Khan Academy on a Stick

Scale of the small and large

We humans have trouble comprehending something larger than, say, our planet (and even that isn't easy to conceptualize) and smaller than, say, a cell (once again, still not easy to think about). This tutorial explores the scales of the universe well beyond that of normal human comprehension, but does so in a way that makes them at least a little more understandable. How does a bacteria compare to an atom? What about a galaxy to a star? Turn on your inertial dampeners. You're in store for quite a ride!

Light and fundamental forces

This tutorial gives an overview of light and the fundamental four forces. You won't have a degree in physics after this, but it'll give you some good context for understanding cosmology and the universe we are experiencing. It should be pretty understandable by someone with a very basic background in science.

Scale of earth, sun, galaxy and universe

The Earth is huge, but it is tiny compared to the Sun (which is super huge). But the Sun is tiny compared to the solar system which is tiny compared to the distance to the next star. Oh, did we mention that there are over 100 billion stars in our galaxy (which is about 100,000 light years in diameter) which is one of hundreds of billions of galaxies in just the observable universe (which might be infinite for all we know). Don't feel small. We find it liberating. Your everyday human stresses are nothing compared to this enormity that we are a part of. Enjoy the fact that we get to be part of this vastness!

Time scale of the cosmos

Not only is the universe unimaginable large (possibly infinite), but it is also unimaginably old. If you were feeling small in space, wait until you realize that all of human history is but a tiny blip in the history of the universe.

Big bang and expansion of the universe

What does it mean for the universe to expand? Was the "big bang" an explosion of some sort or a rapid expansion of space-time (it was the latter)? If the universe was/is expanding, what is "outside" it? How do we know how far/old things are? This tutorial addresses some of the oldest questions known to man.