Galactic Interactions

Astronomy talk in Second Life : Solving the 3-Body Problem

Posted on September 18th, 2009 — permalink

I’ll be giving a talk in Second Life on Saturday at 10AM SLT (Noon CDT, 17:00 UT). This is part of the regular series Dr. Knop Talks Astronomy.

Double and Triple Stars: Solving the 3-Body Problem

If you look at the stars in the night sky, you discover that a very large fraction of them are not isolated, but are in fact in binary star systems, or even in larger groups. Using Newton’s gravity, we are able to perfectly solve for the orbits of a system involving just two bodies, but it’s impossible to analytically solve it for more. In this talk, I’ll describe why we care– not only in trinary star systems, but three-body interactions also matter in rich clusters. I’ll describe how we’re able to solve the 3-Body problem and figure out the orbits of stars in such system, and give a demonstration of a working computer that actually solves the system in Second Life, right before your eyes….

The talk will be at the MICA Large Amphitheater in Second Life. Remember, a Second Life account is free!

In related news, I’ve now uploaded the slides to all of my previous talks to the MICA website.

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The other horrors of 9/11

Posted on September 11th, 2009 — permalink

Many people will consider this post to be in extremely poor taste.

But there are things that I think that we really need to keep in mind as we’re remembering the lessons that we learned, the tragedies and the horrors of 9/11. (And, this won’t be the first time I made a post that many considered in poor taste….)

To frame the whole thing, let’s start with what I call George W. Bush’s most egregious untruth— not a lie, for I don’t doubt that he meant it when he addressed the nation on the evening of 9/11, but what in retrospect turned out not to be true:

None of us will ever forget this day, yet we go forward to defend freedom and all that is good and just in our world.

What was the legaciy of this moving forward to defend freedom, justice, and goodness?

• The passage of the PATRIOT Act, rushed through in less than two months, voted on so fast in a political climate where legislators would be viewed in a light similar to how this blog post will be viewed if they voted against it. It was a massive piece of legislation that incorporated all sorts of expansion of powers for law enforcement and limitations in the checks and balances. Many of the things in there would have been the subject of vigorous debate and public scrutiny if they had been proposed individually. Yet, in the climate of “We MUST do something” after 9/11, it was rammed through, and public opinion would have had it no other way.

  And, yet, despite how controversial the authoritanrian tenets of this act should have been in the “land of the free”, one senator and only 15% of the House of Representatives voted against it. Many (all?) of those who voted for it hadn’t read the act, and I wouldn’t be surprised of most of them didn’t really know what was in the act they were voting for.

  This kind of “must do something” response is the legacy of 9/11 that I hope we learn the most from. We open ourselves to manipulation from people who would love to pass all kinds of authoritarian laws when we respond in haste and in fear to a horrific event such as the 9/11 terrorist attacks.

• The Iraq war. Bush & co. were going to go into Iraq anyway. 9/11 made it easy for them. They could frame the whole war in terms of terrorism and defending America. A large proportion of American citizens were led into believing that Saddam Hussein was connected to the 9/11 terrorist attacks, even though there is absolutely no evidence for that. (The USA Today article I link to cites 70%; other numbers I’ve seen are closer to 1/3 or 40%. In any event, a significant fraction of Americans believed the lie.). 3,000 people died on 9/11. In Iraq, 4,200 Americans and something like 100,000 Iraqis have died as a result of the war. (And we won’t even talk about the cost of this war, rushed into, in compraison to, say, any potential cost of a much-reviled universal health care plan.)

  Was Saddam Hussein evil, and did his regime need to go away? Yes. Did the US make a complete mess out of the war, as a result of disastrous misplanning and lack of understanding about rebuilding after Saddam was ousted? Absolutely. I will say that over the last year or so, I’ve actually been almost optimistic that Iraq may be able to get back on its feet; I had not been for years before that. And, heck, the war in Afghanistan is looking scary now… I can’t help but wonder if much of that results from our redirection of focus from that war (which had broad international support) to Iraq long before the Afghanistan war was anywhere near complete.

• Many US citizens and many US politicians have started to speak out in favor of torture. Why? Fear. Because 9/11 has convinced us that we have to do whatever it takes to fight back against those who would do those sorts of things. Never mind that torture doesn’t work and generates bad intelligence. Never mind that it sullies the image of America internationally, gives those who hate America a great reason to hate America, and will only make things harder on Americans who get captured by terrorists. Never mind that it makes us evil that we do it. We want us our revenge. We suffered from the horrors of 9/11, so we want to make sure somebody else suffers in kind. We have seen it be effective week after week in the TV show 24, so we think we’re being courageous and doing the hard thing to support it. It makes me sick. I have some hope that perhaps we’re going to hold those at the top accountible for the decisions they’ve made, but for the most part, we’re probably going to throw some lower-level scape goats to the dogs as a way of pretending “accountability” while we still debate whether or not we should continue this barbarous and ineffective tactic.

• The end of due process. OK, that’s overstating it; due process still exists. And, as the link at the bottom of this paragraph shows, finally, years later, we’re reevaluating what we did and realizing that it was wrong. But there remain lots of ways for the government to work around it when they want to. Hoards of people picked up for the slightest suspicion have wasted away years of their lives in Guantanamo Bay as they are held without trial, without hearing. Yeah, they may not be American citizens, and thus not subject to protection from our authorities by our Constitution, but what of our ideals? What happened to defending freedom and justice? And, indeed, being an American citizen doesn’t stop you from being held without due process if the right part of the executive branch declares that you’re a material witness, without any proof whatsoever.

There are other things. The general paranoia we have about photography of public places, and how cops and security guards come down with unreasonable suspicion against those who are just taking pictures. The UK’s institution of universal surveillance and a lack of law enforcement oversight. The fact that anybody is still paying any attention to Dick Cheney as he tells us we should be torturing away as his administration always did. Folks’ laptops being seized, searched, and (effectively) confiscated at national borders without reasonable suspicion, in blatant violation of the spirit of the fourth amendment to the Constitution. The complete squandering of the sympathy and goodwill that the US had in the international community after 9/11 as a result of our aggressive and self-righteous posturing.

I believe it’s just a matter of time before some nutcase— be it a terrorist of the 9/11 variety, or a homegrown white guy of the Oklahoma City bombing variety— is able to get his hand on a “weapon of mass destruction” and blow it off in some highly populated area. And, I’m talking something nuclear here (be it a “dirty bomb” or a small nuke or some such), not just an airplane full of jet fuel— because the N-word makes everything so much scarier. And, I have to admit, I despair in the authoritarian rules that will be passed by widespread popular demand, quickly, in response to that.

We should never forget the horrors of 9/11. But we should also never forget the terrible mistakes we made in response to 9/11.

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“The Stars in a Galaxy” — talk Saturday at 10AM PDT / 17:00 UT in Second Life

Posted on September 4th, 2009 — permalink

I’ll be giving the latest installment of my the regular talk series “Dr. Knop Talks Astronomy” (usually, but not always, given by me) in Second Life tomorrow (Saturday) morning. This time I’ll be talking about the stars that make up a galaxy:

We now know that most of the mass of a typical galaxy is Dark Matter. But, when you look at an image of a galaxy in optical or near-infrared light, the light you’re seeing comes from the stars. It turns out, however, that the stars that are responsible for most of the light you see are not representative! Most of the stars in a galaxy, and indeed most of the stellar mass of a galaxy, aren’t the ones emitting the light that you see in a typical image. In this talk, I’ll describe what we know about the kinds of stars that one finds in a typical galaxy. How typical is the Sun? What are the stars that we’re mostly seeing when we look at a galaxy? And what makes up most of the stars in a galaxy?

Drop by and see us in the StellaNova Large Amphitheater in Second Life. Second Life accounts are free; you can join at the registration portal offered by the SciLands.

This talk will use Second Life Voice.

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Physics GRE Considered Harmful

Posted on September 3rd, 2009 — permalink

“As presently constituted, it’s quite possible that the GRE physics subject test does more harm than good, and we should either fix it, or seriously consider getting rid of it altogether,”

A quote from Jennifer Siders in this article at aps.org, that really we ought to take seriously. I doubt we will, though, because the Physics GRE is well entrenched at most graduate programs across the country, and making changes like that is always tough. Indeed, the article I linked to (as a result of seeing it in Pamela Gay’s Facebook status) was written 13 years ago, and yet the Physics GRE is still going strong.

I’ve been grouchy about standardized tests for some time. When it comes to things like the general GREs and the SATs, I believe that it does correlate with overall academic performance. Whether or not it’s testing the right stuff, there seems to be some correlation between what it tests and what we’d really want to test. But, it’s not perfect. That is, for (say– I’m making this number up) 80% of students, the SAT and general GRE might a good indicator of how successful they’ll be in college. As such, from a mercenary college admissions’ point of view, it’s worth keeping using them. Most of the time, they get the right students, and damn but it’s really easy to cut down on the number of applications you actually have to put work into thinking about by sorting on a simple number. Of course, from an individual fairness and a humanity point of view, it’s pretty sad to think that the other 20% (or whatever) who would have thrived at a certain college aren’t even considered because of a bad test….

The Physics GRE, however, has bothered me since I started as an assistant professor. Now, mind you, this is not personal sour grapes. My Physics GRE score back in 1990 was 89th percentile. At the time, I felt a little bad about that; I was one of those geeks who always did well on standardized tests, and thought that I should get over 90% on anything math/science related. Much later, I realized that 89th percentile is damn good for the Physics GRE. I did not personally suffer as a result of the Physics GRE, so I’m not posting this out of bitterness.

But, there is evidence that the Physics GRE does not correlate very well with how you do in Physics grad school. It seems completely unsurprising. In grad school, you do well by doing well at research. Yeah, you have to pass your classes, but even there it’s very different from what the Physics GRE tests. The Physics GRE tests your ability to think uberfast (which may be relevant in conference arguments, but is not terribly relevant for most research), your ability to recall things you’ve memorized, and your ability to quickly go through canned problems about basic physics. It’s not completely irrelevant, but it’s not testing what is most important about graduate school.

Of course, all the hand-wavy justifications for why it’s the wrong test only mean so much. As I said, there is evidence that the Physics GRE does not correlate very well with how you do in Physics grad school. What’s more, there’s evidence that women who do just as well as men in grad school on average score lower on the Physics GRE. In other words, either because of societal conditioning or because of intrinsic differences, the Physics GRE is more unfair for women, on average, than it is for men. Given that we’ve got a recruiting and retention problem for women in Physics, we should take this very seriously.

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