Report: Brian Greene @ BYU

Brian Greene coming to BYU for the forum address was exciting for me in a few ways. First off Brian Greene came to BYU and secondly, I got to give the forum invocation and spend some extra time with Dr. Greene. It was a lot of fun to sit on the stand and feel 'all official' and then the fancy catered lunch afterwards was for 14 or so people in the Hinckley building. Anyway, I am sure that you're all not as interested in that stuff as I am, so I will move onto the meat of Dr. Greene's visit: string theory.

The address itself was very exciting; from Dr. Greene's initial wandering around the podium and his intensity to his great explanations of how the concepts of space and time have changed throughout the years. There were also two Q&A sessions: one right after the forum and then another for physics students later. I attended both and I will list, in bullet form, some points that he made.

• There is no stringy big bang model yet
• He does not 'believe in string theory' and will not until experimentally verified. It was nice to hear him say that
• Earth stays in orbit due warping in 'time.' I am not sure what he meant by that exactly
• Dark matter might be 'regular' matter hidden in extra dimensions
• Quantum foam is 'smoothed' out due to the minimum length scale introduced by strings. It does so because it prevents you from probing scales smaller than the string length. Also, this minimum length scale is what allows string theory to couple GR with quantum and it does not break Lorentz invariance
• As of now, there are no definite energies we need to probe at the LHC, but it could be soon when we get those numbers
• There are no practical application for string theory yet, but that's what they first thought when QM was first discovered
• String theory might come close to an eternal truth
• String theory unifies forces since all the force mediating particles come from the same strings
• Each of the 5 string theories is a different perturbative expansion

So that's a little of what Dr. Greene discussed. It really was a wonderful forum; he's a great speaker and is very enthusiastic about strings. You might be curious what he said when asked about rumors that string theorists are leaving string theory by the droves or what he thought about the last few books that claim string theory is wrong. He did address those issues and said that people are not abandoning string theory and that those books basically say the same that all string theorists say: that string theory has not yet been experimentally verified. Here is a link to the BYU NewsNet (not quite accurate) article reporting on the forum address.

Cosmology May Be The Key

I've said it before and now I have reason to say it again: Cosmology may be the field which will determine the properties of fundamental physics in the future. You may not be able to build a particle accelerator powerful enough to reach the plank length, but the big bang was energetic enough to possibly probe those energies.

Another one from Science Daily:

Peering backward in time to an instant after the big bang, physicists at the University of Wisconsin-Madison have devised an approach that may help unlock the hidden shapes of alternate dimensions of the universe. A new study demonstrates that the shapes of extra dimensions can be "seen" by deciphering their influence on cosmic energy released by the violent birth of the universe 13 billion years ago. The method, published today (Feb. 2) in Physical Review Letters, provides evidence that physicists can use experimental data to discern the nature of these elusive dimensions - the existence of which is a critical but as yet unproven element of string theory, the leading contender for a unified "theory of everything."

So using data from the Big Bang we now should be able to tell the geometry of the extra dimensions. The group says the new Planck Satellite going up may be sensitive enough to determine the geometries. It's a great time to be going to graduate school. If they can tell the extra dimensions are there it would be strong evidence for string theory.

String Dimensions Must Be Less Than 44 Micrometers

String Emitting Gravitational Waves

Yesterday in statistics I was sitting next to a math major who was trying to convince me to ditch physics and go to into math since I have a talent for pure mathematics. I told him I want to do more than just prove theorems all my life. I like using math to construct models. I like pure math since I feel it is beautiful and has lots of potential as physical theories become more advanced. But I want to use math to describe things, not just prove theorems.

My friend then told me physicists are like functions trying to map every aspect of reality to some sector of math. I'll think about that for a while. In the meantime I am pleased to report that we have another experiment putting constraints on fundamental theories. According to a research group from the University of Washington, if higher dimensions exist, they must be less than 44 micrometers. They came to this conclusion measuring gravity. If there were extra dimensions, they would affect gravity on distances similar to length of the extra dimension. In fact their wiggles might even produce gravitational waves! They found no gravitational change at all to a small enough scale to rule out dimensions larger than 44 micrometers. These results are printed in this week's Physical Review Letters.