http://www.youtube.com/watch?v=DfPeprQ7oGc

Someone who's studied physics please confirm that this is not bullshit.

Haven't studied physics, but most of this experiment was mentioned in a Michael Crichton book I read (Timeline). I don't recall the observation part, though.

Yes it is correct. It's known as wave function collapse and it's damned weird. Quantum mechanics boggle the mind, truly.

We did this at GCSE level physics, but obviously not in detail.

Yeah, it's weird, but it's legit. What's striking the wall is the sum of two different wavelengths. If they're in phase with each other when they reach the wall, they'll stack up (constructive interference) and create a bright fringe, if they're out of phase with each other when they reach the end, they'll cancel each other out (destructive interference) and have a dark fringe.

100% legit stuff.
Not sure it is "quantum physics", but it for sure is "modern physics" since its about waves.
I have an exam right about this tomorrow: kind of funny.

What I was more concerned with was that having an observer forces an outcome. It's very strange, I wonder if somehow the observer is making a difference in the waves, rather than it being the universe going "someone is watching." Crazy stuff.

By the way, if you want more info about that Double Slit Experiment, search for "Young's experiment".
And I'm not quite sure about this, but here's my guess: by observing something on the micro-scale, you place yourself in its direct environment. Your presence, and even mass, has an effect on it.
That's a very basic thought, though.

Yeah, the act of measuring or observing affects the interaction somehow. What payne said. It's related to Schrodinger's Cat and multiple Universe theories.

This isn't too hard. I read books about this when I was in 8th grade. Think of it like you would any child that's smart enough to know when you're watching, punishment comes quicker. While you're looking, it'll do what it wants, but when you look, it acts differently. That doesn't explain why, I know, it just makes it easier to understand

If you like stuff like this, you'd love a "quantum" garden hose (vs. an ordinary one). Increasing the flow of a regular hose always corresponds to a steady increase in the length of the stream of water coming out, if nothing else interferes. However, a quantum hose will spit out a stream that goes for exactly one unit, and increasing does nothing until you break a "threshold", where it suddenly and instantly jumps to two units, with no drops falling in between.

Yes, the video is correct. I don't like the way they construe the measurement thing though - yes, measuring single photon diffraction causes the pattern to collapse, but it is because "observing" which slit the particle went through is fundamentally inextricable from altering it. You cannot just look at a particle: think about it, if you observe something at the macroscopic level, you are irradiating with light, or some other perturbation which you read the signal to make your observation. So it's not like the electron "magically" knows it is being "observed" - whatever method you use to observe it has a direct effect on the electron itself.

All matter is not a solid as we think it is - the really weird part of quantum mechanics is not that it contradicts itself, but only that it is completely counter-intuitive to anything we interact with at the macroscopic level.

The only way you can detect something is by hitting it.

The bigger question:
Is it probability? Or intensity?
And what's the difference?

Actually, this makes me wonder if there have been slit-tunneling experiments. Where you put one slit and one thin barrier or something. I don't think they would add much knowledge to anything but they would be interesting to see. Phase differences could be used to analyze the barrier somehow.
http://rugth30.phys.rug.nl/quantummechanics/movies/qmb17.mpg
Video of single slit that is blocked on one side. (So there is actually no slit, just a wall that gets thin in one spot.)

Post has been edited 2 time(s), last time on Apr 6 2011, 1:23 am by Rantent.

The only way to detect electrons is to do so with light, since light is absorbed in quanta by electrons, doing so alters it. Heisenberg's Uncertainty Principle expands upon this. If we had a way to detect the electron without actually affecting it, then things would become much more clear.

It's legit. I think it has something to do with the wave-particle duality.

You're late.

Not true, light is only a common means. Neutrons, electrons, magnetic fields are other common means. Really, anything can be used as a detector, but it has to interact with what your looking at. Interacting means that it changes it though.

Apparently "weak measurement" makes new things possible:

New Experiment

Bah, it's better to make no measurement at all.

xkcd's forums have a science section that has a bunch of stuff regarding quantum phenomena and pretty much everything else sciency. Here is a good thread from there regarding quantum stuff. It's by no means the only one.