Friday, February 29, 2008

Michael Turner at UC Irvine

The department talk this week was by Michael Turner. He and Kolb wrote the book on early universe physics, literally. (It's the standard on the subject.) He is a member of the national academy of sciences and is the one responsible for the idea of dark energy. (He coined the term.)

His talk was based on his recent review paper here. It is a great review. I will try to address the highlights.

1. The standard model of particle physics and the hot big bang of cosmology are two of the greatest achievements of 20th century physics.

2. About 95% of the matter and energy of the universe is made of unknown substances: Dark energy and dark matter.

3. The solution to dark matter may be in our grasp: for example supersymmetric dark matter candidates make sense and good experimental predictions. Soon we should be able to test them. Dark energy is harder to pin down. Again, supersymmetry is probably best candidate.

4. The power spectrum (above) tells us the geometry and matter content of the universe. The location of the first peak along the x-axis tells us the geometry. The location is consistent with a flat universe. The hight of the first peak corresponds to the matter density of the universe and the ratio of the first to second peak indicate the baryon density of the universe.

5. Evidence from galaxy clusters, the CMB anisotropies and type 1A supernovas put the density of the universe due to dark energy at about 76% and do to dark matter at about 24%. (See below.)

6. The universe is accelerating now but at one time was decelerating. This is important for otherwise matter could never clump up and lead to large scale structure. (See below.)

7. If dark energy is the cosmological constant, which in every way it seems to be, then supersymmetry is the most probable answer. Supersymmetry has the cosmological constant = 0 but if supersymmetry is broken it becomes nonzero but close to zero as we see. No current models fit perfectly though.

The string landscape provides another elegant solution but Dr. Turner didn't have a lot of kind remarks for string theory. Related things like extra dimensions and topological defects are also suggestions.

It could be we need to modify the whole theory of gravity all together. This is a much more extreme and hard approach, but it might do the job. (Hard to know since it hasn't been done very well. He also wasn't kind about people who think GR solves the problem we just don't take it into account properly.)

8. Lastly, he was excited about the upcoming experiments like CERN, the plank satellite and future weak lensing projects. We should learn much from these experiments and maybe some of the above physics will prove to be true! :)


  1. Michael Turner also spoke at CU three weeks ago. His talk was a good overview of the past 10 years of cosmological research. As I listened, I thought about how much Joe would enjoy his talk. Luckily, Joe got the chance to hear it for himself.

    Every Monday we get to have lunch with the colloquium speakers and Dr. Turner spent most of that time discussing the future of astrophysical research. He has worked for the NSF and so he understands the funding process very well. He had a lot of very positive things to say about funding in astrophysics, but he didn't sound terribly convincing. Hopefully he's right but I sure wasn't convinced that the outlook for funding in astrophysics is as rosy as he claimed.

  2. I personally think that there will always be funding for research in areas where there are big experiments.

    I couldn't imagine pumping tons of dollars into Lisa or the James Webb Telescope or some new gamma ray detector etc... and not fund the people who will study the physics that goes along with these expensive projects.

    This is another reason I want to do high energy theory, mixed with cosmology. Over the next decade all these cosmological experiments that Dr. Turner mentioned, plus CERN, and more, will be going up. Theorists will have to be funded to "build models" that account for what is being seen.


To add a link to text:
<a href="URL">Text</a>