The Stern–Gerlach experiment is probably one of the easiest ways to understand or visualize the weirdness of quantum phenomena and the concept of indeterminacy. Here is a nice flash animation that let's you do the experiment.
Flash Animation of Stern–Gerlach experiment
To demonstrate and understand the sheer bizarreness of quantum physics, set the flash animation up in the following manner.
Spin orientation: +z
Number of magnets: 3
Angle 1: 0
Angle 2: 90
Angle 3: 180
Before you start, first try to understand what this setup may imply.
A) One can say that an electron with a spin of z=+½ (spin pointing upwards along the vertical axis) is prepared and released.
B) Magnet 1 is pointing upwards along the vertical axis as well in the positive direction. This means that all electrons with spin of z=+½ will move through the "plus" hole. After the electron move passed the first magnet, the electron should still have a spin of Sz=+½. For arguments sake one can assume some sort of determinism and say that it may be conceivable that some electrons face either to some degree along the positive horizontal x-axis or the negative horizontal x-axis. So you can have an electron that is z=+½ and x=-½ like this:
Figure 1: Electron with z=+½ and x=-½ spin.
So for arguments sake to see if a deterministic interpretation can be true, all the electrons that pass through the first magnet may have a 50:50 chance of having a positive x-spin or a negative x-spin while all the electrons will have a positive z-spin. And we can predict, using deterministic assumptions that this will be the case.
C) Magnet 2 is pointing along the horizontal axis and along the negative direction. In this case all the electrons with spin of x=-½ will pass through the red hole in magnet two. So, when the electron moves through magnet 2, one can possibly expect them to move through both holes at 50%. So we can at least expect 50% of the electron to pass through magnet two's red hole. And it may mean that all the electrons going out of this red hole will have spin z=+½ and x=-½ if our deterministic interpretation and predictions are true.
D) Magnet 3 is pointing along the vertical axis and along the negative direction. In this case all the electrons with spin of z=-½ will pass through the red hole of magent three. Assuming a deterministic interpretation, after all this we may rightly expect AND predict that ALL the electrons coming out of magnet 2's red hole will pass through the blue hole in magnet 3 since none of the electrons will have a spin of z=-½.
Ok, now run the experiment and see what happens.
If you let it run long enough you will notice that 50% of the electrons coming out of magnet two will come out of the red hole in magnet three. So our deterministic interpretation is obviously wrong and it appears there is no way we can predict the outcome. The event is indeterministic. In other words we cannot predict the specific value of the spin of an electron before it exists the magnet if the magnet faces a different direction. All we can say is that there is a 50-50 chance that it will come out of one of the holes.
So now you can begin to ask interesting questions:
Can you explain why this happens?
Is there a reason for this indeterminateness?
What causes an electron to pass through one hole and not the other?
Does this violate the principle of causality?
etc.
Flash Animation of Stern–Gerlach experiment
To demonstrate and understand the sheer bizarreness of quantum physics, set the flash animation up in the following manner.
Spin orientation: +z
Number of magnets: 3
Angle 1: 0
Angle 2: 90
Angle 3: 180
Before you start, first try to understand what this setup may imply.
A) One can say that an electron with a spin of z=+½ (spin pointing upwards along the vertical axis) is prepared and released.
B) Magnet 1 is pointing upwards along the vertical axis as well in the positive direction. This means that all electrons with spin of z=+½ will move through the "plus" hole. After the electron move passed the first magnet, the electron should still have a spin of Sz=+½. For arguments sake one can assume some sort of determinism and say that it may be conceivable that some electrons face either to some degree along the positive horizontal x-axis or the negative horizontal x-axis. So you can have an electron that is z=+½ and x=-½ like this:
Figure 1: Electron with z=+½ and x=-½ spin.
So for arguments sake to see if a deterministic interpretation can be true, all the electrons that pass through the first magnet may have a 50:50 chance of having a positive x-spin or a negative x-spin while all the electrons will have a positive z-spin. And we can predict, using deterministic assumptions that this will be the case.
C) Magnet 2 is pointing along the horizontal axis and along the negative direction. In this case all the electrons with spin of x=-½ will pass through the red hole in magnet two. So, when the electron moves through magnet 2, one can possibly expect them to move through both holes at 50%. So we can at least expect 50% of the electron to pass through magnet two's red hole. And it may mean that all the electrons going out of this red hole will have spin z=+½ and x=-½ if our deterministic interpretation and predictions are true.
D) Magnet 3 is pointing along the vertical axis and along the negative direction. In this case all the electrons with spin of z=-½ will pass through the red hole of magent three. Assuming a deterministic interpretation, after all this we may rightly expect AND predict that ALL the electrons coming out of magnet 2's red hole will pass through the blue hole in magnet 3 since none of the electrons will have a spin of z=-½.
Ok, now run the experiment and see what happens.
If you let it run long enough you will notice that 50% of the electrons coming out of magnet two will come out of the red hole in magnet three. So our deterministic interpretation is obviously wrong and it appears there is no way we can predict the outcome. The event is indeterministic. In other words we cannot predict the specific value of the spin of an electron before it exists the magnet if the magnet faces a different direction. All we can say is that there is a 50-50 chance that it will come out of one of the holes.
So now you can begin to ask interesting questions:
Can you explain why this happens?
Is there a reason for this indeterminateness?
What causes an electron to pass through one hole and not the other?
Does this violate the principle of causality?
etc.
