Physics - Cosmology.

Hubble. Not the big telescope.

Back in the days of Columbus, people thought that the world was flat! We know better now, but imagine yourself in those days. You believed that the Earth was flat because that was the limit of your experience.
For years, people believed that the Earth was the center of the solar system. It wasn't until Copernicus' theory that the sun was the center of the solar system did we think otherwise. It was Copernicus' theory and Galileo proving it that changed our thinking.
Now let's expanding our brains for a second, think big. Bigger. BIGGER! The universe, now that's big. It wasn't until 20th century did we even think our views of the universe were wrong. Even Einstein had the wrong impression, which was why he included the cosmological constant in this equations. Everyone (or nearly) thought that the universe was static, I mean, it was huge and it couldn't be moving that much. Surely not enough to throw a wrench into our equations.
Hubble started out by looking up at the stars in sky, he saw farther into the universe than anyone had looked before. In fact, he saw other galaxies. So he started keeping track of them, position, size, and brightness. He saw in his data that the stars he was looking at were red-shifted which were consistent with the distance they were. This proved that they were moving away from us.
OK, let's pause the history lesson for a second. Light comes in 'waves.' There are different wavelengths, different colors. We've probably all done it in elementary school, where we held up a prism to the sun a looked at the rainbow it produced on the ground. Well, if you were curious like me, you twisted it back and forth; the colors would stretch out until it snapped back when the prism side was turned. Red-shifting just meant that the light was moving away, whereas blue-shifting meant it was coming closer.
Back to Hubble. So this idea that galaxies were moving away from us was a revolutionary idea, just like a round Earth or a solar system rotating around the sun. Yet, the proof was there in his notes. This shattered the scientific community, because up until this point, the smartest people in the world thought that universe was static, or stationary.
Not just because the fact that they were moving away from us, but the other implications that came with it. If something is moving away from us, you walk it backwards in time that meant that it was closer to us, keep walking backwards and evidentually you get back to us. We all know that two objects can occupy the space at the same time. (You can try this with your hands, the best you can do is have one on top of the other. Now press the top one into the bottom one, still not occupying the same space at the same time, but they are occupying less space total.) So, uh-oh, at one point we're pressing together very tightly. Which would be fine, but how did we split up? Something must've caused it to expand... perhaps some sort of BIG BANG!
Whoa. Who would've thought of that? The expanding universe supports the Big Bang Theory, we're living proof, and you can look into the sky and see it. Yet, it isn't fully accepted by religion that believes that God basically willed everything into being. And I'll talk more about this subject later.