Talk:Hawking radiation

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[edit] Pending confirmation

Removed pending confirmation:

Recent observation of Black Holes has confirmed that they do emit radiation, for example a recent example showed that one Black Hole was emitting sound at 47 octaves below middle C.

I don't think so... I think this person is getting Hawking radiation confused with gravitational radiation -- Tim Starling 06:45, Sep 10, 2003 (UTC)

Let's see. Middle C is 278 hertz I think, so the 'sound' frequency would be 278/247 Hz, corresponding to a period of 16000 years. Nah...
—Herbee 14:04, 2004 Feb 25 (UTC)

Physicists are working hard to directly detect gravitational radiation but haven't done so yet (21 October 2006). I think he's getting Hawking radiation confused with rapidly rotating pulsars or with a rotating pulsar - black hole pair - AG, Stockport, UK.

In case anyone wants to follow this up, the observation that seems to have spurred this debate is reported here: http://science.nasa.gov/headlines/y2003/09sep_blackholesounds.htm.
Xarqi 02:30, 24 May 2007 (UTC)

[edit] Area of a sphere

The area of a sphere is normally 4πr², but space near a black hole is curved so this probably needs a correction. What is the expression for the surface area of a Schwarzschild black hole's event horizon? This has bearing on my calculation of the power emitted in Hawking radiation.
—Herbee 22:13, 2004 Feb 24 (UTC)

It is 4πr2 because the blackholes metric is spherically symmetric, and thus on the surface of the sphere we can treat it as though it were imbedded in euclidean geometry(so long as we do not refer to anything off the surface).
JeffBobFrank 04:31, 25 Feb 2004 (UTC)
I'm not buying that. A circle drawn on a sphere is also symmetric, but its circumference is certainly not 2πr.
—Herbee 13:52, 2004 Feb 25 (UTC)
The metric tensor of the sphere is not equivalent to that of a plane, even when we limit ourselves to the circle, and discard the components that lead out of the circle, whereas in this case distances are the same as long as the time component and the radial component(the only ones that changed from what it would be without the black hole) are 0. Since the sphere being considered is at constant time and distance from the black hole it does have the same surface area.
JeffBobFrank 19:49, 26 Feb 2004 (UTC)
Isn't the radial coordinate *defined* to be such that the area of a sphere at radius r is 4πr2?? -Lethe | Talk 10:37, May 4, 2005 (UTC)
That's correct. If you look at the Schwarzschild coordinates page, you can see that the part of the metric involving r, dtheta and dphi is exactly the same as in flat space spherical coordinates. So the area of a sphere located at coordinate radius r is 4πr2.
The sublety is that if you wanted to get to this sphere from r=0 you wouldn't go a physical distance r, but some other distance... This is how the curvature of the Schwarzchild metric enters. Wesino 23:21, 9 November 2006 (UTC)

[edit] Hawking cracks black hole paradox

See http://www.newscientist.com/news/news.jsp?id=ns99996151

After nearly 30 years of arguing that a black hole destroys everything that falls into it, Stephen Hawking is saying he was wrong. It seems that black holes may after all allow information within them to escape.

Sombody who knows about this stuff can put it in the article. Walter 09:51, 16 Jul 2004 (UTC)

[edit] Information paradox

I've added a note to this article and Hawking's article explaining that the vaporization of particles at the event horizon has been called incorrect by Hawking. I've also noted that he will present new findings at the 17th International Conference on General Relativity and Gravitation in Dublin, Ireland in July 2004.

I'll try to update the article once Hawking has presented his findings.

Hawkings talk in Dublin was not to disprove Hawking radiation, but rather Information loss in evaporating black holes. Since information loss is not mentioned in this article (although it should be), nothing in this article was disprove by Hawking's Dublin talk, therefore I am removing your notice. -Lethe | Talk 21:46, Sep 17, 2004 (UTC)
Since anything falling into the black hole affects the black holes mass, and since the black hole's mass affects hawking radiation, then how come Hawking thinks that information is lost when a black hole radiates? Even if the virtual particle pairs appear randomly, would the radiation still not be directly caused by the fact that something fell into the black hole so that the event horizon is exactly at the location where it will obsorb one and let the other escape? -70.51.209.90 15:47, 1 January 2007 (UTC)

[edit] Confirmed by observation?

One thing I think this article could use (I can't add it because I don't know anything about the subject) is to what extent this phenomenon has been confirmed by astronomers' observations, as opposed to being a theoretical prediction. The article kind of makes it sound like a theoretical prediction...?

Paragraph 3 of the main articles states: "However, the existence of Hawking radiation has never been observed, nor are there currently viable experimental tests which would allow it to be observed." Perhaps this should be qualified by reference to the University of St. Andrews experiments reported here: http://www.eurekalert.org/pub_releases/2008-02/ns-llc021308.php Bridgewater (talk) 19:11, 14 February 2008 (UTC)

Interesting link, thanks. I'm not clear to what extent they are modelling their expectations or actually making empirical progress, but interesting stuff anyway. --Michael C. Price talk 00:16, 15 February 2008 (UTC)

[edit] First equation unclear

Could someone please consider cleaning up the following, which is totally unclear without following the link to Plank units:

"Tsub(h) = κ/2π,

... where G, c, ħ and k are all equal to 1..."

There are no G, c, ħ or k in the equation!

It is frustratingly unclear to have to follow the Natural Units link to understand the explanation for the equation

It's only frustratingly unclear if you have some perverse engineer's insistence on particular units. In natural units, all those constants are 1, which is why they do not appear in the equation. Many people (including me) think that this makes the equation more clear, not less clear. Here is what the equation says in words: the temperature is proportional to the surface gravity. The constant of proportionality is whatever combination of G, c and h it takes to turn temperature units into acceleration units (plus an additional 2π). What is that combination? Who cares!? Not I.
It is true that natural units can be somewhat confusing if you're not too familiar with them. But then again, so can a lot of things in physics. Maybe the equation would be easier for dilletantes if equations in theoretical physics were written in SI units. But this is tedious and does not conform to the actual practices of physicists. -Lethe | Talk 10:06, May 4, 2005 (UTC)

Dear Lethe: Wikipedia is for the general public, not just physicists (like you and me). Can't we find a succinct way of making the point without going far offtopic? - AG, Stockport, UK.

[edit] Hawking radiation and matter/antimatter bias?

With “classical Hawking radiation”, a “dark star” in a universe predominantly made of matter should be emitting particles that are also predominantly “normal” particles rather than “antiparticles”. If dark star radiation is technically “proper” Hawking radiation (Visser), then presumably the QM rules for Hawking radiation, applied to dark stars, will be able to predict this.

But for a GR&QM black hole, if we explain particle production as a purely quantum effect, with particle-antiparticle pairs constantly being created and destroyed above the horizon and a few pairs being wrenched apart by tidal forces so that one escapes . . . if the escaping material is again predominantly normal matter, to match the characteristics of the hole’s background, then how does the hole’s gravity “know” that it is supposed to be catching the antiparticles from the pairs in preference to the “normal” particles? How does the particle-production process know to polarise itself so that the “antiparticle” is aimed more towards the horizon and the “particle” is aimed more away from it?

On the other hand, if the previous paragraph is wrong, and the hole’s particle-catching abilities affect matter and antimatter equally, and the hole emits equal amounts of particles and antiparticles as Hawking radiation, then presumably the external behaviour of GR&QM black holes isn’t really the same as for QM-modelled dark stars after all. And presumably a certain amount of the escaping matter-antimatter mix would then mutually annihilate, so that the Hawking radiation would contain a higher proportion of EM radiation over particulate matter if it came from a black hole than if it came from a dark star.

I think that either result would be interesting. Has anyone tackled this problem yet? ErkDemon 14:17, 13 July 2005 (UTC)

[edit] Relative masses

From the "Black Hole Evaporation" section:

For a black hole of one solar mass, we get an evaporation time of 1067 years—much longer than the current age of the universe. But for a black hole of 1011 kg, the evaporation time is about 3 billion years. This is why some astronomers are searching for signs of exploding primordial black holes.

I'm not familiar with the Sun's mass in scientific notation. Can it please be expressed numerically, to compare with the 1011 kg value?

—The preceding unsigned comment was added by 216.93.216.253 (talk • contribs) .
Added. It's listed at Sun. --Christopher Thomas 16:34, 23 December 2005 (UTC)

[edit] Silly question...

So, I "get" the explanation given, that Hawking radiation is the emission of one half of a particle-antiparticle pair, and that one of the two particles is absorbed by the black hole while the other is emitted...

The problem I have is that I don't understand how it's the black hole that is losing mass from this process, when it appears to me that 1. the matter originates with zero-point energy virtual particles (the energy to create these particles being lost by the vacuum) and 2. the particle of the virtual pair that the black hole absorbs doesn't turn out to give it a net-positive mass from the transaction instead of the net-negative that is asserted.

Is there a simple visualization or explanation that could be inserted to explain the process without resorting to, for instance, purely abstract explanations via scalar fields?

If the black hole is losing the energy to create the virtual particles, in such a manner that it's losing half the transaction energy from the process via the lost particle, I'd understand this better, but as it's explained it doesn't appear the inital energy cost is deducted from the mass of the singularity at all.

~ lilewyn

There's a good explanation here: [1] 67.87.115.207 18:34, 11 March 2006 (UTC)
Okay, so I read that... tell me if this is completely and utterly wrong, okay? A particle-antiparticle pair appears near a black hole horizon, which would normally be okay even if it's a net energy defecit, because after a short period of time the defecit would balance itself out due to matter/antimatter annihilation. In this case, though, one of the pair is released, one of the pair is trapped, and the black hole has to pay for the defecit in equivilent loss of mass (equal to the total mass of both particles, though it absorbs one) to balance out the defecit... i.e. while both particles are positive mass, they're negative an amount of energy equal to the square of the mass of the particle, per particle (E=MC^2 and all that) which the black hole has to pay for. Sound about right? ~ lilewyn
Just identifying who lilewyn is for future reference ... me. :) —This unsigned comment was added by Kylu (talk • contribs) on 23:23, 2 April 2006.
Mmm... not quite. If I understand the article correctly (and it was written by an extremely smart guy (John Baez) who admits that even he doesn't fully get what's going on, so that's a big if), the mathematical basis for Hawking radiation is that regions of spacetime with substantially different curvature can disagree on what energy states are what. Since vacuum is just the lowest-energy state, what's vacuum near a black hole is not the same as vacuum out in flat space. It's a thermal state, and emits energy into the relatively cooler cosmos. Since energy must be conserved, the black hole's mass decreases accordingly as a result. The "virtual-particle pair" heuristic explanation doesn't appear directly connected to the usual mathematical process, but it might be. Presumably the guy who came up with it knows. 164.55.254.106 19:29, 11 April 2006 (UTC)
My understanding is that both virtual-particle and other explanations are valid ways of looking at it, and that which makes the most intuitive sense depends on the approach you take to working the math. There was some discussion of this over at Talk:Casimir effect and Talk:Virtual particle a while back, if memory serves. --Christopher Thomas 05:23, 12 April 2006 (UTC)
I'm really dissapointed that I'm not bright enough to understand this concept intuitively...
On the other hand, I'm happy I'm not the only one with that problem. Sonoluminescence makes more innate sense. :P
lilewyn 03:05, 14 April 2006 (UTC)
Based on Einstein’s comments calling some aspects of quantum theory incomplete because it would require logical paradoxes, I think he might have similar problems Hawking Radiation. He [Einstein] might politely call [the theory of Hawking Radiation] incomplete and suspect that if Hawking Radiation is observed it might cause micro black hole growth as common sense seems to suggest. --Jtankers (talk) 03:35, 10 March 2008 (UTC)
Einstein thought up some experimental results which were predicted by quantum theory, but which (according to Einstein's intuition) could never possibly occur in reality; these are the "logical paradoxes" you're referring to. You know what happened when we did the experiments? They agreed with quantum theory, and disagreed with Einstein's intuition. If Einstein had, in fact, objected to Hawking radiation based on his intuition, it might merit a mention in the article, but would hardly steer scientific consensus in the face of carefully-calculated work to the contrary. The fact that you object to Hawking radiation, and that you imagine that Einstein might have agreed with you, carries even less weight than that. As an aside, you must realize that your "common sense" intuition (black hole growth from radiation emission) violates energy conservation? Bm gub (talk) 14:29, 10 March 2008 (UTC)

[edit] Virtual particles again

I've moved the following comment by Kokot.kokotisko (talk • contribs) here:

Actually, John Baez said that the above explanation is not even simplified, but outright flawed and misleading, but I personally cannot judge it.

--Christopher Thomas 20:36, 25 April 2006 (UTC)

[edit] Opening phrase

The phrase "in physics" seems to be me to overly colloquial. If it is correct to introduce the Hawking radiation topic with "in physics", then it would be conceivable that articles on just about everything should start with "in <something>". I would prefer to see that phrase removed. Peashy 09:23, 5 December 2006 (UTC)

[edit] Power source for an "advanced" civilization

It occurs to me that this could be a power source for a not too advanced civilization. The main drawback is a small black hole would be enormously dangerous. There a re a couple of easy way to make a small black hole, in theory. A quantum black hole may be spontaneously created in a high energy supercollider (like CERN) or it may be possible to collapse enough matter in a bose einstein condensate. Anyway it should be theoretically possible to MAKE a very small black hole, and then feed it with raw matter before it evaporates so that it grows to a size with manageable characteristics.

Using the link to the hawking radiation calculator, a black hole with mass 80 million metric tons would radiate about 50,000 megawatts. Thats a bunch of power, enough to power a medium to large city. Unfortunately the block hole might swallow the earth if you lost control of it, but if you put one in safely in solar orbit (where it could not possibly fall in to the earth or the sun) You would have a handy source of abundant power in space.

You would not even need exotic materials to extract the power, a plain old steam turbine generator, like any jumbo sized municipal power plant would have, could easily handle this much power. Either create a large hollow spherical metal water cooled jacket around the black hole, with sufficient size, or a free floating tank which you could park near the black hole to generate power, and move it away if you had to do maintenance or something.

Just a thought —The preceding unsigned comment was added by Rich.lewis (talk • contribs) 23:27, 12 January 2007 (UTC).

[edit] Can some knowledgeable person fix this please?

"Loop quantum gravity has made a detailed studies of the quantum geometry of black hole horizon." I could make it grammatically correct, but I'm not sure exactly what is intended.

Thanks. Xarqi 03:46, 18 May 2007 (UTC) xarqi

[edit] Power-lifetime discrepancy

According to the article,

P=\hbar\,c^6/15360G^2M^2

As power is energy per time, and the total energy of the black hole is Mc2,

Mc^2/t_{\operatorname{ev}} = \hbar\,c^6/15360G^2M^2

Dividing this by Mc2 and inverting this gives:

t_{\operatorname{ev}} = 15360G^2M^3/\hbar\,c^4

Why is this three times greater than it should be?

Because you haven't considered that the power production rate increases as the mass decreases.

Instead, we get

dM/dt = \hbar\,c^4/15360G^2M^2

dM/dt M^2 = \hbar\,c^4/15360G^2

d(M^3)/dt / 3 = \hbar\,c^4/15360G^2

d(M^3)/dt = \hbar\,c^4/5120G^2

as expected. Ben Standeven 01:51, 26 July 2007 (UTC)


[edit] Thermal?

As I understand this hawking radiation is pair particle production where one particle escapes and the other is sucked into the black hole. Two Questions:

  • Why is this called a thermal process in the top half of the article? Is heat actually involved or just similar statistical mechanics to thermal systems?
  • Is there some mechanism by which the particle falling in must have negative energy or is it more of a "We have to conserve energy and there would be energy coming out so the total left in there must drop" Sort of an idea

Also are there any observations of this?

Thanks

CaptinJohn 15:17, 11 September 2007 (UTC)

  • Given the context, I assume 'thermal' means 'following a Planck distribution'.
  • I don't know - wouldn't that violate causality? To have the black hole 'pick' which particle to choose so's it won't break a physical law in the future... On the other hand, it's past midnight and I'm tired. I would also like to hear an answer to your second question. 79.74.220.35 (talk) 00:29, 11 April 2008 (UTC)

[edit] Problems with the theory

The "Problems with the theory" section doesn't really talk about problems at all, i.e., not problems that weren't addressed decades ago --Lionelbrits 03:46, 30 September 2007 (UTC)

I'm not sure that the problems with HR have been resolved to everyone's satisfaction. If you have a definitive source on it please do cite it. Or do you mean that we should be talking about the information paradox of black hole evaporation here instead? --Michael C. Price talk 05:55, 30 September 2007 (UTC)

[edit] Non-electromagnetic contribution

P={\hbar\,c^6\over15360\,\pi\,G^2M^2}

This is only the electromagnetic contribution to the Hawking radiation. Black holes will also radiate neutrinos, axions, gravitons, etc. etc. Count Iblis 22:37, 14 October 2007 (UTC)

True, but the EM contribution is (overwhelmingly) dominant, just as it is for black body radiation generally. --Michael C. Price talk 23:24, 14 October 2007 (UTC)
I don't see how that can be the case for massless or almost massless particles. E.g., normal "black bodies" are transparant to neutrinos, but black holes are not. If you have a hypothetical black body that would absorb incident neutrinos, then it would emit neutrinos according to the Fermi-Dirac distribution at chemical potential zero. Count Iblis 00:20, 15 October 2007 (UTC)
Could be. Would also apply to gravitons. Presumably by the equipartition of energy the formula would be modified by the multiplication by a factor n = number of massless particle species, where the photon currently contributes 2 (due to polarisation). Someone must have published on this. --Michael C. Price talk 09:31, 15 October 2007 (UTC)

[edit] I think this section should be expanded.

I'm essentially a laymen (highschool physics and one university level physics paper). I think this article is pretty good on the whole, but what I feel is a very important sentence evades my understanding: "A more precise, but still much simplified view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle which fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole)." Why would the antiparticle have to fall into the black hole? That way, the black hole looses energy and the rest of the universe gains it. The alternative, with the particle falling in, and the antiparticle being emitted, the black hole gains energy and the rest of the universe looses it. Both ways, conservation of energy seems happy. As I say, maybe a bit more explanation would be in order? Bilz0r 22:29, 2 December 2007 (UTC)


[edit] Inconsistency

The cited source for the phrase "In even more speculative extensions [4], these black holes would not evaporate and might be dangerous." directly contradicts the assertion of danger. As quoted from the source, "However, even if the ball of plasma is a black hole, it is not thought to pose a threat. At these energies and distances, gravity is not the dominant force in a black hole." Either provide a source that indicates danger or remove the false assertion. 68.230.161.164 (talk) 05:55, 26 January 2008 (UTC)

    • I don't believe that it refers to the "black hole" like object created at RHIC, which is not a gravitational micro black hole. Instead, that phrase "in even more speculative ..." refers to true micro black holes. This is not an inconsistency. —Preceding unsigned comment added by 4.248.4.76 (talk) 18:26, 28 January 2008 (UTC)

[edit] new section: problems with theory. let us try to do among all of us a proper one

Rewrritten and readdressed all the doubts of likebox with quotes of hawkings on the arrows of time, which seems to be what likebox don’t understand. I recognize I have a short fuse bt likebox is not qualified to erase this article, he is not even an expert in relativity. And certainly it is not qualified to call names anyone. So let us return to a civilized way and try to agree in a non-biased article that shows the many possible errors of this theory given its importance for the future of mankind 76.89.246.73 (talk) 21:56, 1 February 2008 (UTC) This guy erased the entire section without comments 5 days after it was accepted by the rest... again i believe wikipedia should restrict people that vandalize many hours of hard work... Probably a change of 'policies' like the need of '2' people wanted to erase, before it comes to an effect. This is what the guy says in his talk: I am Count Iblis. My mission on this planet is to enlighten the primitive creatures living on this planet (a.k.a. humans) with my infinite knowledge. I also post regularly on my blog. No need to coment further... Please do not vandalize Count Iblis... (apart from that thanks all of you Likebox, Price, etc. for accepting the need to an Einsteinian perspective to Hawking work in this section… we will discover the meaning of it all, whoever is right, but with sound physics and hopefully not risk to mankind… just a bit of patience is what we need and less people self-assured of their infinite knowledge! )… —Preceding unsigned comment added by 76.89.246.73 (talk) 23:03, 5 February 2008 (UTC)

Reposted and added coda, defining in strict terms what is this theory relevant for... If thermodynamics of black holes is proved experimentally then quantum gravity is possible if not then both arrows, as i believe, are independent and the Universe is a fractal of multiple branes. Obviously the students who edit this section ignore the present state of physics and the on going debate in those terms, as they seem to be fans of old XIX c. theories.

[edit] Fantaphysics

I have deleted this entire section from this talk page as it was virtually all totally gibberish that was in no way related to improving the article. It seems we have a lunatic in our midst who thinks it suitable to vandalize Wikipedia talk pages with their warped ideas of reality. Please find something more constructive to do with your time. Dazza79 (talk) 13:08, 3 March 2008 (UTC)

Agreed. --Michael C. Price talk 13:40, 6 March 2008 (UTC)

[edit] differences between evaporation and radiation, between real scientists and oportunists

I took the liberty of deleting this post as it was long, rambling on about nothing related to the article and sounded like the musings of an idiot. This talk page is supposed to be related to improving the article, not spouting gibberish Dazza79 (talk) 15:24, 3 March 2008 (UTC)

Well, that was certainly a long and interesting post. I did manage to read all of it, and I agree that much of what is presented as physics these days is a mess of disjointed theories. If 76.89.242.7|76.89.242.7 would provide citations, and his criticism in shorter form, I'm sure that he'd have a post on the article page that would not be deleted. It appears that his work is not really OR, but unfortunately to us less informed, we need those citations. I've read many criticisms of Wikipedia, and the most frequently noted is that there are too many requests for citations [i.e. the poster seems to think it's obvious and common knowledge; the challenger is ignorant of those facts], and that when someone posts that 2 + 2 = 4, some challenger comes along and requires a citation [sorry if you don't like my exaggeration example].

I've recently read that CERN is now trying to prove Hawking radiation by using a neutron star analogy, that if cosmic ray produced MBH's did not evaporate by Hawking radiation, then we'd not have neutron stars. What does not make sense is how they treat neutron stars any differently than regular stars for the passage of a relativisitic MBH. They both have roughly the same number of nucleons [actually, the neutron star has somewhat fewer than its original parent star], and an MBH transiting the diameter of either a neutron star or a regular star would pass by the same number of nucleons [since the 'diameter' of such MBH is way smaller than the 'diameter' of the nucleon]. The person making the argument [Mangano, I believe] did also equate near-relativisitc MBHs as being neutrino like, and since neutrinos pass easily through a star, why not a near relativstic MBH also passing easily through a star? I don't see that that argument in any way proves that Hawking radiation must therefore exist to evaporate MBHs created by near-relativistic cosmic rays to keep the MBHs they form from eating stars. Oldnoah (talk) 20:04, 20 February 2008 (UTC)Oldnoah

You are mistaken. Neutron stars have a radii 10^5 times smaller than (say) the Sun. Therefore the density is 10^15 times higher, and the quantity relevant to particle stopping (path length x density) is 10^10 times higher. Bm gub (talk) 05:32, 22 February 2008 (UTC)

I agree with your density calculation. However, you missed the point. If you start out with, say, a star like our sun, and then shrink it down in size so it is pure neutrons [protons and electrons combined so there is no longer coulombic repulsion], the total number of nucleons remains the same [and protons and neutrons are of about the same 'diameter' too]. Thus, taking an infinitely tiny diameter line [i.e. a true line, and not a rope with a diameter to it] across the diameter of the [spherical] star [whether neutron star or Hydrogen star], that line would intersect just as many nucleons in a neutron star, as it would in the parent Hydrogen star, as the nucleons do have a finite diameter to them. While the diameter of the MBH is not infinitely tiny, it's close -- i.e. it is much smaller than the diameter of the nucleons. Thus, as it transits a neutron star, or a regular star, it will pass by the same number of nucleons, and those are the only ones it would be capable of interacting with - if they happened to be in the "exact path" [read, have the proper cross-section for interaction]. These would be few and far between for a very neutrino-like MBH.

As an added note, the cross-section for interaction would likely increase greatly at slower speed for an MBH, just as it does for neutrons [by many many orders of magnitude - why don't you read up on thermal vs. fast neutron cross-section interactions - and keep in mind they are not actually tiny marbles, but mathematical probabilities of interaction] as they pass by the nuclei of atoms [whether for fission, or elastic collision, etc.]. Oldnoah (talk) 19:14, 22 February 2008 (UTC)Oldnoah

As a further clarification, the reason the typical density stopping formula doesn't work is because of the tiny size of the MBH being much smaller than that of a single nucleon. If it were much greater than the diameter of the nucleons, then you'd have those other two spatial dimensions at play [x & y, as the MBH travels along the Z dimension], and the formula would be the correct one to use. Oldnoah (talk) 17:46, 23 February 2008 (UTC)Oldnoah

Sorry, your reasoning is incorrect, whether you treat it geometrically or quantum-mechanically. A geometrical line passing through a collection of spheres will intersect (# spheres per unit volume) x (length of line) x (cross-section area of single sphere) which scales as I said. The quantum treatment, with (as you say) is an interaction probability, scales exactly the same way: total interaction probability is proportional to density x path length x cross section---indeed, that's why use the term "cross sections". This is a standard, well-known calculation; it's one of the first things you would learn in an undergrad particle physics class; look up Perkins or Griffiths intro particle textbooks if you need a reference. It's true for baseballs, neutrons, gammas, muons, neutrinos, etc.. The only limit in which this breaks down is that, obviously, the interaction probability can't exceed 1.0 even if the cross section is huge.
The statement that the "cross section would increase ... as it does for neutrons" is a false generalization; you have presumably read that, e.g., 3He, or 10B, or 235U neutron absorbtion cross sections increase at low energies, but this behavior is particular to neutrons and to certain nuclei; many, many other cross sections increase (including some neutron-nucleus interactions, all neutrino interactions, etc.) at high energy. Bm gub (talk) 03:28, 24 February 2008 (UTC)

Sorry, your reasoning is incorrect.

First, the statement that the "cross section would increase ... as it does for neutrons" is a generalization, that is true, but neither you nor I know whether the statement is true or false. It is true for neutrons in many circumstances. It might well be true for MBHs, which was the point I was trying to make. We don't know. We learned about neutrons from empirical evidence, and we'd have to do the same for MBHs I would imagine.

If that's the point you were trying to make, why did you say the cross section "would probably increase just as it does for neutrons"? Bm gub (talk) 06:48, 24 February 2008 (UTC)

Second, why don't you imagine two spheres filled with equal numbers of large marbles. In the much larger sphere, the marbles are separated by great distance many orders of magnitude greater than the diameter of the marble. In the much smaller sphere, the marbles are all touching each other. The smaller sphere has a much greater density of marbles than does the larger sphere. Now, shoot a BB of great penetrating power [that doesn't stop but passes through each marble] through the diameter of the spheres. The BB would intersect a certain number of marbles in the larger sphere. It would intersect the same number of marbles in the smaller sphere, only encountering them sooner. The marbles across the diameter have all come closer together in the smaller sphere, but there aren't more of them along the diameter line. The rest of the marbles have all moved closer to that central line of marbles to the point of touching them, but the BB never passes through them or comes close to touching them. That is the scenario for a MBH passing through either a regular star or a neutron star.

Now substitute a bowling ball for the BB. Now the bowling ball will hit far more marbles as it plows across the diameter of the smaller sphere. Clearly, the diameter of the particle traversing the two spheres is a factor which Mangano has ignored. Oldnoah (talk) 04:20, 24 February 2008 (UTC)Oldnoah

Oldnoah, please simply try out the geometry in 2D---put 100 pennies randomly on a 12" circle on a table, then draw a line across them and see how many are encountered. Repeat for 100 pennies on a 24" circle. The number of encounters is twice as high in the denser disk: events = cross-section * density * length (in 2D, with pennies on a table, it's not 3D density but areal density, thus the factor of density^1 here rather than density^2 as the 3D case.) The increase in event rate (effectively) comes from targets crowding in from the side, if you want to think of it that way. Seriously, every physicist does this calculation 5 times a day; we teach it to undergrads, we put in on tests for incoming grad students; your line of reasoning is a common mistake which would get you marked down. If you require a WP reference, go to Nuclear_cross_section Bm gub (talk) 06:48, 24 February 2008 (UTC)

OK, I was examining the fact that the area of the neutron star is also reduced by a factor of E10 [making them a tiny target compared to a normal star, which is not the correct way to look at it, since the presumption is apparently that the MBH would be created at the surface of the neutron star]. While such neutron star would be an even smaller target than earth [by about roughly E6 smaller, I believe], it would present a much larger cross-section for capture by about E10, once created at the surface, compared to the normal star. That's why we have these discussion pages, to cover such musings, before posting to the article page. These might well serve as a "trap" for MBHs if they are created at a neutron star surface, leaving no old neutron stars if enough MBHs are created over time and trapped. We would thus have to examine the flux of MBHs being created by such a small target, the abundance of neutron stars and their ages, etc. I presume that is what Mangano is doing, though I have not seen his work. This might possibly be the proof that CERN has been lacking all these years. Oldnoah (talk) 20:33, 25 February 2008 (UTC)Oldnoah

[edit] Semi-protection

I have requested semi-protection for the article, since this is getting quite silly. --Michael C. Price talk 17:52, 11 March 2008 (UTC)

The article has now been semi-protected. --Michael C. Price talk 17:58, 11 March 2008 (UTC)
Please semi-protect the talk page too.Likebox (talk) 19:50, 13 March 2008 (UTC)
I 2nd that. --Michael C. Price talk 22:52, 13 March 2008 (UTC)
I also agree Count Iblis (talk) 00:33, 14 March 2008 (UTC)
I have placed a request here. Add to it as necessary. --Michael C. Price talk 01:04, 14 March 2008 (UTC)
Thanks!, I'll add my comments there. Count Iblis (talk) 01:29, 14 March 2008 (UTC)

CENSORSHIP NOT ORIGIANL RESEARCH he, michael this is whatever less silly, now you will tell me that the 'reductio ad absurdum', a logic prove with 2400 years of tradition is Original research... and Einstein's analysis of particles and antiparticles as a simultaneous, present event is origianl research? and I am wilcezk? iT IS obvious taht this is censorship and you just did what obviously people do in your position,censor, and protect your FAITH. Pathetic. Already socrates explained that EVIL=anti-LIVE behavior is synonimous of stupidty, which is what is going on here. Stupidity of people who cannot see the obvious contradictions of Mr. hawking's arguments, eviL=anti-Live people who censor facts that can provoke the biggest genocide of life on Earth . Funny thing is that as Kurosawa put it, 'the bad sleep well'. I have offered you to give you my credentials inprivate to rpove this is not OR, you rejected the offer, and INSTEAD YOU WENT IN THE BACK THROUGH ADIMINISTRATION WITHOUT EPXLAINING OUR DISPUTE AND ASKED FOR CENSORSHIP. I ASK THE REVERSION OF THIS by any common editor with common sense, and the opposite nature, INTELLIGENCE to see hawking contraictions and LIVE feelings, the opposite of eVIL, the true antiparticle that hawking represents. . —Preceding unsigned comment added by 76.89.246.73 (talk) 22:29, 12 March 2008 (UTC)

I have not censored anyone -- all I have done is prevent you using the cloak of anonymity to push non-consensual changes onto an article in violation of Wikipedia policy, and in particular in violation of WP:OR. Something which has been explained to you by many editors many times. As for your inappropriate use of the caps key and general ranting, I suggest you score yourself on the crackpot index and see how highly you rate. --Michael C. Price talk 23:02, 12 March 2008 (UTC)
Wikipedia does not care whether you are a "leading time theorists". If you are, and your ideas are notable, then where have they appeared in peer-reviewed journals? We will not permit you to add "A reductio ad absurdium disproves Hawking radiation" to this article until you can cite a notable article in a reliable source which clearly states "a reductio ad absurdium disproves Hawking radiation". This is not censorship, this is how Wikipedia works; it's a tertiary source. If you have a new or novel logical/mathematical/etc. discovery about Hawking radiation, no matter how obvious you think it is, it belongs in a primary source like Physical Review Letters, not here. Bm gub (talk) 22:48, 12 March 2008 (UTC)

[edit] Black Holes and Baby Universes

I have moved the following two paragraphs from the article, as I think they are not anything like the the common wisdom among physicists, and need to be discussed. Although I see some links to other articles within the paragraph, can you provide references to verifiable, primary research articles, published in refereed papers like Phys.Rev or other mainline journals? Here is the text removed:

As a black hole gives off particles and radiation, it will lose mass. This will cause the black hole to get smaller and to send out particles more rapidly. Eventually, it will get down to zero mass and will disappear completely. What will happen then to the objects, including possibly spaceships, that have fallen into the black hole? The answer is that they will go off into a little baby universe of their own. A small, self-contained universe branches off from our region of the universe. This baby universe may join on again to our region of space-time. If it does, it would appear to us to be another black hole that formed and then evaporated. Particles that fell into one black hole would appear as particles emitted by the other black hole, and vice versa. This sounds like just what is required to allow space travel through black holes.
You just steer your spaceship into a suitable black hole. It had better be a pretty big one, though, or the gravitational forces will tear you into spaghetti before you get inside. You would then hope to reappear out of some other hole, though you wouldn't be able to choose where.

I think the first three sentences are OK, and the question raised in the forth. After that, I get a queasy feeling, starting with "The answer is...." This stuff has been mentioned as a possibility, but I believe it is highly controversial at present. If it is, then text for the article would have to be qualified to reflect that uncertainty. (Kip Thorne's book, Black Holes and Time Warps might be a good place to start looking. But make sure you find unequivocal support for your statements above, not just a "maybe".) You also might consider whether this really has anything to do with Hawking radiation -- maybe it would better go in the article on Black holes, or some other place more directly concerned with the spacetime interior to the event horizon.

Thanks, hope you can substantiate it! Best, Wwheaton (talk) 06:58, 14 March 2008 (UTC)

Bill: I read your home page. You appear to have a credible background in physics/Spitzer-astronomy. Can you detail why you believe that a Baby Universe would not form, and what the "controversy" is you reference? Oldnoah (talk) 18:23, 14 March 2008 (UTC)Oldnoah

Hi! Sorry to say I don't have a really firm opinion myself, being more of a spectator on these arcane subjects, but I am essentially certain the matter has been very controversial. The spacetime geometry inside the event horizon of a static BH does seem to have paths that connect to other asymptotically flat spacetimes -- I think that much is more or less agreed -- but I believe it remains disputed whether real photons, matter, or information can pass through them. At the moment (based on User:MichaelCPrice's arguments yesterday in the BH talk page) I am actually in doubt at the moment as to whether static BHs even exist (though I gather from the New Scientist article Price cites that 't Hooft does not buy it), and also I do not see much connection between Hawking radiation and the existence (or not) of other universes, the former seeming to be a matter of the spacetime geometry near the event horizon, the latter of the interior geometry in the neighborhood of the singularity.
Anyhow, the issue is really the Wiki process, not the physics. If a fact is challenged on the main article page, it has to be verified by reliable sources (external to Wikpedia), or it is liable to be reverted. In case of dispute, consensus of the editors (generally those involved on the talk page) is usually the guide. You might look at the Five pillars, especially the material on WP:NPOV about verifiability, sources, and original research.
Anyhow, the bottom line is that the burden of proof is on you if a point is challenged. It is a hard and horrible truth, but apparently necessary to the integrity of the project. I've learned this the hard way myself, alas, and have needed lots of hand-holding. So -- good luck! Bill Wwheaton (talk) 19:18, 14 March 2008 (UTC)

Does that mean that Hawking Radiation is also controversial? Or is it not controversial, just the follow-through leading to Baby Universes? Oldnoah (talk) 22:54, 14 March 2008 (UTC)Oldnoah

I think is is generally accepted, but not confirmed, and some people still have serious doubts. When and if confirmation comes, Hawking will probably get a Nobel [wild speculation, disregard at will...] if he lives long enough. But I do not see a strong connection between Hawking radiation and baby universes; maybe you could enlighten me about that. Why is it you see the one leads to the other? Thanks -- Wwheaton (talk) 01:10, 15 March 2008 (UTC)


Bill:

It just seems strange that most everyone jumps on board the Hawking bandwagon, and claims what a great mind he has [while feeling sorry for his physical condition], when a few of us question whether Hawking radiation is actually something that can exist. Einstein believed that black holes were black, not "hot" and evaporative, and that they only absorbed matter, never emitting matter/energy. Hawking said to look in the Galactic Halo for Hawking Radiation from evaporating primordial black holes. We looked, and saw no signature. We'll look again in May, 2008 when we launch the GLAST satellite.

For example, the information I posted on the Article page on "Baby Universes" was a direct quote from Steven Hawking's 1993 book entitled "Black Holes and Baby Universes", Bantam Books, page 121.

I agree, it is silly, but it is what Hawking himself wrote. Yet apparently when it is not recognized as Hawking's own work, it is denounced for being silly or "controversial".

So the real question is: Is it safe to make black holes on Earth if Hawking radiation isn't real?

Regards, Oldnoah (talk) 02:25, 15 March 2008 (UTC)Oldnoah

Noah,
I have read only a little of Hawking's stuff (skimmed A Brief History of Time, too easy; tried The Large Scale Structure of Spacetime, too hard...), but I think that his accomplishments are sufficiently substantial that if he said it, it probably passes the notability test for mention on the main page, with suitable weasel words, maybe, to give due notice about the unsettled state of the understanding of the community. In defense of the Wiki project, we just have to be very careful not to put anything, on the main page for an article, that is clearly wrong; or borderline without appropriate qualification. Other editors might want to weigh in on all this, as I am really not qualified to judge.
Re the LHC, which I guess may be the elephant in the talk page, I know little, but naively suppose the cosmic-ray argument is pretty strong. If not, by Feynmans's old deep inelastic scattering argument, I envisage a 7 TeV proton to be longitudinally compressed by a relativistic factor of ~7000, so that the three quarks are in a flat pancake. Thus the interaction should be essentially pure quark-quark I guess, and I do not see that making a BH. If a BH were made and it did not evaporate immediately, I suppose it would go right through the Earth (v > 12 km/s), or else be captured into an orbit inside. Then in the absence of Hawking radiation it would slowly grow. How fast? Its initial mass could not be greater than about 14 TeV, right? That corresponds to way less than a Planck length, and a gravitational capture cross section of << 10-65 cm2, no? So it should grow very very slowly. At some later point the Eddington limit should inhibit its growth rate.
But obviously I don't really know, and these are just cheap shots. Yet personally I trust that very good people, with small children of their own, have thought about these issues, and found them to be negligible compared to the other risks our planet, and our species, face every day; which are considerable. But neither would I bet everything on the certainty of Hawking radiation alone.
Best regards, Bill Wwheaton (talk) 03:57, 15 March 2008 (UTC)

Thanks for the thoughtful reply. I agree pretty much with everything you wrote. Essentially, it becomes an ethics questions, since we don't have the knowledge of physics required to answer the question whether or not Hawking radiation is real. Certainly if a mini black hole could be created [which has been suggested by several theorists, and even propagandized by CERN as something they'd welcome], and clearly that is not certain [and many suggest, as apparently do you, as highly doubtful], then we should want to be certain that it does evaporate. I don't see how we can at this point. I agree too, that it would likely grow slowly initially, and indeed, it might grow so slowly to never be a problem. Again, I believe we don't have enough information to make a meaningful conclusion. Your argument which I quote ["Yet personally I trust that very good people, with small children of their own, have thought about these issues, and found them to be negligible compared to the other risks our planet, and our species, face every day; which are considerable."] is not sound, though it may be true. The Challenger astronauts, and the people who decided to "go for launch" on that fateful cold wintry morning, had small children, and had the best of intentions for mankind, and were well aware of the other risks facing humanity. That didn't stop them from making the wrong decision. Here the situation is amplified somewhat, as our spaceship Earth carries a passenger manifest of some 7 Billion people, not merely 7 people as for the Challenger. Regards, Oldnoah (talk) 18:37, 15 March 2008 (UTC)Oldnoah

And I in turn have to agree with your point about the Challenger accident, and similar situations. Best, Bill Wwheaton (talk) 19:43, 15 March 2008 (UTC)

Noah, based on your citation above, of Steven Hawking's 1993 book entitled "Black Holes and Baby Universes", Bantam Books, page 121, I withdraw my concern about including it in some way in the article. I think the reality of Hawking radiation is less in doubt than the existence (meaning and nature, really) of baby universes, and I still (personally) do not understand how the former necessarily implies the latter, or that the latter are even very relevant to the subject of this article. So I think you might want to move it to the Black holes article if that seems appropriate. Anyhow, I have removed my "unreferencedsection" template above.

Re. the LHC, I think the LHC safety worries reference this Hawking radiation issue, but the LHC has nothing important to say in reverse about HR. Just as a visceral reaction, predicting my personal surprise level, I would give the HR better than 90% chance of being correct, but probably less than 99.9%, with 1% (of being wrong) as my best shot. (Wouldn't even want to guess about baby universes.) As I said above, I would not risk the planet (nor would anyone, I suppose) on that kind of odds alone, but the cosmic-ray and BH growth time scale arguments both seem much more secure, assuming more careful calculations have backed up my top-of-the-head guesses above. That is where I would expect the CERN reviewers to have done it carefully, or else be real scared for themselves and their families. Best, Bill Wwheaton (talk) 18:36, 16 March 2008 (UTC)

[edit] Detailed balance argument: What about scattering of long wavelength photons?

Just a note: I have been a little puzzled by this discussion, not being clear where it originated or the question that started it. I think it connects to the "differences between evaporation and radiation, between real scientists and oportunists" section that apparently originated in or before Feb 2008, but was clearly cut way back when extraneous material was removed. Anyhow, am I right that it goes back to the discussion of the MBH/Neutron star interaction probability? If not, if someone could replace this with the right link to the earlier discussion I'd appreciate it. Thanks -- Wwheaton (talk) 18:09, 21 March 2008 (UTC)

No, this discussion is unrelated to any of the deleted stuff. Bm gub (talk) 18:37, 21 March 2008 (UTC)

Surely photons with a wavelength much longer than the Schwarzschild radius will have a large probability of being scattered compared to being absorbed by the black hole? Count Iblis (talk) 15:48, 14 March 2008 (UTC)

Sounds reasonable, but would we be able to distinguish them from the background or from the Hawking radiation from the BH, since they would have an awfully low temperature?--Michael C. Price talk 22:26, 14 March 2008 (UTC)
My point was actually the following (should have explained it better): We consider a BH inside a big box filled with thermal radiation and assume that the system is in equilibrium. The BH then must absorb as much radiation as it emits and, assuming detailed balance, this is the case at each frequency.
If photons with a wavelength much larger than the BH radius have a relatively large probability of being scattered (you would expect this on general physical grounds), then the thermal radiation emitted by a BH should start to deviate from the ideal Planck curve at wavelengths much larger than the BH radius.
Now, if I'm not mistaken, the typical wavelength of Hawking Radiation is of the order of the BH radius, so it seems to me that this effect is not extremely small... Count Iblis (talk) 02:33, 15 March 2008 (UTC)
Would not that argument apply to any black body (and not just black holes) in a thermal bath? --Michael C. Price talk 20:55, 15 March 2008 (UTC)
Yes, it is well known that small dust grains will radiate less at wavelengths larger than their dimension, simply because they are not black bodies at such large wavelengths. Count Iblis (talk) 22:09, 15 March 2008 (UTC)
Then perhaps this is the answer -- the small grains / black holes radiate less at large wavelengths and, by detailed balancing, they absorb/scatter less as well at these wavelengths. I wasn't aware that this was a deviation from being a perfect black body; I would be surprised if this was true -- although I am often surprised!--Michael C. Price talk 23:18, 15 March 2008 (UTC)

[edit] RHIC Experiment

I contend that this line is not correct:

In well accepted physics, there is a nongravitational black hole analog whose formation and evaporation is currently observed at RHIC.

The evidence that RHIC observed a black hole is not at all certain. The article quoted as a reference to this is a BBC news article, quoting the Brown University Physicist, Horatiu Nastase, who wrote an article that is posted in the arkiv.org database ([2] and [3]). I cannot find any evidence that this work was (a) peer-reviewed, (b) referenced elsewhere, or (c) verified or confirmed by any other physicists. The only articles in arkiv.org that talk about black holes and RHIC are two from Nastase and one from elsewhere ([4]). Moreover, Nastase left Brown shortly after the publication of this article in 2005 (see his web page).

A less scientific point is this. The world of accelerator physics experiements is inhabited by hundreds of people who desperately need to publish (or perish). Papers in the field that are "well accepted" have dozens, if not hundreds, of authors. The papers referenced here are authored by him alone.

This work by Nastase is not well accepted.

Therefore, I recommend that line be removed. Simkiott (talk) 17:44, 29 March 2008 (UTC)

The existence of a QCD analogy to AdS/CFT is indeed real physics, but (IIRC) it's strictly true only in some weird QCD limit with massless quarks and an infinite number of colors, or something like that. It's a real stretch to say that a RHIC fireball "is" a black hole analogue, and this particular (uncited) article doesn't justify that stretch. In any case, why cite it at Hawking radiation rather than Black hole? I've removed the line. Bm gub (talk) 14:16, 1 April 2008 (UTC)
While I agree that this line is better off staying in Black hole, there were people challenging the reality of Hawking radiation when I originally put it in and this is the best experimental evidence. AdS/QCD is just the same narrow-resonance/QCD-string/large-N approximation that has appeared and reappeared, except that now it is a fully quantitative theory because there is a known limit in which it is exact. The main prediction is that viscosity/entropy ratio in the quark gluon plasma should match known weirdly low black-hole values, and I have heard that this is confirmed. I don't think that there is much debate about whether the fireball is a black hole analog, only on how good the analogy is.Likebox (talk) 17:59, 7 April 2008 (UTC)

[edit] Trans-Planckian problem??

Is that a problem really? If the Hawking radiation is traced back to the event horizon, it would be a problem, but as I've been related to the pair creation/separation, it won't need to happen at the event horizon, just near enough that the energy levels of the (from our POV) virtual particles are locally real. This so called problem must have been debunked decates ago! And I've even never read university physics, so any fool (me as an example) can understand it. Said: Rursus ☻ 17:19, 6 April 2008 (UTC)

The Trans-Planckian problem is a mathematical problem--- it is something that puzzles people only when doing a calculation. Why is it that an effect that does not involve the Planck-length or any microscopic wavelengths ends up talking about such small distance scales?Likebox (talk) 18:01, 7 April 2008 (UTC)

[edit] Suggestion: avoid natural units

Currently the article reads:

"The radius of a black hole is twice its mass in natural units, so the entropy of a black hole is proportional to its surface area:"

There are various sets of suggested natural units, and this statement is not true in all of them. Because of the switch to NUs, the equations following this statement are not dimensionally consistent. I would recommend removing the reference to natural units and writing the equations with the constants of proportionality present.

Ordinary Person (talk) 03:45, 28 April 2008 (UTC)

I agree. Natural units are not helpful for non-technical readers. --Michael C. Price talk 14:22, 28 April 2008 (UTC)
I also agree, we must make the article as easy to follow as is possible. The "not dimensionally consistent" thing is really an artifact of our conventions. We want to have the freedom to use three incompatible units at the same time, the price we pay for that is that 3 conversion factors pop up in our equations. The fact that these are "dimensionally incompatible" is simply because we have assigned them incompatible dimensions (for historical reasons because before relativity and QM there was no way to compare mass to length and length to time).
Unfortunately, in schools we are still taught that dimensions in physics are somehow fundamental and even many physicists think that way, sometimes leading to strange results.
Michael Duff has tried to explain what is wrong with "fundamental dimensional constants" a few times. Count Iblis (talk) 15:53, 28 April 2008 (UTC)
Great link, BTW. --Michael C. Price talk 20:39, 29 April 2008 (UTC)
I agree that it is merely a convention, but it's useful to stick to them. Ordinary Person (talk) 08:30, 29 April 2008 (UTC)
Agree, especially for the article page. I think less formal discussions on the talk page might relax that rule a bit, as equations in natural units can be a lot more transparent to understand, for me at least (and easier to write out), once you are familiar with the conventions, but this is only true for shop talk among the initiated. Shouldn't burden the innocent pedestrian with that.
Note that the lead sentence Ordinary Person quotes can be fixed simply by changing it to "The radius of a black hole is proportional to its mass, so its entropy is proportional to its surface area." This is even simpler, and sidesteps the problem. Wwheaton (talk) 14:43, 29 April 2008 (UTC)

[edit] Discussion of Large Hadron Collider risks

This subject has been knocking around several talk pages: here, LHC itself, and Black holes, in particular. I have just proposed to separate the subject into a separate article; see the Talk:Large Hadron Collider page if you are interested. I think it could help to keep some of these other articles on-topic. Cheers, Wwheaton (talk) 19:43, 4 June 2008 (UTC)