This experiment will measure nothing, but very precisely (Patreon)

 [This is a transcript with links to references.]

The physics paper that I’m most excited about this week is about an experiment that will measure nothing. But not any nothing, a very specific nothing, that’s the vacuum of quantum electrodynamics.

You might think that if you remove all the particles from within a container, then the only thing that’s left inside is space. But that isn’t so. It’s because particles in quantum physics are like waves atop of an ocean. If you take away the waves, you still have all that water! And the water underneath the waves is like the quantum vacuum. It contains what we call “virtual” particles, or sometimes they are called “quantum fluctuations”. They can’t be measured in detectors because, they’re not real particles. However, they affect real particles, and that’s measurable.

In this new experiment they want to measure the effect of those virtual particles on a very elementary process that you’re all familiar with. It’s that light doesn’t affect other light. If you cross two light beams, they’ll just go through each other. This is why light is good for seeing the world around us, because it points back to the source in a straight line.

However, that light doesn’t affect other light is strictly speaking not correct and that’s because of these virtual particles in the quantum vacuum. You see, beams of light are made of quanta of light, that are the photons. And every once in a while, a photon creates a few of those virtual particles in the quantum vacuum, and those then affect another photon! So, this is how light can, sometimes, affect other light.

The issue is that this happens very very rarely, so you can’t just take laser pointers and cross their beams, you need very powerful lasers. These researchers want to do it with the European XFEL laser. That’s an X-ray laser of super high intensity. It works by accelerating electrons with magnets in a tunnel that’s more than three kilometres long. The electrons are slightly forced off a straight line which makes them emit X-rays.

In the new paper now they suggest to cross the pulses from this X-ray laser with not one but two beams from opticallasers. This triple laser crossing is supposed to coax the virtual particles in the vacuum into interacting with the real particles in the beams. They calculate which angles would be ideal and say that this experiment might become feasible within the next couple of years with the XFEL laser that’s located in Hamburg, Germany.

I find this an interesting proposal because the quantum vacuum is kind of the essence of our problems with quantum mechanics. It’s always there, whether you observe it or not, so maybe it’s the origin of the random jumps in quantum mechanics? Well maybe not, but still, I fully support this attempt to measure nothing.