Cosmological constant

We need to introduce one more thing before we turn the page to the experiments that are ongoing.

Einstein came up with the cosmological constant, which is signified by the Greek letter lambda.

And later on he said it was the worst mistake he ever made.

We need the cosmological constant.

Is that correct?

That's right, because the cosmological constant that Einstein once introduced was in effect an accelerating force in empty space.

And back then he thought maybe I should never have introduced it because, well, later cosmological observations, they seem to indicate that it was not necessary.

But now we are discovering that the universe is accelerating, that the expansion is speeding up.

So, but that's bad, thought Einstein, because it ought to be static.

So, he invented an additional term for his equation, an additional term, which he wrote down as a capital Lambda and called the Cosmological Constant.

And this had generated a repulsive force that would gravity and lead to a static universe.

And it was allowed in the equations.

If you don't know calculus, ignore that last sentence.

Okay.

And so, he invented this repulsive force, this cosmological constant, to balance gravity so that you could have a static universe.

Then, Hubble discovers that the universe isn't static.

So, this is Ωmatter equals 1 quarter, and Ωλ equals 3 quarters.

And, as you will recall, The explanation for this, or the first explanation that was offered, was the fact that Einstein had this figured out eighty years before, except he decided he was wrong.

And so, the first explanation of this was Einstein's Cosmological Constant.

That's this symbol lambda that I keep writing down.

And so, once people believe this result, you have to start worrying about what the heck this actually is in real life.

And it has some very peculiar properties.

In particular, there is the issue of what is constant about Einstein's cosmological constant.

So, let me first tell you what it is, and then I'll tell you why it's so bizarre.