Posted: Sep 05, 2012 1:59 pm
DavidMcC wrote:Adco, MOST photons are certainly invisible to us. It's only those with energies corresponding to wavelengths in the region of about 400nm to less than about 800nm that are actually visible to us. That is a rather narrow range, corresponding to about 1.5 to about 3eV. EM radiation covers a hugely greater range than that, such as wavelenths up to Km and photon energies of many MeV. At photon energies of less than about 0.5MeV, they cannot interact with each other, but as soon as that threshold is exceeded, electon-positron pairs can be created by the collision of two photons, so they do interact at these high energies. Obviously, these are gamma rays, and we don't want to interact with them, and certainky don't see them.
I know about photons being EM radiation. That's another mind boggler for me. I was thinking more about those in the visible spectrum. Don't know why because they are all the same, just how my thoughts went. We are being bombarded by countless photons every second. There are so many zipping around in the form of radio, TV and other communication waves and yet we are hardly affected by them, luckily. Of course there are dangerous ones that do harm us like X-rays and Gamma rays to name a couple.