2
$\begingroup$

I'm trying to get my head around what "photon energy" means. It's counter-intuitive to me, because when thinking about radio frequencies it's easy to "detect" a 1000 kHz signal with some wire and a chunk of ore whereas microwave signals are easily "lost" in coax — so it seems like the higher the frequency the weaker it is in practice.

But the Planck-Einstein relation says just the opposite: the low frequency waves that the early radio pioneers noticed and could experiment with have laughably minuscule "photon energy" compared just a single gamma ray photon. Yet this sort of particle physics seems stereotypically the realm of "Big Science" in multinational labs with with bazillion dollar equipment or at the bottom of deep mine shafts where there's nothing else to interfere — meanwhile people are listening to the tiny energies through their dental fillings!

How come we're so seemingly unaffected by TeV-magnitude particles, but can see electrical arcs caused by μeV-scale particles?

$\endgroup$
  • $\begingroup$ Count the photon number output of a radio station. Related. $\endgroup$ – Cosmas Zachos Mar 22 '17 at 0:40
  • 2
    $\begingroup$ The energy you detect is the energy of a photon times their number. Count them. $\endgroup$ – Cosmas Zachos Mar 22 '17 at 0:46
3
$\begingroup$

Photons are particles when they interact with matter, as the electrons of the antenna. Electromagnetic waves are a confluence of an enormous number of photon particles. Your question is almost the same as asking " I can feel water on my skin, but not a single atom".

An antenna is not detecting a single photon. Actually it is not possible to design an experiment that would measure a single photon from a 1000 Herz electromagnetic wave.The conversion to electron volts, which is a measure of particle-photon energy of interaction:

1 hertz [Hz] = 4.13566553853599E-15 electron-volt [eV]

One x-ray photon has an energy of order electon volt and leaves a dot on a film.

A single photon of 1000 herz cannot interact with anything. It is the collective coherent "stream" of 1000herz photons that can create a coherent electric field that can move the electrons on the conduction level of the antenna and generate signals. This is similar to a stream of water, a single atom can do nothing, it is the collective coherent mass that digs up the earth and generates floods.

$\endgroup$
  • $\begingroup$ You describe single photons perfectly. Why do so many people on this site believe photons are not real? An electromagnetic wave can only be described as you have with millions of coherent photons. $\endgroup$ – Bill Alsept Mar 22 '17 at 6:19
  • $\begingroup$ Thanks! I guess this also explains why most people would never "notice" something like a bit of gamma radiation (with hopefully so few particles) but yet just one of its photons them could seriously damage a cell's DNA (due to the high energy), right? $\endgroup$ – natevw Mar 22 '17 at 23:52
  • $\begingroup$ Yes, if a high energy photon hits a DNA molecule it can do a lot of damage which will be transferred to the cell. That is how malignant mutationsmaystart, if the cell is not killed. $\endgroup$ – anna v Mar 23 '17 at 4:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.