Comment by dools | Hacker News Reader

Comment by dools | Hacker News Reader

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They are prepared that way from the start. They are prepared in a state such that measurements along the same axis (for spin) will be anit-correlated.

the "spookiness" only comes into it when you try to understand how this would happen in a classical system.

This isn't a classical system, it's a quantum mechanical system. It's just how quantum mechanics works.

A good analogy is: how do electromagnetic waves travel through a vacuum? If you try to understand "how" from the perspective of someone who only has experience of sound waves which travel mechanically through a medium, the fact that electro magnetic waves travel through a vacuum may appear spooky.

But it's not, that's just what electro magnetic waves do. We can express this behaviour mathematically and predict how electro magnetic waves will behave and then verify those predictions experimentally.

Does this mean we know how they travel? No. We only know that they do. Do we know how quantum entanglement works? No, we only know that it does. We can express the behaviour mathematically and make predictions that are verified experimentally. No more spooky than radio.

QED pop science articles are deliberately confusing people.

The wave-particle duality is also often explained misleadingly. It’s not that particles sometimes behave as particles and sometimes as waves—it’s that they behave in the normal fashion, and sometimes our models for explaining their behaviours are wave-like and sometimes particle-like.

My intuition about the travel of photons is that, because of length contraction, there’s no distance to travel, so they don’t actually travel through a vacuum at all, and of course that’s why they don’t need a medium, and it takes no time at all—from the photon’s perspective, anyway.

The thing that blows my noggin is that this system we’re in is complex enough to express us, who may eventually have the ability to understand it from the inside. That’ll be the real trick. :)

> My intuition about the travel of photons is that, because of length contraction, there’s no distance to travel

This is not correct. Length contraction, as a concept, doesn't apply to photons, because there is no inertial frame in which they are at rest. Or, to put it another way, length contraction and time dilation arise from the way that Lorentz transformations act on timelike and spacelike vectors; they rotate them (in the hyperbolic sense of "rotation"). But Lorentz transformations act differently on null (lightlike vectors): they don't rotate them, they dilate them (physically, this means that changing frames changes the frequency/wavelength of photons, rather than their speed).

Oh wow, thanks for the eye-opener. Was it a different term than length-contraction that I was looking for? I thought that acceleration toward c resulted in the contraction of distance, and at c the distance would simply be reduced to zero. Where did I miss the point?

> My intuition about the travel of photons is that, because of length contraction, there’s no distance to travel, so they don’t actually travel through a vacuum at all, and of course that’s why they don’t need a medium, and it takes no time at all—from the photon’s perspective, anyway.

How is there length contraction in this experiment?

There isn’t, at least not as far as I understand. (Physics is just a hobby interest for me.) I was referring to GP’s comment about an intuition for how electromagnetic waves travel through vacuum.

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