Galactic Interactions

This Saturday : “The Discovery of the Accelerating Universe” in Second Life

Posted on April 1st, 2009 — permalink

“Dr. Knop Talks Astronomy”, in association with MICA (www.mica-vw.org)

Saturday, April 4, 10AM SLT

http://slurl.com/secondlife/StellaNova/213/210/32

The Discovery of the Accelerating Universe

In 1998, two teams of astronomers observing supernovae discovered that the expansion of the Universe is accelerating. The speaker, Dr. Knop, was on one of the two teams, working with Saul Perlmutter. In this talk, I will describe just how it is that you can measure the expansion history of the Universe by observing distant exploding stars, and what surprising things we saw in our results that indicated to us that the expansion of the Universe was in fact accelerating. At the end, I’ll briefly mention some things about “dark energy,” the mysterious substance that is causing this surprising universal acceleration.

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Astronomical References in Shakespeare

Posted on February 14th, 2009 — permalink

Thanks to Brian Cooksey for the shout out last time I was a contributor to the 365 Days of Astronomy Podcast. I’ve also done today’s podcast, all about astronomical references in Shakespeare’s tragedies… starting with Romeo & Juliet, what with it being Valentines day and all. Go and listen to the podcast!

For your viewing pleasure, I’ve also got a transcript of the podcast here:

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The Big Bang and Evolution : when does a theory evolve so much that it deserves a new name

Posted on November 21st, 2008 — permalink

I am currently visiting Colgate University, giving a physics colloquium about dark energy. I’m hosted by my friend Jeff Bary (who’s a first year professor there). Yesterday evening, his class gave presentations about discoveries that they’d researched. A few of the talks touched on the Big Bang. Afterwards, I was sitting around musing with Jeff and the departmental chair, Thomas Balonek. Thom was saying that it’s disingenuous for us to claim that we’re still talking about the Big Bang as it being the same theory that we had all those decades ago. What with the introduction of inflation, cold dark matter, dark energy, it’s changed so much that really it’s not entirely the same theory any more. I argued that the basic picture is the same– the Universe expanded from a very hot, very dense state to its current form– that it warrants having the same name.

I then asked the question: which theory has evolved more, the Big Bang or Biological Evolution? To point a finer point on it, let’s go back to the (say) 1950’s or early 1960’s, when people were arguing about Big Bang vs. Steady State cosmology, before the discovery of the Cosmic Microwave Background, well before the introduction of inflation to solve the flatness and horizon problems. Take what people were talking about then as the Big Bang, and compare to what we talk about today. Has that changed more or less than the Theory of Evolution has changed from what Darwin originally envisaged when he wrote the Origin of the Species?

To be sure, the theory of Evolution is better understood and understood in better detail than the Big Bang theory. They both share the feature that they are theories describing the evolution of a system, not it’s origin (although both the name of the cosmological theory, and the title of the work that started Evolution, both would seem to indicate that they do). We know a whole lot more about both today than we did then. Both have features today that people in the early days couldn’t have anticipated. (I understand the cosmology better, of course, but know, for instance, that DNA and the genetics gives us an actual mechanism for Darwin’s Evolution.)

So, what do you think? Which one has changed more? And is either theory similar enough to what was originally proposed that it deserves the same name, or should we have changed the name by now?

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Popular Astronomy Talk in Second Life, Friday 8AM PDT (11AM EDT)

Posted on October 9th, 2008 — permalink

I’ll be giving a talk entitled: “We Are Starstuff: the Cosmic Origins of the Chemical Elements” as a part of the MICA public talks series. The talk will be at the Galaxy Dome in Spaceport Bravo.

Remember, a Second Life account is free!

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Randall Munroe and the Size of the Observable Universe

Posted on October 4th, 2008 — permalink

Randall Munroe of the fabulous webcomic xkcd has a great logarithmic height poster showing the size of everything from folks all the way up through the edge of the Solar System, on to the radius of the observable Universe. As a logarithmic plot, each gap of the same size vertically on the plot represents a doubling of the distance from the surface of the Earth; this is why he can show things of such vastly different scales as people and the whole Universe in the same plot.

But, wait, I thought you cosmologists kept saying that the Universe was infinite! How can this picture show the whole Universe then?

It doesn’t… it shows the observable Universe. Because the Universe is only 14 billion years old, and the speed of light is finite, we can only see things that are as far away as light has had time to reach us from. There is more Universe beyond that, but the light hasn’t reached us from it yet; the part of the Universe beyond our horizon is not the observable Universe.

But wait… if the Universe is only 14 billion years old, then, we should only be able to see things that are 14 billion light-years away… yet the xkcd pictures says the top of the Universe is 46 billion years away. What’s up with that?

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Astrophysics in Second Life : 7D mapping of the Galaxy with SDSS

Posted on September 27th, 2008 — permalink

Yesterday (Friday Sep. 26), MICA heard its first Journal Club of the academic year. (We’ve had these before, but it was very slow over the summer.) The talk was Mario Juric from IAS Princeton, talking about mapping density, velocity, and metallicity as a function of spatial position within the Milky Way galaxy, using photometric data from the Sloan Digital Sky Survey.

click for a larger image

There were a few conclusions that came out of this. First, unsurprising to anybody who’s read anything about the structure of the Milky Way, the disk and the halo really are completely separate components. The disk appears to have a vertical (i.e. perpendictular to the plan) gradient of metallicity, whereas the halo has a constant (and lower) metallicity distribution. Some density outliers from the smooth background are there, which were known previously, including the Monocerous Tidal Stream discovered by my friend and one-time collaborator Heidi Newberg

However, there were also some surprises. There’s basically no gradient of metallicity radially along the disk. I had previously been under the impression that the disk had a metallicity gradient, with higher metallicities towards the center. One caveat to this: the data does not include the very center of the plane of the disk, so there may well still be a metallicity gradient within the plane.

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“Planets Around Other Stars” — talk in Second Life this Friday at 8am PDT

Posted on July 31st, 2008 — permalink

I’ll be giving the latest in the “Dr. Knop Talks Astronomy” series of talks associated with MICA this Friday at 8am SLT (aka PDT). The talk will be at the Galaxy Dome in Spaceport Bravo. The topic is Planets Around Other Stars:

Until the last decade of the 20th Century, we knew of exactly one star system that had planets: our own. At the dawn of the 21st Century, we knew about a few handfuls of exoplanets, or planets around other stars. Today, we know about more than 200. In this talk, I’ll describe the history of exoplanet searches and discoveries, I’ll describe the methods that we have used to find planets, and I’ll give you an update about the current count and nature of exoplanets that are out there.

Remember that a basic Second Life account is free!

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Public astronomy talk in Second Life, “Kepler, Newton, and Einstein: ‘Wrong’ Theories and the Progress of Science”

Posted on June 11th, 2008 — permalink

I’ll be giving this talk in Second Life tomorrow (Thursday) at 10AM PDT (in-world time). This talk was originally scheduled for last Friday, but Second Life was having serious problems at the time as a result of networking problems from our upstream ISP.

The talk will be part of the Dr. Knop Talks Astronomy series hosted by MICA. It will be at the Galaxy Dome in Spaceport Bravo.

Remember, basic Second Life accounts are free, as is the client software!

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Technical talk on Dark Energy and Vacuum Fluctuations in Second Life this Friday

Posted on May 8th, 2008 — permalink

In addition to the popular-level astronomy talks I’ve started doing as part of MICA, there will also be regular “journal clubs.” This is something you’ll see in physics and astronomy departments sometimes: people take an interesting paper from the recent literature (really, from preprints nowadays), and lead a discussion about it with their colleagues. It’s one way of trying to keep up with some of what’s going on in the literature, and it’s also a way that one scientist can share his particular area of interest with his immediate colleagues.

This Friday, George Djorgovski will be leading a journal club in Second Life at 8AM SLT (pactific time) on the paper Dark Energy from Vacuum Fluctuations by Djorgovski and Gurzadyan. Note that while in this case, the author of the paper is talking about his own paper, that’s not always the case. In journal clubs I’ve been too, sometimes people talk about their own work, and sometimes they talk about other interesting papers from the literature. For instance, when I was at Vanderbilt and still working with the Supernova Cosmology Project (which used optical and infrared astronomical data), I gave a journal club about the WMAP 3-year results — very releavant to cosmology and my work, but not something in which I was involved.

The journal club will be where all of the MICA meetings currently happen, at the ISM Workshop in Spaceport Bravo.

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Popular Astronomy Talk in Second Life : The Death of Stars (2008-May-02)

Posted on April 28th, 2008 — permalink

I’m going to be giving my second “Dr. Knop Talks Astronomy” popular talk in Second Life as part of the fledgling Meta Institute for Computational Astrophysics.

The talk will be at The Galaxy Dome in Spaceport Bravo, this Friday (May 2) at 8AM pacific time (which is the same as in-world time in Second Life).

Drop by if you’re interested! Here’s the longer description of the talk:

In Fire and In Ice : The Death of Stars

Stars live for millions or billions of years, but they don’t liveforever. When a star reaches the end of its lifetime, spectactular fireworks can result. In this popular talk for interested layman, Dr. Knop will outline what it is that keeps a star together during its lifetime, and what happens to stars of various different sizes when that process finally breaks down. He’ll talk about the ejection of planetary nebulae, the cooling of white dwarves, and the most spectacular of stellar events, supernovae.

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