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Comment count is 17
ProfessorChaos - 2009-02-13

If you think you understand Quantum Physics
You don't understand Quantum Physics.

Baldr - 2009-02-13

I don't remember Feynman ever trying to explain it in his books. Maybe this is why.

alltogethernow - 2009-02-13

Hey girls, how'd you like to see my reality tunnel?

Don't be afraid... touch it.

Gamara II - 2009-02-13

Ugh, why can't people stop using a rough understanding of quantum mechanics to support their philosophical claims?

Quantum mechanics is just part of physics. Physics is just a method of mapping out the rules and patterns of cause and effect that our observable reality seems to follow. The better our map, or "model" is, the better it predicts the outcome of cause and effect. We constantly tweak the models to get better predictions, and more fundamental (i.e. general) sets of rules, like in the striving towards unified field theory. Physics by definition has nothing to say about anything "outside" of what we observe, which would be the realm of philosophy.

When Anton says that experiments change when we observe them, he's somewhat correct, but for the wrong reasons. People tend to think of "looking at something" as a passive activity, and therefore attribute observation as some effect caused by the mind of the observer. It is not. "Observation" always requires, at the most fundamental level, some sort of interaction of two particles, like bouncing a photon off an object and having the photon hit our eyes, or a detector which we then get a readout from.

For large objects, like a baseball, a photon only changes the baseball's momentum by millionbillionthwhatevers of a percent, so nobody cares. If we get down to the scale where we're looking at an atom though, the photon can change the momentum of the atom significantly!

Here's the tricky part. With quantum mechanics, the basic pattern we observe is that fundamental particles only have *probabilities* of interacting with each other in any given location based on their wave functions.

Another tricky part is, how do we know the position, even roughly speaking, of a particle in the first place? Well, we can't just magically know the position of it. We have to hit it with something and see if we get any sort of interaction. This is analogous to "observation". Well, when we hit a particle with a photon, we've altered the properties of the particle, changing its wave function to some degree, which is also unknown, since the the photon's properties were slightly indeterminate too!

So, in these crazy wave-slit experiments, the fallacy comes from trying to think of the electron wave function as a particle travelling from point A to B. If you try to "catch" the particle in between by bouncing a photon off of it, you've changed the wave of the electron, completely altering the experiment when we talk about point B! There's no way to passively observe the experiment, as we intuitively think we can do on a large scale.

But sadly, people jump to the conclusion that one's mind during "observation" is what changes the experiments, and all sorts of bad philosophy results from this misunderstanding. At least if people are going to use physics as some support for philosophical musings, they should have their facts straight.

I'll at least concede that getting one's facts straight would take way more time and devotion than most people would want to spend. But come on, don't give lectures on the subject with an air of authority.

Baldr - 2009-02-13

Gamara is full of meat.
Gamara is really neat.

We've been eating Gamara!

Gamara II - 2009-02-13

Maybe I should put this more succinctly. I just had beef with how he said that when we look at an electron, it has a defined position, but when we look away, it's everywhere.

What I'm trying to say is that isn't quite what's going on when we talk about electron behavior. It's not as simple as "looking"; we have to have something else interact with it.

MongoMcMichael - 2009-02-13

Sorry the video pissed you off, but thanks for the four stars! :3

Syd Midnight - 2009-02-13

Feynman giving a pretty good example of it, http://www.poetv.com/video.php?vid=48968 There are no uninvolved observers.

RAW strikes me as a clever, entertaining writer who bought into his own rumors of omniscience

simon666 - 2009-02-13

Gamara II needs to be the next Carl Sagan or Brian Greene, but instead using the tone of cynicism. I'm not joking, books like that would be very entertaining to read.

smoothbrain - 2009-02-13

Quantum mechanics is only weird if you are bigger than an electron.

Miskimo - 2009-02-13

Gamara II, I agree completely with the sentiment of your first sentence. But you're description of the reason for the uncertainty principle makes it sound a bit less weird than it actually is.

Within the standard theory of quantum mechanics, the effect of measurement is more fundamental than just the fact that interaction must occur to make measurements (this can be an issue in classical physics too). Indeed, the notion of mesaurement is built right into the standard postulates of quantum mechanics. (e.g. http://www.umich.edu/~gevalab/Geva/lecture/chem461/Chapter3.pdf) For instance, while the destruction of the interference pattern in the double slit experiment is often attributed to the interaction with whatever particle we're sending through, with those that we use to make the measurement, this is not the whole story.

Experiments have been done, where simply creating the *possibility* of measuring which way the particle has gone through, by marking them in such a way that their momentum is hardly affected will destroy the pattern. And, what's more, the marker can be removed (without ever using it to actually determine which way the particle went) and the pattern will reappear! (See e.g. http://grad.physics.sunysb.edu/~amarch/).

I didn't bother to actually watch what Wilson said, but I'm guessing its pretty vague.

Miskimo - 2009-02-13


Gamara II - 2009-02-13


Yeah, I did over-simplify things a little bit. I was mostly trying to show that fundamentally we can't think of matter or light as having a specific position and ignore its wave function spread throughout space. And especially I wanted to show that it doesn't jump from one form to another in accordance with our mind.

I think your second link is awesome though. I think it also highlights that thinking of photons as just localized points in space doesn't work well if we want to understand how photons behave. Asking where the photon goes and ignoring the wave function and entaglement is basically asking the wrong question. The "intuitive" model of thinking of it as just a particle doesn't have meaning since that's not how it behaves, but it might be "close enough" in certain circumstances. This is why quantum mechanics has been so useful, since it predicts behavior on small scales and in general cases much better than Newtonian physics.

In the video Anton makes it sound like when we look at an electron, it is a particle, and when we look away, it becomes a wave, and that this says something about our mind. Maybe I'm missing what he's trying to say. The clip was brief, and definitely vague.

Infamous - 2009-02-13

This place is at its best when videos like this are posted.

Jeff Fries - 2009-02-13


Camonk - 2009-02-13

It's baird-fa-say, dammit.

RoyCastle - 2009-02-13

the music is Zoetrope by Boards of Canada from the album "In a Beautiful Place Out in the Country"

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