What Does an Expanding Universe Mean?

From Robert Lawrence Kuhn, host and creator of Closer To Truth:

That our universe is expanding is one of humanity’s monumental discoveries. Starting from something infinitesimally small, the universe has become something majestically large. How could this happen? What could this mean?
Normal people hardly ever think about the expanding universe; I think about it all the time. That’s why I love speaking with Alan Guth, whose theory of cosmic inflation revolutionized cosmology.
As Guth puts it, “Surprisingly, in spite of its name, the ‘big bang’ really says nothing about the big bang itself: what’s the bang, why it banged, or what happened before the bang. The ‘big bang’ is really the theory of the aftermath of the bang.” As for “why the bang,” Guth says that “inflation is what [likely] propelled the universe into this gigantic expansion, which we still see today. … [Inflation’s] gravitational repulsion leads to an exponential expansion, which means that in a certain [incredibly short] period of time, the universe doubles in size, then in that same time period, doubles again and again and again … ”
To transform the universe from the size that Guth thinks it had at the beginning of inflation—far far smaller than one single atomic particle—to what it needs to have had at the end of inflation so that the universe could ultimately include everything that we see today, would require about 100 doublings. These doubles happen unbelievably rapidly.
Using what particle physicists call “grand unified theories,” the time for each doubling, Guth says, was determined to be “about 10-37 seconds, a decimal point followed by 36 zeroes.” This means that 100 doubles takes only 10-35 seconds (10-37 x 100 = 10-35)—one hundred million billion billion billionths of a second!
While most people assume that the big bang was the absolute beginning of the universe, the big bang actually didn’t begin until after inflation ended—in fact, it is the end of inflation per se that is said to have triggered the big bang in the first place. The reason given is that the repulsive gravity that drives inflation is unstable, so when it decays, it releases vast energy and generates normal forms of matter. It is this release of energy and matter at the end of inflation that becomes the energy and matter of the present universe.
So cosmic inflation is what makes the big bang “go bang,” creating energy and matter, nicely balanced with gravitational energy, in what Guth calls the “ultimate free lunch”: According to him, one gram of this very special matter, worked by the stunning powers of inflation, generates the entire universe.
For decades, cosmologists assumed that while the universe was expanding, driven by the outward-pushing explosive force of the big bang, it would eventually have to slow down, resisted by the inward-pulling counterforce of gravity generated by all the vast amount of matter in the universe.
But a huge surprise was laying wait: The expansion of the universe was discovered to be accelerating, not slowing down as everyone expected. Cosmologists were dumbfounded. Saul Perlmutter is one of the discoverers of what was one of the biggest shocks in scientific history.
“The expansion of the universe allows us to ask these fundamental, philosophical questions,” Perlmutter says. “How could you get better than, ‘Will the universe last forever?’”
Will the universe get ever larger and more diffuse? Or could it reverse direction, go the other way? Could the universe begin to contract and eventually collapse? Could the universe end? To Perlmutter, these are scientific questions.
His mechanism of solution: Weigh the universe! That’s right, weigh it, like a piece of meat. Because if there would be more than a certain critical amount of stuff in the universe, then, as a result of the gravity of this stuff, gravity would eventually win the power struggle and the rate of universal expansion would slow down and perhaps reverse.
“When we actually did the measurements,” Perlmutter says, “the results told us that not only was the expansion of the universe not slowing down, it was actually speeding up! That was really a shock. Apparently, there’s something that we had not accounted for in our physics that’s driving the universe, making it expand faster and faster. … We’re calling this energy which pervades all space ‘dark energy,’ but this name is just a placeholder to describe our ignorance—we simply do not know what this stuff is.” Making the mystery deeper, this so-called “dark energy” seems to constitute about 70 percent of all the energy density in the entire universe (all energy and all matter). “Most of the universe is something we know very little about,” says Perlmutter.
With such breathtaking new visions of an expanding universe, does new meaning emerge? I ask Andrei Linde, who extended the theory of inflation in our universe to eternal, chaotic inflation that generates innumerable universes.
“My personal attitude maybe differs from that of other cosmologists,” Linde says. “Physicists study things because they’re interested in how the world works. I also look at the universe with this perspective. But sometimes I have a different perspective. The universe is our cosmic home, and maybe if I want to know something about ourselves—something about our lives, our deaths—maybe the universe will provide cosmic perspective. … Look at us. We emerge from what? From nothing! We are born and then we die. What was with us before? What will be with us later? Maybe the study of cosmology will not tell us anything new about ourselves. But maybe, parallels can teach. Maybe, by learning something deep about the birth and death of the universe, we can learn something profound about ourselves. This is one of the most interesting if speculative consequences of cosmology.”
That the universe is expanding is sure. That the expanding universe bears meaning is not. Though some cosmologists do see meaning, many see no meaning—the universe is a “brute fact.” It is what it is; that’s all it is—and that’s all there is.
If there is meaning, what kinds of meaning? Multiple universes, created by the same repulsive energies that power the expansion? This is an increasingly common opinion. Window into new realities? A prevailing consciousness? Theistic fingerprints? Grand harmonies of birth and death between the universe and humans? Views of these kinds are entertained more by philosophers and theologians than by cosmologists.
Though debate about the meaning of the universe’s expansion continues, there is little debate about the uniqueness of our time. In little more than 100 years, humanity has progressed from virtual ignorance of the universe to be able to see, and largely explain, the staggering vastness of the cosmos.
Of this one thing I am sure: If there is meaning in the cosmos, the expansion of the universe is a clue, bringing us closer to truth.

Robert Lawrence Kuhn speaks with Alan Guth, Paul Steinhart, Saul Perlmutter, George Ellis, and Andrei Linde in “What Does an Expanding Universe Mean?” —the third episode in the new season of the Closer To Truth: Cosmos, Consciousness, God TV series. The series airs on PBS World (often Thursdays, twice) and many other PBS and noncommercial stations. Every Thursday going forward, participants will discuss the upcoming episode.

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