Around 15 million years after the Big Bang, the ambient temperatures was about $24^\circ {\rm C}$, which is in a range where water could be liquid. Could liquid blobs of water be existent then?

PS: I am not talking about water on the surface of any solid planet.

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    $\begingroup$ Finding enough oxygen to make water might be problematic... $\endgroup$
    – Jon Custer
    Apr 13, 2021 at 13:56
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    $\begingroup$ There probably was no oxygen in the early Universe, until stars formed. $\endgroup$ Apr 13, 2021 at 14:33
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    $\begingroup$ The Wikipedia BBN article has a link to Standard big bang nucleosynthesis and primordial CNO Abundances after Planck, which uses simulations to calculate a BBN CNO/H ratio (by number) of $\approx (5-30) × 10^{-15}$, and possibly as high as $10^{-13}$. So there was (probably) some oxygen before stars existed but it was spread very thinly through the predominant H & He. $\endgroup$
    – PM 2Ring
    Apr 13, 2021 at 16:16
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    $\begingroup$ However, even if some water was formed in that era, it wouldn't be in liquid form: liquids tend to evaporate at low pressure. See en.wikipedia.org/wiki/Phase_diagram $\endgroup$
    – PM 2Ring
    Apr 13, 2021 at 16:20
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    $\begingroup$ The pressure war far below the triple point of the water, so the very little water which existed, was either vapor or ice (second is unlikely because there was not enough to form crystals, due to the very little O2). $\endgroup$
    – peterh
    Apr 14, 2021 at 16:06

3 Answers 3


Let's interpret your question to be about whether the conditions would permit blobs of water to remain liquid, whether or not water existed yet. And the answer is No, because the pressure was by then far too low. Basically, space was already a vacuum, just not as hard a vacuum as intergalactic space is now.

It is appealing to imagine an era when the universe was simultaneously dense enough and cool enough for liquid water (and thus perhaps humans) to exist. But alas it is not so. At the time of the creation of the cosmic microwave background, around 370 thousand years after the Big Bang, the temperature was around 3,000K, but the pressure was around $10^{-17}$ atmospheres (see the Wikipedia article Chronology of the Universe, and search for "Recombination").

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    $\begingroup$ This is a useful answer - at very low pressures (below about 0.006 atmospheres), only the solid and gas phases of water exist. So even in our own solar system, in the space between Earth and Venus for example, the equilibrium temperature is between 0 and 100 C, but liquid water cannot exist there because of the low pressure. $\endgroup$ Apr 14, 2021 at 1:14
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    $\begingroup$ Okay, so not 15 million years after Big Bang. Was there at some earlier point a combination of pressure and temperature to permit liquid water? I think it would make the answer much better if you can answer that too! $\endgroup$ Apr 14, 2021 at 12:57
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    $\begingroup$ @DanielDarabos It seems by implication that the answer is no... if the temperature was 3000K at 370k years at 10E-17 atmospheres at it would seem both temperature and pressure could only drop from that point, the pressure is already too low while the temperature is still way too high. $\endgroup$
    – Michael
    Apr 14, 2021 at 21:34
  • $\begingroup$ Awesome explanation, thanks! $\endgroup$ Apr 14, 2021 at 22:10
  • $\begingroup$ A somewhat literal take on "The Mists of Time" here! $\endgroup$
    – Rowan
    Apr 15, 2021 at 12:06

As others have mentioned in the comments, there wouldn't have been any oxygen to form water. Soon after the Big Bang, the protons were hot or dense enough to fuse up to helium and some lithium but nothing heavier. Heavier elements were eventually fused in the first stars and partially dispersed in space by their winds and when they exploded as supernovae, but the first stars probably didn't form for a few hundred million years after the Big Bang.

For more information, have a look at the Wikipedia articles on Big Bang nucleosynthesis and the chronology of the Universe.

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    $\begingroup$ According to this article journals.aps.org/prd/abstract/10.1103/PhysRevD.75.087304 , big bang nucleosynthesis yielded about 1 oxygen nucleus per 4 x 10^19 protons. $\endgroup$
    – DavePhD
    Apr 14, 2021 at 12:18
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    $\begingroup$ @DavePhD : Their preprint only has $<2.7\times 10^{-20}$ of ${}^{16}$O/H (from Table I). Did their result shift by a factor of $20$ between 23 April 2007 (the arXiv v2) and 23 April 2007 (Phys. Rev. D)? $\endgroup$ Apr 14, 2021 at 20:54
  • $\begingroup$ @EricTowers no, 1/(2.7 × 10^(-20)) = ~4 x 10^19 . I just worded my statement in terms of the reciprocal, and rounded to 1 digit. The paper gives 3 values in table 1 (1.8, 2.7 and 2.7 × 10^(-20)) like the preprint. $\endgroup$
    – DavePhD
    Apr 18, 2021 at 13:25

So, the big bang started 13.7 billion years ago, and for the next 380,000 years, the universe expanded and cooled, so atoms could start forming later on. 13,685,000,000 years ago, the early universe was too hot and dense for liquid water to form. So, the answer is NO, liquid water could not form about 15 million years after the big bang.

Hoping this was helpful, I'd like to say something afterwards; Welcome to Astronomy Stack Exchange, @Cerelic!

  • $\begingroup$ I specified down to the fact that you're new to Astronomy Stack Exchange, but not other Stack Exchange sites. Don't worry, it happens to me all the time! I'm new here, but not to Physics, Mathematics, or Academia Stack Exchange. $\endgroup$
    – Questioner
    Apr 16, 2021 at 14:16

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