who was the first one to say universe is expanding?

[LSulayman]

Who was the first one to come up with the idea that the universe is expanding, and also had a form of evidence for it?
Was is Friedmann, Sitter, Hubble or Einstein himself? Or was it someone else?

[Calimero]

Hubble.

[LSulayman]

Hubble.

Was it really Hubble? So he came up with redshift before Friedmann came up with the Friedmann equations?

[cristo]

Friedmann came up with the expanding solution of GR in the early '20s, but it was not until 1929 when it was tested against observations by Hubble.

[LSulayman]

Friedmann came up with the expanding solution of GR in the early '20s, but it was not until 1929 when it was tested against observations by Hubble.

So Friedmann came up with the idea of an expanding universe first with his solutions, but it was not until Hubble's observations that it could be proven?

[Calimero]

Well, Hubble, for sure, is the first man who came up with observational evidence. It is, I think, true that Friedmann came up with EFE expanding universe solution few years earlier, but as far as I know, he was not at all convinced that it has anything to do with physical reality, let alone that his work will become the standard for modern cosmology.

[LSulayman]

Well, Hubble, for sure, is the first man who came up with observational evidence. It is, I think, true that Friedmann came up with EFE expanding universe solution few years earlier, but as far as I know, he was not at all convinced that it has anything to do with physical reality, let alone that his work will become the standard for modern cosmology.

So if I want to explain the expanding universe to someone I should first talk about Hubble and then Friedmann? (keeping all the other things aside for now)

[Calimero]

Well, that depends on your narative skills, but probably. Keep in mind that Hubble also showed that our universe is not consisting of only one galaxy (Milky way), which was prevailing thought at the time.

[LSulayman]

Well, that depends on your narative skills, but probably. Keep in mind that Hubble also showed that our universe is not consisting of only one galaxy (Milky way), which was prevailing thought at the time.

Was Hubble also the first one to measure the age of the universe? (by using Hubble's law)

[Calimero]

He provided first direct observational evidence that universe must be finite in age, but his estimates of that age were far from values that we today consider correct.

[Phrak]

A)
B) Steady-state theory, Hermann Bondi, Thomas Gold, and Fred Hoyle.
C) Einstein field equations with cosmological constant included to have a theory consistant with steady state.
D) Fredmann equations for expanding universe.
E) Hubble

[LSulayman]

He provided first direct observational evidence that universe must be finite in age, but his estimates of that age were far from values that we today consider correct.

But he was actually the first one to do that using the Hubble Law?
I'm also measuring the age by using redshift, H etc., that's why I want to know...

[LSulayman]

A)
B) Steady-state theory, Proposed in 1948 by Hermann Bondi, Thomas Gold, and Fred Hoyle.
C) Einstein field equations with cosmological constant included to have a theory consistant with steady state.
D) Fredmann equations for expanding universe.
E) Hubble

Weren't Einstein's equations before 1948?

[fillipeano]

Is it true that General Relativity showed the universe was expanding, but Einstein did not believe this to be true?
That is, until Hubble came along?

[turbo]

Hubble was not an iconoclast regarding Universal expansion. Far from it. Even in a paper published in 1953 (after his death), he said "c x z = velocity is not formally correct". Gamow et al enshrined him as the "discoverer" of Universal expansion, but Hubble would not have been willing to make that leap. Throughout his career, he spent his efforts showing that (using distance indicators like Cepheids and extrapolations from galaxy morphology and luminosity) redshift was correlated in a linear fashion with distance.

I once had two sites bookmarked with access to full-text HTML files of his papers, and both links seem to be dead right now.

[LSulayman]

Is it true that General Relativity showed the universe was expanding, but Einstein did not believe this to be true?
That is, until Hubble came along?

Yep, right to the point you can actually say that's true.

[Phrak]

Weren't Einstein's equations before 1948?

Not much of a time line is it? There was no general concensus for a few decades. Einstein published his field equations between 1905 and 1916. You could say general relativity was completed in 1916 with cosmological constant included. Hilbert actually got the jump on the last brick in the wall in 1915. Though even as late as perhaps the 1980s, Hoyle was still advancing a steady state theory. Alexander Friedmann, Georges Lemaitre, Howard Robertson and Arthur Geoffrey Walker developed expanding universe solutions in the 20s and 30s.

[Amanheis]

Not much of a time line is it? There was no general concensus for a few decades. Einstein published his field equations between 1905 and 1916. You could say general relativity was completed in 1916 with cosmological constant included. Hilbert actually got the jump on the last brick in the wall in 1915. Though even as late as perhaps the 1980s, Hoyle was still advancing a steady state theory. Alexander Friedmann, Georges Lemaitre, Howard Robertson and Arthur Geoffrey Walker developed expanding universe solutions in the 20s and 30s.

According to Simon Singh's "Big Bang", Einstein introduced the cosmological constant to have a static solution. It was considered an ugly modification by most scientists, even by Einstein himself, but a steady state universe was the only imaginable possibility at the time. Friedmann then came up with his famous equations, but while Einstein acknowledged the correctness of the solutions, he still rejected it and deemed it "unphysical". And at the time, if you wanted the approval of the scientific community, you needed Einstein's approval. Friedmann died shortly after and his solution was largely ignored until Lamaitre came up with the same solution independently and actually applied them to the universe, thinking of a primeval atom and such, unlike Friedmann who was a mathematician first and an astrophysicist second. The big bang theory was born, but Einstein didn't change his mind, so Lemaitre gave up as well. Then Hubble measured the recession of galaxies and Einstein finally gave in, along with the rest of the physicists.

It's all in the book, a great read. I highly recommend it.