Suppose the current model is correct that the universe will expand and thin out forever, and eventually all potential energy will be used. Will space-time still exist? Will “quantum foam” keep it propped up, maybe?
I don’t understand how all potential energy could be used up since matter is energy but it is in a very stable form.
In heat death all mass is converted to energy. Don’t quote me on this one, but absolute heat death will only come about after an infinite period of time.
Very stable, but over the long run, it will dissolve.
Only if energy is not quantized. Otherwise, it doesn’t come in arbitrarily small amounts, and we’ll either reach it in a finite amount of time, or we wouldn’t reach it even after infinite time.
Even so, there’s a point after which the heat death is, for all intents and purposes, complete.
remember that other basic law…energy is neither created nor destroyed…so in effect, it’s all there…just in a different form…
No you misunderstand me: only after an infinite amount of time would it be impossible for one quantum of energy to interact with another quantum of energy thus making heat death absolute, though I have ignored the fact that there is no such thing as truly empty space (but after an infinite period of time this may no longer hold true). But yes, again ignoring the fact that there is no such thing as empty space, there would after a finite amount of time no longer be any interactions between quanta, though there would be a definte, but receding, probability that there would be.
This may be a sort of dumb response, but, well, why would space-time cease to exist? Eventually, to be sure, we’d have a space-time in which, for all practical purposes, nothing happens, but I’m not sure that means that it fails to exist. It’d just be really boring.
Space and Time may ceace to exist, in a philosophical way: when all the matter and energy in the universe has decayed away, there will be no “events” to define, nothing to measure against “there, then”.
A blank coordinate system is meaningless.
IIRC, energy doesn’t decay or disappear or anything. There will always be the same amount of energy in the universe, it’s just entropy that is increasing.
When you “use” energy you don’t “use it up.” Instead you are converting it from one form to another (usually to heat in the final analysis). A car releases energy from the fuel and “uses” it, but the final product is just as much energy in the final combustion products and heat energy (as well as an increase in entropy).
Eventually (also, IIRC my thermodynamics) entropy will reach a chronological maximum in which there are no localized decreases of entropy (such as complex molecules) and the universe will consist of a vast soup of heat energy (the “lowest form” or highest entropy form)- no energy pent up in chemical bonds, no matter in complex form, etc. Just one big amorphous random soup.
PC
Oh right, potential energy doesn’t have much to do with space-time, does it? Why would the state of energy affect space-time? Or does local “loss” of potential energy have some local small effect?
PC
A slight metaphysical remark.
In another thread, a case was made that “absolute utter nothingness [+ various qualifying remarks]” has no meaning and cannot logically function as a name (ie, a signifier).
Accept that argument, and there must always and everywhere be a certain “somethingness.” (Ugh, re the terminology!)
Also–though it’s not a rigorous argument–the notion that Time might have a last moment renders more plausible the notion that it had a first moment as well. If this set of moments had a first one, mightn’t there be another such “first one?” Of course, we can’t say that it “happens after” the last moment of our Time, as the disconnect is total; but neither can we deny it. My point being that the “heat death of the universe” is not the same as the notion of Reality in general having a “limit”–a universe may be finite while Reality is infinite, offering an unending number of Spaces and Times.
Well, sure, it’d be meaningless, except in the sense that some random higher dimensional being (pretending for the moment that RHDBs exist) could come waltzing on by and point out to its children that things used to happen in this particular set of four dimensions. But I’m not sure that we could claim it doesn’t exist just because it serves no useful purpose.
Presumably, the universe would continue its expansion even though nothing interesting would be happening inside. Assuming I’m correct in recalling that an expanding and empty universe is a valid solution to Einstein’s equations, then something (said expansion) is still happening, even if there’s no one around to see it. It’s not absolute utter nothingness per se, it’s an empty but expanding coordinate system.
Whether this constitutes existence or not is a question I’ll leave up to people more qualified to answer it.