Why is time special?

[warpus]

Yes we do. It is because things change and there is always a before and after. When you stop change (all change) time goes away.

Change is there because of time - you couldn't take away change without taking away time first...

According to my astronomy teacher, if you travel at the speed of light, t stands still.

But things still move when that happens, right?

 

[Bluemofia]

But things still move when that happens, right?

What do you mean?

If you mean that the thing moving at c is still moving, then yes.

Otherwise, I have no idea what you are talking about.

 

[warpus]

What do you mean?

If you mean that the thing moving at c is still moving, then yes.

Otherwise, I have no idea what you are talking about.

What happens from the point of view of a photon?

Time is still - but is there movement?

I move that there is.. no pun intended.

 

[Birdjaguar]

Change is there because of time - you couldn't take away change without taking away time first...

So we are down to which came first, time or change. I would suggest that since change actually takes place within the physical world and time is a concept, that change came first and our recognition of that change is how we discovered time.

If one believes in the big bang, then, time began "just after" the first instant of change in the most finite appearance of the most finite force, mass energy that came into being.

If the entire universe were to cool down to -273 K and all atomic and sub atomic and quantum behavior were to stop, if there were no movement or vibration or spin, no photons or forces or gravity, then time would stop. There would be a uniform stillness of an eternal, unchanging now. Perhaps that was the state of things prior to the big bang.

In theory, change could be stopped. You cannot stop time in any "independent" way. Hence my thinking that time depends upon change and the other way around.

 

[warpus]

If the entire universe were to cool down to -273 K and all atomic and sub atomic and quantum behavior were to stop, if there were no movement or vibration or spin, no photons or forces or gravity, then time would stop. There would be a uniform stillness of an eternal, unchanging now. Perhaps that was the state of things prior to the big bang

What about random quantum effects? Those would still be happening - even if everything were to cool down to absolute zero.

 

[Birdjaguar]

What about random quantum effects? Those would still be happening - even if everything were to cool down to absolute zero.

They would have to be stopped too. I used absolute zero for convenience sake. I'm not sure we know if quantum activity stops there. If there happens to be a sub quantum level of "stuff" that makes up quarks and leptons, then all of that would have to stop too. My contention is that time is dependent upon the most fundamental and basic "activity" (which is change) of the universe whatever that is.

 

[warpus]

They would have to be stopped too. I used absolute zero for convenience sake. I'm not sure we know if quantum activity stops there. If there happens to be a sub quantum level of "stuff" that makes up quarks and leptons, then all of that would have to stop too. My contention is that time is dependent upon the most fundamental and basic "activity" (which is change) of the universe whatever that is.

I think it's the other way around.

Plus I don't think it'd be physically possible to stop random quantum effects, so you couldn't stop time that way - even if that's how it "worked".

 

[Birdjaguar]

I think it's the other way around.

Plus I don't think it'd be physically possible to stop random quantum effects, so you couldn't stop time that way - even if that's how it "worked".

How so? What is time? How does time induce change?

 

[warpus]

How so? What is time? How does time induce change?

I would argue that time doesn't induce change - but it rather creates a framework in which change can happen. Physical laws take care of the rest.

 

[Birdjaguar]

I would argue that time doesn't induce change - but it rather creates a framework in which change can happen. Physical laws take care of the rest.

Ok, but what is time? Is this framework an actual one? If physcial laws operate within such a framework, then are you saying that time is more fundamental than the known basic forces of the universe?

 

[betazed]

...and collapsing wavefunctions in QM.

The collapsing wavefunction may just be an artifact of the way we do maths in QM. However, Roger Penrose has a theory that the wavefunction collapses when a certain mass-energy criteria is met; this is highly speculative of course. In any case, I do not see why this has to relate to time's arrow.

Hmm, CPT... I heard that C, P and T were violated in the weak interaction, and am now vaguely remembering that even though they are violated individually (as well as CP being violated), together, they represent a symmetry in nature. That's interesting... I wonder how they'll reconcile this with entropy?

Weak interaction violates C, P and CP.

Actually since thinking about this I've wondered how entropy is reconciled with even classical laws, given that classical mechanics is entirely reversible in time... If we were to compute the evolution of a system that increases entropy by considering the equations of motion of the composite particles, and then run that system in reverse, we would end up with a perfectly physical system that decreases entropy.

Not quite. The thermodynamic arrow (increasing entropy) is completely independent of the other arrows. So theoritically we could have completely reversible time and still have always increaing entropy. (something like we reverse time in some system making entropy decrease there but entropy of the universe as a whole increases). Hence, as I said earlier we really need to explain why the thermodynamic arrow points in the same direction as the other arrows.

And then there's Maxwell's Demon...

Any real implementation of the demon will not violate the 2nd law over any extended period of time.

Yes we do. It is because things change and there is always a before and after. When you stop change (all change) time goes away.

That is a circular definition. The question is why is there a before and after? You cannot explain the arrow of time while using it in the explanation itself. As for change, you can have change without time. Pressure changes with Volume (independent of time), potential energy changes with position (independent of time), etc. etc. Even when the change is w.r.t time, the problem is not with the change, but with the direction of the change. If all changes were perfectly reversible then also we will not have a arrow of time. So theoriticaly we can have time, change and still have no arrow.

 

[Souron]

I would say that The thermodinamic arrow of time and the consious arrow of time Have to point in the same direction, becouse thinking, like most natural processes, increase enthropy. It makes sence to me that the more information we process, the more net entropy we create.

 

[Bluemofia]

What happens from the point of view of a photon?

Time is still - but is there movement?

I move that there is.. no pun intended.

From the point of view of the photon, an eternity would pass in no time (literally).

Time is still, and it covers an infinite distance in no time in it's point of view. Assuming it doesn't hit anything. An eternity would pass for the outside world from the photon's point of view.

 

[Mise]

Not quite. The thermodynamic arrow (increasing entropy) is completely independent of the other arrows. So theoritically we could have completely reversible time and still have always increaing entropy. (something like we reverse time in some system making entropy decrease there but entropy of the universe as a whole increases). Hence, as I said earlier we really need to explain why the thermodynamic arrow points in the same direction as the other arrows.

I'm not convinced by that. I'll believe it when I see it

Like take the typical isolated partitioned box, where all the particles are held in one side of the partition. If the partition is removed, the particles spread out evenly. Theoretically, we could compute the motion of each individual particle using classical mechanics from the initial state to the equilibrium state. Then we could flip time (i.e. flip the sign on all the velocities), so that it goes from the eq'm state back to the initial state. The system is completely isolated -- no interaction occurs between the particles within the box and the rest of the universe. So what happens to the entropy?

 

[Birdjaguar]

As to why there is an arrow at all, we have no frigging idea.

Yes we do. It is because things change and there is always a before and after. When you stop change (all change) time goes away.

That is a circular definition. The question is why is there a before and after? You cannot explain the arrow of time while using it in the explanation itself.

I am missing how what I said is circular. I've tried to break down my previous post with added explanation but no change in the logic. Please show me where it is circular.
1. Things in the universe change at all levels from quantum to universal
2. There is a "before" state and an "after" state for each change
3. We calibrate the interval between "before" and "after" and call it time
4. When you stop all change, there are no more "after" states
5. Without an "after" state, there is no interval to calibrate
6. There is no time. Time goes away.

As for change, you can have change without time. Pressure changes with Volume (independent of time), potential energy changes with position (independent of time), etc. etc. Even when the change is w.r.t time, the problem is not with the change, but with the direction of the change.

This makes no sense to me except as a mathtmatical exercise. If pressure changes from X to Y as volume changes from A to B, you may not need a time factor to make the calculation true, but in reality, you cannot change either without some interval of "time".

Or are you saying that in a laboratory, you can go from one pressure or volume to another instantaneously? If so, then you are implying that you can have two pressures (or volumes) at the same time. That sounds a bit odd to me.

If all changes were perfectly reversible then also we will not have a arrow of time. So theoriticaly we can have time, change and still have no arrow.

For me, the fact that there seems to be a direction to the arrow of time (a before and after state) implys a fundamental purpose to creation.

 

[Odin2006]

I rember reading in an older (80's) book on QM for a lay readership that a particle going forward in time is equivalent to an anti-particle going backwards in time and vice versa.

 

[Birdjaguar]

I rember reading in an older (80's) book on QM for a lay readership that a particle going forward in time is equivalent to an anti-particle going backwards in time and vice versa.

I'm sure anti matter would put a whole new spin on all this.

 

[betazed]

I rember reading in an older (80's) book on QM for a lay readership that a particle going forward in time is equivalent to an anti-particle going backwards in time and vice versa.

Yes they are mathematically equal (but that equality is just a math gimmick).

@BJ: You are still missing the point. The point is not that there is a before and after (which is just an ordering issue - we can have before and after in space dimensions too; in the line from here to Saturn's orbit, Mar's orbit comes before Jupiter's orbit), but that in the time dimension the before and after cannot switch places always (they can sometimes) (like in space, draw the line from Saturn to here and Jupiter's orbit comes first). Why am I failing to communicate?

 

[warpus]

1. Things in the universe change at all levels from quantum to universal
2. There is a "before" state and an "after" state for each change
3. We calibrate the interval between "before" and "after" and call it time
4. When you stop all change, there are no more "after" states
5. Without an "after" state, there is no interval to calibrate
6. There is no time. Time goes away.

I don't like this argument. It's like saying that if all the matter in the universe was put in 1 place - length, width, and height would just 'go away'.

 

[Birdjaguar]

1. Things in the universe change at all levels from quantum to universal
2. There is a "before" state and an "after" state for each change
3. We calibrate the interval between "before" and "after" and call it time
4. When you stop all change, there are no more "after" states
5. Without an "after" state, there is no interval to calibrate
6. There is no time. Time goes away.

I don't like this argument. It's like saying that if all the matter in the universe was put in 1 place - length, width, and height would just 'go away'.

IIRC, isn't that the starting point for the big bang?

I do understand "not liking" the argument and I am open to other suggestions.