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?


Where do cosmic rays originate? Cosmic rays are mostly high-energy protons from deep space that hit Earth’s upper atmosphere, creating showers of other particles that can be detected at the surface. Some of these protons are so incredibly high energy—meaning they’re moving just a whisker slower than the speed of light—that only exceptional astronomical events could accelerate them. The prime suspect: supernova explosions. Up until now, though, nobody had confirmed this suspicion. However, a new observation using gamma ray emissions from supernova remnants found the telltale signature of particle collisions, which could only be present if protons were getting that extra boost of energy.

On October 15, 1991, a high-energy proton from deep space struck Earth’s upper atmosphere. Known as the “Oh My God Particle”, this proton was by far the highest energy cosmic ray ever seen. This one proton’s energy was equivalent to a regulation soccer ball traveling at 15 meters per second (34 miles per hour). In the two decades following, observers spotted several similarly energetic cosmic rays, which left a big question: what was accelerating these protons to higher speeds than anything we can achieve in on Earth? [Read more….]

High-energy cosmic rays are sped on their way by exploding stars

Vesta is the second-largest asteroid in the Solar System, and recent measurements by the Dawn mission showed that it’s actually a protoplanet: a piece of planet-like material left over from the early days of our Solar System. However, Dawn is significantly non-spherical and very battered. Most notably, it has two huge overlapping craters near its south pole, marking impacts that nearly shattered the asteroid, and which raised a mountain higher than any other in the Solar System. Now, a computer simulation may have showed how Vesta came to be the fascinating, scarred, wonderful object we see today.

As with other Solar System bodies, Vesta bears the scars of its history. The most substantial of these scars are the two large impact basins, Veneneia and Rheasilvia. (Both craters were named for virgins who served the goddess Vesta in Roman mythology—the vestals.) Rheasilvia formed about 1 billion years ago and is larger. Veneneia is smaller and formed at least 2 billion years ago; its presence was partly obscured by the later impact. Meteorites from Vesta, possibly ejected by the impacts forming Rheasilvia and Veneneia, have been found on Earth. [Read more….]

Kaboom! A simulation shows how impacts shaped and nearly destroyed Vesta

The shell game is a classic con, a rigged contest meant to separate a person from their money. The quantum shell game described in a new paper is meant to elucidate the role of measurement in the outcome of an experiment, separating the quantum and classical aspects clearly. This was accomplished using measurement of the spin of a nitrogen atom in a diamond, and rules out the naive idea that the act of measurement is responsible for quantum weirdness.

Another approach to probing this distinction involves strong measurements that have no classical counterpart. Richard E. George and colleagues demonstrated incompatibility of the naive classical view in measurements on a modified diamond. As they described in a new PNAS paper, the equivalent classical system is similar to the old con known as the shell game: three shells, with a pea under one of them. Here, the act of “measuring” the pea’s location has no effect on the system. But the researchers’ quantum system excludes this classical behavior well beyond reasonable doubt or random chance. [Read more….]

Playing a quantum shell game to win

Astronomers would love to predict supernovas: knowing when and how massive stars die would reveal a great deal about them. An observation of a particular supernova with the license-platish name SN 2010mc actually began 40 days before the final explosion, giving astronomers a lot of data about the final stages of its life. This type of star that produced SN 2010mc is pretty rare, but when it dies, it dies big. The telltale sign of impending doom for stars of this type turned out to be the shedding of a huge amount of mass; watching for that ejection could let astronomers predict some future supernovas.

Supernova SN 2010mc was spotted by the Palomar Transient Factory (PTF), which looks for supernovae and other one-time (transient) events in a wide swath of the sky. As the name suggests, light from SN 2010mc arrived at Earth in 2010. (The first supernova of the year was 2010a; the 27th was 2010aa. Thus, there were a lot before 2010mc, but I’m too lazy to work out what number that was.) Going back in the PTF archives, the researchers discovered a precurser outburst, from the same region of the sky, which occurred 40 days earlier. [Read more….]

Stellar epidemiology: predicting supernovas from death throes of stars

Bose-Einstein condensation occurs when certain particles known as bosons are cooled below a certain critical temperature. Below this threshold, they begin to act collectively as a single system, as predicted by Sateyendra Nath Bose and Jim-Bob Albert Einstein. Typically, the critical temperature for Bose-Einstein condensation is very cold; the original experimental realization used cryogenic rubidium atoms, cooled by lasers and trapped magnetically. However, by using boson quasiparticles—particles that arise via interactions in material, rather than existing independently like electrons and the like—researchers achieved a room-temperature Bose-Einstein condensate.

These systems typically require temperatures near absolute zero. But Ayan Das and colleagues have now used a nanoscale wire to produce an excitation known as a polariton. These polaritons formed a Bose-Einstein condensate at room temperature, potentially opening up a new avenue for studying systems that otherwise require expensive cooling and trapping. [Read more…]

Significant quantum phenomenon seen at room temperature for the first time