[lisper]

It was actually a double-blunder. Einstein missed the opportunity to predict the expanding universe (and, as a corollary, the big bang). And then, when it turned out the universe was expanding, he retracted the CC despite the fact that it actually turned out that there is a (non-zero) CC, the expanding universe notwithstanding. He got the right answer, but he abandoned it because he got it for the wrong reason.

[mbell]

> he retracted the CC despite the fact that it actually turned out that there is a (non-zero) CC

Dark Energy being the CC is just _one possible explanation_, it hasn't been tested.

[garmaine]

I think you have that backwards. Physics doesn’t arise from mathematics; reality just is and the math describes it. The universe is expanding, and the cosmological constant simply describes this relationship between space and the matter inhabiting it.

[lisper]

Exactly right. Einstein had no idea what the physical mechanism behind the CC might be (and we still don't). It was just something he threw into the equations because he believed the universe was static, and the only way to make GR support a static universe is with a non-zero CC.