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

[Arman777]

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.

Thanks. But for example what kind of state of changes ?

In the baby and old man case. I can say that there's change in the molecular level in the body of the person. That molecular changes causes the to be person to be old. It doesn't happen by suddenly. And those molecular change can be expressed as motion. By motion, I don't consider only the change in the time dimension but also in the space. For example, when the body gets old there are molecular motions in our body, Like chemical things. We can understand that the two different states. But for change in that state again, we need a molecular motion.

Or without any motion (in atomic level or in general ) how can we understand the change in the state?

Or again in other words, change of state doesn't happen by motion?

 

[stevendaryl]

Thanks. But for example what kind of state of changes ?

In the baby and old man case. I can say that there's change in the molecular level in the body of the person. That molecular changes causes the to be person to be old. It doesn't happen by suddenly. And those molecular change can be expressed as motion. By motion, I don't consider only the change in the time dimension but also in the space. For example, when the body gets old there are molecular motions in our body, Like chemical things. We can understand that the two different states. But for change in that state again, we need a molecular motion.

Or without any motion (in atomic level or in general ) how can we understand the change in the state?

Or again in other words, change of state doesn't happen by motion?

There is certainly no necessary reason for changes of state to be associated with motion. For example, in particle physics, the neutral kaon, K^0 oscillates with time to change into its own anti-particle, \bar{K^0}.

 

[kent davidge]

for example what kind of state of changes ?

We have to be carefull about the use of the term "state". For your question I would use the situation given by @rede96. In that case there is change of state, because the very act of thinking about something involves brain activity, which changes the state of the brain from "before thinking about something" to "after thinking about something" --and this something may be the simplest of all the thoughts.

But, yet, the inteligent being may not be moving at all in space (we could not say that he/she is or is not moving in time, because we are actually trying to define time.)

 

[PeroK]

Thanks. But for example what kind of state of changes ?

In the baby and old man case. I can say that there's change in the molecular level in the body of the person. That molecular changes causes the to be person to be old. It doesn't happen by suddenly. And those molecular change can be expressed as motion. By motion, I don't consider only the change in the time dimension but also in the space. For example, when the body gets old there are molecular motions in our body, Like chemical things. We can understand that the two different states. But for change in that state again, we need a molecular motion.

Or without any motion (in atomic level or in general ) how can we understand the change in the state?

Or again in other words, change of state doesn't happen by motion?

I don't find this argument satisfactory, because age is not defined by motion. If you count my grey hairs, for example. That must be due to a difference in my body's processes from when I was younger. Okay, things must have "moved" somewhere along the line as part of that change, but it's stretching a point to say that the biological processes that produce grey rather than dark hairs are defined by that motion.

 

[Sean Nelson]

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

I agree. To say that using this description, also leaves question to an inability to know if you are static or in motion. Without a point of reference with your description of your solidarity in space. How do you know if you are not traveling. What is your frame of reference to show you are not traveling 25,000 km per hour. This said you have removed your question of time.

 

[jbriggs444]

also leaves question to an inability to know if you are static or in motion.

That is precisely the point. That the notion of "motion", a variation of "position" in some (three dimensional?) space is not essential to the notion of time.

 

[PeroK]

Additionally, if we take a quantum system, then the conventional concept of motion.of a particle breaks down and it's actually the state (vector) that is changing.

In a harmonic oscillator, for example, it's not that the particle has moved from A to B, but that the state has changed, leading to the change in the expected value of a position measurement from A to B.

And, if we consider the spin state of a particle, then that and the expected value of spin measurements can change, with time, independent of the motion of the particle. Or any motion.

 

[Arman777]

That is precisely the point. That the notion of "motion", a variation of "position" in some (three dimensional?) space is not essential to the notion of time.

Then I am asking again how can you define time without using the notion of motion ?

 

[PeroK]

Then I am asking again how can you define time without using the notion of motion ?

As in post #97, you could, theoretically, use spin precession of an electron in a uniform magnetic field to measure time.

In general, the state of a quantum system changes with time.

 

[Dale]

Even you count numbers there's "speed" (motion).

. "Decay" itself is the motion.

I disagree with those descriptions. That is just redefining “motion” so that it loses all meaning and therefore can be used to justify your (now meaningless) claim.

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

None of that is motion. After the decay then the decay products move, but the decay itself is not motion.

The usual hyperfine transition used in standard atomic clocks is not motion, and in fact must be corrected for any motion that does occur.

 

[Sorcerer]

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.

Yeah but computers only work because electric signals move around inside them, right?

 

[Arman777]

As in post #97, you could, theoretically, use spin precession of an electron in a uniform magnetic field to measure time.

In general, the state of a quantum system changes with time.

Okay then can you show mathematically for us how you do that ? Build a clock for us.

 

[Arman777]

therefore can be used to justify your (now meaningless) claim.

I don't see how can you do that ?

None of that is motion. After the decay then the decay products move, but the decay itself is not motion.

The usual hyperfine transition used in standard atomic clocks is not motion, and in fact must be corrected for any motion that does occur.

If, after decay particles don't move, then how can you possibly understand that decay "happened". I am really curious about that.

I am not sure you guys understand me. Motion happens at any level in the universe. there's has to be change in the system so we can understand the change but the change happens also in the space. Becasue that's where we live in and it can be count as motion.

The usual hyperfine transition used in standard atomic clocks is not motion, and in fact must be corrected for any motion that does occur.

So the atoms in the clock don't move at all (also the electrons) and we can perfectly know their position and nothing happens to them or etc right ? They are not excited or we don't measure things. Well Of course not there's no such thing as not moving particle. Your definition doesn't make sense at all actually.

Motion is everywhere. Everything is in motion respect to something at any level. And to measure the time you need motion.

 

[PeterDonis]

as soon as you start to do physics it's the time derivatives (of spatial coordinates among other things) that appear

Careful. We're in the relativity forum here, where there is no such thing as a "time derivative" in any coordinate-independent sense. There are only "spacetime derivatives". This is a "B" level thread so it's hard to get too technical about this, but I don't think it's useful to focus on just time coordinate derivatives in a relativistic context.

 

[PeterDonis]

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.

Sorry, you're contradicting yourself again. If you had left out the last sentence I would probably have let it pass; but if you insist on using the word "directional" you can't get away from the fact that there are two "time" directions, past and future. More generally, any time you have an ordered set--and the proper times along any worldline are an ordered set--there are always two "directions" to the ordering.

As it’s impossible for a system not to change

This is wrong. A system in an energy eigenstate does not change. The fact that it does not have a definite value for all observables does not make that false. If you measure an observable of the system that does not commute with energy, then you change the state of the system so it's no longer in an energy eigenstate; yes, at that point you can say the system will "change", but that's because you changed the state when you measured it, not because it was changing before you measured it.

all systems are constantly evolving forward. Which is how I understood that the flow of time was always forward.

"Forward" is not an inherent property of time, it's a choice we make; we label one of the two directions of time the "forward" direction because that's the direction we can only predict, not remember. Ultimately this is because of the second law of thermodynamics and the fact that our universe started out in a very low entropy state. The underlying laws of physics are time symmetric; they don't pick out either direction of time as "forward"--both directions are the same as far as the underlying laws are concerned. The fact that our universe started out in a very low entropy state is a contingent fact about the particular solution of the laws that we live in, not about the laws themselves.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

This thread has run its course and will remain closed.