Interview: Juan Collar and Detecting Dark Matter (MP3, 28.3MB, 41:10, Show Notes)

I just came back from the astro-drinking-blogger meetup. It was a lot of fun. With apologies to the people my brain is too dim to name individually, there was a very nice group of people there including Phil, Pamela, Chris, Sean, Nick and Nancy.

I’ve had a couple of beers, if you’ll excuse me, but we are really lucky to have such a thriving and friendly community of astro-blogging. Note I don’t mean the bloggers, I mean you, the people who enjoy reading about astronomy.

The life astronomy improves is your own. I hear over and over from people — one of the major joys of astronomy are the human connections that we weave together. Understanding the universe is a compelling and important goal and I don’t understand why all people aren’t astronomers. Then I remember — they are. Everyone loves astronomy because you have to be bat-sh*t crazy to not appreciate the wonder, beauty and complexity of the universe.

So here’s a toast to you, Mr. and Ms. Astronomy Enthusiast. We aren’t just on a quest, we are on a quest together. It’s a lot of fun.

Check this sh!t out:

Credit: Brant Robertson, Spitzer Fellow, KICP/UChicago

This interview is quite long so we’ve uploaded low and high rez versions. The low rez version is the one in the RSS feeds.

If you subscribe to the feed, the audio is probably already on your box. Or you can check out the show notes or download the MP3 file directly:

Slacker Astronomy podcast interview with Brant Robertson (low rez) (MP3, 24.7MB, 1:11:20)

Slacker Astronomy podcast interview with Brant Robertson (high rez) (MP3, 65.6MB, 1:11:20)

Via Cosmic Log:

Ten years after supernovae provided the first evidence that the expansion of the universe is accelerating, a survey of more than 10,000 galaxies has provided independent confirmation that the cosmic speed-up factor known as dark energy is for real.

Cosmic Log provides a very nice analysis of this press release from the European Organisation for Astronomical Research (ESO).

So it seems that the expansion of the universe is indeed accelerating. This means that cosmological constant is non-zero and dark energy, or some alternate explanation, is necessary to explain the observations. Our cosmology seems to be consistent and correct in terms of what is happening, we just don’t know why it is happening.

Slackerpedia Galactica 8.0: A Brief History of the Universe (MP3, 17.2MB, 36:12)

In this show Doug and I discuss the the cosmological timeline as I wrote about in a previous post. We also talk a little about asteroid 2007 WD5 and its possible upcoming impact with Mars.

In the beginning t equaled zero seconds (t=0). A Big Bang-like thing happened and the universe began expanding. It was very hot and very dense cold and empty^[1]. The universe expanded exponentially in a period known as inflation. Inflation ended around t=0.000000000000000000000000000000001 seconds.The universe was so hot that everything was relativistic and “radiation like”, so the universe was considered radiation-dominated.

At around t=1s neutrinos decoupled, meaning they stopped interacting with matter or radiation and just continued on their way forever. This is the elusive CNB — the cosmic neutrino background. Around the same time the ratio of protons to neutrons “froze out”.

At around t=200 seconds the temperature had dropped enough that deuterium could start to form. These were the first nuclei in the universe. This is the beginning of the era known as Big Bang Nucleosynthesis (or BBN). After less than 15 minutes, BBN ceased and the initial ratio of helium to hydrogen was established. The universe was now about 20 minutes old and for the next 50,000 years it was a hot bath of radiation and light elements that continued to expand and cool.

At t=50,000 years or so, the temperature got low enough that matter started to dominate the universe and by t=350,000 years the universe was entirely transparent to radiation, giving rise to the “last scattering surface” which we see as the CMB (cosmic microwave background).

By t=250,000,000 years or so, stars and galaxies had formed. The universe continued to expand and cool even as the the universe evolved to what we see today.

At about t=10,000,000,000 years, about 75% of the present age of the universe, matter ceased to dominate the universe and Λ (lambda) know as the ominous “Dark Energy” began to take over. Thus, the universe is not just expanding, it’s expansion is accelerating.

Currently t=13.7 billion years and the energy density of the universe is comprised of roughly 0.00008% radiation, 30% matter and 70% Λ, the temperature is T=2.7 degrees Kelvin and the Hubble rate, which is a measure of the expansion of the universe, is H=70 km/s per megaparsec.

^[1] My cosmology professor was kind enough to read my post and to this point he said “The universe wasn’t hot during inflation. It was actually cold and empty; the inflaton field was a condensate, totally different from a thermal bath; the best analogy is a Bose-Einstein condensate at T = 0. The condensate at the time t =0.000000….1 you say decayed. The decay products then thermalized to very high temperature.”

Nothing could be further from the truth. Cosmology is a physical science and it is a rigorous science. While there are certainly mysteries and unknowns, cosmology is on a very firm basis and really doesn’t resemble philosophy in the slightest.

If you are interested, our textbook is very readable and was recommended to me previously by another cosmology researcher. It’s Introduction to Cosmology by Barbara Ryden. Dr. Ryden does a very nice job of laying out the context in the early chapters and then delving into the details of physical cosmology in the later parts of the book.

Today in class we talked about the evolution of the universe in 3 main eras — the radiation dominated early universe, the long matter dominated universe, when galaxies formed and the present era where the universe is dominated by “dark energy” (known to cosmologists as Λ). The radiation dominated era was quite brief, lasting only about 50,000 years. The matter dominated era was about 9 billion years long and Λ has dominated for about the last 4 or 5 billion years or so.

We know this.