3 ms·

> We are using different definitions of mass. I'm calling invariant energy mass, you are calling rest energy mass. Modern physics only refers to rest mass [1]

by tfgg 11y ago

> We are using different definitions of mass. I'm calling invariant energy mass, you are calling rest energy mass. Modern physics only refers to rest mass [1] as 'mass', otherwise people tend to get confused about how 'relativistic mass' (γm) affects gravity. [1] E/c^2 in a centre of momentum frame, which doesn't exist for an object travelling at c

ars 11y ago
You misunderstand the difference between rest mass, invariant mass, and relativistic mass. Invariant mass is the same in all reference frames, so light can possess it (if there are multiple photons, or they are in a box). That is my preferred mass. Rest mass excludes photons, but there is no reason to do so most of the time, since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity. Relativistic mass is special and depends on the relative motion between the objects. In any case gravitational waves posses invariant mass, so essentially they do have mass, and if you could hold them you could weigh them on a scale.
- deleted 11y ago
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- drjesusphd 11y ago
  Nothing you're saying makes any sense. > since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity Right: inertia. Funny that. The fact that photons are affected by gravitational fields, even though they're massless, was a major victory for the theory of general relativity. It wouldn't be a big deal if you could just say the photon has mass. Because it doesn't. A photon is massless. Fullstop. To say otherwise is to use a nonstandard definition of "mass". At best, people won't know what you're talking about. At worst, they will assume you don't. You should be more specific next time.
  - jeff_tyrrill 11y ago
    The parent comment's explanations and terms match the explanations throughout https://en.wikipedia.org/wiki/Mass–energy_equivalence https://en.wikipedia.org/wiki/Mass–energy_equivalence. Is the Wikipedia article all wrong?

by tfgg 11y ago

ars 11y ago

You misunderstand the difference between rest mass, invariant mass, and relativistic mass. Invariant mass is the same in all reference frames, so light can possess it (if there are multiple photons, or they are in a box). That is my preferred mass. Rest mass excludes photons, but there is no reason to do so most of the time, since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity. Relativistic mass is special and depends on the relative motion between the objects. In any case gravitational waves posses invariant mass, so essentially they do have mass, and if you could hold them you could weigh them on a scale.

deleted 11y ago
[deleted]
drjesusphd 11y ago
Nothing you're saying makes any sense. > since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity Right: inertia. Funny that. The fact that photons are affected by gravitational fields, even though they're massless, was a major victory for the theory of general relativity. It wouldn't be a big deal if you could just say the photon has mass. Because it doesn't. A photon is massless. Fullstop. To say otherwise is to use a nonstandard definition of "mass". At best, people won't know what you're talking about. At worst, they will assume you don't. You should be more specific next time.
- jeff_tyrrill 11y ago
  The parent comment's explanations and terms match the explanations throughout https://en.wikipedia.org/wiki/Mass–energy_equivalence https://en.wikipedia.org/wiki/Mass–energy_equivalence. Is the Wikipedia article all wrong?