🚀 go-pugleaf

In article <1992Oct3.134653.20562@oracorp.com> daryl@oracorp.com (Daryl McCullough) writes:

[a neat article on the quantum zeno effect - thanks, Daryl]

Just one minor point: I don't think this effect can be used to slow
down radioactive decay.  That's an exponential process, ie if the
atom is undecayed at time 0, then the probability it is still
undecayed at time t is

	P(t) = exp(-kt)

where k = log2/halflife.  So, if we observe the atom at time t and
again at time 2t, the probability we will observe it undecayed the
first time is exp(-kt), and, presuming this "resets the clock", we
get the same probability for the second observation.  So the joint
probability that it is undecayed both times is

	P(t) . P(2t)|P(t) = exp(-kt) . exp(-kt) = exp(-2kt)

But if we simply leave it alone for time 2t, and then observe it
once, we get

	P(2t) = exp(-2kt)

which is the same answer. (It's also pretty easy to show the converse,
that exponential decay is the only process unaffected by intermediate
observation.)

However, as I said, that's a minor point.  Your major point is that the
act of observing a system, and finding it seemingly unchanged from a
previous observation, can indeed affect the subsequent behaviour of the
system.  In other words, a "null observation" has an effect on the
thing observed.

Ah, but on *what* does it have an effect?  Not on the perceptible atom,
which is seen to be unchanged, but on the imperceptible, and evolving,
wave function, whose evolution has been perturbed.

Yes, food for some very deep thought.