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- Thread starter BernieM
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tom.stoer

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No information is lost.

I am not familiar with quantum information theory, but the relevant mathematical issue is whether time evolution is unitary or not. An example where information seems to be lost is the black hole (Hawking) radiation where the time evolution is given by

"pure quantum state = single ray in Hilbert space" → "mixed state = thermal density matrix"

This is not allowed in quantum mechanics and was the starting point of the discussion regarding black hole information paradox.

In the proccess you are describing there is a perfectly unitary evolution like

"pure quantum state = single ray in Hilbert space" → "new pure quantum state = new single ray in Hilbert space"

The two states are different b/c they describe different particle content, but the time evolution is unitary and therefore no "information" is lost.

I am not familiar with quantum information theory, but the relevant mathematical issue is whether time evolution is unitary or not. An example where information seems to be lost is the black hole (Hawking) radiation where the time evolution is given by

"pure quantum state = single ray in Hilbert space" → "mixed state = thermal density matrix"

This is not allowed in quantum mechanics and was the starting point of the discussion regarding black hole information paradox.

In the proccess you are describing there is a perfectly unitary evolution like

"pure quantum state = single ray in Hilbert space" → "new pure quantum state = new single ray in Hilbert space"

The two states are different b/c they describe different particle content, but the time evolution is unitary and therefore no "information" is lost.

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Charge conservation forbids any information is lost.

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What is "information" and how much does a particle carry?

- #7

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What is "information" and how much does a particle carry?

Well if we are talking about two photons, the information they carry are intrinsic properties, such as angular momentum, ect.

Photon-photon collision is just a very special type of decay process which can carry on the information when it creates two new particles and it's the observable properties which we could call the information.

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- #9

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Well if we are talking about two photons, the information they carry are intrinsic properties, such as angular momentum, ect.

Photon-photon collision is just a very special type of decay process which can carry on the information when it creates two new particles and it's the observable properties which we could call the information.

So, are you identifying "information" with angular momentum, and then deducing that "information" must be conserved because there is a law of conservation of angular momentum?

If that is the case, then I don't really see the need for the term "information" because it carries the same content as the term "angular momentum". If that is not the case, then I don't really understand your explanation of the term "information", I guess.

- #10

tom.stoer

Science Advisor

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No information is lost.

I am not familiar with quantum information theory, but the relevant mathematical issue is whether time evolution is unitary or not. An example where information seems to be lost is the black hole (Hawking) radiation where the time evolution is given by

"pure quantum state = single ray in Hilbert space" → "mixed state = thermal density matrix"

This is not allowed in quantum mechanics and was the starting point of the discussion regarding black hole information paradox.

In the proccess you are describing there is a perfectly unitary evolution like

"pure quantum state = single ray in Hilbert space" → "new pure quantum state = new single ray in Hilbert space"

The two states are different b/c they describe different particle content, but the time evolution is unitary and therefore no "information" is lost.

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So, are you identifying "information" with angular momentum, and then deducing that "information" must be conserved because there is a law of conservation of angular momentum?

If that is the case, then I don't really see the need for the term "information" because it carries the same content as the term "angular momentum". If that is not the case, then I don't really understand your explanation of the term "information", I guess.

No.

I am trying to be as simple as possible. No more, no less.

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