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Name: Andrew M.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2001-2002


Question:
Is there a theoretical upper limit to the energy of a photon? Since wavelength decreases as energy increases is there a "quantum limit" to the wavelength? If there is no "theoretical limit" is there a practical limit based upon our ability to detect a very high energy photon?


Replies:
Andrew,

I am not aware of any limit to the energy of a photon. Energy is inversely proportional to wavelength: as wavelength approaches zero, energy approaches infinity. There are, however, two practical limiting factors to photon energy. The first is the supply of energy. The universe may have a great deal of energy, but it is not infinite. For a photon to exist, something must produce it. The photon can not have more energy than that which produced it. The second limit is particle creation. A photon traveling through space has the ability to change into other forms. One common occurrence is a photon transforming into an electron and a positron (anti-matter electron). For this to happen, the photon must have enough energy to create the mass of the particles (according to E=mc^2). It must also have enough energy for some motion of the particles. The greater the photon energy, the greater the number of things the photon can become. As a result, a photon of greater energy is more likely to transform. These are not quantum limits, but they are factors that make very high energy photons less common.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Dear Andrew, As far as we know, there is no upper limit to the energy of a photon, or of any other particle. The most energetic particles known at the present time are observed in cosmic rays; they have energies which extend up to over 10^20 eV (that is, of course, 1 followed by 20 zeroes).

What mechanism is capable of accelerating protons or photons to that energy is not known. It is also interesting that they must be produced in our astronomical neighborhood since at that energy the cross section for interacting with a photon is very large and so, even though the microwave background is very dilute, a proton or photon will collide with one and lose some fraction of its energy before it has gone very far. "Very far" here means some 150 million light years

Best, Dick Plano...



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