One of the coolest classes I took at U.F. was Intro To Astronomy, taught by a funny old German guy named Heinrich Eichorn who, I later learned, was Chair of the Astronomy Department. (Yes, this was back in those quaint old days when top-notch professors had to actually, you know, teach class. And not just to grad students!) While Professor Eichorn’s lectures tended to meander a bit, he had a genuine enthusiasm for the subject that students, myself included, could sense and respond to. I remember one particular class when, in one of his usual, off-topic asides, he said, “We know the universe is not infinite. If it were, then every point in the sky above us would always be as bright as a star.”
For me, this was one of those mind-blowing moments when one is exposed to the wisdom of the ages. In this case, it was that of another German astronomer, Johannes Kepler, who in 1610 realized that if the universe really were infinitely large, and infinitely old, then every line-of-sight direction one looks at in the sky should eventually hit a star. Thus, the entire sky should be as bright as (and, worse still, as hot as) the surface of a star. Nevermind the fact that most of these stars would be very, very far away. Their light would still have an infinite amount of time to reach us, and there would be an infinite number of them shining down on us.
We should all be broiling alive right about now.
This simple observation, now known as Olber’s Paradox (named thus for yet another German astronomer, Heinrich Olbers) seems profoundly simple and obvious, in retrospect. Yet it was compelling enough to satisfy most astronomers for four centuries (including today) that the universe is probably not infinite. It’s just very, very big. Wicked big. Like freakin yuge.
And it keeps getting bigger. I’m not just talking about the stunning revelations made by astronomers in the early 1900s that the universe is expanding in all directions. I’m talking about that fact that, with each new generation of astronomers, the estimated size of the universe continues to increase.
Back in Galileo’s day, the solar system was assumed to be the entire universe, and those strange spiral nebulae that Galileo observed were thought to be mere swirls of gas orbiting not far away the outer planets. The situation improved markedly around the turn of the 20th Century, when astronomers began to tackle the size problem with some real scientific vigor.
The difficulty in estimating the size of the universe is simple and obvious. When looking at a dim star, it’s almost impossible to tell whether it is really dim or just very far away. Conversely, when looking at a bright star, you can’t tell if it’s really bright or just very close. Fortunately, there is a type of star called a Cepheid variable that can be identified at any distance and whose true brightness is relatively fixed. This so-called “standard candle” meant that astronomers merely had to spot them, measure their apparent brightness, and thus calculate their distance.
The situation improved still further when Edwin Hubble began to make the first comprehensive, accurate tally of the red-shifts of individual stars—that is, how far to the red a star’s spectrum appears shifted, and thus a measure of how fast the star is moving away from us. It was already known that virtually everything in the universe, other than a few of the closest nebulae, is moving away from us. Hubble’s great discovery was that the farther a star is away from us, the higher its red-shift. In other words, the farther away it is, the faster it is moving from us.
This implications of this discover were obvious: the entire universe, it seemed, was expanding like a loaf in a hot oven. If one could measure rate of this expansion, then one could extrapolate backwards to a point where the rate was zero, and the entire universe was crushed into a single point. And, thus, one could determine the approximate age and size of the universe.
Simpler said than done. The epic history of the scientific struggle to calculate these figures is recounted in Timothy Ferris’s excellent book, The Red Limit: The Search for the Edge of the Universe. As Ferris writes,
With each revision the universe was perceived to be larger and older, and therefore to be expanding at a more gradual rate, than had been thought before. When Sandage was a graduate student at Caltech, the Hubble constant was being quoted at about a hundred miles per second per million light-years. That is, for every million light-years farther out one looked, one would observe galaxies receding at an additional hundred miles per second velocity. Baade’s work on Cepheid variable stars cut this figure in half; in 1956, astronomers on three continents reduced it further; Sandage scaled it down still more in the 1950s and again in the 1970s, until the “constant” wound up at 10 percent of its original value. According to Sandage’s 1976 figures, galaxies recede at ten miles per second per million light-years distance. Sandage claimed a margin of error of under 15 percent. “It’s a real number now,” he said. This would make the age of the universe (meaning time since expansion began) eighteen billion years, give or take some three billion.
This figure of eighteen billion years meant that the universe would be thirty-six billion lightyears from edge to edge (assuming it has an edge). Of course, this value has continued to fluctuate as telescopes have continued their relentless technological improvement, right up to our current day of space telescopes. Just this year, research made using the James Webb Space Telescope suggests that the universe might actually be twice as old (and twice as big) as previously thought, weighing in at a whopping 53 billion lightyears.
Of course, all of these estimates address the size of the so-called observable universe. That actual, whole Universe is that remainder that has already gotten so far away from us that its stars are receding faster than the speed of light. Thus, most of the actual universe is forever lost to us (unless, of course, people figure out how to travel faster than the speed of light).
Most astrophysicists believe that the whole universe is much, much larger than the observable universe. One theory estimates that the actual universe might be 256 times larger. But this is peanuts compared to some implications of the cosmic inflation theory that has been around since the 1970s. The inflation theory, which posits that the universe underwent a second phase of sudden, explosive expansion not long after Big Bang, has remained popular because it solves many unresolved problems in cosmology, most notably the flatness problem. However, if true, inflation theory would also mean the actual universe is 100 sextillion (1023) times bigger than the observable universe. In other words, if the actual universe were the size of the earth, then the observable universe would be smaller than a single proton.
Of course, there remains the possibility that the universe is, in fact, infinite. After all, Olber’s Paradox falls away when one realizes that most of the universe is already receding from us faster than the speed of light. This infinite universe might be filled with stars, or it might be mostly empty, with an infinite number of “island universes” like our own observable universe expanding within.
Why does this fascinate me so much? Good question. In my experience, whenever people are confronted with such information about the size of the universe (the “billions and billions” of stars that Carl Sagan made so famous), they react in one of two ways. Some merely shake their heads and recoil in a sort of mini-version of the Cosmic Horror that H.P. Lovecraft wrote about. For these people, cosmology is a depressing subject, a reminder of our (humanity’s) puny insignificance in a vast, indifferent universe. Other people, however, react with amazement and wonder. They find that their imaginations are kindled by this incredible, inexplicable vastness.
I am firmly in this second group (which, unfortunately, is much smaller than the first). Maybe it’s because I’m a life-long nerd and fan of science fiction, and I keep thinking of how much room we have to grow in as a species. For all practical purposes, the universe is basically endless.
Another reason is that, even though I write thrillers and hard-boiled detective novels, I am still something of a woo-woo, New Age mystical type. Unapologetically. How can one not believe in some form of the supernatural when confronted with the staggering, sublime size of the universe, not to mention the century-long struggle to measure that size.
And one more fact about the struggle gives me a bit of mystical hope: the universe never gets smaller. With each new technological advancement—that is, with each new generation of telescopes, and each new generation of astrophysicists—our estimate of the size of the universe gets bigger. And more complex. It never gets simpler.
Why do I find that comforting? Because it strongly implies that we’ll never figure everything out. That there will be an end to the struggle, or the story. There will always be another frontier, which means that there will always be hope.
What can I say? I’m an optimist.
Ash Clifton, Writer 