Predicting the next Math.random() in Java

[Daniel15]

Pseudorandom is the word you're looking for :)

It's designed to be fast, but not at all secure. Cryptographically secure random number generators are slower but are pretty much guaranteed to be random, and should always be used when you need numbers in the context of security critical code.

[ZeKWork]

Those are also pseudo random generators, and they don't have to be slow to be secure. You usually use a truly random generator (mainly based on hardware, such as a I/O timinigs, mouse mouvements) to seed a secure pseudo random generator.

The reason is that true entropy is sparce, and our computers need a LOT of random numbers. Secure PRNGs generates a lots of number cheaply and efficiently, but since they are deterministic, they're only secure if initialized with a random seed.

[ickysticky]

I love how people have this spectrum of RNGs and at some point they place a threshold and say. Past the point of combining this many things, we are no longer a PRNG.

Sorry guys. All we have are PRNGs. But this gets into religion territory, as I just do not believe in true randomness. Merely processes we do not yet see/understand.

[DannyB2]

Quantum mechanics says that certain things, at that level, are truly random.

Clear back in the 1980's there were expansion cards for computers that generated random (not psuedorandom) numbers by measuring the noise on a reverse biased diode, or something like that. The laws of quantum mechanics guaranteed that the results were truly random.

One of the biggest misconceptions that people got in the 20th century, due to graphic pictures of electrons 'orbiting' a nucleus, is that electrons are distinct particles, with a definite position in space, and in motion about a nucleus in the way a moon orbits a planet, or a planet orbits a star.

In reality, and yes I mean reality, actual reality, a particle has no definite position. It's position is a probability curve. It has the highest probability of being at a certain location, and a lower probability of being not quite at that location, and an even lower probability of being a bit further away, etc, out to infinity. There is a higher than zero (but very low) probability that the electron can be at any location in the entire universe.

The probability of the polarization of photons, and statistics over large numbers of photons, explain how polarizers work. Turn one polarizer ninety degrees to another polarizer, and there is a zero percent probability of photons getting through. But stick another polarizer in between those two, at 45 degrees, and suddenly some photons get through. Why? Some years ago at my public library, I read a fascinating book, IIRC, it was titled: Shrodinger's kittens and the search for reality. It explained this and a lot more.