RE: http://groups.yahoo.com/group/mukto-mona/message/20915


Maybe Avijit did not explain it properly, but the decay of an INDIVIDUAL
nucleus is an unpredictable event, i.e Quantum Mechanics(QM) cannot
predict exactly whether a PARTICULAR nucleus will deacy or not or if it
does, then exactly when. So for a PARTICULAR nucleus the decay is
a random event, no cause can be cited, because knowing the cause
would imply knowing whether a PARTCULAR nucleus will decay or
not, which is not the case. It is a very subtle point that many
beginners in QM do not get. QM is a statistical law. It can provide
only a probabilistic prediction of an event. In the case of
radioactivity QM only assigns the probabilty of a radioactive decay to
occur in an ENSEMBLE of radioactive nuclei, the cause of that
probabilistic decay in an ENSEMBLE being the instability due to
proton/neutron ratio. QM provided that precise value of probability
from the transition probability derived by Fermi (Fermi's Golden Rule)
based on time dependent perturbation theory of QM. So, not ALL
radioactive nucleus in an ensemble will decay, even though all of them
have the same instability (n/p ratio). Only a certain number of them
will, the precise number being given by QM. And for those nuclei which
do decay, QM can only predict the most probable time it will decay, not
the exact time. So if we focus on an individual nucleus (Call it John),
then there is no reason for John to decay, and no one can tell when
John will decay if it at all decays. But QM precisely predicts that a
certain number of nuclei in an ensemble of nuclei will decay, but it
cannot tell which ones, Paul? Tom?, Joe?. So when John decays, it
can very well say "Why me?". Same goes for nuclei Paul, Tom or Joe..
QM cannot answer that why. Don't underestimate QM. Giving a precise
probabilty for an ensemble, is no mean feat. That feat alone has
provide us with so many Quantum based devices.

More appropriate example of acausal evenrts at rthe microscopic
quantum level would be the appearance of electron-positron
pair by the decay of a photon. Again an individual photon does
not have to decay into a particle-antiparticle pair in an empty
space. And unlike radioactive decay, there is no underlying
reason (like instability due to certain neutron/proton ratio) for
it to happen. QM (Field Theory) only predicts that it is probable
and again assigns transition probability for it to happen. So
for a individual photon John say, a decay into a pair production
is an event with no rhyme or reason. So it is not too far fetched
to make the plausible case for an acausal appearnce of
singularity of space time from true vacuum, an event which by the
QM process of inflation can end up into a universe of space time
and matter to the grand scale as we observe it today.


- Aparthib