As I was lying in bed late the other night, I was still thinking about the physical universe, and a bunch of images arose in my mind. Earlier that evening, I had watched an episode of Nova called “Hunting the Edge of Space: The Ever Expanding Universe.” As I lay on my back, I thought about what surrounds each of us – there are one’s immediate surroundings, of course, as well as the Earth below and the atmosphere above, and then there’s the neighborhood of our solar system with its wide variety of planets, and then there are the stars, planets, and other things that populate our Milky Way galaxy, and beyond that, a hundred billion other galaxies, each containing at least a hundred billion stars. And so I lay in bed bathed in images and awe – it’s pretty hard not to be astounded by the immensity and beauty of the physical universe.
Many of the images that emerged in my mind that night were supplied by the Nova program I had watched earlier. Like many people, I owe a dept of gratitude to the people behind Nova. Nova does such a terrific job with physics and astronomy – watching an episode is kind of like hiking on a highline trail in Rockies: though you’re going along at a very comfortable pace, your adrenaline is running high, and you encounter one breathtaking vista after another. After the hike ends, the exhilaration lingers for quite a while, and the trail is easy to revisit in memory during the weeks and months to come.
The ongoing partnership between humans and telescopes figures prominently in this particular episode of Nova. Early in the episode, the narrator talks about Edwin Hubble, who fastidiously studied images generated by an enormous telescope – the largest of its time – located atop Mount Wilson near Pasadena, California. At one point in his research, Hubble was paying particular attention to what appeared to be a fuzzy, star-filled patch of light located in the constellation of Andromeda. This fuzzy patch of light was then known as the “Andromeda Nebula.” With painstaking care, Hubble studied many images of the Andromeda Nebula, always on the lookout for a certain kind of variable star called a “Cepheid variable.” Cepheid variable stars act as standard candles – astronomers know how bright Cepheid variables are intrinsically, so when they locate such a star and measure its brightness (relative to us), they can calculate how far away it is. Hubble eventually succeeded in locating a Cepheid variable within the Andromeda Nebula and was thereby able to show that the distance between us and the Andromeda Nebula is many times the distance between us and the most distant stars of our own galaxy. In this way, he showed that the universe stretches far beyond the borders of our particular galaxy. (It’s hard to imagine how extraordinarily exciting Hubble’s discovery must have been – presumably, for Hubble himself, all of that painstaking work must have seemed a more than fair price to pay for such an experience.)
Due to Hubble’s work, what was then called the “Andromeda Nebula” is now familiar to us as the “Andromeda Galaxy.” We know now that the Andromeda Galaxy is part of a cluster of galaxies to which our Milky Way Galaxy itself belongs, a cluster containing between 30 and 40 galaxies that astronomers call the “Local Group.” The Andromeda Galaxy is stunningly beautiful, perhaps in part because it is a particularly lovely spiral galaxy – its spiral arms wind away from its bright, bulging center in airy, luminous arcs. Under good conditions, you can see the Andromeda Galaxy with the naked eye. It’s pretty thrilling to look at, especially when you think about how far and long its light has traveled on its way to the encounter with your eye: the Andromeda Galaxy is about two and a half million light years away, so by the time its light reaches your eye, that light has been traveling for about 2.5 million years.
(If you’ve never seen the Andromeda Galaxy in the night sky and you’d like to do so, it’s pretty easy to find. One way to find it is to first locate the constellation of Cassiopeia, a prominent constellation that looks like a ‘W’ (or an ‘M’, depending on how you’re looking at it). On the chart to the right, the Andromeda Galaxy is right in the center, directly below Cassiopeia, marked in red and labeled ‘M31’. In the actual sky, the galaxy looks a bit like a fuzzy thumbprint of light.)
It seems hard to believe that the discovery of galaxies beyond our own occurred so recently in human history. It wasn’t until the 1920s that Edwin Hubble located a Cepheid variable star within the Andromeda Nebula and used it to establish that the physical universe extends far beyond the borders of the Milky Way. So even as recently as a hundred years ago, the known universe did not extend beyond the galaxy we inhabit, which is in fact only one of at least a hundred billion galaxies. Of course, these days, powerful telescopes enable us to see all kinds of galaxies. During one particularly striking segment in the Nova episode, the narrator describes a project involving the Hubble Space Telescope: in 1995, astronomers pointed the Hubble toward what seemed to be an empty region, a place of plain, old, dark space. Here’s an excerpt from the transcript of this particular part of the program:
NARRATOR: In 1995, Hubble’s ability to look back in time is put to the test. Astronomers decide to turn its gaze onto one dark point in the universe, just to find out what they can see.
MARIO LIVIO: We picked one tiny point in the sky, in which there was, essentially, nothing there.
MATT MOUNTAIN: We stared, for 10 days, at a single dark spot on the sky.
NARRATOR: It is as if Hubble was peering through a tiny keyhole of our Milky Way galaxy, to the universe beyond.
MATT MOUNTAIN: The size of the spot that we looked through was no more than a drinking straw.
NARRATOR: What Hubble sees is extraordinary.
MATT MOUNTAIN: And what we saw were 10,000 galaxies in that single spot.
MARIO LIVIO: Every point of light that you see in the image represents a galaxy with a hundred billion stars like the Sun.
NARRATOR: The image is called the Hubble Deep Field. It shows light from galaxies four-billion times fainter than anything we can see with the human eye, light that set out on its journey billions of years ago.
MARIO LIVIO: If there is something to give you a sense of the size of the universe and its depth, it’s this kind of image.
This is the kind of anecdote that gives one gooseflesh, yes? An itty bitty part of the sky looks dark and dead, but look more closely, and it’s full of thousands of galaxies – thousands of galaxies, each containing billions upon billions of stars. Scratch the surface of the physical universe, and there’s incredible detail, color, complexity, and beauty.
The Nova episode also describes how telescope data helped astronomers determine that the universe is expanding, that it had a beginning as a tiny singularity, and that its rate of expansion is increasing (rather than staying the same or decreasing). The narrator explains that dark energy is responsible for the expansion. At this point in human history, the nature of dark energy is largely mysterious, though astronomers are confident that 72% of the universe as a whole is constituted by dark energy. Another 23% is constituted by dark matter; whereas dark energy pushes things outward, dark matter pulls things inward – were there no dark matter, galaxies would fly apart. Only a measly 5% of the physical universe is constituted by stuff that’s familiar to us: protons, neutrons, electrons, and photons, for instance.
So if you lie face-up under the night sky and think about the billions of galaxies that surround you on all sides, each with its billions of stars, don’t forget to include the reams and reams of dark matter and dark energy that weave through all of those galaxies.
Do you ever wonder how your experience of the night sky (on a cloudless night) differs from what it would have been had you lived a hundred years ago and been unaware of anything beyond the Milky Way Galaxy? Do you wonder how your experience would have been different had you lived, say, 3000 years ago? When I do these kinds of thought experiments, my first inclination is to think that my experience would be very different, and that a more limited view of the universe would naturally be associated with a more mundane experience of the night sky. But upon reflection, I find myself questioning my initial inclination. Perhaps, the night sky is just simply astounding, whatever its nature.
In any case, when one considers all of the physical structures that make up the universe, from tiny quarks to clusters of galaxies, it’s hard not to feel amazed. And it’s hard not to be amazed by the laws of physics themselves: the laws that give the universe’s constituents their physical natures and, in some sense, shape the furniture of the universe into the forms it takes. As I think about this experience of amazement and awe, science writer Martin Gardner comes to mind. Gardner offers a particularly satisfying expression of this kind of amazement in his book The Whys of a Philosophical Scrivener.
(Gardner is perhaps best known for his work as a columnist for the magazine Scientific American. He was an extremely creative person, excelling in mathematics, delighting in science, dabbling in philosophy, and participating in all sorts of endeavors. He just recently died – less than a year ago – at age 95.)
One particularly intriguing idea that Gardner discusses is the view that the laws of physics will never be fully understood and codified, that there will always be much that lies beyond our current understanding of physical reality, just as there is much that lies beyond what we can see with the naked eye when we look up at the sky during a clear night. He is drawn to the view that “nature is infinitely exhaustible, and there will be always be wheels within wheels, and wheels outside wheels. Murray Gell-Mann once compared physics to the task of perpetually cleaning out a cluttered basement. No sooner is the basement’s outline seen than somebody finds a cleverly hidden trapdoor leading to a vast subbasement. David Bohm and Stanislaw Ulam are among those who believe that the universe has infinitely many levels of structure in both directions, toward the large and toward the small.” (p. 328 of The Whys of a Philosophical Scrivener)
Late in the book, Gardner writes about a certain sort of sensation, “the sensation of overwhelming awe that comes upon certain people at times when they reflect on the fact that anything exists at all.” (p. 296) Gardner does a superb job of conveying that sense of awe – awe in the face of what exists, awe in the face of the forms and shapes that the furnishings of the universe happen to take (furnishings from elementary particles to superclusters of galaxies), and awe in the face of the mathematical equations that in some sense mold the universe and give it its own distinct character.
Even though Gardner’s understanding of physics and astronomy was much deeper than that of a typical PBS viewer, I can’t help but wonder whether he was a fan of Nova…