Talk:Heat death of the universe

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Contents 1 THE NAME 2 Heat-death vs Big Freeze 3 Helmholtz or Clausius 4 Third law of Thermodynamics 5 Fate of the Black Holes is wrong 6 Ultimate fate 7 Timeline for heat death 8 Question 9 Role of Dark Energy and Dark Matter 10 Tweaks to "current status"

[edit] THE NAME

I'm not so sure about despite its name. Heat death to me has always meant the death (nonexistance) of heat, rather than death through overheating. But maybe this is because I don't remember being confused when i first heard the term? Morwen 20:46, 10 Nov 2003 (UTC)

Hmm, I think alot of people will disagree with the idea thatan a universe that contiunes to expand will approach heat death asymptotically.

The first line of disagreement I can see is that although the 19th century scientist who came up with the idea of the heat death of the universe meant it to refer to the maximal entropy state of the universe, he was talking about a steady state model. However heat death conventionally means total thermal equilibrium (which is obviously the same as a maximal entropy state in what we'd normally think of a s a closed system) and I see no reason why an expandingf universe cannot be in thermal equilibrium before it reaches it's maximal entropy state. I'm pretty certain that in general the 'heat death of the universe' is used to describe a state that will occur after a finite period of time (i.e. the usuage I've detailed above) rather than that detailed in the article.

Secondly even if we do take heat death as equivalent to maximal entropy, does it approach really maximal entropy asymptotically? I can see why it would approach in a declerating infinitely expanding model, but I don't see why it should in one with linear or accelerating expansion. I can't say I'm 100% sure about this but in the latter two models what stops them from having arbitarily high entropies?

I think these two points do need to be clarified in the finished article.

[edit] Heat-death vs Big Freeze

As far as I can understand (and as suggested here), heat death means a flat universe dying from max entropy, and the Big Freeze is an open (constantly expanding) universe dying from expansion causing heat to be spread out - the effects are the same, but the causes different. I've updated the article a little accordingly and linked to that page, but it would be useful if someone could check that this is correct and if so explain it a bit more clearly than I've done :) --Jomel 16:17, 13 Aug 2004 (UTC)

There defintely needs to be more clarification here. As far as I, an amateur, can perceive, the only difference is that "heat death" involves an exhaustion of all entropy whereas "big freeze" involves matter being so spread out that any residual energy is nearly useless. BOTH of these articles need a "compare & contrast" section or else I'd say that an overzealous editor may ask for them to be merged. (Which I don't feel that they should be.) Again, without it being spelled out, it's somewhat difficult to differentiate the two items. JD79 17:47, 1 June 2006 (UTC)

[edit] Helmholtz or Clausius

Does anyone please remember who originated the concept?

Acc to: http://webplaza.pt.lu/fklaess/html/HISTORIA.HTML

it was helmholtz in 1854

interestingly, Clausius is listed LATER with the second law in 1865 ..

Admittedly, there are a few references on the web to this (only a few!) but can anyone actuall give a citation of where Helmholtz actually said this? Cutler 11:41, July 13, 2005 (UTC)

[edit] Third law of Thermodynamics

Doesn't the third law of thermodynamics play a role here, too? As in, assuming an expanding universe, the temperature will decrease to approximately zero - hence the entropy will go to zero, which I guess actually avoids the whole Heat Death at the end, ultimately going towards the Big Freeze. Or is there a way in which the temperature stays at a non-zero value? (I guess this would be possible with a critically flat universe.) Mike Peel 21:56, 15 March 2006 (UTC)

It is my understanding that the temperature will not reach zero because heat is the "basest" form of energy and since energy can neither be created nor destroyed (more or less) then there will always be heat. There will just be a lack of any type of mechanism to change heat into anything else, and everything will be the same temperature. JD79 17:50, 1 June 2006 (UTC)

[edit] Fate of the Black Holes is wrong

Black holes will only boil away if their temperature is greater than the temperature of the background radiation. Otherwise they will continue to absorb more energy from the background radiation than they give up through Hawking radiation. At the moment (temp = 2.73 K), the tipping point is for a black hole to have approximately the mass of the planet Mercury.

The scenario in the article at the moment appears to be based on the Big Freeze scenario, with the CMB temperature continuing to fall as the universe continues to expand.

But what happens with the Heat Death scenario? Any little black holes presumably boil away. But bigger black holes continue to grow, taking energy from the CMB, which makes it cooler. This may make more of the black holes too small to survive. Eventually, presumably, only the biggest coldest black hole of the lot survives, in thermal equilibrium with the CMB.

At least that's how it would seem to me to have to go. Jheald 13:10, 6 July 2006 (UTC).

I copied the detailed walkthrough of the scenario from an old verion of Timeline of the Universe, which was later merged into Timeline of the Big Bang, to the exclusion of this material. The relevant version, which was the last major one before the merge, is at http://en.wikipedia.org/w/index.php?title=Timeline_of_the_Universe&oldid=28769719

I don't actually have a lot of familiarity with the topic myself. At least, not enough to spot and correct technical errors. If you've got some relevant sources, by all means, go ahead and make the edit. The information here is well over a year old now, and even if it was correct at the time it wouldn't be surprising if this is now outdated. Arturus 03:45, 7 July 2006 (UTC)

I'd prefer to leave any final change to someone who's more of an expert. I just think what's in the article at the moment is not correct, if we're not talking about the Big Freeze. Jheald 17:51, 7 July 2006 (UTC).

[edit] Ultimate fate

"even smallest perturbations make the biggest difference in this era"

I suspect that this is poorly worded and should say something more like ""even small perturbations make a big difference in this era".

[edit] Timeline for heat death

I'm no Wikipedia formatting expert, so I'll just pose the question: is there a way to preserve the formatting in the "Timeline for heat death" in the table of contents on the main page? It looks like the black hole age is just 1040 years away, rather than 10^40 years away. Jyoshimi 18:42, 17 October 2006 (UTC)

You could just right 10E40 instead of 10⁴⁰. I assume most people would understand. (68.98.52.155 01:17, 1 November 2006 (UTC))

I just changed all headers to the 10Exx format instead of the 10^xx format, this made the table of content more correct but a bit less pretty. Someone with knowledge might be needed to step in Lyml 15:02, 26 December 2006 (UTC)

I've replaced the 10Exx format with 10¹⁴, etc., using Unicode superscript characters (¹²³⁴⁵⁶⁷⁸⁹⁰) which looks better, but requires better Unicode support.—Ketil Trout 20:55, 7 February 2007 (UTC)

[edit] Question

How does this theroy explain the whole "energy can not be created or destroyed" law. If the universe is going to be nothing but photons, etc, in what form will all of the energy be in? --Cngodles 16:03, 6 March 2007 (UTC)

Energy is defined as the ability to do work. I think that the form of energy for a photon would be related to its wavelength. --Comosabi 17:53, 30 March 2007 (UTC)

Photons do indeed have energy, and this would be where most of the energy of the universe would be at heat death (unless some mechanism converts a lot of mass to neutrinos or what-have-you instead of photons). Entropy doesn't change the amount of energy present; instead, it's a measure of how much energy is "unavailable" (i.e., can't be tapped to do further work). A universe experiencing heat death could be described as being at maximum entropy, but an equally valid description is to say that all of its energy is unavailable (heat, but no heat gradients to tap for power, and so forth). --Christopher Thomas 04:08, 31 March 2007 (UTC)

[edit] Role of Dark Energy and Dark Matter

Keep in mind that ordinary matter accounts for less than 5% of the matter in the universe, while the rest is comprised of Dark Matter, ~20%, and Dark Energy, ~75%. While Dark Matter is not known to contribute to the expansion of the universe, Dark Energy does cause the universe to expand, since Dark Energy repels itself. The understanding of Dark Energy is still in its infancy, but any discussion of the Heat Death theory requires the inclusion of Dark Energy and Dark Matter. Comosabi 17:49, 30 March 2007 (UTC)

I've updated the relevant section to make it clearer, and to remove the flagged weaselling (or at least, to clarify where it comes from). As far as the question of whether the universe is open or closed is concerned, dark matter and normal matter are equivalent (only the total mass density of the universe matters). Dark matter may affect the final form in which matter exists in a universe that experiences heat death (in particular, if it's the most stable form of matter, normal matter may be converted to it by some mechanism). However, the best guess is that all normal matter decays into photons (via being absorbed into black holes that later evaporate), and that dark matter is either processed in the same manner (if it has enough self-scattering to diffuse into one or enough time to tunnel into one), or stays dark matter (decaying to the most stable dark matter particle, if it isn't already in that state).

Dark energy, on the other hand, causes the universe to expand in an accelerating manner. Dark energy that behaves in a manner similar to the cosmological constant, which is the simplest assumption, just perturbs the final state of the universe a bit (it's still a Big Freeze, but the universe doesn't quite reach heat death). Dark energy with the properties needed to produce a Big Rip scenario gives you a very different situation, but I'm not sure how entropy is affected under those conditions. My impression is that you end up with an arbitrarily large amount of usable energy, and so low entropy, but I could easily be wrong about that. One of the lurking physics-types may be able to give a better answer. --Christopher Thomas 04:42, 31 March 2007 (UTC)

[edit] Tweaks to "current status"

I've partly rewritten the "current status" section to avoid weaselling. To the best of my knowledge, it reflects the current beliefs about the probable fate of the universe, and for completeness it touches on noteworthy past conjectures (while making clear which ones are current). Two things are needed: The crew from Wikipedia:WikiProject Physics or a similar crowd needs to check it for accuracy, and all of the statements marked with "citation needed" templates need to get properly referenced. These references certainly exist; I just don't know them off the top of my head (whereas physics and cosmology types might). --Christopher Thomas 04:52, 31 March 2007 (UTC)