Astronomy talk in Second Life : Solving the 3-Body Problem
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.
The other horrors of 9/11
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.
“The Stars in a Galaxy” — talk Saturday at 10AM PDT / 17:00 UT in Second Life
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.
Physics GRE Considered Harmful
“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.
Sedalia, MI makes Christians look bad
You’ve probably seen this if you follow the science blogosphere at all. The Smith-Cotton High School in Sedalia, MI has done a forced recall on T-shirts made for their band. Why? Because the T-shirt riffed on the classic “primate turning into human” motif used as a symbol for evolution.
Parents got all upset about this— the shirt didn’t even promote evolution, it just referred to it. I can’t help but wonder if parents in similarly backward and ignorant communities might object to iconography of Greek mythology on shirts related to sports teams named appropriately? Or, are they smart enough there to recognize that just because somebody used a very recognizable image, it doesn’t mean that it’s true? Asserting that the Greek gods are real is, of course, anathema to a strict interpretation of Fundamentalist Christianity, just like evolution.
And, of course, there’s also the fact that evolution is real. That there was such an uproar that the school had to repossess the shirts really just makes Christians in America look backward, ignorant, and in denial of reality. It gives fuel to the fire of those who would argue that being religious is inconsistent with accepting modern science— for, assuredly, religion is the reason why many Americans refuse to accept modern science. Those who are small-minded and knee-jerk in their reactions to things that challenge their interpretation of their religion go nuts when a school “associates itself” with Evolution. And, in so doing, it makes it harder for those of us who are trying to remind the world that religion doesn’t necessarily lead to bad science. It’s just extreme wingnut religion that does.
The principal of the school repossessed the shirts claiming that the law required the school to remain neutral on the subject of religion. This is, of course, complete bullshit, because the shirt didn’t say anything about religion at all. There is a difference between saying anything about religion, and doing something that might offend some religious sensibilities. This argument he makes is essentially the “politically correct” argument. Yes, usually one associates “politically correct oversensitivity” with political forces on the left, but the truth is that this behavior can come from either side of the political spectrum; it’s just a matter of which sensibilities they are oversensitive to.
Rejection of Evolution is just as obsolete a religious concept as is the geocentric Solar System. That something like half of the USA doesn’t agree with this doesn’t make it any less true. If we’re going to object to iconography associated with Evolution, we really ought also to reject to any iconography that suggests the planets orbit the Sun.
“Big Bang” : A terrible name for a great theory [from the archives]
[This was originally posted in June of 2006 on an earlier incarnation of this blog that's no longer available. It was collected in "The Open Laboratory: The Best Writing on Science Blogs 2006" I'm reposting it here so that it will again be available to the broader net.]
Perhaps, from a marketing point of view, “Big Bang” is a great name. It’s short, it’s punchy, it evokes memorable images, and it’s easy to remember. But, marketing is something I really don’t understand; as we all know, it’s easy to fear what we don’t understand (particularly when it has a huge amount of control over us and the world around us), and to hate what we fear, and as such I’m very convinced in my opinion that Marketing is Evil.
So why is the Big Bang a terrible name? Because the name itself evokes and supports many misconceptions about the theory. Read on for my musings on the matter.
The Big Bang was not an explosion.
The name suggests an explosion: some point that blew up, and everything outside it is now rushing away from it due to the force of the explosion. It’s an analogy that does provide some useful intuition (without Dark Energy, the Universe is expanding because of the left over expansion that started way back when and hasn’t been stopped by gravity), but there are a lot of problems with it. Most notably, galaxies are not in fact flying away from each other! A much more modern way to look at it, and a way that matches the mathematics that physicists and astronomers really use when they work with the model of the expanding Universe, is that galaxies (except for little local motions) are pretty much fixed, but space itself expands. Galaxies get farther apart from each other because, as space expands, there’s more space between them. (Note that the galaxies themselves are not expanding; they are held together by their own forces.) An analogy is rising raisin bread: the bread expands, and the raisins get farther apart, but the raisins aren’t moving through the bread. Another analogy would be pennies pasted on the surface of a balloon.
[Addendum added 2009-08-21: there is some debate in the astronomical community as to whether "galaxies flying apart" or "space expands" is a better qualitative description of the mathematics of the Big Bang. Obviously, I'm in the "space expands" camp. I'll write more about this in a later post.]
The Universe didn’t all start from one point.
Sometimes you will hear people say this. The classical Big Bang model (but see below) has an initial singularity; at that beginning, any two points which are separated by a finite distance now were separated by zero distance. That sure seems like things begin at an initial point. It is, however, much better to say that the initial singularity is a point where our models break down, and that all we can really say is that densities in the extremely early universe, just “after” the “bang”, were extremely high. The problem with thinking of it all starting from a point is that it suggests that there is a center that everything is rushing away from. In fact, however, the Big Bang happened everywhere. If you must think about it as that point, that point has itself expanded to the whole infinite Universe… and we, right here, are within that point, as is a distant galaxy a billion light-years away. In the Big Bang theory, the Universe has no center. Any point is as good as any other, and indeed, an observer looking from any point would see things around her as if she were at the center of the expansion! Which leads me to the T-shirt I want to have made one day. On the front: “Yes, in fact, I am at the center of the Universe!…” ; on the back: “…but so are you.”
We know little or nothing about the moment of “Bang” itself.
This is perhaps the most egregious. The Big Bang theory is tremendously successful, tremendously well supported by observations, yet… the thing that the theory is named after is something that the theory as it exists right now really can’t address. Sad, huh? What the Big Bang theory tells us is that the Universe evolved from a hot and dense state to what we have now. There are various different epochs we have been able to probe using different techniques, and the whole picture hangs together very well using these very different techniques. Right now, we have the expansion of the Universe. At a moment a few hundred thousand years after the “beginning”, we have the cosmic microwave background observed by the WMAP satellite and large numbers of other ground, balloon-borne, and space experiments. A few minutes after the Big Bang, we have the time when the Universe was so hot and dense that nuclear reactions routinely happened, at which the primordial elements were created… in proportions that match what we observe. And, finally, a tiny fraction of a second after the beginning, we have Inflation, which isn’t as well supported as those other bits, but which does explain a lot and even has stood up to one test from recent WMAP results. (Indeed, many people, myself included, are attracted to the notion of calling the end of Inflation “the beginning”, as subtracting that tiny fraction of a second from any later epoch won’t make any difference in the time we quote, and to talk about things before that you need Physics we don’t know how to do.)
All those different epochs, tied together by one expanding Universe theory that started from an extremely hot and dense state, all supported by a vast array of different observations. Pretty cool.
The classical Big Bang– what you get if you just look at the Universe with Einstein’s General Relativity, ignoring Quantum Mechanics– gives a well-defined “beginning”, that time we call t=0 and measure all the other times from. That beginning is the singularity, where things diverge, where densities go infinite. “What caused it” is something we don’t even know how to address (unless you’re a string theorist talking about branes, but that’s a whole nuther issue).
The problem is, the classical Big Bang ignores Quantum Mechanics, which is a bad idea: Quantum Mechanics is another extremely well-supported theory in Physics we know to be right. It’s the theory of the very small (speaking very roughly). At some time a tiny fraction after the moment of the classical Big Bang, the Universe got large enough that it became reasonable to do your Quantum Mechanics (e.g. for the nuclear reactions a few minutes after the beginning) without worrying about gravity, and to do General Relativity (which describes gravity) without worrying about Quantum Mechanics. However, before that moment, you have to worry about both at once. Here’s the rub: the two theories don’t work together. At the moment, we don’t have a working theory that can handle gravity and quantum mechanics at the same time, although the string theorists keep telling us that they’re working on it.
What the previous paragraph says is that our extremely successful physical theories are incapable of predicting what happened during the first tiny time interval after the moment of the classical big bang. Indeed, if you think about it in reverse– start now and go back in time– we reach an early period before which we can say almost nothing. We can go back through the present day expansion, through the epoch when galaxies first formed, through the epoch when the Universe was a plasma and the Cosmic Microwave Background was emitted, through the epoch when the elements formed, through the epoch when quarks and gluons were all mushed about in one big continuous mess, to Inflation… but we can’t go before that.
We don’t know what happened before that. Was there even a “t=0″ beginning? Dunno. Was there really a singularity? Dunno. What happened before Inflation? Dunno. What was the deal with the actual Big Bang itself? Dunno.
Kind of sad that this extremely successful, extremely well-tested theory, a theory so good that we can call it right and true, doesn’t really address the moment it seems to be named after.
That’s why, marketing reasons aside, Big Bang is a terrible name for that theory. But I sure as hell can’t come up with a better name that doesn’t violate all sorts of marketing, so I guess we’re stuck with it.
My message to creationist Christians about faith and science
You can still accept Jesus Christ as your Lord and Savior, while accepting all of the wonderful things that modern science has taught us about our Universe.
I know there are many Christians out there who believe in Biblical inerrancy— that it is the literal word of God, and that each and every word must be literally true. What I want to convince you is that you can take a broader view without losing what is essential about being Christian. You need not abandon your faith in order to accept Evolution or the Big Bang, but you will need to think about it in certain ways.
The wonder and beauty of our Universe is amazing. And, by this, I’m not just referring to the tremendously beautiful images we’ve seen come out of astronomy. Rather, I’m referring to the beauty that is inherent in what all fields of science have discovered. The fact that we can understand how natural processes work, that we can make predictions about them and learn about things that happened millions of years ago, is astonishing. Science is a creative human endeavor, the greatest works of which are on par with Beethoven’s 9th symphony. Indeed, that there are harmonies intrinsically pleasing in music is in fact the result of one of the observations of science— that mathematics is the language that seems to describe the mechanisms of the natural world. Musical pitches come in resonances as a result of the mathematics of wave mechanics. Similarly, the fundamental things about our world that we know to be true are beautiful when understood. That protons, neutrons, and electrons can combine together in ways not just to produce the fascinating and complicated things that we call atoms, but can on larger scales produce elephants and trees and waterfalls, is mind-boggling. What’s even more amazing is that we can understand how all of this works through science, and through science we can come to more deeply appreciate the beauty of our Universe.
There are some things science has taught us that make clear that all of the Bible cannot be read as literal history. Humans as a species evolved from earlier species, as did all other species present on Earth today. The Universe is billions of years old, several times older than the 4.5 billion years that is the age of our Solar System. Evolution and the Big Bang are two of the main things that creationists object to. Yet, they are lynch pins of their scientific fields, biology and astronomy respectively, without which much of the rest of the field doesn’t make sense. Everyday experience— be it modern medicine, or the unmanned spacecraft we’ve sent through the Solar System— indicates that these fields are on to something, for we’ve been able to use them to great effect. It just doesn’t make sense to throw out these lynchpins, and then, by necessity, much of the rest of those fields.
However, just because the Bible cannot all be literally true does not mean that it cannot be true. Before the wedding of a good friend of mine, the Episcopal minister told a parable about Biblical literalism. He said that, suppose after they’ve been married a few years, Mike gets home from work before Margo, and is tremendously moved watching a very beautiful sunset. When Margo comes home, Mike wants to convey this to her. Does he say, “because cross-section for scattering of light is higher at shorter wavelengths, a greater fraction of longer wavelength light was transmitted through the atmosphere, allowing a preferentially red hue to reach the clouds overhead”? No… that doesn’t really convey how he was moved by the sunset. Rather he says, “The sky was on fire!” Does he literally mean that there was a runaway exothermic process of Oxygen combining with other molecules in the sky above? No! And, yet, the latter statement better conveys what he is really trying to say than does the factually true statement.
Jesus himself taught in parables. Humans frequently learn and pass on understanding through stories, and we frequently are able to internalize and relate to lessons when they are taught in the form of stories. As such, there is truth in many of the Bible stories that we know from modern science cannot be literally true. If you think about it, the Bible becomes more interesting, and indeed worthy of greater thought, if you realize that the divinely inspired Word of God need not be a mere dictation of historical events, but rather are stories that we are meant to think about and learn from, and to bring new things to as we come to understand more about our Universe.
You can find some prominent science bloggers who will assert that it is not consistent both to fully accept modern science, and to hold religious faith. They are wrong. Science addresses the mechanisms of the natural world. It is true that in the past, when we didn’t understand the natural world as we do today, we used religion to explain how some things happened. Today, however, science has proven to be the process whereby we can understand how the world works. But science does not provide meaning. This is why I am asking you, if you are a creationist, to please consider that your faith can remain an important part of your life, even if you cast away the need to deny things that humanity knows to be true as a result of the efforts of modern science.
Did God create the Universe in seven 24-hour days? No. Did God create humans in their current form from nothing? No. But neither of these need reduce in any way the role of God the Creator, once we understand that God is ineffable, that God is something that works and exists in a way that humans cannot fully understand. It appears that we can fully understand the workings of nature. We don’t, but every year we know more. Personally, I think it greatly reduces the role of God as Creator to say that his role was simply to will things into existence. That’s such a mechanistic feat. To consider that to be what is meant by God’s Creation undermines the mystery of God. It makes God no more than a video game programmer, who wills into existence the worlds of games by tapping away on a computer keyboard for a while, and then lets them go on their way.
I have to admit that I don’t fully understand myself what I believe to be God’s role as Creator— but then again, why should humans expect to fully understand any aspect of God? God’s Creation is something that is ongoing. It’s not God reaching in and pushing things about here and there, making things happen like a software programmer debugging his code. Rather, God’s Will is a desire for the Universe, a way that would seek to have things become better. Science has given us a view of the Universe that experimentally works, and that view does not include a supernatural entity coming in and deliberately making conscious and directed changes. On the other hand, it’s very clear that there are natural conscious entities making changes all the time— us. And, when those changes are for the better, might they not, at least sometimes, be divinely inspired— whatever that really means? To me, the miracle of God’s Creation is both just the possibility and potential inherent in the Universe that may come to pass as a result of natural means, and the actions of conscious beings when they seek to make the world a better and more beautiful place. Whether God is the “condition of possibility of any entity whatsoever” (to quote Terry Eagleton), or whether it is an integral property of conscious thinking beings, I don’t know, but I do know that God is more than a dude with a flowing white beard who makes stuff sometimes.
In summary, the Universe is an amazing and inspiring place. There is so much elegant beauty in the scientific truths known as Evolution and the Big Bang. There is so much wonder in our world and in our Universe, that it is sad to reject those on the basis of a particular reading of the Bible. You can fully accept God the Father and Jesus the Savior without having to reject these things humans have come to learn about the natural world. I’m asking you to take a broader view of Christianity, to be able to understand the Bible as holding truths that need not always be simplistic literal accounting of events. To seek to further understand the Universe is a wonderful calling. It is not necessary then to hide the light of that understanding under a bushel when it requires us to think more deeply about our faith!
(Afterward: I’m going to be fairly strict moderating the comment thread of this post. I do not want atheists who feel the need to denigrate religion commenting here; this post is not for you. The goal of this post is not to argue in the debate about whether or not it’s OK to be both religious and scientific; I personally consider that issue settled, but will continue to address it in other posts. Rather, the target audience of this post is the religious, and in particular creationists, in an attempt in a small way to show how I see Christianity being able to accept the modern scientific world-view.)
This morning in Second Life : Comets Crashing Into Jupiter
I’ll be giving a public-outreach astronomy talk as part of MICA this morning at 10AM PDT in Second Life entitled “Comets Crashing Into Jupiter”.
A few weeks ago, an amateur astronomer spotted a scar on Jupiter, which was later confirmed to be the result of an impact of a comet fragment with the giant planet. This is not the first time we’ve observed comets smacking into Jupiter; in 1994, comet Shoemaker-Levy 9 collided with Jupiter after having been torn into several fragmets by an earlier pass with the planet, leaving scars on Jupiter over the course of a week. In this talk, I’ll describe the gravitational interactions that lead to these comet collisions, as well as what we may be able to learn about Jupiter as a result of these collisions.
To keep track of what popular talks are upcoming in MICA, see our Upcoming Public Events Page.
Creationism is not like belief in the virgin birth or the bodily resurrection of Christ
There are some out there who assert that a belief in God is not compatible with accepting science. Some try to put a finer point on it; they assert that belief in either the virgin birth of Christ, or the bodily resurrection of Christ, is not compatible with science. I want to argue that it is.
First, I do not mean to assert that I personally believe in either. I have addressed the latter (bodily resurrection) in a blog post several years ago that is currently offline as a result of a dead disk. I’ll dig up the text of that and repost it here at some point. Short form: my answer to “did the bodily resurrection physically happen?” is “probably not.” Believe it or not, I am not alone among Christians in thinking that. However, it is reasonable to hold that belief while accepting science, without any need for hypocracy. It’s not consistent with “philosophical materialism”, no, but that’s a question of philosophy, not of science.
Some say that the scientific world view is not consistent with miracles. The reason is that the hypothesis that supernatural intervention happens has not stood up to scrutiny. There is no scientific evidence for it, and in the centuries in which we’ve been doing science, if it was happening we would have seen the evidence for it. What’s more, many things that were previously believed to be the fiat of God have come to have naturalistic explanations (e.g. the ignition of the Sun, the origin of the human species). So, science would seem to rule out miracles.
In fact, it does not, and any scientist who is being careful enough, and precise enough in his language, will say that. Science certainly gives no reason to believe in supernatural intervention! And, it gives many reasons to believe that supernatural intervention is an obsolete concept. However, as with many things that we do not detect in a scientific experiment or an observational program, science doesn’t rule out miracles; it merely sets an upper limit on their frequency. In other words, miracles (in the form of supernatural intervention) must happen extremely infrequently and irregularly to be consistent with the body of scientific observations.
Consider creationism. Creationism makes factual claims about the creation of the Universe (created in 7 24-hour days a few thousand years ago, with a specific order of events) and about the origin of the human species (created in its current form by God). These factual claims are false; we know them to be false, because we have extensive scientific evidence that points to other explanations. Creationism is wrong, and belief in creationism is not consistent with accepting modern science.
On the other hand, consider the bodily resurrection of Christ. Now, we know that biological organisms that have died and stayed dead for three days decay enough that they cannot be revived. (It may well be that one day we will revive some of the cryogenically frozen people we have right now, but I think we can all agree that Jesus was not cryogenically frozen.) However, the bodily resurrection of Christ is a singular event. To believe in it is to claim that once, one guy, was bodily resurrected. (Let’s leave Lazarus out of this for simplicity.) Believing in the bodily resurrection of Christ does not claim that this happens regularly. What’s more, this belief does not make any claims that contradict any scientific evidence we have. It says that once, there was a miracle, and something that cannot happen according to our understanding of biology, did happen.
Could this be disproved? Probably not. I seriously doubt that if we found the remains of Jesus that we would be able to convince ourselves to any reasonable probability that that is what they were. Likewise, with the virgin birth, if we were to somehow find the remains of Jesus, Mary, and Joseph, perhaps we could do DNA comparisons to find out of in fact Jesus is carrying Joseph’s DNA. (Interesting theoloigcal aside: he’d better be if he’s of the house of David, but then again, I’m not writing about inconsistency in the Bible… inconsistency in the Bible is well established.) But, again, this has not been done, and indeed I would be very surprised if we were able to collect the samples (or, invent the time travel) that would allow us to do that test.
Science tells us that miracles really cannot be happening very often at all. But it sets an upper limit, it does not tell us that miracles never happened. The methodology of science requires us to omit miracles in our explanations; something we cannot explain through naturalistic means remains an open question, at least for the time being, to science. Science tells us that the creation story in Genesis is not history, but it does not tell us anything directly about the specific bodily resurrection of Christ or the specific virgin birth of Christ. Science does not have a mechanism for it, so if it happened, it was miraculous, and outside science as we understand it. Science gives no reason to believe in miracles, and indeed convinces us that they are not happening with any regularity at all. However, because we cannot absolutely rule them out, it is not inconsistent to believe that those specific miracles happened, while accepting the results and methodology of modern science.
How much Dark Matter do you hold in your hands?
Via a Cosmic Variance blog post, I found this astro-ph paper by Catena and Ulio that claims the local density of Dark Matter is 0.39 GeV/cm3.
What does this mean?
Well, first, you may object that GeV is a unit of energy, so really what we’ve got here is an energy density of Dark Matter, not what most of us mean when we say “density” all by itself (which is mass density). Physicists, however, know that converting between energy and mass is so easy (via E=mc2) that they will very often, especially when talking about fundamental particles, cite masses in energy units. Divide by the speed of light squared to figure out that this is a density of 6.9×10-25 grams per cubic centimeter.
Second, “local” means “in our area of the Galaxy”. Dark Matter clumps on scales of hundreds of light-years, at the smallest, so if you’re looking on a scale smaller than that, it’s going to look smooth. It’s similar to our atmosphere; if you climb a mountain and get five miles above sea level, the air will be noticably thinner. But, if you go up just a few meters, you’re not going to notice any difference in the density of air.
What is the density of air? Well, if you believe Wikipedia’s Answer (and you should in this case), it’s about 0.075 lbm/ft3… or, in more reasonable units, 0.0012 grams per cubic centimeter. (That’s at room temperature and standard sea level pressure.)
And, while we’re at it: the density of Dark Energy in the Universe is about 75% of the critical density, the critical density being 3H02/8πG, or 9.7×10-30 grams per cubic centimeter (for a Hubble constant of 72 km/s/Mpc).
So let’s put this all together. Cup your hands. That makes a box roughly 5cm on a side, or 125 cubic centimeters in size. In your hands, you are holding:
- 0.15 grams of air
- 8.7×10-23 grams of Dark Matter
- 9.1×10-28 grams equivalent of Dark Energy
Strictly speaking, “holding” isn’t the right term, because the Dark Matter particles are passing right through your hands as if they weren’t there… but at any one moment, that’s how much Dark Matter is on average within the box you make by cupping your hands. (Air is coming in and out as well, because you probably have cracks in the box you make, but it doesn’t pass through your hands.) And, it’s hard to say whether Dark Energy is passing through your hands, or is a property of the vacuum and as such it is just how much energy density is there as a result of the volume you’ve cupped, but you get my drift.
Oh, and I suppose I should mention that every second, about 140 million neutrinos from the Sun pass through your cupped hands (based on the neutrino flux cited at this page from HyperPhysics). However, they’re going so bloody fast (very close to the speed of light) that at any moment, there’s only about a 2% chance that one of those neutrinos is right then within your hands. (A similar consideration is probably true with Dark Matter particles, but I’d need to know the mass of said Dark Matter particles (nobody does), and I’d need to know their velocity (there are estimates, but I haven’t tracked them down) to actually give you numbers.)