Where is everybody? : Starts With A Bang. “If the Universe Is Teeming with Aliens… Where Is Everybody?”
-Stephen Webb As egocentric as we are, we know that not only are we but one planet of many orbiting our Sun, but that when we look up in the heavens, every point of light we see is another chance — another opportunity — for planets, for life, and even for intelligence. Image credit: Ned Wright, COBE / DIRBE, and NASA. With hundreds of billions of stars (visible here in infrared wavelengths) in our galaxy alone, we have many, many chances for life to have evolved similarly to how it did here on Earth. With hundreds of billions of galaxies in the Universe, it seems unfathomable to us that we would be alone as the only self-aware, intelligent, sentient lifeforms in the Universe.
Image credit: Hubble Ultra Deep Field team, NASA, and STScI. The question atop — where is everybody — is known today as Fermi’s Paradox. Image credit: M. Is there really anything paradoxical about it at all? Image credit: Space Shuttle Atlantis mission 110. Inbox (18) - Avignon Day 1: Calculating Non-Gaussianities. Greetings from Avignon, where I’m attending a conference on “Progress on Old and New Themes” in cosmology.
(Name chosen to create a clever acronym.) We’re gathering every day at the Popes’ Palace, or at least what was the Pope’s palace back in the days of the Babylonian Captivity. This is one of those dawn-to-dusk conferences with no time off, so there won’t be much blogging. But if possible I’ll write in to report briefly on just one interesting idea that was discussed each day. On the first day (yesterday, by now), my favorite talk was by Leonardo Senatore on the effective field theory of inflation. In the effective field theory of inflation, you try to characterize the behavior of inflationary perturbations in as general a way as possible. At a first approximation, cosmological perturbations are gaussian: the fluctuations at every point are drawn from a normal (bell curve) distribution.
Avignon Day 4: Dark Matter. Yesterday’s talks were devoted to the idea of dark matter, which as you know is the hottest topic in cosmology these days, both theoretically and experimentally.
Eric Armengaud and Lars Bergstrom gave updates on the state of direct searches and indirect searches for dark matter, respectively. John March-Russell gave a theory talk about possible connections between dark matter and the baryon asymmetry. The density of dark matter and ordinary matter in the universe is the same, to within an order of magnitude, even though we usually think of them as arising from completely different mechanisms. That’s a coincidence that bugs some people, and the last couple of years have seen a boomlet of papers proposing models in which the two phenomena are actually connected. Tracy Slatyer gave an update on proposals for a new dark force coupled to dark matter, which could give rise to interesting signatures in both direct and indirect detection experiments. This is science at its most intense. Is space like a chessboard? Physicists at UCLA set out to design a better transistor and ended up discovering a new way to think about the structure of space.
Space is usually considered infinitely divisible -- given any two positions, there is always a position halfway between. But in a recent study aimed at developing ultra-fast transistors using graphene, researchers from the UCLA Department of Physics and Astronomy and the California NanoSystems Institute show that dividing space into discrete locations, like a chessboard, may explain how point-like electrons, which have no finite radius, manage to carry their intrinsic angular momentum, or "spin. " While studying graphene's electronic properties, professor Chris Regan and graduate student Matthew Mecklenburg found that a particle can acquire spin by living in a space with two types of positions -- dark tiles and light tiles. The particle seems to spin if the tiles are so close together that their separation cannot be detected. Progress on Old and New Themes in cosmology (PONT) 2011 (18-22 April 2011) Non-Gaussianities in the CMB. "Non-Gaussianities in the temperature fluctuations of the Cosmic Microwave Background" sounds like a perfect conversation topic to put your date to sleep, but if you have an interest in Cosmology or Quantum Gravity, it's definitely something you should have heard about.
The Cosmic Microwave Background (CMB) is radiation we receive today from a time when the universe was about 300,000 years young. At that time, radiation decoupled from matter and since then, photons could travel almost undisturbed. The CMB shows the temperature, or the inverse wavelength, of the microwaves that we receive on Earth from these early times. The mean temperature of the CMB is approximately 2.7 Kelvin, and is a blackbody spectrum to truly amazing accuracy. What we will be concerned with here however is not the mean temperature, but tiny fluctuations around this temperature. One way to extract information from the data is to look at correlation functions. Chiral perturbation theory. There are several power counting schemes in ChPT.
The most widely used one is the -expansion. However, there also exist the and expansions.