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# Some musings on quantum theory then

One strange idea in quantum theory is that the behavior of particles can be dependent on whether they have been observed or not. Another one is that quantum theory allows communication faster than the speed of light, where Einstein assumed this would not be possible.

One strange idea in quantum theory is that the behavior of particles can be dependent on whether they have been observed or not. Another one is that quantum theory allows communication faster than the speed of light, where Einstein assumed this would not be possible.

A light beam

Imagine we can generate a special light-beam, consisting of 50% horizontally polarized light and 50% vertically. For now, I will assume this beam is made up of fast-flying particles: photons. Einstein argued in favor of this using the photo-electric effect.

But first, I would like to start with a little definition. I am a programmer, after all. Want to keep my variables separated.

A photon in the beam has a polarization-state: horizontal or vertical. I would like to also give it a quantum-state: know or unknown. The quantum-state indicates whether we know the polarization-state or not.

If we do not know the state of a particle and there are more possible states, we can still apply statistics to a large group of them. For example, 50% of the photons in our beam would be polarized horizontally, 50% vertically. Statistics.

Quantum theory assumes that a single photon in this beam has a 50% chance of being horizontal and 50% of being vertical. Seams a reasonable assumption to me.

But interestingly, the theory (Feynman) then stipulates that one particular photon will only actually be polarized in a certain direction when it is observed, but until that time it is not.

Why is this important? You may ask.

Well, according to quantum theory, the different quantum-state (known or unknown) actually makes the photon behave differently.

One experiment often used to prove this point: The double-slit experiment.

A light beam shining through a suitable double-split will produce an interference pattern.

If you turn down the intensity of the light beam, the double-slit experiment still produces a (fainter) interference pattern. This is not really surprising yet…

However, if you tone down the light beam to the point where you can actually see the individual photons come in over time, they will still land on your measuring surface in an interference pattern. That is surprising! (but are we really looking at individual photons? An interesting question for later…)

Faster than the speed of light

If we took two photons in our light-beam and we could somehow ensure they are both polarized in the same direction. If we do not know the polarization state (quantum-state=unknown) of the two photons, we could call them ‘entangled’.

So suppose we have managed to create two entangled photons, flying away from each other. When we measure the polarization-direction of one photon we could say we have changed the quantum-state of the photon to ‘known’. We then also know the direction of the other, at that moment in time.

Quantum physics assumes that not only do we now know the polarization-state, but the entangled photons are now polarized in a certain direction. The polarization-state will be determined when we observe. Both photons at the same time.

The photon on the far end of the experiment has changed because of an observation on my end AND this happened at the same time.  This then implies something must have travelled faster than the speed of light.

However, to be able to verify if the other photon has actually gone through the same state transition, we would need to communicate with the other end of the experiment. If this can only be done at light speed, we would always be limited to that.

So, even if the quantum-state information travels faster than the speed of light, my ‘known world’ would always be limited to this maximum speed

This would fit in neatly with my simulated reality. In my personal simulated reality, things happen fastest at the speed of light.