how can photons arise out of pure energy?

g.lemaitre

In the First Three Minutes, S Weinberg wrote:

I thought mass gives rise to pure energy in the form of photons. I didn't know pure energy could give rise to photons, I thought photons were pure energy.

Vanadium 50

There is no such thing as "pure energy". That's not a scientific concept - it's science fiction, and popularizations of science sometimes steal the term. But there is no way to measure the "purity of energy", so it's not a scientific concept.

alemsalem

yeah, I think the concept is just used in the sense that if you have enough energy around you can create particles and photons (conservation of energy),, but that energy didn't come in a "pure form" it was already there in the state of the particles.

Hawkwind

Of course, you are right when saying that it is no scientific concept. However, I guess that people using the term "pure energy" will usually emphasize that no matter is involved, i.e. photons do not carry any matter quantum numbers like "lepton number", "baryon number", "electric charge" etc..

mfb

Photons carry spin. The definition of "matter quantum number" looks a bit arbitrary, but I know what you mean.