Quantum Mechanics is Strange

I wish to comment on why pure science matters. Before I write about that, I wanted to first cover why I think quantum mechanics is strange.

Seasoned experts on quantum mechanics will tell you that it doesn't make any sense. They might qualify it by saying that our big world differs from the small world inside things. But that doesn't explain away the really strange things that happen on small scales.

The experiment that really elucidated the the peculiarities for me was infamous Two Slit Experiment. I first read about it in Stephen Hawking's excellent book A Brief History of Time. It goes like this:

There was a long running argument back in the late 1800s and early 1900s concerning whether light (and electricity and magnetism) is a wave or a particle. There was evidence for both. If you shine some light through two slits in a board, it will create a pattern of lighter and darker areas on a screen behind it. This is evidence of waves interacting with each other — exactly like waves going around two poles in a lake. That effect was well known at the time.

Einstein was able to show that light is also made up of particles. This was a source of great stress and fascination for physicists of the time. Wave particle duality supposedly applies to particles as big as a baseball or a planet, but the particle is so big, you'd never be able to detect the wave portion of it's behavior.

Electrons, on the other hand, are ideal for playing with. To settle the question once and for all, experimenters fire single electrons through the two slits and record the single electron strike on a screen behind the two slits. The peculiarities of the detection should be relatively obvious to readers not using an LCD. Your CRT uses an electron gun (cathode ray tube) to shoot electrons at phosphorus detectors which produces the image you're reading.

Personally, I find it rather horrifying that when you record the single strikes of several thousand singly fired electrons, they'll create an interference pattern on the detector screen over time. What does that mean? The single electrons interfered with themselves? To do this, they have to pass through both slits at the same time!

Gross.

And it gets worse. In SCIAM this month, they wrote of an experiment you can do at home to demonstrate quantum erasure. The article covers the topic very well (in layman's terms thank god), so I'll be brief. If you know (or could have known) the path of the electron through the two slits, the interference patterns disappear.

That is, if you come up with some way to detect the path of the electrons through the slits (polarizing lenses in the SCIAM article); then the quantum superposition breaks down and it no longer goes through both slits. Most disturbing is that if you set up detectors to reveal the path of the electrons and then closer to the detector you set up a device that obscures that signal, the interference comes back!

The author's of the article are quick to point out that you can explain the interference pattens (and their erasure) with regular old wave theory. This, I think, is because your home-brew laser setup fires many millions of photons simultaneously. That's somewhat less convincing.

But in the lab version of the experiment, it is my understanding, they fire single particles through the slits. For a detector, they shoot another particle at the "beam" ... occasionally this will bounce some other particle to a detector across the room. The detector need not detect the path of the beam, the interference patterns go away because the information could have been detected.

For the erasure, they used a lens that obscures which path the particles actually took — in the case that the particle was actually deflected in the direction of the detector. The interference patterns come back with the lens in place. So interfering with what you can detect after the particles have already gone through the slits affects whether they go through both or not.

Gross.

That literally made me sick to my stomach the first time.

My first exposure to quantum effects was actually much earlier. I was utterly fascinated by the simplicity and the brilliance of the Ruttherford Gold Foil experiment. He was also shining single particles at something. His goal was to figure how how big atoms of gold really were (or something like that). They were expecting very small deflections and instead found that some of the alpha particles were coming nearly straight back. This was the first (really famous) indication of the existence of sub-atomic particles.

I learned of this experiment in a chemistry class shorly before we learned about the very odd shapes of electron orbitals. They take on the shape of spheres (expected), dough nuts, raindrop-lobe things, tetrahedrons (in molecules) and other assorted nonsense.

I could not reason out the possible path a particle could take while it was orbiting the nucleus. It just didn't make any sense. When I asked my teacher about it, he explained that the particles don't really "orbit" at all. In very carefully measured reality, they constnatly pop into and out of existence and that they're probably going to be found roughly inside the orbitals.

Gross.

At the big particle accelerators, they really do see particles pop in and out of existence and carefully measure the mass and electric charge on the particles. They have other measurable attributes as well. Having already overloaded positive/negative, north/south and various other ideas, some of these particles take on truly strange names: up/down, strange/charmed, etc...

And the absolute peculiarity and sickening unreality of this small world is why I feel that Quantum Mechanics is very strange.

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