Lois & Clark Forums Forums General Discussion Off Topic The Big Bang and the Universe, Part 9: Don't forget about inflation!

I'm sure you all know about inflation:



Children playing with paper money that has become worthless because of inflation.

Ah, but in astronomy inflation has a completely different meaning!



This is cosmic inflation. The graph shows a period of time ten to the power of minus 35 seconds after the Big Bang. When this period started, the universe grew by forty magnitudes in a time period lasting less than ten to the power of minus thirty seconds. This is such an incredible expansion of size in such an incredibly short period of time that the expression "an explosive expansion of the universe in the blink of an eye" doesn't even begin to do it justice.

I once read that if this period of "cosmic inflation" close to the beginning of time had never happened, then the universe today wouldn't have been larger than a basket ball!



I must emphasize that I have read this once and never again. I don't think that many astronomers today would agree with that statement.

Still, the astronomical community seems to be in all but complete agreement that inflation really did happen in the very beginning of our universe, and if it hadn't happened, then the universe would have been very different from what we see today.

Inflation says that our entire universe emanates from an inconceivably tiny region of the original universe, created in the Big Bang. Because this region was so tiny, it was "the same" all over, so to speak. It was this "homogenous" patch of universe that got blown up and turned into our own large-scale universe. And because the original tiny "patch of universe" was "the same all over", today's universe is also more or less "the same all over":



This is a large-scale representation of our universe. You can see how similar it looks all over. The "grainy" and "filamentary" structures represent concentrations of mass. Take a look at the picture again and try to pick out a filamentary structure. What this filament represents is nothing less than clusters of galaxies lined up in a "string formation". Bright points represent particularly huge clusters of galaxies. Darker areas represent regions of space where the number of galaxies goes down.

But what you can see most of all, when you take a look at this "large-scale structure of the universe", is that the universe looks pretty much the same in all directions. It is "homogenous". If it hadn't been homogenous, then there might have been a huge concentration of galaxies in the "upper quadrant" of this picture and hardly any galaxies at all on the lower left. But that is not what the universe looks like. It is "the same all over". Astronomers believe that this very "sameness" of the universe is a clear indication of an "inflationary phase" of the universe.

Another argument for cosmic inflation is that the universe definitely appears to be "flat":



A flat universe, a positively curved universe and a negatively curved universe.

Our universe appears to be all but perfectly flat. Even the cosmic microwave background radiation, the echo of the Big Bang, bears witness to the flatness of the universe:



The size of the individual temperature variations in the cosmic background radiation, shown here as colored patches, appear to be just what theory predicts that they would be if the universe is flat.

But flatness is an unlikely state for the universe. If the universe is flat, it means that it "balances on a knife's edge" of equilibrium. If the universe had contained a bit more mass and energy than it does for its size, then it might already have "crashed back upon itself" and squeezed itself out of existence in a catastrophic "Big Crunch". If it had contained less mass and energy than it does for its size, then it might already have blown itself apart in an expansion so violent that it would have had little or no time to form stars and galaxies, much less terrestrial planets and people.

A flat universe is unlikely. But ours appear to be flat. If our universe wasn't flat, we probably wouldn't be here.

Here is where cosmic inflation comes in again. By violently inflating the universe, inflation reduced the "curvature" of space.



Our universe might still not be perfectly flat. But if our universe started out as something highly curved, and then only a part of that curved space got "blown up in size" due to inflation, then much or most of that curvature would disappear. If we live in a universe that is just a "strongly-blown-up-part" of an original, highly curved universe, then we will find ourselves living in an all but flat universe.

Today, inflation is a real buzz word in the astronomical community. When astronomers discuss the origin of the universe, they invariably take inflation into account.

Cosmic inflation is certainly an accepted reality in the world of astronomers today.

Ann