What is the initial temperature of the Big Bang?

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Discussion Overview

The discussion revolves around the concept of the initial temperature of the Big Bang, exploring how this temperature is defined and calculated. Participants engage with theoretical implications, the nature of the Big Bang as a process, and the relationship between temperature and time in the early universe.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants assert that the temperature of the cosmic background radiation is 3K, questioning how the initial temperature of the Big Bang is determined.
  • One participant argues that there is no meaningful concept of an "initial temperature" since the Big Bang is a process rather than a singular event.
  • Another viewpoint suggests that the temperature right after reheating, caused by the end of inflation, could be considered, but emphasizes that the energy density of the inflaton is currently unknown.
  • Some participants propose that the temperature of the Big Bang is thought to be around the Planck temperature, while others challenge this by stating that properties like time and temperature are undefined at t=0.
  • There is a claim that the temperature at the earliest moments is not the Planck temperature but rather about one-third of it, highlighting the uncertainty surrounding this point in time.
  • One participant compares the question of initial temperature to asking how far it is to a location, suggesting that the framing of the question may not be appropriate.
  • Several participants express skepticism about sources that attempt to define the initial temperature, emphasizing the complexity of the Big Bang as a process.

Areas of Agreement / Disagreement

Participants generally disagree on the concept of an initial temperature of the Big Bang, with multiple competing views on what this temperature might be and whether it is meaningful to define it at all.

Contextual Notes

There are limitations in the discussion regarding the definitions of temperature and time at the earliest moments of the universe, as well as the dependence on theoretical models such as inflation and alternatives to it.

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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