# Why does mass in the universe have no limit in large size, but has a limit in small size?

We found VY Canis Majoris, a star so big it can't even be seen in scaled illustratations with the sun itself.

However, we stop at particle physics, or quantum mechanics, i.e. particles, subatomic, etc.

If stars keep getting bigger, and we keep finding things bigger, and the size of the universe still is unknown, why does the size (oppositely) have a limit?

Like, why is the atom the "smallest mass", but the "largest mass" is indeterminate?

I hope you get my point. If not, please tell me how I should improve.

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What is the "smallest mass" then, going by these same measures? – Strong Oct 19 '13 at 19:27
That is going solely by mass, not volume. For example, photons may have no mass, but they can be evidently smaller than others things which do. Are you calculating "mass" as measurable weight, energy, or volume? – Strong Oct 19 '13 at 19:29
And "0" is a number that says nothing. However, numbers are abstractions. – Strong Oct 19 '13 at 19:30
Saying that the photon has zero mass has a very specific and precise meaning. – dmckee Oct 19 '13 at 19:32
@Sancho The problem with saying the total mass of the Universe is that it's not defined in General Relativity: physics.stackexchange.com/questions/2838/… – jinawee Oct 19 '13 at 19:45

Rest mass isn't necessarily determined by stopping the particle (since of course a photon can't be at rest). We can use other methods, like measuring energy and momentum and applying $E^2-p^2=m^2$. Countless such experiments have been made, and nobody doubts that photons are massless (within current error, anyway). – Javier Jun 2 '15 at 20:15