Archive for the 'Physics & Astronomy' category

The Minimum Size of the Whole Universe

The Observable Universe

When we talk about our Universe, we make a distinction between "the Universe" and "the Observable Universe". The latter includes only what we can see. By "can see", I don't mean what we have the technology to detect. Rather, I mean all objects out there from which light has had time to reach us given the age of the Universe, the speed of light, and the history and future of the expansion of the Universe. The age of the Unvierse is 13.8 billion years. Because the speed of light is finite, we can't see anything that is so far away that light would have taken longer than that from us to reach us. This isn't a technological limitation; this is a limitation on whether or not there is light, even in principle, for us to see given as much technological prowess as you could want.

Indeed, as we look towards the edge of the Observable Universe, we're looking back in time. If light took us 13.7 billion years to reach us, then we're seeing the Universe out there as it was 13.7 billion years ago, not as it is now.

The Universe as a whole, however, is probably infinite. This is easy enough to say, but it's a rather difficult concept to wrap your brain around when you really start thinking about it. One solution is not to think too hard about it. If you find yourself asking questions like "if it's already infinite, how can it expand?", you're not thinking properly about infinity. Infinity is a concept, not a number.

However, the Universe doesn't have to be infinite. According to General Relativity, there are other possibilities. I'm going to lump those possibilities into two categories, but only really talk about the latter.

Interesting Topologies

It's possible that our Universe has an interesting topology. Topology is different from geometry. Geometry includes things like lengths of lines, radii of curvature, sums of angles inside polygons, and so forth. Topology talks about how different parts of space are connected.

As an example, consider the classic video game asteroids:

[Asteroids!]

This game takes place in a (very small) two-dimensional universe. The geometry of the Asteroids Universe is Euclidean— that is, parallel lines will never cross, the ratio of the circumference to the diameter of a circle is π, the sum of the three interior angles of a triangle is 180°, and so forth. However, if you ever played this game, you know that if you go off of the left of the screen, you come back on the right side of the screen. Likewise, if you go off of the top of the screen, you come back on the top. This universe is unbounded; you never hit a boundary, or an edge. However, it is also finite. Its topology is toroidal; it has the same topology as the surface doughnut, although it does not have the same geometry of a doughnut. (The surface of a doughnut has curvature.)

It's possible that our Universe is similar. It may have a flat geometry, but a topology that means that if you kept going in one direction, you came back where you started. If it does have this topology, it's on spatial scales larger than the Observable Universe. Otherwise, we would have seen the signature of this topology (i.e., the fact that parts of space are effectively repeats of each other if you keep going far enough in one direction) on the Cosmic Microwave Background.

For the rest of this post, I shall assume that the Universe does not have any interesting topologies like this. Either it's just infinite space, or it's finite space that is the 3d equivalent of the surface of a sphere.

Possible Geometries of the Universe

The geometry of our Universe doesn't have to be Euclidean. Depending on the total energy density (including the density of regular matter, dark matter, and dark energy), there are three possibilities for the curvature of our Universe.

[Possible Shapes of the Universe
Two-dimensional visualizations of the possible shape of the Universe. Our Universe would be the three-dimensional equivalent of one of these, depending on the total energy density of the Universe.

The parameter Ω is a convenient way of talking about the density of the Universe. There is a critical density, which depends on the current expansion rate of the Universe. That critical density is about 9×10-30 g/cm. That doesn't sound like a lot, but remember that the Universe is mostly empty space! Where we live, on Earth, is an extremely high-density place compared to most of the Universe. The parameter Ω is defined as the ratio of the density of the Universe to the critical density. If Ω=1, then the Universe has a flat geometry. Note that "flat" here doesn't mean "two-dimensional", the way you may used to be talking about flat. Rather, it means that the geometry of space is Euclidean, just like the geometry you probably learned about in high school.

On the other hand, if Ω>1, the Universe has a "closed" geometry. In this case, the geometry of the Universe is the same as the three-dimensional surface of a four-dimensional hypersphere. If that sounds like gobbledygook, think of it as the 3d equivalent to the surface of a sphere. Note that there doesn't need to really be a fourth spatial dimension or a 4d hypersphere out there. It's just that the geometry of the Universe— how parallel lines will behave when extended, how the angles of triangles will add up, what the ratio of the circumference to the diameter of a circle will be— is the same as the geometry of the surface of a sphere. It's possible to describe the mathematics of this geometry entirely using only three spatial dimensions, so there's no need for a higher spatial dimension in which to embed our Universe. However, for purposes of our visualization, it's worth thinking about the surface of a sphere, as that helps us get some idea about what sorts of things would be true in such a universe. The surface of a sphere is a two-dimensional closed universe. Remember, that the universe is the surface. There is no center to this universe, not within the universe— for everything within the universe is on the surface of the sphere, and no point there is any different from any other point.

If Ω<1, the Universe has an "open" geometry. This is harder to visualize. It turns out that you can't embed a slice of an open 3d universe into three dimensions to visualize it, the way you can with a closed universe (in which case you get the surface of a sphere, as described above). However, the closest two-dimensional equivalent would be a saddle or a potato chip (each of which is a hyperboloid or hyperbolic paraboloid). This is an unbounded and infinite universe. It keeps on going forever. However, it's also clearly not flat, and so will have an interesting geomoetry.

The Geometry of Our Universe

You can figure out the geometry of your universe several ways. One way is to create a triangle by drawing three straight lines through space. Then, measure the angle between each of those pairs of lines. If the three interior angles add up to 180°, you're in a flat universe. If they're more than 180°, then you're in a closed universe; if they're less than 180°, you're in an open universe. The problem is the precision needed for this measurement. In order to be able to tell whether or not the angles add up to 180°, you either need to measure them mind-bogglingly precisely, or you need to draw huge triangles, such that the length of one side of the triangle approaches the radius of curvature of your universe. (How close it approaches it depends on how precisely you can measure angles.)

Effectively, we have done this. Measurements of the Cosmic Microwave Background (CMB) give us triangles. One leg of the triangle is given by the characteristic size of fluctuations in the CMB. We know the physical size of those fluctuations. The other legs of the triangle are given by the path of light travelling from either side of one of those fluctuations. By measuring the angle between the light coming from either side of a fluctuation, we can figure out what the geometry of this isosceles triangle is. We did this. The answer: our Universe is flat. However, as with all physical measurements, there is uncertainty on this measurement. The latest form of this measurement tells us that Ω must be between 0.9916 and 1.0133, to 95% confidence (see "Reference" at the end for the source of these numbers). That means that there still is the possibility that our Universe is either infinite (in the case of Ω≤1) or finite (in the case of Ω>1).

The Minimum Size of Our Universe

The Universe is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to the Universe.

With all due apologies to Douglas Adams, let's quantify how big our Universe is.

First, the age of the Universe is 13.8 billion years. That is a long time compared to you and I, but as compared to the age of the Universe, it's just about right. The edge of the observable Universe, right now, is 48 billion light-years away. "Wait!" you may cry. "How can light from something 48 billion light-years away have reached us in a mere 13.8 billion years!" Remember that while that light was working its way towards us, the Universe was expanding. The light, in a sense, had to try to "catch up" with that expansion. This is imperfect language, and indeed if you know Special Relativity you should object to it. However, it does (sort of) make sense in the context of General Relativity.

How does this size compare to the size of the Universe as a whole? If we make the assumption that Ω=1.0133— the highest total energy density consistent with our current data, and thus the smallest closed universe consistent with our data— it's possible to calculate how big the Universe is. The result looks something like the following:

[Observable Universe in the Minimum Total Universe]
Click for a bigger version

In this picture, the surface of the sphere is meant to represent the whole Ω=1.0133 Universe. The parts that are "greyed out" are outside our Observable Universe; the patch at the top that you fully see is the Observable Universe. The radius of curvature of this universe is 120 billion light years. Its circumference is 760 billion light years. That means that the diameter of our Observable Universe is just 1/8 of the full length of a line you'd have to draw through space if you wanted it to connect back go yourself. The volume of the whole Universe is about 100 times the volume of our observable Universe. (If you object to the fact that 83 is not equal to 100, remember that we're not talking Euclidean space here, so your intuition for how radii and volumes of spheres relate doesn't entirely apply.)

Remember, though, that this is the minimum size of the Universe given our current data. Most of us suspect that the Universe is really a whole hell of a lot bigger than that, and indeed may well be infinite.

Size and Fate Are Separate

If you read almost any cosmology book written more than 12 or so years ago, and some written since, you will probably read something about a closed universe being one that recollapses, and an open universe one that expands forever. This is true only if the dark energy density of the universe is zero! Implicitly, those texts assumed that our Universe was matter dominated, and as such the geometry and fate of the Universe were linked. In a universe such as ours, where there is dark energy, the fate and geometry are not so tightly linked. Dark matter and dark energy both affect both the shape of the Universe and its ultimate fate, but they affect it differently. Exactly what will happen to our Universe depends on the details of what dark energy really turns out to be. However, for what most of us consider to be the most likely versions of dark energy, the Universe will keep expanding forever, with clusters of galaxies getting ever more and more separated. This is true whether the geometry of the Universe is flat, open, or closed.

References

The numbers for the current expansion rate of the Universe (used to derive the critical density) and for the limits on the curvature of the Universe come from the cosmological implications of the WMAP 7-year data as described in Komatsu et al., 2011, ApJS, 192, 18. The image used to wrap the universe sphere is the Hubble Ultra-Deep Field.

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Charged Particles and Magnetic Fields

Magnetic Fields

You are probably familiar with magnets. Magnetized bits of iron can stick to metal things such as your refrigerator or paperclips. (It's always a fridge or paperclips, for some reason.) You may even have made an electromagnet by wrapping a wire many times around a nail (or some other iron thing) and running a current through that wire by attaching it to a battery.

When physicists want to describe the forces that result from magnetized objects like this, we talk about magnetic fields. Really, a magnetic field means the strength and direction of this abstract physical thing (called, er, the "magnetic field") in all regions of space around the spot we're talking about. We then know how to use the numbers associated with the strength and direction of this magnetic field to calculate how it will interact with other things, such as iron objects (that react to magnetic fields), other magnetic fields, and charged particles. We will often visualize these magnetic fields by drawing "magnetic field lines". These lines point along the direction of the magnetic field. Where magnetic field lines are closer together, it's a stronger magnetic field. Iron filings will tend to line themselves up along magnetic fields, allowing a pretty direct (and physical) visualization of small segments of magnetic field lines. The weakness of this visualization is that how "close together" the lines appear depends on where the iron filings fall as well as how strong the magnetic fields are.

[Iron filings lining up along a magnetic field]
Iron filings line up along the magnetic field lines of a bar magnet. Image from Black & Davis, 1913, Practical Physics, via Wikimedia Commons

Magnetic Fields... innnn... Spaaaaaace

There are magnetic fields all over the place in space. The Earth has a magnetic field associated with it. Indeed, the Earth's magnetic field is very similar to that of a huge bar magnet embedded in the Earth, with the south magnetic pole of the magnet pretty close to the North Pole of the Earth.

[Earth's magnetic field]
Earth's magnetic field. Image by Zureks, via Wikimedia Commons.

When a magnetic field is embedded in plasma— and plasmas are very common in space— the dynamics of the magnetic field and the dynamics of the plasma are closely linked. Charged particles interact with magnetic fields, and the motion of charged particles gives rise to magnetic fields. Wheres you can use simple [sic] fluid dynamics or hydrodynamics to describe the motion of a non-charged fluid (a liquid or a gas), when that fluid is made up of charged particles (and is therefore a plasma), you have to take into account the magnetic fields and start using what is called magnetohydrodynamics. The most important result of magnetohydrodynamics is that the magnetic field lines and the plasma will, for the most part, move together. If the plasma is dense enough, as it moves around, it will convect the magnetic field lines along with it. If the plasma is being compressed, or if it is twisting around, it can stretch out or squeeze magnetic field lines (which corresponds to a strengthening and weakening of the magnetic field), and it can also distort and twist up the magnetic fields. Just as there is energy in electric or gravitational fields, you can also store energy in magnetic fields, and as magnetic field lines get compressed and twisted up, a lot of energy can be stored in them.

Like the Earth, the Sun has a magnetic field. Unlike the Earth, the Sun is entirely gaseous, not solid. What's more, throughout much of the Sun the gas is ionized— that is, electrons are free, not trapped on atoms. That means that the particles in the gas are charged, and the gas is a plasma. While the physics of the Sun is by far dominated by the balance between its tremendous gravity and the tremendous pressure generated by the nuclear fusion at its core, magnetic fields are important, and give rise to things such as the Solar Corona (that wispy "crown" of extremely hot gas that you may have seen in pictures of Solar eclipses) and the various loops and prominences you see on the Sun, as well as solar flares and ejections of groups of charged particles from the surface of the Sun. The big loops you see sticking out on the Sun in some images such as the one below are where bundles of magnetic fields have blooped out of the surface of the Sun, and plasma has been carried along with them.


The Solar Corona during an eclipse. Image by NH53, via Wikimedia Commons

A solar prominence, imaged in ultraviolet light. Charged particles are streaming along a magnetic field; this particular image captures the light from ionized Helium. Image from the Solar Dynamics Observatory, via Wikimedia Commons.

The Sun rotates, about once every 24 days or so. However, that rotation is not uniform; the poles rotate faster than the equator. This means that the magnetic fields in the Sun are always getting twisted up and distorted. Every so often the magnetic fields will "break", and relax to a less twisted state, releasing the energy that was stored in the magnetic fields. This is what causes so-called "coronal mass ejections" (CME). There is a constant stream of charged particles coming off of the Sun; when there's a CME, the sun briefly sends out charged particles at a much greater rate into the Solar System. If that mass ejection is pointed more or less in the direction of the Earth, then those particles will hit us.

Charged Particles Intersecting Magnetic Fields

Whereas an electric field points exactly along the direction that it will push a charged particle (or exactly opposite it, if the charge on that particle is negative, as is the case with an electron), when a charged particle comes across a magnetic field the force on it is perpendicular to both its direction of motion and to the magnetic field line. If you imagine that you're going straight, and then you feel a force to your left, you'll curve to the left. If you keep having a force to your left (your new left, now that you've curved), you'll eventually go around in circles. This is what happens when charged particles come into a region of magnetic fields. It depends on much energy the particles have— how fast they're moving— as well as the strength of the magnetic field. If they're moving very fast, they may just get deflected a little before going on their way. However, if the magnetic field is strong enough, and especially if the particle loses a little energy, say by colliding occasionally with other particles, it can get trapped by the magnetic field, at which point it will circle around it. In fact, particles will tend to spiral around magnetic field lines, moving along the lines as they orbit around them. That part of their velocity that is pointing along the magnetic field is not affected, but the part that's perpendicular circles around them.


A charged particle (red) spiraling around a magnetic field (blue).

Because the Sun is continually throwing charged particles at us, the Earth has an ample source of particles to collect in its magnetic fields. There are belts of radiation above the Earth, called the Van Allen Belts, where charged particles (mostly protons, or Hydrogen nuclei, and electrons) spiral around the Earth's magnetic field.

Look at the picture above of the Earth's magnetic field. Pick one of the field lines that is away from the surface of the Earth at the equator. If you follow that field line along, you'll see that as you get closer to the poles, eventually the field line plunges down into the Earth. If you trap charged particles on these field lines, as the charged particles move along them they will eventually intersect the atmosphere. As these charged particles plow into the atmosphere, they run into atoms in the atmosphere, giving them energy and exciting their electrons. When the atoms in the atmosphere release this energy, they glow. This is what we observe as the northern and southern aurorae. This also explains why you only tend to see the aurorae if you're fairly far north or fairly far south: you have to be there for the magnetic field lines that trap the charged particles to intersect the atmosphere. It also explains why you might expect more impressive aurorae after a big mass ejection from the Sun. When there are more charged particles coming off of the Sun, there's more basic material for the Earth's magnetic fields to capture and spiral down into the atmosphere.


The southern aurora, imaged from space. Image from NASA.

Acceleration of Cosmic Rays

When a supernova explodes, it sends a blast wave out into the circumstellar blast. This blast wave is driven by the outer layers of the star that get blown off in the supernova, and the blast wave then sweeps up the existing circumstellar gas into its expansion. Remember above that we talked about magnetic field lines being locked into the fluid. If you have gas crashing into other gas in a shockwave with this expansion, you'll have gas getting highly compressed right at the shock. That also means that you're going to be squeezing together magnetic field lines right at the shock. As the magnetic field lines squeeze together, some of the kinetic energy from the expanding gas goes into accelerating the particles spiraling around those magnetic field lines. The result is that they spiral faster and faster around the stronger and stronger magnetic fields.

Eventually, with all those particles there, some particles will run into other particles and be knocked free. By this time, however, they will have picked up a lot of energy because of these compressing and strengthening magnetic fields, and the from the process of them spiraling faster and faster around those magnetic fields. As a result, by the time the particles are kicked out they might have quite a lot of kinetic energy. This fast-moving charged particles then go flying through the galaxy, and they're what we observe as cosmic rays here on Earth.

There is a constant stream of charged particles coming off of the Sun. Cosmic rays tend to have higher energy than that, though, and there are a lot of them that are too energetic to have come off of the Sun. Indeed, there are some cosmic rays that are too energetic, we believe, even to have come from supernovae, and their origin is still something of a mystery (or at least was last time I checked). However, the vast majority of the higher-energy cosmic rays that show up here at Earth were accelerated long ago through this mechanism, called the "Fermi mechanism", in the magnetic fields in the shocks of supernovae. Ever since then, these charged particles have been wandering about the Galaxy, steered by the magnetic fields of the galaxy, until by chance some of them run into our planet.

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Why go to graduate school in Physics?

I just came accross an article at The Economist entitled The Disposable Academic: Why doing a PhD is a waste of time. This has prompted me finally to write this post, which I've intended to write for a long time (like so many other posts on my too-quiet blog).

There is one, and only one, reason why you should go to graduate school in Physics or Astronomy. (This is probably true for any other field as well, but I'm going to stick to the field where I actually know what I'm talking about.) That one reason is: because you want to be a graduate student in physics for five or six years. That's it.

It is true that if you want to teach physics at the University level, or that if you want to have a career in physics research where you're leading and doing you're own research, you need to get a PhD. This isn't 100% true; you can certainly teach at the community college level with a masters' degree, and you can get a job working with a physics research group (although those are quite rare). However, for the most part, it's true. This leads many people to conclude that, because what they really want to do is spend their life as a professor at a University, they need to go to graduate school.

However, going to graduate school because that's what you want to do is similar to buying a lottery ticket because you want to be a millionaire. Yes, buying a lottery ticket is a prerequisite for winning the lottery, just as getting a PhD in physics is a prerequisite for being a physics professor. However, the fact that you've met that prerequisite is very far from assurance that you'll be able to do either. Thankfully, the chances of getting a physics professor job aren't quite as bad as the chances of winning the lottery. However, in both cases, they're bad investments.

There is a tremendous opportunity cost associated with being a physics graduate student. It's not as bad as being a humanities graduate student. For the most part, if you can get into a physics graduate school, your tuiton will be paid, and you will receive a stipend of something like $20,000/year. You may be able to make this as a research assistant— a good deal, because you're essentially being paid to do your PhD research. Or, you may have to teach some classes... which I also personally view as a good deal, but that's because I like to teach. (And, the teaching you do as a PhD student is lower stress and less time consuming than what a professor at a small liberal-arts college does.) However, there is still the opportunity cost. With your skills and abilities, you would be able to make a lot more money doing something else.

If you think you want to pursue a profession in academic physics, but you are going to view the years you spend working on your PhD as a sacrifice, then it's not worth doing it. The probability of getting that academic research job is just not high enough, even if you go to one of the top schools out there. What's more, ironically, the experience you get doing something else may well serve you better for any other job you might get thereafter, and it will almost certainly look better on your resume than the PhD will.

On the other hand, the life of the physics graduate student isn't necessarily a bad one. Yes, you will spend several years of your young life making a whole lot less money than you could otherwise. Yes, you will live the "graduate student lifestyle", meaning that you're still more or less pond scum in the hierarchy of your institution, and that you're still in training, still living the life of an apprentice. However, you do get to spend five or six years studying very interesting stuff, and performing original research. It can be a very cool thing to do. Yes, no matter who you are, you will go through moments of self-doubt where you wonder just what the hell you're doing, and you may go through periods of despair. But, overall, it can be a very fulfulling way to spend several years. That is, if you go into it recognizing that you're doing it for the sake of doing it, not as an investment in a future career that you'll have any assurance of achieving.

And, of course, to enjoy the graduate student lifestyle, you have to keep some perspective on life. If a professorial job were guaranteed, then perhaps one could stomach the idea of living several years with your life on hold, being underpaid and undervalued for working too hard. But, since that professorial job is far from guaranteed, you can't sacrifice your whole life to be a graduate student. Some will consider this heresy, will believe that graduate students are supposed to work really really hard because "your education is an investment in your future". But, again, a PhD program is today a terrible investment. Yes, you should probably expect to work up to 50 hours a week... not because you're overworking, but rather because you're inspired by your subject. But you should not, under any circumstance, join one of "those" labs where the professor expects you to work 10 hours a day, 7 days a week. You need to have a life. Work hard, but keep perspective. Recognize that you need to value your life right then.

What's more, you'll need to recognize that the culture of the PhD program is a bit dysfunctional. You almost certainly will feel cultural pressure to want to achieve the highly valued research professor position after graduate school, especially if you go to a top tier graduate school. You will feel this pressure from peers, and from your institution. (They partially judge the "success" of their graduate program based on the "placement" of their graduates.) Take it all with a grain of salt. It's your life. You are decidedly not a failure if you don't get one of the vaunted research positions, and indeed there's nothing shameful about deciding that you don't want one. Try to get one if you want one, and it's inevitable that you'll be disappointed if you don't, but don't feel ashamed, don't feel like a failure, and don't feel like you're letting anybody down if you don't get one. After all, most of us, if we're honest, will admit that we're overproducing PhDs in all fields, including physics, for the number of jobs out there that Physics PhDs are "supposed" to want.

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The End of Nobel Week

The Sunday (Dec. 11) after the Nobel Prize ceremony was a slow and quiet day. I slept in a bit (due to having gone to bed so late the night of the cermoney), but not as much as I had intended. That was fine, though, as late in the afternoon I fell asleep, to wake up briefly in the evening, only to fall asleep again. So, the day before yesterday, I slept a lot. (If only you could bank sleep.) The one fun thing I did on Sunday was head down to the Vasa Museum. The Vasa was a ship that was launched in the early 17th century, commissioned by the then-king of Sweden, Gustavus Adolphus II. Its trip didn't last long; on its first voyage, it tipped, took on water, and sank. In the mid-twentieth century, it was rasied again, and today forms the basis of a museum all about early 17th-century Swedish ships, shipbuilding, and life related to these things. The Vasa was a warship, loaded with cannon. At the time, Sweden was perenially at war with Poland (and sometimes Denmark as well). Ah, the Renaissance.

[Vasa]
The Vasa

On Monday, I did a bit more gratuitous walking about Stockholm, and then in the afternoon there was a symposium at the Albanova University Center. This is where SCP member Ariel Goobar is headquartered, along with the graduate students and post-docs who have worked with him and continue to work with him. The symposium was introduced by saying that we'd heard a lot from Saul, Adam, and Brian at the Nobel Lectures; for these two hours, we'd hear from other members of the team. The three laureates moderated, while four different panels representing four different eras of the whole supernova search business gave short talklets about the prehistory of the whole thing. That included Rich Muller talking about the LBL robotic search, as well as Rich's Nemesis idea that (if I am not mistaken) was the topic of Saul's thesis, and Bob Kirshner talking about supernova work "back in the day" when he was the thesis advisor for both Brian Schmidt and Adam Reiss. It also included Richard Ellis talking about the original Danish high-redshift supernova search (which wasn't really succesful; they found only one supernova, and after maximum light). Mark Phillips talked about the genesis of the Calan-Tololo supernova search, which established Type Ia supernovae as calibratable standard candles suitable cosmology, and whose supernovae served as the low-redshift comparison set for both high-redshift teams.

[Saul on the Phone]
Many people commented on Saul's propensity for calling people at observatories, as Richard Ellis does here

The second panel was about the early days of the project. Carl Pennypacker, Brian Boyle, Heidi Newberg, and Warrick Couch talked about the early days of the SCP, when the weather was extremely frustrating, and Heidi figured she'd get a thesis out of it even if they didn't manage to find even a single supernova. (The first supernova was found in 1992.) Nick Suntzeff talked about the genesis of the High-Z team.

The next batch of people included Alejandro Clocchiatti and Chris Smith from the High-Z team, and Peter Nugent and myself from the SCP. After Peter told a very funny story abuot observing at the CTIO and neary running over Brian Schmidt in a runaway CTIO volkswagon bug whose brakes had failed, it was difficult to follow myself. In the SCP, we'd only been told what the program was and what we were going to be talking about an hour or so before the thing began, and I had no idea what anybody else was going to say, so I didn't really plan anything. The result was that I just blathered a little bit about Moore's Law and computer (and network) technology having made it all possible, and I completely failed to make any of the two or three points I was hoping to make about what it was like to adopt the search software from Alex Kim and Ivan Small, and spend 40-hour days processing the data as it came in during a search run.

Next, Alex Filippenko, Isobel Hook, Chris Lidman, Ron Gilliland, Saurabh Jha, and Alex Kim talked about spectroscopy (showing off how much better an 8m telescope is than a 4m telescope for the more distant supernovae), using HST to observe supernovae, and some other things. Saurabh told an amusing story about performing the supernova photometry. Adam Reiss had been put in charge of the analysis that lead to the High-Z team's discovery paper by team leader Brian Schmidt. Adam, in turn, had farmed out the work of getting the photometric lightcurves to several team members. When the due date came, he sent out an e-mail to all of them saying (I paraphrase) "thank you! Everybody but one (you know who you are) have turned in your data." This made Saurabh, a young grad student at the time, feel terrible, because he was the one. He went nuts over the next 36 hours, and managed to get his data in. Only after that, running into Peter Garnevich and Ron Gilliland, did he figure out that in fact nobody had managed to get their data in, and Adam's message wasn't entirely serious.

Finally, Ariel Goobar, John Tonry, Peter Garnevich, and Craig Hogan talked about the cosmology analysis. Craig Hogan, the theorist, went last. He pointed out, as we all know, that while we've established that the Universe is accelerating, we don't know why. "Dark Energy" is the name we give to the phenomenon, but we don't know what it is, or even if it is stuff at all; it may in fact be that we're seeing the breakdown of General Relativity. Craig and John did, at the end during a Q&A period, rain a bit on everybody's parade by saying that this field is more or less a dead field. I've had similar feelings myself for a few years, but few would agree with me. There are parameters about Dark Energy that can be measured; my suspicion is that we're just going to keep narrowing the errorbars around the default, not-terribly-interesting answer. (If the values are even slightly different from that answer, it's extremely interesting. However, you can never prove that that answer is right, you can only shrink the error bars around it. There are arguments, however, why it's not a waste of time to do this, and I won't get into it here.)

During the Q&A period, Hubble Space Telescope director Matt Mountain asked a leading question about "can't we all just get along?" He talked about repeated semesters where the HST time allocation committee would assign time to either Adam or to Saul; inevitably, he would then hear from the other one shortly thereafter. He suggested that with HST having only perhaps five years left, and nothing to follow it very soon, it was a crucial time for them to figure out ways in which the community as a whole could work together. Indeed, it sounded to me like he was inviting them to get together and put in a proposal to ask for a truly impressive amount of HST time, even more than the already-impressive amounts of time that has gone to supernova cosmology work. (This was what triggered Craig Hogan and John Tonry to caution that perhaps beating down the error bars on the two parameters we've identified, rather than trying to be more creative, might not be the best way to proceed.)

[Big Rodent]
For example, the human-sized rodent was pretty scary

After the symposium, both groups retired to the Junibcken museum, a museum dedicated to Swedish children's litrature, in particular the stories of Astrid Lindgren (the author of the Pippi Longstockings books). (I have to admit to being nearly compltely ignorant about those.) We all rode their Story Train (in little cars of 3), that took us through 15-minute tour of lovingly recreated dioramas of scenes from these stories... none of which I recognized. I was sitting with Shane and Stormy Burns as we made the trip, and we agreed that these would probably be delightful to kids who were fans of the books. We also thought that some of the scenes would be quite scary.

At the end of the train ride was a dinner, for both of the teams together. Of course, at the end of the dinner, there were some speeches, which were all quite nice. Alex Filippenko— who started collaborating with Saul on the SCP, but defected to the High-Z team in what I gather was a rather unpleasant falling-out— gave a nice speech crediting the two teams' differences with being strengths, as each team learned from the other. (And, of course, he mentioned, as did a man from the Royal Swedish Academy (whose name I didn't get) involved in the Nobel selection, that the fact that there were two different teams with the same result is part of why the world couldn't just dismiss it right away, as we so far have more or less done with the FTL neutrino result.) Several other peple told stories about various things, including Saul's father, and the woman from the Swedish diplomat service who had been appointed as Saul's liaison and shepherd during the whole process. She had only met Saul just this week, but said that she was impressed with how gracious he was talking to nearly everybody. Whether it was a 15-year-old or a colleague, he was always interested when talking to them.

[Santa Lucia]
Santa Lucia showed up to help banish the darkness; she brought with her a rather nice group of a capella singers who sang Christmas songs. At least, I think they were; but for "Deck the Halls", they were all in Swedish.

In the end, several people remarked that it was unusal for a group this large, especailly including collabortors, to come out to the Nobel Prize Ceremony. Brian, Adam, and Saul may be the ones with the glory, they may be the ones that history will remember, but they did a good job of sharing some part of the glory with the rest of us during this week. Somebody (I forget who, but it may also have been Alex Filippenko) commented that it's too bad that too many members of the public think that science is done by individuals working away all by themselves— antisocial individuals, even. For these groups that's certainly not the case, and indeed this science could never have been accomplished in such a mode. The fact that the Nobel Prize celebrates individuals only serves to cement this model in the public mind. However, as I said, Saul, Brian, and Adam were very generous with making it clear that there are a lot of people who share the credit for this discovery.

And now I'm on my way home; I've composed this post in fits and starts along my way home, and won't finish getting all the pictures embedded until after I'm home in Squamish. (I decided not to attend the Lucia Ball on the 13th, but to head home.)

This last evening, I also got what I think is the coolest souvenir of the trip. The Astrophysical Journal put out a special "Nobel" commemorative reprint of the Perlmutter '99 paper (as well as the corresponding Riess '98 paper, although I didn't see that one). We were all given copies of it. At the end of the night, those of us who were still there passed the copies around to each other to sign. A few signatures are missing, but I do have this Nobel commemorative reprint with the signatures of Saul and all the other authors (including myself). That's going to get framed and put on my office wall next to the Gruber prize!

[Signed Paper]
Perlmutter et al., 1999

I can't help but get a wee bit choked up when I think about this last week— when I think about the fact that I was a major contributor to one of the coolest discoveries in science in the last couple of decades, and that the world has now recognized that discovery with its highest honor. It's been quite a week.

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The Nobel Prize Ceremony and Banquet

[chair]
Saul's, Brian's, and Adam's chair

On the morning of Saturday, December 11, I walked down to the Nobel Museum, planning to have lunch with Shane Burns (my college thesis advisor at Harvey Mudd, and later a collaborator when I was a post-doc at LBNL). Because the English "tour" (really, lecture with people standing around) was starting just as I got there, I went along on that. Among other things, I learned that while there are 800 some-odd Nobel Laureates, only just over 40 of them are women. The Nobel Museum is only 10 or 20 years old. They have a rotating exhibit; right now, there's one about Marie Curie. (Ironically, even though the fraction of female Nobel laureates is small, Marie Curie is probably the most iconic physics laureate.) When the museum opened, and some laureates first showed up, they realized that they ought to have a guest book; they hadn't planned to do that, so at the last minute they decided to make the cafe the guest book. Somebody grabbed a white paint-pen, and got the laureates to sign the bottom of a chair. Now, if you turn over a chair, you can find signatures of laureates. (At lunch, I sat on the chair signed by David Gross. I felt very asymptotically free, and very colorful.)

At lunch, I chatted with Shane, sharing war stories about teaching on the block system, and telling him a little more about Quest. Shane teaches at Colorado College, the school that (decades ago) pioneered the idea of the block system, and the place Quest got the idea from. We also shared some stories about being bitter about tenure denials of years past. Shane was denied tenure at Harvey Mudd. I asked him if he was still bitter; he said he had been, but when he started at CC, he got over it. He's much happier at CC (among other things, he and his wife would much rather live in Colorado than Southern California), and it's where he always wanted to be. I feel similarly about Quest. I wouldn't say I'm over my bitterness from Vanderbilt (the experience of which provided so much great fodder for this blog during its glory days), but Quest is much more the sort of place that I've always wanted to be. (I just hope that stupid Canadian immigration doesn't prevent me from staying there long-term.)

[Shane & I]
Shane and I in front of a Marie Curie quote

After lunch, I hoofed it back to the hotel to put on my tails, and my way-too-tight shoes. I have a pair of shiny black shoes that I wear with my tux... although my use of the present tense is perhaps somewhat deceitful. While I've worn my tux recently, I'm not sure I've worn these shoes in over 10 years. And, just like the Universe, I've expanded in the last 10 years. Yes, most of that's at the waist, but when you get fat, you get fat everywhere. (This can lead to sleep apnea, it turns out, as you get fat on the inside of your windpipe.) What's more, I brought thick black socks, for very rational reasons. (Sweden, winter, ergo thick socks.) My feet were crushed in them, and I was in intense pain throughout much of the evening, especially when I had to stand up. At dinner, I took off my shoes (my feet were under the table, and nobody knew, so I didn't get ejected), which was quite nice.

From there, I went down to the Grand Hotel to pick up the bus for the Nobel Ceremony. It was quite nice. There were a lot of very well-dressed people about. Down on stage, there were chairs on one side for the Swedish Royal party, and chairs on the other side for the laureates. (That is, except for the three Peace laureates, who are three women from Africa and the Middle East, honored for their work in improving womens' rights. The Nobel Peace Prize is presented in Oslo, Norway, each year, as it's a committee formed by the Norwegian Parliament that chooses the Peace laureates.) Behind them were chairs for what I assume were members of the committees that choose all of the Nobel prizes.

[Nobel Ceremony]
Left, front: a bunch of white guys about to get their Nobel Prizes. Right: front: the Swedish Queen, King, and Crown Princess.

I have to admit that I wanted to jump up and down and cheer and shout when Saul got his Nobel. Not only was it personally very exciting, what with my having been one of the core members of the team when we were doing the supernova searches and the analysis the last year or so before the announcement, but the man really deserved it. Yeah, in a sense, we all deserved it, and indeed we all got some recognition four years ago with the Gruber Prize. But, it was Saul who created this field. Adam and Brian, the two from the other team who shared the prize with Saul, also deserved it. They made an independent measurement of the acceleration, and the fact that there were two teams that came out with the measurement at the same time is the reason that people took the measurement as seriously as they did when it first came out. However, Saul was the one who was pushing it in the early days, back in 1988, and who persevered in pushing it through what sounded like several very early trying years. He kept pushing it, cajoling observatory time allocation committees to allow him to schedule the time the way he needed, even as some members of what would become the other team were still swearing up and down that it couldn't be done. I seriously doubt I would have had the perseverance to stick with the program for so long, taking four years before even one supernova was discovered, and another two before a batch of a mere 7 were discovered, and another three after that before the answer that he'd been looking for all along came out. But Saul is extremely optimistic, and extremely perseverant.

[Saul Getting the Nobel Prize]
Saul Perlmutter getting his Nobel Prize from the King of Sweden

I do have to admit, I took the opportunity to give in to my jetlag during the ceremony. Except for the first speech, all of the rest were in Swedish. My knowledge of Swedish is less than my knowledge of Klingon, for at least I know one word in Klingon. ("Kaplah!") We did have booklets with translations of the speeches. However, I could read those faster than those giving the speeches could say them, so I had a bit of time after each one to doze off.... As I write this, it sounds pretty horrifying to say that I napped during the Nobel prize ceremony, but, well, it was practical! I was always awake as the King gave each prize. (Everybody in the room stood up when the King stood up. I would hate to be King.)

After that was the Nobel Banquet, which was quite an exercise in pomp and circumstance. The banquet was in this huge hall at City Hall, which is nicely designed to look like an outdoor venue. The (very high) ceiling is a projection screen, on which are projected vaguely cloudy-looking things, and the inner walls look like outside walls of Swedish buildings, so the illusion is quite effective. (Yes, I couldn't help making a comparison to the ceiling at Hogwarts.)

[Banquet Room]
The room where we had the Nobel Banquet (after it was over)
[Banquet Ceiling]
The Hogwarts-style ceiling

During the three-course meal, there were some ballet/theater/music numbers, where performers would move through the room and do... something. I didn't completely follow what was going on, but it was fun. As they were finishing, an extremely efficient regiment of waiters would come, stand by every table, and then, all at once, serve everybody. I've been at many big events where the head table is served... and by the time the last table is served, the people at the head table have already finished, gone home, had a full-night's sleep, started their next day, quit their job, and moved to another city. Not here. Everything was very efficient, very synchronized, and very well managed by the professional cadre of waiters.

[Dessert]
Dessert had red hair

The dinner was quite good. Others at the table who I guess are much more into gourmet food than I was were poo-pooing it ("only a three course meal"), but hey, it was way better than I usually eat!

After that was over, there was "dancing in the Golden ballroom". On display were the medals and individually customized diplomas for the laureates. Had security not been watching, I would have grabbed a snapshot of it. (Indeed, we were not supposed to take pictures at all during the banquet, but I figure, what's the point of being an iconoclast if you can't take pictures when you aren't supposed to?)

From there, we retired to the University of Stockholm, where the students there put on the nightcap ball. This was a huge party and masquerade, attended it seemed mostly by undergraduates. Some people were in quite interesting costumes. There was a huge array of themed rooms, with different things going on in different rooms. Because my feet were utterly killing me, I spent a bit of time sitting in one place listening to a nice jazz combo. Later on, in another room, I found a stage where a string quartet plus a clarinetist (all with painted-on masks on their face) started playing the Mozart Clarinet Quintet. They were really quite good, but alas being in a party room where everybody was talking, I was able to sort of hear them standing right next to the stage. Saul, a violinist himself, was elsewhere in the same room; he didn't even realize that the chamber group was there playing. Sadly, I didn't get to stay to hear them complete even the first movement, because the SCP had planned to take more group photos at 1:15 AM.

[Quintet]
Masqued Swedish students playing the Mozart Clarinet Quintet
[The SCP]
A Well-Dressed SCP Staircase Photo in need of some image processing to balance the contrast in the front and back

Next followed group photos. We started with what is a bit of an unofficial occasional SCP tradition: the staircase photo. We then did photos standing around, and then every conceivable combination of people had their picture taken with Saul. (I told Saul he was going to have to sign each and every one of the photos later.)

At 2AM, I took a taxi home, and took off my shoes, and then goofed off a bit on the computer to unwind. Ufda. My feet still hurt the next day. Excedrin helped me sleep through the night... that is, insofar as sleeping from 4AM to 8:30AM is "through the night". I sense a nap coming on.

A month ago, when I was in the throes of my third block in a row and reaching the burnout stage that all professors who teach on the block seem to at the very least flirt with when that happens, I was considering not coming. I'm not somebody who loves to travel, and having to deal with getting (and paying for...) the formal wear and all of that made the thing seem a bit like a pain. But, I'm extremely happy that I've come. It's been great catching up with members of the SCP (including chatting with Brad Schaefer about our mutual student, Andrew Collazzi, who did research with me as an undergraduate at Vanderbilt and just recently finished his PhD with Brad at LSU). The pomp and circumstance surrounding all of this is, really, a little bit silly (much as the Academy Awards in the USA are silly, or even for that matter the Presidential Inauguration), but it's a good kind of silly. It's celebrating the furthering of human knowledge, which is a great thing to celebrate. And, it's all a very classy kind of silly. Except for my still-tingling feet, I thoroughly enjoyed it, and although it's barely over 12 hours later, watching Saul being given that Nobel Prize is one of those life events I wouldn't want to have missed.

[SCPers from the Late-1997 Berkeley Analysis Team]
(Some of the) people who were in Berkeley during the 1997 push to complete the analysis that led to the discovery of the accelerating Unvierse. Front, L to R: Patricia Castro, me, Saul Perlmutter, Nelson Nunes. Back, L to R: Peter Nugent, Sabastien Fabbro, Robert Quimby, and Greg Aldering either completely wasted, or just facpalming at it all.

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Nobel Week Festivities Part 1

I'm out here in Stockholm for the ceremonies surrounding Saul Perlmutter's Nobel Prize. Most of the members of the group who were on the 1999 paper are here.

The Big Event (not to be confused with the Bang) comes tonight, when the prizes themselves are presented. However, there's been a fair number of festivities already. I arrived on Wednesday afternoon terribly jetlagged. It seemed odd that it was Wednesday to me, what with my having left early Tuesday morning. The flights were very long, but not that long. From this, I'm concluding that the Earth must be round, and that there must have been a 9 hour change in the clock time to account for the position of the Sun relative to my position on the planet. That it was already dark at 3PM didn't help much.... We're so far North that the Sun never gets very high in the sky in the winter, and it doesn't stay up very long. It was also cloudy when I arrived, so the deep twilight was even deeper.

I went to my room and crashed for a 1-hour power nap before putting on my jacket and tie and the shoes in which I'm not as happy walking as I am in my Birkenstocks, and, with Don Groom, wandered in the vague direction of the Grand Hotel, eventually finding it through not the most efficient route. From there, we went over to a reception at the Royal Swedish Academy of Sciences. I foolishly forgot to bring my camera, and also didn't take any pictures with my phone, so no snaps from that night.


Susana Deustua before the Nobel Lecture

The next morning (Thursday, 8-December) was the Nobel lectures at the University of Stockholm. The physics lectures lasted about two hours. They started with Brian Schmidt, went through Adam Riess, and ended with Saul's. For the last 15 minutes of Saul's lecture, he made a point of describing how the whole team worked together. It evolved over time. Different members of the team were active in different eras. When he got to the era of the couple of years before the discovery, he was describing the distributed effort with people at telescopes all over the world, and the team in Berkeley working on a variety of things. What he said when my picture popped up was: "Rob Knop, who thinks, types, and programs faster than I talk." (Saul talks pretty fast, so this was a nice complement.)


Saul giving the Nobel Lecture

After the physics lecture, our team snuck out of the hall. (All due apologies to the Chemistry and Economics laureates.) We had scheduled a team lunch for the SCP at a smorgasbord restaurant. Where was it? I don't know... we got on a bus, and then on a boat to make our way over to the restaurant. The boat ride was nice, although up on the top deck it really was rather cold. Yesterday, I posted a group photo of the members of the SCP who were present at the lunch. There were a few people who were on the discovery paper who weren't there, because they hadn't arrived yet (I'm presuming), including Patricia Castro, Isobel Hook, and Matthew Kim. (Also on that paper was Alex Filippenko, but in 1996 he defected to the other team, so he hasn't been going to SCP team meetings for a decade and a half now.) Standing in for Gerson Goldhaber is his daughter, three from the right; Gerson died in 2010.


On the boat after lunch. Left to Right: Saul Perlmutter Alex Kim, Ivan Small, Julia Lee, Julia's Husband (Andrew, I think), and me

Joseph Calleja and the Royal Stockholm Philharmonic Orchestra at the 2011 Nobel Prize Concert

Finally, on the evening of December 8, I went to the Nobel concert. It's much easier to buy extremely expensive concert tickets when they're in a foreign currency, and you don't know the exchange rate. I blithely put down my credit card and was charged 1,500SEK, not realizing until later that that was in the neighborhood of $250...! I don't know if I've ever spent that much to go to a single concert before. The concert was good; I've been to other concerts that cost a quarter as much that were just as good, but you don't get the opportunity to go to the Nobel Concert very often, so what the heck. Tenor Joseph Calleja was the soloist, and he was quite good. I must admit, though, as a violinist myself, my favorite piece on the program was Dance Macabre by Saint-Saens. At the concert, I was sitting next to Rich Muller, about whom there's been a buzz in the science blogosphere recently because of his coming out and saying that, yeah, when he reanalyzed the data, it turns out that climate change is real just like all the people in the field who were working on it all along had said. I didn't talk to him about climate change, but I did talk about my general sense of despair about the world in general. (I feel more like we're screwed now than I did in the Cold War 1980s.) He doesn't share it at all; he thinks 2011 is the best time to be alive of all of human history. I must admit myself that I'm in a teaching job now that's more like the job I'm supposed to be in (and that I've always wanted) than any other job I've ever had, so perhaps 2011 is the best year for Rob Knop... but for the world at large? I honestly think that the world was a better place before Sep 11, 2001; not because of the terrorists directly, but because of how the world (mostly the USA) responded to it. But, enough gratuitous philosophizing.

Yesterday (Friday December 9) was a quiet day for me. There were events, but I didn't have tickets to any of them. There are finite tickets to each event, so Saul has been parceling them out. There was a reception at the Nordic Museum last night, but because I went to the December 7 reception, I sat out last night's. A bunch of team members also went to their national embassies for some sort of celebration or another. I'm not sure if I would have been sent to the USA or Canadian embassy... and, in any event, I spend too much time criticizing the government on microblogging platforms for them to want to be seen with me. I took the opportunity of the free day to sleep a lot...! Also, I had lunch with MICA director and Caltech astronomer George Djorgovski and his wife Leslie Maxfield (with whom I was in a production of Hello Dolly at Caltech a bit under 20 years ago); they were randomly in Stockholm for a conference.


George, Leslie, and myself

As an afterthought, I do need to read my camera's manual and figure out how to use it better. I've got blurry pictures of Saul and others from a great distance giving the Nobel lectures, and blurry pictures from the Nobel concert. It's not the world's most expensive camera, and it's already better than my skill with a camera for normal snapshot situations. However, I do know enough to be able to take advantage of some of its low-light tweaks, and to be able to take advantage of "focusing at infinity", so I should figure out what all the mysterious icons on the screen really mean when you're futzing with the settings.

Today (Saturday December 10) is the big event. Mid-afternoon, I'll start putting on my formal outfit. Once those two hours are done, I'll head down to the Grand Hotel, where we'll all get on the bus to go to the Nobel Banquet. After that is the midnight ball. I'm not sure exactly what that means, but I'm sure it has something to do with "rolling without slipping down a plane inclined at angle ϑ". That's how I usually encounter a ball.

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The SCP during Nobel Week in Stockholm

Much pomp and circumstance in Stockholm this week. I'll blog a bit more about it when I get a chance, but for now, here's a photo of the group that was taken yesterday during an enormous smorgasbord lunch.

Front, L to R: Alex Kim, Pilar Ruiz-Lapuente, Andy Fruchter, Richard Ellis, Julia Lee, Susana Deustua, Saul Perlmutter, Warrick Couch, Heidi Newberg, Silvia Gabi, Chris Lidman, Don Groom.

Middle: Nelson Nunes

Back, L to R: Ivan Small, Sebastien Fabbro, Greg Aldering, Robert Quimby, Brad Schaefer, Rob Knop, Reynald Pain, Carl Pennypacker, Shane Burns, Rich Muller, Ariel Goobar, Peter Nugent

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Online Talk Tomorrow (12-03) About FTL Neutrinos

Tomorrow morning, December 3, at 10:00AM pacific time (18:00 UT), I'll be giving the MICA public outreach talk about the faster-than-light neutrino results from CERN and Grand Sasso. The talk will include an overview of the OPERA experiment that has led to the result, a summary of the result, my own headscratching about whether or not it's real, and some notes about what this does (and, more importantly, does not) imply about our confidence in the theory of Relativity.

The talk will be at the MICA Large Ampitheater, and all are welcome. Remember, a Second Life account is free!

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Accelerating universe wins 2011 Nobel Prize in Physics

Saul Perlmutter, Brian Schmidt, and Adam Riess have shared the 2011 Nobel Prize in physics for the 1998 discovery that the expansion of our Universe is accelerating. This acceleration is what led us to conclude that most of the energy density of the Universe is made up of dark energy, although in the time since then there have been independent observations that point to dark energy.

My favorite comment was the one made by Martin Rees, who wishes that the Nobel Prize could be shared by more than three people, as the two groups deserved recognition in addition to the leaders of the two groups. Indeed, in 2007, the Gruber Prize in Cosmology was divided four ways: Saul, Brian, Saul's Group, and Brian's Group. (I thus shared in the "Saul's Group" part of the prize.)

Here is a link to a talk that I gave in Second Life a couple of years ago about the discovery of the accelerating universe. An audio recording of the talk is online, in addition to slides in PDF format.

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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 [wikipedia.org] and aether [wikipedia.org]. 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?

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