If you are aware of an interesting new academic paper (that has been published in a peer-reviewed journal or has appeared on the arXiv), a conference talk (at an official professional scientific meeting), an external blog post (by a professional scientist) or a news item (in the mainstream news media), which you think might make an interesting topic for an FQXi blog post, then please contact us at forums@fqxi.org with a link to the original source and a sentence about why you think that the work is worthy of discussion. Please note that we receive many such suggestions and while we endeavour to respond to them, we may not be able to reply to all suggestions.

Please also note that we do not accept unsolicited posts and we cannot review, or open new threads for, unsolicited articles or papers. Requests to review or post such materials will not be answered. If you have your own novel physics theory or model, which you would like to post for further discussion among then FQXi community, then please add them directly to the "Alternative Models of Reality" thread, or to the "Alternative Models of Cosmology" thread. Thank you.

Please also note that we do not accept unsolicited posts and we cannot review, or open new threads for, unsolicited articles or papers. Requests to review or post such materials will not be answered. If you have your own novel physics theory or model, which you would like to post for further discussion among then FQXi community, then please add them directly to the "Alternative Models of Reality" thread, or to the "Alternative Models of Cosmology" thread. Thank you.

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FQXi BLOGS

May 24, 2019

Scott Aaronson (in B&W because he's sophisticated) |

The morning session was a bit of a grab bag of topics. Officially the title was "Measuring and manipulating information" but due to the dreadful weather in the US several speakers were heavily delayed and so Ray Laflamme, who was supposed to speak on Monday, actually swapped places with Andrew Briggs and spoke on Tuesday. Ray gave a general overview of his work on quantum error correction and talked a bit about some of the work he’s doing on the experimental foundations of quantum theory (again, I’ll defer the details to the conference videos which will be posted after appropriate post-processing). The other speakers were Scott Aaronson and Caslav Brukner. Caslav spoke about his work on indefinite causal structures. Scott’s talk was typically provocative in that he likened objections to the Church-Turing thesis to people who keep claiming to have invented perpetual motion machines that violate the Second Law of Thermodynamics (photo, above left).

I think it is safe to say that everyone agrees that, at the most fundamental level, the universe is stochastic in some sense, whether that be quantum or classical which ultimately means probabilistic in some fashioned (note that this does

At any rate, we could go even deeper than that as Gregory Chaitin has done (as someone pointed out) by asking where the intrinsic stochasticity, i.e. randomness (or near randomness) ultimately comes from. Chaitin’s claim is that it arises from mathematics which puts him firmly in Max’s camp. On this point--whether the universe is really purely mathematical or not--there is still definite disagreement.

Sean Carroll |

Personally, what I think Sean is doing is conflating certain pure states with static states. So, for instance, an entangled state is a pure state. But a pure state need not be static. I think what he’s trying to say is that the fluctuation requires repeated observation. So, for example (though this is

Alan Guth also spoke and, in particular, discussed the fact (which I made to several people independently at dinner one night) that time-reversal is really a full CPT reversal (there’s a bit more to it than that, but I’ll leave it there for now). At any rate, his key idea is that if the

Anyway, I said I wasn’t going to summarize all the talks individually and I just violated my rule a bit. The only thing I’ll say about Yasunori Nomura’s talk is that he reinforced the prevailing view (agreed to by nearly everyone) that quantum mechanics is of fundamental importance in any of these discussions.

"Information and Cosmology" panel |

Additional discussions during the panels session served to further accentuate the fact that the cosmologists and the quantum folks really speak vastly different languages. In particular, the cosmologists make numerous claims about probability theory that no quantum person (particularly anyone who has read E.T. Jaynes) would ever make. But then the discussion devolved into one about the quantum measurement problem.

So, if there was a single, consistent thing everyone from yesterday could agree on, I would say that it was the fact that quantum mechanics is of fundamental importance to any discussion of the nature of information, how it is processed in the universe, and, frankly, to anything else in physics, for that matter.

--

Ian Durham is a quantum physicist and FQXi member based at Saint Anselm College, New Hampshire. You can visit his blog here.

this post has been edited by the author since its original submission

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"what is the difference between a standard thermal fluctuation, i.e. the translational, vibrational and rotational modes of particles, and a quantum fluctuation?" An answer to Sean Carroll's question, at least for free quantum fields, is that thermal fluctuations are translational and 3-dimensional Euclidean invariant, whereas quantum fluctuations are Poincaré invariant. From a free quantum field perspective, there is no other difference. See my Physics Letters A 338 (2005) 8-12, arXiv:quant-ph/0411156v2, with the overlong title "A succinct presentation of the quantized Klein-Gordon field, and a similar quantum presentation of the classical Klein-Gordon random field". Of course one cannot be certain that this carries over nicely to interacting fields.

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Concerning, Ian Durham's post today: "At any rate, Anthony also (provocatively) claimed that an infinite universe and a really, really, really big (but finite) universe might not be observationally distinguishable (and, believe it or not, the two provocative claims actually are related!)"

Observationally indistinguishable, probably right. But IF the starting premise for the two is same, i.e. if both observers are agreed that there was a beginning ,which by definition is not an infinite state, then at what time was the infinity attained? Can infinity even be attained by definition, or is it not more correct to say "tends to infinity"? Can zero change to infinity without passing through the number line? On this premise, logically and in a mathematical universe, really, really, really big (but finite) must carry the day, unless there is no beginning.

Akinbo

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Observationally indistinguishable, probably right. But IF the starting premise for the two is same, i.e. if both observers are agreed that there was a beginning ,which by definition is not an infinite state, then at what time was the infinity attained? Can infinity even be attained by definition, or is it not more correct to say "tends to infinity"? Can zero change to infinity without passing through the number line? On this premise, logically and in a mathematical universe, really, really, really big (but finite) must carry the day, unless there is no beginning.

Akinbo

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Aaronson's thesis fails the completeness criterion. That perpetual motion (continuous measurement functions) is forbidden by local methods of computation does not imply that it is forbidden by global physical principles of conservation.

Probabilism itself, in fact, is the most "absurdly constricted physical principle."

For if all physical quantities are conserved (see Emmy Noether), effective computation is not identical to continuous functions in nature. The local-global distinction created by information processing, whether the processor be a brain-mind or an engineered computing machine, is an arbitrarily effective boundary and cannot be otherwise.

Consider that Chaitin's Omega (halting probability of a universal Turing machine) is algorithmically incompressible and algorithmically random. That there is, therefore, no effectively calculable probability on the interval [0,1] strongly suggests that nature's "programming without a programmer" in Chaitin's words, is complete even while our own programming cannot be.

Tom

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Probabilism itself, in fact, is the most "absurdly constricted physical principle."

For if all physical quantities are conserved (see Emmy Noether), effective computation is not identical to continuous functions in nature. The local-global distinction created by information processing, whether the processor be a brain-mind or an engineered computing machine, is an arbitrarily effective boundary and cannot be otherwise.

Consider that Chaitin's Omega (halting probability of a universal Turing machine) is algorithmically incompressible and algorithmically random. That there is, therefore, no effectively calculable probability on the interval [0,1] strongly suggests that nature's "programming without a programmer" in Chaitin's words, is complete even while our own programming cannot be.

Tom

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" ... the cosmologists make numerous claims about probability theory that no quantum person (particularly anyone who has read E.T. Jaynes) would ever make."

I think with good reason, Ian. Cosmology necessarily assumes an undivided universe.

Which is why I think you are misreading Sean Carroll's point about the universe in an energy eigenstate being non-static when observation is introduced.

Quantum persons who object to many-worlds think quantum fluctuations are physically real and subject to a probabilistic interpretation. However:

Were this true, there would be no sufficient reason for the universe to exist at all. The probability for global decoherence would quickly approach unity. So long as we have a comprehensible universe with observers in it, I think we can reasonably say that thermal fluctuations are a real physical result of a non-static universe -- the participatory kind of universe of which Wheeler spoke and always manifestly local, constrained at the boundary of many-worlds bifurcation. ("The boundary of a boundary is zero.")

The static quantum fluctuations of many-worlds preserve the non-probabilistic universe against collapse of the wave function and the assumption of nonlocality. The logic of computability is not always the logic of science, particularly at the cosmological limit.

All best from Mars,

Tom

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I think with good reason, Ian. Cosmology necessarily assumes an undivided universe.

Which is why I think you are misreading Sean Carroll's point about the universe in an energy eigenstate being non-static when observation is introduced.

Quantum persons who object to many-worlds think quantum fluctuations are physically real and subject to a probabilistic interpretation. However:

Were this true, there would be no sufficient reason for the universe to exist at all. The probability for global decoherence would quickly approach unity. So long as we have a comprehensible universe with observers in it, I think we can reasonably say that thermal fluctuations are a real physical result of a non-static universe -- the participatory kind of universe of which Wheeler spoke and always manifestly local, constrained at the boundary of many-worlds bifurcation. ("The boundary of a boundary is zero.")

The static quantum fluctuations of many-worlds preserve the non-probabilistic universe against collapse of the wave function and the assumption of nonlocality. The logic of computability is not always the logic of science, particularly at the cosmological limit.

All best from Mars,

Tom

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