The Big Bang Theory is the most widely accepted explanation for the origin and evolution of the Universe, though some scientists dispute it and many say it may never be proven.
Respected Princeton University professor P. James E. Peebles has said that all of the matter and energy we can now observe was once concentrated in a spot the size of a dime. Peebles has put the date at 12 billion years ago. Others variously set it at 10 to 20 billion years ago.
Then a great cosmic explosion flung the matter and energy at great speeds in all directions. Eventually, individual stars and galaxies begin to form, though scientists don’t know for sure how this happened.
As the Universe expands it increases the distance between our galaxy and other galaxies. The expansion of the Universe bends light rays, converting blue light to red light and red light into infrared light. This is how scientists measure the expansion; distant galaxies appear redder.
The idea of a great explosion was first proposed in 1927 by Belgian priest Georges Lemaître. It became more popular when Edwin Hubble found that distant galaxies where speeding away from us in every direction.
The theory fits well with Einstein’s theory of relativity, which envisions an somewhat uniform distribution of matter throughout space. The Big Bang Theory also predicted the existence of a thing called cosmic background radiation, which was in fact discovered in 1964 by Arno Penzias and Robert Wilson.
Though the theory has previously withstood attacks, there are many unresolved questions within it. The largest, perhaps, is this: What was there before the Big Bang?
And there is the hot debate over whether the Universe will continue to expand, or whether gravity might eventually win out and cause it to fall back on itself. The prevailing thinking, recently challenged, is that gravity is slowing the expansion of the Universe. If the Universe is dense enough, the idea goes, the expansion will eventually reverse and the everything will collapse. If not, then the expansion will continue forever.
David Malin of the Anglo-Australian Observatory is a respected expert on the topic. We recently asked him to share his thoughts about the controversy:
“While I understand that such an outrageous idea as the Big Bang would have its skeptics, that’s entirely healthy, and is a reflection of the way science works,” Malin says. “If the skeptics can produce a model of the origins of the Universe that fits the known facts better than the Big Bang, they will win the argument.”