Creating light is something that's usually done with a light switch, right? But what if you didn't have a light switch? A team of Swedish physicists were presented with such a conundrum, so they've gone and convinced a bunch of photons to spontaneously create themselves out of nothingness.
Creating something out of nothing really should be impossible. Yes, making photons is easy, but they all have to come from somewhere, right? The answer appears to be no, they don't, and we'd call it black magic and weigh all these scientists against ducks if this didn't have everything to do with quantum mechanics, and we already know that most of quantum mechanics is basically just one big scientific parlor trick.
Quantum theory predicts that empty space isn't really empty. No matter how empty it seems, there will constantly be this seething foam of "virtual particles" that pop in and out of existence for no particular reason. These particles don't usually last long enough to do much of anything, but if you're clever, you can measure whether they're there or not.
If you're very clever, like these Swedish
witches physicists, you can take those virtual particles and turn them into real particles, effectively creating something out of nothing. If you can get a mirror to move incredibly fast* (at about 25% of the speed of light), some of the virtual photons that pop into existence on its surface won't have time to disappear again before the mirror runs into them. The energy of these virtual photons then gets absorbed by the mirror, which then spits the energy back out, but as real photons. The upshot is that you can turn this thing on, and all of a sudden a whole bunch of microwave photons will appear quite literally out of nowhere.
In principle, it's possible to use this same technique to create other particles out of nothing (including protons and electrons), but it would take an impractical amount of energy. So at least for now, this is simply a demonstration of how utterly bizarre quantum mechanics can be.
*The mirror wasn't moving at 5% of the speed of light in one direction; instead, a superconducting magnet caused an electromagnetic field that acts as a mirror for microwaves to wiggle back and forth several billion times per second.