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Intergalactic space is 2.7K (https://en.wikipedia.org/wiki/Outer_space) Interstellar space is a little warmer. My understanding is that these will decrease over time.

The phase diagrams of helium I can find vary a little bit; eg

helium phase diagram

but they all show a superfluid state at 0 pressure and a sufficiently low temperature. (Helium 4 at 2.17K (http://ltl.tkk.fi/research/theory/helium.html)

This suggests that eventually, the helium in the intergalactic, and later, the interstellar medium will condense.

My questions:

  1. Is this prediction accurate?
  2. What effect will this have on someone observing space at that time?
  3. What other interesting effects would this have?
Qmechanic
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Alex K
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1 Answers1

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The "temperature of space" is a little misleading. The Cosmic Microwave Background indeed has a temperature of around 2.7 Kelvin. The baryonic matter, including helium, contained in the ISM and IGM has temperatures between $10^5$ and $10^7$ Kelvin. The CMB and baryonic matter are not in equilibrium. I suspect that the thermal coupling is weak enough that the time needed to come to equilibrium is longer than the age of the universe, but a more knowledgable cosmologist might correct me. The helium may eventually radiate enough heat to reach temperatures low enough to condense, but then the density is still too low.

Grond
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