Most people think of the vacuum of space being empty. At a glance it is. But if you look at a small enough spot, it is teaming with virtual particles that pop in and out of existence. These particles also have some very high energies which is also directly translates to mass leading to the most astonishing idea that “empty” space is actually very much not empty, at least for very short periods of time.
In the field of Quantum Physics, this affect is called electric-field “Vacuum fluctuations.”
This is counter to our normal understanding of reality where we have to have conservation of energy: You can’t just have things coming into existence or dropping back out again for that matter. In Quantum physics however, you can violate the laws of classical physics if you do it for a short enough time. Sort of like that 5 second rule of food hitting the ground.
It also turns out that when doing things in very small spaces, this violation of classical mechanics has some curious implications. In the 1940’s it was theorized that if you had two flat mirrors in space placed closely and parallel to each other, that you’d get a force between them that brings them together.
The way this is supposed to work is that if you have those mirrors closer than the wavelength of the virtual particles (remember that particles have wave nature and waves have particle nature), that the number of these virtual particles between the mirrors ends up being smaller than the number of particles on the other side of the mirrors. This creates a force that can, in theory, be used to create a non-virtual photon – light from nothing!
A group of physicists in Sweden noticed that you don’t have to have 2 mirrors but can do that with one mirror if you move the mirror fast enough. They built a device to do just that and, indeed, got sparks from it – light from nothing.
The original thought experiment around this phenomenon revolves around a pair of atoms doing something similar. If you have two atoms that are quite close together, one of them can emit a virtual photon and the other absorb it without violating the laws of energy conservation if you look at it over a longer time period than it takes for the virtual photon to come and go. The act of it happening modifies the local vacuum around them and creates an attractive force between them which tends to be quite strong but only at very short distances.
One of the reasons for that is that the emitting atom emits in a random direction that isn’t necessarily the direction of the other atom. If you can somehow direct that emission, then you’ll be able to increase the distance that force works at. Sure enough, a team in Israel figured out how to do that and demonstrated orders of magnitude better distance.
None of this is all that interesting from a practical viewpoint today, but suppose you can harvest this seething energy of “empty” space for use in a rocket motor? That might well be possible with photon emissions that these experiments show.
Along the same lines, a team from Germany is claiming to be able to directly sample the Vacuum Fluctuation, meaning that they can measure and map it. To do this, they stop time.
Yup, you read that correctly.
When you’re down in this realm of reality, things work in space-time, not space as we’re used to. They go hand in hand; mess with one and you can mess with the other.
So to do this, some interesting things have to happen. First of all you have to make a conceptual shift from attempting to measure things in the frequency domain (e.g color of light) to making measurements in the time domain (i.e. what is the value at a particular point in time). This technique is, by the way, a very useful problem solving technique: change how you look at the problem and a different set of solutions will present itself. I digress.
Anyway, what they did was to use very short laser pulses – less than half the wavelength of light in the spectrum they were using. This short a pulse, couples with the quantum field under study and allows them to look at the electric field amplitude at a particular point in time. You just have to look a lot and often to get the picture of what is going on the rest of the time (they run about 20 million observations per second).
Because of the coupling here, the measurements don’t disturb the underlying quantum state of the system either which is a directly strange thing. Such a contraption should be able to tap quantum cryptography too.
The other odd thing about this experiment is that to get the measurements they use a very intense, very focused, very short pulse from the laser. What this does is to “bunch” up the vacuum fluctuations and deliberately changes the speed of light over short distances. This then “un-bunches” the fluctuations in other places which allows them to measure the actual (natural un-bunched) “ground state” of empty space.
Now all this creates some serious questions about reality itself as you might imagine. One of those is about the nature of light. What is it really? “Classical” quantum physics says that light behaves as a wave (like a radio wave) or a particle (a photon) depending on how you look at it. In fact, the two are interchangeable in all matter.
These experiments suggest that photons aren’t so much “packets of energy” as a local measure of the quantum statistics of the electromagnetic fields in space-time. To put it another way, photons aren’t so much “things” as possibilities at any given time and place.
Which makes me question the nature of reality itself. Physics is a blast.
Tech Talk is a new monthly online column. Trained in Nuclear Engineering, Randy has been working the bleeding edge of various fields of technology for over 40 years.