What is spin up and spin down?

[lightarrow]

[...]
If you look at the history of physics, you will see that the assumption of light/photon propagation is the best game in town, for both classical and quantum physics.(Recall Hughens.) If you don't like that assumption, then put it to the test. Move the screen around, say directly toward the source:you will find experimental evidence that the photon does indeed propagate as advertised.
Regards,
Reilly Atkinson

Ok. To perform this experiment I have to send a new photon and have a, let's say, closer to the source, screen position. But in this way the situation is different because:
1. it's not the same photon anylonger.
2. the new photon is in a different environment (different screen position).
Furthermore, the photon hits the screen in a point but we don't know where exactly; we only know the probability to find it in an area dA around point P is proportional to $$|\Psi|^2{dA}$$

 

[MeJennifer]

Excellent objections!
I believe that physicists avoid talking about these things for two reasons:
1. They do not know the answers.
2. If they dare to talk about it, they will be accused for being too philosophical rather than scientific.

But it can get worse, some physicists like to pretend they do know the answers, so obviously discussing these "philosophical' matters make them feel uncomfortable to say the least.

 

[reilly]

Let's suppose I wanted to check bullet trajectories, rather than photon ones. In either case I must repeat the experiment with new bullets of new photons; in both cases , with a wide enough screen, I'll get a hit at any distance from the source. Check out the details of statistical sampling theory; will set your mind at ease.

Coherent or not, photons propagate, but "spread differently' according to the construction of the photon packet.
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Originally Posted by Demystifier View Post
Excellent objections!
I believe that physicists avoid talking about these things for two reasons:
1. They do not know the answers.
2. If they dare to talk about it, they will be accused for being too philosophical rather than scientific.But it can get worse, some physicists like to pretend they do know the answers, so obviously discussing these "philosophical' matters make them feel uncomfortable to say the least.

Are there no honest physicists? What's the problem? Examples?
Regards,
Reilly Atkinson

 

[Anonym]

Coherent or not, photons propagate, but "spread differently' according to the construction of the photon packet.

But the coherent states are spreaded but do not spread. That makes them very special cases. I do not know another example with that property. Do you?

Regards, Dany.

 

[lightarrow]

Let's suppose I wanted to check bullet trajectories, rather than photon ones. In either case I must repeat the experiment with new bullets of new photons; in both cases , with a wide enough screen, I'll get a hit at any distance from the source. Check out the details of statistical sampling theory; will set your mind at ease.

I don't understand what you mean. With bullets is completely different: I detect a bullet's position in two different points of space while it is "in fly" and then I can find its velocity, compute its trajectory and so find the exact point on the screen it will hit; and it will hit exactly that point. You can't do it with (low energy) photons.