Antimatter Mystery

In 1897, physicist J.J.Thomson discovered a particle known as the electron. In the century-plus since, scientists have been on the hunt for the answer to a deceptively complex question — Are electrons round? — and based on what we currently know, the answer is yes. As Mordecai-Mark Mac Low, an astrophysicist at the American Museum of Natural History, told Futurism, electrons are round "within measurement error."

Unfortunately, this answer just leaves physicists with more questions.

According to the standard model of physics, when our universe first came into existence with the Big Bang, it should have contained equal amounts of matter and antimatter, and that's a problem. "As is well known to all 'Star Trek' fans, when matter and antimatter come together, they annihilate in a burst of photons," said Mac Low. Based on that, the universe shouldn't exist at all, and yet, here it is.

To that end, scientists have been searching for any sign of asymmetry between matter and antimatter that could explain why the universe wasn't instantly annihilated and why it currently contains far more matter than antimatter. If electrons were lumpy and roundish instead of perfectly spherical, that could imply the much-sought-after asymmetry, but electrons are round, as far as we can tell.

Now, researchers from JILA have demonstrated a new method for looking at the shape of electrons that could perhaps reveal a distortion.

If an electron had an electric dipole moment (EDM), it would indicate a non-spherical shape. In their search for EDM, scientists have typically looked at electrons within beams of specific atoms and molecules. Unfortunately, the motion of a beam places a limit on the amount of time the electrons can be measured, and so far, observations have turned up zero signs of EDM.

The JILA researchers are taking a different approach. Rather than looking at electrons within beams of neutral particles, they trapped molecular ions of an inorganic compound called hafnium fluoride within a rotating electric field. Instead of flying away like they do within a beam, the ions in this situation trace out tiny circles. So far, the JILA researchers have been able to track electrons' spin for .7 seconds straight. That's 1,000 times longer than the observations using beams.

Puzzling Phenomena

Confirming that electrons are round might seem inconsequential, but the observation would have major implications. Currently, we operate under the assumption that, whether time is moving forward or backward, physical processes look the same. If a non-zero EDM is observed, it would alter our understanding of time-reversal symmetry and some of the most basic foundational layers of physics. It would also potentially solve the great antimatter mystery at the core of our very existence.

Click to View Full Infographic

Now that they've been able to prove their method works, the JILA researchers can begin pushing it, according to Mac Low. Indeed, they have already refined their method, and lead researcher Eric Cornell told Science they think they'll be able to boost the sensitivity of their experiments by about a factor of 10 within just a couple of years, which should allow them to produce a measurement of electron's sphericity that's better than the ones currently in existence.

Other groups are also working on projects to produce more sensitive measurements of the shape of electrons. The current record for sensitivity belongs to an ACME collaboration at Harvard and Yale, and they believe they'll be able to reduce the uncertainty of their observations by a factor of 20 within the next year. A group at Penn State has set a target of a 30-fold improvement on the ACME measurements.

Physicists at Imperial College think a 1,000-fold gain in the next five years is possible using the methods they're currently working on, and as Hinds, leader of that group, told Science, that level of sensitivity should be enough to "rule out a whole range of theories" centering on an electron EDM. If at that point, the answer is still the same — electrons are round — theorists will just have to start looking elsewhere for the answers to these mysteries of the universe.

Share This Article