The answer is laziness. The actual unit is MeV/c^2 where c is the speed of light. But when you’re talking about mass, sometimes you’ll just say MeV (which is a unit of energy) and the /c^2 is implied.Stephen Bulking said:
Hah it's as simple as that, thanks man.Isaac0427 said:
That could be a bit harsh. When you are amongst workers who are all doing the same thing, a choice of 'different' unit is quite acceptable. A measuring instrument may present its answers in a certain unit. Alternatively, you could be dealing with photons (Hz?) and massive particles (kg?) at the same time (nuclear reactions). The Energy would be a suitable common currency.Isaac0427 said:
Right, and I agree there is a conversion factor. To me, measuring mass in eV is like measuring mass in pounds. The conversion is implied, but it’s technically incorrect and can confuse students.sophiecentaur said:
A very common convention is to use units where ##c=1##, and then measure time in units of length, or length in units of time (that's what a light second is - we just drop the "light" prefix). This is actually quite natural in relativistic physics because time is another direction in spacetime and it's odd to use different units for different directions. In such a system, mass and energy have the same unit because ##E=mc^2## simplifies to ##E=m##. Note that this isn't the same as your mass and weight confusion example, since weight is an interaction while mass is a property of a body.Isaac0427 said:
That's more or less where I am. I don't dislike setting c to 1, as long as there is an understanding that there is a factor of c there. Personally, though I may not always use it in my work, when I report results I always stick the c's back in, to cause minimal confusion. The OP seemed (and for a good reason) troubled by the missing /c2, and I believe the best answer to that is that physicists understandably like to get rid of factors of c and just set them to 1, and they are implied in the units, though not explicitly mentioned.Ibix said:
Isaac0427 said:
Since the pound (mass) is a unit of mass, measuring mass in pounds is entirely appropriate.Isaac0427 said:
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