Why can we not see the future?

[aberrated]

Why cannot we see the future? You see, all the laws of relativity, quantum mechanics and the other physics interaction laws are time-reversible

Then why cannot we see the future as well? I mean, when I look at the sky, I'm supposed to see ALL the stars that have zero-space-time-interval with me, not just those who have zero-space-time-interval AND of past.

 

[michael879]

not that this has much to do with ur question but if the multiple universe theory isn't true I think quantum mechanics isn't reversible.

 

[michael879]

o yea, and the answer is that light takes time to reach us. There is no way to see something before it happens.

 

[MeJennifer]

Then why cannot we see the future as well? I mean, when I look at the sky, I'm supposed to see ALL the stars that have zero-space-time-interval with me, not just those who have zero-space-time-interval AND of past.

Actually we do not see the stars themselves at all. We only see the photons that traveled from the stars to our eyes.
And from our frame of reference it takes time for the photon to reach us since their speed is finite.

 

[cesiumfrog]

There is no way to see something before it happens.

It remains a valid physics question (that may eventually be answered through GR/cosmology), why do we remember the past and not the future?

 

[DaveC426913]

The short answer is that, while most of the laws of physics are time-reversible, entropy is not; it only travels from past to future. As do our experiences.

 

[masudr]

An argument is as follows:

The universe was apparently in a state of low entropy to start with. And since entropy can only increase in all thermal processes, time only flows in one direction.

If the universe was not in such a low-entropy state, who knows, perhaps things would have been different.

 

[Astronuc]

Why cannot we see the future? You see, all the laws of relativity, quantum mechanics and the other physics interaction laws are time-reversible

Then why cannot we see the future as well? I mean, when I look at the sky, I'm supposed to see ALL the stars that have zero-space-time-interval with me, not just those who have zero-space-time-interval AND of past.

Because it hasn't happened yet. Because time is one way. Of course one can contrive a mathematical model that will permit anything, but then one might not be able to physically realize what one's model indicates.

People should be careful not to confuse models with reality.

 

[cesiumfrog]

If the universe was not in such a low-entropy state, who knows, perhaps things would have been different.

The odd thing (from a fluctuation theorem standpoint) is not that we observe our solar system to have had such improbably low-entropy at one time (since our existence seems to demand roughly that much), but that at the same time conditions were just as locally-improbable across our entire galaxy and every other galaxy we observe beyond..

 

[cesiumfrog]

People should be careful not to confuse models with reality.

Einstein famously made quite the business of that: QM sprang from "confusing" Planck's model with reality, and GR from refusing to distinguish between real gravity and a model of gravity (acceleration).

 

[JesseM]

Because it hasn't happened yet. Because time is one way. Of course one can contrive a mathematical model that will permit anything, but then one might not be able to physically realize what one's model indicates.

People should be careful not to confuse models with reality.

That's not really a physically meaningful answer. If the universe had a future low-entropy boundary condition and no past one, then we would remember the future according to the current understanding of physics, although presumably we would think of it as the past.

Think of it this way--suppose we had a giant supercomputer that could simulate a collection of particles as large as those that make up the solar system, for billions of years, according to the fundamental laws of physics. And suppose we could do multiple multibillionyear simulations with different starting conditions, and we simply chose the initial conditions completely randomly. This would mean that on the vast majority of runs, the initial conditions would be at or very close to maximum entropy, and would stay at or close to maximum entropy throughout the entire run, so that there'd be no overall entropic arrow of time. With a mind-bogglingly vast number of runs, though, there'd occasionally be runs which happened to start out at very low entropy, similar to that of the nebula that our solar system formed out of, which could then form a simulated star and simulated solar system, perhaps one where sim-life would arise and evolve intelligence. There'd also occasionally be runs which started out at high entropy, but with just the right combination of positions and momenta so that entropy would continually decrease, such that the end of the simulation would be in a very low-entropy state similar to that of the nebula the solar system formed from. Both types of runs would be vanishingly rare--maybe 1 in a googolplex, who knows--but if the fundamental laws were time-reversible, they would have to be equally rare, the second type would be no rarer than the first. And the second type would really be a time-reversed version of the first type in every respect, including the fact that any intelligent life in the simulations with low-entropy final conditions would remember the future and not the past, in spite of the fact that these events "haven't happened yet" from our outside perspective watching the simulation.

 

[jeryst]

It remains a valid physics question (that may eventually be answered through GR/cosmology), why do we remember the past and not the future?

We don't remember the past. We remember events that happened to us, and their relationship to one another in relation to our existence. You can't look into the future (just liike you can't look into the past) because time is only a concept created by us to help us explain those relationships.

 

[JesseM]

We don't remember the past. We remember events that happened to us, and their relationship to one another in relation to our existence. You can't look into the future (just liike you can't look into the past) because time is only a concept created by us to help us explain those relationships.

Do you disagree with my conclusions about the results of the thought-experiment where you simulate a solar-system sized collection of simulated particles with randomly chosen initial conditions? Specifically, do you disagree that runs where the system started at low entropy and went to high entropy, with any intelligent life that evolved during the run remembering the past and not the future, would be no more common than the reverse, runs which start at high entropy and go to low entropy with life in that run remembering the future and not the past? This is a necessary consequence of time-reversible laws, since there must be a one-to-one relationship between paths in the phase space that match the first description and paths that match the second, so that each type occupies an equal volume in phase space, and choosing initial conditions randomly corresponds to picking a random starting point in the phase space.

It is also the position of all the physicists I have read addressing the "arrow of time" issue that all arrows of time, including the fact that we remember the past but not the future, are consequences of the low entropy of the universe around the time of the big bang. For example, on pp. 145-145 of A Brief History of Time, Stephen Hawking writes:

It is rather difficult to talk about human memory because we don't know how the brain works in detail. We do, however, know all about how computer memories work. I shall therefore discuss the psychological arrow of time for computers. I think it is reasonable to assume that the arrow for computers is the same as that for humans. If it were not, one could make a killing on the stock exchange by having a computer that would remember tomorrow's prices!

A computer memory is basically a device containing elements that can exist in either of two states. A simple example is an abacus. In its simplest form, this consists of a number of wires; on each wire is a bead that can be put in one of two positions. Before an item is recorded in a computer's memory, the memory is in a disordered state, with equal probabilities for the two possible states. (The abacus beads are scattered randomly on the wires of the abacus.) After the memory interacts with the system to be remembered, it will definitely be in one state or the other, according to the state of the system. (Each abacus bead will be at either the left or the right of the abacus wire.) So the memory has passed from a disordered state to an ordered one. However, in order to make sure that the memory is in the right state, it is necessary to use a certain amount of energy (to move the bead or to power the computer, for example). This energy is dissipated as heat, and increases the amount of disorder in the universe. One can show that this increase in disorder is always greater than the increase in the order of the memory itself. Thus the heat expelled by the computer's cooling fan means that when a a computer records an item in memory, the total amount of disorder in the universe still goes up. The direction of time in which a computer remembers the past is the same as that in which disorder increases.

For a good general discussion of the arrow of time issue, I also recommend Huw Price's book Time's Arrow and Archimedes' Point.

 

[Farsight]

I think I agree with jeryst. Jesse, all of the language you use contains preconceptions which colour your thoughts. Take a look at The direction of time in which a computer remembers the past is the same as that in which disorder increases. I think there is no time. And there is no past. What you really have is things moving, and being recorded. There isn't necessarily any disorder. There are no arrows. There is no future. Even now is a figment of our imagination. All there is is space. And things in it. Moving. Changing. We see this, we recall our records, and we invent time and talk about time travel. But it isn't really out there.

 

[cesiumfrog]

We don't remember the past. We remember events that happened to us, and their relationship to one another in relation to our existence. You can't look into the future (just liike you can't look into the past) because time is only a concept created by us to help us explain those relationships.

According to current physics, time does exist (just as three spatial dimensions exist) and the "past" is correlated with the "future" (each is correlated with the present, and in a completely symmetric manner).

Now, if you accept that, why do you say we remember events that "happened to us" but not events that "will happen to us"?

JesseM: I borrowed that book after Huw Price gave a talk here on different interpretations of QM, it was especially interesting/curious after just having read Paul Davies' Physics of Time Asymmetry..

 

[JesseM]

I think I agree with jeryst. Jesse, all of the language you use contains preconceptions which colour your thoughts. Take a look at The direction of time in which a computer remembers the past is the same as that in which disorder increases. I think there is no time. And there is no past. What you really have is things moving, and being recorded. There isn't necessarily any disorder. There are no arrows. There is no future. Even now is a figment of our imagination. All there is is space. And things in it. Moving. Changing. We see this, we recall our records, and we invent time and talk about time travel. But it isn't really out there.

This seems like philosophical talk rather than anything with actual physical consequences. When physicists talk about time all they mean is that you can use clocks to assign time-coordinates to different events, when they talk about "arrows of time" all they mean is that for certain processes event X will consistently be assigned a later time-coordinate than event Y and not vice-versa, and when they talk about disorder all they mean is that there are well-defined rules for assigning a value of entropy to any given system. Unless you disagree that these procedures work fine in an operational sense, I can't see what the relevance of debating whether time or arrows of time or disorder "really exist", or what you think this philosophical talk is even supposed to mean.

 

[Farsight]

Jesse:

I didn't intend to bring philosophy into it, but instead focus on the physics of what's actually there. I do agree with procedures working fine in an operational sense, and I wasn't challenging entropy.

How can I clarify? Please try your paragraph above with different instead of later time coordinates. Or compare the arrow of time with the arrow of space.

 

[jeryst]

According to current physics, time does exist (just as three spatial dimensions exist) and the "past" is correlated with the "future" (each is correlated with the present, and in a completely symmetric manner).

The key word here is "current". Just because theories are current, doesn't mean they are correct. They are current because it's the best we have been able to come up with, that the majority agrees with. Every time we send up a new satellite, or launch a new probe, we are "surprised" to find that what we currently believe may not be, or is not, correct. For all we know, the Theory of Relativity may be just as inaccurate as any of the thousands of other "current" views that man has held to be true.

Now, if you accept that, why do you say we remember events that "happened to us" but not events that "will happen to us"?

I don't accept that. Any time you accept something, you close your mind to what may be the truth. Our brain records events as they occur, as a survival mechanism, otherwise we would keep putting our hand in the pretty fire. We can't remember what will happen to us, because we have not experienced the events for our brain to record them. Imagine what it would be like, if time does exist according to "current physics". At the moment of your birth, you would know everything about every event that will take place in your life, and there would be nothing you could do to change it (How depressing). You would know everything that you will ever learn during your life (Now there's a paradox). You would know every mistake that you will ever make, and what the consequences will be, but you will make them anyway. The universe would be unchangeable. Obviously, that's not the way things are. There is no set future, which means that there is no past or present, which means that time doesn't exist, except as a concept.

 

[DaveC426913]

The key word here is "current". Just because theories are current, doesn't mean they are correct. They are current because it's the best we have been able to come up with, that the majority agrees with. Every time we send up a new satellite, or launch a new probe, we are "surprised" to find that what we currently believe may not be, or is not, correct. For all we know, the Theory of Relativity may be just as inaccurate as any of the thousands of other "current" views that man has held to be true.

(It smacks of condescension to imply that all of us do not already know this. It really does go without saying.)

But it does not change anything. A theory being "our current understanding" does not reduce it to some sort of pseudo-theory.

 

[JesseM]

I don't accept that. Any time you accept something, you close your mind to what may be the truth. Our brain records events as they occur, as a survival mechanism, otherwise we would keep putting our hand in the pretty fire. We can't remember what will happen to us, because we have not experienced the events for our brain to record them. Imagine what it would be like, if time does exist according to "current physics". At the moment of your birth, you would know everything about every event that will take place in your life, and there would be nothing you could do to change it (How depressing). You would know everything that you will ever learn during your life (Now there's a paradox). You would know every mistake that you will ever make, and what the consequences will be, but you will make them anyway. The universe would be unchangeable. Obviously, that's not the way things are. There is no set future, which means that there is no past or present, which means that time doesn't exist, except as a concept.

That's nonsense, the idea that the future is set does not in any way imply that your physical brain would be capable of remembering future events in advance. We can certainly run computer simulations where the laws governing the simulated worlds are known in complete form, and they are both deterministic and time-reversible, but this doesn't mean we can look at any records that form within the simulation and find out about both past and future events within it! Any records in such a simulation will only record events in the direction of lower entropy, for reasons outlined by Hawking in the quote I posted earlier.

 

[JesseM]

Jesse:

I didn't intend to bring philosophy into it, but instead focus on the physics of what's actually there. I do agree with procedures working fine in an operational sense, and I wasn't challenging entropy.

How can I clarify? Please try your paragraph above with different instead of later time coordinates. Or compare the arrow of time with the arrow of space.

True, there is no inherent reason to label one direction of time "future" and one "past". But "arrow of time" just means that, regardless of which direction we call which, there will be certain processes that all face the same way in time. If we look at the worldlines of a bunch of eggs which hatch into baby chicks, we see that the place on the worldline where they are hatched is always further in a particular time-direction than the place on the worldline where the egg was laid, regardless of whether we call that direction "past" or "future"--the orientation is the same for all eggs, we don't see some eggs that hatch before they are laid while others are laid before they are hatched (again, regardless of which direction we call 'before' and 'after'). Similarly, we could talk about an "arrow of space" if there were some extended objects fixed in space (the way worldlines are fixed in spacetime) which were always oriented in a way such that part X of the object was always further along a particular spatial axis than part Y, regardless of whether we called this direction "further left" or "further right" or whatever.

 

[Farsight]

Jesse: it's very difficult it is to talk about time without talking about things like later and before. OK "worldline" is a good substitute, but it is perhaps just a cover, and again a concept. So I'm still not happy with "the arrow of time". Morever it arguably takes us into "block time" territory, which is further removes us from what we can actually see, measure and experiment upon.

 

[JesseM]

Jesse: it's very difficult it is to talk about time without talking about things like later and before. OK "worldline" is a good substitute, but it is perhaps just a cover, and again a concept. So I'm still not happy with "the arrow of time". Morever it arguably takes us into "block time" territory, which is further removes us from what we can actually see, measure and experiment upon.

But again, do you disagree that all this can be defined operationally in terms of measurements, without getting into philosophical issues of what it all "means"? If we have a procedure for assigning time-coordinates to events using a system of synchronized clocks, and we measure some process that always occurs in the same time-direction like the hatching eggs, what that means operationally is that for every given egg we will find the event of hatching takes place at a later time-coordinate than the event of being laid, or that for every given egg the event of hatching takes place at an earlier time-coordinate than the event of being laid, depending on which direction we define as the positive one. Either way, we will not find that some eggs hatch at an earlier time-coordinate than they were laid while others hatch at a later-time coordinate than they were laid, the direction will always be uniform.

 

[Farsight]

Jessem: No, I don't disagree.

But we're relating the spatial motion within clocks against the spatial motion within eggs, and since our measure is incrementing we must end up with a higher coordinate value for the hatching than the laying. We are then treating the incrementing measure as a spatial measure, and people ask "Is time travel possible?" as if we really did take a spatial measure.

 

[JesseM]

But we're relating the spatial motion within clocks against the spatial motion within eggs, and since our measure is incrementing we must end up with a higher coordinate value for the hatching than the laying.

Couldn't we just use clocks that counted "backwards" relative to the normal clocks we're used to, and then define the direction in which their reading increased as "forwards in time"? Using this procedure, we'd find that eggs would always hatch at smaller time-coordinates than they were laid.

We are then treating the incrementing measure as a spatial measure, and people ask "Is time travel possible?" as if we really did take a spatial measure.

I don't quite understand what you mean by "treating the incrementing measure as a spatial measure". For physicists, "time travel" would just mean that if you used a system of clocks and rulers to assign space and time coordinates to every point on the object's worldline, then you'd find that the worldline formed a loop in spacetime which revisited the same set of coordinates, just like a loop drawn on a 2D piece of paper--this is what's known as a "closed timelike curve", and it seems that Einstein's theory of general relativity does allow them in certain circumstances, although many physicists would bet that when quantum effects are incorporated into general relativity they will turn out to be impossible.

 

[Farsight]

Couldn't we just use clocks that counted "backwards" relative to the normal clocks we're used to, and then define the direction in which their reading increased as "forwards in time"? Using this procedure, we'd find that eggs would always hatch at smaller time-coordinates than they were laid.

I guess so. I suppose you could count using any method, though it will always involve motion of some kind. For example you could throw beans into a bucket. Or take them out. But the only direction that is actually there, is the direction of the beans' motion into or out of the bucket. The "fewer beans" direction is not a direction, it's something defined by you. And the only way you can "move" along this "direction" is by effecting some motion of the beans.

I don't quite understand what you mean by "treating the incrementing measure as a spatial measure".

See above.

For physicists, "time travel" would just mean that if you used a system of clocks and rulers to assign space and time coordinates to every point on the object's worldline, then you'd find that the worldline formed a loop in spacetime which revisited the same set of coordinates, just like a loop drawn on a 2D piece of paper--this is what's known as a "closed timelike curve", and it seems that Einstein's theory of general relativity does allow them in certain circumstances, although many physicists would bet that when quantum effects are incorporated into general relativity they will turn out to be impossible.

I'm aware of such, along with Godel, Cosmic Strings, Wormholes, etc. But I have to say I now think of time travel to the past as something like negative motion.

 

[jeryst]

That's nonsense, the idea that the future is set does not in any way imply that your physical brain would be capable of remembering future events in advance. We can certainly run computer simulations where the laws governing the simulated worlds are known in complete form, and they are both deterministic and time-reversible, but this doesn't mean we can look at any records that form within the simulation and find out about both past and future events within it! Any records in such a simulation will only record events in the direction of lower entropy, for reasons outlined by Hawking in the quote I posted earlier.

The original question was "Why can't we remember the future?" Both of us seem to agree as to why. We just differ on our views of time. I don't believe that the future is set, which means that time cannot exist as we define it, or as current physics defines it.

 

[ZapperZ]

This thread has gone on far too long, and has verged on many speculative ideas. I believe that we have been more than generous in allowing it to go on this long. Please review, especially those of you who are NEW here, the PF guidelines regarding the policy on speculative ideas and theories.

This thread is closed.

Zz.