What is the initial temperature of the Big Bang?

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SUMMARY

The initial temperature of the Big Bang cannot be defined as a singular value due to the nature of the Big Bang being a process rather than an event. The temperature right after reheating, caused by the decay of the inflaton, is the closest approximation, but the exact energy density remains unknown. The temperature of the cosmic microwave background (CMB) radiation is approximately 3K, while the temperature at the earliest moments is thought to be around one-third of the Planck temperature. Understanding these concepts requires recognizing that properties like time and temperature are undefined at t=0.

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wolram
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We all know that the temperature of the back ground radiation is 3k, but how have we calculated the intiial temperature of the big bang.
 
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No such thing.
 
wolram said:
We all know that the temperature of the back ground radiation is 3k, but how have we calculated the intiial temperature of the big bang.
The closest thing to an "initial temperature" that makes sense in this context would have been the temperature right after reheating, which was caused by the end of inflation. Because reheating would have been caused by the inflaton decaying, the temperature at that time would have been determined by the final energy density of the inflaton. That energy density we don't currently know.

Note that there are also some alternatives to inflation, and some of them may have rather different early temperatures, while others won't have anything that can be referred to as an "initial temperature" at all.
 
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The temperature of the BB is thought to be around the Planck temperature [really, really hot]. The temperature of the plasma which emitted CMB photons is proportionate to its redshift [z~1090].
 
Chronos said:
The temperature of the BB is thought to be around the Planck temperature [really, really hot].

Where do you get this? As the BB is a process, not an event, I don't think this is even meaningful.
 
I agree properties like like time, space and temperature are undefined at t=0. It is not until after the briefest possible span of time has passed following the BB [t=10E-43 seconds], that temperature has any meaning, and that temperature is the Planck temperature. I'd call that close enough for government work.
 
But it's not the Planck temperature. It's like 1/3 the Planck temperature. It's also the least understood point.

The question is analogous to "how far is it to Boston?". Arguing whether the best starting point is Worcester Mass. or Worcester England seems not to be a good answer to this question.
 
There's lots of such things out there. I don't get my science from them.

The Big Bang is a process, not an instant, so there is no "temperature of the Big Bang". That's more important than the factor of three you bobbled in trying to define one.
 
  • #10
As this is a beginner's level question which has been adequately answered, I think its time we closed this thread.

Thank you all for your contributions.

Take care,
Jedi
 

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