The nature of time. Which books to read?

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Discussion Overview

The discussion revolves around the nature of time, exploring various philosophical and scientific perspectives. Participants express interest in reading materials that address the complexities and debates surrounding the concept of time, including its implications in physics and philosophy.

Discussion Character

  • Exploratory
  • Debate/contested
  • Philosophical
  • Technical explanation

Main Points Raised

  • Some participants suggest notable books on the nature of time, including "The Philosophy of Space & Time" by Hans Reichenbach and "A Brief History of Time" by Stephen Hawking, while others critique the depth of Hawking's treatment of the subject.
  • One participant expresses concern that many physicists lack engagement with philosophical discussions about time, questioning the relevance of philosophy to physics.
  • Another participant argues that the fundamental difference between science and philosophy lies in the testability of claims, suggesting that philosophical debates about time may never reach resolution.
  • Some participants propose that time may not exist in a meaningful way, citing reversible descriptions of physical systems as evidence.
  • There is a discussion about the implications of time-reversibility in fundamental laws of physics, with participants questioning the role of time in theoretical frameworks.
  • Several participants engage in a debate about the significance of time in physics, with some asserting that all interactions occur at specific points, while others challenge the necessity of time in understanding physical phenomena.

Areas of Agreement / Disagreement

Participants exhibit a range of competing views regarding the nature of time, its relevance to physics, and the relationship between scientific and philosophical inquiries. There is no consensus on these issues, and the discussion remains unresolved.

Contextual Notes

Participants highlight limitations in understanding time, including the dependence on definitions and the unresolved nature of certain philosophical questions. There are references to specific theories and concepts that remain contentious.

  • #31
ZapperZ,

Don't worry, I drop my claim about "non existence of time" without any feeling.
It is wrong even from the initial conditions point of view, since the initial conditions involve position and velocities.
Therefore, time is implicit already in the initial conditions.

:blushing: ... note that this could be further discussed if one considered position and momentum as coordinates and momentum as a time-independent concept ...
... so many points of view for the same thing ...
... Could we say that we obviously live in a 7-dimensional space? :blushing:

Only remains:

- the fact that time has a unique signature as compared to the three other dimensions,
- and the macroscopic irreversibility that has no spatial equivalent
 
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  • #32
lalbatros said:
ZapperZ,

Don't worry, I drop my claim about "non existence of time" without any feeling.
It is wrong even from the initial conditions point of view, since the initial conditions involve position and velocities.
Therefore, time is implicit already in the initial conditions.

But I've mentioned this explicitly way in the beginning, in terms of the equation of motion. In fact, if you think about it carefully, you have no way of defining "position" without an implicit assumption on the existence of time. Think about how you would measure position at the most fundamental level. If you buy SR, it can only be unambiguously done with light.

Only remains:

- the fact that time has a unique signature as compared to the three other dimensions,
- and the macroscopic irreversibility that has no spatial equivalent

I could easily say that it is space that has the "unique signature" when compared to time. Not only that, if you write down a coordinate position in terms of spherical polar coordinates, there are no "negative r" positions (r as in the scalar length, not the vectorial length), because that is unphysical. So I've just constructed a non "macroscopic irreversibility" for space as well!

My point is that using such things to single out time is meaningless. It certainly hasn't bothered enough physicists since they use time reversibility symmetry (or broken time symmetry) with enough frequency to make such a thing common. The fact that the P and T symmetries are 2 of the 3 fundamental symmetries in elementary particle physics is my proof that time and space are inseparable, and you can't have one without the other.

Zz.
 
  • #33
I agree, of course.
But time and space being inseparable does not mean that they are the same thing or that they are interchangeable.
Any event has 3 space coordinates and 1 time coordinates in any frame of reference.
Interchanging one spatial coordinate with another is perfectly meaningful.
But interchanging one spatial coordinate with the time coordinate make no sense.

I also doubt about your polar coordinates example.
The time coordinate could cover the range [-Inf,+Inf] even when describing irreversible physics.
Irreversibility in time has to do with how the system may change when it evolves from t1 to t2>t1.
I don't see any analogue for a spatial coordinate.
Well ... maybe I have an idea ...
 
  • #34
lalbatros said:
I agree, of course.
But time and space being inseparable does not mean that they are the same thing or that they are interchangeable.
Any event has 3 space coordinates and 1 time coordinates in any frame of reference.
Interchanging one spatial coordinate with another is perfectly meaningful.
But interchanging one spatial coordinate with the time coordinate make no sense.

You will note that I've never said that they are the same. In fact, I have mentioned the fact that they are not the same. But not being the same does not mean that they cannot be on equal footing. C, P, and T symmetries are all not "the same", yet, they are of equal importance in terms of symmetry principles. So again, no one here should think that they are "the same". This has never been in any of the arguments here, other than the omission of "c" that you made in your metric equation.

I also doubt about your polar coordinates example.
The time coordinate could cover the range [-Inf,+Inf] even when describing irreversible physics.
Irreversibility in time has to do with how the system may change when it evolves from t1 to t2>t1.
I don't see any analogue for a spatial coordinate.
Well ... maybe I have an idea ...

Er.. I have no clue what you are trying to do here.

Zz.
 
  • #35
lalbatros said:
I also doubt about your polar coordinates example.
The time coordinate could cover the range [-Inf,+Inf] even when describing irreversible physics.
Irreversibility in time has to do with how the system may change when it evolves from t1 to t2>t1.
I don't see any analogue for a spatial coordinate.
Well ... maybe I have an idea ...

I think this might help

Consider a 2d universe, as a piece of paper. On this page there is an object, say a square with a non symmetrical pattern of polka dots along it's edges. within the universe you can plot the square's location only if you use 3 values, it's X and Y position, and a rotation around an axis perpendicular to the page (that is Z.)

You might object that the rotation's magnitude isn't necessary for observers within the page (say the triangle guy some ways off) but it is critical if you really think about it.

A 2d person would be very confused about what this third axis was exactly since cannot experience translations along it but only rotations, where as for the other two dimensions they see translations but not rotations. (note that to the triangle if you move the square along Z it disappears from the universe. If you rotate the square along X or Y, the square either becomes a point or just changes texture, depending on the exact positions of the two shapes. A texture change in this case would be like your organs suddenly becoming visible to the person across the room.)

If you were to make a book by taking snapshots of each page from a higher (or lower) Z and stacking them upon one another, the book as a whole would describe the history of the universe. This does not mean that such a book "must" exist in order for the 2d universe to exist and go about it's business. Travel (that is translation) along this axis does not have to occur for this 2d world to have the symptoms of time. But were a very smart triangle to come up with an intellectual concept that allowed him to make such books in it's mind, the resulting tool would be very useful.

By analogy, our 3 dimensional history could be recorded in a 4 dimensional book without the universe "being" such a 4d object (in fact a list of positions and times for a moving object is a projection of such a 4d book.) This may be why space and time aren't interchangeable. If time is this type of abstraction we would see exactly what we do see. This would also explain why, while we can talk about time coordinates in a way that is meaningful, we can't necessarily traverse time the way we do space. (note certain statements made about relativity make this seem weird. I'm not qualified to say whether they make it in fact weird. Maybe I should make a topic about that discussion. Could be fun.)

We make books like this all the time, calenders as a simple example.
-----------------------------------------------
When you choose a point to make a measurement, or start a simulation you have to record which page you're talking about. That's the minimum that the time coord represents.

Is our universe book like? Or do things actually move along our "page?" For physics generally it doesn't matter, that's more of a cosmology question.

Many of these ideas are presented in a fun way in a book called "Flatland: A Romance of Many Dimensions" by Edwin A. Abbotte. (maybe all of them, I can't tell how much I've elaborated on it since I last read it years ago)
 
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  • #37
ZapperZ said:
After all, more than 1/2 of the general population doesn't even know that the Earth revolves around the sun...

Zz.

What?? Where did you hear THAT? Certainly cannot be the "general population" of the United States.
 
  • #38
RetardedBastard said:
What?? Where did you hear THAT? Certainly cannot be the "general population" of the United States.

It is. I think I linked to the survey already in one of my earlier posts somewhere on PF, but I'll try to look for it again.

There were several other questions in that survey that tests the science literacy (or illiteracy) of the general population. It was very disheartening to read the result.

Zz.
 
  • #39
I heard that more than 90% of Harvard students thought the seasons were caused by the Earth getting closer to and farther away from the sun... but 1/2 of the general population not knowing that the Earth revolves around the sun?!? I don't believe it... do they think the sun revolves around the Earth or something... or were they too dumb to understand the question in the first place
 
  • #40
ZapperZ said:
It is. I think I linked to the survey already in one of my earlier posts somewhere on PF, but I'll try to look for it again.

There were several other questions in that survey that tests the science literacy (or illiteracy) of the general population. It was very disheartening to read the result.

Zz.

I just did a search on here and one on google using "site:physicsforums.com" and using various combination of the words zapperz, science, literacy, survey, and I did not find a thread about half the population not knowing that the Earth revolves around the sun. If you could help me out, I would really love to see the results of this survey.

ps. Doing a search on this site was agonizingly slow and the results were not accurate so you may want to try using a search engine to search this site instead (in case you didn't already know).
 
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  • #41
RetardedBastard said:
I just did a search on here and one on google using "site:physicsforums.com" and using various combination of the words zapperz, science, literacy, survey, and I did not find a thread about half the population not knowing that the Earth revolves around the sun. If you could help me out, I would really love to see the results of this survey.

ps. Doing a search on this site was agonizingly slow and the results were not accurate so you may want to try using a search engine to search this site instead (in case you didn't already know).

I know. I've been trying to find the thread where I posted the source and I too haven't found it. So I'm digging elsewhere.

I'm also having doubts that I recalled this correctly.

Zz.
 

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