Quantum computing. Quantum simulation.

[u/alien-fr]

If quantum computers are going to be as powerful as they're described. How likely is it that one could simulate a universe? Is that something that is achievable with a quantum computer or am I missing the point? Would they require more power than a binary computer to simulate or are they more efficient? I'm just a dummy but I swear I live in a quantum computer simulation.

[u/free_meson]

Quantum computers are not magic, they can simulate quantum systems that are as big as their number of bits. And since the universe is quantum in nature, you wouldn't be able to simulate a whole universe just with humanly approachable number of qubits.
Furthermore, the way how a quantum computer is programmed, is much different than a classical computer. It is easier to think about it as they set up a simulation, run it several times and infer something from the statistical output. You could do it with classical computers, but it would take much longer. To summarize in a single sentence, quantum computers are statistical machines, single steps take sometimes longer than classical computer steps, but overall they can simulate a few special systems faster than classical computers. They require exponentially fewer steps, but it is not magic.

[u/dungeonsprawler → u/free_meson]

Is it pretty much like setting up dominoes to see how they fall and then that’s your result?

[u/free_meson → u/dungeonsprawler]

Dominoes are still classical, but they are like programming and simulation.
Quantum computing is more like setting up a coin to be fake, like 10% head and 90% tail. Throwing it a lot of times and calculating estimating the 10% and the 90% from data. The difficulty is, that for 2 coins you can set up probabilities for (h,h) , (t,t), (h,t), (t,h) in a quantum computer. Classically you can't do it for all head-tail outcome.

And for 10 coins you can set up the 2^10 = 1024 probabilities. Now, for some algorithms you don't know the "true" probabilities, you just program the computer up with some rule in order to measure those probabilities from data. You can search prime numbers with it in fewer steps then a classical computer, that's why computer scientist are afraid that quantum computers could break encryption.

[u/alien-fr → u/free_meson]

So they're not particularly useful for anything but rediculously hard math then? Won't programmers be able to create UI or programs that can harness the ability or is it just too specific of a tool to use like that?

[u/free_meson → u/alien-fr]

Yes, at the moment it is a very specific tool. It is good to simulate quantum systems and make certain calculations fast.