# Heat Death of the Universe **URL:** \ **Category:** Factual Questions\ **Created:** [September 15, 2019, 4:27pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272 "2019-09-15T16:27:31Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [September 18, 2019, 1:43pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/21 "2019-09-18T13:43:14Z")
[Here](https://www.youtube.com/watch?v=Qg4vb-KH5F4) is a pretty good lecture on the heat death of the universe. It _starts_ at the end of the Age of Stars when the last red dwarf flickers out, some 100-trillion years from now, so we’re talking really deep time. ---
**Author:** ![FlikTheBlue](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fliktheblue/32/10972_2.png) [@FlikTheBlue](https://boards.straightdope.com/u/FlikTheBlue)\ **Post date:** [September 18, 2019, 2:12pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/22 "2019-09-18T14:12:12Z")
I am not a physicist so this is my armchair understanding from a couple of semesters of freshman level physics and reading a few books on cosmology. The way I understand it is that protons and neutrons are not stable when we start considering really long time periods, maybe something of the magnitude of TREE(3) years or some crazy number like that. Eventually all the neutrons decay into photons / electromagnetic radiation. The protons decay into positrons and radiation. The positrons and electrons destroy each other leading to more radiation. At this point all the particles would be gone, and we would be left with radiation that continues to slowly cool to almost absolute zero. Will this happen in the far distant future? I have no idea, but on the other hand I don’t see any reason to doubt such an outcome either. I suppose it could be possible that space is stretched out to such a large extent by that time that maybe some of the electrons and positrons simply never encounter each other, but that probably doesn’t help things much. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 18, 2019, 10:06pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/23 "2019-09-18T22:06:16Z")
The longest timescales you’ll ever have to consider will be the evaporation of supermassive black holes, which will take about a thousand googol seconds (I was really excited when I did that calculation; it’s so rare that one encounters a googol of _anything_). But a googol is still far, far short of TREE(3). ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [September 19, 2019, 12:42am UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/24 "2019-09-19T00:42:10Z")
I was under the impression that the universe just got very boring. In a book I read on teh subject, the implication was that if the universe continues to accelerate that by 10^100+ years from now, there will only be 1 particle per physical area that is something like 10^80 larger than the entire current universe. So it wouldn’t die, it’d just be boring as hell. THis assumes protons do not decay. The book was ‘the five ages of the universe’ ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [September 19, 2019, 2:17pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/25 "2019-09-19T14:17:10Z")
> [@FlikTheBlue](#): > > The way I understand it is that protons and neutrons are not stable when we start considering really long time periods[snip] [Nobody’s sure](https://en.wikipedia.org/wiki/Proton_decay). All that can be said for certainty is that _if_ they decay they’ll last somewhere around 10[sup]30[/sup] years. Like I said, we’re talking deep time here – deep enough to make a geologist gasp. The PBS lecture I linked to above covers both the _protons are stable_ and _protons aren’t stable_ scenarios. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 19, 2019, 8:22pm UTC](https://boards.straightdope.com/t/heat-death-of-the-universe/840272/26 "2019-09-19T20:22:31Z")
So far as I know, all of the proposed Grand Unified Theories (models which would unify the Strong and Weak Forces, with or without gravity) predict that protons are unstable, though they might make different predictions about their lifespan. So folks would be surprised if it turns out they don’t decay at all. The figures you’ll usually see bandied about are the experimental limits on proton lifespan: We’ve never verifiably seen a decay, and if it were less than that, with the experiments we’ve run, we would have seen it. The actual lifespan could well be far greater than that. [Previous page](https://boards.straightdope.com/t/heat-death-of-the-universe/840272.md?page=1)