Reflections in Cosmology 17: Inflation Does Solve a Lot of Problems!

Alan Guth, a cosmologist at MIT, proposed the idea of an inflationary universe

The theory of inflation, proposed by Alan Guth, posits that the Universe went through a short period of highly accelerated expansion early in its history. Although it has yet to be confirmed observationally, it is generally accepted as a standard model by many cosmologists, mainly because it solves some of the most perplexing problems in cosmology today.

Inflation solves the magnetic monople problem

For all intents and purposes, there is no reason why there should be isolated positive and negative electrical charges but no isolated north and south magnetic monopoles. No matter how many times we divide a magnet, it always retains its north and south poles. Didn’t James Maxwell show us that electrical and magnetic forces were one and the same? Modern grand unified theories suggest that the symmetry of the electromagnetic forces was broken when the universe cooled down to a certain temperature. But it also predicts that there should now be an abundance of magnetic monopoles in the universe. So why have we not detected them? An inflationary universe solves the problem. Magnetic monopoles could only have been created at very high temperatues that existed prior to the inflationary period, and these were spread out over cosmological distances during inflation, so that they are now extremely rare. As Edward Harrison states, inflation saves the universe from monopole domination.

Inflation solves the flatness problem

For some reason, we live in an astonishingly flat universe. Of all the values of curvature that the universe could have had, it had to be one that was flat. But maybe we shouldn’t be so surprised after all. Life would not have been possible in any other universe (the anthropic principle rears its head again). A universe that had a positive curvature, no matter how small its value, would have collapsed back on itself long before life could have developed (there needs to be a number of generation of stars beforehand, but I’ll save the details for another time). On the other hand, a universe with even a slightly negative curvature would have had its constituents separated so far apart that the particles would not have been able to come together to form atoms and molecules, not to mention stars, galaxies and life. So the universe had to have been flat from almost the beginning of time. But if inflation did happen, our universe could have begun with any sort of curvature, and due to its large rate of expansion would have been stretched out to such an extent that the observable universe looks flat to us.

Imagine being an ant on a balloon that is being inflated. Though initially curved, by the end, it appears flat to the ant - just as the Earth appears to be flat to us locally.
Inflation solves the horizon problem

When we look out at the universe around us, we see that they look alike in every direction, on large scales at least. Recently, the cosmic microwave background has also been found to be extremely isotropic. So what is wrong with that? Well, the cosmic microwave background radiation travels to us from the dawn of the universe. It took them about 13 billion years to arrive at the Earth. The CMB radiation from one side of the observable universe has not had the time to travel to the other side of the observable universe, since nothing travels faster than the speed of light. There was thus not enough time for the two widely separated regions to communicate with each other and to inform each other how they should be like. More precisely, there just wasn’t enough time for the different regions of the observable universe to interact so that they could reach a state of equilibrium, even considering the current rate of expansion and that these regions were much closer to each other in the distant past. Inflation resolves this, by having only a very small self-interacting region expand at an accelerating rate, so that different parts of the observable universe today were once in equilibrium.

Points A and B are at the edge of the observable universe from the Earth, but they are not a part of each other's observable universe. This means A and B could not have interacted with each other, unless there was a period of inflation earlier in history.

Last but not least:

And don’t forget inflation also solves the problem of a flat automobile tyre. ~ David van Blerkom


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