Why do we need cosmic inflation?

Paul Sutter is an astrophysicist at Ohio State University and chief scientist at the COSI Science Center. Sutter is also the host of "Ask a Spaceman", "Space Radio" and directs AstroTours around the world. Sutter contributed this article to Expert Voices: Op-Ed & Insights from Space.com.

The Big Bang model is our most successful explanation of the history of the universe in which we live. It is ridiculously easy to summarize its basic framework in a single phrase that can be t-shirt: A long time ago, our universe was much smaller. From this simple statement come verifiable predictions that have been verified by decades of observation. The rate of expansion of the universe. The cosmic microwave background. The production of the lightest elements. Differences between near and far galaxies. All the juicy proofs that make cosmology a science.

But there are some problems. [The Universe: Big Bang to Now in 10 Easy Steps]

The Big Bang "vanilla" model, without further additions or modifications, can not explain all the observations.

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Eyes on the horizon

We can see a huge volume of raw space. Our observable universe is over 90 billion light years in diameter. And further we look deeper we look in the past. All around us, the cosmic background of microwaves, the remains of fossil light released when the universe was barely nascent – it was only 270,000 years old, well over 13.8 billion years ago.

This light comes to us from the confines of the cosmos, so far away that it is now inaccessible to us. And different sections of this background light are inaccessible to each other. In the marvelous jargon of physics, the regions of the cosmic microwave background are not connected causally. In other words, for a part of the boundaries of our observable universe to communicate with another party over the previous 13.8 billion years, the signals it sends would have had to be faster than the speed of light.

Which would not matter at all if the cosmic background of the microwaves was not perfectly smooth. The infant universe had the same temperature for a share on a million. How is everyone so well coordinated when changes in one area have not had the time to influence others?

Straight and narrow

As far as we can judge, the geometry of our universe seems to be perfectly, totally, so boringly flat. On large cosmic scales, the parallel lines remain parallel forever, the inner angles of the triangles add up to 180 degrees, and so on. All the rules of Euclidean geometry that you learned in high school apply.

But there is no reason so that our universe is flat. On a large scale, it could have had any old desired curvature. Our cosmos could have had the shape of a giant, multidimensional beach ball or a saddle of riding. But no, it took flat. And not just a little flat. In order for us to measure no curvature to a precision of a few percent in the present universe, the young cosmos had to be flat at one percent.

Why? Of all the possible choices for curvature, does not it seem a little suspicious, almost perfectly flat? And indeed, we suspect that there is a reason for flatness, and that it's not just a fluke of the die.

Just a pole

Magnetic monopoles are theoretical beasts; Fractures in the space-time itself that present only one of the magnetic poles – imagine a particle at north or south pole wandering in its solitary. (In matter as we know it, an object with a magnetic north will also have a magnetic south at its end.) According to our best models of the extremely ancient universe (as in the age of 10 ^ -35 seconds, and no, it's not a typo) an exotic process should have absolutely overwhelmed our cosmos with these villains.

These monopolies should be so common that they would be part of our daily cosmological life. And yet, we have not seen evidence for one. Zero. Nothing. No monopoly monster seems to be hiding in the brackish waters of the dark universe.

So where did they go? They should have been made in abundance by the time our universe became interesting, but they could not be found.

Just do things big

The best solution we have to these puzzles is a process called inflation. The idea was first proposed – and invented! – by physicist Alan Guth in 1980, when he suggested that the same exotic process that flooded the universe with magnetic monopoles could have resulted in the cosmos in an era of extremely rapid expansion.

Imagine if I inflated you – your body, your guts, your brain, your skeleton, everything else – to the size of all our observable universe. And imagine that it takes me less than 10 ^ -32 seconds. This is a serious expansion, and precisely what we mean by inflation. Guth proposed that when our universe was incredibly young, inflated to such gargantuan scales in less than a blink of an eye.

For Guth, it was the cleanest way to solve the problem of monopoles. By making the universe so damn largemonopolies simply dilute. Our observable parcel of the universe is only a small corner of all shebang, and there is so much volume that we should not expect to encounter a monopoly like never before.

This inflationary era also solves the other two weaknesses of the Vanilla Big Bang. The pre-inflationary universe had ample time to coordinate and equalize temperatures before switching to a much larger state, projecting previously connected regions out of any future contact. And in such a huge cosmos, we could not help but measure a flat geometry in our observable patch. Who cares about the curvature of the entire universe? She is so great that she will seem flat to us. The Earth is curved, but my backyard is beautiful and flat, because it is so much smaller than the surface of our planet. Just apply the same logic to cosmological scales and you are in gold.

Nevertheless, the underlying mechanisms of inflation are poorly understood and, to be considered a half-decency scientific theory, it can not simply explain current observations, but make predictions for those to come .

And it will be history for another day.

Learn more by listening to the episode "Why do we need a cosmic inflation? (Part 2)" of the Ask a Spaceman podcast, available on iTunes and on the Web at http: // : //www.askaspaceman.com. Thanks to Massimiliano S., Lorenzo B., @ZachCoty, Pete E., Christian W., @up_raw, Vicki K., Thomas, Banda C., Steve S., Evan W., Andrew P., @MarkRiepe, @ Luft08, @kazoukis, Gordon M., Jim W., Cosmic Wakes, Floren H., Gabi P., Amanda Z. and @scaredjackel for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter. Follow us on twitter @Spacedotcom and on Facebook. Original article on Space.com.