Tuesday, January 25, 2011

Quantum questions

The figure below is from my talk on many worlds quantum mechanics. I've tried to boil the issue down to its essentials below. (Warning: basic understanding of quantum mechanics required.)

Objects of increasing complexity can be placed into superposition states in laboratory experiments. Proposals for viruses and bugs (tardigrade arthropods) have been discussed.

Can an "observer" (person) be placed into a superposition state?

Or do they necessarily "collapse" wavefunctions?

If a virus or bug can be placed into a superposition state, why can't you?

See related post: Schrodinger's virus.


steve hsu said...

> "Most" universes in a stochastic branching evolution world obey the laws of probability. ... But I wonder what this says from a foundations of probability perspective? Can we remove a postulate of probability theory using this argument? <

Not sure I followed your question? Could you elaborate?

Re: Bloch sphere, yes the picture is misleading. We don't mean that there are fixed regions which are realizable and others aren't. Actually our proposal isn't very well-defined other than it says to drop relative states of really small norm (thereby eliminating mavericks). The rest is just hand-waving to motivate the proposal. I haven't thought about the possibility that the uncertainty could involve mixed states -- we were just thinking about pruning the tree of offending (pure) subcomponents.

wolfgang said...


if I understand your talk you solve the 'probability problem' of many worlds by introducing a 'discrete' Hilbert space.
Is evolution still unitary in this 'discrete' Hilbert space?

steve hsu said...

The "discrete" Hilbert model isn't very fleshed out. As I mentioned to Dave it's really just a hand waving reason to drop maverick sub-branches with very small norm. I guess I kind of have in the back of my head that the quantum simulation is running on a device of finite resources, so it is forced to eliminate very small norm components. But we never said explicitly how this happens.

When I give the talk I typically conclude by saying that there are no solutions to the probability problem that I find completely satisfactory :-)

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