Our Antimatter, Mirrored, Time-Reversed Universe

SPEAKER_1 (0:01)

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Matt O'Dowd (0:59)

The foundations of quantum theory rest on its symmetries. For example, it should be impossible to distinguish our universe from one that is a perfect mirror opposite in charge, handedness, and the direction of time. But one by one these symmetries were found to be broken, threatening to break all of the physics along with them.

In his famous lectures on physics, Richard Feynman talks about what it means to expect the universe to be identical in the mirror, for it to be parity symmetric. He invites us to imagine a clock in a mirror reflection. Numbers are backwards, components are all flipped left to right, and it ticks counterclockwise.

And then he asks us to imagine building that same mirror clock in reality, everything is constructed as though reflected. Numbers get painted backwards, every screw with right-handed thread or right-spiraling coil is replaced with a left-handed version. Our intuition tells us that the mirror clock should tick in exactly the same way, except counterclockwise.

Our intuition would be wrong. The laws of physics and so the laws of clocks are not symmetric to this sort of parity transformation.

As we saw in our recent episode, the experiment that first proved this found that cobalt-60 nuclei decay by spitting an electron out in the opposite direction to their nuclear spit axis. But in a mirror-reflected universe, the same decay should be in the opposite direction, so with that spin axis, which is fundamentally different physical behavior. So what does this have to do with Feynman's clock? Well, he proposes a clock whose ticks are governed by the decay of cobalt-60.

Imagine an array of cobalt-60 atoms in a magnetic field. The cobalt nuclei have angular momenta that will align with the magnetic field, let's say upwards, so the decay electrons travel down. A detector is placed to intercept those electrons, and the clock ticks with every captured electron. In our reflected clock, we need to replace the cobalt atoms with their parity-inverted counterparts. But now, the decay electrons travel upwards with the nuclear spin, and away from the detector, such a clock wouldn't tick at all. Taken to its literal extreme, a perfectly constructed mirror-reflected clock behaves differently. So, what's the big deal? Well, the violation of parity symmetry poses a threat to an even deeper symmetry, CPT symmetry, the combined flipping of charge, parity, and time. And this symmetry lies at the foundations of quantum field theory. Physics must work the same if we flip all of these properties. If not, physics as we know it goes out the window, which does seem like a big deal. To save physics, Richard Feynman proposes that we build a copy of our clock out of antimatter. Sure, Feynman, why not?

Electrons become positrons, quarks become antiquarks, and vice versa, sending protons and neutrons to their anti-versions in the nuclei of our now anti-cobalt-60 and other anti-atoms. Sending matter to antimatter is the C part of CPT. Charge conjugation. All charges switch sign. Electric charge, but also quark color charge, weak hypercharge, etc. That's what a switch to antimatter means. How does this work in our antimatter clock? Well, antimatter atoms have negatively charged nuclei, which means their nuclear magnetic fields point in the opposite direction to regular matter, relative to their angular momentum. The magnetic field in our clock will align antimatter nuclei in the opposite direction to matter nuclei. So in our mirror-reflected antimatter clock, the direction of the decay electrons are flipped, once due to the mirror reflection.

SPEAKER_1 (4:57)

This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome? That's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses set up required compatibility and availability varies 18 plus.