How do we know that the singularity was incredibly warm and not incredibly cold, meaning that the universe is heating

Question: How do we know that the singularity was incredibly warm and not incredibly cold, meaning that the universe is heating up which would contribute to global warming
- Keywords:
  Big Bang,
  singularity,
  space,
  universe
Asked by LoganC on 25 Nov 2020.
- Duncan Wallace answered on 25 Nov 2020:
  
  Mass, energy, and heat are all connected. The sun is hot mainly because it is so massive. A more massive sun would be hotter still. As such it’s easy to say that the point at which all matter in the universe was condensed into a small area that it would have been incredibly warm.
- Danny Hnatyshin answered on 25 Nov 2020:
  
  We know that the early universe was very hot because the university was smaller! If you expand things temperature goes down (in chemistry you can look at the ideal gas law which says the bigger the volume the lower the temperature). As you go towards teh big bang the universe gets smaller and is more compressed which means it gets hotter! If you take this to the extreme you would get an infinite temperature at the big bang since the singularity would be zero size (although physicists do not think that is quite right!).
  
  Regardless, the temperature of space is very cold (since the universe has expanded so much), a few degrees Celsius, so it doesn’t affect global warming at all! Actually it allows to earth to remove heat since heat will flow from hot (earth) to cold (space)

Question: How do we know that the singularity was incredibly warm and not incredibly cold, meaning that the universe is heating up which would contribute to global warming