[yoyohello13]

Im fully willing to believe I just don’t “get it” but I took a pretty deep dive into quantum computing and the underlying mechanics and I kind of got the sense (with QC) that nobody really knows what they are talking about. I got this feeling so strongly that stopped studying the topic all together.

I’m probably way off base and I’m probably missing some insights that I could get by going to school or something but that’s was just my experience with the subject.

[beloch]

"I think I can safely say that nobody understands quantum mechanics."

--Richard Feynman

You're far from alone. Quantum physics is tricky because it frequently doesn't agree with our physical intuition. Humans are used to dealing with macroscopic objects. They surround us for our whole lives. Matter behaves in surprisingly different ways at the level of single quanta. Seemingly impossible things flop out of the math and then clever experiments show that reality is consistent with the math, but we struggle to reach the point where that reality feels correct. When we try to translate the math into human language, we often wind up overloading words and concepts in a way that can be misleading or even false.

Perhaps we just haven't reached the point where things are sufficiently well explained and simplified, but it may be be that quantum physics will always seem strange and counter-intuitive.

[sampo]

> Quantum physics is tricky because it frequently doesn't agree with our physical intuition.

Quantum physics tricky for two separate reasons.

(i) The mathematical theory (Schrödinger equation, wave function, operators, probabilities) is solid and well-defined, but may feel unintuitive, as you say.

(ii) But quantum mechanics is also an incomplete theory. Even if you learn to be at peace with the unintuitive aspects of the mathematical theory, the measurement problem remains an unsolved problem.

"The Schrödinger equation describes quantum systems but does not describe their measurement."

"Quantum theory offers no dynamical description of the "collapse" of the wave function"

https://en.wikipedia.org/wiki/Wave_function_collapse#The_mea...

[tbrownaw]

> is solid and well-defined, but may feel unintuitive

I'm thinking that the nature of intuition is about training your neurons to approximate stuff without needing to detour through conscious calculation.

And QM is in too high of a complexity class for this to be a thing.

[itemize123]

it's not complexity but lack of training data right

[blueprint]

Feynman, a famous man from an older era who tried to inspire, remind, and spur people...

> macroscopic objects

It's not about scale at all though. It's just that small systems tend to be observed with this other, specific property that we associate with causing "quantum" like effects. Not only do those effects happen at mesoscopic scale but aside from gravity, quantum theory already can be and is used to describe things on large scales too. Classical computers and desks are still "quantum" systems. Recently theory and experiments have developed to connect with gravity in many ways. I'm more confused when people say something is mysterious. They're usually referring to apparent randomness but I think even that is explained already with partitions or even just wave math (complementarity).

[dwd]

I like that quote.

I always fell back on "Spooky action at a distance"; If Einstein found it weird, I shouldn't feel that bad if I can't quite make sense of it.

[sampo]

> I’m probably way off base and I’m probably missing some insights that I could get by going to school

A school would usually teach the "shut up (about philosophy) and calculate" approach. These philosophical problems about the meaning of quantum mechanics have been with us for 100 years, and mainstream physics sees them as too hard or even intractable, and thus as waste of time.

[tbrownaw]

Hard /intractable is on an axis orthogonal to philosophical stuff like meaning.

[superposeur]

These debates over the interpretation of Quantum Mechanics (i.e. what ultimately happens when a “measurement” takes place) are important but don’t bear on the effectiveness of quantum computing. Regardless of your favorite interpretation (almost) everyone agrees that quantum computers should work and be able to do things classical computers cannot.

[eru]

Well, to be slightly more sophisticated (to paraphrase Scott Aaronson):

Either quantum computers work (at least in principle), or our understanding of the universe is way off and we are getting exciting new physics.

[gerdesj]

Credo.

[B1FF_PSUVM]

... quia absurdum est?

[gerdesj]

"(almost) everyone agrees that quantum computers should work" is what I was commenting on. It seems I touched a nerve!

[colechristensen]

>nobody really knows what they are talking about

The mathematics of QM works extremely well.

The interpretations of what the math is saying happens a varied and sometimes contradictory.

We can predict what's going to happen extremely well, we just can't tell the story of what's happening. And there's been a century of trying to avoid the weirdness and failing. The problem might just be our brains evolved in a world that behaves so much differently that we can't understand.

[danbruc]

The mathematics of QM works extremely well.

Yes but also absolutely not. The evolution of the wavefunction when nobody is looking is unitary, which among other things means it is time-reversible. That math works extremely well and predicts the correct outcome.

When we are measuring a quantum system, the probability distribution of the measurement outcome is described by the Born rule, the amplitude of the wavefunction squared, and the collapse postulate tells us that after the measurement the wave function will be in the measured state, which is a non-unitary and non-time-reversible process. That math works extremely well and predicts the correct outcome.

But - really big but - what is a measurement device but a huge quantum system, what is a measurement but a quantum system and a measurement device and an environment undergoing time evolution? So both descriptions should apply, unitary time evolution and wave function collapse, but that can not be the case because they are incompatible, one is unitary, the other is not. The mathematical description is inconsistent.

[Terr_]

I often observe that humans are wired to create causal stories, whether we intend to or not, even in circumstances, we know are false.

A great example involves flipping a coin. Even people who know it's basically an independent 50/50 chance every time get drawn into thinking about "hot streaks" and "overdue for the opposite."

It's arguably a superpower that has given us lots of agriculture and tools and technology and culture, but like hunger and obesity we can't just turn it off when it gets maladaptive.

[colechristensen]

Philosophy calls this a "just so" explanation

Humans are very good at pattern matching and explanation and that's what's given us success, but false-positive matches sometimes are the result and need to be corrected down a bit

[blueprint]

> nobody really knows what they are talking about

Could you form a specific question that you're wondering about? (Have you looked at condensed matter physics yet?)

[cpncrunch]

There is a somewhat easily digestible explanation of the quantum Darwinism theory here:

https://arxiv.org/pdf/1811.09062

However, it still doesn't really address the core question of when the collapse actually occurs. All it really seems to add is that the environment is an "observer" and that decoherence actually causes the collapse.

[eru]

Isn't 'collapse' just something that the Copenhagen Interpretation people made up?

[cpncrunch]

Its either collapse or many worlds.

[eru]

Or 'shut up and calculate'.

[eru]

> [...] and the underlying mechanics and I kind of got the sense (with QC) that nobody really knows what they are talking about.

The math is fairly well known, and people can successfully apply it. As evidence in eg modern CPUs and GPUs and RAM actually working. And lots of other marvels of modern engineering that requiring an understanding of quantum mechanics to design and engineer.

[anon291]

Funny, I looked into quantum computing and came away knowing pretty well how to use a future quantum computer. The math is pretty straightforward and useful. Now, getting an actual quantum computer with error correction that is scalable... that is still elusive.

Nevertheless, commercial quantum computers exist and do exactly what scientists predicted they would do.