9 January 2013

Black hole entropy in 2013

Did you ever look at the calculation of black hole entropy with the spaghetti model?  It is on the pages 256 to 258 of the pdf on the strand/spaghetti model.  Schiller starts with a drawing of a horizon and the definition of entropy from spaghetti.  The first approximation of black hole entropy he gets is one bit per Planck area.  Then he improves the calculation, until the final approximation yields the usual formula, with the correct factor 1/4.  The calculation is simple and can can be understood by anybody who knows the definition of the number e=2.71828... No hard math is needed.  All other calculations are either complicated, like those from string theory, or need fudge factors, like those from loop quantum gravity.  So I asked a few experts for an assessment.

Male expert 1: "The assumed microscopic degrees of freedom are wrong - I tell you. I do not know the correct ones, but these are wrong.  I do not like them."

Female expert 2 and male expert 3: "The calculation is much too simple to be true. It is nonsense."

Male expert 4: "The calculation does not work for more than 3+1 dimensions,  thus it is wrong."

Expert 1 says that in quantum gravity, male authority counts more than results. Experts 2 and 3 say that personal wishes decide about true or false.  And expert 4 says that personal fantasy can be used to criticize reality.

And such reactions are typical.  Quantum gravity, a field without experiments, has become the playing ground for people that pretend to do research but in fact run in circles, without any results.  A friend told me once that quantum gravity is a field with only one important issue: "What are the microscopic degrees of freedom of space-time"?  Triggered by her remark I went through the past five years of research in arxiv/gr-qc.  I found four papers adressing the issue.  Over 99% of all researchers avoid it.

In a previous post I mentioned that almost nobody in high energy physics is actually working on a theory of everything.  Something similar holds for quantum gravity: researchers are avoiding the most important issue.  They are a group of people searching for a solution, all pointing to a specific spot, and whispering to each other: "Do not look there!  Look elsewhere!"

So, if somebody claims to have searched the forbidden spot, despite all the whispering, instead of shouting "Wrong!", we should look carefully. The question is this: "Are spaghetti the microscopic degrees of freedom of space or not?"  If they are, the calculation of black hole entropy follows.

Space made of spaghetti?  How can this crazy idea be tested?  Schiller claims that it implies the entropy of black holes, and thus indirectly, also general relativity.  He even says that quantum gravity effects cannot be detected.  This is dangerous: there are no possible gravitational tests for the spaghetti claim!

So spaghetti are similar to strings: both predict gravity (curved space) and both do not allow any gravitational tests.  Gravity experiments cannot be used to check whether space is made of strings or of spaghetti. And this holds for any other proposal of microscopic degrees of freedom. That is why quantum gravity is an ideal field for theoreticians: tests are next to impossible! But not completely: experiments in particle physics can be used to check whether any proposed microscopic degrees of freedom are correct or not. What will 2013 bring us?

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