Читать книгу String Theory For Dummies - Andrew Zimmerman Jones - Страница 45

A second type of infinity, proposed by John Wheeler in 1955, is the quantum foam or, as it’s called by string theorist and best-selling author Brian Greene, the quantum jitters. Quantum effects mean that space-time at very tiny distance scales (called the Planck length) is a chaotic sea of virtual particles being created and destroyed. At these levels, space-time is certainly not smooth, as relativity suggests, but is a tangled web of extreme and random energy fluctuations, as Figure 2-1 shows.

FIGURE 2-1: If you zoom in on space-time enough, you may see a chaotic “quantum foam.”

The basis for the quantum jitters is the uncertainty principle, one of the key (and most unusual) features of quantum physics. This is explained in more detail in Chapter 7, but the key component of the uncertainty principle is that certain pairs of quantities — for example, position and velocity, or time and energy — are linked together, so that the more precisely one quantity is measured, the more uncertain the other quantity is. This isn’t just a statement about measurement, though; it’s fundamental uncertainty in nature!

In other words, nature is a bit “blurry” according to quantum physics. This blurriness only shows up at very small distances, but this problem creates the quantum foam.

One example of the blurriness comes in the form of virtual particles. According to quantum field theory (a field theory is one where each point in space has a certain value, similar to a gravitational field or an electromagnetic field), even the empty void of space has a slight energy associated with it. This energy can be used to, very briefly, bring a pair of particles — a particle and its antiparticle, to be precise — into existence. The particles exist for only a moment, and then they destroy each other. It’s as if they borrowed enough energy from the universe to exist for just a few fractions of a second.

The problem is that when you look at space-time at very small scales, the effects of these virtual particles become very important. The energy fluctuations predicted by the uncertainty principle take on massive proportions. Without a quantum theory of gravity, there’s no way to really figure out what’s going on at sizes that small.