High School Why do we Experience a 'Flow' of Time?

[PeterDonis]

Doesn’t that just mean the energy of that system doesn’t change?

Yes.

I thought all systems must have zero point energy as if the didn’t it would violate the uncertainty principle?

Sort of. The idea of "zero point energy" originally came from the fact that, if you solve the most basic QM harmonic oscillator, there is a term in the Hamiltonian that is present even when the oscillator is not oscillating at all (i.e., where classically we would say that it had exactly zero energy). But that term in the oscillator Hamiltonian does not "vary"; it isn't uncertain at all. It's a definite value. So all it really means is that the vacuum--the state with zero oscillations--is also an eigenstate of the Hamiltonian. It doesn't mean there is any "uncertainty" that drives the vacuum to have "zero point energy". (This also means that the common idea of "vacuum fluctuations" is, at best, somewhat misleading. I believe there is a series of PF Insights articles on this.)

More generally, any physically reasonable Hamiltonian must have a ground state, i.e., an eigenstate of lowest energy. Often, if you just solve the equations and don't make any adjustments, the energy of this eigenstate won't be zero, just as for the harmonic oscillator. But, as I said before, absolute values of energy in QM have no physical meaning; only energy differences do. So you can always just subtract the ground state energy from the Hamiltonian to get a Hamiltonian whose lowest energy state has exactly zero energy. That's what is normally done.

A better reason for thinking of real systems as having "zero point energy" is that, for any real system, it's impossible to get it exactly into the vacuum state--because that state would be a state with nothing at all present, and if nothing at all is present, how can you have any equipment that prepares anything in any particular state? So what actually happens when you try to get some particular system into its vacuum state is that it is in a state which is "close" to the vacuum, but also has nonzero amplitude to be in some non-vacuum state--i.e., its state is not an exact eigenstate of the Hamiltonian. That means that, when you measure the system's energy, it will not always be the same, and some people interpret this in terms like "vacuum fluctuations". (IIRC, the Insights series I referred to above talks about this.)

Just to be clear ‘no change’ to me means no change in anything. Momentum, position, energy etc.

That's not possible, because, for example, momentum and position can't both have definite values in any state. An energy eigenstate will generally be a momentum eigenstate, but certainly not a position eigenstate. So it is impossible to have any quantum state that does not "change" by your definition. Which means your definition is unhelpful, since it doesn't pick out any particular states at all.

going up or down is change

Change in two different directions (up vs. down), yes. Not "just one direction of change", which is what you were claiming.

 

[PeroK]

I think there's no "flow of time" the only thing that we can say objects are moving in space-time relative to someone and that's all.

If there is no flow of time, what do you mean by "moving"?

 

[Sean Nelson]

If there is no flow of time, what do you mean by "moving"?

Time is part of the uniform larger fabric of the universe, not something moving around inside it

 

[Arman777]

Time is part of the uniform larger fabric of the universe, not something moving around inside it

Yes,

If there is no flow of time, what do you mean by "moving"?

By moving I mean velocity of the object (or motion) in space-time. And this is the point where everything should be clear. We can describe an object that only moves in the "time" axis or only on the "space". But that doesn't reflect the reality due to SR. All objects move in space-time hence all motions can be desrcibed as velocity. We define time using the motion. Thats what I am thinking at least.

 

[Dale]

All objects move in space-time hence all motions can be desrcibed as velocity.

Hmm, the common “block universe” view of spacetime would probably say that no objects move in spacetime. In that view, instead of “motion” you have tangent vectors to worldlines.

 

[Arman777]

Hmm, the common “block universe” view of spacetime would probably say that no objects move in spacetime. In that view, instead of “motion” you have tangent vectors to worldlines.

I see well okay then.

 

[PeroK]

I see well okay then.

It's not okay. If someone can be really clever and describe physics without using the notion that time "flows", then all well and good. But, all you're doing is declaring that you don't need this concept, but that leaves you with no way to describe physics. Put simply, we use a time parameter to put events into a sequence. You can study 1D, 2D or 3D problems, but you always need a time dimension. You can't drop the time dimension and study physics in two spatial dimensions.

If you want to move away from this view, you need something more sophisticated than a wave of the hand and a vague reference to "spacetime".

 

[Arman777]

It's not okay. If someone can be really clever and describe physics without using the notion that time "flows", then all well and good. But, all you're doing is declaring that you don't need this concept, but that leaves you with no way to describe physics. Put simply, we use a time parameter to put events into a sequence. You can study 1D, 2D or 3D problems, but you always need a time dimension. You can't drop the time dimension and study physics in two spatial dimensions.

If you want to move away from this view, you need something more sophisticated than a wave of the hand and a vague reference to "spacetime".

I am not saying we don't need time or time dimension. I am saying that there's no such thing as just "time" or "space" there's only spacetime

You cannot separate space and time and treat them as different things.

Or in general, objects "flow" in spacetime not just in time.

 

[PeroK]

I am not saying we don't need time. I am saying that there's no such thing as just "time" or "space" there's only spacetime

You cannot separate space and time and treat them as different things.

Or in general objects flows in spacetime not in "time".

Time and space are different. For example, as soon as you start to do physics it's the time derivatives (of spatial coordinates among other things) that appear. You don't have equivalent formulations of the laws of motion in terms derivatives with respect to the spatial coordinates.

 

[rede96]

Change in two different directions (up vs. down), yes. Not "just one direction of change", which is what you were claiming.

Ah ok. No that’s not what I was claiming at all. What I was trying to say was along the lines that change, as in the evolution of the system is absolute. Something either changes or it doesn’t. So in that sense evolution is one directional. Always moving forward, never static. And if it can never be static then it can’t reverse as it can’t go through zero change. Hence why the flow of time is always forward.

That's not possible, because, for example, momentum and position can't both have definite values in any state.

Again, that was my point. As it’s impossible for a system not to change all systems are constantly evolving forward. Which is how I understood that the flow of time was always forward. And our perception of time is just how we perceive those changes. In very layman’s terms.

 

[timmdeeg]

Yes,

All objects move in space-time hence all motions can be desrcibed as velocity. We define time using the motion. Thats what I am thinking at least.

If we talk about the flow of proper time how can you "model" it using motion? Proper time is invariant but motion isn't.

 

[Arman777]

If we talk about the flow of proper time how can you "model" it using motion? Proper time is invariant but motion isn't.

For a light clock it can be defined as $\frac {2d}{c}$ where the $d$ is distance between two mirrors.

Here again there's $c$ which is motion of a light.

I don't think its possible to measure/define time using motion.

Time and motion are linked together. We can't define motion without time but also vice versa

 

[PeroK]

For a light clock it can be defined as $\frac {2d}{c}$ where the $d$ is distance between two mirrors.

Here again there's $c$ which is motion of a light.

I don't think its possible to measure/define time using motion.

Time and motion are linked together. We can't define motion without time but also vice versa

What about studying, say, the posts on PF? The number of posts per hour, average, maximum etc. There you clearly have the concept of time, but no immediate concept of motion through space.

Or, it would seem artificial to consider the concept of carbon dating, say, in the context of four dimensional spacetime.

 

[Stavros Kiri]

why do we experience a flow of time? Why is everything in the 'now' flowing toward the future, and not the past? Also, why do we all experience this flow the exact same way?

From the practical standpoint, the flow and arrow of time is connected to motion, processes and the 2nd law of thermodynamics. Especially irreversible processes "leave their mark" and they cannot but be (potentially) observed, especially since we also take part. I think that explains (partially [?]) of what we feel etc. ...

 

[Arman777]

What about studying, say, the posts on PF? The number of posts per hour, average, maximum etc. There you clearly have the concept of time, but no immediate concept of motion through space.

Or, it would seem artificial to consider the concept of carbon dating, say, in the context of four dimensional spacetime.

To post something you need to write something that's motion. Also making a clock using PF posts per hour is not a great idea. Anyway I don't think this example is a proper example ??

For carbon dating well, for decay we have also some motions that we can describe for atoms etc.

 

[Dale]

the fact that we remember the past and not the future has to do with entropy. And this is what gives us a sense of "flow" of time.

I think this actually answers the title question. Our mental experience of time is based on this.

It has always struck me that we walk through time backwards, “looking” at where we have been and unable to “see” what is right in front of us.

 

[Stavros Kiri]

I think this actually answers the title question. Our mental experience of time is based on this.

It has always struck me that we walk through time backwards, “looking” at where we have been and unable to “see” what is right in front of us.

Cf.
https://www.physicsforums.com/threads/why-do-we-experience-a-flow-of-time.941255/page-4#post-5954695

 

[Dale]

For carbon dating well, for decay we have also some motions that we can describe for atoms etc.

Radioactive decay, and other state transitions (like the hyperfine transition) do not appear to require thermal motion. In fact, it is a confounder that we try to eliminate or compensate.

 

[Arman777]

Radioactive decay, and other state transitions (like the hyperfine transition) do not appear to require thermal motion. In fact, it is a confounder that we try to eliminate or compensate.

"Carbon-14 dating, also called radiocarbon dating, the method of age determination that depends upon the decay of the nitrogen of radiocarbon (carbon-14). Carbon-14 is continually formed in nature by the interaction of neutrons with nitrogen-14 in the Earth’s atmosphere; the neutrons required for this reaction are produced by cosmic rays interacting with the atmosphere."

https://www.britannica.com/science/carbon-14-dating

I mean this a type of motion. Carbon 14 just don't produce by itself and also to understand the decay part, again we need the motion. "Decay" itself is the motion.

 

[jbriggs444]

"Decay" itself is the motion.

Decay is not a "motion" in any relevant sense.

 

[Arman777]

Decay is not a "motion" in any relevant sense.

The process of decay is motion. In decay, it emits an electron and an electron antineutrino. So there's "motion".

I mean really any of you think that we can measure time without using "motion" or in other sense "velocity". Is this really how universe works or you guys just want to think that way?

Even when you measure the time you are measuring the cycles of a motion of a thing.

I am asking this seriously without motion how can you even define time? If I am wrong tell me a way to measure time without motion in any sense.

If any of you can prove this with math, I ll stop arguing. Otherwise I can assume that I am right and you guys are wrong.

And I ll be really happy If I am wrong because I want to see a way that its possible.

 

[Sorcerer]

What about studying, say, the posts on PF? The number of posts per hour, average, maximum etc. There you clearly have the concept of time, but no immediate concept of motion through space.

Or, it would seem artificial to consider the concept of carbon dating, say, in the context of four dimensional spacetime.

But wouldn’t someone in motion with respect to Earth measure those same coordinates as mixed between space and time as described by the Lorentz transformation?

 

[rede96]

I am asking this seriously without motion how can you even define time? If I am wrong tell me a way to measure time without motion in any sense.

Imagine a universe where you are the only thing that exits. You are floating in space, you have no sight, hearing, touch, taste or smell. Only your thoughts. It is impossible for you to define ‘motion’ in the way you have used the term ‘motion’ in your posts. Yet you can still count the seconds in your mind.

 

[Arman777]

Imagine a universe where you are the only thing that exits. You are floating in space, you have no sight, hearing, touch, taste or smell. Only your thoughts.

A problematic description. First thing is how can you define only yourself in the entire space and nothing else?

Yet you can still count the seconds in your mind.

I don't see any math in your description. I don't think this argument will be valid.
How you defined time? by just counting seconds in your mind? Whats seconds for you ? just counting numbers? Even you count numbers there's "speed" (motion). I can count 10 number faster than you.
In this sense there's also speed of how fast you count.

In any case I don't think this is valid

 

[jbriggs444]

A problematic description. First thing is how can you define only yourself in the entire space and nothing else?

I don't see any math in your description. I don't think this argument will be valid.
How you defined time? by just counting seconds in your mind? Whats seconds for you ? just counting numbers? Even you count numbers there's "speed" (motion). I can count 10 number faster than you.
In this sense there's also speed of how fast you count.

In any case I don't think this is valid

None of those objections are substantive.

 

[Arman777]

None of those objections are substantive.

What about his objection. Do you think its valid?

Is it solves my question? I don't think so

I still didn't get any mathematical answer to my question rather then I get 1 philosophical answer. Which doesn't make any sense at all

 

[stevendaryl]

I don't see any math in your description. I don't think this argument will be valid.
How you defined time? by just counting seconds in your mind? Whats seconds for you ? just counting numbers? Even you count numbers there's "speed" (motion). I can count 10 number faster than you.

Well, you're now at the point of defining any change between moments of time to be motion. Obviously, the phrase "between moments of time" makes it circular if you're using "motion" to define "time". If you eliminate "between moments of time" in your definition of motion, then it no longer has to do with time. The change in temperature between the North Pole and the equator doesn't imply time or motion, unless you assume that there is an observer who observed the temperature at one place at one time and observed the temperature of the other place at another time.

So, that might be the key to the notion of time: When two different objects with different properties are described as the same object at different times. There's one object, which is me as a baby. There's another object, which is me as an old man. Time connects the two and allows us to think of them as two different states of the same human being.

 

[PeroK]

But wouldn’t someone in motion with respect to Earth measure those same coordinates as mixed between space and time as described by the Lorentz transformation?

I don't really see the relevance of that. In fact, information technology in general is a human endeavour which has a time parameter, but no recognisable map to spacetime.

For example, a computer program, is not a physical object, has no spacetime coordinates - the physical location of the program is largely irrelevant - but it does have a history. Both as a logical object, it has a version history, and as a run time object it has a usage history, say.

Time, but not space, is very much a factor in IT systems. Especially in any sort of logical rather than physical view of a system.

 

[kent davidge]

Time connects the two and allows us to think of them as two different states of the same human being

And with that being noticed, a better explanation is that time happens when there's change of state of a system, not necessarly of motion. (This always has been my thought about time, good to see that someone else also thinks so.)

 

[kent davidge]

So I think @Arman777's point is valid, the only thing is that change of state is not always change of position --it's only one possible case.