Άλλα σωματίδια πάλι, μπορεί να μην έχουν ούτε μάζα αλλά ούτε και σημείο (πχ φωτόνια).
Η ύλη μπορεί να μετατραπεί σε ενέργεια και η ενέργεια σε ύλη. Δεν είναι το ίδιο πράγμα όμως.
it’s dreadfully confusing for the non-expert, because in each of these contexts a different definition for `matter’ is being used, and a different meaning — in some cases an archaic or even incorrect meaning of `energy’ — is employed. And each of these ways of speaking implies that either things are matter or they are energy — which is false. In reality, matter and energy don’t even belong to the same categories; it is like referring to apples and orangutans, or to heaven and earthworms, or to birds and beach balls.
...
- Matter and Energy really aren’t in the same class and shouldn’t be paired in one’s mind.
- Matter, in fact, is an ambiguous term; there are several different definitions used in both scientific literature and in public discourse. Each definition selects a certain subset of the particles of nature, for different reasons. Consumer beware! Matter is always some kind of stuff, but which stuff depends on context.
- Energy is not ambiguous (not within physics, anyway). But energy is not itself stuff; it is something that all stuff has.
- The term Dark Energy confuses the issue, since it isn’t (just) energy after all. It also really isn’t stuff; certain kinds of stuff can be responsible for its presence, though we don’t know the details.
- Photons should not be called `energy’, or `pure energy’, or anything similar. All particles are ripples in fields and have energy; photons are not special in this regard. Photons are stuff; energy is not.
- The stuff of the universe is all made from fields (the basic ingredients of the universe) and their particles. At least this is the post-1973 viewpoint.
https://profmattstrassler.com/articles- ... dichotomy/
