Wednesday, August 17, 2011

Scientific Truths, Quantum Mechanics, and Quantum Mechanics to Auto Mechanics

C. Ewings asks,

"Are "scientific truths" actually true?"
By true, I'll take it you mean "can be known with certainty." In that case, it depends upon which scientific truths you are speaking of. There are statements of observable behaviors of parts of the universe, say, water freezes at 32 degrees Fahrenheit at sea level. These are testable true or false. Yes, as Pierre Duhem a Willard Van Orman Quine pointed out, they also require certain other propositions to be true and you are testing not just that claim, but an entire web of claims, but even so we can say that there are facts about the universe that can be known.

There are theoretical propositions, parts of theories that are used to explain how the universe works, that are then tested by these observation statements, that is, for which these observation statements are used as evidence. These more interesting claims are never known to be true with absolute certainty, but in light of evidence and the results of novel predictions are inductively supported and thereby given a weaker or stronger degree of rational belief.

That is a quick sketch of the standard view, but if anyone is interested in the details of the contrasting positions on this question...have I got a book for you -- available in both paperback and hardback.

Jynx asks,
"With regards to Quantum Physics, do you see a problem with the position of most scientists that certain particles exist in an intrinsically indefinite state, as opposed to the much more defensible position that certain particles' positions/velocities are simply unknown. Another way to phrase the second question would be: Are most physicists guilty of mistaking the epistemological with the metaphysical as it pertains to the position and velocity of particles?"
Actually, the more defensible position is the other way around, but the way it is usually taught to undergrads is unfortunately backwards.

In quantum mechanics, when particles are unobserved, they are found in what is called "superposed states," that is, for a given observable property, say position, they simultaneously occupy every possible value, that is, are to a degree in every possible place in the universe they could possibly be found. Observable properties come in pairs, we call them "non-commuting observables," such that when you observe one property of the pairs, the particle will acquire a single value for that property. When I look to see where a particle is, it will be in a single place. But the act of measuring that property, of seeing where it is, causes the value of the other member of the pair, in this case velocity (position and velocity are the most famous pair of non-commuting observables) to go into a superposed state, that is to not have a single value, but to be a mathematical combination of every possible value.

Einstein held the view that this superposition is not an actual state, that there was a single value for both position and velocity simultaneously at all times, we just don't know it. It is not that superposition is real, it is just that the theory of relativity is incomplete, it is missing some "hidden variables," and when we figure out what these variables are and figure out how to determine them, we'll be able to fully assign values to all observables in a system. We should take these superposed states not to be a reflection of a strange reality at the micro-level, but rather as an indication that it provides an incomplete description of reality which must be well-behaved even at the very smallest sizes.

Unfortunately, every result indicates that there are no hidden variables, that the theory is, in fact, complete. Bell's theorem and the Kochen-Specker theorem all but make impossible the idea that the position or velocity is simply unknown when we measure the other. It is metaphysical and not epistemological. (David Z. Albert's book Quantum Mechanics and Experience is an excellent one for anyone interested in working through this material). Oddly, though, when the Heisenberg uncertainty principle is taught, it is usually portrayed as being merely epistemological and not metaphysical, that is undergrads are told that the process of measuring the position alters the velocity in a way that our former measurement of it no longer is correct, implying that it still has a value, we just don't know it. But, in fact, what happens is that the act of measuring the position actually causes the velocity to return to a superposed state where it ceases to have a single value for that observable property. Quantum theory shows us that the world just is that weird.

71 asks,
"When did you start doing AM to QM and where did the idea come from?"
I took my first philosophy class as an undergraduate with Bruce Goldberg in a lecture hall filled with a couple hundred people. He would lecture from a stage and towards the end of the semester was clearly annoyed with the lack of interaction that was possible in the arrangement. So, one day, he did something he had never done. He asked if there were any questions. But he did it at a point in the class when there was really nothing philosophically contentious on the table, a point when there would be no natural questions or objections to be put forward. There was complete silence. He asked again. Again, nothing. He asked a third time saying, "Guteral noises, belch, anything, I'll make something of it." From the back row, someone yelled out, "Who won the 1926 World Series?" It was clearly an attempt by a smart ass to disrupt. Goldberg, without missing a beat, said the Cardinals over the Yankees in seven. He walked to the chalkboard and described how the series ended with Hornsby tagging out Ruth and related it seamlessly back to free will and determinism which had been the topic of the day. I thought to myself, "Man, you're good." After that day, I noticed that there was a different dynamic in the lecture hall and thought that if I ever taught, I'd try to disrupt the distance between teacher and the class in the same way. So, I did and it worked like a charm. Auto mechanics to quantum mechanics has been with me since the beginning.