I'm sitting here in a Cafe on a drizzly day in the Castro district; my last day in San Francisco.
Yesterday, I went by my offices at SLAC and Stanford's ITP on campus, for the last time. I was pleased to bid farewell to BJ Bjorken, Michael Peskin, Lenny Susskind and Steve Shenker. BJ is truly amazing; our interaction was all about physics as usual. We were discussing my latest research project, which is looking into experimental ways to detect parity violation in gravity. Two years ago I wrote a paper which argued that the origin of matter over anit-matter in our universe is a direct consequence of the fact that space-time is chiral (in 3-dimensions reflection asymmetric). While the model is pretty and all that (mathematically consistent), the only reason why we should believe it is, of course, through some experimental signature. So BJ was being a critical ear for my arguments as to why parity violation should show up in the cosmic microwave background radiation.
Some of you out there have expressed confusion about the common lore of structure formation (galaxies, stars) in the universe. So let me take some time give a simple (yet accurate) description of this process.
When we look at the night sky with powerful telescopes we see that in every direction objects such as galaxies are moving away from us at a speed proportional to their distance from us. This is the famous Hubble redshift relationship, which confirmed the prediction of Einstein’s Relativity that the universe is expanding. Think of baking raisin bread. As the bread expands, every raisin appears to move away from every other raisin; if you were living on a raisin, the other raisins would play the role of the receding galaxies. The cool thing is that every other raisin would perceive the same thing about the other raisins (that the other raisins are moving away at a rate proportional to the distance). So analogously galaxies really aren't moving away from each other like we think, instead the space itself is stretching (analogous to our rising raising bread in the oven), an immediate consequence of general relativity (space-time itself is dynamical and is influenced by matter and energy)
Hubble's law tells us that way back in the past (billions of years ago) the universe was denser and hotter. So hot that all the matter had disintegrated into pure radiation energy. So how did the radiation filled universe turn into matter? The answer to these questions rests on a simple fact about gravity; it’s the only force that’s purely attractive. Before we go on I have to admit that I lied to you. We know from condensed matter physics experiments, that matter and radiation under extreme pressures and temperatures (temperature divided by frequency is proportional to Planck's constant) that substance becomes subject to the physics of quantum mechanics. So in the past our universe was a quantum soup of pure radiation energy. The uncertainty principle tells us that this radiation will vibrate. This vibration will affect gravity in such a way that the attractive force of gravity eventually leads these vibrations (quantum fluctuations) to collapse. This collapse is often called a Jean's instability. The cool thing is that we can calculate this effect and make predictions to compare to observations of the fluctuation of this quantum radiation in the past with the WMAP satellite data.
The collapse of this radiation-matter complex in the early universe eventually develops into stars and galaxies. There are puzzles still unresolved in this picture, such as: How did the universe begin expanding in the first place? What happened before the 'beginning'? What is the meaning of before? (What is physical time?) Etc. Etc.
To answer these questions we really need to understand the nature of gravity fully in terms of quantum gravity.
Well this is why I'm going off to Penn State, to work with the great Abhay Ashtekar at the Center for Geometry and Quantum Gravity; where the focus is in constructing a theory of quantum gravity and its cosmological and other experimental consequences. I hope to keep you updated.
Well I must sign out for now. Before I go, I ask you all to please take a look at webpage below and keep those less fortunate close to heart during the holiday season and the rest of the year.