What the @&#*$ do we know? ***Part 2***

[kermit911]

There was one other secon about the same object being in 2 places at the same time. The guy said that this has been provem and you can see it even, you can also take a picture of it. It is a dot or something. How is that posible?

thanx
Kermit

[bernardo]

If you shine a light through a narrow slit, it splays out in all directions and creates a fuzzy blob of light on a screen that it hits on the other side.

If you shine a light through two narrow slits next to each other, the light will splay out from both slits.

The way in which the light rays from the two slits interact with each other causes a series of lines to appear on the screen, instead of just a smooth fuzzy blob. (This is because of stuff to do with the wavelength of the light). This only works because there is one bit of light going through one slit, and another bit of light going through the other slit. It doesn't work if there is only light going through one slit.

There is also a funny thing called "wave-particle duality". Light is a funny sort of stuff, and scientists sometimes find it useful to think about it as a smooth wave, like ripples on a pond. In other contexts, it is sometimes useful to think of light as being made up of zillions of little particles, or packages (called "quanta"). One quantum of light is the smallest amount of light that you can have.

The weird thing is that when scientists did the two-slit experiment with only enough light to make up one quantum, the interference pattern on the screen still happened. This meant that the light must have gone through both slits, even though there was only one package of it.

Therefore the same particle of light must have gone through both slits at the same time.

Did it really happen? Yes, because it has been proved.
How did it happen? Er... nobody knws really.

[jake-the-peg]

This is one of the best sites I know for this sort of thing - it's even got some pretty fun applets

http://www.colorado.edu/physics/2000/schroedinger/index.html

have a go

[Skids]

In the experiment described by bernardo, they used only enough light to make up a quantum, or particle, of light, but was it actually a particle? Who knows? No one can say whether a single particle of light passed through both slits at the same time because no one can prove that light travels in particles. Wave particle duality is there so that scientists have something easy to work with when they don't actually know whats happening. Yes, light behaves (key word) as if it is travelling in waves and also as if its travelling as photons (particles, quantums, whatever) but no one actually knows what its doing.

[jake-the-peg]

I think the point about wave-particle duality is that you're trying to force an analogy on light (or an electron )

Light isn't wave-like or particle-like it's light-like.

We have a tendancy to think of light as little bullets (photons) or waves because it's easier for us to understand.

Then we look really carefully and the analogy breaks down and we scream and shout about it!

The photon does not actually necessarily exist (whatever that means) as a point travelling through space but may occupy many locations and has a probability of occupying any of those locations

This is basically the Copenhagen interpretation of quantum mechanics Wikipedia have a page on it here:

http://en.wikipedia.org/wiki/Copenhagen_interpretation

Yes it's pretty daft sounding and Einstein loathed it. In fact he and two others came up with an experiment called the EPR paradox which was meant to show it was wrong it pitted relativity against QM. He didn't live to see the testing of it in 1980 - Relativity lost.

There are other interpretations such as "many worlds" where the universe splits at quantum events in one universe the photon goes through one split and in the other it goes through the second.

All of them will screw with your head though