If the Universe were to undergo a vacuum decay event, where we transitioned from a false vacuum to a true vacuum state, the fundamental laws and properties of the Universe would change, destroying all forms of matter thant we know. A bubble of destruction would move outward at the speed of light, and if we were located within 18 billion light-years of such an event, it would destroy us, too. (Credit: public domain/pxfuel)

Ask Ethan: What if the Universe lives in a false vacuum state?

There’s a big difference between the notions of ‘false vacuum’ and ‘true vacuum’ states. Here’s why we don’t want to live in the former.

One of the great existential worries that plagues the minds of theoretical physicists is that the vacuum of space might not be in its true vacuum state, but could instead reside in a false vacuum instead. If you were to remove everything you could imagine from a large region of space, including:

• matter,
• radiation,
• neutrinos,
• external electric and magnetic fields,
• and any gravitational sources or spacetime curvature,

you’d be left with purely empty space, or as close as we can come to a physical definition of “nothing.” You might expect that if you were to draw an imaginary box around this region of “nothing” and measured the total amount of energy inside, you’d find that it was precisely zero. But that’s not what we find; we find that there actually is a positive, non-zero amount of energy inherent to space itself, even if we remove all the identifiable quantum and classical sources of matter and energy. What does this mean for the nature of the quantum vacuum, and in particular for the distinction between “true vacuum” and “false vacuum?” That’s what Eric Mars wants to know, asking:

“Could you please explain what false vacuum and true vacuum mean and its implications in the existence of the universe.”

It’s a great question, and requires that we start with the idea — specifically for physics — of zero.

This artist’s illustration depicts how the foamy structure of space-time may appear, showing tiny bubbles quadrillions of times smaller than the nucleus of an atom that are constantly fluctuating and last for only infinitesimal fractions of a second. Rather than being smooth, continuous, and uniform, at the quantum scale, spacetime has fluctuations inherent to it, which likely correspond to a non-zero zero-point energy to it. (Credit: NASA/CXC/M. Weiss)

In mathematics, zero is simply a number, signifying the absence of either a positive or negative amount of any quantity. In physics, however, there’s another way to define zero: the zero-point energy of a system, or the lowest possible energy state that it can achieve while still remaining the same system we were initially talking about. For any physical system we can dream up, there will be at least one…