[donovanr]

I've always been curious: I understand that h.nu from cell phone radiation isn't big enough to ionize (say) DNA, but since the molecules in our body are in thermal equilibrium, can't h.nu + kT get it done every once in a while?

[edited because using an asterisk to denote multiplication was a bad idea]

[tiplus]

kT is very little energy compared to a chemical bond. Take for example [0], they give an excitation energy for water of about 8 electron Volts which is ~750 kJ/mol, whereas kT at room temp is about 2.5 kJ/mol.

[0] http://scitation.aip.org/content/aip/journal/jcp/128/10/10.1...

[donovanr]

Right, but it's the 'every once in a while" part that I wonder about, i.e. the variance of that distribution. Maybe you could argue that since the Maxwell-Boltzmann distribution is narrower the lower its mean, if kT is small then it's an exponentially tiny effect.

[tiplus]

So yes, kT is small on average (does fluctuate) and it is also 1 kT per degree of freedom. So yes, in principle a few hundreds of atoms could randomly fluctuate in energy to create this effect. However, this is hyper unlikely. I would be suprisd if it happened once in the life time of the universe. Also consider that you cannot create Maxwell demons[1].

[1] https://en.m.wikipedia.org/wiki/Maxwell%27s_demon