Georges Henri Lemaître: Biography
Georges Henri Lemaître, biographical essentials: born 1894, Belgium; formulated the big bang theory of the origin of the universe (1927) , died 1966.
Georges Henri Lemaître took a degree in engineering at the University of Louvain, but joined the army when Germany invaded Belgium during WWI. After the war he returned to Louvain but switched to theoretical physics and religious studies.
After becoming a priest, he spent a year in Cambridge with Sir Arthur Eddington and went on to do a Ph.D. in cosmology at MIT. Then, in 1925, he returned to take up an academic post at the University of Louvain. He began developing cosmological models based on Einstein's general theory of relativity. He rediscovered the Friedmann model of cosmology, but pushed the implications of an expanding universe even further.
Lemaître agreed with other theorists that the universe is not expanding because galaxies are moving through space. The universe is expanding because space is stretching—like a balloon being inflated. Galaxies themselves do not expand because gravitation is too strong. The fact of an expanding universe is a major component of the standard model of cosmology. An open question is whether this expansion is slowing down, speeding up, or constant.
The velocity of the galaxies is given by their red-shifts. Given their distances, we can work out the rate at which the universe is expanding. But the distances to the galaxies are not known with great accuracy, as they have to be measured indirectly by using Cepheid variable stars.
In 1924 Edwin Hubble demonstrated that our Milky Way galaxy is not the only galaxy, thereby settling the Great Debate.
We now know there are roughly 1011 galaxies, each with roughly
1011 stars. Our galaxy is about one hundred thousand light-years across, and the sun is an average star in one of its spiral arms.
The light from distant galaxies is shifted towards the red end of the spectrum. This red-shift is explained by the
Doppler effect, and means the galaxies are moving away from us, and the universe is expanding.
The velocity at which a Galaxy is receding is given by Hubble's
law.
If strong enough, gravity will cause the universe to stop expanding and start contracting; otherwise the universe will expand forever.
Newton’s universal law of gravitation implied this, but the belief in a static universe persisted into the early twentieth century.
Albert Einstein, at first, assumed the universe was static and added a
cosmological constant to his general theory of relativity
to produce his model (Einstein's cosmological model).
lemaître reasoned that if the universe is expanding, and you go back far enough, space must have been compressed into a tiny region. He concluded that the universe began with this small region of space exploding--this was the first serious account of what we would now call a Big Bang model.
Lemaître was familiar with how Uranium breaks down into smaller atoms while emitting elementary particles and energy. He speculated that, before the explosion, all the matter in the universe might have been compacted into a uranium-like primeval atom - its decay resulting in the origin of the universe.
Lemaître published his model in 1927, but it initially met with the same rejection from Einstein and the scientific establishment that Friedmann's model had encountered five years earlier. Instead, cosmologists continued to believe in Einstein's model of cosmology, until Edwin Hubble's observations of galactic redshifts in 1929. Then, in 1930, Sir Arthur Eddington published a letter praising Lemaître's work because it explained why the universe was expanding.