Blackhole temeperature and bigbang

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Classical blackholes said to have zero temperature...but in BBT,it is same like a blackhole where matter is compressed but it said to have high temeprature...both blackhole and matter at bigbang is very compressed then why classical blackholes have zero temeperature and big bang has high temperature...

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Wallace
The Big Bang is not like a black hole. It's a common misconception though. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html" [Broken] FAQ for some info.

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The Big Bang is not like a black hole. It's a common misconception though. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html" [Broken] FAQ for some info.
So you say blackhole singularity and Bigbang singularity is different.
So classical blackholes can have zero temperature and bigbang singularity can have high temperature...is it correct...

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The Big Bang is not like a black hole. It's a common misconception though. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html" [Broken] FAQ for some info.
So you say blackhole singularity and Bigbang singularity is different.
So classical blackholes can have zero temperature and bigbang singularity can have high temperature even though both looks similar...is it correct...

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Wallace
So you say blackhole singularity and Bigbang singularity is different.
Yes, they are quite different. As I say the FAQ I linked to explains it.

So classical blackholes can have zero temperature and bigbang singularity can have high temperature even though both looks similar...is it correct...
The error is assuming that these two things are similar. They are in fact very different mathematically and physically. If they is something in Baez's FAQ that confuses you please don't hesitate to ask, but read that first.

Thanks Wallace..i went through that site...But i am looking both blackhole singularity and bigbang singularity as compression of matter and that pushes to raise this question....in both case matter is very dense but having opposite temperatures....
Normally, what would happen when you compress matter? will the temperature increase or decrease?

No response to that one, and I'm not surprised...

Most physicists agree (theoretically: nobody "knows") that "black holes" have a "singularity" at their core, and that a black hole has a really low "temperature".

"Temperature" is a measure of molecular (maybe even subatomic) "motion," usually referred to as thermal activity.

Since "infinite density" implies zero room for thermal activity, the "temperature" of such a beast would have to be really really close to 0K. No?

If no, can someone explain? How was the "big bang singularity" different from a "black hole singularity," especially in terms of its degree of (room for) thermal activity.

My (intuitive) take on the issue is that "singularities" do not exist, other than as indications that the math involved is in error... And that the true difference between a "black hole" and the "big bang" is that black holes actually exist, whereas the "big bang" never happened. The Universe always was, and always will be, what we're looking at is some sort of "energy recycling," very likely involving black holes.

phinds
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My (intuitive) take on the issue is that "singularities" do not exist, other than as indications that the math involved is in error... And that the true difference between a "black hole" and the "big bang" is that black holes actually exist, whereas the "big bang" never happened. The Universe always was, and always will be, what we're looking at is some sort of "energy recycling," very likely involving black holes.
Yes, but the universe doesn't care about your intuition. Do you have any evidence?

To say that the "big bang never happened" seems to miss the point. The phrase "big bang" has two meanings. The first is the singularity and the second is everything since the singularity.

The singularity is just the name we give to WHATEVER happened back at t=0 where, as you correctly note, the math breaks down. Since it's just a name for WHATEVER happened, it doesn't seem very meaningful to say it didn't happen. SOMETHING happened and we call it "we have no idea what" === "singularity"

The second meaning is very well understood (there ARE holes in our knowledge) and I assume this is not what you are saying didn't happen.

Phinds wrote: "The phrase "big bang" has two meanings. The first is the singularity and the second is everything since the singularity."

OK, so let's concentrate on the first "singularity": Extrapolation of the expansion of the Universe backwards in time, using general relativity, yields infinite density and infinite temperature at a finite time in the past. The question remains:

In an "infinite density," how can there be any room for any thermal activity?

The temperature of a "black hole" depends on its mass, but is always very low... like a few nanokelvin... Is this not due to the immense density of "the hole"?

phinds
Gold Member
2019 Award
The singularity was not known to be infinite density, it is a place where our models break down.

If "The singularity was not known to be infinite density," does that mean that all those references listed below are wrong? And as you imply knowledge, can you please guide me to a site where I too can learn?

The key question that I have is still "If density is near-infinite, can there really be any room for near-infinite thermal activities (molecular/atomic wiggling around), yielding near-infinite temperature?"

http://en.wikipedia.org/wiki/Gravitational_singularity: [Broken] According to general relativity, the initial state of the universe, at the beginning of the Big Bang, was a singularity.

http://assa.saao.ac.za/features/cosmology-articles/Stephen-Hawking-Turns-70.pdf: [Broken] Together with Roger Penrose he [Stephen Hawking] used Einstein’s equations to prove that the universe could have originated from a singularity, a point of infinite density, gravity and temperature. Initially Hawking described the singularity as a point of infinite density, temperature and gravity. He changed this from “infinite” to “incredible,” because he realized that the universe could not have evolved from a point of infinite gravity.

http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html: [Broken] Extrapolation from the present to the moment of Creation implies an origin of infinite density and infinite temperature (all the Universe’s mass and energy pushed to a point of zero volume). Such a point is called the cosmic singularity.

http://www.journaloftheoretics.com/articles/6-3/SM.pdf: [Broken] Mathematical infinity is applied also in calculations about pressure, temperature, and density in singularity of big bang and black holes, where all of them have infinite values.

http://debunkingwlc.wordpress.com/2010/07/09/standard-big-bang-model: the universe began as a state of infinite density, infinite temperature, and zero size which is often referred to as a singularity

http://www.infidels.org/library/modern/quentin_smith/uncaused.html: [Broken] As d2a/dt2 increases and a decreases, the density of matter p increases, until at t0 the value of p is infinite. At this time the entire universe is squeezed into at least one point of infinite density, infinite temperature, and infinite curvature. We have reached a space-time singularity.

http://www.stephenjaygould.org/ctrl/archive/hawking_universe.html: general relativity shows that under certain reasonable assumptions, an expanding universe like ours must have begun as a singularity.

http://www.astro.umd.edu/~miller/teaching/astr422/lecture27.pdf: [Broken] in general relativity, if we project backwards in time we get to a point of actually infinite density and temperature.

http://12tuesday.com/william-lane-craig-vs-stephen-hawking: general relativity predicts there to be a point in time at which the temperature, density, and curvature of the universe are all infinite, a situation mathematicians call a singularity.

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