Evidence of Hawking Radiation: What We Know

[wolram]

can anyone tell me if "hawking radiation" has been observed?
or if there is evidence of its existence?
nasty stuff..

 

[marcus]

Originally posted by wolram
can anyone tell me if "hawking radiation" has been observed?
or if there is evidence of its existence?
nasty stuff..

wolram, to my knowledge hawking radiation has never been observed

but I imagine that there may arguably be some indirect supportive evidence
of the following kind


small BH may have been produced in large numbers under the high-energy-density conditions of the early universe

but we DO NOT SEE multitudes of small BH holes, therefore
(wolram I am not responsible for this argument) where did
they all go?

perhaps they evaporated


indeed, according to hawking's theory, small BH should be much hotter and evaporate more quickly than the sort of large BH which we see around and about

this then (the fact that we do not see them) it can be argued, is evidence that quite small BH are able to evaporate,
which they do by emitting the nasty hawking radiation

 

[jcsd]

No Hawking radiation has never been observed 'cos for a normal size black hole it's less than the CMBR.

Marcus, the lack of small black holes doesn't necessarily indicate that they've evapourated what it probably indicates is that the early universe was very uniform and therefore they were never created.

 

[jcsd]

If anyone's interested Hawking radiation is one of the processes where baryon number and lepton number is not conserved, with the particles randomly emitted being mostly photons and neutrinos along with a wide range of other species.

 

[jeff]

The idea that black holes evaporate is a semi-classical result. We don't really know how holes too small to be described semiclassically will behave.

 

[wolram]

peter pan and tinkerbell, what man controles there strings?

 

[jeff]

Originally posted by wolram
peter pan and tinkerbell, what man controles there strings?

The idea that some man controls peter pan's and tinkerbell's strings is a semi-classical result. We don't really know what controls their strings when they're too small to be described semi-classically.

 

[wolram]

http://www.nature.com/nsu/011004/011004-8.html

And these high-energy events will generate vast numbers of minuscule black holes, Savas Dimopoulos of Stanford University in California and Greg Landsberg at Brown University in Providence, Rhode Island now calculate1.
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this is news to me. anyone have the latest?



http://casa.colorado.edu/~ajsh/hawk.html

Black holes get the energy to radiate Hawking radiation from their rest mass energy. So if a black hole is not accreting mass from outside, it will lose mass by Hawking radiation, and will eventually evaporate

 

[wolram]

http://superstringtheory.com/forum/dualboard/messages9/130.html

The very early universe could be regarded as a White Hole in some but perhaps not all respects, so "information" is coming out - Knowledge in my terminology as the semantic part of that of which Information/Entropy is the syntactic part - is increasing, and if White Holes become universes like ours, then Entropy also increases as disorder.

That would make a black hole OPPOSITE but only in part - not only is a star collapsing, but it is "taking its knowledge down with it" so to speak, while its Entropy/Information is increasing - Disorder is increasing. Its Knowledge is decreasing in the sense that it is going out of the usual universe in which the original star was located and out of the universe in which observers external to a close vicinity of the black hole are located.
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anyone know any white hole theory?

 

[wolram]

http://hypatia.ss.uci.edu/lps/psa2k/black-hole-remnants.pdf
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Planck scale physics may shut down hawking radiation.

 

[marcus]

you came up with some interesting articles
I had a look at that one on information loss
by the guy at notre dame
cant comment---too speculative and over my
head in places---but glad to have glanced at it
long way to go before the issues around BH
are resolved

 

[wolram]

you came up with some interesting articles
I had a look at that one on information loss
by the guy at notre dame
cant comment---too speculative and over my
head in places---but glad to have glanced at it
long way to go before the issues around BH
are resolved
-------------------------------------------------------------------
i am shocked to the core "over my head"??
live long and prosper marcus.

 

[wolram]

http://curious.astro.cornell.edu/question.php?number=108

What is a white hole?

The short answer is that a white hole is something which probably cannot exist in the real universe. A white hole will turn up in your mathematics if you explore the space-time around a black hole without including the star which made the black hole (ie. there is absolutely no matter in the solution). Once you add any matter to the space-time, the part which included a white hole disappears

 

[wolram]

http://casa.colorado.edu/~ajsh/schww.html

The negative square root solution inside the horizon represents a white hole. A white hole is a black hole running backwards in time. Just as black holes swallow things irretrievably, so also do white holes spit them out. White holes cannot exist, since they violate the second law of thermodynamics.
----------------------------------------------------------------------this is the best information i can find on the net.

 

[jeff]

Originally posted by marcus
small BH may have been produced in large numbers under the high-energy-density conditions of the early universe

but we DO NOT SEE multitudes of small BH holes, therefore where did they all go?

perhaps they evaporated


indeed, according to hawking's theory, small BH should be much hotter and evaporate more quickly than the sort of large BH which we see around and about

this then (the fact that we do not see them) it can be argued, is evidence that quite small BH are able to evaporate,
which they do by emitting the nasty hawking radiation

It could also be that their initial number density inflated away if they formed before some period of inflation.

 

[marcus]

This is my original unedited post of a few days ago:

Originally posted by marcus
wolram, to my knowledge hawking radiation has never been observed

but I imagine that there may arguably be some indirect supportive evidence
of the following kind


small BH may have been produced in large numbers under the high-energy-density conditions of the early universe

but we DO NOT SEE multitudes of small BH holes, therefore
(wolram I am not responsible for this argument) where did
they all go?

perhaps they evaporated


indeed, according to hawking's theory, small BH should be much hotter and evaporate more quickly than the sort of large BH which we see around and about

this then (the fact that we do not see them) it can be argued, is evidence that quite small BH are able to evaporate,
which they do by emitting the nasty hawking radiation

In case anyone wants to compare, this from the preceding post.
__________________________
small BH may have been produced in large numbers under the high-energy-density conditions of the early universe

but we DO NOT SEE multitudes of small BH holes, therefore where did they all go?

perhaps they evaporated

indeed, according to hawking's theory, small BH should be much hotter and evaporate more quickly than the sort of large BH which we see around and about

this then (the fact that we do not see them) it can be argued, is evidence that quite small BH are able to evaporate,
which they do by emitting the nasty hawking radiation
--------------------------------------------------------------------

It is implicit in this argument for the evaporation of small BH that
they formed in substantial numbers AFTER inflation. There is no one prevailing scenario for inflation but typically the inflation era is supposed to have been extremely early and brief and to have been followed by "reheating" to roughly Planck temperature

As I understand it, some people posit that black holes of greater than Planck mass may have formed from highly energetic particles after reheating----these would of course not be "inflated away"----and would then, because of their small mass have evaporated very quickly.

There is a plausible and widely credited idea that magnetic monopoles were created in substantial numbers BEFORE inflation and that indeed the monopoles were "inflated away".
There is a pretty good discussion of this in Ned Wright's
Cosmology Lecture Notes (for the UCLA course Astro 275) on pages 71 and 72. There is a technical reason (goes by the name of "symmetry breaking") that monopoles would not have been generated AFTER inflation. Let's not confuse BH with magnetic monopoles---a different kettle of fish.

In any case this is not my argument, as I made clear in my original post. Wolram asked if there was any (including indirect) evidence for BH radiation and my point was that according to some people a bunch of BH (I suppose several Planck mass in size but don't consider this terribly important) were created and
since they have been looked for and not found, they quite possibly may have evaporated by means of radiation.

 

[jeff]

Originally posted by marcus
...small BH...formed in substantial numbers AFTER inflation. There is no one prevailing scenario for inflation but typically the inflation era is supposed to have been extremely early and brief and to have been followed by "reheating" to roughly Planck temperature

For quantum fields at temperature T, an energy density ~T⁴ is expected in the form of vacuum energy. The vacuum-driven expansion produces a universe that is essentially devoid of normal matter and radiation; these are all redshifted away by the expansion, so the temperature of the universe becomes << T. A phase transition to a state of zero vacuum energy, if instantaneous, would transfer the energy T⁴ to normal matter and radiation as a latent heat. The universe would therefore reheat: it returns to the temperature T at which inflation was initiated, but with the correct special initial conditions for the expansion.

The transition in practical models is not instantaneous, however, so the reheating temperature is substantially lower than the temperature prior to inflation. In fact, the largest values obtained are ~ 10¹⁵ GeV which is much lower than the Planck energy ~ 10¹⁹ and occur only for special choices of parameters.

Having said that however, it's important to note that reheating is an essentially nonequilibrium process which means it's possible that there could be pockets of energy great enough to form the kind of BHs that we're discussing here, but their number density would be quite low to begin with.

Originally posted by marcus
...black holes of greater than Planck mass may have formed from highly energetic particles after reheating----these would of course not be "inflated away"----and would then, because of their small mass have evaporated very quickly.

As I said, BH evaporation is a semi-classical result so we don't know what happens with very small BHs. It's possible that evaporation shuts down as the plank scale is approached.

 

[marcus]

Originally posted by jeff

The transition in practical models is not instantaneous, however, so the reheating temperature is substantially lower than the temperature prior to inflation. In fact, the largest values obtained are ~ 10¹⁵ GeV which is much lower than the Planck energy ~ 10¹⁹ and occur only for special choices of parameters.

Several things you say here are certainly correct (in my opinion) and indeed familiar to me.

The survey article I like to recommend on inflation, big bang, CMB etc (Lineweaver astro-ph/0305179) uses a rough estimate for the temperature at "reheating" which is about are 10¹⁴ GeV

You say "largest values obtained are are ~ 10¹⁵ GeV"
which is very much in line with this.

As I said to Wolram, this is not my argument. I believe there are people who argue along these lines---but I'm not interested or able to argue for them.

You seem to have thought some about it, and want to discuss it, so I will try to hold up my end.

Personally I am happy with Lineweaver's temp of 10¹⁴ GeV (even a bit more conservative than your 10¹⁵ GeV)

Of course particle energies are of the same order as the temp.
Assuming a Planck curve for them would make the average about 3 times the temperature and allow for considerable numbers at 10 times the temperature (not to forget the tail of the distribution). So maybe we get fairly large numbers at your
10¹⁵ GeV energy even if the temperature itself is not that high!

But, you are perfectly right, Planck energy is around 1.25x10¹⁹ GeV!
And indeed the energy density in this case goes as the 4th power of the temperature.
As far as creating BH goes, it seems likely to me that one would want to look both at the energy density and at prevailing particle energies. For simplicity I will look at the particle energy.

Well! it is 4 orders of magnitude too small!

But somewhere I have seen or heard discussion of the creation of BH in early universe---and although I was not especially interested by it at the time (seems altogether too speculative for my taste) now I am interested to know what those people could have been talking about.

They must have some different basic assumptions.
In this case my assumptions seem to agree fairly well with yours.
From our perspective, then, it does not appear to make sense to search for primordial BH or even to imagine their existence.

[[If they existed BEFORE inflation, then presumably they would have been inflated away, like magnetic monopoles.]]

So what are people talking about when they discuss small BH forming in considerable numbers in early universe? Do you happen to know?

 

[jeff]

Originally posted by marcus
So what are people talking about when they discuss small BH forming in considerable numbers in early universe?

Among possible black hole creation processes, the one by which primordial black holes might form is the most speculative. The idea is that if sufficiently large inhomogeneities in density were present in the early universe, regions of enhanced density could collapse directly to black holes rather than follow the cosmological expansion. Although large numbers of black holes might be produced this way, as far as I know, there are no reliable predictions of how many - if any - primordial black holes might exist in our universe. In fact, one of the best limits on density inhomogeneities on small mass scales comes from the requirement that they not overproduce small black holes.

An important feature of primordial black holes is that they could've been produced at any mass scale since pressures were high enough to compress virtually any concentration of energy beyond it's gravitational radius no matter how small.