[ExI] The Quantum Zeno effect

scerir scerir at alice.it
Wed Dec 15 06:05:10 UTC 2010

The Quantum Zeno effect has me perplexed. Riddle me this, quantish thinkers: If
simply observing unstable particles can keep them from decaying, then why do
Geiger counters work at all?


Dunno if Asher Peres explains all that here
or here

Anyway, the observation that a quantum state has not decayed causes the reduction
of the wavefunction to the non-decayed state. Thus it is possible to argue that a
very frequently (or continuosly) observed state cannot decay. This is difficult to get.
The probability that the state decays goes quadratically with time (in the range of short
times). In spontaneous decay, the interval during which the probability goes quadratically
is very short if compared to the time required to make a measurement.

"G.C.Ghirardi, C.Omero, T.Weber, A.Rimini, "Nuovo Cimento", 52A, 421, (1979),
have shown, by general arguments based on the time-energy uncertainty relations,
that the dependence of the lifetime on the frequency of measurements, although
present in principle, would be extremely difficul to observe.". This in usual cases.
But there are very specifically designed experiments in which the Zeno effect
has been observed. 

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