Our own universe may be but one bubble of space-time in a much bigger multiverse.
Credit: Greg Smye-Rumsby
This article is an edited extract of the book From Here to Infinity: The Royal Observatories Greenwich Guide to Astronomy, published by the University of Western Australia Press.
Credit: University of Western Australia Press
INFLATION
All this makes it relatively simple to describe in mathematical terms, and one feature of that description is that the equations tell us that it is possible for quantum effects to produce tiny bubbles within the spacetime of the cosmos.
Quantum physics is the branch of physics that describes what happens on the scale of atoms and fundamental particles. Since these quantum fluctuations, as they are known, are much smaller than an atom, they might not seem to have much in common with a universe as large as ours, which has been expanding for nearly 14 billion years and contains hundreds of billions of galaxies.
But at the beginning of the 1980s the American theorist Alan Guth realised that there is a way to make one of these quantum fluctuations expand very rapidly indeed for a short time, growing to become the seed of the Big Bang.
The process is called inflation, and it works in exactly the same way as the dark energy that is making the universe expand faster today, but much more powerfully.
The dark energy associated with inflation could take a quantum fluctuation about 100 billion billion (1020) times smaller than a proton and 'inflate' it into a region 10 centimetres across (about the size of a grapefruit) in a tiny fraction of a second.
Then, Guth showed, the dark energy is converted into the energy of a hot fireball, expanding so rapidly after this initial push that even though gravity immediately begins to slow it down it would take hundreds of billions of years to halt the expansion.
Inflation comes with a great bonus. During that first split second, what is now our visible universe would have doubled in size a hundred times. This had the effect of smoothing out any irregularities, in the same way that the wrinkly surface of a prune smoothes out when the prune is placed in water and swells up.
Inflation also makes space very, very flat, just as we see in the real universe. The surface of the Earth already looks pretty flat, even though we know we live on the surface of a sphere. Imagine doubling the diameter of the Earth a hundred times; doubling once makes it twice as big, doubling twice makes it four times as big, doubling three times makes it eight times as big, and so on.
Doubling a hundred times makes it 2100 times as big. It would be almost impossible for people living on the surface of such a huge sphere to tell that the surface was curved at all. As far as any measurements were concerned, it would be indistinguishable from a flat surface.
Inflation predicts that the universe should be flat, in the sense we have already described, and that it should contain only tiny irregularities at the time of the Big Bang. These are exactly the kind of tiny irregularities we see in the background radiation, which we know are exactly the right size to account for the existence of galaxies.
The stunning implication of inflation theory is that galaxies exist (and therefore, planets and people exist) thanks to quantum fluctuations that were imprinted when the entire universe we see around us was smaller than an atom.
Inflation is such a successful explanation of the way the Big Bang got started that it is included in almost all of the modern ideas about how the universe was born, not just the eternal Cosmos model that we particularly like.
The big debate in cosmology today really concerns the way inflation got started, but the huge expansion of the universe during inflation smoothed away so much information about what went before that we may never know exactly how the universe got started.
It may be, though, that inflation is linked to the fate of the universe, as well as its origin. When dark energy in its current form has done its work, long after the galaxies have receded so far apart that they are invisible to each other, the dark energy will rip apart the structure of matter itself and produce the ultimate void.
These are ideal conditions for the kinds of quantum fluctuations that have been linked to the birth of our universe. It may be that the death of our universe will lead to the birth of other universes, and that we are just one link in a cosmic chain of universes extending infinitely far into the past and infinitely far into the future. Another idea is that each quantum fluctuation produces a different 'bubble universe'.
That rather overwhelming image makes us seem pretty insignificant on a cosmic scale. But putting speculation aside, coming back down to Earth and concentrating on our own universe, we find that there are intimate links between life itself and the universe at large.
An astrophysicist turned science writer, John Gribbin has worked for Nature and New Scientist, and has contributed articles to The Times and Guardian newspapers. He is the author of more than one hundred books and often collaborates with his wife, Mary Gribbin, the author of several books on scientific topics for young readers.
This article is an edited extract of their book From Here to Infinity: The Royal Observatories Greenwich Guide to Astronomy, published by the University of Western Australia Press.
The shape of the universe
Regarding the way we see the shape of the universe,"open","closed","flat".Maybe it's possible that there are other geometries,just not avilable to the common eye.Of course this point does spill over into 'religion',but maybe for to long now we have been seeing the universe through scientific blinkers. Maybe there is a need to take a more "holistic" view?
Excellent science writing
Thanks to John Gribbon for laying out all these ideas with exceptional clarity.