The miserable near future of Cosmology March 27, 2007Posted by dorigo in astronomy, Blogroll, news, physics, science.
I have no energy nor time to discuss yesterday’s talks in any detail, so I decided I’d skip them and pretend they did not happen, and use today’s lunch break for giving some highlights about the things I heard this morning. As previous ones on the same topic, this post is a bit more technical than I would like it to be, so be patient with me. I have a hard time understanding everything myself…
PS: the title of this post comes from the talk of Lawrence Krauss, see below.
- Shaun Cole talked on “Galaxy and Mass Power Spectra“. He asked himself the question: do uncertainties in modeling non-linearity and galaxy bias compromise constraints on cosmological parameters coming from measurements of the galaxy power spectrum? And he went on to discuss it by analyzing data from 2dF and SDSS, surveys of galaxy distributions in the universe which have small overlap and different sensitivities. Biases come from the Sloan survey’s higher sensitivity to red galaxies, which has to be taken into account, and their non-fixed magnitude limit. It seems that at large distance scales the Sloan survey finds less power in the spectrum, which implies a slightly higher value of the matter fraction of the matter-energy budget of the universe than current best estimates – although within uncertainties things agree. At small scales, blue galaxies are less clustered than red galaxies, but if one takes the color bias away and compares the two surveys, results agree better.
- Douglas Scott (above) talked about “The Standard Model of Cosmology versus the Other One“. He compared the model of Cosmology to the model of Particle Physics, and tried to gain some insights in what is in store for cosmology. I really hope that the comparison yields no similarities, being fed up with the static nature of theory in my research field, but he seemed more optimistic about it. Douglas pointed out the many successes of the standard cosmology, a string of results which indeed looked impressive from his perspective. He showed that Peebles and Yu back in 1970 had already predicted the acoustic peaks in the microwave background that would be later confirmed by COBE and measured so well by WMAP.
- Lawrence Krauss (pictured above with his last slide on the background) talked about “Cosmic Ignorance: What We Don’t Know about Dark Energy, and Dark Matter, and Might Never Know“. He discussed how miserable cosmology will be in the short term – he had discussed long-term forecasts at the dinner banquet yesterday (see my last post below). He said that the geometry of the universe is irrelevant for one’s destiny. We actually are in a position to being unable to tell. The only meaningful question for Krauss seems to be, is Dark Energy any distinguishable from a Cosmological Constant, and will it ever be ? Now, since the most reasonable theory predict w=-1, and other alternative models do not depart from that value, measuring it will tell us nothing. And the highest precision we can ever hope to obtain on it is only of about 0.06, which will not shed any light on the matter. As for Dark Matter candidates, he discussed the detection of wimps (weakly-interacting massive particles), but was quite pessimistic about the possibility of resolving the issue in the next few decades, given the fact that one would not just need to detect a few hundred of those particles in the high-noise underground detectors, but also measure their direction. In the Q/A session Richard Lieu called Krauss a pessimist (to which he replied with a surprised “meeee ?“). In his concluding slide, Krauss indeed had a sentence which read “It is not unlikely that we will never empirically determine the nature of dark energy”, and he argued this was not actually too pessimistic. There followed a funny dialogue with Douglas Scott, who was mentioned by Lieu in his question: LK – “I always agree with Doug“. DS (from the audience) – “No you don’t!“. LK – “No I don’t“.
- John Cowan (see picture above, where he is comparing the abundance of atoms from a particular halo star to the favorite model) gave a enlightening talk on “The age of the oldest stars as a constraint on cosmological models“. He discussed measurements of the abundance of high-Z elements in stars from the outer halo of our galaxy, which are quite old. These stars are the relatives of the first stars in the Universe. Neutron capture is the mechanism by which the heavy elements are created, but there are two: slow capture or fast capture. In the fast capture mechanism, the average time for a capture is much smaller than beta decay of the nucleus. Measuring the abundance of these rare elements (a part in 10^12 with respect to the abundance of Hydrogen) is hard but it has been performed on a few stars from the galactic halo. These spectra – which comprise as many as 57 elements in the case of a particular star - show great agreement with rapid neutron capture models. With these heavy elements one can fit the ratio of abundances, for instance thorium to europium (thorium has a half-life of 14 billion years and is thus a “chronometer” of the age of the Universe). Absorption spectra of Thorium can be fit with various models, and the abundance of this element is measured. At the end of the day, one obtains the age of the universe with a uncertainty of two to three billion years, and the method is quite independent from the particular cosmological model of one’s liking.
- Finally, Andrew Jaffe (see his blog here) discussed “Constraints on the Topology of the Universe“. He started by explaining the topology of a torus by analogy with the old “Asteroids” game (see picture above). He discussed how the cosmic microwave background can provide hints on the repetitive appearance of the sky, which is a signature for peculiar topological structure of the Universe. He showed that the low-l data could be better fit by models implying some particular topology, but “not much improvement can be done in a fit which is already less than 2-sigma away from the data”.
That’s all folks!