## Wednesday, October 20, 2004

### Comments for Peter Woit and Lee Smolin

Appendix to a discussion at Asymptotia.

Because Clifford Johnson "routinely deletes" comments by your humble correspondent (yes, primarily politics because Clifford is a secretary of the far left-wing PC police), they must be posted at a different place.

Dear Peter,

your answer to Mark Srednicki is absurd. The quark theory that Mark was writing about talks about physics at essentially the same energy scale as the effective theories with hundreds of hadrons from the first part of his story, namely hundreds of MeV. Also, the quark theory would be hard to test using the normal experiments at the QCD scale - which is essentially a low-energy scale - because one would have to calculate very complicated properties about bound states of quarks, and there are many of them etc. QCD is only easily testable at higher energies where it becomes weakly coupled.

Marks gedanken experiment was designed to be isomorphic to the situation of string theory and if there is a difference, then the difference is that the natural scale of string theory is way above the observable scale so that the gap in string theory is greater than in the nuclear story, not in the other way around as you incorrectly wrote. Every physicist who has read Marks comment knows it and understands it. The only reason why you argue that there is a significant difference between the two examples is that you dont understand how these theories actually work.

The fact that you find quantum gravity uninteresting is not surprising for me at all. At any rate, the key arguments - the mathematical robust ones - about questions such as the information loss came from string theory and everyone who was interested in these things - such as Stephen Hawking - knows this, too. Hawking admitted that the information is preserved primarily because of the AdS/CFT correspondence.

Concerning the anthropic principle, every scientist who has a sufficient talent and who has looked into it understands that there have emerged all kinds of reasons - not just pure string theory research - to think that the anthropic picture could be correct which is why this possibility must be seriously investigated, together with other possibilities. The people who are completely ignorant about everything could of course share your simple-minded and radical opinions but I think it would be a very bad idea
if the people who are ignorant were deciding about the direction of the research done by the people who are not ignorant. You are effectively confessing that your goal is to manipulate people who can be easily manipulated - because they know nothing about the current state of knowledge in high-energy physics - and use them as a political force. I think it is deeply immoral and unscientific.

Dear Clifford, your value has increased in my eyes after the individual above compared you to me!

All the best
Lubos

...

Dear Lee,
your speculations about the fate of the black hole have several serious problems.

First, they follow neither from any theory nor from any rough sketch of a theory. They dont even follow from loop quantum gravity. One cant of course answer any of these questions because LQG probably doesnt contain smooth space (or, if I am very optimistic, the existence of space cant be derived at this moment) which also implies that it cant contain (or one cant derive) objects such as black holes that require smooth space around.

So this really means that all your guesses about the fate of black holes after evaporation are completely disconnected from any conceivable fundamental theory. For example, the detail that you remove the black hole interior for simplicity is just one manifestation of the inability of LQG-like theories to predict anything. What happens with the degrees of freedom inside the black hole is exactly the type of a question that a theory of quantum gravity must be able to explain.

Second, your picture of the black hole evaporation strikingly contradicts virtually everything that has been learned and settled about the subject in the last 30 years. The most obvious is your speculation that remnants are still alive and black holes can have a much greater entropy than the BH entropy. Thats of course ridiculous. Remnants are safely falsified and the BH entropy describes the whole entropy of the object. The highly non-trivial match of the entropy of e.g. those seven-parameter families of nearly extremal black holes in various backgrounds with the microscopic model make it very clear that the BH entropy is everything there is when the object is present. There cant be any extra additional entropy inside the black hole. Another way to see it is that the interior of the black hole is, via black hole complementarity, just another copy of some degrees of freedom outside the black hole.

Also, remnants violate all entropy bounds we know as well as holography. When we have a picture where everything makes sense and can be made quantitative at an arbitrary accuracy in many seemingly inequivalent (dual) formalisms, you should understand that it is extremely hard to take seriously any comment that tries to deny virtually everything we know, especially if it offers no pair of ideas that would fit together.

The correct answer is that there are no remnants whatsoever after the black hole evaporates. As the black hole becomes very small (Planckian mass or so), it should be described as an excited type of an elementary particle (such as a highly excited string). The transition between black holes and particles is quasi-continuous. In the final stages, the black hole just becomes indistinguishable from a generic excited particle that decays into many other particles. It is very clear that this happens. In
any string theoretical vacuum, one can study these processes very explicitly, but even without string theory it is clearly the case.

If someone wants to pretend that the black hole is still there after it becomes extremely small etc., it just means that his theory (or non-theory) hasnt resolved the singularity. By definition, tiny remnants are still singular. It makes no sense and disagrees with all kinds of very different descriptions of evaporating black holes we have - including Matrix theory, AdS/CFT, weak coupling limit of black holes in perturbative string theory that transform them into D-branes, and so forth.

It is rather hard to believe that you cant understand these arguments that easily show that all your ideas about the quantum nature of black holes
are simply flawed.

Best wishes
Lubos