RE: [asa] (planck limits) Thermodynamics & Eternal Universe - A Question

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Date: Thu Oct 02 2008 - 11:50:39 EDT

  To flesh this out a bit more, you can't measure space or time intervals smaller than the Planck values. That is because of the joint effects of the uncerratinty principle & the influence of gravitational fields on rods & clocks. If you try to measure smaller & smaller time intervals with precision the uncertainty principle requires greater & greater uncertainty in the mass (=energy) of your clock, & that uncertainty in energy means a large uncertainty in the gravitational field & thus in the clock's measurement.

This is worth emphasizing because presentations of loop & string quantum gravity theories sometimes give the impression that the Planck limit is just an ad hoc assumption.

---- "Dehler wrote:
> Dividing numbers can go on ad infinitum, because numbers are figments of our imagination. Dividing spacetime, according to accepted theory, has limits. Of course, if you conceptually isolate one of those smallest possible elements of spacetime, you can conceptually mark off subdivisions; but such subdivisions would have no relevance to any physical process.
> In response to "Coope": My understanding is that physicists believe the 2nd Law holds everywhere in our expanding universe, but I guess it would not hold everywhere in a contracting universe, because ultimately that would be like having the air go spontaneously back into the balloon--in obvious violation of the 2nd Law.
> Don
> ..........
> RE: 2nd law:
> I don't think it should matter if the universe is expanding or contracting- in both cases, it is adjusting per the theory of relativity (e=mc^2). The only breakdown, I think, is when you hit the singularity event.
> As for breaking down a length to planck length, it sounds like you couldn't divide anymore because, although you'd have a number, the unit wouldn't make sense, since it doesn't exist. It is like having a bowl of 100 pennies, 100 of them. You could divide then to 50, then 25, then 12.5; but you can't get 12.5 because if you cut a penny in half it is no good. You start making nonsense money, which is no longer money. Same with space and time, limited by planck length and planck time.
> ,,,Bernie
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Received on Thu Oct 2 11:51:06 2008

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