What Physically Causes Time to Progress and Vary in Different Places?

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SUMMARY

The forum discussion centers on the nature of time and its progression as described by special relativity, particularly in the context of the Twin Paradox. Participants confirm that time does not progress uniformly; rather, it varies based on an observer's velocity relative to the speed of light. The discussion highlights that while the speed of light remains constant across inertial frames, the physical cause of time's progression is still a mystery, with entropy increase being a significant factor. The conversation also touches on geometric interpretations of time and their implications within General Relativity.

PREREQUISITES
  • Understanding of special relativity concepts, including the Twin Paradox.
  • Basic knowledge of the speed of light as a constant in physics.
  • Familiarity with entropy and its relationship to time.
  • Awareness of General Relativity and its implications for spacetime geometry.
NEXT STEPS
  • Research the implications of the Twin Paradox in special relativity.
  • Explore the relationship between entropy and the arrow of time.
  • Investigate geometric interpretations of time in General Relativity.
  • Read about Self Creation Cosmology and its approach to time and gravity.
USEFUL FOR

Students of physics, particularly those interested in relativity, cosmology, and the philosophical implications of time, as well as researchers exploring the fundamental nature of time and its geometric interpretations.

  • #31
Don't you think that it is possible, in principle, to arrange such initial conditions that entropy decreases with (the coordinate) time in a small region of the universe?
 
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  • #32
Don't you think that it is possible, in principle, to arrange such initial conditions that entropy decreases with (the coordinate) time in a small region of the universe?

If you take the belief that time is a result of entropy changes (B1) then yes. But the probability is too small. And in a really, really small bit of the universe, if things momentarily, for a very, very short moment of time, go the other way, does it make a difference?

I have a question too: Assuming the above belief B1 is true, if the universe started off (started off doesn't even make sense in this context, but bear with me) in a state of high entropy, then there would be no noticeable evolution of time. Am I correct?
 
  • #33
Entropy, anyone?

Well, any serious discussion of entropy on cosmological scales raises all kinds of issues, not least of which is that there are many things one might mean by "entropy". However, a good place to begin would be the very readable book by Lawrence Sklar, Space, Time, and Spacetime. See in particular the discussion of ergodic theory. Then see Poincare and Kac recurrence theorems, plus the relationship between measure-theoretic and topological entropy in Walters, Introduction to Ergodic Theory. Note that measure-theoretic entropy is related to a purely combinatorial notion, Boltzmann entropy, which can be interpreted in terms of group actions... and so on and on and on. There are many distinct but interesting notions of entropy, which tend to bear specific relationships to each other, and ferreting these out is a fascinating task for mathematicians.
 
  • #34
Demystifier said:
Don't you think that it is possible, in principle, to arrange such initial conditions that entropy decreases with (the coordinate) time in a small region of the universe?

Yes, you are the result.
 
  • #35
masudr said:
I have a question too: Assuming the above belief B1 is true, if the universe started off (started off doesn't even make sense in this context, but bear with me) in a state of high entropy, then there would be no noticeable evolution of time. Am I correct?
Yes you are.
 
  • #36
quantum123 said:
Yes, you are the result.
Thanks, you too. :smile:
 

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