"Pierre COLLET" <Pierre.Collet@...
> > From: Norman Paterson [mailto:norman@...-and.ac.uk]
> > Several people have said that radioactive decay is "truly"
> > random. I guess
> > what they mean is that the theory of radioactive decay is that it is
> > random, and that so far the real world fits the model quite well.
> To confuse things even more:
> If I am not mistaken, radioactivity decreases over time (period of the
> So is it really *truly* random ? :-)))
> my 2 eurocents,
> Pierre COLLET
Radio-activity decreasing over time == not random?
Random (as far as physicists know), but not uniform. The distribution
is exponential (assuming a large number of unstable nuclei), or step-wise
uniform for smaller numbers of nuclei (ie, the probability proportional
to period and number of nuclei).
[Random is still "with respect to" a distribution/process. Of course,
you can have philosophical speculations which go beyond this,
and have random selection of processes, etc. That evades the
issue. Random == prediction about next (and subsequent) events
is not better than chance due to no information, eg, given an
average rate if available. Chaotic == prediction about subsequent
events becomes closer to chance, over time, due to
disappearance of significant information].
Physicists assume a random decay process (given by a probability
in a time T interval of lambda*T) for a single nucleus (hence half-lives,
etc). [NB: The rate, lambda, can be increased by bombardment by
neutrons - depending on nucleus - and other particles, which change
the nucleus into something more unstable. Hence chain reactions].
Some psychic researchers claim they can influence the rate, which goes to
show that some people will believe just about anything.
An alternative "random" sequence for the pragmatists out there: Take some
financial time-series (eg, USD-AUD) and build a suite of predictor models.
Combine (bag) the models. Keep the residuals of the bagged models (as
the pragmatically random sequence), as your predictions pulled out as
much information (as your skill would allow).