Hawking radiation

[paddoboy]

Huh? Seeing double while looking in a mirror? You were rattled! Honestly, why not just follow RU and quit pretending to be capable of evaluating non-trivial concepts in physics.

And the psychoanalysis continues. I follow many things, RU and RL are just two of those things. Concepts in physics and cosmology is another, and keeping fools honest on a science forum is another.

You can't meet it. Be honest for a change.

And you certainly are unable to meet my challenge! If you did your collective ignorance of GR and 21st century cosmology would be dazzling to say the least.

Forgotten already? To repeat - this is a bloody FORUM - nitwit! Go check the dictionary definition.

Calm down sonny boy!.....Of course this is a forum.....and as such discussions and debates take place, but near certainly no new revelation in cosmology or physics will ever be forthcoming.
You see the true scientists [which you claim to be ] are out there gathering the data, examining same and making observations...they have their heads down and their arses up, nose's to the grindstone.

If I were The God, that piece would be the last straw. There are I assume still in place strict forum rules regarding making repeated false accusations. This may have an interesting finale.

Yep there are forum rules, and those same rules would be applied to your conceited self.
Again, I believe the god is rajesh, and others do also.
And I do have evidence for that. The similarities are astounding.
I would suggest though you grow up, and learn to take what you dish out and stop acting like a big baby.
To be refuted by a lay person may be hard to swallow, but you have already had one anti GR thread shifted to the fringes in which I played a part, and that makes it even harder to swallow.
http://www.sciforums.com/threads/fr...-is-bs-or-dont-just-trust-authorities.142870/

And of course speaking of accusations......who could forget this.....

That call for details of who why when in #35 has gone unanswered. What disrespectful, arrogant coward or cowards. But paddoboy, your final "It's done and dusted." remark in #33 gives a strong hint you were at least involved in pulling strings behind the scenes. Care to come clean? Who else do you know had a hand in it - paddoboy?

 

[paddoboy]

Very short GRBs may be Hawking radiation source A particular group of gamma-ray bursts, those of very short duration, have characteristics that suggest they may be the signature of an evaporating primordial black hole – the Hawking radiation proposed by Stephen Hawking in 1974. Very short gamma-ray bursts (VSGRBs) last less than 0.1second and have been detected by several GRB instruments including the BATSE experiment on the Compton Gamma Ray Observatory, the KONUS experiment, and NASA’s Swift gamma-ray burst mission. The evaporation of primordial black holes was postulated as a possible high-energy source for GRBs as a whole, but these events do not in general fit the characteristics of such an event. Hawking, in collaboration with Bernard Carr, proposed that the evaporation of black holes left over from the early universe would produce a burst of energy; GRBs in general are too bright and too uniformly spread over the sky to have come from primordial black holes. Now David B Cline and colleagues from the University of California in Los Angeles argue that these VSGRBs are a distinct population that does fit the characteristics of primordial black hole evaporation, notably their anisotropic distribution in the sky and lack of significant afterglows. Cline presented these results to the GRB2010 meeting in November. http://www.physics.ucla.edu/hep/vsgrb/ vsgrb_ichep2010.pdf

 

[paddoboy]

It is important to use clear language in discussions like this. Words like fact, theory and even speculation, have very different implications on whatever subject they are associated with.., and none of them mean exactly the same thing.

Your comment re "clear language" is of course correct, and as you recognised in my tutorial and my use of the words, "approx" "around" and "about"

Hawking radiation does not even rise to the level of a theory, since it does not describe anything that is or can be observed. At best it is speculation, about a possible solution to one of the problems that emerges from what is believed may happen at the event horizon of a black hole.

Not sure though that I agree fully with what you have said above.
What we do know about quantum theory is near all unobservable...we just are not as yet technologically advanced enough to observe at those levels.
But again, as per our differences in the past, one can invoke some level of certainty on certain issues based on likelyhood and logic and acceptance within the scientific mainstream community.
We also do not directly observe BH's, but the indirect evidence can only be attributed to such an entity.
Virtual Particle pair creation is essential to our limited understand of quantum theory. If we doubt that, we may as well shelve all of quantum physics that we have learnt.
My own opinion then is that Hawking Radiation, seems to be an extension of virtual particle pair creation....I see it as a legit scientific theory, though certainly not in the class of SR/GR theories.
And isn't this what mainstream have accepted....Isn't it far more certain that Hawking Radiation is a real entity, based on what we already know, and certainly more likely the any other alternative that has been offered on this forum?
And does not the virtual particle pair creation theory, mean that while virtual, they are not contained by the laws of physics such as "c"?
The debate and some nonsense in this thread appears to simply be about what mainstream accept as likely and what is proposed by others that are not generally accepted and what I see as anti GR agendas anyway.
Does science really need to directly observe something for it to be a scientific theory? I don't believe so.

 

[Q-reeus]

It disgusts me that a mathematical illiterate and not even half a trick pony like paddoboy can get away with continually spewing out the sort of s**t displayed in #61. Why the hell does admin mollycoddle such a cretan rather than life ban it?
[I seem to recall recall someone else suggesting why - as a chronic obsessive/compulsive poster, that cretan boosts the stats for this site. A triumph of quantity over quality - and certainly over morality. Sigh.]

 

[brucep]

So, a mistaken use of the word?

My initial question was only because I thought you had worded that sentence badly. Not because I disagreed with what I thought you meant! That said...



It is important to use clear language in discussions like this. Words like fact, theory and even speculation, have very different implications on whatever subject they are associated with.., and none of them mean exactly the same thing.

Hawking radiation does not even rise to the level of a theory, since it does not describe anything that is or can be observed. At best it is speculation, about a possible solution to one of the problems that emerges from what is believed may happen at the event horizon of a black hole.



theoretical fact....?

• Theories attempt to describe things we can observe.
• Facts are things we can observe, or direct conclusions based on observation.
• Speculation is even step further from what we do know to be, than a theory. It's more like exploring the implications of how we imagine, what we know as a fact or theory, may apply to conditions we are unable to observe or test.

What is a theoretical fact?

Hawking radiation is speculation about something that is imagined or believed to occur. Even the concept, of virtual particles (which are inherently untestable), is speculative.., emerging initially from within an unrelated theory.



No one has detected Hawking radiation. An analogue is something that is similar to or comparable to something else. In this case a situation or system that is similar to what is speculated to occur in the case of Hawking radiation. But the conditions in any classical system that we can observe and test, are so far from what we believe the conditions existing at an event horizon would be, that the analogue system at best demonstrates a similarity, it can not prove anything about black holes or the factual existence of Hawking radiation.



Where in the paper you referenced is there a claim to have detected Hawking radiation? Again, no one has detected Hawking radiation, even where in an analogue system there are similarities. No one has even detected virtual particles, even while they remain a significant prediction of an otherwise successful quantum theory (that does describe things we can observe and test).

Read the one I posted for you. Specifically the discussion. Why should I provide you with another reference that you won't actually read?
Oh well here is the William Unruh paper on the results of the analog experiment to measure Hawking radiation. It's always cool when the theorist participate in the experimental side of physics.
http://arxiv.org/abs/1401.6612
Circa 2014.

 

[tashja]

Maybe tashja is busy contacting experts that can actually do so. We shall see.

Hey, guys

Hi, Q. I just saw your posts this morning, so I got in touch with Prof. Unruh to see if he can help us with it. Below is his reply:

For those of us who are not versed in QFT but do exercise the faculty of critical thinking, that ostensibly standard account has some evident issues.

Maybe QFT can actually make sense of the notion that negative frequencies = negative energies, but it's use elsewhere has no such exotic inference - e.g.:
http://www.bitweenie.com/listings/negative-frequency/
Nothing more or less than an arbitrary coordinate dependent designation of forward vs reverse propagation direction. Actual energies always positive. Hence E = h|f| is what's physically significant, regardless of any mathematical convention where f < 0 is used. A similar thing could be said for the convention of 'complex frequencies'.

Brings me to another troubling aspect of that piece - always referencing HR to particle/anti-particle pairs. The anti-particle always having negative energy somehow. Yet an assumed initially stellar mass BH would have an exceedingly low effective T for the vast bulk of it's slowly shrinking existence. The assumed radiation would be EM, not e.g. electron-positron and higher energy particles.
It's well known a photon is its own anti-particle. Hence both necessarily having positive E = hf energy. By what seeming magic then does an intrinsically positive energy 'anti-particle' photon somehow 'go negative' once it crosses the dreaded EH? Oh yeah, that's right - 'space becomes time, and time becomes space' there. Really? Well gee, if that's truly the case in a physically sensible way, one has to ask why nobody suggests that dropping say a positive energy stone into a BH has that mass magically turning negative and reducing the overall exterior M value of BH. Something special about photons then?

One could go on and e.g. question the logic behind assertion that somehow only the 'negative energy partner' is selected for swallowing. The above though is probably enough to stimulate possible doubts in those not given to unquestioning devotion to orthodoxy. Maybe a QFT expert can now step in and graciously alleviate my doubtlessly unwarranted scepticism.

Standard HR narrative has that negative energy particles are always swallowed by BH hence never observed. Only inferred indirectly as a supposed BH mass loss. However, as a supplement to my last point in #15:
, it may be more pointedly asked why on earth the selection process would not in fact exclusively select the supposed -ve energy particles for expulsion.
Since -ve energy surely logically equates to -ve gravitating mass! Hence, one might reasonably conclude, impossible for a -ve energy particle to ever reach EH let alone sink without trace.

Anyone else think there may be more than a whiff of insanity with the standard narrative? I do NOT apologize if this makes devoted followers of consensus position hurt in their heads.

a) If positive energy goes out to infinity, then there must be negative energy
somewhere since energy is conserved.

b) If we look at the system from the point of view of the Schwarzschild time
(which is what we use to define energy at infinity) then near the black hole,
the quantum field (whether electromagnetic or electron) near the horizon
corresponds to that seen by an accelerated observer. As is known even from
flat spacetime, this is a flux, in both directions, of thermal particles. A
similar thing happens near a black hole. From the point of view of the
accelerated observer a flux of thermal particles comes out from the black hole.
Now at low frequencies, these meet a potential barrier-- set up both because
of the angular momentum of the particles, and the curvature of the spacetime,
which reflects almost all of them back. At higher energies ( energies higher
than the peak energy in the thermal spectrum) instead of being reflected back
they escape as Hawking radiation.

Now in flat spacetime we know that the energy of the out plus ingoing
radiation has zero energy ( well it is infinite actually, but as with many
things in quantum field theory one must renormalize it, and it is zero as far
as the gravitational effects are concerned.) If we subtract some of that
incoming radiation (because it escaped out to infinity) the remainder must
have negative energy. Ie, the reason why there is a negative energy flux into
the black hole is not because somehow the "partner" carries negative energy,
but because of the absence of the reflected radiation.

The actual "partner" of the outgoing radiation is all trapped inside the black
hole, beyond the horizon.

The picture, that Hawking developed in the 70s in his Scientific American
article of that "pair creation" is a beguiling, but in detail misleading
picture. Even at that time it was backed by no calculation. Some of the
"predictions" one would make from that picture are true, and some are
misleading.

As is often the case in science, when developing simple pictures to describe
subtle phenomena, the subtlety gets lost, so I do not blame you for getting
confused.


William G. Unruh | Canadian Institute for|
Physics&Astronomy

 

[brucep]

Read the one I posted for you. Specifically the discussion. Why should I provide you with another reference that you won't actually read?
Oh well here is the William Unruh paper on the results of the analog experiment to measure Hawking radiation. It's always cool when the theorist participate in the experimental side of physics.
http://arxiv.org/abs/1401.6612
Circa 2014.

Since this thread is about Hawking Radiation it begs the question about analog experiments and confirmation of theoretical predictions. Several other key contributers along the path to Hawkings revelation. Such as Jacob Bekenstein. May he rest in peace.

 

[Daecon]

You actually believe that 'black body' = 'black hole'?!

What?

Black bodies aren't black holes, but a black hole is a black body, according to the Wikipedia article on black-body radiation.

 

[brucep]

So, a mistaken use of the word?

My initial question was only because I thought you had worded that sentence badly. Not because I disagreed with what I thought you meant! That said...



It is important to use clear language in discussions like this. Words like fact, theory and even speculation, have very different implications on whatever subject they are associated with.., and none of them mean exactly the same thing.

Hawking radiation does not even rise to the level of a theory, since it does not describe anything that is or can be observed. At best it is speculation, about a possible solution to one of the problems that emerges from what is believed may happen at the event horizon of a black hole.



theoretical fact....?

• Theories attempt to describe things we can observe.
• Facts are things we can observe, or direct conclusions based on observation.
• Speculation is even step further from what we do know to be, than a theory. It's more like exploring the implications of how we imagine, what we know as a fact or theory, may apply to conditions we are unable to observe or test.

What is a theoretical fact?

Hawking radiation is speculation about something that is imagined or believed to occur. Even the concept, of virtual particles (which are inherently untestable), is speculative.., emerging initially from within an unrelated theory.



No one has detected Hawking radiation. An analogue is something that is similar to or comparable to something else. In this case a situation or system that is similar to what is speculated to occur in the case of Hawking radiation. But the conditions in any classical system that we can observe and test, are so far from what we believe the conditions existing at an event horizon would be, that the analogue system at best demonstrates a similarity, it can not prove anything about black holes or the factual existence of Hawking radiation.



Where in the paper you referenced is there a claim to have detected Hawking radiation? Again, no one has detected Hawking radiation, even where in an analogue system there are similarities. No one has even detected virtual particles, even while they remain a significant prediction of an otherwise successful quantum theory (that does describe things we can observe and test).

For somebody who doesn't know much about this science you sure have a lot of irrelevant opinions.

 

[brucep]

What?

Black bodies aren't black holes, but a black hole is a black body, according to the Wikipedia article on black-body radiation.

You and the wiki are correct. Hawking radiation radiates in the black body spectrum.

 

[Daecon]

Would Hawking radiation have a temperature of about 2.7 Kelvin, the same as the cosmic microwave background?

 

[paddoboy]

It disgusts me that a mathematical illiterate and not even half a trick pony like paddoboy can get away with continually spewing out the sort of s**t displayed in #61. Why the hell does admin mollycoddle such a cretan rather than life ban it?
[I seem to recall recall someone else suggesting why - as a chronic obsessive/compulsive poster, that cretan boosts the stats for this site. A triumph of quantity over quality - and certainly over morality. Sigh.]

Your opinion is just that...your opinion....My opinion of you is to grow up, stop being so falsely indignant and utterly pretentious and you may get some respect.
In the meantime have a disprin and a good lay down and take an anger management course.
As long as I'm being criticised by nuts, I must be doing something right.
And just like your previous GR thread, you should be in the fringes. Take it easy my friend.

 

[paddoboy]

Hey, guys

Hi, Q. I just saw your posts this morning, so I got in touch with Prof. Unruh to see if he can help us with it. Below is his reply:

Thanks once more for a grand effort tashja.

 

[brucep]

Would Hawking radiation have a temperature of about 2.7 Kelvin, the same as the cosmic microwave background?

The Hawking temperature. This is derived from the Unruh temperature and is part of the text Exploring Black Holes by Edwin F. Taylor and John A. Wheeler.




T_Unruh = h*g_conventional/4(pi)^2*k_Boltzmann*c [eq.1]
g_conventional/c^2 = (M*c^2/r^2)(1-2M/r)^-1/2
g_shell = g_conventional/c^2 = (M_meters*c^2/r^2)(1-2M/r)^-1/2 [eq.2]
Substituting [eq.2] into [eq.1]
T_Unruh = [h*M_meters*c] / [4pi^2*k_B*r^2 (1-2M/r)^1/2)]
Let r > 2M the Schwarzschild event horizon. Account for the redshift measured from remote coordinates(1-2M/r)^1/2 / 1-2M/r)^1/2 =1

T_Hawking=[h*c*M_meters/4pi^2*k_Boltz*4M_meters^2]
T_Hawking = h*c/16pi^2*k_Boltz*M_meter

The only variable is the mass expressed in meters. The larger the mass the smaller the Hawking temperature. For one solar mass it would be M_meter=1477 meter. For the solar mass that works to a prediction around .000000061787 Kelvin. So they are really cold generally. With a little algebra you could predict the mass where the Hawking is around the 2.7 K.

 

[Daecon]

Ah, I see. So supermassive black holes are supercold.

 

[Q-reeus]

Hi, Q. I just saw your posts this morning, so I got in touch with Prof. Unruh to see if he can help us with it. Below is his reply:

Thanks for quietly working on this one tashja. As you will later see below, I would be interested in a follow-up from Prof. Unruh.

Professor William G. Unruh said:..

a) If positive energy goes out to infinity, then there must be negative energy somewhere since energy is conserved.

b) If we look at the system from the point of view of the Schwarzschild time (which is what we use to define energy at infinity) then near the black hole, the quantum field (whether electromagnetic or electron) near the horizon corresponds to that seen by an accelerated observer. As is known even from flat spacetime, this is a flux, in both directions, of thermal particles. A similar thing happens near a black hole. From the point of view of the accelerated observer a flux of thermal particles comes out from the black hole.
Now at low frequencies, these meet a potential barrier-- set up both because of the angular momentum of the particles, and the curvature of the spacetime, which reflects almost all of them back. At higher energies ( energies higher than the peak energy in the thermal spectrum) instead of being reflected back they escape as Hawking radiation.

So ok we choose the vantage point of a hovering observer not one in free fall. And yes given as taken an UE thermal bath seen by such an observer, it makes sense that lower frequency modes will be reflected, with a trickle escaping as HR. So far, so reasonable.

Now in flat spacetime we know that the energy of the out plus ingoing radiation has zero energy ( well it is infinite actually, but as with many things in quantum field theory one must renormalize it, and it is zero as far as the gravitational effects are concerned.)

Right here I have an issue. Not with the renormalization bit but with the assumption of zero net energy of thermal radiation. The picture has it that enormous tidal g gradients 'tear apart' zero-point EM fluctuations so as to create real photon quanta - yes? How is that not a net gain in energy - given as I pointed out earlier this thread, photons are their own anti-particle? Or put it another way, what *physical sense* can there be to the notion of real -ve energy EM quanta? Energy density is after all a parametric function of field strength - or it was when I went to school. I can see that mathematically putting an 'i' in front of an E or B could do such a trick, but is that not just mathematical trickery? Explaining what an actual -ve energy EM quanta 'looks like' seems problematical to me.

If we subtract some of that incoming radiation (because it escaped out to infinity) the remainder must have negative energy. Ie, the reason why there is a negative energy flux into the black hole is not because somehow the "partner" carries negative energy, but because of the absence of the reflected radiation.

Again, I question the 'must have' there. Take the case of Schwinger 'vacuum polarization' expected when very intense E fields are generated. Owing to the opposite signs of charge for electron-positron virtual pairs, just a uniform E of sufficient strength is all that's needed to 'tear apart' such virtual pairs so as to create real electron-positron pairs. No-one suggests there the net energy of such real pairs is other than large and positive. How then is that same general condition not true when the 'tearing apart' is owing to tidal g gradients rather than an applied E? Is it not so net positive energy is first required then created in such pairs in either case? Of course for Schwinger vacuum polarization, the resulting current quickly neutralizes the E source. In the BH case though, it gets back to that EM quanta don't surely have opposite 'gravitational charge'. And if one gives them such by mathematical fiat declaration, one is left to actually explain how '-ve gravitational charge' could logically allow such to be other than violently expelled - with only +ve energy quanta capable of being trapped inside EH. At the end of it, if you wish to insist the energy book is balanced and have real +ve energy quanta ejected, real -ve energy quanta have to be trapped/swallowed somehow - DESPITE THEIR IMPLIED NEGATIVE GRAVITATING MASS!

The actual "partner" of the outgoing radiation is all trapped inside the black hole, beyond the horizon.

See above.

The picture, that Hawking developed in the 70s in his Scientific American article of that "pair creation" is a beguiling, but in detail misleading picture. Even at that time it was backed by no calculation. Some of the "predictions" one would make from that picture are true, and some are misleading.
As is often the case in science, when developing simple pictures to describe subtle phenomena, the subtlety gets lost, so I do not blame you for getting confused.

William G. Unruh | Canadian Institute for| Physics&Astronomy

Well thanks for taking the time and effort there to 'unconfuse me', and maybe the fine details somehow add up to a sensible and consistent final picture. As per above comments though, I still have serious reservations.

 

[Q-reeus]

What?

Black bodies aren't black holes, but a black hole is a black body, according to the Wikipedia article on black-body radiation.

I admittedly jumped a little too soon on that one, and only later realized the reference to para 4 linked the two. But - so very strange. That you waited all this time to respond - not until after that reply from Prof. Unruh. How come - given you were on line during and for hours after I posted the original query? Spine issues?

Incidentally, you give yourself away asking that inept question in #71:

Would Hawking radiation have a temperature of about 2.7 Kelvin, the same as the cosmic microwave background?

Might as well ask how long is a piece of string.

 

[paddoboy]

Casimir Effect, Black Holes and Hawking Radiation.
Featuring Professor Mike Merrifield from the University of Nottingham -

 

[paddoboy]

Would Hawking radiation have a temperature of about 2.7 Kelvin, the same as the cosmic microwave background?

Great question Daecon and admirably answered by bruce.

 

[Daecon]

I admittedly jumped a little too soon on that one, and only later realized the reference to para 4 linked the two. But - so very strange. That you waited all this time to respond - not until after that reply from Prof. Unruh. How come - given you were on line during and for hours after I posted the original query? Spine issues?

Incidentally, you give yourself away asking that inept question in #71:

Might as well ask how long is a piece of string.

Spine issues? No. I just couldn't be bothered because you hadn't appeared to have read the Wikipedia article I linked to.

Exactly how did I "give myself away" by asking a question?