It was new at the time, anyway. The model being spoken of is the Big Bang, first suggested by Father Georges-Henri Lemaitre in 1927. (The expanding-universe solutions to general relativity had also been derived by Alexander Friedmann in 1922, but he hadn’t emphasized the nature of the intial singularity in such models.) Lemaitre, a Belgian priest who studied at Harvard and MIT, proposed what he called the “Primeval Atom” or “Cosmic Egg” model of the universe, and derived Hubble’s law, two years before Hubble and Humason actually discovered that the universe is expanding. Einstein wasn’t all that fond of Lemaitre’s idea — having been assured by his astronomer friends that the universe was static — but he encouraged Lemaitre in his investigations.
All of which springs to mind because the Modern Mechanix blog has unearthed a Popular Science article from 1932 by Donald Menzel, an astronomer at Harvard, that explains Lemaitre’s ideas. (The time between Hubble and Humason’s discovery and Menzel’s article is somewhat less than the time between the 1998 discovery of dark energy and Richard Panek’s New York Times Magazine article from yesterday.) Menzel’s piece does a great job of explaining the basics of the Big Bang model, long before it was given that name by Fred Hoyle. Indeed, he touches on many of the questions that still arise in a good Cosmology FAQ! For example, he emphasizes that the redshift is due to the expansion of space, not to the Doppler effect.
The case of the universe is analogous, except that the expansion, being of a three-dimensional volume, cannot be visualized. The phenomena are, however, comparable. The nebulae are not running away from us. Their recession is due to expansion of space. This may, perhaps, seem to be quibbling over terms, since it amounts to the same thing in the end. Nevertheless, the distinction is worth keeping. According to the relativity theory, there is a difference between the running away of the nebulae and expansion of the medium in which they are imbedded.
Sadly, he also appeals to the much-hated balloon analogy for the expansion of the universe, although he uses the surface of the Earth rather than the surface of a balloon; in fact, it’s a better choice. And he’s not afraid of diving into the sticky questions, like “What happened before the Bang?”
DR. LEMAITRE’S hypothesis does away with the old query as to the state of affairs before the beginning of things. Going back to the parent atom we may inquire about what happened before the cosmic explosion took place. The answer is: — Nothing. – Computation shows that space would have closed up around the massive atom and, certainly, nothing can happen where there is no room for it to happen. Time has no meaning in a perfectly static world. The age of the universe is to be reckoned from that prehistoric Fourth of July, when space came into existence. Since then, space has been continually expanding before the onrushing stars, sweeping the way for them, forming a sort of motorcycle squadron to make room for the star-procession to follow.
Like many contemporary cosmologists, Menzel is a little more definitive about this than he really should be. When asked “What happened before the Bang?”, the correct answer is really “We don’t know. According to general relativity, space and time do not exist before the Bang, so there is no such thing as ‘before.’ However, we have no right to think that general relativity is correct in that regime, so… we don’t know.” Few people are sufficiently straightforwardly honest to give that answer.
And what about the future?
SO MUCH for the present. What of the future? Einstein and the noted Dutch astronomer, Willem de Sitter, have talked of some future contraction, which might sweep up the stars along with cosmic dust and eventually bring the world back to its original state. Dr. Lemaitre thinks that such a contraction cannot occur. He prefers to believe that the whole universe was born in the flash of a cosmic sky-rocket and that it will keep expanding until the showering sparks which form the stars have burned to cinders and ashes.
We still don’t know the answer to this one, but the smart money is on Lemaitre (and against Einstein, who liked his dice unloaded and his universes compact). Now that we know the universe is not only expanding but accelerating, the simplest hypothesis is that it will keep doing so. To be honest, of course — we don’t know!
Lemaitre passed away in 1966, a year after Penzias and Wilson detected the microwave radiation leftover from the Primeval Atom.
Pingback: Update: Lemaitre vs. Hubble | Cosmic Variance