Thread: Adjective for "having mass"

When discussing physics it is often useful to distinguish between particles that have mass (such as protons and electrons) and particles that have no mass (such as photons). In English it is easy to categorize the latter - we can call them "massless" particles. But what about the former? The term "massive" evokes something enormous, several millions (if not billions or trillions or more) orders of magnitude greater than a mere proton. So what adjective can we use (or is being used) to describe particles that have mass? I realize this is a question as much for linguists as it is for physicists, but I though I would ask here first.

One alternative name for a massless particle is luxon, a term that refers to the fact that the particle moves at the speed of light. The equations of special relativity show that a particle that has no mass must move at the speed of light. Solving the equations for a particle with non-zero mass show that such a particle must move either slower or faster than the speed of light.

Particles that move faster than the speed of light are speculatively referred to as tachyons. No such particle has ever been verified to exist, and mainstream thought generally considers tachyons to be mathematical artifacts that have no real world counterpart.

If you consider tachyons to not exist, then a particle with mass could be defined equivalently as one that moves slower than light. Unfortunately, there is not a universally accepted term for "particle that moves slower than light" any more than there is one for "particle that has mass". Tardyon probably has the widest acceptance as a term for "particle that moves slower than light". But some physicists prefer the term bradyon or ittyon.

The standard term is, I believe, "massive". This is just another case where you have to get used to the fact that the "technical" use of the word is different from the common one.

See, for example: Quantum properties of massive particles
Where they explicitly what they mean by the word.

Originally Posted by Strange

The standard term is, I believe, "massive". This is just another case where you have to get used to the fact that the "technical" use of the word is different from the common one.

See, for example: Quantum properties of massive particles
Where they explicitly what they mean by the word.

At first the usage confused and displeased me but as soon as I understood I came to like it.

The only downside is that you cannot use the word to someone who doesn't know the difference without an extra explanation or a circumlocution (eg "which has some mass").

As the opposit of mass-less is "massive" and this is confusing since this term implies having unusually large amounts of mass, it is probaly better to just specify that the particle in question has mass. The short and clear form is "having mass".