Starting with a Bang
- Wednesday, August 04, 2010
Hoyle and his colleagues were motivated at least in part by a reluctance to accept that the universe had a beginning. For entirely philosophical reasons, they were allergic to the idea of a ‘big bang' origin. In fact, when Fred Hoyle coined the term ‘big bang' he intended it as a term of derision. Eventually, the force of evidence persuaded him to abandon ‘continuous creation' but he was never entirely happy with the idea that the universe actually began.
So let's take a look at this idea that no one really wanted to know about — the big bang theory of the origin of the universe, also known as the ‘standard model' of cosmology. Having done so, we shall then return in the next chapter to the strenuous attempts that are still being made by theoreticians to get around its theological implications.
Anyone for tennis?
It is a striking fact that even at the start of the twentieth century the book of Genesis was something of a lone voice in proposing that the universe did have a beginning. Although the heavens had always displayed frenetic activity in terms of local celestial motions (the sun, moon, planets, comets, asteroids and meteorites or ‘shooting starts') the more distant ‘fixed stars' didn't seem to move at all. Scientists generally believed that, taken as a whole, the universe was static and unchanging. This did not entirely rule out a beginning of some kind but it certainly didn't lend any support to the idea. Indeed, the prevailing belief in an unchanging cosmos was dramatically demonstrated by Einstein himself when he produced his theory of general relativity in 1915. Much to his dismay, he found that his equations were incompatible with a static universe. Picture it like this. When a tennis player throws the ball into the air in the process of serving, the ball rises, stops momentarily at its highest point, and then begins to fall. It is stationary for a split second at the top of its trajectory but this is an unstable state — it can't last. Stability requires that the ball is either rising or falling.
In a similar way, the equations of general relativity said that the universe could be either expanding or shrinking but it could not be static. But instead of accepting this, Einstein's belief in a static universe was such that he added to his equations a fudge factor which he called the ‘cosmological constant' and which had the effect of balancing the gravitational attraction that would otherwise cause the universe to collapse. When, later, it was found that the universe actually was expanding, Einstein discarded the cosmological constant, describing its inclusion as his ‘biggest blunder'. Ironically, cosmologists have since fished it out of the rubbish bin, dusted it down and put it back on the mantelpiece. There are now reasons to believe that the cosmological constant could play a significant role in cosmology after all, but that's another story.
The expanding universe
In one sense, as we have seen, the idea of an expanding universe began with Einstein's general relativity theory in 1915 but the elephant in the room was deliberately ignored until Aleksandr Friedmann in 1922 and Georges Lemaître in 1927 independently found solutions to Einstein's equations that described evolutionary as opposed to static models of the universe. This implied a beginning which could be represented mathematically as a ‘singularity' in Einstein's equations. (A singularity is a point where some physical quantity becomes infinite — in this case the density and temperature of the universe, implying a ‘hot big bang' beginning.) Much later, George Gamow, Ralph Alpher and Robert Herman developed the big bang theory of the early universe in a paper titled ‘The origin of chemical elements' published in the Physical Review on 1 April 1948. In spite of the date it was no ‘April fool' spoof and turned out to be one of the most celebrated scientific papers ever.
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