A friend was complaining recently about an “absurdity” of multiple universes as portrayed on a recent PBS/Nova broadcast. Here’s a slightly edited version of my reply:

There are two general concepts of alternative universes; one is unknown and unknowable in our present understanding, the other is an absurdity that is considered by some to be real because the math seems to work.

### Bubbles and Worlds

The first one was discussed here already; the idea of bubble universes. (As an aside, the evidence for the Big Bang is quite strong.) But bubble universes, while interesting, don’t seem at current time to have a possibility of interacting with ours or being detected; in fact, any such contact would generally be destructive were it even conceptually possible. So, there may be bubble universes out there, each with its own set of physical laws and thus very different from ours — but it doesn’t matter.

There is a possibility that our understanding may increase to the point where this knowledge can be useful; however small, this is worth spending some time and treasure on. For one thing, this “quantum foam” that gives rise to the idea of bubble universes is connected to the idea of zero-point energy. And if we were able to figure out how to tap into *that*, our energy problem would be permanently solved.

The second multiple-universe notion is named after its originator: Everett’s Many-Worlds Hypothesis. This addresses the probability notion of events at the quantum level with a new world created for each possible outcome. It is implied by the math of probabilities, but rather than assuming our understanding is incomplete, Everett assumed that every possible outcome comes true.

The scale of Everett’s Many Worlds idea takes a moment to appreciate. Defenders of this, and there are some such as this one, use the “classical” example of Schrödinger’s Cat. No matter which way the event is observed, cat dead or alive (this fellow more gently assumes “asleep or awake”), the one universe becomes two separate universes, one for each of these outcomes.

### And Another and Another…

All right, somehow another universe has come into being, this flatly states. You now have twice as much mass, twice as much energy (yes, sort of the same statement), and twice as much space that this arrangement exists in. How was one displaced from the other so that they do not interfere or interact? Where did all of that come from, the force that could create the second universe as a replica of the first without disturbing it? We have a sense of where the Big Bang got its mass and energy, but that was a very messy event that we can still see echoes of, literally, nearly fourteen billion years later.

But it’s not just two universes. Unlike the (maybe) poor cat, each quantum scale particle has an infinite number of possible positions. The “expected” positions are *the most probable*, but *all* others are possible.

### Quantum Tunneling

A quantum particle may even appear on the other side of an impenetrable barrier; this is called “quantum tunneling.” The particle did not pass “through” the barrier, it simply appeared on the other side. You can actually calculate for a given distance and situation how often this would happen.

In fact, this odd effect is the key to radioactive decay. In an atomic nucleus, a particle may appear (move, sort of) at a point far enough from “normal” to cause a sensitive nucleus to fall apart from the now unbalanced forces. This is with no outside force acting upon it or influencing events. Since it is governed by probabilities, it happens at a steady rate, predictable from the structure of the nucleus, and thus radioactive decay rates are calculable and stable. (In essence, *all* elements are radioactive, but most have such long half-lives that they don’t have a decent chance of even one decay event in a universe-long lifetime.)

Quantum tunneling has practical, real-world uses. For example,this odd idea allows extraordinary images down to the level of individual atoms using a scanning tunneling microscope. This image is of the surface of platinum, for example:

*How* Many?

So now back to Everett: In that paradigm, *every quantum-scale particle in the entire universe can be in every possible position every tiny fraction of a second*, and according to the Everett interpretation, every one of these possibilities is a real outcome and creates another universe. But this is an infinite number of possibilities times a near-infinite number of particles times a near-infinite number of occasions (the smallest element of time is Planck time; it’s pretty small) — and all of this has been going on since the beginning.

So, to make the math of quantum probability more comfortable, the Everett folks (and here’s another, more detailed discussion) imply a number of universes and mechanism for creating them with math that makes its own horrendous new problems.

I’d agree with you: This notion is an absurdity. And it will go away, eventually, with new insight into quantum probabilities.

===|==============/ Keith DeHavelle