Empty Isn't Empty

It easy to think of empty space as, well, empty. But just as "elements" aren't elementary and "atoms" aren't indivisible, "empty" turns out to be something very different from what it seems at first glance.

Before looking into emptiness, it might be helpful to look at a surprising behavior called "tunnelling."

A very tiny particle (like an electron) can be confined to a small area with energy applied in the right manner. The energy serves as a barrier which the particle can't penetrate.

On the other hand, if the particle's energy is raised enough, it can gather the strength to penetrate the barrier.

Logically, one would expect that if no energy is given to the particle, it will never cross the barrier. Once again, nature demonstrates that logic is a limited human construct.

As explained by quantum physics' uncertainty principle, a particle's energy cannot be known precisely at any one moment in time. Put another way, over a very brief time, a particle's energy is highly unpredictable. What scientists observe in laboratories is that at one moment the particle will be found on one side of the barrier, and at the next moment the particle is found on the other side -- without any noticeable change in energy, and apparently without disturbing either the particle or the barrier in any way. The particle just seems to "disappear" and "reappear" on the other side.

Scientists interpret this as meaning that the electron did gain a large amount of energy for a very brief amount of time, so brief that the energy could never be observed by measurement, but long enough for the particle to jump the barrier. By the "law of energy conservation," energy cannot magically appear or disappear over any time long enough to be measured -- but nothing stops it from appearing and disappearing when we can't measure it!

Where did that energy come from?

We now return to emptiness. Modern science discovers that what we call empty space -- a vacuum -- may be empty of "real" things, but that doesn't mean it is completely empty.

Modern theory predicts, and experiments demonstrate, that just as particles can tunnel through a barrier in very brief amounts of time, so, too, can "virtual particles" appear and disappear in a vacuum.

In a very tiny space over a very brief time, a vacuum can give birth to twins: a particle and its antiparticle. This creation subtracts energy from the vacuum, which is empty of any energy to begin with. The two particles are instantly attracted to each other, and destroy each other in a burst of energy that repays the debt. The net effect is zero, and it all happens so quickly that we can never actually measure it happening, which is why they are called "virtual" particles.

Virtual particles do behave exactly like real particles, and they have been discovered in labs by measuring their effects on real particles. We can never measure virtual particles directly, but by observing real particles reacting to them, we know they were there briefly.

First, modern science discovered that what we call solid matter is mostly empty space. Then, it discovered that what we call empty space isn't really empty! Scientists do not have a firm understanding of what a vacuum is, but it seems to be more like a smooth, constant, undetectable background of energy, than nothingness. What we call matter and energy may simply be disturbances in the smoothness of the vacuum. It seems that everything depends on how you look at it.

Next: It's All Relative