system
Given the following post, respond as if you're commenting on Reddit:
human
What are the requirements for a number to be truly random?

Does such a thing even exist?  

I imagine the only thing that would make a random number generating process truly random would be if there are unknown or unpredictable inputs.  For example each time you throw dice you might shift them around in your hands, throw them with a different force and there might be environmental effects that change the outcome such as different surfaces, air resistance, etc.  But if there were a computer that could sufficiently track and account for ALL the variables involved in a the throw I would think it'd be able to predict the exact outcome.  So is the only thing that makes a number random the fact that there are unknown inputs or an intractable process?

I've heard of quantum random number generators being truly random, but is that only because we currently don't completely understand quantum physics?  If we knew all there was to know about the process of quantum events would these numbers cease being truly random or are they somehow inherently random even if we knew all the inputs?  and if so how is that the case?

To me it seems like there could be no such thing as truly random and the only way we emulate it is by hiding inputs or processes in generating the number from the observer, but if the observer were aware of all the inputs and processes it'd be impossible to create a truly random number.

sorry if i'm all over the place, i was just randomly reflecting about the thought earlier.
gpt
You're very perceptive. Pretty much all of the numbers generated currently by computers are the result of algorithms that produce a long chain of numbers that *appear* to be random, but will eventually repeat if you keep running it for long enough. This is plenty random for almost everything we need in everyday life; only in advanced cryptographic applications or very long monte carlo simulations can it prove problematic.

That said, quantum random number generators really are *truly* random. It's tough to think about, because our intuition for the real world so totally fails at the level of the very small, but quantum mechanics is very thoroughly probabilistic. Though it's *possible* that the result of a quantum mechanical event (e.g. the determination of a spin) *could* be deterministic, this would require a hidden variable that we so far have not been able to detect. It turns out that these "hidden variable" theories don't really agree with the way reality seems to function--they violate either causality or locality. Until a **major** breakthrough occurs in quantum mechanics, we can continue to use quantum random number generators as sources of truly random numbers.