Our place in the cosmos

Neil Swidey writes:

The Big Bang theory offers an explanation for how the early universe expanded and cooled and how matter congealed, from a primordial soup into stars, planets, and galaxies. What it describes, then, is the aftermath of the Bang. But it is effectively silent on why or how that first massive expansion happened or where all the original matter came from.

As Alan Guth, the physicist who holds the MIT professorship named after Weisskopf, puts it, “The Big Bang theory says nothing about what banged, why it banged, or what happened before it banged.”

Did you know there was a "flatness problem" with the Big Bang theory?

The flatness refers to the geometry of our continually expanding universe, where its mass density and expansion rate remain exquisitely balanced. If that balance tipped even slightly in either direction, the universe would either fly apart or collapse on itself. Yet because the universe has been expanding for 14 billion years, even slight variations in the beginning should have become exaggerated by now, to disastrous effect.

Yet the Big Bang theory offered absolutely no explanation for how that exceedingly precise balance might have come about. It would seem crazy to assume that it was just a coincidence.

ANOTHER TALK, BY THEN Harvard physicist and future Nobel laureate Steven Weinberg, convinced Guth that there was important science to be done pondering the universe’s first infinitesimal fraction of a second. Other researchers dismissed this as impossible to study and best left to science-fiction writers.

Guth (rhymes with “truth”) has had opportunity to trot out some version of that line for more than three decades now, ever since he came up with his revolutionary prequel to the Big Bang theory. For most of that time, Guth, a short, slightly rumpled man who displays a refreshing mix of modesty and self-confidence, has been making his case in academic lectures. He began using flimsy overhead transparencies and later moved to PDFs, but the message has remained the same. He has continued to promote it with undiminished enthusiasm, even as observational evidence remained elusive and seemed unlikely to emerge in his lifetime, if ever.

Then in March, he received an e-mail from Harvard astrophysicist John Kovac, who had spent a good chunk of the past eight years looking at data from highly sophisticated telescopes planted on the South Pole. “Dear Alan,” the e-mail began, “I am eager to talk to you about a topic that concerns both your research and mine. It is important and somewhat urgent, and I would be grateful if you would keep my request to speak with you confidential.”

The next day, Kovac appeared in Guth’s MIT office, having used a back staircase to avoid detection. A week after that, Alan Guth, at age 67, became an academic celebrity, treated not just as a scientist who finally had backing for his theory, but also as a sort of seer who could help explain our place in the cosmos.

Here is how Guth's theory of an inflationary universe works:

Using the theories of Einstein and others, Guth points out that at extremely high energies, there are forms of matter that upend everything we learned about gravity in high school. Rather than being the ultimate force of attraction that Newton and his falling apple taught us, gravity in this case is an incredibly potent force of repulsion. And that repulsive gravity was the fuel that powered the Big Bang.

The universe is roughly 13.8 billion years old, and it began from a patch of material packed with this repulsive gravity. The patch was, as Susan notes, tiny — one 100-billionth the size of a single proton. But the repulsive gravity was like a magic wand, doubling the patch in size every tenth of a trillionth of a trillionth of a trillionth of a second. And it waved its doubling power over the patch about 100 times in a row, until it got to the size of that marble. All that happened within a hundredth of a billionth of a trillionth of a trillionth of a second. As a point of comparison, the smallest fraction of time that the average human can detect is about one-tenth of a second.

The ingredients of what would become our entire observable universe were packed inside that marble. While the density of ordinary material being put through that kind of exponential expansion would thin out to almost nothing, a quirk of this repulsive-gravity material allowed it to maintain a constant density as it kept growing. But at a certain point — while the universe was still a tiny fraction of a second old — inflation ended. That happened because the repulsive-gravity material was unstable, and, like a radioactive substance, it began to decay. As it decayed, it released energy that produced ordinary particles, which in turn formed the dense, hot “primordial soup.” At that point, after Guth’s model has explained what banged, why it banged, and what happened before it banged, he takes a bow and lets the standard Big Bang theory take over from there.

In what another scientist termed “a telegram from the first moments of time,” Kovac’s team found the smoking gun for inflation: evidence of gravitational radiation, or more specifically, swirling patterns in the polarization of the cosmic microwave background. In the viewfinder of their telescope on the South Pole was light formed just 380,000 years after our universe banged onto the scene. And in that ancient light they detected gravitational radiation that is far older, having been emitted during the universe’s first fraction of a second of existence.

We already know that our sun is just one of at least 100 billion stars in our galaxy and our galaxy is just one of 100 billion in the observable universe. But Guth says the most plausible models of inflation suggest something called eternal inflation. That means that once inflation starts producing universes, it never stops.

And, by extension, Guth says, that would mean that we’re not just part of a vast universe, but that ours is merely one “pocket” universe in an ever-expanding multiverse. So if you’ve just come to terms with how infinitesimal a speck we earthlings are in the whole cosmic scheme of things, get ready to feel even smaller.

Read more here.