True random number generation

Question

How is exactly that we talk about "true random" numbers when we are actually measuring something. I mean, isn't measuring almost the opposite of randomness.

Som articles says that, for example, throwing a dice is "true random". Of course it isn't Pseudo-random, but is it even random?? If you could have a machine that throw dices from de exactly same position and always in the same direction with the exact same force always: woudn't it always turn out the same number? (I thing it does).

Please, can someone help me understand "true random" numbers??

Answer 1

Randomness is essentially a measure of how much we don't know. The universe may or may not be truly deterministic, it doesn't matter - we don't know (and have no foreseeable way of knowing) what the exact time between 2 cosmic ray impacts will be. For pseudorandom numbers, we do, in principle, have a way of knowing, because we can recreate the initial conditions and get the same output again.

Answer 2

Quantum effects are the source of this "True Randomness". E.g. the Heisenberg Uncertanity Principle says that your dice thrower can't exactly define both impulse and location of its throwing arm. (Reading up on pop-sci quantum physics can be scary - the predictability and stability of our world seems to be no more than a great feat of statistics.)

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[edit] Since it came up in the comments: There are other, less "obscure" processes "looking random", e.g. wear and air turbulence for a die roll. However, all these things could be argued to be beyond our knowledge but fundamentally deterministic (assuming an objective reality.) Quantum processes are truly random at least under the widely accepted Copenhagen interpretation. [/edit]

There are - as mentioned in other replies - appliances that turn quantum effects into observable random number generators. There are algorithms to "extract" the randomness of any stream of data. There are test algorithms to check if a stream of data "behaves" like a random stream.

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OTOH you can argue rather successfully that "random" is a man-made concept, i.e. something that isn't integral part of the objective world, but our limit of understanding (though the uncertainty principle is considered to be not just an observer effect).

When someone asks for any random number generator, the counter question should be: for what application? In the context of this discussion: who do you need to fool? Pseudo vs. True are just generation mechanisms, not fundamental opposites.

In that sense, chaotic beahvior is often "random enough" for most purposes, and can be created with few degrees of freedom already.