By Richard Bleil
To date, I have written over 250 posts, so I hope you’ll forgive me if I begin duplicating topics. I don’t believe, however, that I’ve yet spoken of that crazy kooky cat that has stolen everybody’s hearts and imagination, Schroedinger’s Cat.
See, Schroedinger had a cat. And he didn’t have a cat. At the same time. Seriously.
Okay, this is a topic from the realm of quantum mechanics, which I’ve written on earlier and discussed how, exactly, we, you and I, can never fully understand the laws of the quantum realm because we follow the laws of classical thermodynamics. While we may never be able to understand quantum law, we can, nonetheless, understand the lessons therein.
As a review, Heisenberg is the one who proved, mathematically, why classical thermodynamics fails at the quantum level. The big difference is one of knowledge. Heisenberg showed us the theoretical limit of knowledge. In classical physics, we can measure position (where something is) and momentum (where it is going) simultaneously. In fact, classical (Newtonian) physics depends on this ability. Heisenberg showed that when you multiply the error in any simultaneous position measurement times the momentum error, there is a minimum error that must be inherent, no matter the accuracy of our measuring instrument.
There will always be a minimum error.
This error is insignificant on a macroscopic scale, so we, you and I, and Newton and his physics, will never notice it, but something the size and speed of electrons sure will. Physicists have even tried to cheat, by separating the measurements. They ran a remarkable experiment where they measured where an electron passes through a region of space, thereby measuring the position, with extremely high accuracy. Later, they measured the exact momentum in a second and separate experiment, the hypothesis being, HA, we’ll BEAT the uncertainty principle. But when they tried to predict where the electron would be, based on the independent position and momentum measurements, the electrons refused to be where they were supposed to be. HA right back at ’em!
Position and momentum not withstanding, there are some quantum properties that we can measure, whether we understand them or not, such as spin. As you may (or may not) recall, spin is a mathematical solution of Schroedinger’s equation, and can either be positive one half, or negative. It’s not charge, and Heisenberg tells us we’ll never be able to know exactly what spin is, but, we can measure it. It started with ESR Spectroscopy, which allowed chemists to measure when the spin changed sign. A later experiment measured spin on a surface in an attempt to determine if electrons have a preference for up or down. Today, spin is used in some computing devices that you may well own already.
This is where Schroedinger’s cat had to put her paws all over quantum theory. You see, since the normal laws of physics don’t apply to the quantum world, who says that the electron has to be either? In fact; the electron naturally exists in neither state on its own, but rather, in both states simultaneously, and it does not fall into one state (spin up or spin down) until some damned fool tries to measure it.
To explain this, Schroedinger devised a thought experiment.
A thought experiment is one that, as you might well imagine, occurs in the mind. Newton used this to prove all objects fall at the same speed, regardless of mass. Consider a tennis ball and a bowling ball. If we ignore wind resistance, and drop them both from a great height in a vacuum, conventional wisdom used to say that, obviously, the larger mass will fall faster than the slower. But, Newton reasoned, what if we tie them together? Then will the now larger mass fall faster than both of them, or will the smaller mass act as a drag on the larger one, so the two will fall at a speed somewhere between the two alone? The reality is that both arguments are valid, logical and true, and since they cannot both be true at the same time, the conclusion must be that our initial assumption that the larger mass falls faster must be wrong, and therefore, all objects fall at the same speed regardless of mass.
Schroedinger’s thought experiment went like this. If we put my cat into a box that is rigged with a deadly poison and a quantum trigger that has a certain probability that it will kill the cat at any given moment, is the cat alive and dead? A statistician might calculate the odds, but the reality is that we just don’t know. At any given moment, the only way to know if the cat is alive or dead is to open the box and look (to measure it). Until we do so, it is both alive and dead at the same time.
I would imagine the anger of the cat would tell us. It’s not a great analogy. Spin can change from one to the other, but death is permanent unless you’re a comic book hero. Despite this flaw, however, the Schroedinger’s Cat thought experiment basically applies to any situation where there is more than one possible outcome, and we just don’t know until we perform the experiment.
But is it reasonable to assume that the electron can actually be in both states simultaneously? The quantum world is strange, and Schroedinger’s Cat tells us that the electron will be in both states simultaneously…unless…we measure it…
An ingenious experiment measured this hypothesis experimentally. Starting with a Beryllium atom, chemists shot the atom with three lasers. See, Beryllium has four electrons. Electrons exist in pairs, but only if they are opposite spin (one up, one down). So, step one; shoot the element (in a very high vacuum so it won’t collide with any other atoms or molecules) to knock off one of the electrons. This results in a positive ion which can be isolated in a magnetic field. This also leaves one unpaired electron, but, is it spin up or spin down? The hypothesis says both, so long as we don’t actually try to measure it, so in comes the second laser.
Highly tuned, it excited the spin up state of the electron into a higher energy level, leaving spin down at the lower ground state. A third laser pushed the higher energy state away from the lower energy state.
Here’s the mind freak part. What they ended up with is the same Beryllium atom coexisting in two locations in space about ten times the diameter from each other. They didn’t split the atom; they proved the atom was alone. It was one atom, coexisting in space in two locations for a fraction of a second. It’s like a happy you, and a sad you, standing ten feet apart…just looking at each other.
It’s a freaky world, this quantum reality on which our lives are built!