# Will the universe run out of hydrogen? **URL:** \ **Category:** Factual Questions\ **Created:** [January 8, 2008, 3:44pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741 "2008-01-08T15:44:04Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [January 8, 2008, 3:44pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/1 "2008-01-08T15:44:04Z")
Stars continually consume hydrogen and have been doing so for 15 billion years. When they die, new stars form in their remains consuming more hydrogen. Is the amount of hydrogen in the universe decreasing or is it in equilibrium? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 8, 2008, 3:46pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/2 "2008-01-08T15:46:48Z")
Yes, it is being used up - fused into helium and other elements in stars as they live and die. I don’t think there’s an imminent shortage crisis though. ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [January 8, 2008, 5:36pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/3 "2008-01-08T17:36:22Z")
It will run out eventually though. I believe the current hypothesis for how the universe will end is that cosmic expansion will eventually carry all but the nearest galaxies out of view of Earth. The Local Group will remain, but their stars will get dimmer and dimmer as they consume the last of their hydrogen. Black holes will gobble up the burnt-out reminants of the stars and the universe will cool down to a few fractions of a degree above absolute zero, illuminated only by the feeble Hawking radiation given off by evaporating black holes. ---
**Author:** ![mikemo](https://avatars.discourse-cdn.com/v4/letter/m/41988e/32.png) [@mikemo](https://boards.straightdope.com/u/mikemo)\ **Post date:** [January 8, 2008, 6:10pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/4 "2008-01-08T18:10:58Z")
[QUOTE=Pochacco] It will run out eventually though. I believe the current hypothesis for how the universe will end is that cosmic expansion will eventually carry all but the nearest galaxies out of view of Earth. The Local Group will remain, but their stars will get dimmer and dimmer as they consume the last of their hydrogen. Black holes will gobble up the burnt-out reminants of the stars and the universe will cool down to a few fractions of a degree above absolute zero, illuminated only by the feeble Hawking radiation given off by evaporating black holes. [/QUOTE] I don’t think the _universe_ will actually run out of hydrogen, though. There may not be enough left to allow stars to continue forming. But between interstellar (and intergalactic) gas and hydorgen locked up in brown dwarfs, planets, comets, etc. there will still be hydrogen in the universe. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 8, 2008, 6:27pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/5 "2008-01-08T18:27:09Z")
Big bang nucleosynthesis gave us a universe composed of about 75% hydrogen, and 24% helium. After 13.7 billion years, about 74% of all atoms are _still_ hydrogen. That’s within error of 75%. We’ll not run out of hydrogen anytime soon. ---
**Author:** ![shijinn](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@shijinn](https://boards.straightdope.com/u/shijinn)\ **Post date:** [January 8, 2008, 6:44pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/6 "2008-01-08T18:44:39Z")
time passes awfully quick when you’re dead. ---
**Author:** ![vertizontal](https://avatars.discourse-cdn.com/v4/letter/v/ad7895/32.png) [@vertizontal](https://boards.straightdope.com/u/vertizontal)\ **Post date:** [January 8, 2008, 7:26pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/7 "2008-01-08T19:26:31Z")
Won’t protons themselves decay after awhile, say around a googol years from now? After the last proton in the universe decays, couldn’t we say that all hydrogen had been “used up”? ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [January 8, 2008, 7:47pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/8 "2008-01-08T19:47:47Z")
[QUOTE=Squink] Big bang nucleosynthesis gave us a universe composed of about 75% hydrogen, and 24% helium. After 13.7 billion years, about 74% of all atoms are _still_ hydrogen. That’s within error of 75%. We’ll not run out of hydrogen anytime soon. [/QUOTE] You’re just a shill for big hydrogen, admit it. We are probably within one or two billion years of peak hydrogen, I mean it isn’t like the universe is getting bigger or anything. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 8, 2008, 9:08pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/9 "2008-01-08T21:08:09Z")
Ohh man, let me guess. Next you’ll be going on and on about how cosmic star formation peaked 5, or even 8 billion years ago, and has been slipping downhill ever since ([see figure 6](http://www.americanscientist.org/template/AssetDetail/assetid/39133/page/4;jsessionid=aaa5LVF0#39439)). That has nothing to do with the _amount_ of hydrogen that is left, merely its _distribution_. So what if the suns go out and we’re all left sitting in the cold in a mere 20 billion years? The vast majority of hydrogen will still be there, waiting for some enterprising soul to figure out how to collect it, and use it! ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [January 8, 2008, 11:15pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/10 "2008-01-08T23:15:54Z")
[QUOTE=vertizontal] Won’t protons themselves decay after awhile, say around a googol years from now? After the last proton in the universe decays, couldn’t we say that all hydrogen had been “used up”? [/QUOTE] Despite people spending a lot of time looking for it, there’s no experimental evidence for decaying protons. But I think it’s still fair to say that most particle physicists would bet on them being unstable on timescales longer than about 10[sup]35[/sup] years. Certainly speculations about the ultimate fate of the universe invariably assume proton decay. So, yes, in such extrapolations hydrogen does get “used up” in the sense that it decays into stuff like positrons. And it makes no difference whether the protons are in the form of some loose hydrogen gas or locked inside (non-black hole) stellar remnents. ---
**Author:** ![ouryL](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ouryl/32/6067_2.png) [@ouryL](https://boards.straightdope.com/u/ouryL)\ **Post date:** [January 9, 2008, 9:34pm UTC](https://boards.straightdope.com/t/will-the-universe-run-out-of-hydrogen/432741/11 "2008-01-09T21:34:35Z")
I thought by definition stray protons are considered hydrogen ions?