Archive for July, 2010


There are entire libraries of coffee table conversations about the multiverse. A lot of them explore the what if and are usually fun over a couple of drinks. When its done professionally however… On second thought I think I’ll not go there this time around.

There is an online comic that is devoted entirely to the bizarre occurrences of the multiverse: it is aptly called “Scenes of a multiverse“. I recommend it highly. Usually you can expect intelligent Hamsters and evil geniuses running amok.  The one today is particularly apt if you’re up to snuff on the inner debates of academic multiverses: that it is a dream of something (aka, the simulated universe, aka The Matrix) and that there is no testable prediction, but postdictions aplenty. Or at least one.

If you’re in the mood for it, you might want to read some of the books by Michael Moorcock. They give you a different view of the multiverse.

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Predictions of the future

I remember the promises of the future: we would all have our personal jets. Cars would have glass domes. We would all have robots doing everything for us and the computers would have conversations with us. Moreover we would all be eating like astronauts: pills for breakfast lunch and dinner, with the occasional toothpaste tube full of nourishment. I also remember that all children would be born from big water tanks, they would be immune to all diseases and there would be a pill to cure cancer. We would also teleport from one place to another. We should have conquered the other planets in the solar system by 2010. Space travel would be commonplace and safe. And the year 2k bug would be the end of the world.

Here’s something to celebrate all those failed predictions:

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I recently gave an interview about my research to a newspaper run by my Alma matter mater. The article can be found here. It is in Spanish. As with most newspaper articles, very little science ends up punching through. It is extremely hard to communicate with the public without falling into my usual jargon. I learned that people like hearing about black holes, that it inspires a little fear of the unknown and that they think that the back holes just about eat everything. At least I was able to tell them that there is good evidence for  a super-massive black hole in the center of the Milky Way and that my work hopes to disentangle some of the mysteries of black holes.

Another thing that happened recently, is that a book for which I made a contribution finally got published. The book is called ” Geometric and Topological Methods for Quantum Field Theory“. The book is a set of lecture notes of a school that I attended two years ago. In my section I  try to explain some sring theory basics and the rudiments of the AdS/CFT correspondence. Unfortunately I was not allowed to post the notes in the arxiv when I asked. If your library happens to buy it you might want to give it a look.

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Not exactly physics

Professional banter is as old as professions. This is a dramatization of my idle chatter on Saturday, when I bumped into someone that does condensed matter physics for a living. Bear in mind that this was a fun conversation and we were laughing all around.

Other person: I heard you do physics.

Me: yes.

Other person: What kind of physics?

Me: I work on high energy theory, more precisely string theory and such.

Other person: Ha ha. That’s not considered to be `physics’ in my community.

Me: I’m also interested in quantum computing …

Other person: There is still hope for you.

Well, seeing how many times I’ve heard the phrase “that’s not physics” uttered in different contexts when talking about different sub-communities of physicists as relating to each other I can happily say that I don’t do physics, even  though I do.

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I happened onto an article on the New York Times abut Erik Verlinde’s take on gravity as an Entropic force. The article was written by Dennis Overbye who most of the time does  a good job of covering high energy physics.  Erik’s work dates from earlier this year and can be found here. To tell the truth, I don’t understand what he’s trying to say in that paper and to me it feels like it’s almost certainly wrong.

However, I don’t want to discuss that paper. What I want to discuss is the following  provocative quote

“We’ve known for a long time gravity doesn’t exist,” Dr. Verlinde said, “It’s time to yell it.”

I don’t believe this is taken out of context,  so we should take it at face value. The statement is obviously wrong, so it sounds like ultra-post-modern pap and makes all physicists working on the subject of quantum gravity look like crazy mad men. I’m sure this sells newspapers, but that is not the point.

When asked for a sound byte can’t people at least say something that is correct and not just provocative?

The proper way to write that statement is that “Gravity is not really a fundamental force “, which is more correct and does not deny gravity its proper place as something that has been observed in nature, however it is less catchy. If we apply the same criteria as used in the above construction, all of the following statements are also correct:

  • Hydrodynamics does not exist (it only happens for collections of atoms, but not for individual ones)
  • Space and time do not exist (often used when talking about quantum gravity being emergent from somewhere else)
  • All emergent phenomena do not exist (they are not fundamental after all).
  • I do not exist (I’m an emergent phenomenon).

Reminds me of discussions I have read before at Backreaction, here and see also  here in the Discover magazine about time not existing.

You should also read the following from Asymptotia: But is it real? and also a discussion on What is fundamental, Anyway?

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Holland 2, Brazil 1

Well done!

Holland just eliminated Brazil from the World cup by 2-1, defeating the odds.

Even though Holland played a bad first half making a huge defensive mistake to give Brazil a first goal and it looked like they were going to go down very badly, they took over in the second half and played really well. The first goal for Holland was a huge defensive mistake from Brazil.  After that Brazil lost concentration and the dutch defense was actually doing a very good job.

The second goal from Holland was a well executed play and it was an incredible double header against a taller  Brazil.

In the last few minutes Holland wasted what should have been a third goal when they had three forwards going on against the goalie and I still can’t understand how they screwed it up. Here’s the winning goal.

Also, here is a link to the highlights.

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New evidence against cosmic censorship in five dimensions was announced today in the arxiv. The evidence is numerical, but it is done by a very good group of people working on numerical general relativity: Luis Lehner and Frans Pretorius. They argue that in the black string Gregory Laflamme instability the system develops `singularities in finite time’ as seen from the outside. This is due to the way the system evolves ins a self-similar way.

This is important because for these systems one can not ignore quantum gravity effects for  a ‘generic’ set of  initial conditions. For a long time the system of the black string Gregory-Laflamme instability was believed to provide a counterexample for cosmic censorship, but various technical results made it hard to prove and showed that the problem was rather difficult to approach.

Once again, higher dimensions show that they are very different from four dimensions when it comes to the study of Einstein’s equations. The first statement that went out was the ‘no hair’ theorem when people found all kinds of super-tubes, black rings,  etc where one could have many stationary solutions to Einstein’s equations (with some matter) with the same quantum numbers and with black objects involved in their description.

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