Yes, Virtual Particles Can Have Real, Observable Effects
“Now that the effect of vacuum birefringence has been observed — and by association, the physical impact of the virtual particles in the quantum vacuum — we can attempt to confirm it even further with more precise quantitative measurements. The way to do that is to measure RX J1856.5-3754 in the X-rays, and measuring the polarization of X-ray light.
While we don’t have a space telescope capable of measuring X-ray polarization right now, one of them is in the works: the ESA’s Athena mission. Unlike the ~15% polarization observed by the VLT in the wavelengths it probes, X-rays should be fully polarized, displaying right around an 100% effect. Athena is currently slated for launch in 2028, and could deliver this confirmation for not just one but many neutron stars. It’s another victory for the unintuitive, but undeniably fascinating, quantum Universe.”
If you think about empty space at a quantum level, you’ll find that it isn’t so empty, after all. Due to the inherent effects of quantum uncertainty, particle/antiparticle pairs pop into and out of existence continuously, including electrically charged particles. If you look at the quantum vacuum in the presence of a strong enough external magnetic field, the positive and negative particles, even though they’re only virtual particles, will move differently, and therefore will affect the real particles that pass through them differently than if there were no magnetic field. This leads to a real, observable signal that can be seen in space: around neutron stars!
Heisenberg first predicted this in 1936, and today, we know it’s true. Get the story of the first observable effect of vacuum birefringence today.
In A Quantum Universe, Even Mass Is Uncertain
“It’s one of the most remarkable and counterintuitive results of the quantum Universe, that every unstable particle that you make has an inherent uncertainty to the most seemingly fundamental property of all: mass. You can know what the average mass of a typical particle of any particular type, and you can measure its width, which is directly related to its mean lifetime through the Heisenberg uncertainty principle. But every time you create one new particle, there’s no way to know what its actual mass will be; all you can do is calculate the probabilities of having a varieties of masses. In order to know for sure, all you can do is measure what comes out and reconstruct what actually existed. Quantum uncertainty, first seen for position and momentum, can now be convincingly stated to extend all the way to the rest energy of a fundamental particle. In a quantum Universe, even mass itself isn’t set in stone.”
There are a few properties you can say intrinsically belong to a particle: things like mass, spin, electric charge, and certain other quantum numbers. If your particle is completely stable for all eternity, there’s no reason to question any of this. But if a particle you create, even a fundamental one, has an inherent instability and can decay, all of a sudden Heisenberg comes in to mess everything up! Suddenly, the fact that you have an uncertain lifetime means you have that pesky energy-time uncertainty, and the energy of your particle is intrinsically uncertain, too. Because E = mc^2, that means your mass is uncertain, too. And the shorter-lived your particle is, on average, the more uncertain your mass is. This means when you make a top quark, for example, it could have a mass of 165 GeV, 170 GeV, 175 GeV, 180 GeV, or anywhere in between those values. (Including some values outside of that range!)
In a quantum Universe, even mass is uncertain. Here’s the fundamental physics story of how that came to be, both theoretically and experimentally.
Baseball And The Atom Bomb
“Moe Berg, who left baseball in 1939, and was eager to get involved in the war effort, was appointed to Project Larson, part of Alsos and hence connected with the OSS. Berg was sent to Italy to speak with Italian scientists and find out what he could. Then, when the Alsos mission learned that Heisenberg would be speaking in Zurich in December 1944, Berg was issued a pistol and a cyanide capsule.
Berg blended right in with the audience listening to Heisenberg’s lecture. What a relief that the talk had nothing to do with nuclear weapons or even nuclear energy, but was rather about quantum matrices and other physics topics without a clear nuclear connection. Attracting no suspicion, Berg left the talk and returned to the United States, reporting that he found no evidence of German progress.
Later in life, Berg was offered the Presidential Medal of Freedom for his heroic efforts, the highest honor the United States can award a civilian. But for unstated reasons, Berg declined the honor. He remains the only major league baseball player whose card is on display at the CIA’s headquarters.”
When it comes to the history of the world, there are few developments that were more critical than the allied development of the atomic bomb during World War II… and the failure of the Nazi regime to do so. In hindsight, it became clear that the Nazis were quite far from weaponizing nuclear fission, but with scientists like Werner Heisenberg and Otto Hahn on board, the danger was clear and apparent to all. Yet World War II also saw the beginnings of what would become the US Central Intelligence Agency, and one of their first field agents was Moe Berg, a former major league baseball catcher. This average-at-best baseball player spoke many languages fluently, joined the Office of Strategic Services (OSS), and almost assassinated Heisenberg in 1944!
Come take a dive into this fascinating and mostly-forgotten bit of history, thanks to the incredible writing and researching of Paul Halpern!
Ask Ethan: Where Does Quantum Uncertainty Come From?
“Explain to me what information is gained from the quantum mechanical commutation relation. There’s more to it than, “we just can’t measure both properties at the same time.””
It’s absolutely true that, in quantum mechanics, there are certain pairs of properties that we simply can’t measure simultaneously. Measure the position of an object really well, and its momentum becomes more uncertain. Measure its energy, and its time becomes more uncertain. And measure its voltage, and the free charge becomes more uncertain. Although this is disconcerting to some, it’s a fundamental part of the quantum nature of the Universe. But there’s also more to it than that! Not only are pairs inherently uncertain, but each component has some built-in uncertainty that you can never take away. Moreover, it arises from a simple fact that isn’t true classically: the order of operations – whether you measure position or momentum first – makes a fundamental difference in what you get out. This quantum commutation relation is where so much of the fundamental quantum weirdness in our Universe comes from.
It’s also why we have technologies like atomic clocks, hydrogen masers, and MRI machines! Come find out where quantum uncertainty arises from, and why it matters, on this week’s Ask Ethan!