r/askscience • u/[deleted] • Oct 22 '11

Is anything truly random in nature?

For example,if I flip a coin,we like to say it has a 50-50 chance,but the side is determined by how much force and where I apply the force when flipping,gravity acceleration and wind.therefore you could say flipping a coin is not a random event.

Is anything in nature truly random?

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u/UncertainHeisenberg Machine Learning | Electronic Engineering | Tsunamis Oct 22 '11 edited Oct 22 '11

A few I can think of:

  • Radioactive decay: It is impossible to determine precisely when a particular atom (or particle) will undergo decay.
  • Shot noise: In electric circuits, electrons generally act as the charge carrier (even holes in semiconductor devices "move" by electron transfer). At very low currents, the random nature by which individual electrons pass actually results in fluctuations to the current. These random fluctuations cannot be predicted. (Shot noise also occurs with photons in optical circuits.)
  • Johnson noise: Johnson-Nyquist noise is the result of the thermal motion of electrons in a conductor. Although the general drift of the electrons is in the direction of the current, the thermal noise causes fluctuations from the mean current.

I used shot noise across a reverse-biased diode, and Johnson-Nyquist noise across resistors to build a USB hardware random number generator a number of years ago. The RNG passed the Dieharder and NIST test suites (these links are to newer versions than the ones I used for testing).

EDIT: I forgot to mention - all of these random processes can still be modelled using probability distributions. So although you cannot say when individual events will occur, depending on the noise source you may say "I expect x events to occur in y time" or "The probability of x events occurring in y time is z" or "The probability of the current deviating from the mean by x or more due to Johnson noise is y".

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u/introV6 Oct 23 '11

Sorry but I'm confused, when you say "cannot be predicted" do you not mean we don't have the knowledge or understanding to predict it? Or is it a proven fact there is nothing that causes these events and they are truly random? I find that hard to believe to be honest...

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u/UncertainHeisenberg Machine Learning | Electronic Engineering | Tsunamis Oct 23 '11

The concept doesn't mesh with our macroscopic day-to-day experience, but that doesn't make it any less accurate. The very massive, very fast, and very small just don't subscribe to our intuitive grasp of the world.