# Retrocausality

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it's going to be in that state until it interacts again.

When it interacts again, does it enter a different eigenstate, or does it convert to a wave?

I read everything I could read in 2 hours on eigenstates, but I'd appreciate a customized definition here.

Thanks

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5:21 am?! Holy cow, Swansont. Don't you sleep?

"detection is typically destructive for a photon, but not so for interactions that collapse the wave function."

I'm afraid I don't follow. If you wouldn't mind, dumb it down a little. I'm trying to distinguish between a particle’s natural interactions and those with a detector.

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Simple question that I hope is pertinent - from a time perspective would conservation of energy resist matter traveling in reverse from the past into the future in order to allow this retrocausality to initiate?

Time reversal symmetry doesn't affect conservation of energy. Causality is an issue of relativity and not permitting information to travel faster than c.

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When it interacts again, does it enter a different eigenstate, or does it convert to a wave?

I read everything I could read in 2 hours on eigenstates, but I'd appreciate a customized definition here.

Thanks

It can; it depends on the measurement. If it's in the same basis, it will be in the same state. If you use a different basis, then the original state has to be viewed as a superposition of states.

An example is polarization. You polarize light and send it through another polarizer oriented in the same direction, all the light is transmitted. But if you rotate the polarizer by 45 degrees, half the light is transmitted and half is stopped, and the transmitted light has this new polarization.

"detection is typically destructive for a photon, but not so for interactions that collapse the wave function."

I'm afraid I don't follow. If you wouldn't mind, dumb it down a little. I'm trying to distinguish between a particle’s natural interactions and those with a detector.

A polarizer will collapse the superposition, but can allow the light to pass through — this is nondestructive. But to detect a photon, it typically needs to be absorbed.

There are exceptions, and lots of possible scenarios, if you look through the literature.

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