Does randomness of an event depend on the observer? For example, when a coin is tossed it the outcome may appear random to the person who tossed it, yet to say a supercomputer which had at that time analysed the wind conditions, the gravitational force, angle etc. the outcome would not be random. so in short, can pseudo randomness be equated with randomness if the observer cannot predict the outcome?

  • This question feels very similar to philosophy.stackexchange.com/questions/2439/…... can you edit your answer to highlight how it's different? May 27, 2014 at 15:20
  • @James Kingsbery: My question is whether randomness of an event depends on the observer, on how much he knows about the event and the factors that cause it. The question given in the link asks plainly if anything can be held random in an 'absolute' sense, here the conditions are 'weakened' a bit. May 27, 2014 at 15:58

3 Answers 3


To ask "is this random" is a question ambiguous between the two senses of random? Here, we need to distinguish between epistemic (concerned with what we can know) and metaphysical (concerned with what a thing or system in fact is) conditions for randomness.

What you are describing is when we epistemically cannot distinguish between randomness and a complex system which makes an events outcome deterministic (or free) rather than random. In answer to your question as to whether something epistemically random qualifies as random, that would depend greatly on how yo think what we can know relates to reality itself. And it can also depend on the particular case.

So your intuition is right. We might call something random and use it for those purposes even though it is not in fact random on a metaphysical level-- like the random number seed on your computer which depends on jitter in electronic magnetic pulses or on background radiation. But then do we ever care that the thing is metaphysically random rather than random to our knowledge.

  • Well, so it all depends on how we see it and why we would? May 25, 2014 at 6:03
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    @user3660112 to word it another way, it depends on what you mean by "random." Do you mean something people cannot predict or do you mean something that arises with no reason or order? If the latter, you are looking for metaphysical randomness. If the former, you are looking for epistemic randomness. Usually, we only care about what will be from our perspective random.
    – virmaior
    May 25, 2014 at 7:51

Can pseudo randomness be equated with randomness if the observer cannot predict the outcome? No. Consider this thought experiment. You and I are playing a card game. As far as you know, the deck is fairly shuffled, so the sequence of cards is random. But in fact, I stacked the deck, so it appears random to you, but the sequence is entirely known to me. Clearly, I have a strong advantage in the game.

In other words, just because the observer can't tell the difference, it does not mean the impact is the same. Even in the case that no other conscious observer knows the pattern, the fact that there is a pattern could alter the results in a way that might be significant. This is a problem with practical implications. (See this article for how this impacts cryptography, as an example.)

This is especially significant given that it's unclear whether true randomness exists in the universe, or whether what we experience as randomness is just patterns we don't as yet understand.


Something random is something not able to be determined. A coin flip is random if you don't know what the outcome will be but when you do it is no longer random.

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    Randomness = level of ignorance? So if I failed freshman physics, I think heavy objects fall to the ground randomly. If I passed freshman physics, I think it's due to Newton's law of universal gravitation. If I passed relativity class, I think it's due to Einstein's gravitational field. But then if I get a PhD in physics and study multiverse theory, I know we just happen to live in the universe where gravity has the value is does; so it's random after all. Randomness is tricky!
    – user4894
    May 25, 2014 at 18:21
  • I guess you mean randomness as in our perception of randomness. So, if our deterministic then is nothing random? May 26, 2014 at 10:02

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