This is part two in a three-part series on legendary physicists and their biggest blunders.

Today we tackle Albert Einstein, whose biggest mistake actually ended up benefiting science in the end.

Albert Einstein was a physics rebel. He overthrew centuries of thinking about gravity and revolutionized our understanding of space and time.

But there were certain things that Einstein was kind of fussy about preserving, like the size of the universe.

In Einstein's day, most scientists believed the universe was constant inside. It never got any bigger or any smaller, and it never really changed at all.

This was called the steady-state view of the cosmos. And Einstein liked that view. It pleased him to think of the cosmos as never changing, having no beginning and no end.

It just was, and always shall be.

The problem was, Einstein's own theories disagreed with him.

General relativity deals with gravity, and gravity is an attractive force.

If you have a big cloud of dust in space, the dust will eventually contract together and crunch down into a central mass.

The same basic idea applies to the universe. All the stars and galaxies are spread out now, but in theory they should eventually crunch back together as gravity pulls them in.

That's not a steady-state cosmos. That's a crushed cosmos. And Einstein just didn't like that. So he fudged things.

In 1917, he took one of his general relativity equations and added another term to it. He named this term Lamda, after the Greek letter.

This Lamda fudge factor was supposedly a repulsive force that pushed matter apart. It counteracted gravity and kept the universe from crunching in on itself.

Now, there was no good reason for adding this repulsive force. And Einstein really did fudge things here.

He just wrote down a plus sign, and then added Lamda times another factor at the end of his equation.

Kind of like how we would scribble, oh yeah, plus eggs to a grocery list. He just made it up.

Other scientists didn't know what to make of this Lamda fudge factor. Most of them ignored it. Others even opposed it.

For example, there was Georges Lemataire, a Belgian priest-slash physicist. And yes, you heard that right, a priest-slash physicist.

Lemataire came up with the idea that maybe the universe was far smaller in the past. Perhaps it started as a tiny ball or something, and it's been getting steadily bigger since then.

Lemataire published this idea in 1927, and it wasn't taken very seriously, at least not until 1929.

That year an American astronomer named Edwin Hubble found that the old steady-state view of the cosmos, where it was static and always one size, was wrong.

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