Quote:
Originally Posted by Hawksmoor
Ugh... How anything exist and not have any mass... Physics give me headaches, although I would so love to understand some more.
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These do have mass, just very little.
As for photons, which actually have no mass, recall the most famous (and least understood) advanced physics equation ever: E=MC^2. This isn't quite the case for high-speed photons, but energy is also a property that can help to define something. The expanded equation, that is accurate when dealing with things that have a great deal of momentum, does include momentum.
Without too much detail, you can view energy as an intrinsic property that helps to set something apart from something else, like mass, and photons do have momentum by another twist of physics/magic/hoobladoop. Basically, the energy carried by a photon is 'good enough' to make it count as something that exists because energy is in some ways more important than mass.
Jeff