Re: Randomness

On Thu, 17 Nov 2005, "John Bode" <john_bode@xxxxxxxxxxx> wrote:

> The word "random" gets tossed around a lot on t.o., and I just want to
> make sure I'm understanding and using the term as intended.
>
> An event is random if previous events do not affect or predict future
> events. A coin toss is random because previous tosses do not affect or
> predict the next toss (assuming a fair coin, anyway). Tossing 50 heads
> in a row does not change the probability that the next toss will be
> tails.

That's because the tosses are _independent_ random events. The general
definition of randomness does not require independence. For example,
when a lottery machine drops the numbered balls into its "output" tube,
the selections are not _independently_ random because once a ball is
removed from the tumbler the probabability of selection for all the
remaining balls is changed. OTOH, if you put each ball back in the
tumbler before selecting the next one, the selections would then be
independent. (Ignoring the fact that the whole thing is a determinate
mechanical system, above the quantum level.)

Also, re the fair coin, a system can be random even if its states do
not all have the same probability. E.g., the flip of an unfair coin
is still random; it's just that its outcome doesn't have a flat
probability distribution. (The definition of "fair" is "has a flat
probability distribution".)

Creationists almost always miss that fact, and sometimes their arguments
suffer as a consequence. To give an irrelevant example (because I can't
think of any relevant ones right now), we think of the motion of a
molecule in the air as random, but nevertheless the position of the
molecule at any time is more likely to be close to the ground than
twenty miles up, because there are other effects that bias the movement
of the molecule (i.e., gravity). That doesn't make the molecule's
movement un-random; it just makes it un-"fair".

--
Bobby Bryant
Austin, Texas

.

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