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RE: The Tao of Physics
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kitarist
Posts: 1715
Joined: Dec. 4 2012
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 RE: The Tao of Physics (in reply to Ricardo)
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quote:
ORIGINAL: Ricardo
quote:
ORIGINAL: Beni2
https://arxiv.org/abs/1902.05080
https://mitpress.mit.edu/books/objectivity
Is objectivity possible?
What can anyone in the foro agree on, if anything?
The key is “in the quantum world”.... the answer can be “no”. So once we can define the boundaries between the quantum world and the macro world, we can allow objectivity I think.
Speaking of boundaries and objectivity, enter something called the Leggett-Garg Inequalities. These are a class of inequalities that would have to be true for all macrorealistic physical theories. Here, macrorealism (macroscopic realism) is a classical worldview defined by the following three principles:
(1) Macrorealism per se: "A macroscopic system/object, which has available to it two or more macroscopically distinct states, is at any given time in a definite one of those states."
(2) Noninvasive measurability: "It is possible in principle to determine which of these states the system is in without any effect on the state itself, or on the subsequent system dynamics.", and
(3) Induction: The outcome of a measurement on the system cannot be affected by what will or will not be measured on it later.
There is a review paper from 2014 on Leggett-Garg Inequalities (LGIs), experimental attempts (and their pitfalls) at violating them and LGI's possible applications, here: https://arxiv.org/abs/1304.5133
From it: "Whilst classical mechanics conforms with [..] these assumptions, quantum mechanics certainly does not — the existence of a macroscopic superposition would violate the first, and its quantum-mechanical collapse under measurement, the second."
So the inequalities can be used as test to see how far the quantum world's coherences can penetrate before collapsing into definite states in the macro world.
From the conclusion section: "Thus, it is clear that we are only at the outset of the journey in testing the penetration of quantum coherence into the macroscopic world with LGIs. Further progress involves not only moving up in scale to address ever-more macroscopic entities, but also in confronting the challenges posed by the clumsiness loophole."
What is the "clumsiness loophole"? It means when experimental tests of LGIs show apparent LGI violations, however that turns out to be a result of the unwitting invasivity of the measurements, rather that the absence of a macroscopic-real description of the system. Heh.
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Konstantin
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Date Apr. 25 2019 20:16:27
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Paul Magnussen
Posts: 1805
Joined: Nov. 8 2010
From: London (living in the Bay Area)
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RE: The Tao of Physics (in reply to Ricardo)
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quote:
I remember Roger Penrose talking about wanting to study the quantum gravity effects of “a mote of dust”
Penrose, for my money, is one of the few authors of popular books that writes clearly about quantum physics. Speculation about the rôle of consciousness seems especially fuddled. Penrose is of the few who goes into what actually constitutes an observation.
So if we place a a detector at one slit, we don’t get an interference pattern. But what if we arrange that we don’t know whether it’s turned on or off? Or, we don’t look at the print-out, and destroy it before anyone else can do so?
What if the result is seen only by the laboratory cat, or just a passing spider?
If the Universe doesn’t exist when we’re not observing it (as some hypothesise), then how can we be here at all (since the Universe is considerably older than we are)?
These are some of the questions that bugged me when I first started reading such stuff. I’m not saying these topics can’t be addressed, but they seldom are, in my experience.
I’ve just started Einstein’s Unfinished Revolution (2019), by Lee Smolin, which looks promising.
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Date Apr. 28 2019 16:10:43
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kitarist
Posts: 1715
Joined: Dec. 4 2012
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RE: The Tao of Physics (in reply to Ricardo)
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quote:
ORIGINAL: Ricardo
So... 811 atoms it is then. Objectivity and gravity appear at 811 or more atoms in size.... where is my Nobel prize?
Yes  [from here on not in response to what you said]
But in general, it is more complicated. There is so much confusion sowed even with the various explanations - or is it mostly with the misinterpretations of the scientific theories when journalists try to convey them to the public.
Example 1: Schrodinger's cat. Shrodinger brought that up as a reductio ad absurdum argument - in other words, he was mocking the Copenhagen interpretation (or perhaps its popular extensions) with what he thought was an obvious absurdity - to posit that a macro object such a as cat can be dead and alive at the same time until its "wave-function" collapses upon measurement.
However, these days you can find as many if not more people bringing it up as a straight argument FOR that interpretation, as if Shrodinger was its supporter. I blame journalists.
Example 2: Double-slit experiment. The interference pattern at some distance from the slits is not produced by the same "particle" going through both slits at once as if it is actually a wave; that's not what the paradox is. All these micro objects, from single particles to 800+atom molecules, definitely go through either one slit or the other. The apparent interference pattern is produced only over time as you send thousands of these objects over and over, each only hitting at one definite point on the screen. The puzzle is, how do these different objects "know" to mostly hit the areas where the constructive interference would be IF what was sent through was some sort of wave? But that's different than imagining a multi-atom molecule ghostly splitting itself and going through both slits, isn't it?
Example 3: Quantum coherence. Coherence effects do exist in the macroworld, but that does not necessarily mean anything about determinism or objectivity - it seems to depend on what the phenomenon is. Laser is a quantum coherence phenomenon on macro scales, for example; so are superconductivity and superfluidity. BTW macroscopic or macroscale for these purposes is understood to have at least an Avogadro's number's worth ( 6.022 x 10^23) of particles; or extend to macro distances.
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Konstantin
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Date Apr. 28 2019 21:50:27
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Piwin
Posts: 3559
Joined: Feb. 9 2016
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RE: The Tao of Physics (in reply to kitarist)
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Thanks for the article kitarist. That was an interesting read. Oddly I was introduced to Bohm not through physics but through linguistics. His "rheomode" bears some connection to the idea of linguistic relativity.
Thanks for the recommendation Paul. I'll have to add it to my list of upcoming purchases.
One book that might be tangentially pertinent to this discussion is "Lost in math: how beauty leads physics astray" by physicist Sabine Hossenfelder. It's a fairly light read but raises some interesting questions. In a nutshell (spoilers ^^), she notes that, in areas where the data are not yet in, physicists often go by "mathematical beauty" as a standard to separate viable theories from unviable theories. And she goes looking for an answer to whether and why that assumption might be justified or not. After having read her book, I started noticing how often this reference to beauty comes up in science communication. Even during the press conference on the "shadow of a black hole", one of the researchers answered a question by saying "in my experience, nature wants to be beautiful". This doesn't say anything about objectivity per se, but it does point to possibly unjustified expectations we have about what reality should look like.
Another aspect of this that could be considered is the effects of evolution on our own perceptual strategies. A common assumption is that a more accurate perception of reality equals more evolutionary fitness. However, that idea has slowly started to be challenged, some going as far as arguing that the two may have an inverse relationship. Such a prospect wouldn't call into question that there is an objective reality out there, but it would call into question our ability to ever perceive it, suggesting that we are in fact "designed" not to perceive it.
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Date Apr. 29 2019 4:38:24
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