On Friday, June 5, 2020 at 7:31:56 PM UTC-6, Alan Grayson wrote: > > > > On Friday, June 5, 2020 at 5:07:58 PM UTC-6, Bruce wrote: >> >> On Sat, Jun 6, 2020 at 3:11 AM smitra <smi...@zonnet.nl> wrote: >> >>> >>> There obviously do exist quantum fluctuations. A down to Earth example >>> is Johnson noise. Connect a sensitive voltmeter to a resistor and you'll >>> detect fluctuations in the voltage. The average voltage is zero, but >>> there are fluctuations due to thermal motion of the electrons. If you >>> cool down the resistor these fluctuations will become smaller, but even >>> at absolute zero there will still be fluctuations in the voltage. >> >> >> >> Can you point to experimental evidence of this? As far as I know, >> absolute zero temperature is intrinsically unattainable. >> >> >> These fluctuations at zero temperature are what we call "quantum >>> fluctuations" >>> in physics. >> >> >> >> I think you are confusing the zero point energy of quantum fields with >> "quantum fluctuations". The zero point energy, whatever it might be, does >> not "fluctuate". "Fluctuate means change with time, and the zero point >> energy is just a value, and it does not change with time -- it does not >> "fluctuate". >> > > Another point worth mentioning is that when a quantum system is measured, > we get some specific eigenvalue. And if THAT system is measured again, the > measured value remains the same. No fluctuation. (I forget exactly why > that's the case.). But if we measure a different system represented by the > same wave function, the measured value changes. So the message is, again, > that no single system fluctuates. AG >
Oh, now I recall. After the measurement, the system's state is the eigenfunction of the eigenvalue measured. Previously, it was in a superposition of states. So when we measure that specific system again, the probability of measuring the same eigenvalue is unity. AG > >> Bruce >> >> >> Now I remember an old discussion with Bruce on this list >>> about this, and insisted that what I called quantum fluctuations are >>> actually "thermal fluctuations at 0 K". But at 0 K the system is in the >>> ground state, so it doesn't matter what you name you give to the >>> fluctuations, these are purely quantum mechanical in nature, they don't >>> arise from an initial randomness in the initial state. >>> >>> Saibal >>> >> -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/04b0d598-f945-473e-9d0d-8e9c48c76b68o%40googlegroups.com.
