Atmospheric noise & fair coin flipping

[Jim Choate]

On Sun, 14 Jul 2002, gfgs pedo wrote:

> hi,
> 
> Does a fair coin exist in real world?

Depends on what you mean by fair and how long you have to throw it to get
a usable string. If you're using it to play a game over the span of a few
minutes to a few days, probably most coins are 'fair'. If you need to use
it over a very long period (very few current applications I'll grant you )
then no coin is 'fair'.

Note that this bias of the coin isn't a function of air resistance, it
would still show the bias in space; though it might be a bit different in
atmosphere than in space - the faces are not the same. What makes the
difference is the distribution of mass and where the resultant CG is
located. Any two coins will have a slightly different CG location within
the volume of the coin.

> Like as according to Allan Turing-an event is defined
> by set of  certain parameters governing the event at
> that instant.
> 
> by redoing the same experiment-do we always have the
> same set of parameters that previously defined the
> coin.

See 2nd Law & Uncertainty Principle.

> it is said that atmospheric noise is random but how
> can we say for sure.

A thunderstorm is not random. By 'atomospheric noise' you're making
refrence to the individual particles that strike your eardrum (seashore
in a shell effect). Not quite the same thing, your wording is too vague to
be meaningfull.
 
> so can we say atmospheric noise is random or a coin
> flipping is random-only because it passes die hard
> test or other randomness tests-which is an indicator
> of randomness with the current defenition of
> parameters in determing randomness?

Actually these tests are not perfect and are used on 'short' strings. A
string from a supposad RNG that's only a few million billion gigabytes
long isn't a very long string. It's also probably not boing to be used for
very long at each invocation, so the discrepency is below the error.

The point is these tests are statistical. They say, only with a certain
degree of confidence (in other words "I could be wrong") that the string
looks 'random'.

> is there truly random or that we can say with certain
> degre of confidence that they are nearly random as all
> current evidence poits so.

Several physical systems, radioactive decay and magnetic pendulums being
my two favorite examples, are random by definition. If they aren't then
the world would be a lot different place than it is.


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