What is the value and units of Einstein's cosmological constant?

Question

Where did he get that from and why is it considered today in cosmology?

Answer 1

Einstein introduced the cosmological constant, then discarded the idea.

The units of Λ are 1/meter^2.

The need for Λ in physical theory is still debated.

Disparate values have been calculated but nothing settled.

Aloha

Answer 2

Einstein's cosmological constant isn't exactly a neat constant in the otherwise very elegant equations to describe the development of the universe.

It has a somewhat curious history that very much shows it complexity. Einstein introduced this constant in order to produce a static universe (when solving the Friedmann-equations (describing the universe) Einstein believed the universe whas static). When Hubble later showed that the universe was in fact expanding, Einstein himself was very quick to discard the cosmological constant, calling it "biggest blunder".

Whitin the last few years, observations have shown that not only is the universe expanding, it is actually accelerating. Since other studies have shown that the geometry of the universe is what we call "flat" - we have found that we have a shortage of "something" in the universe. The baryonic matter (us and everything we can see) and the dark matter make it out for only 1/4 of what is in the universe - the last 3/4 is commonly referred to as "Dark Energy". Dark Energy isn't the same as Dark matter, because Dark matter exerts a "negative pressure" - in other words, Dark Energy is what's causing the expansion of the universe to accelerate.

Since Einsteins cosmological (when it was introduced) was exactly describing "something" with negative pressure - The Cosmological sollutions made by Einstein have therefor been called back into active duty. The only difference is simply that today, the cosmological constant isn't a small correction as Einstein predicted, the cosmological constant is the dominant factor in the universe.

I know this isn't pretty, but it simply is the best possible fit we have to the data at hand today.

Answer 3

The cosmological constant isn't actually agreed upon.

It is the constant Einstein used to try to balance his relativity equations when applied to the expansion of the universe.

Many physicists and astronomers are still undecided whether we have dark matter in the universe or the equations are just wrong.

If the equations are wrong then we need a cosmological constant to fix it.

If we have matter we can't see then the equations are right and we don't need a constant.

Problem is no one has actually proved the existence of dark matter directly, we think it is there because the equations of relativity tell us we have a bunch of mass that should be present to explain the universe's expansion rate.

If we confirmed either one, it would be an automatic Nobel prize.

Answer 4

Jens F meant to say dark energy exerts a negative pressure. Otherwise excellent comments.

Answer 5

explain.