Thread: two slits

1. I watched this a while ago. Please explain how OBSERVATION has anything to do with anything.

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

2.

3. Because observation of a photon effectively destroys the photon as it is completely energy. the observation of it causes its energy to be absorbed by the observer, and in the case of something like this, it is then "spit out" by the observer in the same direction as it was received.

4. Arcane_Mathematician,

Is that what they call the Heisenburg(spelling?) Uncertainty Principle?

- TR

5. I can't say for sure that that's not covered by the Uncertainty Principle, but that's not what's it's usually talking about. The Uncertainty Principle says that the more accurately you measure the position of a particle, the less accurately you can measure its momentum, and vice versa.

6. Originally Posted by Shaderwolf
I watched this a while ago. Please explain how OBSERVATION has anything to do with anything.

http://www.youtube.com/watch?v=DfPeprQ7oGc
Observation collapses the wave-function of the electron.

When you fire the electrons one by one through the two slits the wave-function allows them to behave as if each electron is passing through both slits and interfering with itself to form the interference pattern.

However, if you try to observe the electrons as they pass through the slits ( rather than just the interference pattern they form), you collapse the the wave function so that now the electrons pass through one slit or the other and the interference pattern goes away. By oberserving the electrons as they pass through the slits you are forcing them to choose a slit.

7. Originally Posted by Shaderwolf
I watched this a while ago. Please explain how OBSERVATION has anything to do with anything.

http://www.youtube.com/watch?v=DfPeprQ7oGc
I have seen this video before and I do not like how they do not give a good explication for what is meant by observation.

In the macroscopic world that we live in the act of observation does not effect the out come of an experiment (unless you are trying to video tape kids ). If I watch a scene outside my window like a blue car driving by or if I did not look out the window the blue car would still have gone by. This is a macroscopic observation. In terms of the quantum mechanical type of "observation" in both cases the car was "observed". By this I mean that as the car went by light (photons) had interacted with the car and scattered in all directions. Photons that scatted off the car will go through my window if I'm there or not.

However, in the microscopic world of quantum mechanics observation means "to interact with". There does not have to be a thinking mind behind the observation. If I wanted to see which slit the electron went through (Remember we can not see electrons with our eyes) I would place a coil of wire or some kind of charge detector or maybe I could direct a laser at one slit and look for some scattering. All of these acts of "observation" change the state of the electron by localizing its wave function. This is what the others mean when they say "collapse" the wave function.

Once the electron has been measured at one of the slits the diffraction pattern it makes will be that of a single slit diffraction.

Quantum mechanics is a non-local theory which makes no sense! But I have grown up, and built my sense of what makes sense in a macroscopic world. All experiments show that quantum mechanics is non-local. This means that when the electron is not observed it "goes through" both slits. It takes all possible paths!

See: Bell's theorem for more info

8. Thank you. I understand a little better now. My thirst for knowledge though cannot be quenched. Right now I am looking for some top notch literature to study. Even text books would be nice. I am in school right now for the US Marine Corps. I am becoming a Support Equipment Electrician. Until I get out of school I can't even start thinking about College. Know any good books?

9. Originally Posted by Shaderwolf
Thank you. I understand a little better now. My thirst for knowledge though cannot be quenched. Right now I am looking for some top notch literature to study. Even text books would be nice. I am in school right now for the US Marine Corps. I am becoming a Support Equipment Electrician. Until I get out of school I can't even start thinking about College. Know any good books?
You might try Silverman's More Than One Mystery It is a pretty good overview of some aspects of "quantum weirdness".

Another good one is QED by Richard Feynman which is the text of some lectures for a general lay audience on quantum electrodynamics.

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