Category Archives: Science Education & Outreach

The Big Bang Wasn’t All At One Point (Cosmos Commentary)

I finally got around to watching the first episode of Cosmos. I quite enjoyed it, although probably not as much as I would have were I still 9 (which is the age I was back when I used to watch Carl Sagan doing Cosmos… and that, indeed, is probably a nontrivial part of why I’m an astronomer today rather than a paleontologist). I think it’s awesome that once again we’ve got a very charismatic astronomer on TV sharing the wonders of the Universe with us. Alas, I doubt it will have anywhere near the cultural impact that the original Cosmos did, simply because there is so much more out there to pay attention to now. (Not only is there more out there to pay attention to, but over time American society has become more and more ADHD.) Back in the late 1970s, there was little more than three networks of TV to choose from; it was the rare household that had cable. Now, most people have many more options for TV, never mind the ability to download stuff off the Internet on demand. Even if it’s just as high-quality, just as cool, and just as engaging as the old Cosmos was, I fear that the new Cosmos will not be noticed by as large a fraction of the population, and will be more quickly forgotten as people move on to the next shiny thing.

As for the show itself: it all seemed pretty basic to me, but then again, I’m a PhD physicist and professional astronomer who does a fair amount of astronomy outreach, so I was not the primary target audience. I liked the homage to the old show– not just the explicit one at the end (which brought a tear to my eye), but the “we are starstuff” comment, and the Ship of the Imagination (which, as Tyson points out, allows you to travel much faster the speed of light, something I’m doing all the time when I teach astronomy classes).

I did have a couple of quibbles, though. My first was when he was flying through the Solar System’s asteroid belt. The asteroid belt was thick with rocks, creating a massive hazard. The real asteroid belt is not like that. There is less mass, total, of asteroids, than there is in any single planet, and they’re spread out over a huge area in the disk of the solar system. This is why we can fly spacecraft through the asteroid belt without worrying about weaving and dodging. There, asteroids just aren’t that thick.

What, is this Cosmos, or The Empire Strikes Back?

To be fair, when he was out in the Oort cloud, although yet again they were shown too thick (I know, for purposes of actually being able to see something), he did mention that the Oort cloud objects are typically as far apart as Earth is from Saturn. Still, the visual image will stick with people more than the words.

My primary quibble with the show, though, is the title of this post. One sentence of what he said promulgated one of the primary misconceptions about the nature of the Big Bang. “Our entire universe emerged form a point smaller than single atom.” GAH! No! Indeed, Tyson was (perhaps deliberately) cagey about the difference between our Universe and our Observable Universe. He did use the term “Observable Universe”, with a good description. (It’s as far away as we can see, a horizon defined by the speed of light and the 13.8-billion-year-old age of the Universe.) However, thereafter, he seemed to be conflating the Universe with the Observable Universe. While there are some good reasons why one might do this, the way in which he did it fed into a very common misconception about the Big Bang.

Even though our observable universe is finite, the whole universe is much bigger– indeed, perhaps (probably?) infinite.

Here’s the real story, given the Big Bang model as we best understand and use it in astronomy: the Big Bang didn’t happen all at one point. Rather, the Big Bang happened everywhere. The problem with describing it as happening at one point is that it gives you the misconception that we could identify a point in space away from which everything is rushing. This is not the description of our Universe that shows up in modern cosmological models. Every point in the Universe is equivalently the center. Any point in space you can identify: that is where the Big Bang happened. Everything is rushing away from everything else. It’s really not like an explosion, where there’s a center everything rushes away from. (I wrote about this years ago in my blog post “Big Bang”: A terrible name for a great theory.)

Strictly speaking, it is true that our observable universe was once upon a time compressed into a size smaller than the size of an atom. However, saying that by itself implies a misconception: that that compressed, less-than-an-atom size of extremely dense, extremely exotic matter is all there was. In fact, that’s not right. Our Observable Universe was that small… but just as today there is other Universe (filled with galaxies) outside the boundaries of our Observable Universe, at that early epoch there was more extremely exotic dense-matter Universe outside the atom-sized ball that would one day expand and become today’s Observable Universe. Indeed, if the Universe today is infinite, it was always infinite… even back at that early epoch we’re talking about.

The Observable Universe (or a 2d projection thereof) at a period a tiny fraction of a second later than what I’m talking about in the text.
The whole Universe (or a 2d projection thereof) at the same epoch.

This may seem like a minor quibble, but the notion of the Big Bang as an explosion, something everything is rushing away from, is a very tenacious misconception that leads to other misconceptions about our Universe amongst many people I run into. It’s a little difficult to wrap your head around the real model– indeed, people find talks about cosmology that try to describe the real situation (and also the cosmology section of my current ongoing astronomy class) very brain-hurty. But, to my point of view, that’s part of the fun!

There was one throwaway comment about the Big Bang that Tyson made in Cosmos that I really liked. Just before the comment about the atom-sized Universe that got me worked up to make this post, he said about this early Big Bang epoch that “It’s as far back as we can see in time… for now.” That “for now” is great, and spot on. If you read A Brief History of Time by Stephen Hawking, he’ll talk about how the Big Bang was the beginning of time, and how it’s not even really meaningful to ask what was “before” the Big Bang. While that’s true in a purely classical General Relativity description of the Big Bang, we know that such a description can’t be right… because our Universe also has Quantum Mechanics in it, and we have huge amounts of experimental evidence telling us that we need to take Quantum Mechanics seriously. The real story is that there is an extremely early epoch in the Universe (what I tend to think of as “the beginning” nowadays) about which we can make supportable statements based on our understanding of physics. However, we also know that we don’t understand physics well enough to really know what the Universe was like before that early epoch. So, it is meaningful to talk about a before, it’s just that that before is a “known unknown”.

For now.

The Higgs Boson: a talk in Second Life tomorrow morning (April 6)

It’s been a year since I’ve given a public outreach physics and astronomy talk in Second Life. I used to do these things fairly regularly as a part of MICA (the Meta-Institute of Computational Astronomy). However, the MICA project has completed, its island in Second Life has gone online, its Second Life groups have been disbanded, and MICA no longer really exists. (Its website is still up, and should stay up for at least a little while. If I were smart, I’d probably make sure to download and archive elsewhere all of the audio recordings of my own talks….) A write-up of what MICA did and was all about is available at, and was published in the conference proceedings of a SLActions conference on virtual worlds

I’ve always meant to find other venues for continuing to do popular talks in virtual worlds. Someday, I’d like to escape from Second Life’s walled garden and start doing these talks in an OpenSim grid, and even did the first steps for trying to get set up to do them in my own region on OSGrid. However, of course, the audience in Second Life for now is still far bigger.

Fortunately, the Exploratorium, the excellent science museum in San Francisco, has a presence in Second Life. This Saturday (tomorrow, 2013 April 6) at 10AM pacific time (17:00 UT) I’ll be giving a talk about the Higgs boson in the Exploratorium region in Second Life. Remember, basic Second Life accounts are free. Drop by if you’re interested.

Image of a Thermomnuclear Supernova Progentior

Holy cow, it’s been a long time since I blogged.

The class I’m teaching right now is 3d Computer Modelling and Animation. Perhaps the hardest thing about it is figuring out if the word Modelling has one or two l’s in it… it depends on whether you’re in the USA or Canada, I think.

For this class, I’m making all of the students do a major project. Some of them are doing some pretty interesting things, and already several of them have figured out things about Blender (the 3D software we’re using, a quite powerful free package that you should check out yourself) that I don’t know myself. A couple are playing around with motion tracking, in order to add 3D rendered elements into a live action video scene. One is building a game using the Blender game engine. Others are doing various other animations.

I’ve decided to take on a project myself. For this project, I am going to model a white dwarf in a mutual orbit with a main sequence or red giant star, pulling matter off of it into an accretion disk. During the animation, the white dwarf will go critical, and explode in a supernova, blowing itself way, and blowing off some of the outer layers of the companion star.

So far, I’ve managed to create the basic progenitor model, and do a little bit of animation of the textures so that the disk is spinning, the star’s surface is roiling, and the gas bridge between the star and the disk looks a little like it’s streaming. Here’s a rendered frame from what I’ve done so far:

Click to embiggen (CC-BY-3.0)

I’ll certainly post the full animation once I’ve completed it. Next, I’m going to have to start worrying about how to deal with the supernova. Eventually, I’ll set the whole thing to music.

A muddled article on Relativity in the Oberlin alumni magazine

My wife graduated from from Oberlin college in 1992, and as such she gets the Oberlin alumni magazine. The summer 2012 issue includes a one-page article entitled “The Entirety of Relativity”, which I find to be a very unfortunate presentation of Relativity. (As a pedantic point, it’s only talking about Special Relativity (SR), and doesn’t address General Relativity (GR) at all, but that really is a pedantic point. When a physicist says “Relativity”, she likely means GR (especially given that SR is a subset of GR, so nothing is lost), but when presented publicly we often use “Relativity” as a shorthand for SR.)

The basic problem with the article is that it presents the theory as if its nature were the way that SR has been taught to students for a long time. The article starts with three things that are correct as far as they go: moving clocks run slow, a moving rod is short, and moving clocks aren’t synchronized. Where the article loses me, however, is on point number 4, “That’s All There Is To It.”.The brief text after this says that the first three points are the basis of relativity, and the rest of the article claims that all of SR is a consequence of these three points. This is at the very least a perverse way of describing the theory.

A lot of texts at both the high school and college level present Relativity by first presenting these three points. You’re given formulae for each of these consequences; parts of them resemble each other, but they’re each presented as if they were a fundamental formula that couldn’t be derived from anything else, for you to memorize (or, in a more modern way of thinking about it, look up) and use. However, this is a back-assward way of presenting SR, and I would argue that stating that the rest of SR is a consequence of these three observations is not just back-assward, but in fact wrong.

In fact, these three points are themselves consequences of the theory of Relativity. The formulae for them can be derived from more fundamental considerations. They’re no more fundamental than all of the various kinematic formulae you memorize or look up (such as da2) when you do a non-calculus Newtonian mechanics class; those kinematic formulae themselves are just results of the definition of velocity and acceleration as, respectively, the rate of change of position and the rate of change of velocity, together with Calculus. Those definitions are the fundamental thing, not all the various kinematic equations you learn to use if you take a non-Calculus physics class. I could start with da2, take a couple of derivatives, and say, “hey, acceleration is the rate-of-change of the rate-of-change of position, and that’s a consequence of this kinematic equation”. That would be back-assward and indeed wrong, and it’s just as wrong to say that everything else in Relativity is a consequence of moving clocks running slow, separated moving clocks not being synchronized, and moving rods being short.

Special Relativity itself starts with just two very simple postulates— “simple” in the sense of “not complex”, not in the sense of “easy to understand”. Those postulates are:

  • The laws of physics are the same for every freely-falling observer
  • The speed of light is one of those laws of physics; every freely-falling observer will measure the speed of light in a vacuum to be 2.998×108 meters per second.

Everything else in SR— including moving clocks running slowly, separated moving clocks not being synchronized, and moving rods being short, as well as other things (such as the Doppler shift, focusing of light emitted by a moving object in the direction of motion, an apparent rotation of a moving object) are consequences of these two postulates.

I should note that both of these postulates do require more explanation to be truly precise. For the first postulate, you have to carefully define “freely-falling observer”. You get it basically right if there are no net external forces other than gravity acting on that observer. (However, if you allow gravity to be around, things can get a little subtly complicated. It doesn’t ruin the postulates, but you have to be careful in treating the consequences.) For the second postulate, in fact it’s not the speed of light that’s absolute, it’s the speed of any object that both carries energy and is massless. Light just happens to be the thing that we think about the most that works like this, and thus we call the cosmic speed limit “the speed of light”, even though we really ought to call it “the speed of spacetime” (at least in the context of Relativity).

One of the most interesting consequences of these two postulates it that you have to change the way you think about time. Most of us live our lives with a Galilean/Newtonian view of time: it’s an absolute, that advances at the same rate and is the same for everybody. However, you can’t maintain that idea and have the speed of the same bit of light be measured at the same rate by everybody regardless of how they’re moving. Galileo and Newton would say that the latter is wrong; Einstein’s postulate, from which all of Relativity springs, was that in fact it’s this speed of massless objects that is absolute, and as such we just have to give up on the idea of absolute time. Some of the consequences of this are that separated moving clocks aren’t synchronized and moving clocks run slow… as well as other things.

I’m fond of the way that Thomas Moore’s Six Ideas That Shaped Physics presents Special Relativity. (This is the book series that I currently use when teaching introductory calculus-based physics.) His Book R of the series is written for college-level physics who have had Calculus (and indeed have had some Calculus-based Newtonian physics). It presents SR not in the old-fashioned and unfortunate pedagogical way that the Oberlin article does— by starting with the consequences such as time dilation and with their formulae, and only later getting to the fundamental structure of spacetime implied by Einsteins postulates— but rather by starting with the fundamental structure of spacetime implied by Einstein’s postulates, and then developing the consequences out of that

Yes, it’s easier to just learn the formulae and do calculations about time dilation and so forth, and presents fewer difficult abstract conceptual challenges to students coming across this for the first time. However, if you learn it this way, you’re given a warped perspective of what the theory of Special Relativity really is. My beef with this Oberlin alumni article is that it presents Relativity as if the theory itself is based and structured in the way that it has often been taught.

In Which I Compare the Slashdot Commentariat to the 17th-Century Catholic Church

I am regularly struck, when giving public outreach talks, or when hearing the topic of Dark Matter discussed amongst the general non-Astronomer public, at the separation between acceptance of Dark Matter between astronomers and the general (informed) public. (The general public at large probably doesn’t have enough of a clue about Dark Matter even to have a wrong opinion, alas!) Most astronomers know the evidence, and accept that non-baryonic dark matter is a real component of our Universe. Many in the public, however, seem to view Dark Matter as a horrible kludge, an ex-rectum fudge factor that astronomers have invoked in order to explain discrepancies between observation and theory. Indeed, topics related to this will be the subject of my upcoming August 16 365 Days of Astronomy podcast.

For a popular level discourse on the evidence for dark matter, I shall point you to two sources:

And now I can get to the snarky bits of this post. Yesterday, on Slashdot there showed up a post entitled CERN Physicists Says Dark Matter May Be An Illusion. In the paper indirectly referenced by the Slashdot article, a theoretical physicists explores the idea of negative gravitationally charged antimatter and the polarization of the vacuum as an explanation for the rotation speeds of galaxies (the mainstream explanation for which is, yes, Dark Matter).

What’s interesting is the tone of the Slashdot comments. Some are informative, and ask exactly what I ask: what about the Bullet Cluster? However, a fair number of the comments show the same tenor as these excerpts:

I hope so. Dark matter is the ugliest kludge to the standard model ever.

Agreed. I have always had a hard time stomaching the theory that dark matter and dark energy exist. It seems far too much like aether, i.e. something made up to fill a gap in knowledge without much evidence backing it up.

Yay for phlogiston [] and aether []. Dark matter might end up on the list of ideas that physcists turned to in order to explain things that had other explanations. La plus ca change

Dark matter, too, has never been observed, and possesses properties of matter previous unseen or indeed thought impossible, and exists solely to bridge a gap between our model of how things should behave, and how things actually behave. This does not bode well for it.

There is a strong general sense among a large (majority? hard to tell) subset of the Slashdot commentariat that astronomers are all on the wrong track and propping up a failing theory, and that dark matter is a kludge that just can’t be right.

The thing is, they’re wrong. They just know that Dark Matter can’t be real, because they are not comfortable with the idea that a substantial fraction of the Universe is made up with stuff that we can’t see, that doesn’t even interact with light. Much as… the 17th century Catholic church just knew that Galileo (and others) were wrong about Heliocentrism, because it’s obvious to everyday observation that the Earth is still and the Sun is going around it. (Also, the Bible says so.) And, just as the leaders of the Catholic church completely discounted (and indeed refused to look at) Galileo’s observation of Jupiter’s moons orbiting Jupiter (and, crucially, not the Earth), armchair pundits completely ignore (probably mostly through ignorance!) the wide range of evidence for Dark Matter that goes beyond the “accounting error” represented by the motion of stars in galaxies, and galaxies in galaxy clusters. (Those motions are indeed one part of the evidence for Dark Matter, and historically formed the first evidence for it, but they’re far from all of the evidence nowadays.) They cling to notions of how science ought to work, and how the Universe ought to be made up in a familiar way that seems natural to us humans, and use this to assert that an entire field full of scientists must all be on the wrong track for having a different model.

Specifically with regard to comparisons to the luminiferous aether, I would point you to my June 2010 podcast: “Dark Matter: Not Like the Luminiferous Ether”. (And, yes, I’m conscious that I’ve spelled aether two different ways in this paragraph!)

Indeed, I would say that the comparison between denial of Dark Matter and denial of Heliocentrism goes deeper than that. The Copernican Principle is that the Sun, not the Earth, is at the center of… well, today we would say the Solar System, but in Copernicus’ day that was also what was thought to be the whole Universe (the stars not at the time being understood to be things like the Sun). An extension of this is the Cosmological Principle, which stated succinctly says “you are nowhere special”. We’re not at a special center of the Universe, we’re just at a typical random place in the Universe pretty much like any other. Observations (of galaxy distributions, of the Cosmic Microwave Background, and so forth) bear up this assumption or postulate, which is why we call it a principle. Think about it in broader terms, though. We are made up of “baryonic matter”, which is Physicist for “stuff made of protons, neutrons, and electrons”. In light of the Cosmological Principle, however, why should we expect that most of the Universe is made up of the same general kind of stuff as we are? In the face of evidence otherwise, many still insist that most of the Universe must be made up of baryonic stuff that interacts with other baryons and our familiar photons. Is this not just as much hubris as insisting that the Earth, where we live, must be the center about which all the other Solar System bodies orbit?

“Galaxies in Collision” : public online talk today at 10:00AM PDT

As of this writing, in just over an hour I’ll be giving a talk in Second Life on the topic “Galaxies in Collision”.

Second Life is an online virtual world. Basic accounts in Second Life are free. I regularly give these talks as a part of MICA, the Meta-Institution of Computational Astronomy. Most Saturday mornings at 10AM pacific time (17:00 UT if we’re during Daylight Savings), MICA has a public outreach astronomy talk. (However, like many academic institutions, we tend to slow down and get spotty over the summer.)

This talk will be at the MICA Large Amphitheater.

“More Things in Heaven and Earth” — the interaction of physics and astronomy

365 Days of Astronomy is a daily podcast about astronomy, entirely recorded by volunteers. The topics are all over the place; some are about amateur astronomy, some are about the history of astronomy, some are about recent discoveries in astronomy. I’ve done a number of these over the last couple of years, and am doing more this year.

I recorded today’s podcast— and, if I am to be perfectly honest, I have to admit I recorded yesterday, way after when I was supposed to get it in. The topic is the interaction between fundamental physics and astronomy. I talk a little about ancient physics, where the realm outside the sky and the Earth were viewed to be separate realms. Newton’s universal gravitation unified those two realms. Some chemical elements were discovered originally in astronomical objects, and it was from observations of astronomical objects that we learned about neutrino oscillations.

You can check out today’s entry if you want to hear more.

Online talk tomorrow morning : “Neutrino: Placeholder Particle”

I’ll be giving a talk in Second Life tomorrow morning at 10AM pacific time. (That’s Saturday, Feb 5, at 18:00 UT.) This is part of a regular talk series; follow that link to find the slides and audio recordings from most of the previous talks I’ve given in the series. Remember that a Second Life account is free! Come and hear the talk. You can also ask questions in text chat, which I generally try to respond to as the talk is ongoing.

Tomorrow’s talk is entitled “Neutrino: Placeholder Particle”. I’ll talk about the history of the discovery of the neutrino. Even Pauli, the guy who proposed the neutrino, was uncomfortable with making up a new particle that nobody had seen to explain things that seemed to be missing from other observations. There are clear parallels to Dark Matter today, with many being uncomfortable that we’ve got most of the Universe made out of stuff that we can’t identify. I’ll also talk about our current state of knowledge of the neutrino, and I hope to get into the issue of how the “mass neutrinos” are not the same as the “flavor neutrinos”, and even though there are three of each, there are still only three total neutrinos. (It’s a Schrödingers Cat sort of thing.)

Here’s the abstract I sent to Paradox Olbers, the organizer of the MICA talks:

Sometimes critics of nonbaryonic dark matter will characterize it as a “placeholder particle”– the name we give to the fact that we can’t find particles doing the things that we see happening gravitationally. Of course, dark matter is not new in astronomy; Uranus, for instance, was originally detected indirectly. Nor are palceholder particles new in particle physics. The neutrino was originally proposed more than 20 years before it was first observed. In this talk, I’ll go over the history of our discovery of the neutrino, and how it was in fact astronomy that led to some relatively recent important discoveries about these elusive little particles.

One-Slide Explanation of Tides

I realize that this Bill O’Reilly quote is two weeks old, which in Internet time is a substantial fraction of the age of the Universe. And, the Internet being what it is, a top conservative commentator can’t say something this butt-ignorant without having bloggers jump all over him within seconds. So, yes, I realize that I’m way, way behind the times, sort of like somebody getting all snarky to the dinosaurs because they didn’t invest in programs tracking near-Earth asteroids. But, still, I think it bears repeating, to remind ourselves collectively the kind of people who are shaping the agenda of an entire political party in the USA right now.

Here’s my one-slide explanation of how the tides work:

Click image for larger version

This slide does go along with some speaking, normally. Indeed, it is one (of 28) slides that I’ll be using in the talk I’m giving in Second Life in about half an hour, all about interacting galaxies and whether or not they’re connected to the phenomenon of active galactic nuclei. (Really, tides are relevant to this story!)

Online talk tomorrow morning: “Observational Evidence for Black Holes”

Tomorrow morning, I’ll be giving a public lecture entitled Observational Evidence for Black Holes. This is part of a regular series of talks sponsored by MICA, Saturday mornings at 10:00 AM pacific time (1:00 PM Eastern, 18:00 UT). They’re open to anybody.

These talks are in Second Life. A basic Second Life account— everything you need to attend the talk— is free. Go to the Second Life page I just linked in order to sign up. Once you’ve downloaded the Second Life viewer, and have created an account and logged in to Second Life, you can follow the link on our Upcoming Public Events page to find the talk.

Here’s my blurb for tomorrow’s talk:

Black holes are a theoretical prediction of Einstein’s Relativity. But do they really exist? The answer is a nuanced “yes.” We have observational evidence for two sorts of black holes. In our Galaxy, we observe black holes that are several times the mass of the Sun. At the core of almost every big Galaxy, we find a supermassive black hole that’s a million or more times the mass of the Sun. In this talk, I’ll give an overview of the evidence that these objects are in fact black holes. I’ll also point out that the observational definition of “black hole”, meaning those things that we know exist, isn’t exactly the same as the definition of the objects predicted by Relativity, although most astronomers suspect and assume that what we observe are in fact the things that Relativity predicts.