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# Astrophysics/What temperature is assumed there was at the time of the big bang?

Question
Greetings to you all,
I could clarify one thing (assuming they can clarify it?)

What temperature is assumed that there has been during the big bang or singularity? I mean in the beginning, not after 1 second or less.
I ask this because sometimes I read that in the beginning the temperature was infinite. But my opinion is that this idea is a logical fallacy, because if we start from an infinite number (the number that represents the temperature), we could never reach the temperature of the universe we have today (although the big bang to date have passed 15 billion years).
You taught me that if we start from an infinite number and then subtract from this number the degree of which we assume has cooled the universe, as a result we will have another infinite number ....
But then (always starting from the assumption that at the beginning the temperature was <infinite>, and then after 15 billion years that we have the current temperature is about 3 degrees Kelvin ..... how do you explain that?
Even if the universe had cooled down (random numbers) of 10 billion degrees from the big bang to the present, I should do (infinite - 10000000000 = 3 degrees), but this as you know,we can not do .. .

Ugo

Hello,

You ask a very good question! Technically speaking, given that the concept of 'temperature' implies an *averaged* macroscopic property - i.e. implying two systems have been in thermal contact (e.g. a thermometric medium with another body) then there is no temperature that can be registered at the exact Big Bang singularity.

Another aspect to that: given this singularity is presumed to be 'atom-sized' there can be no temperature since one cannot take the temperature of an atom (or a molecule) for that matter.

A plasma in space, or the outer corona of the Sun would be a different matter, since the kinetic energies of the particles will yield what we call a 'kinetic temperature' (for the corona it's roughly 2 million Kelvin).

But this makes no sense applied to the exact instant of the Big Bang.

Alas, too many astronomy texts are guilty of claiming absurd magnitudes - like "infinite" temperature - even when this is only a metaphor and ought to be stated as such.

Astrophysics

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