhaps I have this wrong.

I might misunderstand you, but my view is that a non-local entanglement, as thought of in EPR, would look like two events on opposite sides of the same light cone, or branch-lets of the same bough in your analogy.

So the paradox is not that there is entanglement (because there is a shared event in the past of the two later events - the moment that created their entanglement) but that then there can be some non-local constraint that acts "instantly" to span the full width of the lightcone. So observe a particle's spin on one side, and it determines also the spin on the other side of the light cone.

In your analogy, if one bough touches another (the equivalent of an observer measuring the spin of one particle) then branchlets over the far side of the bough also shiver with that touch.

And indeed, this would be an accurate portrayal I would think. Decoherence would travel in timeless fashion to constrain everything within the light cone. The tree branch analogy might even have the advantage of giving the image of the path by which things "travel all the way back to the fork and back up the other side" rather than the alternative view of a constraint acting "instantly" across the current breadth of the light cone.

I've been thinking about weird topologies for spacetime that would make nonlocal correlations possible using a realist perspective. A topology/geometry that would allow a dBB interpretation of quantum mechanics to meld with general relativity. A lost cause perhaps, I know, but hey, I've always liked working on the impossible.

The idea of fractal branching seems to me a very natural one as it gives you an actual mathematical representation of dissipative structures - it is how entropy spreads out to fill a space of the possible. So as a "weird topology" it is in fact well motivated and quite realistic.

But again, when it comes to QM, I would see the collapse of a wave function in sum over histories terms. So before collapse, the lightcone of an event was in an indeterminate state in which "anything" was possible. After the collapse, you have some actual determined path (a branch representing a thermalising event) plus all the "air" around the branch, which is now the equally definite places within the lightcone where the event did not happen.

So nonlocality can either be seen as a constraint that "jumped instantly" across the lightcone, or instead - using the branching analogy - that the nonlocality is written into the branching structure itself. The entirety of the branch was decohered - all the way back in time to its origin - at the "moment" of observation (the brush of one branch against another).

[petm1]

I can't technically observe the past from my perspective either, I'm just aware that it exists due to information which I identify as having been stored in my brain at a prior date.

I am aware that the future exists as well, though I can not observe it from my perspective either.


All I see is the past, formed within my eye as an image. This image is what I think of as the leading edge of my "now", a one second frame that I will only lose upon my death. What is "real" funny to me, is that what I think of as the future are the same signals that make up this image from the past I see as the present. :tongue2:

[ThomasT]

So nonlocality can either be seen as a constraint that "jumped instantly" across the lightcone, or instead - using the branching analogy - that the nonlocality is written into the branching structure itself. The entirety of the branch was decohered - all the way back in time to its origin - at the "moment" of observation (the brush of one branch against another).Your discussion of branching topologies is over my head, but wrt the applicability of nonlocality to the OP's question my first thought is that since there really isn't what I would call a significant difference between local realist models of entanglement and the quantitative results, I think it's a bit early to start speculating from the assumption that reality is nonlocal.

To answer the question in the title of the thread we just need to objectively define the terms reality and time. Such definitions do exist, and from them it follows that it's correct to say that time is real.

Of course, given the inferential speculative possibilities of modern physics, there's much more that can be said wrt the OP's considerations. And, as usual, after reading what several posters have had to say on this, I'm thoroughly confused again.

[petm1]

can I not determine an absolute definition of simultaneous events, and thus destroy the very foundations of relativity?

The very foundation of relativity lies in the the little twist called big bang, this one event and when it flew apart, it was simultaneous motion that was lost in space. :rofl:

[Max™]

The very foundation of relativity lies in the the little twist called big bang, this one event and when it flew apart, it was simultaneous motion that was lost in space. :rofl:

Twas a rhetorical question, I'm pretty well informed regarding relativity.

[petm1]

Twas a rhetorical question, I'm pretty well informed regarding relativity.

Sorry, did not mean to offend with my light joke.

[inflector]

I might misunderstand you, but my view is that a non-local entanglement, as thought of in EPR, would look like two events on opposite sides of the same light cone, or branch-lets of the same bough in your analogy.

That makes sense. I was viewing the light cones of the two measurements as two separate light cones.

Clearly, the light cone of the entangling photon generating event contains the two photons as they are measured.

In your analogy, if one bough touches another (the equivalent of an observer measuring the spin of one particle) then branchlets over the far side of the bough also shiver with that touch.

And indeed, this would be an accurate portrayal I would think. Decoherence would travel in timeless fashion to constrain everything within the light cone. The tree branch analogy might even have the advantage of giving the image of the path by which things "travel all the way back to the fork and back up the other side" rather than the alternative view of a constraint acting "instantly" across the current breadth of the light cone.

I'm just thinking of possibilities for the observed nonlocal behavior. So the tree analogy gives two separate potential approaches, touching branches and decoherence traveling up and down the branches in some superluminal fashion.

So nonlocality can either be seen as a constraint that "jumped instantly" across the lightcone, or instead - using the branching analogy - that the nonlocality is written into the branching structure itself. The entirety of the branch was decohered - all the way back in time to its origin - at the "moment" of observation (the brush of one branch against another).

Either one of these options is one that merits further thought. The possibility (however slight) that there could be some realistic explanation is what keeps me working on these sorts of ideas.

[Descartz2000]

I have seen several responses here that claim the present is all that is real and true. I agree with this, but every state is a present state. So, more accurately I can't claim that this particular 'now' state is only real and true. When any state is in a physical form and in a specific set of configurations, it is physically present and real. But, this logic applies to all states. So, when I claim, "my present moment 'now' as I write this is most real", I am in error because the same logic applies to all observed states. So, the viewpoint of 'now' carries no extra value than the viewpoint of yesterday's 'now' observation. So, inherently all 'now' states are equal. Therefore, I can't claim this 'now' state is more real than a percieved 'past' or 'future' state, because they all carry the same value and logical principles.

[Descartz2000]

If you believe that the state of things has to be crisp and definite - something either is or it isn't - then you indeed face a logical bind. Past and future are either states that are - which ends up in the deterministic block time view where the now is an illusion - or instead only the now is real, which makes past and future the illusion.

So yes, think that way and you are trapped into mutually contradicting positions, neither of which feels right.

Which is why I stressed the further dimension to reality, the dimension of development that runs from the vague to the crisp, from becoming to being, possibility to actuality, etc. This is a traditonal idea in metaphysics even if it has become largely lost in physics.

So the past is definite (it cannot be changed) while the future is indefinite (it is still full of vague potential, a capacity for change, while also of course highly constrained because of a weight of accumulated history).

The best kind of model of this could be a scalefree network or other "edge of chaos" model where the "now" is a mix of past and future - a powerlaw mixture of the changed and the changing, islands of stasis and flux.

Look inside the "now" of the universe - which can be measured in a general way by its current temperature - and you will be able to see that it is in fact an average of local "nows".

This follows from the transactional interpretation of QM, a la Cramer, I believe.

I don't understand where the contradiction lies. Why shouldn't things be crisp and definite especially when we are talking about the macro world? Leaving QM aside, I think on the large scale most things and events are deterministic, maybe not predictable, but deterministic. So, where is this area of non 'crispness' that you talk about especially when we are referring to everyday real world events? The future is not 'open' so to speak, at least no objectively. It is open from your perspective of 'now', but this viewpoint is not preferred over any other viewpoint. If it is 'open', then your viewpoint of 'now' is more valid of a perspective, than your viewpoint in the future. yet, this is incorrect. According to Relativity, no 'now' state is more valid than any other.

[apeiron]

I think on the large scale most things and events are deterministic, maybe not predictable, but deterministic. So, where is this area of non 'crispness' that you talk about especially when we are referring to everyday real world events? The future is not 'open' so to speak, at least no objectively. It is open from your perspective of 'now', but this viewpoint is not preferred over any other viewpoint. If it is 'open', then your viewpoint of 'now' is more valid of a perspective, than your viewpoint in the future. yet, this is incorrect.

Take a seed. It could turn into many different potential trees - different branching patterns depending on the vagaries of soil, weather, disease, angle of sun and wind, competition from other trees. So its future state is relatively unconstrained in some regards. Its future is broadly determined (by its genetic history, an accumulation of past information) but is open, indeterminate, in its detail.

According to Relativity, no 'now' state is more valid than any other.

Yes, but this is just because time is modelled as a locally reversible or symmetric dimension. It leaves out any attempt to represent an arrow of time, a gradient. So relativity may tell the truth, but not the whole truth!