Is There a Connection Between Movement Through Space-time and Aging?

[Naty1]

I simply don't understand the part where he says entropy OUGHT to get higher back in time just as it does as you go forwards in time. Why?

Maybe what he is getting at is that 'time' is reversible in many scenarios, and entropy aught to get higher regardless of the 'so called' direction of time.

that's just what Greene describes ...in my book, page 160:

Since Newtons laws ..have no built in temporal orientation...the reasoning we used to argue that systems will evolve from lower to higher entropy toward the future works equally well when applied toward the past...not only is there an overwhelming probability that the entropy of a physical system will be higher in what we call the future, but there is the same overwhelming probability that it was higher in what we call the past.

Page 161:

...entropic reasoning yields accurate and sensible conclusions when applied...to the future, but gives apparently inaccurate and seemingly ridiculous conclusions...when applied to the past...we will shortly find a way out of this strange place...entropic reasoning has taken us...

In my opinion, he spends far too many words on this incorrect view...I see I even have margin notes written in my book to remind myself of some of the incorrect conclusions based on the above reasoning...which he corrects later...


I wish he would have mentioned more modern ideas...

We discussed one set here:
emergent gravity
https://www.physicsforums.com/showthread.php?t=618397&page=2

involving:
Thermodynamics of Spacetime:
The Einstein Equation of State
Ted Jacobson, 1995

http://arxiv.org/abs/gr-qc/9504004


Ted Jacobsen, for example, has these insights:

The origin of large entropy is the vacuum fluctuations of quantum fields. ...and he points out that classical GR 'knows' that causal horizon area would turn out to be a form of entropy...and that entropy is proportional to causal horizon area...which increases over time...

 

[dubiousraves]

Greene on Spacetime

Greene explains time dilation using his analogy about a car having less eastward motion because it heads more northward. So, he says, we are all moving at the speed of light through spacetime. If we thus increase our speed through space, we have less speed for time, so time slows down. All good so far. But doesn't this assume we are naturally at rest moving 0 speed through space? I.e., could we move slower through space, and thus move faster through time? Why not? Also, why can we only control our motion through through the space half of spacetime, only affecting time corollarily?

 

[Naty1]

All good so far. But doesn't this assume we are naturally at rest moving 0 speed through space? I.e., could we move slower through space, and thus move faster through time? Why not? Also, why can we only control our motion through through the space half of spacetime, only affecting time corollarily?

It does not appear anyone or anything can 'move slower through space' than sitting still.
You are asking more than science can explain. We don't know a lot...like the origin of space and time, the mass of the electron, and why there is gravity.

All we can say is that so far in this universe, the speed of light seems to be the maximum velocity that information can be communicated...and no mass can travel quite that fast.

 

[Haelfix]

In my opinion, he spends far too many words on this incorrect view...I see I even have margin notes written in my book to remind myself of some of the incorrect conclusions based on the above reasoning...which he corrects later...

This is not an incorrect statement, just incomplete. In classical physics, and in quantum mechanics, one can show that entropy increases in either direction in time. The operation of sending t--> - t does not reverse the H theorem's arrow.

The reason there is a distinction between the past and the future is understood to be simply a statement about asymmetric boundary conditions between the past and the future. You simply have to postulate a low entropy initial condition in order to have any distinguishable directionality.

 

[Chestermiller]

For conceptualization purposes, some of us like to visualize space-time as a stationary absolute entity which replaces absolute space as it is described by the pre-relativistic Newtonian model. Within this framework, the 4 velocity of a particle represents its velocity relative to stationary space-time, and is equal to the speed of light when reckoned from the particle's rest frame of reference. But, as reckoned from a different inertial frame of reference, the particle has components both in the time direction, and in the spatial directions. The component in the time direction is γc. Unlike Euclidean 4D space where the Pythagorean theorem is satisfied, space-time is non-Euclidean and features a metric in which the square of the differential time component is opposite in sign to the squares of the differential spatial components. This is why, from the standpoint of an observer in another inertial frame of reference, the component of 4 velocity in the time direction (γc) is greater than the speed of light. Of course, this component can't be measured directly since, as mere 3D beings, we suffer from the inherent physical limitation of not being able to see into our own time dimension. I hope this visualization works for some of the PF readers that are struggling with these concepts.

Chet

 

[dubiousraves]

Thanks. I'm going to have to ponder this one for a while.

 

[DarkMatterHol]

Thanks. I'm going to have to ponder this one for a while.

I found an exploration of 'light cones' to be very informative and intuitive, as an introduction to this stuff. As a bonus there's no difficult math involved to get the basics of light cones down.

 

[dubiousraves]

Thanks. Where can I find this stuff on light cones?

 

[DarkMatterHol]

Thanks. Where can I find this stuff on light cones?

I first read about light cones in a book called "Special Relativity" - don't remember the author, but there is a lot of stuff on it on the Internet now. Here's a taste:
http://www.phy.syr.edu/courses/modules/LIGHTCONE/minkowski.html
The link i provided doesn't look like the best place for an easy introduction to light cones, but it looks like there are a lot more links be had just by doing a search.
I'll see if i can find the name of the author of "Special Relativity"...
OK, this book looks like it might be a good one on the subject:
Special Relativity by Anthony P. French and A. P. French

 

[DarkMatterHol]

Back to the 'spacetime loaf' - if every moment in time already exists, as suggested in the 'time Warp' episode, and 'spacetime loaf' segment, then i don't see how God could possibly play dice with the universe... [unless, of coarse, the quantum dice are loaded, and that's no fair].
.
So which is it? What am i missing?

 

[Dale]

So which is it?

How could you test the difference?

 

[DarkMatterHol]

How could you test the difference?

I guess that's usually the right question.
.
So that leads me to ask, can the spacetime loaf assertion that all time already exists be tested?
Maybe that's the first question...

 

[Dale]

So that leads me to ask, can the spacetime loaf assertion that all time already exists be tested?

Not that I am aware of.

 

[bobc2]

I guess that's usually the right question.
.
So that leads me to ask, can the spacetime loaf assertion that all time already exists be tested?
Maybe that's the first question...

DarkMatterHol, you have just raised a fundamental question that has been discussed in many threads here. And those discussions have been quite heated and contentious at times. There are two opposing views held: 1) The spacetime loaf is just one possible interpretation of SR, and 2) SR explicitly predicts the spacetime loaf model (mathematical prediction related to relativity of simultaneity and time dilation). Einstein clearly held the spacetime loaf model view.

It is the position of this PF that the loaf model should be regarded as just one possible interpretation of special relativity. Accordingly, I think the implication here is that it is not possible to know if the loaf model is a correct representation of physical reality.

The objections to the loaf model may even go deeper; it has also been argued that special relativity does not have experimental verification at the fundamental level since it is believed by this PF that the one-way speed of light cannot be verified experimentally--that fundamental problem cascading throughout many aspects of special relativity theory.

 

[bobc2]

Nice summary, Chestermiller. (just wondered about your "...greater than the speed of light comment."

For conceptualization purposes, some of us like to visualize space-time as a stationary absolute entity which replaces absolute space as it is described by the pre-relativistic Newtonian model. Within this framework, the 4 velocity of a particle represents its velocity relative to stationary space-time, and is equal to the speed of light when reckoned from the particle's rest frame of reference. But, as reckoned from a different inertial frame of reference, the particle has components both in the time direction, and in the spatial directions. The component in the time direction is γc. Unlike Euclidean 4D space where the Pythagorean theorem is satisfied, space-time is non-Euclidean and features a metric in which the square of the differential time component is opposite in sign to the squares of the differential spatial components. This is why, from the standpoint of an observer in another inertial frame of reference, the component of 4 velocity in the time direction (γc) is greater than the speed of light. Of course, this component can't be measured directly since, as mere 3D beings, we suffer from the inherent physical limitation of not being able to see into our own time dimension. I hope this visualization works for some of the PF readers that are struggling with these concepts.

Chet

 

[Dale]

Accordingly, I think the implication here is that it is not possible to know if the loaf model is a correct representation of physical reality.

An implication which gains weight each time an adherent of one model or the other fails to meet the challenge to propose an experiment which could decide the question.

 

[DarkMatterHol]

An implication which gains weight each time an adherent of one model or the other fails to meet the challenge to propose an experiment which could decide the question.

Perhaps one or more paradoxes in physics, such as 'entanglement' for example, might be used to decide the question, prove the spacetime loaf model, and also resolve the paradoxes at the same time.

 

[OCR]

can the spacetime loaf assertion that all time already exists be tested?

Not that I am aware of.

Lol, that's a rather clever answer... I think, or thought it was, anyway.

I'm not sure why, though... lol


OCR

 

[Dale]

Perhaps one or more paradoxes in physics, such as 'entanglement' for example, might be used to decide the question, prove the spacetime loaf model, and also resolve the paradoxes at the same time.

How? What could you measure about entangled particles that would be different in the two cases?

 

[bobc2]

Perhaps one or more paradoxes in physics, such as 'entanglement' for example, might be used to decide the question, prove the spacetime loaf model, and also resolve the paradoxes at the same time.

That is not an unreasonable thought, DarkMatterHol. Entanglement in fact does offer such an opportunity since it has been verified experimentally. However, I'm afraid that the inference one could draw from this result, which is compatible with the 4-D loaf model and not compatible with an evolving-with-time 3-D model (such as LET), is a discussion that would be considered out of bounds for this PF since it has not been established in the peer reviewed literature.

 

[Dale]

I'm afraid that the inference one could draw from this result, which is compatible with the 4-D loaf model and not compatible with an evolving-with-time 3-D model (such as LET), is a discussion that would be considered out of bounds for this PF since it has not been established in the peer reviewed literature.

And why isn't it established in the peer reviewed literature? Many professional scientists (myself included) prefer the block universe interpretation. Experimental evidence conclusively excluding alternative models would surely be of interest to the community. So, if entanglement could be used to experimentally decide the question, why would the peer reviewed literature be silent on the topic?

There simply is no such experiment. Neither with entanglement nor any other mechanism. There cannot be any such experiment since both models use the same Lorentz transform to make all of their experimental predictions.