(Since my weekly round-up experiment seems to have failed horribly, I’m going to try to go back to linking and summarizing individual articles I’ve written around the web on this blog. We’ll see if I keep it up!)

The great physicist Chien-Shiung Wu in 1958. [Credit: Smithsonian Institution]

The great physicist Chien-Shiung Wu in 1958. [Credit: Smithsonian Institution]

Chien-Shiung Wu is one of those physicists that everyone should know about, but not enough do. A veteran of the Manhattan Project, she went on to become the world’s expert on beta decay: the process by which an atomic nucleus changes into another element, emitting an electron (or positron) in the process. In the 1950s, she realized beta decay would be a way to test a fascinating new theory of the weak force, which predicted that there should be a fundamental asymmetry between processes occurring in different directions. Her experiment was the first observation of parity violation, which opened up a wealth of new results, leading ultimately to the discovery of the Higgs boson.

For Double X Science, I commemorated this discovery, explaining why it’s important and how weird it is. It would seem that the laws of physics shouldn’t depend on which direction a process occurs, yet that’s the way the Universe works!

Wu realized she could test this idea in the lab after discussions with her colleagues Tsung-Dao Lee and Chen-Ning Yang, who laid the theoretical groundwork for understanding the weak force. She recruited Henry Boorse, Mark Zemansky, and Ernest Ambler, who were skilled at experiments at very low temperatures. It’s a great illustration of the collaborative nature of science: Lee and Yang provided theoretical knowledge, but needed Wu to design and perform the experiment; Wu in her turn brought in experts in low-temperature physics to provide expertise in an area unfamiliar to her. (On a more sour note, Lee and Yang won the Nobel Prize for the discovery of parity violation, but Wu and her fellow lab workers were passed over.) [Read more...]

Madame Wu and the backward Universe

The Solar System boundary and the week in review (September 8-14)

Cthulhu at NASA Wallops, for the LADEE launch last weekend. (I didn't wear the hat the whole time. I'm not that weird.)

Cthulhu at NASA Wallops, for the LADEE launch last weekend. (I didn’t wear the hat the whole time. I’m not that weird.)

‘Twas a busy week!

  • High-resolution observations show how black hole jets churn galactic gas (Ars Technica): One portion of my PhD thesis involved galactic feedback. That’s the process by which jets from black holes at the center of galaxies push material away, potentially affecting star formation and other activity. This article addressed the observation of galactic feedback, showing exactly where the hot jet of plasma from the black hole meets the colder atoms in galactic clouds. Very awesome stuff!
  • Parallel Earth and the Evil Matthew Hypothesis (Double X Science): I don’t know if Star Trek was the original source of the “evil twin from a parallel world” trope, but it’s the most famous. The idea is that there’s a mirror universe to ours, in which things are almost the same, but not quite. I discussed that trope in light of the multiverse, the concept that during rapid expansion right after the Big Bang, the Universe split into a number of disconnected regions that might obey different laws than our own.
  • Do-it-yourself science at GeekGirlCon (Galileo’s Pendulum): We’re still raising money to send a group of us to GeekGirlCon in Seattle next month! We’re willing to embarrass ourselves in public to accomplish this! However, the real purpose is to have hands-on science activities at the con.
  • Status of the book-in-progress (Galileo’s Pendulum): On a more somber note, I have suspended work on my book indefinitely and released my agent. I haven’t completely given up on either the book or getting it published, but the frustrations around the whole process have exhausted me, so it’s time for a break.
  • Cosmic coincidence and a potato eclipse (Double X Science): The Moon is nearly the same size as the Sun in our sky, which has led to all sorts of mystical musings and apocalyptic fears, especially during eclipses. However, that appearance is a coincidence, which we can understand using simple geometry. What’s even more fun to contrast our Moon to Phobos, the larger of Mars’ two moons, which is much smaller than our own but manages to create its own eclipses.
  • Voyager 1 really has left the Solar System…probably (Ars Technica): Sometime last year, the venerable spacecraft Voyager 1 crossed into interstellar space. While there have been a lot of announcements along these lines (I compared the number with Spinal Tap drummers), this time the probe seems to have actually done it. The necessary measurement is the plasma density, which is much higher in interstellar space, but Voyager’s plasma instrument had been knocked out by a solar flare. Researchers pieced together the appropriate data from other instruments. There’s still an anomalous measurement that needs to be accounted for — the magnetic field doesn’t behave as predicted — but I think it’s pretty safe to say that’s an issue for theorists, not ambiguity about Voyager’s position. (See below for a discussion of whether Voyager has actually “left the Solar System” or not.)
  • Mapping the dark matter in the tiniest of galaxies (Galileo’s Pendulum): Dwarf spheroidal galaxies don’t look like galaxies at all. They have so few stars and so little gas or dust, they’re nearly see-through, yet they have as much as 1000 times more dark matter than ordinary matter. (In regular galaxies, dark matter is more like 10 times the amount.) Two astronomers analyzed the motion of stars within dwarf spheroidals to see if they could map the distribution of dark matter, and they found something similar to what is seen in larger galaxies.
  • Finally, I participated in the Weekly Space Hangout, sponsored by Universe Today and CosmoQuest. I joined hosts Fraser Cain and Nicole Gugliucci, along with Amy Shira Teitel, David Dickinson, and Nancy Atkinson to talk about the space and astronomy news from the last week. The whole thing is archived at Google+, or you can watch the video on YouTube.

Where’s the edge of the Solar System?

Returning to Voyager 1, I think stories about its passage into interstellar space fell into two major categories: those saying “Voyager 1 has left the Solar System!” and variations on “Stop saying Voyager 1 has left the Solar System!” Despite what the headline on my story said, the second group of people (which includes writers I respect like Phil Plait and Amy Shira Teitel) is correct: the Solar System includes the Oort Cloud, a diffuse region of icy bodies loosely bound to the Sun by gravity.

A radio image of Voyager 1, as seen by the Very Long Baseline Array (VLBA) and the Green Bank Telescope. Click for a larger image and more information. [Credit: Alexandra Angelich, NRAO/AUI/NSF]

A radio image of Voyager 1, as seen by the Very Long Baseline Array (VLBA) and the Green Bank Telescope. Click for a larger image and more information. [Credit: Alexandra Angelich, NRAO/AUI/NSF]

However, if you want to say Voyager has left the Solar System, I’ll back you up: the boundary between the Oort Cloud and the “rest of the galaxy” isn’t very well defined. Gravity technically extends forever, though it weakens substantially with larger distances. As a result, the Oort Cloud is a fuzzy edge, and one we can’t measure. Is the end of the Solar System the point where the last Oort Cloud body resides?

Now, I agree with the pedants that the Oort Cloud truly does define the end of the Sun’s influence, and therefore is the edge of the Solar System. But the magnetic boundary of the Solar System, which is arguably the more important one from the point of view of astronomy, is defined by the edge of the heliopause, where the solar wind hits interstellar gas. That boundary, while it fluctuates with solar weather, is a much clearer division, and one we could conceivably measure near other stars.

So, I’m a both/and kind of guy in this case. Since there’s no single, sharp boundary between the Solar System and “everything else”, let’s just say there are two edges: one for the Sun’s electromagnetic influence (the heliopause), and one for its gravitational influence (the Oort Cloud). Voyager crossed the first one, but won’t reach the second one for 300 years. Now, can we get back to talking about how awesome Voyager is?

The week in review (August 25-31)

The more money we raise to help us go to GeekGirlCon, the more places I will go wearing my Cthulhu hat.

The more money we raise to help us go to GeekGirlCon, the more places I will go wearing my Cthulhu hat.

Welcome to the weekly round-up of stories I wrote this week, wherever they hide.

  • A tour of physics, Angry Birds style (Double X Science): The odds are good that you’ve played Angry Birds, even if (like me) you don’t own a device that will run the game. My colleague Rhett Allain wrote a book for kids, using Angry Birds as an invitation to learn quite a bit about physics, from particle trajectories to cosmology. I reviewed the book for Double X Science.
  • My book-in-progress, Back Roads, Dark Skies, hit a major snag, and its future is unclear. Based on the responses I’ve received, I will not be able to find a publisher without changing the book in an essential way, so I’m feeling a little stuck. So, to show myself (if nobody else) that I’ve accomplished something in the 18 months I’ve been working on the book, I published two excerpts from Chapter 2: Of Bosons and Bison at Galileo’s Pendulum.
  • Microcosmos: My tour of the DZero detector at Fermilab, with a digression on my favorite New Yorker cartoonist.
  • Naming the animals in the particle zoo: The hows and whys of particle detection, in the context of the Tevatron at Fermilab. This excerpt also includes what may be my best joke yet, if I can say that about my own writing.
  • The Milky Way’s black hole, like Cookie Monster, loses more than it eats (Ars Technica): Astronomers have known for many years that our galaxy harbors a supermassive black hole. Yet, it’s a very quiet black hole: the material surrounding it emits very little light compared to other galactic nuclei. A new X-ray observation may hold the key: only about 1 percent of all the material swirling around the black hole is captured, making it a Cookie Monster-level messy eater. (And yes, I’m proud of combining Cookie Monster and black holes in one article.)
  • This doesn’t count as my writing, but I’m joining a number of friends and colleagues at GeekGirlCon in late October for some do-it-yourself science! Well, I’m going if I can afford it; you can help with that by donating to our cause. We’ve already raised more than $400, so I’ve begun photographing myself around the city wearing my Cthulhu hat. If you give us more money, we’ll do even more embarrassing things. You can’t lose.
  • Atmospheric science in a bolt of lightning (Galileo’s Pendulum): Lightning is powerful enough to split molecules into their constituent atoms, and strip electrons away. For a brief moment, lightning can heat air to 30,000° C, more than 5 times the surface temperature of the Sun. An astrophotographer took an amazing snapshot of a lightning flash, with a twist: he used a diffraction grating to split the light into its component colors. The result is that we can identify some of the chemical components of air produced when the molecules and atoms were blasted by the powerful electric discharge.

This week also marked both my parents’ birthdays. Happy birthday, Mom (Monday) and Dad (Friday)!


My cats, Pascal and Harriet, with a few of my books that deal with the topic of relativity.

My cats, Pascal and Harriet, with a few of my books that deal with the topic of relativity.

Albert Einstein is many people’s archetype of the genius scientist, and his most famous equation is E = mc2. Or is it? When you look at Einstein’s published scientific papers over decades of work, he didn’t (usually) write the equation in that form. In fact, he pointed out that was an inaccurate form, since it’s a limiting case of a far more general principle. In my latest piece for Double X Science, I argued that the form of the equation is far less important than its meaning, and it doesn’t really matter if Einstein wrote E = mc2 or not.

When you study relativity, you find those equations are specific forms of more general expressions and concepts. To wit: The energy of a particle is only proportional to its mass if you take the measurement while moving at the same speed as the particle. Physical quantities in relativity are measured relative to their state of motion – hence the name. [Read more...]

Did Einstein ever write his most famous equation?

The real poop on human digestion

I won’t lie: I love Mary Roach‘s books. She is likely the funniest nonfiction writer working today; her beat is the weird side of science. I reviewed her most recent book, Gulp: Adventures on the Alimentary Canal, for Double X Science:

Consider this question a 6-year-old might ask: Why doesn’t the stomach digest itself? After all, the human stomach contains hydrochloric acid, which is uses to break down some pretty tough substances for digestion. The answer, as Roach points out, is that it does: The acid dissolves the lining of the stomach over the course of a few days, but new cells replace the destroyed ones. When a person dies, no new cells are born, leaving the acid to work undeterred…with predictably gross results.

However, Gulp isn’t a gross-out book, though I don’t advise you read the chapter on coprophagia (poop-eating) during lunch, as I did. [Read more...]

In a certain sense, it’s easy to keep things in orbit around Earth. However, it’s hard to keep satellites in a specific orbit, which is what matters most for communicating with them and they with us, whatever task they’re designed to perform. Thanks to the work of rocket engineer Yvonne Brill in the early 1970s, the process is remarkably automatic.

Brill’s design eliminated this redundancy and lightened the spacecraft in the process. She also used a type of fuel called hydrazine, which is so reactive you don’t need oxygen or another chemical injection to ignite it. (On Earth, we’ve got lots of oxygen available for making things burn, but in space, you need to carry your own fuel for fire.) Brill’s system pumped liquid hydrazine through an aluminum nozzle. The chemical composition of the nozzle reacted with it, splitting it into smaller molecules and releasing a lot of energy. [Read more...]

I’m no rocket scientist, but I can appreciate the challenges of engineering something that needs to stay in the same orbit for years or decades. Yet the New York Times obituary for Brill mentioned her remarkable achievements as a sort of afterthought, as though they weren’t very important, really, in the scheme of things. My piece isn’t an obituary—I mostly write explanatory pieces about science, after all—but Brill’s contribution to spaceflight in general and the communications satellite revolution of the 1980s is astounding.

Yvonne Brill and the technology keeping satellites in orbit

My review of Brian Switek’s forthcoming book, My Beloved Brontosaurus, is up at Double X Science!

Suffice to say, these are not the dinosaurs I learned about as a young kid—and in my opinion, they’re much more interesting. Over the last few decades, the basic realization that modern birds are living dinosaurs has grown, and helped us understand their extinct uncles and aunts: the dinosaurs of the distant past. (Many scientists even refer to the classic dinosaurs as the non-avian dinosaurs, meaning these are the ones that aren’t recognizably modern birds.) For example, hollow yet sturdy bones allow modern birds to fly, but they also allowed sauropods to grow into the biggest animals ever to live on land. We also know now, thanks to a number of recent finds, that probably every dinosaur lineage had feathers of some sort. As Switek wrote, “Just think of how cute a fuzzy little Apatosaurus juvenile would be.” I concur. [Read more...]

Dinosaurs belong to all of us

Double X Science chemistry editor Adrienne Roehrich started a new podcast series, discussing stories of the week. Her first cohost was…me! We talked about important women in biochemistry, the size of protons, the science of procrastination, and cosmic rays—all in 15 minutes.

You can download the podcast from the Double X site, or subscribe through Feedburner. Adrienne is also working on listing our content on iTunes; I’ll update when that happens. Update: the podcast is now available on iTunes!

Procrastination and protons

Pascal the cat knows about particle physics.

Pascal the cat knows about particle physics.

It’s fundamental and natural to ask this question about an object: “how big is it?” For many things—most everyday objects, people, planets, stars—size is easy to measure. However, other things are more challenging, including the size of a proton: one of the three particles that make up every ordinary bit of matter. The major challenge is its tiny size, which precludes using light of any kind to measure it. To make matters worse, the size of a proton may depend strongly on what method you use to measure it, as I explained for Double X Science.

The simplest way to measure the size of a proton involves shooting electrons at it, and measuring the paths the electrons take as they feel the influence of the various forces. Because of those forces, in fact, the proton can’t be said to have a single size! Instead, physicists use three different size measurements, which are all pretty close to each other, but not exactly the same. The one most important to us for this post is the charge radius. Electron bombardment measurements found that to be about 0.88 femtometers.

However, electron bombardment only gets us so far; if we want better accuracy, we need another method. [Read more...]

How big is a proton?

The band has stopped playing, but we keep dancing
The world keeps turning, the world keeps turning.
–Tom Waits

A lot of nonsense has been written over the years about various “prophecies” predicting the end of the world, including stuff by people who should know better. What you see in newspapers, magazines, and TV shows might lead you to believe there is credible reason to think the world will end tomorrow: December 21, 2012. Supposedly this was predicted by the Mayan calendar. However, as with so many things, the truth is much different. The Mayas didn’t predict the end of the world, and there’s no evidence they thought that way. More importantly, there’s no scientific reason to think the world will end tomorrow: nothing we know of could bring about our end so rapidly without warning. That’s a reassuring thought to me, as I wrote in Double X Science today:

My confidence comes from science. I know it sounds hokey, but it’s true. There’s no scientific reason—absolutely none—to think the world will end tomorrow. Yes, the world will end one day, and Earth has experienced some serious cataclysms in the past that wiped out a significant amount of life, but none of those things are going to happen tomorrow. (I’ll come back to those points in a bit.) We’re very good at science, after centuries of work, and the kinds of violent events that could seriously threaten us won’t take us by surprise. [Read more....]

The band has stopped playing, but we keep dancing