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For some reason, when we talk about the age of stars, galaxies, and the Universe, we use "years" to measure time. Can we do better?

The most common element in the Universe, vital for forming new stars, is hydrogen. But there's a finite amount of it; what if we run out?

Life arose on Earth very early on. After a few billion years, here we are: intelligent and technologically advanced. Where's everyone else?

Our Universe requires dark matter in order to make sense of things, astrophysically. Could massive photons do the trick?

Practically all of the matter we see and interact with is made of atoms, which are mostly empty space. Then why is reality so solid?

If the electromagnetic and weak forces unify to make the electroweak force, maybe, at higher energies, something even grander happens?

The Universe is expanding, and the Hubble constant tells us how fast. But how can it be a constant if the expansion is accelerating?

In all the Universe, only a few particles are eternally stable. The photon, the quantum of light, has an infinite lifetime. Or does it?

Yes, the Universe is expanding, but if you've ever wondered, "How fast is it expanding," the answer isn't in terms of a speed at all.

Is the Universe finite or infinite? Does it go on forever or loop back on itself? Here's what would happen if you traveled forever.