Terahertz

In our normal experiences we know that every event is caused by something else. If a window breaks, it happened because a ball went through it, which happened because a kid threw it, and so on.

However, if the history of science teaches us anything, it is that our “normal experiences” have often been wrong.

The Earth is not flat, although it looks pretty flat (especially on the prairies). The Earth moves, although it seems like everything else does. Things tend to stay in motion, even though everything experiences some friction around us and eventually slows down. And not every event has a cause.

An atom can undergo three processes when emitting or absorbing light. First in can experience stimulated absorption, when a photon of light hits an electron in the atom and bumps it to a higher energy level. This is like coming along and picking up a pencil and putting it on a higher shelf – the overall energy is increased. It can also undergo stimulated emission, this is the key to what happens in lasers. A photon comes along, “bumps” the electron (that’s in its excited state) and the electron drops to a lower state, releasing its energy as another photon (1 photon in, 2 photons out). Basically it’s like coming along and knocking the pencil back down to a lower shelf, and as the pencil falls, rather than picking up speed with energy it emits energy in the form of light. These two processes fit our mold of having a nice explainable cause, and there isn’t anything to weird about them.

However, the final process is spontaneous emission. This is when an electron in an excited state, for no reason, drops to a lower state and emits a photon. This is essentially equivalent to a book that’s sitting nicely on a shelf that suddenly falls to the ground. There is no physical cause here!

So what is theoretically happening? The idea is that within the Uncertainty Principle (the idea that we cannot know anything to arbitrary precision) a matter-antimatter pair of particles can spontaneously be created (from nothing!) and can knock that excited electron just enough that it falls to the lower state. This is known as a vacuum fluctuation.

But what does this ultimately mean? Essentially, it is entirely natural that stuff can happen, unpredictably, with absolutely no cause!

But how often does this really occur? It turns out that it happens continuously. The time that an electron can stay in an excited state (without spontaneously emitting) has been measured to be (for some of the longest atoms) only 10 milliseconds. That means that every second there are at least 100 large vacuum fluctuations in the size of a large atom (about a tenth of a nanometer). And many atoms have orders of magnitude shorter lifetimes (often in the nanosecond or 10^-9 range).

So not only can events happen with no cause, but things are happening with no cause more often than they seem to be caused!

So what’s the big deal in the end?

Well it’s not just the emission of radiation from atoms that can have no cause. Since physicists have increased the sensitivities of their astronomical observations, it has lead them to determine that the universe has zero energy (conveniently within a quantum fluctuation).

This leads many to believe that the universe could essentially be nothing more than an uncaused vacuum fluctuation.

As Dr. Victor Stenger puts it: “The universe looks exactly as it would look if there was no God.”

For a more detailed writeup on these ideas, see the Skeptics Guide to the Universe blog post for today.