I've just found the following paper in arXiv written by a Spanish politician who is also a physicist. In it he claims that you can setup a sequential Stern-Gerlach-type experiment in such a way that the particles get energy from the measurement process, hence the title "heating the coffee by looking at it".


He admits that the energy has to come from somewhere and that somewhere is the S-G magnets, however he doesn't give a hint of how that could happen. I have forgotten a lot of the QM I learned from my undergrad days, although I can follow the paper more or less and it sounds a little fishy to me.

I think there is something very odd in having a background magnetic field and then the S-G magnets on top of it. For example, I don't understand how you can have states with spins perpendicular to the uniform background magnetic field right after the second S-G magnet.

EDIT: My question is, in a setup as the one proposed in the paper, is it correct to say that after the second S-G magnet the particles will have spins that are perpendicular to the background magnetic field?

  • 3
    $\begingroup$ Hi and welcome to physics.SE. Currently, this question isn't really a good fit for the site, since it is effectively asking us to review a paper ("is [there] some mistake [in] the equations?"). Please edit it to ask a self-contained question about physics. It's okay to refer to a paper for background or motivation, but you should ask a question that is more than "is this paper correct or not?", since that's for the academic review process to decide, not for us. $\endgroup$ – ACuriousMind Oct 24 '16 at 21:01
  • $\begingroup$ Note that as the whole system before measurements is closed and conservative, by a mere change in the choice where to put detectors you could decrease the total energy as easily as the author increases it: just "detect away" the more energetic particles instead of the less energetic ones. $\endgroup$ – Ruslan Oct 25 '16 at 9:52
  • $\begingroup$ Is it published? $\endgroup$ – Qmechanic Oct 25 '16 at 10:28
  • $\begingroup$ @Ruslan, I believe that its usually assumed that you can make the Stern-Gerlach sensors as "delicate" as you like. I think that a version of the setup can be designed in such a way that the energy that enters or exists the system are as small as we want. But this is my non-expert opinion. The author seems to agree with you (while, at the same time, make it the point of the paper as it if were something unusual.) $\endgroup$ – Hackenbush Oct 25 '16 at 11:45
  • $\begingroup$ @Qmechanic, I think it has been "published" only in arXiv, I don't think a real journal would accept it. At least from a formal point of view (language, quality of citations...) $\endgroup$ – Hackenbush Oct 25 '16 at 11:46

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