Lower limit for the energy of a photon?

Question

the upper limit for the energy of a photon is planck energy (1.22 x 10^19 GeV) once it reaches that energy it turns into a black hole. i was just wonder, is there any research into a possible lower limit on the energy of a photon?

Answer 1

Einstein stated e = mc2.  As mass approaches the speed of light squared, it turns into pure energy.  Would the reverse be true?  As a photon, which we could basically describe is light energy, is it possible for it to lose enough energy that is becomes mass?  Nice question, thanks.

Answer 2

Yes, it's zero.  Or, if the universe is not infinite, it is the energy corresponding to a wavelength the size of the universe.  Oh, and I guess the period can't be longer than the age of the universe.  But all of this is pretty darn close to zero.

Answer 3

As E = hf; you are looking for a very very low frequency photon.  As f = c/L; where L is the wavelength, I would think the lower limit would be where L = 2 D = 4 R; where D ~ 30 billion light years, R is the radius of the known universe, and the wave is a standing wave with its two end and one center nodes affixed to the rim of the known universe.

In the increasing entropy model of our universe, where it just peters out like a blown out candle, the nearly null dead universe is thought to have an occasional very very long wave passing through now and then.  So the L = 2D WAG is consistent with a dead universe with essentially 100% entropy.  Of course D at the end will be almost infinitely larger than the current diameter since our universe is expanding at an accelerated rate.  So the lower limit will be infinitely lower then than it is now.

Just a thought.