Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: fermat!r@la.tis.com (Richard Schroeppel) Newsgroups: sci.nanotech Subject: STM observation of radioactive decay Message-ID: Date: 18 Dec 90 18:41:56 GMT Sender: nanotech@athos.rutgers.edu Lines: 38 Approved: nanotech@aramis.rutgers.edu Patrick Hayes writes: About watching atoms decay with an STM: isn't it true that every time you scan over an atom with the needle, you have observed it, thus collapsing the wave function to "I'm not even thinking about decaying now" state? So the more often you scan it, the less likely it will become that it decays? And JoSH comments: [This isn't as nutty as it sounds. There are in fact demonstrated physical systems where repeated measurement can prevent quantum- mechanical transitions. However, in the specific case of the STM, my guess is that the measurement of the state of the nucleus is far too indirect for it to have that kind of effect. --JoSH] which raises some interesting questions. When Science News reported on the "observing it prevents quantum transistion" phenomenon, some of us wondered about postponing or otherwise altering radioactive decay. A local quantum wizard informed us that the atom would have to be observed 10^13 times per second to have a noticeable effect on radioactive decay. But what, exactly, is an observation? QM asserts that no observation is indirect: If A causes B, or even alters the probability of B, then an observation of B is also an observation of A, and hence should reinitialize the state of A. So no atom can ever decay. Obvious nonsense. What's the flaw? Rich Schroeppel rcs@la.tis.com [A very interesting question but one better suited to sci.physics than sci.nanotech. There are a number of theories out to deal with the problem of wave-function collapse (e.g. the speculations in Penrose's book described here about a year ago). Unfortunately, nothing definitive is really known. --JoSH]