Tuesday, August 22, 2017

Our Eclipse Experience

We watched yesterday's eclipse from home. Totality was only a little over one minute, but you can't beat the fun of seeing a total eclipse from your own front yard.

Here we are banging on drums and trash cans to drive away the dragon eating the sun:


Some people have described a total solar eclipse as a life-changing experience. I won't go that far. Raising a child is a life-changing experience -- a total eclipse, not as much. But it was an amazing spectacle. We managed to see the shadow snakes wiggling up our street just prior to totality. The thing I found most impressive was the suddenness of the darkness -- after half an hour of gradual dimming, totality was like turning off a light bulb. The solar chromosphere (I think) was visible as a red band at the edge of the moon, although some of my kids thought it looked more purple than red. And what about our chickens?

Monday, August 21, 2017

Eclipse Myths

There are some absurd myths about today's eclipse circulating on the internet. One claim is that your pets will stare at the sun and go blind. This is ridiculous -- animals just don't do that. However, watch out if you own chickens. During eclipses they tend to spontaneously combust.

Tuesday, August 15, 2017

Are Scientific Conferences Obsolete?

Many of you have seen this iconic photo, which hangs in physics departments all over the world:


It's the Solvay Conference of 1927, the formative era for quantum mechanics, when giants walked the Earth: Einstein, Heisenberg, Schrodinger, Curie. I've often wondered what it must have been like to be one of the two or three people in the photo that no one has ever heard of. At least you'd get your photo on lots of physics department walls.

Recently, I attended a physics conference myself, TeVPA 2017, hosted by Ohio State University. The conference covered the overlap between particle physics and astrophysics -- my main interest was dark matter. But the conference itself was something of a Rip Van Winkle experience for me. I've stepped down as department chair after 13+ years (hurray!), so I am just now getting back onto the conference circuit. And I've noticed one tremendous difference between the conferences of my youth and the one I just attended.

Let me first take a step back and talk about a quiet revolution in the way that physicists do their work. It's something that most people aren't even aware of, but it's had a profound effect on the way that physics gets conducted.

Thursday, August 3, 2017

Norse Mythology

Lately I've been reading a collection of Norse myths to my youngest child. Setting aside for the moment the fact that the Norse myth makers clearly stole all of their best material from J.R.R. Tolkien, I've been struck by the fact that compared to the classical Greek/Roman myths, the Norse myths are very, very weird.

At the beginning of the Norse universe, the heat from the land of fire melts some of the ice in the land of frost, producing an enormous giant, Ymir, and an enormous cow, Authumbla. Did I hear that correctly -- a primordial cow? But the zaniest part involves the occupants of the world tree, Yggsdrasil. There's an eagle perched at the top of the tree, looking out for trouble, and serpent under one of the roots, gnawing away at it. Nothing wrong with that -- it sounds appropriately dark and moody, as Norse mythology should be. But running up and down the tree is a squirrel named Ratatoskr, who carries insulting messages back and forth between the eagle and the serpent. A mythological squirrel? whose only job is to trade insults? I think the reason my daughter enjoys these stories so much is that they sound like something a 7-year-old would make up.

Monday, July 31, 2017

A Grand Unified Theory of Bureaucracy

Today marks my final day as the chair of my department - I am stepping down after 13 years, 7 months in office. (Longer than Franklin Roosevelt was President, if you're keeping score, but not quite as long as the reign of Queen Elizabeth).

I've learned quite a bit during this time about the way that organizations function, and I wanted to share one insight. Humans are particularly good at picking out signals from noise. Academics are even better, and academic scientists base their entire careers on this ability. But sometimes that's all there is -- just noise and nothing more.

Tuesday, July 11, 2017

The Physics Problem that Isaac Newton Couldn't Solve

I spent the year before graduate school doing research at the Institute of Astronomy in Cambridge. While I was there, Martin Rees (later Sir Martin, and now Lord Rees) gave a talk to the new graduate students on the best way to choose a Ph.D. dissertation topic. I remember him saying, "Don't choose a problem that Poincare couldn't solve. Choose a problem that Poincare never heard of."

But let me dial up the challenge even more. There's a physics problem so difficult, so intractable, that even Isaac Newton, undoubtedly the greatest physicist who ever lived, couldn't solve it. And it's defied everyone else's attempts ever since then.

Monday, June 26, 2017

Star Trek Dentistry

Upon reaching a Certain Age, your teeth begin to disintegrate -- something to look forward to, kids! Thus it was that I found myself sitting my dentist's office last week, waiting for a new tooth. What I hadn't realized is that dentistry has, over the past decade, entered the era of Star Trek.

Thursday, June 22, 2017

If You Miss Next Month's Eclipse...

In just one more month, the city of Nashville will host part of the Great American Eclipse. I can already feel the excitement building, along with the email inquiries about housing in the area. If you're planning to drive somewhere to view the eclipse, book your hotel early and drive to your viewing destination well in advance. The traffic leading up to the eclipse is going to look like a hurricane evacuation in reverse.

But what if you miss the eclipse? Suppose it's overcast that day, or your car breaks down on the way? No need to despair -- there's another eclipse across the middle of the US only seven years later, in April of 2024.

Thursday, June 15, 2017

The Next AI Frontier: Teaching Computers to Lie

I got into a minor kerfuffle over at Steve Hsu's blog when I commented on this post about AlphaGo, the neural net program that has blown away all of the human competition in the game of Go. I said that I would be more impressed when computers mastered Diplomacy, a comment which was immediately challenged by someone else. But as impressed as I am with AlphaGo, I stand by that comment.

When I was a kid back in the 60s, the local science museum had a computer that played tic-tac-toe. (The local fair had a pigeon that played tic-tac-toe, but maybe that's a topic for another day). I have no idea how the computer worked -- maybe an analog circuit of some sort? The London science museum at one point had a tic-tac-toe computer constructed from Tinkertoys and string. As primitive as these sound, I think you can draw a straight (but very steep!) line from tic-tac-toe to the computer that "solved" checkers, and then to IBM's Deep Blue (which conquered chess), and finally to AlphaGo. These games (tic-tac-toe, checkers, chess, Go) are all deterministic with perfect information, in which the players alternate taking turns, choosing from a finite number of moves. (To be fair, there is a qualitative leap between the earlier "brute force" programs, which relied on simply increasing the number of moves scanned by the computer, and AlphaGo, in which the computer actually "learns" to play better, and in which it's impossible for the programmers to determine why the computer chose a particular move.)

Diplomacy is a very different animal. For those of you not familiar with the game, it's a contest of almost pure negotiation, requiring the ability to form alliances, offer bribes, bluff, lie, and backstab your way to the top. It requires a very different, more "human" set of skills than chess or Go. Computer scientists are already working in that direction, particularly with the game of poker.

I myself wrote two chess programs back in the 1970s, one in high school (in BASIC), and the second in college (in Fortran, the One True Programming Language). Both of my programs were, in one sense, more advanced than Deep Blue. They cheated.

Friday, June 9, 2017

Fr. Georges Lemaitre and Cosmology

If you'd like to see my talk on Fr. Georges Lemaitre and his contributions to cosmology, there is a video posted here. You'll find me about half-way down on the right-hand side. The other talks were also very interesting and definitely worth your attention.

Thursday, June 1, 2017

The Smartest Person Who Ever Lived

Who was the greatest genius in human history? Einstein? Newton? Mark Zuckerberg? (Hint: not Mark Zuckerberg). My vote goes to someone who probably died about 3000 years ago on the shores of the Eastern Mediterranean.

Tuesday, May 30, 2017

The Mystery of Cosmic Lithium

When most people think of lithium, they probably think of antidepressants, or possibly lithium batteries. But to a cosmologist, lithium is the misshapen puzzle piece -- the one that won't quite fit, no matter how hard you push it.

What does lithium mean to you?
Most of the elements were produced in the nuclear furnaces of stars or supernovae, but a handful were made in the first few minutes of the universe, when it was incredibly hot (billions of degrees) and dense. These big bang elements include helium, deuterium (a form of hydrogen with an extra neutron) and one isotope of lithium. Our theory, called "big bang nucleosynthesis," gives beautiful agreement with the observed helium and deuterium abundances, but it fails miserably for lithium -- the theory predicts about three times as much lithium from the big bang as we actually observe.

So what's going on here? As one of my high-school teachers used to say, "half-right equals all wrong." But the fact that big bang nucleosynthesis works so well for helium and deuterium suggests that maybe it just needs a few tweaks, instead of wholesale reworking. Roughly speaking, there are three likely alternatives:

Thursday, May 25, 2017

Physics in the Year 2116

Last year Physics Today ran an essay competition called "Physics in 2116." The idea was to write a science article that might appear in Physics Today 100 years from now. Motivated largely by the enormous prize money, I entered the competition but, alas, mine was not among the winning entries. As the article itself is not really suitable as either a science fiction story or a nonfiction article, I am presenting it here for your amusement. Be sure to read the footnotes.

Friday, May 19, 2017

Lies, Damned Lies, and Astronomy Photos

I'm sure you've all see beautiful images like this NASA photo of the Crab Nebula:

Who you gonna believe, me, or your own eyes?

Just imagine if you looked at the Crab Nebula through a powerful telescope -- you'd see something that looked... nothing at all like this. That's because the colors in astronomy photos are almost never the "true" colors that you would see with the naked eye. They're "false color" photographs, with different colors assigned to different wavelengths of light or (in this case) to images derived from different telescopes.

When I first realized that false color photos were the standard in astronomy, I was dismayed. What else had NASA been fibbing about? The Moon landings? But NASA hasn't been lying at all, and there's no reason to get upset about false color photos. And here's the reason why: your own eyes give you a false-color picture of reality.

Monday, May 15, 2017

Germany's Famous Science Museum

I spent last week in Munich -- my first visit to Germany in 30 years. At this point, I am supposed to insert the obligatory paragraph expressing shock and surprise at how much everything had changed. But frankly, Germany didn't seem all that different from the last time I was there. Societies have a lot more cultural inertia than we realize.

My personal high point of the trip was a visit to the famous Deutsches Museum, the top German museum of science and technology.  It's the largest science museum in the world, and a true monument to Teutonic thoroughness: why include just a few slide rules in your computing exhibit, when you can display one of every type of slide rule ever made?

The high level of the exhibits is remarkable, especially compared to U.S. science museums, which have largely been dumbed down to the level of children's museums in the course of my lifetime. The Deutsches Museum tilts heavily toward physics and engineering -- we skipped the exhibits on machine tools and metallurgy.  But I learned quite a few fun things in the course of my visit:

  • Despite the fact that the wheel was known in ancient times, the wheelbarrow was not invented in the West until the Middle Ages.
  • It's possible to slice a torus (i.e,. a donut) along a Mobius-strip-shaped cut, so that the torus gets cut all of the way through but doesn't fall into two pieces (that's really hard to explain in words, but the museum had a nice model to demonstrate).
  • Germans apparently have a much longer attention span than Americans -- all of the push buttons on the exhibits required you to hold them down much longer than would be the case for an American museum. Several times I thought an exhibit was broken, only to discover that I had not depressed the button long enough.