 Sometimes, my robot vacuum cleaner will get caught on a ledge between rooms and sort of rock back and forth until it can free itself. It's a kind of vacuum metastability event. Okay, so we did the thing about local Maxima, and I'm glad that we did it. Really, it's an important concept. It informs how I think about a lot of stuff, and I think I was able to do it justice. But to make a halfway decent script, I had to cut something that I really wanted to talk about. Well, my editor is out of the country, and she can't stop me this time. Buckle in, folks. We're in for a wild ride. So way back in episode, oh god, 24? Definitely don't watch that. It's probably garbage. Watch the PBS space-time stuff instead. Anyways, we discussed the Heisenberg Uncertainty Principle, specifically the position-momentum formulation of it. Because subatomic particles are very small, figuring out where they are isn't as easy as just, oh hey, there it is. Observing them requires interacting with them in some fashion, and the more precisely you want to know their position, the stronger that interaction has to be, and the less certain that you can be of their momentum at that moment that you punch them with a laser pulse or whatever. But that's not the only version of the Uncertainty Principle. Let's say that you have an electromagnetic wave of some sort, and you want to know its frequency. If you can only measure it for a brief moment, getting a single little squiggle like this, it's difficult to be sure exactly what its frequency is. If you squint at that wave form, you could convince yourself that it's any number of values. But if you can really draw out your measurement for a long time, averaging over 50 or 100 peaks, you can get very, very close to determining the actual frequency of the wave, which is directly proportional to its energy. This is an example of the energy time version of the Uncertainty Principle. The shorter the period of measurement, the less certain we can be of the frequency, and therefore energy of a quantum state. So what about the quantum state of nothing? No particles, no photons, nothing at all. Everything that we might think of that could potentially provide energy to a section of empty space, electric fields, magnetic fields, particles with mass and velocity, if we get rid of all of that stuff, then we can expect that there will be an average energy of zero over enough time. But over very, very short periods of time, the Uncertainty Principle states that we can't be 100% certain how much energy there is in that empty space. That implies something really weird. So long as you get back to zero energy faster than the Uncertainty Principle requires, you can borrow some amount of energy to make, well, anything you want. Protons, electrons, photons, gluons, any of the subatomic particles can suddenly pop into existence in empty space and vanish again. There are a few rules that govern these so-called virtual particles. They must obey conservation of charge and momentum, which means that they're generated in opposing pairs. A virtual electron always comes with a matching positron. A virtual proton always has a sister anti-proton and so on. Also, because of the limitation set by the Uncertainty Principle, more massive virtual particles can't exist for as long as smaller ones. After all, they have more energy. E equals mc squared and all of that. If you don't have any previous experience with quantum mechanics, this all probably sounds like speculative baloney. But check this out. If you take two metal plates and hold them very close to each other, there are a number of particles that simply couldn't exist in that space anymore, like a radio wave with a long, lazy wavelength would never fit. The closer the plates get together, the more frequencies or possible energy states of particles get excluded from the space in between. Now, if there are no virtual particles, no big deal. But if these particles are popping in and out of existence all the time, the bigger ones can only appear outside the place, meaning that they'll only be bouncing off the outsides, not the insides. That's just like what happens if you suck the air out of a bottle. More particles outside than inside would create pressure. And in fact, if you do this experiment with a spacing of just 10 nanometers, the plates will be pushed towards each other with the pressure of one atmosphere. So to recap, the Heisenberg Uncertainty Principle tells us that we can't be certain that empty space doesn't have these spontaneously generated pairs of virtual particles, at least over very short timeframes. If you artificially exclude these virtual particles from the space between metal and plates, you can feel the plates getting sucked towards each other by a real pressure differential. It's called the Kazimier effect and it's fricking bonkers. But hang on, if we're getting some sort of force out of otherwise empty space, that's energy. That means that space with nothing in it, no radiation, no particles, nothing has some amount of energy. The mathematics of quantum physics readily verified this idea. There are a number of equations for quantum fields and particle energy that you can plug nothing into and get some amount of positive energy out. It seems that our universe has a baseline energy level just from empty space that's somewhere above zero. So what does that mean? Can we, you know, use it? I mean it sure would be nice if my phone could just liberate energy from the fabric of space itself instead of needing me to plug it in all the time. Well, it's possible that the energy might be liberated someday. But if that happens, a dead phone is really the least of my worries. The energy of empty space is called vacuum energy and you can calculate it directly using fundamental physical constants like the Planck length and the speed of light. That value is 10 to the 113th joules per meter cubed. For comparison, the atomic bomb that devastated Hiroshima was about 10 to the 11th joules. So, you know, take that, compress it down to one meter on a side, then multiply it by one with 100 zeros after it and you'll only be short by a factor of 100. However, you can also calculate it by measuring its effects in the universe, things like the Kazimir effect and the acceleration of cosmic expansion. That value is kind of tiny, only 10 to the negative ninth joules per cubic meter. I'd need to drain millions of cubic meters of space of energy just to charge a AAA battery at that level. That's quite an embarrassing discrepancy that remains unexplained, so embarrassing that it's known among physicists as the quantum catastrophe. But, speaking of catastrophes, what if the 10 to the 113 number is the actual vacuum energy and the reason we only measure 10 to the negative ninth is because our universe is balanced in a local minimum, like a ball in a little ditch on the side of a mountain. In this scenario, the vacuum energy we're measuring is a false vacuum. The real vacuum energy is 100 zeros down from where we are, and it's just a wacky chance occurrence that we find ourselves in this little metastable divot. If that were the case, we might be in trouble. Quantum particles can spontaneously hop energy states in a weird process called quantum tunneling. You'll occasionally see an electron jump up or down a couple orbitals in an atom without any apparent cause, essentially skipping a high energy in between state. If some pair of virtual particles somewhere in the universe happens to hop to an energy state on the other side of our little hump, they'll drop down to the much, much lower true vacuum state, releasing all that energy on the way down and dragging everything around them with them. This theorized scenario is called a vacuum metastability event, and it's bad news for everything. Not only would this massive cascading release of energy simply boil everything in its path into plasma at the speed of light, the fundamental laws of physics that apply to our current vacuum energy state would be totally changed. The existence of particles, the operation of forces like gravity and magnetism, everything that we know about the universe and how it works would be unmade and replaced by some other system, quite possibly one that doesn't support the formation of matter. Like I said, phone charging, not the biggest problem. A vacuum metastability event would unmake the entire universe at the speed of light. It might have already happened somewhere in the cosmos or in several places. Of course, we don't really have every aspect of quantum mechanics totally worked out yet. Maybe our predictions about what the vacuum energy ought to be are way off. Maybe we're already in the lowest real vacuum energy state and we'll just keep on keeping on the way that we have for the last 14 billion years. Still, whenever anyone asks me to describe an absolute worst-case scenario, it's hard to resist telling them about the false vacuum thing. Is the existence of virtual particles the wildest thing that you've heard for a while? What do you think of the possibility of a vacuum metastability event? Please leave a comment below and let me know what you think. Thank you very much for watching. Don't forget to blah, blah, subscribe, blah, share. And don't stop thunking.