Quantum Theory Cannot Hurt You_ A Guide to the Universe - Marcus Chown [73]
No one knows how close or how far away we are to possessing a quantum theory of gravity. But without it there is no hope of travelling those last tantalising steps back to the beginning of the Universe. However, some of the things that must happen along the route are clear.
Think of the expansion of the Universe in reverse again. At first the Universe will shrink at the same rate in all directions. This is because the Universe is pretty much the same in all directions. But pretty much the same is not the same as exactly the same. Undoubtedly, there will be slightly more galaxies in one direction than another. In the early stages of the contraction this imbalance will have no noticeable effect. However, as the Universe shrinks down to zero volume, such matter irregularities will become ever more magnified. So when the body shrinks to zero volume, the final stages of the collapse will be wildly chaotic. Gravity—warped space-time—will vary wildly depending on the direction from which the singularity is approached by an in-falling body.
Very close to the singularity, the warpage of space-time will become so violent and chaotic that space and time will actually shatter, splitting into myriad droplets. Concepts like “before” and “after” now lose all meaning. So too do concepts like “distance” and “direction.” An impenetrable fog blocks the view ahead. It shrouds the mysterious domain of quantum gravity, where no theory yet exists to act as our guide.
But deep in that fog lie the answers to science’s most pressing questions. Where did the Universe come from? Why did it burst into being in a Big Bang 13.7 billion years ago? What, if anything, existed before the Big Bang?
The fervent hope is that, when at last we manage to mesh together our theory of the very small with our theory of the very large, we will find the answers to these questions. Then we will come face to face with the ultimate question: How could something have come from nothing? “It is enough to hold a stone in your hand,” wrote Jostein Gaarder in Sophie’s World. “The universe would have been equally incomprehensible if it had only consisted of that one stone the size of an orange. The question would be just as impenetrable: Where did this stone come from?”
1 See My World Line by George Gamow (New York, 1970), in which the author writes of Einstein: “He remarked [to me] that the introduction of the cosmological term was the biggest blunder he ever made in his life.”
2 The Big Bang was named by the English astronomer Fred Hoyle during a BBC radio programme in 1949. The great irony is that Hoyle, to the day he died, never believed in the Big Bang.
3 And of magnetrons, which power microwave ovens and radar trans-mitters.
4 Actually, there is thought to be between 6 and 7 times as much dark matter as ordinary matter. This is because the stars account for only about half the ordinary matter. The rest, which may be in the form of dim gas clouds between the galaxies, has not yet been identified.
5 Actually, there is a subtle distinction between the singularities at the heart of a black hole and the Big Bang. The former is a singularity in time and the latter a singularity in space.
GLOSSARY
ABSOLUTE ZERO Lowest temperature attainable. As a body is cooled, its atoms move more and more sluggishly. At absolute zero, equivalent to –273.15 on the Celsius scale, they cease to move altogether. (Actually, this is not entirely true since the Heisenberg uncertainty principle produces a residual jitter even at absolute zero.)
ACCRETION DISC CD-shaped disc of in-swirling matter that