[rndphs]

At the molecular level, basically all photon modes associated with the thermal energy (or lower) will be already thermally occupied. E = hf = k_bT/2. This frequency at room temperature is about 30THz. So on the microscopic level, any frequencies under 30THz are constantly irradiated by thermal fields anyway.

Edit: Furthermore, the Gibb's free energy of any molecular process determines the reversibility of the process at a given temperature. Any molecular process with Gibb's free energy that is lower than the thermal mean energy is going to be essentially a reversible equilibrium process, and stimulating it with radiation will only shift the equilibrium very slightly I believe. I think it's for this reason that we don't see radio catalysed reactions in chemistry, unlike photocatalysed reactions.

[amelius]

I'm not talking about noise. I'm talking about a spike in the frequency spectrum.

If you can build a protein that can tune to e.g. 3GHz (or whatever frequency a phone uses), thus behave differently at that frequency, then basically that proves that radio waves can theoretically alter the reactions in the molecular soup that is a cell. All I'm saying is that I'm not so sure that this can't be done.

[rndphs]

I think though that any biological process using these sorts of energies on the molecular level will be swamped with noise and therefore wouldn't be a useful mechanism. 3GHz is like 0.00001eV. A process with Gibb's free energy change of 10ueV has an equilibrium constant of essentially 1 at room temperature, and so is almost completely reversible.

The reason why we can make things interact with radio waves at all is essentially because electrical conductors provide coherent modes for low energy photons to couple to. Without conductors and their free electron cloud we would have a very hard time building anything to receive or transmit radio in any way that isn't thermal.

It is true that there is some degree of conductivity in cells but without a non-thermal way of coupling between current and molecular processes I don't see how radio waves could affect cells in a non-thermal manner

Edit: I guess nerves have a non-thermal coupling mechanism from low frequency currents to molecular mechanisms, so it must be possible. But the machinery for that has been highly evolved for that specific task, I'm not sure if it follows that such machinery would appear commonly in cell processes.

[jlokier]

Last time I had an MRI scan, I had strong sensations throughout my body where exposed to the MRI's radio emissions. I rather enjoyed the sensation, it felt like a massage and I would have enjoyed it for longer.

I was surprised, as they didn't mention this before the scan. After, I asked about it, and they told me most people don't feel anything, but some do like me, and for a few it's so painful they have to stop the scan.

They told me it was my peripheral nervous system interacting with the radio emissions, not a physical (non-signal) effect as it felt like. From that conversation I learned there was about 10kW transmitted through my body during the scan.

MRIs have been studied for dangerous effects, of course, and all the evidence shows them to be extremely safe... provided there is no metal in the body which can heat up or be displaced by the field, and not counting risks from the contrast agents which are sometimes injected, which some people are more susceptible to than others.

I was never convinced by dismissive arguments that non-ionising radiation "can't" have any biological effect other than localised heating, or that the thermal background spectrum means infrared and below can't have an effect. (I know the physics pretty well; it's not lack of understanding.)

But after those sensations caused directly by the emissions, I'd experienced a biological, non-thermal effect from radio in the microwave-or-below frequency range directly and clearly. That was really interesting.

The body clearly does a lot of things based on countless subtle signalling pathways. Pretty much anything any pathway can sense could have an effect, even if it's not a conventional chemical reaction. One of the more interesting technological ideas around this is the use of high coherence terahertz signals that resonate with DNA molecular dynamics.

[rndphs]

Oh yeah I don't doubt it. I think though that there is many orders of magnitude difference in the field strengths between cell phone radiation and MRI, and this makes all the difference.

THz radiation is a different story too as it has about enough energy such that it could influence irreversible processes.

[ncmncm]

I.e., at random: thus not inducing any coherent electric current, so irrelevant to the discussion.

The only other subjects that induce such confident statements of fact from the profoundly ignorant are economics and politics.

[rndphs]

But the only electric current on the molecular level is coherent current...? Chemical reactions are not macroscale phenomena, and so it shouldn't really matter if the energy comes from a random distribution or not. Also please don't insinuate that I'm "profoundly ignorant", that certainly isn't relevant to the discussion.