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EvgeniyZh | on: I don't understand quantum physics (2018)
Many-worlds is an interpretation and not a theory. It makes no additional predictions beyond what QM does. Believing in any interpretation (or shutting up and calculating) is purely emotional; it has no scientific content.
unparagoned | parent | next
Pretty much all physics for since forever has been about the ontological explanation of what’s happening. If you don’t want to subscribe to an ontological interpretation then that’s something new and the opposite of how people have always done physics. It’s something that has only ever come about with qm.

In normal physics people often use occamz razor and subscribe to what the interpretation with the simplest postulates says.

So the reality is the opposite. You don’t like what the physics is saying so for emotional reasons you’ve come up with a completely new and novel framework to discount what the simplest set of equations is saying.

EvgeniyZh | root | parent
> You don’t like what the physics is saying so for emotional reasons you’ve come up with a completely new and novel framework to discount what the simplest set of equations is saying.

Nah, physics is not saying anything. I do physics because I enjoy discovering and modeling new phenomena. If someone wants to do philosophy and ask questions like "but what is __really__ happening when we measure an atom", it's his business, but I don't believe we'd be doing the same thing, because these questions are impossible to answer with empirical evidence and don't help us model reality in any way. I don't see any difference between QM interpretations; one of them might be "true"

edanm | parent | next
(Disclaimer: I'm nowhere near truly knowledgeable about any of this)

Quantum computing was explicitly proposed as a way to prove the truth of many worlds. As far as we can tell, quantum computing appears to work.

I don't think most people believe QC truly proves many-worlds, but I think it is considered some evidence in its favor, and historically it was I think one of the reasons for the development of QC originally.

antognini | root | parent | next
I've heard this claim, but I don't think it holds up. The idea is that supposedly the calculation is done in parallel across the different universes which allows you to see an exponential speedup in some calculations. But the whole point of many-worlds is that after a branch event the various branched portions of the wavefunction no longer interact. Even if it were true that quantum computing was really a bunch of parallel classical computations (which it is not), there would be no way for any of the other universes to communicate the result back to the universe you observe it in.
rcxdude | root | parent
Many worlds doesn't really feature 'hard branches'. In fact the interpretation is pretty specific that quantum interactions becoming de-correlated and stopping to react is the mechanism by which you get the 'many worlds', and this is a soft and messy process not some global hard split.

OTOH, I don't think any of the other interpretations really struggle to explain quantum computing so I agree it's not much of a distinguishing factor.

thayne | root | parent
I don't think there is anything in quantum computing that is specific yo the many worlds interpretation.
card_zero | parent | next
But if what you want is understanding, you want a good explanation. (Or to quote TheOtherHobbes from elsewhere in these comments, a reasonable metaphor: https://news.ycombinator.com/item?id=50220700)

If you only like predictions and disparage explanations, I might start calling you names, specifically instrumentalist.

spolitry | root | parent
What do call someone who wants good "Just So" story explanations that don't explain anything, but posit the existence of meaningless things?
card_zero | root | parent
Here you are taking "good explanation" and combining it with the term "just so story" which indicates a bad (arbitrary) explanation. So you cast doubt on the idea that explanations can be good. What's this, sabotage?
dbvdh | parent | next
Does it not make any predictions? It states there is no such thing as wavefunction collapse. This means that if you entangle a state with a large system, in theory you could ‘disentangle’ it. Of course, this is no easy feat. But indeed quantum computing to me, is an example of this feat. We can entangle systems on a large scale, then use this feat to make calculations. Inspiration for quantum computing actually came from many worlds.

Many worlds is falsifiable, if you can show wave function collapse actually happens (not just decoherence). I believe that in the not so distant future we will get more and more proof that wave function collapse never happens. Quantum computing at scale to me is an indication that Everett was just right..

unparagoned | root | parent | next
Nope it’s the opposite. The Copenhagen wavefunction collapse is untestable or unfalsifiable.

With many words, every postulate has been tested and very verified. What more can you ask from a theory?

Now objective collapse is a testable postulate but none expects that to pan out.

EvgeniyZh | root | parent
> This means that if you entangle a state with a large system, in theory you could ‘disentangle’ it.

This can be done in any other interpretation? Any unitary evolution on an isolated system can be reversed. This is a mathematical statement.

> Many worlds is falsifiable, if you can show wave function collapse actually happens

So, what experiments do you think would falsify it? How can you show that collapse actually happened?

dbvdh | root | parent
In the Copenhagen interpretation, when I look at schrodingers cat, the wavefunction will collapse. After I have looked at it, no way to go back. Information is lost. In many worlds, I just become entangled with the system - and I could theoretically disentangle after. Like quantum computing going to a deterministic outcome in a certain basis.

Showing collapse happened is really tricky because of decoherence. Similar to unmixing coffee and milk. But all systems we have observed so far do not show wave function collapse (granted these systems are generally small, but otherwise decoherence starts messing about).

These are just fundamentally different theories. Not just an interpretation, physically different outcomes.

abc123abc123 | parent | next
This is the way! It is absolutely amazing that the supposedly "brilliant brains" at lesswrong and other similar outfits, have not learned about the difference between an interpretation and a theory.

Since QM goes beyond our material world intuitions, I am personally loathe to clothe nrs in words, until we have more and better experiments. I think prematurely translating it into material-level intuitions just leads to a waste of time and much confusion.

goatlover | parent
It has mathematical and philosophical content. People can be convinced for reasons other than empirical without it being emotional. Sean Carroll makes logical arguments for why he's convinced MWI is correct.
spolitry | root | parent
I'm not Sean Carroll. I'm interested in logical arguments for why I should be convinced that something completely impossible to ever test, not even in theory, is correct.
mitthrowaway2 | root | parent
How do you test whether the dinosaurs once existed as living animals, vs as fossils that were embedded in the Earth when the universe began 6000 years ago?

Because I only believe one of these propositions, even though I can't imagine any test that would discriminate between the two.

qlte | root | parent | next
...uh, by using the abundant evidence from radiometric dating, geology and archeology that the world is much older than 6000 years old?

Plus astronomical observations used in cosmology to model the state of the universe milliseconds after the big bang which eventually evolved into our locally observable region of space around 13.8 billion (not 6000) years later?

That doesn't prove the dinosaurs were in fact living beings but this isn't necessary to disprove the other assumptions of the alternative hypothesis. By parsimony that leaves the hypothesis that dinosaur fossils emerged by natural processes like everything else we've observed on Earth to date.

Am I missing a joke? Because this is definitely not a good example of a hypothesis impossible to disprove with available evidence.

(If the response is "how do you test whether all that evidence was faked 6000 of years ago to deceive scientists" then we're not actually doing science anymore but games of make believe)

mitthrowaway2 | root | parent
That's exactly what we're doing. Obviously I don't believe the initial conditions of the universe were set 6000 years ago, and just look billions of years older by mere coincidence. My point -- directed at its parent comment -- is that we can scientifically prefer one hypothesis over the other, even though they're indistinguishable by any experiment because they make identical predictions.

Instead, we can use other forms of reasoning, such as probability and Ockham's razor. These are perfectly valid approaches.

You seem to agree with me on this point, so I direct your attention to the grandparent comment:

> I'm interested in logical arguments for why I should be convinced that something completely impossible to ever test, not even in theory, is correct.

habinero | root | parent
Sure you can. There is no predictability and no fundamental laws in a purpose-built universe run by an omnipotent creator because ultimately the creator can do anything they please.

Not to get all reddit atheist here, but as far as we can tell, the universe is predictable and explainable by fundamental mathematical laws. (We don't see, for example, unexplainable violations of conservation as Michael Landon pops in and out of existence.)

This could mean there is no god or they don't interfere or whatever, but in any case it's pretty good evidence that we can reason about how the universe works.

That's about as good as you can know anything. Beyond that is the "Are you a brain in a jar" kinds of philosophical arguments that are fun when you're 21 and get old after.