Check out this Uncertainty Principle episode about the enormousness of the universe, and gravitational lensing (much more interesting than it sounds). Transcript Below
The universe, is a pretty big place. It’s doubtful many people truly understand how staggeringly huge it is. When you start to grasp the immensity of space and even time, “big” and its synonyms cease to really have any meaning. By definition, it encompasses everything that is known to exist as well as the things we don’t yet know about; so when the late astrophysicist Carl Sagan wrote, “The cosmos is all that is or was or ever will be,” (clip?) we can be sure that what he said was true. The observable universe boasts a 92 billion light year diameter and a population of over a hundred billion galaxies. Each galaxy contains perhaps a hundred billion stars. And beyond all this, past the cosmic horizon–the most distant light that has been able to reach us in the universe’s 14 billion year history–who knows? It is not only possible, but likely, that there is much, much more universe beyond that. So much more as to make the known universe inconsequential. If modern inflationary theory is correct, then the actual size of the universe may have a lower bound of 1023 times larger than what we can see. But despite containing all of this stuff, the universe is still mostly empty space. We’ve barely explored our own solar system because of how far apart everything is, but compared to the distance between stellar neighbors, the bodies of our solar system are close friends.
Go out on a clear night, away from any light pollution, and you will see the sky as our pre-civilized ancestors did: full of starlight. You should even be able to see the soft glow of our galaxy, stretching in an arc across the sky. Yet, the amount of stuff in the universe verses it’s emptiness means the distance between even the closest star systems are incomprehensibly immense. Because of this, the sky might as well be pitch black. There’s an eerie closeness in a radiant rural sky–one that seems absent from a more light polluted area. For me, the black, starless city sky exacerbates the emptiness of space, and the distance of the stars. It creates a disconnect, one that embiggens a cosmic perspective. Our immediate terrestrial experience doesn’t allow us to see more than a few miles away, but still the stars are there. They shine brightly enough to be easily seen from hundreds of light-years away–despite being, as of now, completely unreachable. Not only are the stars visible but deep sky objects are as well, objects that are so big that many of them take up a large space in our sky.
Take the Andromeda Galaxy, for example. It is the closest spiral galaxy to the Milky Way with two and a half million light years between us and it. Even though it is so distant, Andromeda itself is so large that if it were bright enough, it would take up as much space sky as six full moons. Granted, the moon is smaller than you think. Being only half a degree across, the moon can be covered up by your thumb held at arms length.
But these are little things, let’s talk big. Having a lot of space allows for a lot of stuff. Our galaxy, the Milky Way, could have anywhere from one hundred to four hundred billion stars, each massive, blinding, and perhaps host to their own planets. Though, our galaxy is still on the small side. Large elliptical galaxies can contain over a trillion stars. These colossal galaxies are the ancient remains of galaxies in the early universe colliding to form a more massive construct–much like the inevitable collision of the Milky Way and Andromeda. Because of their age, very little stellar formation occurs in elliptical galaxies, and much of the stars in them are in the later stages of their lives. You could say this is what a retired galaxy looks like. Though being more-or-less featureless, elliptical galaxies do something very interesting.
Thanks to Einstein’s theory of Relativity, we know that gravity can bend space, and time. The astronomer Fritz Zwicky suggested that large clusters of such galaxies could act as a gravitational lens. The amount of mass in large galaxy clusters can distort space so much that the light of background galaxies can be bent and warped. They can even distort light so much that galaxies can appear multiple times within a single photograph. In January of 2014, NASA released a Hubble image of the 4 billion light year distant galaxy cluster Abell 2744, also known as Pandora’s Cluster. In the lower left hand part of the image, a blue-red galaxy is distorted, and mirrored by the gravity of the foreground galaxies. If gravitational lensing didn’t occur, we wouldn’t be able to see such galaxies, because while being distorted, the light of those galaxies is magnified, brightened, and bent toward us. It’s the universe’s naturally occurring telescope.
The sun can also bend light, but just a little bit. Even you are bending light, because you have mass and you have a gravitational pull, but the effect is negligible at best. But all of this is weak compared to a black hole. There is much more to cover about black holes than can be done here, but the gravity of a black hole is immense, so much so that it earned its name–black hole. It is called black because they don’t radiate any light. The gravity is so strong that they pull in even light, which, I will remind you is the fastest thing in the universe. Light that doesn’t get pulled into a black hole, but gets close enough to one, can actually be caught in orbit around a black hole. Nothing distorts light the way a black hole does.
Now if I’ve done my job, you’re probably feeling a little small right now. My answer to you is: don’t. The universe from the smallest scale to the largest stretches from the Planck Length (1.5×10-35 meters) to the diameter of the universe (4.3×1026 meters). The website scaleofuniverse.com illustrates this perfectly. An individual human is somewhere above the middle. There is more small than there is big in the universe, and keep in mind that all the stuff, big and small in the universe, is made of the same small stuff.
Thanks for listening, and keep exploring.