A last batch of talks before the summaries March 29, 2007Posted by dorigo in astronomy, news, physics, science.
Today is the last day of the Outstanding Questions in Cosmology conference. A lot of short talks have been scheduled for this morning, while in the early afternoon there will be two conference summaries, one by Albert Stebbins and the other by Richard Lieu.
Most of this morning’s talks are quite technical, and I feel I would either have to be cryptic or write baloney if I were to report about them. But let me give some flavor of the talks in a few lines below anyhow. As with other posts this week, I have to apologize to those of you who find these discussions too hard to follow – I will resume outreach-style blogging after this conference is over!.
A talk I followed with some attention was Damien Hutsemekers’ “Large-Scale Alignments of Quasar Polarization Vectors: Observational Evidence and Possible Implications” (a good example of the inverse proportionality existing in conference talks between the length of the title and the duration of the talk allotted by the organizers – 15′ in talks during today’s morning session; compare it for instance to “CMB and the Dark Ages”, “3-year results from WMAP”, or “Does WMAP require Dark Energy”, all 30′ talks given in the previous days).
Hutsemekers explained that most quasars (a well-established contraption for quasi-stellar radio sources) exhibit only a small linear polarization in their optical emission, of the order of a few percent. The polarization vectors appear to be aligned over scales of about one giga-parsec, at redshifts of about 1: therefore their study could shed some light on the existence of large scale structures in the Universe, something which is all the rage in Cosmology these days.
A study of 355 polarized quasars with redshifts up to z=2.5 measured the correlation of the polarization vector of each quasar with its neighbors – or with the average polarization in its neighborhood. The result is that there not only seems to be evidence for a correlation at large distance scales, but that the quasars contributing the most to the correlation appear to line along an axis (see graph in the picture above, where quasars are plotted as spheres whose size depends on the amount of correlation) which is not too far from another axis of symmetry that seems to exist between the low-l multipoles of cosmic microwave radiation. Hutsemekers dismissed the possibility of instrumental bias (the polarization measurements are consistent across different experiments) or due to some interstellar polarization effect. I personally found the evidence shown that the effect is not due to an interstellar medium quite unconvincing…
S.Batthcharya talked on “Cosmological Constraints from Galaxy Cluster Velocity Statistics”. He explained that while the Sunyaev-Zeldovich effect (a modification of the energy of the photons due to collisions with electrons) is responsible for most of the shift of the power spectrum of cosmic microwave radiation, an interaction with moving electrons of the microwaves causes deformation of the shift. From the deformations you can obtain information on the velocity of galaxy clusters. The kinematical effects on the temperature spectrum of cosmic microwave radiation are small, but ACT, a new detector which should provide a survey of 150 squared degrees of sky, could detect the 10 micro-kelvin fluctuations with a good enough angular resolution. The combination of ACT data with WMAP3 and other results is expected to thus provide a 5-fold improvement in the current constraints on some cosmological parameters.
Daniel Sudarsky gave an interesting talk titled “Do we really understand the quantum origin of the seeds cosmic structure?“. Another instance of a rethorical question in a talk title. He mentioned that the last decade saw a big success for inflationary cosmology. Primordial inhomogeneity predicted by inflation is in agreement with observations. However, there is something strange: the universe starts homogeneous and isotropic, has a scalar field (the inflaton) which also satisfies a homogeneous and isotropic potential, and still, we get in a situation which is not homogeneous and isotropic (H&I), despite the fact that the dynamics should preserve that symmetry.
Daniel explained that the departure from H&I cannot be ascribed to quantum mechanics alone, since the universe is the prime example of a closed system. So popular arguments include asking you to accept that quantum mechanics does not describe our universe, but a superposition of universes. Others, Daniel argues, will try to convince you that our universe is actually still H&I. Or that it really does not matter. But the question is not purely philosophical: some of these issues can be studied and tested xperimentally – he remarked that even inflation is at times attacked as being a philosophical motivation.
Sudarsky quoted Penrose, who said that quantum mechanics is incomplete: that is the conclusion you arrive at if quantum mechanics is not just a description of our information about reality, but it is tout court a description of reality.
After discussing at length these issues, Sudarsky found out he had only three minutes left for his talk, and there followed a shooting of slides actually full of complicated quantum mechanical formulas which I could not quite grasp. But then he concluded: Something, related to quantum mechanics, is missing in our understanding of the origin of cosmic structure. Something like a self-induced collapse is required to take us from a state which is completely homogeneous and isotropic to another one lacking those symmetries. Present analysis seems to offer a path to alleviate the need of fine tuning.
I must say I did not understand much of the above discussion, but listening to Sudarsky’s talk was still quite interesting to me…