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The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain

The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist. My favorite from David Deutsch, a main creator of the idea of quantum computing: To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s algorithm works. I do not merely mean predict that it will work, which is merely a matter of solving a few uncontroversial equations. I mean provide an explanation. When Shor’s algorithm has factorized a number, using 10^500 or so times the computational resources than can be seen to be present, where was the number factorized? There are only about 10^80 atoms in the entire visible universe, an utterly minuscule number compared with 10^500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?

pron 9y ago
I don't understand David Deutsch's philosophical justification. Is he suggesting that quantum computing steals computational resources from other universes? If so, in this "quantum computing as theft" view, aren't many of those universes (those similar to ours, doing a similar computation at the same time) stealing computational resources from ours at the same time, yielding the original question again?
- ridewinter 9y ago
  No, nothing stolen. The quantum computer's calculations take place in parallel universes. The difficulty is arranging it so that the parallel universes are identical to eachother other than those calculations in the computer itself. That's the only way that this universe can get the answer back. That's my understanding of the many-worlds explanation of quantum computing. Nice and simple.
- petters 9y ago
  The "different universes" in the multiverse are still parts of the same wavefunction. Therefore they can interact. It's just that after decoherence, they will never interact again and will stay separate.
opportune 9y ago
What if collapsing quantum wave functions simply eliminates the possible futures within our universe in which the computation is incorrect? In that case it's not exactly a multiple-universe problem, and more an issue of imposing constraints on our own single universe. I find this view to make much more sense than the multiple universe view. Those other universes would need the infrastructure to support the same computation, and would also need to be somehow linked to our own. Or perhaps I am misunderstanding you, and we are both saying the same thing.
- ridewinter 9y ago
  Well the calculations to do this elimination would have to happen somewhere. Deutsch and the many-worlds interpretation says it happens in parallel universes. And what makes quantum computing so difficult is that you have to arrange those parallel universes to be identical in every way except the inside of the computer itself. That's the only way to get an answer back. If there's interference with the outside environment, the universes become different outside of the computer and you can't get an answer back. I love this stuff.
mikeash 9y ago
That seems to be begging the question. Qubits do more than this universe is capable of, therefore there must be multiple universes. The obvious refutation is: qubits don't do more than this universe is capable of, because the universe does not run on classical limits. 10^80 atoms implying on the order of 10^80 computations that can be done implicitly assumes that these things operate on classical-ish rules. There's an implicit notion of "a computation" in there, which is assumed to be something roughly like what a standard computer is able to do in a standard machine instruction. What if, instead, the fundamental operations that the universe works on are things like Hadamard transforms?
- ridewinter 9y ago
  Explain the double slit experiment to me. The single photon somehow calculates the interference pattern with photons that don't exist, in our world at least. If there's not parallel universes, how does a single atom calculate that interference pattern? Where do those calculations occur? All other theories say it happens by magic and give all sorts of complicated non-real obfuscations to explain it.
  - raverbashing 9y ago
    Bohmian mechanics seems like a better explanation than "there are infinite universes out there"
    - mr_overalls 9y ago
      "We don't understand the deeper mechanisms yet" is also a valid explanation - although one that's sure to be unpopular with scientists. "Entia non sunt multiplicanda praeter necessitatem" and all that.
    - ridewinter 9y ago
      I'm sure you could confuse the heck out of me trying to explain it. Deutsch would say it's just a clever obfuscation of what's really happening. And his many-worlds explanation is so incredibly simple that my small mind uses Occam's razor to figure out what to believe.
steven777400 9y ago
What about the interpretation that if reality is a computer simulation, certain operations (such as the factoring described) are a form of a security weakness in the simulation, allowing the simulation to "escape" and access/consume host computational resources?
- metafunctor 9y ago
  That seems to me like a multiple universes explanation for people who also like science fiction. I'd bet there's a simpler explanation.
ethn 9y ago
First if you can measure it then it must be in ~physical reality~. If we are directly interacting with it why even consider it to be in another universe? Is my keyboard also in another universe? Second, since when is one atom responsible for a computation? In modern electronics no atom is responsible at all for computation, only the electrons are†. Even then, computation is an emergent property, computation itself is abstract and cannot be physical; but it emerges from physical interactions. † Not even the electrons are directly, it's the energy propagated by the electrons!Hence why electronics are instant while the speed of an electron is a few cm a second
- ridewinter 9y ago
  The coolness of quantum computing is that it harnesses the natural computational abilities of reality itself. So a single atom is doing an amazing number of quantum calculations at any moment. These guys like Deutsch figured out how to harness those calculations. And the only way to interact with parallel universes is if they are totally identical except what's inside of the quantum computer itself. Deutsch posits that the quantum computer essentially proves many-worlds.
  - adrianN 9y ago
    All computing machines harness the universe's innate ability for computation. Quantum computers just do it better.
  - ethn 9y ago
    You didn't defend Deutsch's erroneous assumption that atoms are responsible for physical interactions in computation. Even in quantum computing atoms are not responsible for any computation––especially if you have a system like DWave which uses magnetically induced currents. "The natural computational abilities of reality itself" Additionally you continue to insist that computation is a real physical thing. Are you claiming that nature is aware of the states we assign it to perform computation? The way computation works is that we map various physical states with our own semantic abstractions. I can change the computation for addition into one for subtraction without any physical change to the system. So there is no harnessing of "the natural computational abilities of reality itself". We merely observe natural behavior and semantically map it (which is what engineering is).
JadeNB 9y ago
> My favorite from David Deutsch, a main creator of the idea of quantum computing: It's interesting, but this "I challenge you to answer a philosophical (not scientific) question in a way that I find acceptable" approach surely skirts uncomfortably close to dogmatically creationist arguments. (For the record, my answer, which certainly wouldn't satisfy Deutsch, is: it works because the math proves it works; there's no more "how" about it than there is in "how does the computation 10^(250)*10^(250) = 10^(500) work?")
- opportune 9y ago
  I agree with you. I think the need for philosophical justification stems from our desire to reconcile quantum computing with our classical computing/physics models. But just because we desire such a thing doesn't mean there exists a reasonable one. What I think the truth really is, is that we don't encounter quantum superpositions in an obvious way in our day to day lives. So it's inherently "weird" for us, especially since it seems to violate our notion of object permanence. But that doesn't mean it's wrong, it just means that one of our evolved instincts isn't applicable on a quantum scale.
  - JadeNB 9y ago
    > But that doesn't mean it's wrong, it just means that one of our evolved instincts isn't applicable on a quantum scale. I think that this puts it very well. If a theory doesn't fit with our intuition, then it might mean that the theory is wrong; but it's at least plausible that our intuition is wrong, and goes from plausible to overwhelmingly likely once the theory is backed up by experimental data. (Anyone, even or especially a scientist, who dogmatically trusts his or her intuition over science probably could do with a quick refresher in cognitive biases.)
- ridewinter 9y ago
  Math is used to explain the universe. It isn't an explanation in of itself. We never progressed anywhere by saying "something just works" and leaving it at that. Challenge yourself.
deleted 9y ago
[deleted]
nilson 9y ago
im not "clinging to single universe world view" but i got 2 questions: 1. has this alghoritm actually been executed somewhere? 2. does this mean there is infinite storage posibillity to store any data you want or it must be "special" data. and how much time does it take to access any segment of this data. if the answer is no to both question then my answer is: "it doesn't work."
- Tenoke 9y ago
  > 1. has this alghoritm actually been executed somewhere? Yeah, but so far we have the highest factorization achieved is 21 because we've only built relatively tiny quantum computers.[0] 0. https://en.wikipedia.org/wiki/Shor%27s_algorithm https://en.wikipedia.org/wiki/Shor%27s_algorithm
nol13 9y ago
Not clinging to single universe rule, but multiworld is a big leap, plus seems weird. Still significantly less of a leap than single-world narrative of "two particles have some probability to do something > ????!?? > they did this" so I dunno. Can MWI derive the born rule yet? Either way neither seems likely. Thus my hypothesis that the correct number of worlds is actually a fractal.

pron 9y ago

I don't understand David Deutsch's philosophical justification. Is he suggesting that quantum computing steals computational resources from other universes? If so, in this "quantum computing as theft" view, aren't many of those universes (those similar to ours, doing a similar computation at the same time) stealing computational resources from ours at the same time, yielding the original question again?

ridewinter 9y ago
No, nothing stolen. The quantum computer's calculations take place in parallel universes. The difficulty is arranging it so that the parallel universes are identical to eachother other than those calculations in the computer itself. That's the only way that this universe can get the answer back. That's my understanding of the many-worlds explanation of quantum computing. Nice and simple.
petters 9y ago
The "different universes" in the multiverse are still parts of the same wavefunction. Therefore they can interact. It's just that after decoherence, they will never interact again and will stay separate.

opportune 9y ago

What if collapsing quantum wave functions simply eliminates the possible futures within our universe in which the computation is incorrect? In that case it's not exactly a multiple-universe problem, and more an issue of imposing constraints on our own single universe. I find this view to make much more sense than the multiple universe view. Those other universes would need the infrastructure to support the same computation, and would also need to be somehow linked to our own. Or perhaps I am misunderstanding you, and we are both saying the same thing.

ridewinter 9y ago
Well the calculations to do this elimination would have to happen somewhere. Deutsch and the many-worlds interpretation says it happens in parallel universes. And what makes quantum computing so difficult is that you have to arrange those parallel universes to be identical in every way except the inside of the computer itself. That's the only way to get an answer back. If there's interference with the outside environment, the universes become different outside of the computer and you can't get an answer back. I love this stuff.

mikeash 9y ago

That seems to be begging the question. Qubits do more than this universe is capable of, therefore there must be multiple universes. The obvious refutation is: qubits don't do more than this universe is capable of, because the universe does not run on classical limits. 10^80 atoms implying on the order of 10^80 computations that can be done implicitly assumes that these things operate on classical-ish rules. There's an implicit notion of "a computation" in there, which is assumed to be something roughly like what a standard computer is able to do in a standard machine instruction. What if, instead, the fundamental operations that the universe works on are things like Hadamard transforms?

ridewinter 9y ago
Explain the double slit experiment to me. The single photon somehow calculates the interference pattern with photons that don't exist, in our world at least. If there's not parallel universes, how does a single atom calculate that interference pattern? Where do those calculations occur? All other theories say it happens by magic and give all sorts of complicated non-real obfuscations to explain it.
- raverbashing 9y ago
  Bohmian mechanics seems like a better explanation than "there are infinite universes out there"
  - mr_overalls 9y ago
    "We don't understand the deeper mechanisms yet" is also a valid explanation - although one that's sure to be unpopular with scientists. "Entia non sunt multiplicanda praeter necessitatem" and all that.
  - ridewinter 9y ago
    I'm sure you could confuse the heck out of me trying to explain it. Deutsch would say it's just a clever obfuscation of what's really happening. And his many-worlds explanation is so incredibly simple that my small mind uses Occam's razor to figure out what to believe.

steven777400 9y ago

What about the interpretation that if reality is a computer simulation, certain operations (such as the factoring described) are a form of a security weakness in the simulation, allowing the simulation to "escape" and access/consume host computational resources?

metafunctor 9y ago
That seems to me like a multiple universes explanation for people who also like science fiction. I'd bet there's a simpler explanation.

ethn 9y ago

First if you can measure it then it must be in ~physical reality~. If we are directly interacting with it why even consider it to be in another universe? Is my keyboard also in another universe? Second, since when is one atom responsible for a computation? In modern electronics no atom is responsible at all for computation, only the electrons are†. Even then, computation is an emergent property, computation itself is abstract and cannot be physical; but it emerges from physical interactions. † Not even the electrons are directly, it's the energy propagated by the electrons!Hence why electronics are instant while the speed of an electron is a few cm a second

ridewinter 9y ago
The coolness of quantum computing is that it harnesses the natural computational abilities of reality itself. So a single atom is doing an amazing number of quantum calculations at any moment. These guys like Deutsch figured out how to harness those calculations. And the only way to interact with parallel universes is if they are totally identical except what's inside of the quantum computer itself. Deutsch posits that the quantum computer essentially proves many-worlds.
- adrianN 9y ago
  All computing machines harness the universe's innate ability for computation. Quantum computers just do it better.
- ethn 9y ago
  You didn't defend Deutsch's erroneous assumption that atoms are responsible for physical interactions in computation. Even in quantum computing atoms are not responsible for any computation––especially if you have a system like DWave which uses magnetically induced currents. "The natural computational abilities of reality itself" Additionally you continue to insist that computation is a real physical thing. Are you claiming that nature is aware of the states we assign it to perform computation? The way computation works is that we map various physical states with our own semantic abstractions. I can change the computation for addition into one for subtraction without any physical change to the system. So there is no harnessing of "the natural computational abilities of reality itself". We merely observe natural behavior and semantically map it (which is what engineering is).

JadeNB 9y ago

> My favorite from David Deutsch, a main creator of the idea of quantum computing: It's interesting, but this "I challenge you to answer a philosophical (not scientific) question in a way that I find acceptable" approach surely skirts uncomfortably close to dogmatically creationist arguments. (For the record, my answer, which certainly wouldn't satisfy Deutsch, is: it works because the math proves it works; there's no more "how" about it than there is in "how does the computation 10^(250)*10^(250) = 10^(500) work?")

opportune 9y ago
I agree with you. I think the need for philosophical justification stems from our desire to reconcile quantum computing with our classical computing/physics models. But just because we desire such a thing doesn't mean there exists a reasonable one. What I think the truth really is, is that we don't encounter quantum superpositions in an obvious way in our day to day lives. So it's inherently "weird" for us, especially since it seems to violate our notion of object permanence. But that doesn't mean it's wrong, it just means that one of our evolved instincts isn't applicable on a quantum scale.
- JadeNB 9y ago
  > But that doesn't mean it's wrong, it just means that one of our evolved instincts isn't applicable on a quantum scale. I think that this puts it very well. If a theory doesn't fit with our intuition, then it might mean that the theory is wrong; but it's at least plausible that our intuition is wrong, and goes from plausible to overwhelmingly likely once the theory is backed up by experimental data. (Anyone, even or especially a scientist, who dogmatically trusts his or her intuition over science probably could do with a quick refresher in cognitive biases.)
ridewinter 9y ago
Math is used to explain the universe. It isn't an explanation in of itself. We never progressed anywhere by saying "something just works" and leaving it at that. Challenge yourself.

deleted 9y ago

[deleted]

nilson 9y ago

im not "clinging to single universe world view" but i got 2 questions: 1. has this alghoritm actually been executed somewhere? 2. does this mean there is infinite storage posibillity to store any data you want or it must be "special" data. and how much time does it take to access any segment of this data. if the answer is no to both question then my answer is: "it doesn't work."

Tenoke 9y ago
> 1. has this alghoritm actually been executed somewhere? Yeah, but so far we have the highest factorization achieved is 21 because we've only built relatively tiny quantum computers.[0] 0. https://en.wikipedia.org/wiki/Shor%27s_algorithm https://en.wikipedia.org/wiki/Shor%27s_algorithm

nol13 9y ago

Not clinging to single universe rule, but multiworld is a big leap, plus seems weird. Still significantly less of a leap than single-world narrative of "two particles have some probability to do something > ????!?? > they did this" so I dunno. Can MWI derive the born rule yet? Either way neither seems likely. Thus my hypothesis that the correct number of worlds is actually a fractal.