Is Information Really Preserved in Quantum Systems?

[LightningInAJar]

TL;DR Summary

What physics states that information isn't lost or destroyed?

I don't know what category this fits in but how conclusive is it that information can't be lost or destroyed? Is this mostly just Stephen Hawking talking or do others support this idea?

 

[jim mcnamara]

Usually on questions like this, things are much clearer for everyone if you cite a specific article about your question(s). Take this a friendly notification. Right?

 

[anorlunda]

This PF Insights Article may help you to clarify your question.

https://www.physicsforums.com/insights/how-to-better-define-information-in-physics/

 

[LightningInAJar]

That article is too complex for me. I mean with perfect math we can calculate all that came before the current moment. Even if matter fell into a black hole at some point.

 

[tech99]

If I send a radio message from Earth, it will spread out in space and after a certain time will become weaker than the background noise. Then it is lost.

 

[anorlunda]

That article is too complex for me.

OK, then try this simplified version.

There are many definitions of the word information.

When physicists say that information is conserved (can't be destroyed), they mean the boring definitions that you don't understand.

All of the common definitions of information that you do understand are things that are not conserved.

 

[jartsa]

Summary:: What physics states that information isn't lost or destroyed?

I don't know what category this fits in but how conclusive is it that information can't be lost or destroyed? Is this mostly just Stephen Hawking talking or do others support this idea?

The idea has slowly crawled into physics, starting maybe from this:
https://en.wikipedia.org/wiki/Maxwell's_demon

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If a demon has a container of warm gas, a winch and a black hole, the demon may lower the container into the black hole and get the energy contained in the motion of the gas molecules. And that is some kind of a problem for thermodynamics and information theory.

 

[LightningInAJar]

If I send a radio message from Earth, it will spread out in space and after a certain time will become weaker than the background noise. Then it is lost.

Isn't the background noise also information? And with God sized means couldn't even that we filtered out?

 

[Couchyam]

Most theoretical models of quantum systems assume that the wave function evolves according to a unitary operator, and this approach is supported at a fundamental level by essentially all experimental observations where unitarity is relevant (i.e. it generally isn't supported or refuted by experiments that involve open quantum systems, or where the detailed behavior of all outgoing products of the system of interest isn't important, e.g. when verifying Planck's law of black body radiation.) Moreover, all experimental studies of open quantum systems (or experiments that address questions where it isn't necessary to measure a complete set of observables) are consistent with the non-unitary dynamics of a reduced (incomplete) system induced by unitary dynamics of a ('complete') wave function.