Become a fan of Slashdot on Facebook


Forgot your password?
Slashdot Deals: Prep for the CompTIA A+ certification exam. Save 95% on the CompTIA IT Certification Bundle ×

Comment Re:Entanglement (Score 1) 214

You can have it be both at the same time, at least hypothetically. E.g. (almost surely completely impractical) if you send an operating double-slit apparatus through a larger double-slit apparatus & vary independently whether the small & large ones are configured to show particle-like or wave-like behavior.

Or maybe just send something mundane (photons or electrons or whatnot) but measure one attribute looking for wave behavior & another looking for particle behavior (& obviously choose attributes that can be simultaneously measured).

Comment Re:Angular momentum at the park (Score 1) 126

No, I was apparently just bored & wondered what would happen. I expected to get shocked, but not that badly, since I would have thought that people getting shocked all the time would have prevented so much charge buildup. (In retrospect, that obviously only applies to the outer surface that everyone else touches, not the inner one.)

Comment Re:Angular momentum at the park (Score 1) 126

If the slides are plastic & there are any sticks nearby, kids could still potentially injure themselves...I once stuck a wet stick (it had rained recently) into a crack (between 2 pieces, not broken) in a plastic slide & got a big enough static shock that I just fell down the slide limp & laid there for a while until I could convince my muscles to move again. (Meanwhile, every time I have accidentally made contact with 120V wiring, it merely tingled annoyingly at the site of contact.)

Comment Re:Difficult? (Score 1) 152

If only the passwords (& not usernames or URLs or whatnot) are encrypted & no checksum or other verification is used, then entering the wrong master password could very well cause it to decrypt to completely useless but structurally valid passwords.

Of course, care would need to be taken to ensure the result is always valid...probably have a "password format" field that indicates what format the password is allowed to have (at least 1 of each of these types of character, at least 8 characters & no more than 16, that sort of thing), then do a "base conversion" of sorts so that valid passwords map to consecutive integers. The only remaining problem is if the format does not pack nicely into an integral number of bits, since then you might get out-of-range values with certain choices for the master password, but this can either be ignored (you rule some fraction of the master passwords out but still have to do a lot of searching) or handled by randomly (not necessarily uniformly...) choosing any value that is equivalent modulo the number of passwords allowed by the format.

Comment Re:Koomey's law (Score 1) 101

The space requirement is not infinite for reversible computing unless it is also infinite for irreversible computing (& thus equally impractical), even if you want a polynomial slowdown. The paper proves this. That 3 GHz CPU either has finite external memory (& thus loops or stops after at most exponentially many steps (or, in the real world, suffers hardware failure)) or infinite external memory (in which case, you have already solved the infinity problem).

Comment Re:Koomey's law (Score 1) 101

Reversible Space Equals Deterministic Space says that for a Turing machine running in time T(n) & space S(n), you can get the space & time both linear in T(n) (as I suggested) or space O(S(n) log T(n)) with time O(T(n)^(1+epsilon)) or space O(S(n)) with time exponential in T(n). So there is a tradeoff, but the space does not have to be (more than linearly) worse if you are willing to wait (way too long, of course, unless you are already worrying about the heat death of the universe), & not much worse for space or time in the middle case.

Comment Re:Koomey's law (Score 1) 101

Hmm. I suppose that can be true in an iterative setting (needing to store some data from every iteration), & that the only hope of avoiding that is rewriting the whole loop to be fully reversible so it does not consume space every iteration. (It cannot take more space than linear in the run time, at any rate.) I was imagining recursive functions with stack allocation for each, but I should know better since I use tail recursion all the time. So I guess I was only right about iteration- & tail-recursion-free code.

On the other hand, it should not require more than an exponential increase (hah, only exponential) in space for any terminating & non-interactive computation, since with that you could store every possible state of the original irreversible machine. For non-terminating computation, it is at worst linear in the runtime, as aforementioned.

Thus spake the master programmer: "Time for you to leave." -- Geoffrey James, "The Tao of Programming"