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According to General Relativity, space and time are aspects / dimensions of a unified whole. If the speed at which wave energy travels through spacetime is constant, $c$, then as distance expands, should not time expand by corresponding amount? If so, then would 1 Plank time from Plank Epoch, be something like ~1 picosecond in today's space-time?

FritzS
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    I'm voting to close this question as off-topic because it appears to be gibberish. What does "the speed at which energy travels through space-time" mean? – WillO Dec 01 '19 at 18:22
  • I was only attempting to be general, so the question applied to the very early universe, before electromagnetism separated. – FritzS Dec 01 '19 at 18:33
  • the question applied to the very early universe No, your question explicitly mentions “today’s space-time”. – G. Smith Dec 01 '19 at 18:37
  • It also explicitly mentions Plank Epoch... – FritzS Dec 01 '19 at 19:03
  • What does "today's space-time" mean? Does it mean "today"? – WillO Dec 01 '19 at 19:09
  • Yes. I was attempting to make comparison between duration length in space-time at 1 Plank time (i.e., before light exists) versus today. – FritzS Dec 01 '19 at 19:27
  • There is a book by a respected physicist that addresses something related to the title of the post: Now: The Physics of Time (W. W. Norton, 2016) ISBN 978-0-393-28523-9 – JEB Dec 01 '19 at 19:55

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It’s a meaningless question. Intervals of the cosmological time used in the Friedmann metric don’t change, but intervals of conformal time do. You can use any time coordinate you want in cosmology, and can make coordinate time intervals get longer, shorter, or stay the same relative to proper time intervals as the universe evolves.

Precisely because “space and time are aspects/dimensions of a unified whole”, what is happening to individual coordinate differences such as spatial intervals or temporal intervals has no absolute significance. Only what happens to invariant spacetime intervals matters.

By the way, some energy, such as that of light, travels at the speed of light, but other energy, such as the mass and kinetic energy of an electron, does not and can not.

G. Smith
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  • Thanks for the last clarification. I should have said "wave energy" instead of energy. – FritzS Dec 01 '19 at 18:39
  • Not all wave energy travels at the speed of light. There are “matter waves” that travel more slowly. – G. Smith Dec 01 '19 at 18:41
  • Despite the conventional name “speed of light”, it’s best not to think of $c$ as the speed at which some things like light move, since other things move at other speeds. I suggest thinking of it as the unique invariant speed (same for all inertial observers) or the universal speed limit. – G. Smith Dec 01 '19 at 18:45
  • I am too ignorant for this site. I was only aware of light waves and gravity waves. I am trying to learn, but perhaps you could suggest a more appropriate site. – FritzS Dec 01 '19 at 18:57
  • I can’t recommend any others. I think you can learn a lot of physics from this site. Don’t get discouraged. – G. Smith Dec 01 '19 at 19:05
  • Much appreciated! I have already learned a lot here. – FritzS Dec 01 '19 at 19:06
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    You seem to have a special interest in General Relativity, cosmology, and the early universe. These are all difficult topics, and self-learning makes them even harder. No one understands these things without a lot of effort, so don’t think that you are ignorant. A proper understanding is nearly impossible without getting into the mathematics behind them, so I encourage you to look for resources that will make that math accessible to you. – G. Smith Dec 01 '19 at 19:41
  • I used to be fairly adept at math when in college and grad school in mid 70s - early 80s. But then I did 35 year career as Imaging Scientist for HP. Now, I am retired and able to explore what interests me, singularities, the early universe, alternate analytical approach, Cosmic Thermodynamics. – FritzS Dec 01 '19 at 20:33