4 ms·

One would be the direction of entropy. Breaking the stick is not "particularly fascinating" because you're going in the direction of increasing entropy. Howeve

One would be the direction of entropy. Breaking the stick is not "particularly fascinating" because you're going in the direction of increasing entropy. However, _putting it back together_ is. In the simulation it takes no more effort to go one way or the other, while you probably cannot put the stick back together no matter how hard you tried. A quantum question that is "interesting" would also be similar to finding order out of disorder (e.g. factoring).

glompers 3y ago
Nice comment
tedunangst 3y ago
If I provide two model sticks to a physics simulation, it can work out how to put them back together with no more effort than it took to model the break? Like I can model shooting a cannon ball out of a cannon and it will tell me where it lands. Or I can model a cannon ball sitting on the ground and it will tell me where the cannon was?
- jabbany 3y ago
  A hypothetical perfect simulation should be able to do it both ways indeed! However, the current consensus take of quantum uncertainty means _if_ such a simulator exists, it cannot be of our universe. Or, more likely, such a perfect simulator does not exist. Of course all of this is about a hypothetical of a hypothetical at this point... (This is the same problem as entropy (our current understanding of it). We know it is increasing one-way w.r.t. time, and we can imagine what it means to "reverse entropy" and that there's nothing really theoretically preventing that, but we can't build an actual machine to do that.)
dataflow 3y ago
I really love this comment -- it "feels" like the right criterion -- but I guess I'm wondering what criteria (if any) researchers actually use right now. Do they have any criteria for this?
- jabbany 3y ago
  I'm not a quantum computing researcher but I have friends who work on it. The way they've described this to me (answering a question around "how does one know what quantum stuff is bs") was that it's largely a set of known "hard" questions where we've empirically found hard for classical computing but we maybe could solve with quantum. In a way it's been described as similar to crypto primitives or P?=NP problems where we don't know for certain why it's harder one way vs the other but it seems to be the case based on our current knowledge. It could possibly (but unlikely) be the case that we eventually find classical solutions that are just as fast. They don't seem worried about this though, since at least research-wise just working with quantum as a new tool to solve problems itself is intellectually interesting (and the "solves classically challenging problems" is a good way to frame the work's potential impact to general audiences). Also, there's other supposed uses of quantum beyond just computing, like for communication etc.
  - dataflow 3y ago
    > where we've empirically found hard for classical computing but we maybe could solve with quantum Are we talking complexity classes here, or just "problems we've found hard in practice, but that which may in fact be in P even if P != NP"? Like I would've thought that solving BQP problems like integer factorization would be the criterion (since they're proven to be faster under QC assuming P != NP etc.). But that's evidently the researchers aren't holding themselves up to that standard, so what bar are they using exactly? Are they just going with some sort of "if it walks like a duck then it's a duck" criterion, or are they using problems that they can formally prove lack efficient classical solutions under a well-regarded hypothesis like P != NP?
    - jabbany 3y ago
      Based on what I've heard, I don't think the bar is as high as "formally proven to lack a classical solution" for the whole field. Then again, the caveat is of the two people I know, one is doing cryptography/security in a quantum setting and the other is working on quantum related HW... so take this with as much salt as needed.

glompers 3y ago

Nice comment

tedunangst 3y ago

If I provide two model sticks to a physics simulation, it can work out how to put them back together with no more effort than it took to model the break? Like I can model shooting a cannon ball out of a cannon and it will tell me where it lands. Or I can model a cannon ball sitting on the ground and it will tell me where the cannon was?

jabbany 3y ago
A hypothetical perfect simulation should be able to do it both ways indeed! However, the current consensus take of quantum uncertainty means _if_ such a simulator exists, it cannot be of our universe. Or, more likely, such a perfect simulator does not exist. Of course all of this is about a hypothetical of a hypothetical at this point... (This is the same problem as entropy (our current understanding of it). We know it is increasing one-way w.r.t. time, and we can imagine what it means to "reverse entropy" and that there's nothing really theoretically preventing that, but we can't build an actual machine to do that.)

dataflow 3y ago

I really love this comment -- it "feels" like the right criterion -- but I guess I'm wondering what criteria (if any) researchers actually use right now. Do they have any criteria for this?

jabbany 3y ago
I'm not a quantum computing researcher but I have friends who work on it. The way they've described this to me (answering a question around "how does one know what quantum stuff is bs") was that it's largely a set of known "hard" questions where we've empirically found hard for classical computing but we maybe could solve with quantum. In a way it's been described as similar to crypto primitives or P?=NP problems where we don't know for certain why it's harder one way vs the other but it seems to be the case based on our current knowledge. It could possibly (but unlikely) be the case that we eventually find classical solutions that are just as fast. They don't seem worried about this though, since at least research-wise just working with quantum as a new tool to solve problems itself is intellectually interesting (and the "solves classically challenging problems" is a good way to frame the work's potential impact to general audiences). Also, there's other supposed uses of quantum beyond just computing, like for communication etc.
- dataflow 3y ago
  > where we've empirically found hard for classical computing but we maybe could solve with quantum Are we talking complexity classes here, or just "problems we've found hard in practice, but that which may in fact be in P even if P != NP"? Like I would've thought that solving BQP problems like integer factorization would be the criterion (since they're proven to be faster under QC assuming P != NP etc.). But that's evidently the researchers aren't holding themselves up to that standard, so what bar are they using exactly? Are they just going with some sort of "if it walks like a duck then it's a duck" criterion, or are they using problems that they can formally prove lack efficient classical solutions under a well-regarded hypothesis like P != NP?
  - jabbany 3y ago
    Based on what I've heard, I don't think the bar is as high as "formally proven to lack a classical solution" for the whole field. Then again, the caveat is of the two people I know, one is doing cryptography/security in a quantum setting and the other is working on quantum related HW... so take this with as much salt as needed.