Georges Lemaître And Albert Einstein: The Strange Tale Of The Cosmological Constant

When William Herschel attempted to map out the Milky Way he correctly realized that the general shape of the our galaxy was that of a flattened disk. He, however, mistakenly placed our sun at its center–an understandable error given what was known about the interstellar medium at the time. Herschel perceived the interstellar dust that he observed as “vacancies” or “holes” in the heavens. Astronomers soon realized that these could not be holes in the heavens because that would entail that all of the holes were pointing towards the Earth, and that just seemed too highly improbable. It wasn’t until Edward Emerson Barnard (1857 – 1923) starting photographing these “vacancies” that astronomers realized that they were not holes at all, but rather dense clouds of gas and dust that were blocking the light of stars and other objects behind them.

Harlow Shapley (1885-1972)

Edward Emerson Barnard (1857 - 1923)

It was Harlow Shapley (1885-1972) of Mount Wilson Observatory, by observing Cepheid variables in globular clusters in our galaxy, who was finally able to correctly place our sun not at the center of our galaxy but rather in its outskirts. But while Shapley had correctly placed our sun in its proper place, he at the same time held the view that our galaxy was the entire universe. When Albert Einstein published his general theory of relativity in 1915, it was believed by most astronomers that Shapley was right and that the Milky Way was the entire universe.

It was also believed that the spiral nebulae–as they then were called–outside our galaxy were minor objects that were merely a part of the huge Milky Way complex, instead of the autonomous galaxies that they in fact are. Shapley became the most salient proponent of this view. But, not everyone agreed with him. Among those who dissented were Heber Curtis (1872-1942 ) of the Lick observatory along with Edwin Hubble and Milton Humason who, as chance would have it, worked at the very same observatory as Shapley, namely Mount Wilson Observatory. In point of fact, Humason was a night assistant to Shapley as well as to Hubble at this time and later became a respected astronomer in his own right.

Heber Doust Curtis (1872-1942 )

But, Heber Curtis of the Lick observatory had insufficient evidence to make his case. So, the prevailing view at the time was that the Milky Way was the entire universe. What basically ensued at this time was an argument between the Lick observatory and the Mount Wilson observatory, which later became known as “The Great Debate”.

In the mean time, while all of this was going on between these two prestigious observatories, it was pointed out to Einstein that his general theory of relativity entailed that the universe was dynamic and evolving, and therefore had to be either contracting under its own gravity or expanding as a result of its own momentum. Einstein was not aware of this prediction before this time. This was a serious problem for the young theoretical physicist.

The problem stated simply was this: the consensus at the time was that our galaxy was the entire universe, and from all accounts the Milky Way seemed pretty much unchanging. Einstein soon realized after putting all of this together that without some kind of anti-gravity or repulsive force, our universe (i.e. our galaxy) would quickly collapse upon itself under its own gravity. So, Einstein introduced an extraneous term to his equations known as the “cosmological constant”, something which he later came to refer to as “the biggest blunder of my career”. And, so it seemed to be at the time.

Georges Lemaître with Albert Einstein

The “debate” came to an abrupt halt when in 1925 Edwin Hubble conclusively established that the spiral nebulae which Shapley had reduced to nothing more than small aggregates of the Milky Way, were in fact galaxies in their own right–many of which were as large as our own galaxy. And, Einstein’s cosmological constant became irrelevant when Hubble in 1929 showed that the universe was expanding.

Georges-Henri Lemaître (1894-1966)

An expanding universe implies that at one time the universe was smaller than it is today. And it also begs the question of whether or not the universe had a beginning. Hubble’s seminal discovery of an expanding universe stimulated the imagination of a little known Catholic priest and astrophyicist, Georges Lemaître (1894-1966).

Lemaître not only envisioned the universe as originating from what he called a “primeval atom”, but he also anticipated that cosmologists in the future would discover that the expansion of the universe was accelerating. If indeed the expansion of the universe were accelerating, then this would certainly bring Einstein’s cosmological constant back to life. And according to the results of two competing teams, working independently of each other and not particularly liking one another–the Cosmology with Supernovae: The High-Z Supernova Search and the Supernova Cosmology Project–using Type Ia supernovae as a standard candle to measure the rate at which the universe is expanding, it appears that the rate of expansion of the universe is accelerating and that Einstein was right about the cosmological constant after all. So in effect, Einstein came up with the right conclusion, based on an erroneous premise.

Today the cosmological constant goes by many names: dark energy, quintessence and vacuum energy, but essentially it still remains Einstein’s mysterious repulsive force. Georges Lemaître, whose ideas had finally been vindicated over the years, has since become recognized as the father of the Big Bang theory of the universe which he surely deserves.

In the end, both Albert Einstein and Heber Curtis were vindicated by the almost forgotten hero of cosmology, Georges Lemaître and two pioneering astronomers from Mount Wilson Observatory, Edwin Powell Hubble and Milton Lasalle Humason.

Truth truly is stranger than fiction. But many times, that is exactly how science progresses. Today’s “blunders” may be tomorrow’s breakthroughs.

An Afterthought

Someone may ask how something like the story above could happen. I will say this on the matter: higher mathematics is what the German philosopher Immanuel Kant would categorize as mostly a priori. To put it another way, in physics, once you’ve made an assumption about the physical world, you then go where the mathematics takes you. And that’s precisely what Einstein did with respect to the cosmological constant. His math was impeccable and that is why it led him to the right answer even though his physics was based on a faulty assumption, namely that the Milky Way was the entire universe. Believe or not, this has happened more times in the history of science than most scientist would care to admit. It’s not the steady linear progression that many people think it is. It is full of bizarre twists and turns and lots and lots of mistakes. But, in our efforts collectively, over time, we manage to make some progress and actually gain some insight into how the natural world really works.

Copyright © 2009 Eric F. Diaz

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