Unix forking the universe by running IBM's free online quantum computer

[olooney]

Superposition does not fork the world. This common misconception arises due to confusion between superposition and the many-worlds interpretation of quantum mechanics, but it’s easy to see that the two are only superficially similar. States in a superposition still interfere—that's the essence of the double-slit experiment.

In contrast, when arguing that the timeline 'splits' due to measurements, the resulting universes do not interact at all and remain completely unaware of each other—they can never even know if the others exist.

If quantum computers truly 'forked' the world, they would be equivalent to non-deterministic Turing machines (capable of solving NP-complete problems in polynomial time), but quantum computing experts agree that they can still be modeled as deterministic Turing machines.

It's better to think of quantum computers as a type of analog computer, capable of solving certain problems that fit their model well, but not generally more powerful. It’s like an Intel CPU having SIMD or AVX instructions that allow it to perform certain operations faster, but these don't fundamentally change its capabilities. The no-free-lunch theorem applies.

[andrewp123]

Correct - superposition doesn't fork the world - measurement does. And correct, you can't communicate with the other universe after the split has happened [1]. I'm glad you mentioned that quantum computers can't solve NP-complete problems - my next blog post was going to be about why. Here's an overview of what I plan on saying:

A typical quantum algorithm like Shor's works by sending every possible input through a gate, and so you get every possible output out in a superposition. If you were to just measure that, you'd get a random result - so instead, you need to somehow interfere the output to get the actual result. You do this by taking advantage of the fact that the superposition is a periodic function and the amplitude repeats. This is literally the core assumption of the algorithm.(a common way of doing this using the QFT).

Every quantum algorithm requires some kind of structure in the output like this. Deustch's algo, dumb ones like Simon's algo, etc. NP-Complete problems have no structure to them, so even if you build a gate that creates the superposition you want, it's not possible to destructively interfere it to get an answer (I don't know how to prove that there's no structure to NP-Complete outputs - it just feels trivial, since they're only solvable in exponential time, so there must be an exponential amount of "structure" there).

---

[1] The only way to communicate with the other universe would be to try to use quantum mechanics with something like an entangled pair. But no information can be communicated through an entangled pair if all you just have 1 of the 2 particles! Measurement collapses a state nonlocally, and if you could somehow measure one particle and change the probability distribution of the other, you'd be communicating faster than light. The measurement genuinely changes the state and the amplitudes, but not in a way that the other person can detect. It's really interesting and leads to stuff like teleportation.

[cbsmith]

Thanks for restoring my sanity. Every now and then I read articles about quantum computing that upend my (limited) understanding of how it functions, and I feel like I really know nothing about it. In fairness, I do know close to nothing about it, it just turns out that "close to nothing" is still more than a good chunk of the discussion about quantum computing.

[snarkconjecture]

Quantum computers are generally more powerful in the sense that they can solve a larger set of problems in polynomial time.

i.e. BPP is contained in BQP but the converse is thought to be false.

[floam]

This is potentially useful because people can be very impressionable when it comes to quantum magic. I think if I could build some kind of shiny heavy tangible apparatus to interface with the IBM compute service, with like seven segment LEDs (resist the urge to use Nixie tubes, this is a serious, practical device) with a big loud trigger and some kind of boutique radio, I would have a potentially very persuasive magic 8 ball I could use to influence and manipulate people, with carefully chosen false dichotomies.

Okay team, we’ve effectively entangled the success of our endeavor with the quantum dead man’s switch by all swearing to comply with the protocol. It’s time to start letting the universe tell us what works. QUESTION 1 for the Profit Manifold: promote yours truly to director or stay the course? Click bang hiss: 01.

Note to self: cut “universe B” (or just B? It’d hurt less) into my thigh with a razor blade 6 months before demonstrating The Device, as a plot device to be exploited for purposes TBD.

[jerf]

But why would you resist the urge to use Nixie tubes? https://www.youtube.com/watch?v=gwIGnATzBTg

[ezoe]

1 fork per 4 seconds? That's so inefficient. Just observing Geiger counter will fork the universe faster than article's very inefficient implementation.

[boothby]

I generally try not to comment on work-related stuff in public but I almost fell out of my chair when I saw that sampling rate. Surely they can do better, and that's just a limitation of the free API?

[ggm]

> I genuinely think it's a fun & potentially meaningful way to make a decision.

what difference is there to any 50/50 choice mechanism you chose, other than being horrendously expensive to implement?

[andrewp123]

If you roll a regular coin without any quantum effects, every version of you will either see only heads, or only tails. You need quantum in order to make the choice nondeterministic.

[dwattttt]

I think it's time we had the quantum computing talk: https://www.smbc-comics.com/comic/the-talk-3

[brna]

@andrewp123 cool blog post, tried the experiment like this (the result - 0 is kinda of anticlimactic):

Statement: I will make a minimal BTC transfer today, May 11. 2024, as near noon UTC+2 if the outcome is 1/true.

Result: [ { "0": 0.5140027374683648, "1": 0.4859972625316353 } ] So now we have(will) also split the bitcoin hash forever in more than 2 different branches (I guess way more than 2).

@andrewp123 Check my blog post. https://initsix.dev/in-finite-central-curve/ ,feedback appreciated :D

[bitwize]

Rick: OK, Morty, this program runs by spawning a new universe for each parallel subtask, destroying the universes that throw an exception instead of returning a value, and then aggregating the remaining results. Are you ready to experience quantum hyperspatial optimization, Morty? This'll strap a warp drive to the ass of your gamer shit for sure.

Morty: Aw, geez, Rick, I don't think we ought to--

Rick: Nothing ventured, nothing gained, Morty. Let's goooooooooooo!

[He clicks the mouse, and Solitaire comes up]

Rick: Haha, nice. [He starts playing.]

[We are shown a 16x16 grid of the same moment happening in 256 alternate universes.]

Ricks: Nothing ventured, nothing gained, Morty. Let's goooooooooooo!

[They click the mouse.]

Rick 183: Oh, sh--

Rick 39: Jesus Chr--

Rick 201: NO! We've gone too fa--

[237 of the alternate universes disappear in a white-hot light, their squares replaced by static.]

[paraph1n]

> The outcome provably does not exist until you measure it.

This is not true. It only provably does not exist in local hidden variables.

[red75prime]

It doesn't change much in practice. If the event is influenced by a state outside of its past light cone, you (that is observer inside the universe) cannot predict the outcome even theoretically.

[paulddraper]

> The outcome provably does not exist until you measure it.

My preferred interpretation:

There is a density function across all possible realities (Hilbert space).

Schrodinger's cat has equal density of being alive and dead.

The person who opens the box can be happy or sad.

The density of cat being alive is entangled with the observer being happy. And the opposite for the death.

The original cat distribution did not "collapse" or "resolve" per se. The cat is still equal parts alive and dead. But it did become non-uniformly entangled with the distributions of rest of the universe.

Perhaps this is the many worlds interpretation.

[fred_is_fred]

And what happens when the universe runs out of pids?

[gus_massa]

The "split" happens contantly outside the lab/quantum-computer. Just get a geiger counter, the atoms split randomly using a quantum process. Or just get a digital camera, the photons are absorved in the CCD sensor randomly using a quantum process. Or ...

[hi-v-rocknroll]

Here's a better reduction of CC vs. QC: QC doesn't introduce a new type of magic computing. It only accelerates certain algorithms that a CC could also compute. The present state of manufacturing technology has relegated these to essentially toys because they do not yet contain sufficient numbers of QDs to meaningfully threaten cryptography through accelerated prime factorization or matrix inversion. And I'm sure QC devices also release magic smoke, albeit cryogenically-cooled smoke, when excessive voltage is applied. (ElectroBOOM should investigate.)

[josecastillo]

Relevant short story from Ted Chiang, exploring some possibilities around this idea: https://onezero.medium.com/anxiety-is-the-dizziness-of-freed...

[deadbabe]

Watch the Remedial Chaos Theory episode of Community to see why it is a bad idea to play around with making decisions that can spawn alternative worlds and timelines based off a single unnatural random event. (also probably one of the best episodes ever)

[red-iron-pine]

man we're getting Community and Rick and Morty shoutouts to OP.

probably a sign there is no real discussion here :/

[classified]

We are all incessantly forking the universe with every single decision we make. We probably have at least as many universes by now as the number of atoms in this one. And now it's one more, where I decided to leave this comment.

[nitwit005]

> it's one of the few useful (maybe) things we can do with quantum computers today.

It's theoretically useful, but quantum random number generation has been around for a long time. All you need is a way to detect nuclear decay.

[StanislavPetrov]

Useful for generating truly random numbers?

[captaincrowbar]

Just waiting now for someone to find a spectre exploit in quantum mechanics.

[superb_dev]

Do you think quantum computer just aren’t real?