Because Quantum.

We mostly tend to think of physics as “normal”. Action and reaction, things fall at a predictable rate (in a vacuum, at least), and so on. At least on a macro scale, the universe behaves “nicely”, in ways that we can pretty easily understand.

But when you get down to the atomic and subatomic level, or thereabouts? Things get *weird*.

Disclaimer, I am very much Not A Physicist. I have trouble with some of the trickier bits of “classical” physics (for example, I can never remember which ones are watts, volts, amps, and so on), much less the quantum realm. But I can understand enough to point out some of the real head-scratchers that actual physicists *do* understand, or at least debate about. And, I had an Actual Physicist look this over, and he said it was a bit oversimplified, but basically right.

Let’s start with uncertainty. The short-version explanation of Heisenberg‘s Uncertainty Principle is that you cannot simultaneously know (to a sufficiently precise degree) both the position and the momentum of a sufficiently small particle.

Some of this is due to the observer effect–once you get to a small enough scale, you can’t even look at something without affecting it, because whatever you’re looking at it with (light, for example) will change its position and/or momentum. But, further research suggests that this isn’t just a failure of our technology and whatever, but is instead a fundamental property of the universe. That once you get to a small enough scale, you actually can’t have both a definite position and a definite momentum at the same time.

And, as I understand it, this fundamental, well, uncertainty is at least in part behind a lot of the other weird quantum physics phenomena. But, you might ask, *why* does this uncertainty exist?

As far as I can tell (again, Not A Physicist), a large part of the issue is that, on a small enough scale, matter and energy are basically the same thing. Even if you don’t know what it means, you’re probably familiar with Einstein’s E=MC². Energy=mass times the speed of light squared. But, that doesn’t just mean that matter can be turned into energy. At a fundamental level, once you get to a small enough scale, matter is a *form* of energy. And with energy comes waves.

In everyday life, we’re used to thinking of waves and particles as different sorts of things. As I discussed in my article about how to science, one of the big debates relatively early in our collective understanding of physics was whether light was a particle or a wave. Einstein finally figured out that the answer to that was both. And, eventually, scientists figured out that it, in essence, went the other way, as well. On a small enough scale, particles *are* waves. So it kind of makes sense that we, fundamentally, can’t simultaneously know exactly where they are *and* exactly where they’re going.

On to one of the more famous thought experiments, Schrödinger’s cat. It is, in essence, an attempt to figure out what’s going on with quantum superposition, or the notion that certain events, such as the radioactive decay of individual atoms exist in sort of blended state, consisting of all possible results (in the case of the atom example, decayed and undecayed) until they are observed.

The setup is as follows: you have a box containing a single radioactive atom, a detector that can measure whether or not the atom has decayed, a vial of poison that will be broken open once the detector measures radioactive decay, and a live cat. According to some interpretations of quantum mechanics, the cat would be simultaneously alive (because the atom has not decayed) and dead (because the atom has decayed), until someone opened the box. This is, obviously, absurd.

As I understand it, the solution to this particular thought experiment relies on what constitutes an “observer”. If an event has to be observed by an actual human (or equivalent) mind to break quantum superposition, you’d have the absurdity of the dead-and-alive cat. But if it only has to be “observed” by the larger universe, then, well, as soon as the detector measures the decay (or fails to do so), quantum superposition is broken. So there is no need to torture the hypothetical cat.

Now on to the next bit of weirdness. Quantum tunneling. So, imagine you have a box, that is completely empty except for a single atom, and a thin barrier dividing the box into 2 chambers that the atom will bounce off of. Normally, what you would expect is that the atom would just bounce around in one half of the box. Except, because of uncertainty (and some other weirdness, I think), occasionally the atom will just… stop being on one side of the box, and start being on the other side instead. The barrier would be perfectly intact, and the atom will still bounce off of it normally (it’s not a matter of the barrier somehow being porous or whatever), the atom will just… be on the other side of it.

I believe the reason for this is that, at that scale, things stop being things and start being probability clouds. As I understand it, there’s sort of a blob of space around the “real” position of a quantum-sized particle, and the particle can, in essence, be *anywhere* in that space. So, if a barrier is thinner than the size of the blob, a quantum object could hit one side of the barrier, not have enough energy to in any way penetrate or damage the barrier, but just happen to end up in the part of the blob that’s on the other side of the barrier.

And this one isn’t just a weird thought experiment like Schrödinger’s cat. The weird thought experiment is just a way to illustrate an actual phenomenon that happens in things like nuclear fusion and radioactive decay. It fundamentally limits the minimum size of electronics (if insulators, transistors, and the like are thin enough for quantum tunneling, they stop working). It has implications for issues ranging from photosynthesis to faster than light travel. And it means that Kitty Pryde is arguably one of the more scientifically plausible superheroes.