Was the Early Universe Hot?

[John_Mason]

The big bang is defined as the theory that the universe has expanded from a primordial hot and dense initial condition. Was it hot? I would suspect that the initial condition was in fact cold due to the lack of space and therefore movement. The heat happen directly after the bang. Does this seem correct?

 

[mathman]

The state of the universe (it may not even be definable) before the big bang is unknown. There are a lot of theories out there, but so far there doesn't seem to be any way to test them.

 

[John_Mason]

> It may not even be definable

Yes and no. We know with a fair level of certainly that it has dense and had extremely low entropy. During the first few moments after the bang, should we not be able to determine if the heat was building (which would indicate a cold initial condition) or decreasing (which would indicate a hot initial condition).

 

[marcus]

John you should probably survey the various models of what led up to the big bang. See this book:
http://www.springer.com/astronomy/general+relativity/book/978-3-540-71422-4

when you go there, click on TABLE OF CONTENTS
http://www.springer.com/astronomy/general+relativity/book/978-3-540-71422-4?detailsPage=toc

It is an active area of research. Also various ideas for testing some of the models (using data we can observe) are being studied. It is hard, but might be do-able.

there is more on this, if you are interested.

advice: don't get wed to one particular scenario at this point

 

[DaveC426913]

The big bang is defined as the theory that the universe has expanded from a primordial hot and dense initial condition. Was it hot? I would suspect that the initial condition was in fact cold due to the lack of space and therefore movement. The heat happen directly after the bang. Does this seem correct?

Do you mean initial condition before the bang itself? Because it was extremely hot in the fractions of seconds after the BB. Too hot in fact, for matter to exist. The universe had to cool for ages before it was cool enough for matter to condense from energy.

 

[Chronos]

Conditions that preceeded the BB are unknown - and possibly unknowable. The point is moot until a testable experiment is proposed.

 

[marcus]

... The universe had to cool for ages before it was cool enough for matter to condense from energy.

saying ages may overstate it some, Dave. I mean if you think of quarks and electrons as matter.

but the basic idea is right, that it had to cool before things like quarks and electrons could have stable protracted existence.

if by matter you mean neutral hydrogen atoms then several hundred thousand years---ages is absolutely right.

 

[Chaos' lil bro Order]

I think the word 'hot' is too ambiguous to answer your question. By heat do you mean thermal radiation like Infrared? If so, I would say the Universe was not hot at all at the moment of the BB. I think energy density would be a better term to replace 'hot' and in that case, the Universe was presumably, by definition, infinitely dense at the moment of the BB. You can solve the Friedmann equation for temperature, given in Kelvin, for a given time after the BB. Just note that there are different variations of the equation that you must choose correctly for the time of your choice, for your solution of K to be accurate.