Friday, September 26, 2014

Black holes declared non-existent again.

That's me. 

The news of the day is that Laura Mersini-Houghton has presumably shown that black holes don’t exist. The headlines refer to these two papers: arXiv:1406.1525 and arXiv:1409.1837.

The first is an analytical estimate, the second a numerical study of the same idea. Before I tell you what these papers are about, a disclaimer: I know Laura; we have met at various conferences, and I’ve found her to be very pleasant company. I read her new paper some while ago and was hoping I wouldn’t have to comment on this, but my inbox is full with people asking me what this is all about. So what can I do?

In their papers, Laura Mersini-Houghton and her collaborator Harald Pfeiffer have taken into account the backreaction from the emitted Hawking radiation on the collapsing mass which is normally neglected. They claim to have shown that the mass loss is so large that black holes never form to begin with.

To make sense of this, note that black hole radiation is produced by the dynamics of the background and not by the presence of a horizon. The horizon is why the final state misses information, but the particle creation itself does not necessitate a horizon. The radiation starts before horizon formation, which means that the mass that is left to form the black hole is actually less than the mass that initially collapsed.

Physicists have studied this problem back and forth since decades, and the majority view is that this mass loss from the radiation does not prevent horizon formation. This shouldn’t be much of a surprise because the temperature of the radiation is tiny and it’s even tinier before horizon formation. You can look eg at this paper 0906.1768 and references [3-16] therein to get an impression of this discussion. Note though that this paper also mentions that it has been claimed before every now and then that the backreaction prevents horizon formation, so it’s not like everyone agrees. Then again, this could be said about pretty much every topic.

Now what one does to estimate the backreaction is to first come up with a time-dependent emission rate. This is already problematic because the normal Hawking radiation is only the late-time radiation and time-independent. What is clear however is that the temperature before horizon formation is considerably smaller than the Hawking-temperature and it drops very quickly the farther away the mass is from horizon formation. Incidentally, this drop was topic of my master’s thesis. Since it’s not thermal equilibrium one actually shouldn’t speak of a temperature. In fact the energy spectrum isn’t quite thermal, but since we’re only concerned with the overall energy the spectral distribution doesn’t matter here.

Next problem is that you will have to model some collapsing matter and take into account the backreaction during collapse. Quite often people use a collapsing shell for this (as I did in my master’s thesis). Shells however are pathological because if they are infinitely thin they must have an infinite energy-density and are by themselves already quantum gravitational objects. If the shell isn’t infinitely thin, then the width isn’t constant during collapse. So either way, it’s a mess and you best do it numerically.

What you do next is take that approximate temperature which now depends on some proper time in which the collapse proceeds. This temperature gives via Stefan-Bolzmann’s law a rate for the mass loss with time. You integrate the mass-loss over time and subtract the integral from the initial mass. Or at least that’s what I would have done. It is not what Mersini-Houghton and Pfeiffer have done though. What they seem to have done is the following.

Hawking radiation has a negative energy-component. Normally negative energies are actually anti-particles with positive energies, but not so in the black hole evaporation. The negative energy particles though only exist inside the horizon. Now in Laura’s paper, the negative energy particles exist inside the collapsing matter, but outside the horizon. Next, she doesn’t integrate the mass loss over time and subtracts this from the initial mass, but integrates the negative energies over the inside of the mass and subtracts this integral from the initial mass. At least that is my reading of Equation IV.10 in 1406.1525, and equation 11e in 1409.1837 respectively. Note that there is no time-integration in these expressions which puzzles me.

The main problem I have with this calculation is that the temperature that enters the mass-loss rate for all I can see is that of a black hole and not that of some matter which might be far from horizon crossing. In fact it looks to me like the total mass that is lost increases with increasing radius, which I think it shouldn’t. The more dispersed the mass, the smaller the gravitational tidal force, and the smaller the effect of particle production in curved backgrounds should be. This is for what the analytical estimate is concerned. In the numerical study I am not sure what is being done because I can’t find the relevant equation, which is the dependence of the luminosity on the mass and radius.

In summary, the recent papers by Mersini-Houghton and Pfeiffer contribute to a discussion that is decades old, and it is good to see the topic being taken up by the numerical power of today. I am skeptic that their treatment of the negative energy flux is consistent with the expected emission rate during collapse. Their results are surprising and in contradiction with many previously found results. It is thus too early to claim that is has been shown black holes don’t exist.

73 comments:

CapitalistImperialistPig said...

Thanks for this very clear discussion.

twofish said...

Hi, I've posted my comments on the calculation from here

http://www.quora.com/How-authentic-and-reliable-is-the-conclusion-of-Laura-Mersini-Houghton-a-physics-professor-at-UNC-who-has-proven-mathematically-that-black-hole-can-never-come-into-being-in-the-first-place

I'm quite worried about their numerics. Usually shell crossing is a very bad thing, and I'm worried that the "explosion" they see may be numerical.

The specific thing that I'm worried about is that as you get to the event horizon, time "slows down" but if you use the same numerical time steps, you run the risk that your computer program is spitting out unstable and meaningless numbers.

Also, my background is supernova physics and observationally her conclusions are clearly wrong (if the calculation were valid, we'd see large numbers of a new class of supernova). However, if it wrong in an interesting and novel way, its publishable.

I'm following this closely because I'm trying to figure out if there is any possibility that Hawking radiation would play any role in supernova and accretion disks.

Uncle Al said...
This comment has been removed by the author.
Uncle Al said...

When we see that elfin grin...it's clobbering time!

"the mass that is left to form the black hole is actually less than the mass that initially collapsed" Consider gravitational binding energy, which is negative. Neutron stars are illustrative. Earth 0.0000000319 mass-% gravitational binding energy (GBE) (iron core, graded density with depth); Sun, -0.00031 mass-% GBE versus separated mass; 1.74 solar-mass PSR J1903+0327 –15.3 mass-% GBE (AP4 model); 2.01 solar mass PSR J0348+0432 -18.7 mass-% GBE.

One then wonders whether the gravitational binding energy of a black hole is near 100% of its separated mass.

The Panda said...

Bee: When you say The radiation starts before horizon formation, which means that the mass that is left to form the black hole is actually less than the mass that initially collapsed, can you expand on that?

I always thought that the horizon is the thing that makes Hawking radiation different from Unruh radiation, so the negative energy particles get trapped inside the horizon while the positive ones escape toward infinity.

So, when a star is collapsing but the event horizon hasn't formed yet, what there is is just Unruh radiation, you don't have to worry about the negative energy particles, and the LMH paper was wrong for that reason alone.

Zephir said...

/*..Thanks for this very clear discussion...*/

Unfortunately, just the first sentence is not very clear for me?

/* black hole radiation is produced by the dynamics of the background and not by the presence of a horizon */

Which background? How? The radiation of black hole not generated by Hawking mechanism? Who invented it and where we can read about it?

hush said...

Alice,

My inbox is empty from people afraid to ask me anything ...
and even much less so about what this is all about...so what can I do?
See answer in the closure.

Best,
Bystander Bob

ps.

"I read her new paper some while ago ... - Bee"

You are not a twin...twins exchange unsolicited comments among themselves about everything
up to the point where their inbox remain empty.

Uncle Al said...

Gravitational binding energy (GBE) is important not only during black hole (BH) formation. It must leave (neutrino burst) or the BH cannot collapse. GBE also plays havoc with the black hole's "singularity." After the event horizon closes, GBE cannot be emitted, the BH cannot be more strongly bound. Rather than a point of infinite density (pick your POV), the stuff inside a BH would be an equilibrium soup kept inflated by its adiabatic temperature, yes?

Robert L. Oldershaw said...

Correct me if I am wrong, but I submit that there is ZERO observational evidence for the so-called "Hawking radiation".

This whole topic, and several related topics, are based on the assumption that this aging piece of mind-fluff is something real.

Why create elaborate castles in the air if their foundation (in this case "Hawking radiation") has no basis in reality? Should we not wait for some empirical motivation before getting all worked up over something like this?

Sabine Hossenfelder said...

Panda: I agree with your explanation, but the thing is that I don't think it matters for their calculation that there are no negative energy particles outside the horizon (there clearly shouldn't be). They could just use the positive flux and subtract it and I think this would give the same ansatz. Except of course that they don't seem to integrate over the energy lost, but rather use the stress-energy from the static situation. Best,

B.

Sabine Hossenfelder said...

Twofish:

Thanks for these comments. I haven't even thought about the numerics, I think the problem is already with the equations. But you are right of course that one should be skeptic about the stability in this situation. Best,

B.

Sabine Hossenfelder said...

Robert,

Sorry, I don't understand your problem. You need to make predictions from theory that can be observed, and that is exactly what this paper is doing. Best,

B.

Sabine Hossenfelder said...

Zephir: Why don't you try Google. You have heard of it, don't you?

Zephir said...

Your claim, your proof... The burden of proof lies with the claimant.

Sabine Hossenfelder said...

Zephir: I've tried often enough to explain physics to you to know that you will not understand my explanation and moreover refuse to look up even a very basic textbook. I have no interest in wasting more time on you than I have already done. I suggest you read up on the topic will all the amazing sources that you can find online, this should answer your question. Best,

B.

A. Mikovic said...

I would like to point out that there are integrable 2d field theory models of black hole formation and evaporation. The best known is the CGHS model, but it has a nonrealistic feature reflected in the fact that the minimal coupling of matter to gravity in 2d is conformally invariant, so that matter fields propagate freely. A spherically reduced 4d matter collapse produces a 2d model which is not integrable, since matter couples to the dilaton.

In my paper
Phys.Rev.D56:6067-6070,1997 I showed that if matter is approximated by null dust, then the corresponding 2d system is integrable, so that one can use this model to study the backreaction.

As far as the CGHS model is concerned, one can show that canonical quantization produces a unitary quantum theory which describes an evaporating 2d black hole, see Class. Quant. Grav. 13: 209-220, 1996, while the 2-loop backreaction produces an effective metric without a curvature singularity, a compact apparent horizon curve and finite emitted Hawking mass, see Nucl. Phys. B481: 719-742, 1996. These results were an inspiration for Ashtekar and Bojowald to propose a
plausible scenario of BH formation and evaporation in 4d,
which is a unitary evolution where
the matter collapses, forms a meta-stable state, and then gets released such that the curvature singularity never forms and only a compact apparent horizon surface forms, see Class. Quant. Grav. 22 (2005) 3349-3362. This is the scenario which was recently supported by Hawking.

The Panda said...

Bee: I agree that your analysis is technically correct. The paper is wrong for the reason you describe. I also think it's wrong for additional reasons, and It seems to me that there's a shortcut to the conclusion.

If you're trying the predict the motion of objects in a system -- an electron in a tube, a spaceship accelerating toward light, a ball dropping, whatever -- You wouldn't treat the Unruh effect as a back-reaction to be calculated separately and applied as a correction to the other equations describing the dynamics of the system. I don't think that would make any sense.

If someone did try to calculate a correction to the path of an object from the Unruh effect without a horizon of the objects own acceleration, we'd know the calculation is wrong if it didn't sum to zero, no?

Zephir said...

/* you will not understand my explanation */

This is just the problem, that no explanation was given by you. I just asked you for explanation of "black hole radiation (which) is produced by the dynamics of the background and not by the presence of a horizon".

On this assumption whole rest of your article is based, so it's logical, I stopped right here. If you want to surround yourself with nodding twaddlers, like L. Motl and similar trolls, it's indeed your decision and your blog.

twofish said...

Uncle Al: Rather than a point of infinite density (pick your POV), the stuff inside a BH would be an equilibrium soup kept inflated by its adiabatic temperature, yes?

No. You can show from special relativity that if you increase the energy level high enough that there is no equilibrium.

Special relavity says that nothing can travel faster than light, once the sound speed of a material starts getting close to the speed of light, there is a limit to the amount of pressure that the material can exert and the material loses resistance to collapse.

If you put in enough pressure you can't get an equilibrium situation without something traveling faster than light, which is bad.

twofish said...

Oldershaw: Correct me if I am wrong, but I submit that there is ZERO observational evidence for the so-called "Hawking radiation".

This is correct. Also there is a lot of observational evidence for black holes.

Oldershaw: This whole topic, and several related topics, are based on the assumption that this aging piece of mind-fluff is something real.

No. It's theory. The job of the theorist is to start with a model of the universe, figure out what the consequences of that model is, and then compare it with observations.

Once you have a theorist figure out that the theory says that X should happen, you can then spend the money to get the observers to see if you can see what you predict. If you don't see it, you go back to square one.

Oldershaw: Why create elaborate castles in the air if their foundation (in this case "Hawking radiation") has no basis in reality?

Because you need to give something for the observers to look for. The reason I was interested in this paper was not the "black holes don't exist" part, but because my background is supernova.

If you can create a situation in which a collapsed object can produce a non-trivial amount of Hawking radiation, this would affect how supernova behave, at that point you can tell the observers if they can see X.

Oldershaw: Should we not wait for some empirical motivation before getting all worked up over something like this?

Well, if it turns out that the theory says you should see X, and you don't see X, then there is something wrong with the theory. At that point you stare at the calculation to figure out what is broken.

Also a lot of a theorist is to understand how the math works. If you get a deeper understanding of how the pieces of a theory fit with each other, you are in a better position to compare with observation.

johnduffield said...

IMHO the problem here is the negative-energy particles. There are no such particles. They just don't exist. So Hawking radiation is suspect, so Laura's argument is suspect. See this:

"At the onset of collapse the star gradually starts producing a flux of Hawking radiation. The positive energy flux travels outwards to future infinity and an equivalent but negative energy flux travels radially inwards in the interior of the star towards the center".

There is no negative energy flux! What there is, is time dilation. But there's no mention of that in either paper. Pity.

Uncle Al: binding energy is said to be negative, but all we're really dealing with is less positive energy because of the mass deficit. When a brick falls, some of its internal kinetic energy is converted into external kinetic energy, and is later shed.

Sabine Hossenfelder said...

John,

The negative energy is an artifact of the fixed background. You can't take energy from the background because of this. This means the only way you can produce particles is if one has negative energy. Now this is not a problem if the background is a condensate, there this happens all the time, it's a 'hole'. The best is you think of it this way here too. In any case, this is not a physical particle, so don't overthink it. The particle just has a negative energy relative to plus infinity. Best,

B.

Sabine Hossenfelder said...

PS: And no, this has nothing to do with time-dilation.

Sabine Hossenfelder said...

Panda:

"If someone did try to calculate a correction to the path of an object from the Unruh effect without a horizon of the objects own acceleration, we'd know the calculation is wrong if it didn't sum to zero, no? "

Sorry, I don't understand that sentence, what doesn't sum to zero? The Unruh effect isn't really helpful here because you need some energy for the accelaration to begin with and that energy is not taken into account, even though it should be. In the gravitational case at least it's clear what causes the acceleration and where this energy comes from. Best,

B.

johnduffield said...

twofish: I recommend you look into Friedwardt Winterberg's GRBs. If you drop a 1kg brick into a black hole, the black hole mass increases by 1kg. That's if it ever gets there. The brick falls faster and faster as its internal kinetic mass-energy is converted into external kinetic energy. But the coordinate speed of light is getting lower and lower. You can't keep taking energy out of the brick's electrons etc, and they can't move faster than the local speed of light. Something's got to give. The idea is that the brick is going to turn into a burst of gamma rays, hence GRBs. Here's a copy of his 2001 paper, which IMHO has been rather overlooked and overshadowed.

Sabine Hossenfelder said...

Zephir:

The Hawking effect comes from a non-trival Bogolubiov-transformation. It's the junction condition at the surface of the collapsing matter that makes this transformation non-trivial and this junction condition is non-trivial because the collapse is time dependent. You can convince yourself easily that if you have a static situation you will not get any mixing of frequencies, and not get any particle production from an initial vacuum.

No, I did not explain this because this was not the purpose of this post. The purpose of this post was to put the new paper into context and any additional explanation would have made it less accessible. The above explanation does not explain anything if you don't know what a Bogolubiov transformation is, which I suspect you don't know, because if you knew what it is, then you wouldn't have asked. For the same reason adding this explanation would have been entirely useless.


B.

johnduffield said...

Sabine: your response noted. I've thought long and hard about this. Try writing a blog article explaining how Hawking radiation works. It demands particles popping into existence like magic, borrowed energy from inside the event horizon, negative energy particles which just don't exist, only the positive energy particles escaping, and no infinite time dilation. It's a fairy tale. One that's been around for so long that everybody thinks it's true. If you beg to differ, write the article. Or better still get together with Laura and write a paper: Hawking Radiation Does Not Exist.

Sabine Hossenfelder said...

John,

It would probably support your long and hard thinking if you would read some literature dedicated to the topic, for example Birell and Davies, QFT in Curved Space. No, Hawking radiation does not imply 'particles popping into existence like magic'. Your problem is that you believe there is only one definition of particle. It is in fact an observer-dependent concept. Besides this, the effect underlying this particle creation, and the maths involved in it, has long been known and understood and is nothing specific to black holes. Best,

B.

Robert L. Oldershaw said...

The problem, quite obviously, is related to the fact that Hawking proposed his hypothetical "Hawking radiation" decades ago. Not recently.

It seems to me that it has been treated as something real for decades and played a major role in various teacup tempests, like the recent firewall angst.

So the problem is that all this theoretical dithering is unmotivated by any empirical evidence for the hypothetical "Hawking radiation", not to mention the mythological virtual particles.

The whole physics community can ignore this problem, but only at risk to the deteriorating health of their field.

Yanick Borg said...

If it turns out that black holes do not form, then there is no hope for a big crunch scenario. To me, black holes were the best contender describing a physical system that would best export entropy (eventually reorganising the dissipated universe back into a singular absorbed whole [excuse the pun]). Saying that, perhaps Mersini-Houghton has identified an agent for an inherent instability in the formation of black holes, rather than something which couldn't eventually be overcome by such systems. I can't imagine a back reaction, not having a back reaction of it's own.

johnduffield said...

Yanick, you can forget about the big crunch. A gravitational field alters the motion of light and matter through space, it doesn't suck space in.

Sabine: with respect, Birrell and Davies got the basics wrong. The electromagnetic field, the quantum field, IS curved space. A gravitational field is inhomogeneous space, wherein motion is modelled using curved spacetime. But spacetime is an all-times mathematical model which is static. It's the block universe. There is no motion in it. Do not be limited by a forty-year old textbook, because scientific progress demonstrates where textbooks are wrong. NB: an electron is not some "observer dependent concept". Nor is the photon we used to create it in pair production.

twofish said...

> It seems to me that it has been treated as something real for decades and played a major role in various teacup tempests, like the recent firewall angst.

We can say that if GR is correct and the 2nd law of thermodynamics is right, then Hawking radiation must exist.

If in fact Hawking radiation doesn't exist, then either GR is wrong or the 2nd law of thermodynamics is wrong. Either statement would be a big deal.

> So the problem is that all this theoretical dithering is unmotivated by any empirical evidence for the hypothetical "Hawking radiation", not to mention the mythological virtual particles.

Correct. However, the theoretical dithering has to do that if Hawking radiation doesn't exist then either GR is wrong or 2nd law of thermodynamics is wrong, and you'd then have to spend the effort to show *how* they are wrong.

Assuming Hawking radiation exists is the "least weird" alternative. It doesn't conflict with any known observations, because Hawking radiation is so small.

This is why I found the paper interesting. If the paper was correct then you *should* be able to see Hawking radiation in observations. Unfortunately, it appears that the paper has serious problems.

> The whole physics community can ignore this problem, but only at risk to the deteriorating health of their field.

No one is ignoring the problem. It's just that going from theory A to observation B is hard work. Right now, we can't tell whether Hawking radiation exists or not from direct observations, nor would we be expect to do so. However, the consequences of asserting it doesn't exist are too weird.

twofish said...

10^56 ergs is *much* too much energy for a gamma ray burster. A typical GRB has about 10^51 ergs of beamed energy.

Also how do you get 50 solar masses of stuff to drop into a black hole?

Current thinking of GRB is that they are colliding neutron stars, and you can get 10^51 ergs from that without doing any GR. It turns out that for neutron stars you can do everything with Newtonian physics and the answers you get are "close enough."

Also it's a bad idea to assume new graviational theories when you don't have to. Standard GRB modelling can get you 10^51 by assuming that the energy comes from gas friction, and assuming that gases have friction removes a lot of assumptions about the theory of gravity.

twofish said...

Also the basic argument for Hawking radiation is this. Suppose you have a black hole. It absorbs everything. That corresponds to an infinitely cold object that can absorb all heat that you put into it and not radiate.

You can show that if you have an infinitely cold object that does not radiate has zero entropy. Having something that always has zero entropy is a bad thing, since you take something with positive entropy, toss it into the black hole, and entropy goes down.

All of the stuff about negative energy fields are details, important details, but the reason that people think that Hawking radiation has to exist is that if it doesn't, then the universal would allow for perpetual motion machines.

Uncle Al said...

twofish: "once the sound speed of a material starts getting close to the speed of light, there is a limit to the amount of pressure that the material can exert and the material loses resistance to collapse." I bow to the greater footnote. "8^>)

johnduffield: "binding energy is said to be negative, but all we're really dealing with is less positive energy because of the mass deficit." That is smartless. Electrons and current flow in opposite directions in a circuit, to be consistent. (Thank Ben Franklin for that.) Whether it makes any sense to you personally is irrelevant. Binding energy is negative. Make the Earth's GBE number negative as well.

hush said...

Alice,

This lounge chair laissez-faire plaudern fits the impression you described as having with Laura.

http://iai.tv/video/out-of-darkness#

Like sitting in your living room with a friend.

A trapped surface is INDISTINGUISHABLE from an event horizon of a black hole.

I need both Laura's and Alice's (your)permission to assert and propagate this take away fireplace lounge chair chat message further.

I look forward to the next fireplace lounge chair chat that gives observers the unmistakeable signature of a bounce.

Best,
Bouncing Bob

Yanick Borg said...

johnduffield

"Yanick, you can forget about the big crunch. A gravitational field alters the motion of light and matter through space, it doesn't suck space in. "

That would depend entirely on what space is. Any evidence to show that space itself just isn't energy ? It would seem pretty energetic to me, with the stress-energy tensor seeming to show as much.

Yanick Borg said...

twofish

"We can say that if GR is correct and the 2nd law of thermodynamics is right, then Hawking radiation must exist."


Since when is anything in this universe an isolated system ? The universe itself does not even appear to be isolated.

Yanick Borg said...

Everyone keeps talking about curved space as if it is actually curved, and if it is actually space.

Space is created by humans. It is a relation of points. Euclidean space, Minkowski space, Hilbert space, these are types of spaces attributed to those who created them. Their unreasonably effective success in describing the world we inhabit has limitations.

What is accurately described with spacetime curvature, is probably just a "glow" of force carriers around a gravitational body which is absorbing them. To me, this is the ontological cause for "curvature".

It seems to slip peoples minds that the universe is not innately mathematical, and that a manifold is after-all, a simple artifact of our own geometry.

The Panda said...

Bee: You may be right about that sentence. Maybe it was confusing. What do you expect? I'm a panda I don't know how to use commas.

I will try again to be clearer. Because there is a point here.

You say: I don't understand that sentence, what doesn't sum to zero? The Unruh effect isn't really helpful here because you need some energy for the accelaration to begin with and that energy is not taken into account, even though it should be.

Let me try to unpack the unfortunate sentence. I apologize that it takes me more words rather than less.

I think we agreed before that Hawking radiation is Unruh radiation in the presence a black hole's event horizon.

The LMH paper is trying to calculate the backreaction caused by Hawking radiation before the formation of the event horizon. So it is just calculating as a "backreaction" the Unruh radiation associated with the stellar matter.

That seems fundamentally wrong to me.

Imagine that you wanted to calculate the path of an electron. You take out your standard quantum mechanics toolbox and it gives you a nice prediction. Your standard quantum mechanics toolbox does not, however, take into account any backreaction from Unruh radiation as the electron accelerates one way or another.

Would you, then, to be extra-extra precise, calculate a correction for the Unruh radiation?

I think the answer is "no," because you know that you don't have to.

But you're far too important and busy to be bothered with one little electron. So you give the problem to a graduate student. He or she works very very hard. A month later he or she comes back to you with a nice report. You give it a quick skim first, and notice that one section of the report calculates an adjustment to the otherwise-predicted path of the electron to account for the Unruh effect.

Now, if the conclusion at the end of that section is *not* that the correction is *zero* -- would you (a) read the entire report in detail and spend several days evaluating the math, or (b) take out a red pencil, write a big "X" over that section, hand it back to the grad student with the message "try again, if you're this far off I'm not going to waste time reading it"?

I think the answer is (b). And I think its because we know that in the absence of a black hole's horizon, Unruh radiation has no effect on the motion of the observer. Without something to trap half of them, the particles pop in and out of existence with the ones popping one way exactly balanced by the ones popping the other way.

I hope that loose analogy makes sense. It's really the best I can do -- I am, after all, an herbivorous bear, which doesn't make any sense at all. Why bother with the claws and the muscle strength if I'm going to sit around all day eating bamboo. I'm lucky I'm not already extinct!

Am I missing something?

Thank you for taking the time.

L. Edgar Otto said...

I find myself with little to say all of a sudden.

It seems to me (Borg) not clearly a question of mathematical invention (easy to say if you have a slightly better idea or level of grounding concepts), but without them there is a mess and a matter of debate in passion to which we cannot know if we are even wrong, or for that matter sane. So why are some so passionate about beliefs?

There are distinct kinds of motion and how to observe them. As philosophy we could say that from Newton on everything is interpreted wrong (that is Aristotle's idea of perception by rays from eyes at a distance is right, or that for something to move it takes energy to move it- not just change its inertia. There is not solid idea of action and reaction fundamentally.

If in some abstract coordinate system all coordinates are changed over the dimension then the resultant motion is one linear motion - but if no coordinates are changed the result is no motion ( but math has not made this clear, as in the boost idea over 2pi and so on for binary 2 to zero equals 1 ) So what is radiating really or what is a stream of particles say gluons or gravons?
Is the Hawking and Unruh thing really the same thing? or something Between?

In terms of such physics and motions as Newton did we can extend binominal expansion to the negative case of these abstract motions. If you cannot see the subtle difference in the primitive functions then the debates here are confusing at best.

The numerics ( twofish ) are fine from the black holes do not exist proof. It is simply 3 + 1 squares of orthogonality. A way to draw orthogons, 3/4ths of them anyway and even match them to cube (3D) inversions. But this of course is only one side of the mathematical picture. Firewalls as shells or horizons seem tenable too but not part of a more fundamental picture.

It is disorienting to read some of the lesser comments here with a wider view of things. So before we continue to engage the teachers we should do a little homework, really. That is stuck in our not clearly slow minds or fast minds we have unclear anxiety and do not adapt well. Without the security of jobs enough to make a living it may appear our best scientists are evidently on the autistic spectrum. Or the homeless and poor do not exist. At least some have convinced them so.

Plato Hagel said...

Thanks Bee:)

Robert L. Oldershaw said...

The following items are discussed by various theoretical physicists as if they are real entities in the physical cosmos. Actually none have ever been directly observed and most of these ad hoc unicorns probably never will be observed because they are pure fiction.

Hawking radiation
Virtual articles
Magnetic monopoles
WIMPs
Free quarks
Confined quarks (conveniently hidden)
Sparticles
Strings/branes
Gravitational waves
Gravitons
Sterile neutrinos
Axions
Inflaton field (supposedly powers inflation)
Higgs boson (too unstable to be directly observed; must be inferred via decay products)
Higgs field
Higgs mechanism
Extra dimensions
Quintessence

“But”, you say, “these are crucial components of our standard liturgy for theoretical physics.” Exactly so! All these mythical epicycles make a mockery of science, which is based on empirical testing.

Sabine Hossenfelder said...

Whoever declared that all elements of a theory must be observable? Oh, right, Robert Oldershaw just did. You should re-read your Popper again, you got it wrong.

Amos said...

The paper discusses only collapsing stars and strong fields, and yet the stated conclusions seem to be generic, claiming to rule out the possibility of ANY black holes. I don’t see any mention of supermassive black holes, which could (in principle) form without any particularly strong curvature at any location, and could accrete arbitrarily slowly. Is the paper intended to apply to this scenario as well? It’s hard for me to imagine that building up a supermassive black hole, with arbitrarily low density, by slowly bringing one dust particle at a time into some huge region, could somehow result in the expulsion of enough mass-energy to prevent a black hole from forming... at least if the equivalence principle has any validity at all.

By the way, the paper does say that during the period when a trapped surface exists temporarily a collapsing star would appear as a black hole for all practical purposes. But this is not new. Many people have argued in the past that we can really have only things that appear to be black holes, existing for only a finite time. So, even if we focus on just collapsing stars with strong fields, the conclusions don’t seem to be new, unless the paper is claiming that the period of time when there is an apparent black hole is very brief. Does the paper bound the length of time during which the star may appear to be a black hole?

Robert L. Oldershaw said...

Obviously I am not saying that "all elements of a theory must be observable" directly.

Nice debating tactic, though.

The problem occurs when none of the elements are observable (e.g., string/brane pseudo-theories) or when many key elements of the theory are accepted on faith alone and treated as fact (e.g., most theories emanating from particle physics over the last 40 years).

See the difference? Or is it in one's personal interest to not see the difference?

L. Edgar Otto said...

Robert,

I sympathize with your views on the state of the various physics (or should we say a matter of philosophy?)

I like the old general systems idea that mathematics itself is based on faith, but unlike other faiths it can prove it is based on faith.

So in a sense these wonderful new modern theories have made the universe simpler than expected and yet much more complicated than expected. How then do you account for the universe?

The problem should be able to address some form of reasoning, perhaps in the details to clarify our assumptions as to what is physical.

For those who suggest we live in a universe that is a black hole, and there are no black holes or they cannot form- how did the universe come to exist? Have we discovered and ultimate falsification - that from this view there is no universe or at best we say it is an illusion?

How is it something falling, like water in a waterfall, it becomes hotter? Do we have a reference of something well, infinite but absolute that a moving object radiates something? I thought this is a simplistic question but have seen papers recently taking some stance on this - all such papers to explore the ways out of the paradoxes which we develop, add to and design or if fortunate verify in experiment or at least consistent predictions.

What do we really mean by negative energy of the vacuum - an arbitrary sign to fit our description?

In view of distinct types of particles, three varieties concerned with ideas of conservation and symmetry (can we say there are contained or isolated systems or not, or something in between like we only need five quarks to make a six degree freedom box (on very low complication of the idea of dimension)... the pesky last face in physical construction has to be glued or sewn together from inside (information wise of 8 hypercube cubes the outside of the seven compact is a negative to the others if they are compact or centered). So some information escapes, some path we might call "defects".
In the Archimeden project we attempt to weigh Casmir effects (a paper today) that there is lift in a cavity but this is relative to what, a flat space? that holes don't generally exist? So it is not anti-gravity as such?
While it may be a particular approach is missing some key concept (that is at some point whole dedicated projects of theory may vanish) the enterprise of basic research is not the less for the effort. While I breathe at least I have a deep faith that the universe (at least physically) makes sense and other than we should question our assumptions concluding it all wrong does not add to the needed solutions.


L. Edgar Otto said...

Robert (part2) I said too much, the final paragraphs here beyond 4096 html I post in reverse order...


It is fundamental that in this sense, in a world that seems on the whole not indifferent even if temporary, that as unique it is all our personal interest.

But this is still Philosophy I guess. For those who imagine infinite copies of ourselves, these in a sense are among others with such copies. The numbers can guide and contain our physics equations so far, but to me it is the tip of the iceberg of all these concepts of our day (in dreams what we foresee or do here can change some events it seems, a small thing with great consequences for what seems to be were we are unique and our perspective is unique and thus real as such.

Are baby inflation universes or multiverses real? If five fold symmetry comes to play in the microworld do we give up on the Tarsky paradox or find a better theoretical structure or experiment?

I mentioned the diagonals of a three D box can hold nD any length (and relativistically linked to energy) But what if the vacuum is only filled in thirds of the diagonal, generation wise? A particle as a black hole like concept changes the minimum distance and duration as measured. How much more direct is the evidence?

Yet your idea of acknowledging a wide range of general shapes, the old boxes in boxes like tablecloth fractals (complex analysis requires a little complicated analysis for it to seem to fit in to the general picture) is perhaps helpful in the abstraction- you are not in the negative view of things. What us fractal but the general idea of fractional dimensions somehow in QM to which we now make distinct models?

Robert L. Oldershaw said...

Hi Otto,

Here is my prescription: study nature assiduously, not abstract theoretical models.

L. Edgar Otto said...

Well, Robert, it is hard for me to disagree with that on the face of it so that is still the last word, plain and simple. The child in me remains like Aristotle or Darwin observing things around me as on the beach. Yet the focus, the fresh adventure, strives to think about it - some sense of unity to it all- if you mean our generation, or as we accumulate errors of thought or body I suppose we all collectively are not as adaptable in distinguishing some play game, say soldiers, and the real thing with consequences. Abstraction is lonely foresight, or some form of comfort we settle for thru the fog and mystery. We look inward so are a part of nature too.
Hawking once declared there was no God because string theory proved it. Guess he is still struggling with that "mind of God thing". Not sure why it is discussed as science- not enough data I suppose.
I saw a program on the common parakeet somewhere in native central Australia this morning, a nature show. Clouds of them form as expert fliers and it said collectively they had the ability to see 360 degrees to find resources like water.
Now the predators dive down on them until they give up for they use gravity, individually just fall down. This seems true of many birds who see in four colors (perhaps 3D is simpler for them?) The predators have to spiral down and focus forward.
Now many report out of body experiences where they see in all directions. This abstraction should ring a bell for it is the issue of how we see space as primitive motions. What else can we imagine if there are no particles as such? The parakeets are so sure of themselves between attacks sneak down and drink their fill of water individually.
Surely there is more to it than the simple question of what do we drink, the water or the wave (to ask as John Fowles did, he a Heraclitean).

But I must say your list of abstract errors was quite impressive. I hope Bee forgives my poetry here- I am more like the turtle that sees five colors content to do what turtles do safe in their shells- holding up themselves, perhaps the world all the way up and down as they say. It may not be physics that we need each other and depend so much on our thinkers- but it is a vital part of nature, no?

Plato Hagel said...

I guess Bee, one has to have an understanding of the theoretical minimum?

Best,

L. Edgar Otto said...

Plato + Hegel

The Kugel or K (sphere group) is at once the most interesting and least interesting as far as physical laws go.

Consider Plato's concept of a sphere before it is complicated by simple logic. For one thing as pairs (dialectics anyone?)

At this foundational view the lecture fails from the start to predict the past (or future) beyond the instantaneous moment so all is uncertainty and not predictable if the K principle is not a complete description physical law. QM from this view is not deterministic.

K spheres are abstractions that we can avoid or say do not exist logically from this seeming dynamic view. How far into string theory can we extend qm to gain a unity this way although a unity is there intuitively?

I distrust the log or exponential formulations as not the theoretical conceptual minimum. Is W excluded as a potential infinity or as a zero? It just gives us some arbitrary idea of time.

On the other hand Sabines exploration of superdeterminism is a higher understanding. The geometry and math also shows we need in the actual evolving end and beginning points in some expression of physical laws.

So the issue is not abstract for as a mathematical structure it is dynamic and natural (Robert) for we can describe and logically predict a state of say a biological system. If this more general view, abstract as it is is not useful- really, it allows us to see in fine detail the possible evolving of viruses of which today we see constant new threats. Now I know in our lack of deep understanding a paper says "cure for cancer or a war on cancer" But this is vaguely defined theory and plays to uncontrollable doomed scenarios to imagine threats while not knowing which are expedient or real ones.
I put a sketch (my notes somewhere are right if there are errors here somewhere) on fb status photo. All the properties of such Pascal triangles shift dynamically up and down in configurations - what do we mean by theoretical minimum in general? Even Plato imagined a subatomic theory to his simple spherical top elements.

Plato Hagel said...

Hi Edgar,

Hagel.....not Hegel:)

What I like is that Prof Susskind is speaking to problems that I see through all the conversations that have gone on and about abstract mathematics and how our own limitation provide room for a way to work for areas we do have problems with seeing. So theoretical has a defining point here.

Prof. Susskind is very methodical and overlaps right from the very beginning about dimensional attribute and leads one into the possibilities. Foundationally this a beginning. What begins becomes complex, but it follows a logic that is consistent, and he highlights the term, "updating."


Now the subject Bee is speaking too, helps to keep perspective on the information that has been talked about, or has to some degree been updated?

Best,

L. Edgar Otto said...

Plato Hagel,
I cannot say if its updated. I seemed to have passed a horizon leaving at least Hegel's reason which turns materialism on its head but I do not know when.
I cling to an idea a long time before I change it. But if there are no black holes physics seems dyslexic.
Sabine is the update. Lubos last three blog posts proves there are black holes needing updates on all counts. I mean Laura must have something for him to react with such a nasty attack. The video link shows the man a good teacher BTW.
"Come sit with me by the garden gate. There's time to visit. My work can wait."

Plato Hagel said...

Yes Edgar, Bee is the update, that is why I thanked her.

Bee:In their papers, Laura Mersini-Houghton and her collaborator Harald Pfeiffer have taken into account the backreaction from the emitted Hawking radiation on the collapsing mass which is normally neglected. They claim to have shown that the mass loss is so large that black holes never form to begin with.

Bee:Physicists have studied this problem back and forth since decades, and the majority view is that this mass loss from the radiation does not prevent horizon formation.

It was pretty clear Edgar.

Don Foster said...

On Huffington Post, along side news that butter is in fact good for you, comes word in bold headline:
"This Physicist Says She Has Proof Black Holes Simply Don't Exist"

So the pinball hits the paddle and I can see why physicists should avoid the appearance of too much early enthusiasm for their discoveries.

L. Edgar Otto said...

But is it news or new twists, wrinkles. I mean by standard particle models does the Higgs mass exists?
Of the 24 pips of backgammon where does the checker on the 25 bar go?
This unfolded cube of entangled back reactions?
In the end breaking science news has the upper hand in journalism no matter what is offered as spin.
The amazing thing is that this fact set is the very reason butter is good for you, Don.(

Neil Cornish said...

Something that I haven't seen mentioned in all the coverage of this paper is that even if the assumptions that went into the calculation are correct (I have serious doubts), the solution they come up with has absolutely no effect on astrophysical black holes. The surface of the star still reaches an enormous redshift, and the entire process takes essentially forever as seen by an outside observer (consistent with the evaporation time being much larger than the age of the Universe for any astrophysical black hole). So Cygnus X1, Sag A* and all the other black holes we have come to know and love can rest easy.

Frederic henry-couannier said...

Hello,

Something that disturbs me a bit is that i have always believed that our giant BH candidate at the center of our galaxy could not be bigger than its horizon: i believed that if it was the case people would already have observationnal evidence for that... Indeed as fas as i have understood if the theoretical result is correct, it would mean that not only there are no BH , but even more, there are no genuine BH candidates : no objects smaller than their Schwarzschild radius for instance in case of a non rotating object. (Such BH candidates would not necessarily be genuine GR BH if GR is modified or replaced by some other theory...). Is that correct or did i miss something?

johnduffield said...

Well said Neil. Remember your 156 billion light years wide and the hall-of-mirrors universe? Take a look at the HUDF, find a prominent galaxy, then look over to the left and down a bit.

Yanick, re any evidence to show that space itself just isn't energy? Not from me. At the fundamental level, I just can't separate them. There's shear stress and pressure in the stress-energy-momentum tensor, which "describes the density and flux of energy and momentum in spacetime". It's like space is this ghostly elastic jelly, and to add energy you inject more jelly in the middle. NB: a gravitational field relates to curved spacetime which relates to inhomogeneous space, not curved space.

L. Edgar Otto said...

What I find a little disturbing but inspiring is that I cannot foresee what Bee will make the topic next, a reminder that for awhile I felt I was closer to knowing everything.
I missed whatever Leibniz talk was on her schedule, but that old dude is as essential as ideas of curvature and stresses, tensors and so on. Energy as physics probing the microscale that time so focused and amplified wave like is deep focused energy thru half the time also. Anyway it was the topic of my last facebook note poem... Energy was once a poetic word.

CapitalistImperialistPig said...

Of course we have a lot of things in the universe which look like black holes, so if BH don't exist, what are they?

Sabine Hossenfelder said...

CIP:

As I explained in this earlier post, the observations are well explained by everything that behaves for a sufficiently long time like a black hole. There is nothing in this paper explaining whether this would be the case here, but it doesn't matter because the argument is wrong anyway. Best,

B.

Frederic henry-couannier said...

"What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon."

OK , but probably the fact that this apparant horizon is expected to last for such a long time that it is not possible to make the distinction with a genuine horizon, is a very peculiar feature of GR ... in any alternative theory with a behaviour of the metric field starting to depart from GR solution near the schwarzschild radius (for instance metric terms such as Exp^(2GM/r) instead of 1/(1-2GM/r) thus with no mathematical horizon), even if there is something like an apparant horizon, it might eventually be possible to detect the radiation from either an object with radius smaller than schwarzschild radius, or somewhat larger (not so huge redshift and delay of the radiation to escape the object)...right? I heared a few years ago that astrophysicist were pezzled by an apparant radiation from sagitarius A* that seemed to originate from a region smaller than the theoretical size of the black hole (according GR)...are there new more recent and accurate observations on that?

Frederic henry-couannier said...

Sorry , the neutron star stability limit would be significantly modified with an exponential metric but certainly not enough to be able to imagine that Sagittarius A^* might be a huge neutron star ... so we would have a collapsed object (much smaller than the volume delimited by the Schwarzschild horizon) but with no horizon, however even if it's not a singular at r=0 (quark star ?) the redshift and delay might be huge enough to make the object invisible: remains that gaz falling into the object would still emit detectable light from within the schwarzschild volume which is not allowed in GR...

Frederic henry-couannier said...

i was assuming spherical symmetry in my previous posts, but of course i'm aware that for the spinning black hole the radius of the GR horizon can become much smaller and even if black hole do not actualy exist (for instance if the exponential metric is the correct one) astrophysicist can always play with a free parameter, the unknown spin of the object, to reduce the GR horizon radius in order to fit observations: this is at the price of extreme spin rate , often approaching the theoretical limit as far as i have understood. But apparantly even this game would not allow to understand that Saggitarius main radiation originates from the small region they identified in http://www.nature.com/nature/journal/v455/n7209/full/nature07245.html , unless they assume that this region is a spot in the accretion disk which is for some unknown reason much brighter than the rest of the disk (ad hoc assumption of very asymetrical profile of the accretion disk radiation) which is of course much greater than the BH candidate. They said that future observations would allow to clarify this with radioastron, but i heared nothing new on the subject: i suspect that if there is a real anomaly they will try to put it under the carpet ...

schrodingasdawg said...

Perhaps you can correct me if I'm mistaken, but it appears to me that the statement of the Friedman equation in Eq. (IV.1) is wrong in the first preprint? It doesn't seem dimensionally correct either, and several of the equations that follow from it seem dimensionally wrong too. (Obviously hbar=1 in addition to c=G=1 allows you to convert any units to any units, but for the classical parts of the formula, which remain when you set Hawking radiation to zero, you should not make use of hbar=1 to convert units.)

I haven't seen anyone else say this though, and if it were the problem, I'd imagine cosmologists and physics bloggers would've jumped on it immediately.

qsa said...

This is even more exotic from the same author. Evidence for multiverse.

http://www.thesundaytimes.co.uk/sto/news/uk_news/Science/article1261602.ece


Zephir said...

/*..but the particle creation itself does not necessitate a horizon..*/

You may consider the particles as a miniature quantum gravity black holes. They're just hold together with surface tension instead of gravity, but they've still event horizon at their surface. Therefore, once such a particle appears inside of strong gravity field, its Hawking radiation will take a place there in the same way, like at the case of massive black hole. And because the elementary particles are already tiny, they will evaporate pretty fast. Such an insight essentially says, that the model of black hole evaporation will heavily depend on phenomenology used, not just on the fundamental principles. Once we omit some important mechanism, then the results of formal models will remain significantly different from physical observable reality.

In my opinion, the Mersini model is essentially relevant, but it cannot itself lead to substantial evaporation of collapsing stars. The effect of hers occurs only when the star collapses fast and the pressure of radiation will slow-down this process.

But as I explained already here, in AWT the evaporation of star particles will happen even if the star would collapse very slowly. Or when some particle will fall slowly toward it in isolated way, without collisions with another particles, which would increase their temperature. The strong gravity field will compete with forces, which are holding the composite particles together. First of all it will ripe the molecules into an atoms. Later the atoms will get decomposed into atom nuclei and electrons - just at the distance from black hole, which will correspond the diameter of white dwarfs with degenerated electrons. And even deeper the the atom nuclei will decompose into a free hadrons. Their binding energy will evaporate into outside in form of radiation with increasing energy: radio, visible and X-ray/gamma radiation.

Stephen Paul King said...

Hi Sabine,
I am curious. When you write that "black hole radiation is produced by the dynamics of the background", does this imply that virtual particle pair are influenced by gravity and thus have "real" mass. This makes no sense to me as it would imply a massive cosmological constant. What am I missing?

Sabine Hossenfelder said...

Stephen,

I'm not sure what you mean by 'real' mass and with saying that the cosmological constant is "massive". What does it mean that a constant is "massive"? Let me put it this way: virtual particles do in principle contribute to the cosmological constant, yes. They contribute way too much, that's what's known as the cosmological constant problem (or one of the problems if you want to be precise).

But that isn't what I meant here because in the case of black hole evaporation one doesn't actually take into account backreaction. What I meant is simply that virtual particle pairs do get influenced by background fields. That is, for example, the origin of the Lamb shift. Best,

B.

Phillip Helbig said...

"virtual particles do in principle contribute to the cosmological constant, yes. They contribute way too much, that's what's known as the cosmological constant problem"

Anyone even remotely interested in such topics should read what is probably both one of the most important and one of the most overlooked papers in cosmology in the last few decades.

Unknown said...

It seems to me, the author has made several wrong assumptions, which lead to the calculated outcome (predictably).
She states, that
1. “the very last photon making it to future infinity and thus contributing to Hawking radiation, is produced just before an horizon forms.”
2. “The production of fluxes switches on gradually at the onset of collapse but most of it is produced on the last stages of collapse as the radius of the star is getting close to its horizon value.”
Now comes the interesting part:
3. “the magnitude of the radiation energy density and flux, qH, in the interior is related to Hawking’s radiation luminosity at infinity via the Kodama symmetry”.
Which leads to
4. “The conservation law based on Kodama symmetry, states that the net radiation flux around an imaginary surface with radius R0 enveloping the surface of the star is equal to the net Hawking flux at future infinity…..”
Ok, so far, that seems plausible, but then she continues:
5. “….equal to the net Hawking flux at future infinity, i.e. the mass of the star.”

The Kodama symmetry gave an argument, that the net flux into infinity CANNOT be MORE than the mass of the star, but she is setting the total hawking radiation before the star crosses the Schwarzschild radius (Rs) equal to the mass of the star!

Following this logic, the total mass of the star would have been evaporated just when the mass reaches the Rs which of course it will never reach, since it will have too little mass before that. Therefore, her calculations have to lead to the conclusion, that all the mass above the critical mass will be evaporated before the star reaches the Rs!
But if the star never reaches the Rs, it will never fully evaporate (no black hole formation, and no Hawking evaporation of the black hole), so the total flux to infinity of hawking radiation cannot be equal to the mass of the star, which contradicts here earlier boundary condition assumption.

what do you experts think of that?