Re: [math-fun] dumb question about general relativity
No big mystery. I'm just using "positive" time to mean what it usually means: the direction of time that our clocks go forward. --Dan << Re time reversal: The fact that in our neighborhood in spacetime we see stars radiating only in positive time -- and all the entropic consequences of this -- is usually attributed to initial conditions, not to any actual "law" of physics. (The Ehrenfest urn model is usually considered a good microcosm of thermodynamics, and shows time reversal symmetry.) It's just a guess, but it seems likely to me that we are aware of only a small or infinitesimal fraction of the universe, and that some other time and place have stars radiating in negative time. [What exactly does this mean? How do you experimentally determine whether your stars are radiating in positive or negative time?
_____________________________________________________________________ "It don't mean a thing if it ain't got that certain je ne sais quoi." --Peter Schickele
On Fri, Jul 24, 2009 at 9:06 PM, Dan Asimov <dasimov@earthlink.net> wrote:
No big mystery. I'm just using "positive" time to mean what it usually means: the direction of time that our clocks go forward.
Certainly all the stars we see are radiating in positive time; photons are moving from the star out in all directions, and we "see" the star by percieving these photons. Suppose there were stars radiating in negative time; that is, (as perceived with our time arrow), photons from all over the universe are converging on the star, which absorbs the energy by breaking apart Helium into Hydrogen. Would there be any way we could perceive these objects? Is it possible that some of the "dark matter" consists of these objects? Andy
--Dan
<< Re time reversal:
The fact that in our neighborhood in spacetime we see stars radiating only in positive time -- and all the entropic consequences of this -- is usually attributed to initial conditions, not to any actual "law" of physics.
(The Ehrenfest urn model is usually considered a good microcosm of thermodynamics, and shows time reversal symmetry.)
It's just a guess, but it seems likely to me that we are aware of only a small or infinitesimal fraction of the universe, and that some other time and place have stars radiating in negative time.
[What exactly does this mean? How do you experimentally determine whether your stars are radiating in positive or negative time?
_____________________________________________________________________ "It don't mean a thing if it ain't got that certain je ne sais quoi." --Peter Schickele
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