Quantum Mechanics for Programmers
kim.oyhus.no
Quantum Mechanics for Programmers
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Re: Quantum Mechanics for Programmers
#2Why not categorical quantum mechanics?
Re: Quantum Mechanics for Programmers
#3Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem:
> But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer.
But that is not what the Church-Turing thesis says. A Turing machine cannot mimic a truly random physical process, pretty much by definition.
And then:
> This means that observers can be simulated by a computer.
Except that nobody really understands what kinds of physical interactions qualify as measurements -- or even if that is the right framework to use at all.
Re: Quantum Mechanics for Programmers
#4Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Churc…
I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
Re: Quantum Mechanics for Programmers
#5Why not categorical quantum mechanics?
Yeah I'm reading a nice book from Coecke and Kissinger [1] just issued and am loving it, it's the story of String Diagrams for a wider audience and with all the details fleshed out (not just hinted as in Baez TWFs). Monoidal categories, tensor networks, directed PGMs, quantum computing and even vector space NLP semantics are all particulars seen from this vantage point.
[1] Picturing Quantum Processes, ISBN 1108107710
Re: Quantum Mechanics for Programmers
#6This seems just to be a model of systems evolving according to discrete difference equations, admittedly derived from quantum mechanics; it doesn't seem to have much to say about quantum mechanics per se. It reminds me of a lower-(math-)tech version of SICM (https://mitpress.mit.edu/sites/default/files/titles/content/...).
Re: Quantum Mechanics for Programmers
#7Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Churc…
I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
It is generally agreed (except, perhaps, by the strongest champions of the decoherence program) that decoherence does not completely solve the measurement problem.
Some good references here: http://physics.stackexchange.com/questions/295527/decoherenc...
It helps explain the loss of interference, but it does not resolve the question of why and how we see one particular outcome.
Re: Quantum Mechanics for Programmers
#8Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Churc…
I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
Also see this piece by Steven Weinberg:
http://www.nybooks.com/articles/2017/01/19/trouble-with-quan...
"One common answer is that, in a measurement, the spin (or whatever else is measured) is put in an interaction with a macroscopic environment that jitters in an unpredictable way. For example, the environment might be the shower of photons in a beam of light that is used to observe the system, as unpredictable in practice as a shower of raindrops. Such an environment causes the superposition of different states in the wave function to break down, leading to an unpredictable result of the measurement. (This is called decoherence.) It is as if a noisy background somehow unpredictably left only one of the notes of a chord audible. But this begs the question. If the deterministic Schrödinger equation governs the changes through time not only of the spin but also of the measuring apparatus and the physicist using it, then the results of measurement should not in principle be unpredictable. So we still have to ask, how do probabilities get into quantum mechanics?"
Re: Quantum Mechanics for Programmers
#9Earlier quoted context omitted.
I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
It is generally agreed (except, perhaps, by the strongest champions of the decoherence program) that decoherence does not completely solve the measurement problem. Some good references here: http://physics.stackexchange.com/questions/295527/decoherenc... It helps explain the loss of interference, but it does not resolve the question of why and how we see one particular outcome.
> it does not resolve the question of why and how we see one particular outcome.
agreed. dechoherence doesn't explain particular outcomes. It explains the scale & magnitude of mixing quantum states from different systems.
I thought "what kinds of physical interactions qualify as measurements" was referring to a different part of understanding QM. Decoherence doesn't explain which outcome, it does explains "part" of (or place constraints upon) the mechanism of measurement process.
Re: Quantum Mechanics for Programmers
#10The more I learn about physics and math, especially with regards to quantum theory, I start to get really freaked out. The amount of "neatness" to the universe is staggering. How there's no "inbetween" at the smallest scales. Everything is discrete.
The fact that simple arrangements of symbols on a screen can perfectly describe this behavior is mind blowing. It leads me to think there's no possible way we're not living in some type of computer simulation.