What Is Beyond The Universe?
If you were to fly in a straight line, faster than the speed of light, directly toward the edge of the universe… you'd eventually end up back where you started, because there IS no edge. Take 5 seconds and think about that. Howdy people who want to have their mind blown. Trace here for DNews. This one was super fun to research. A study came out recently in Physical Review Letters, stating that cosmology was safe; the universe was, indeed, isotropic. I know you're relieved. When the ancient Greeks looked up at the sky, they realized the universe could be one of two things, infinite -- stretching forever in every direction, or finite -- with an edge. When Newton described the law of gravity, he thought about this too, and figured it must be infinite, because otherwise all the gravity out there would have collapsed the universe by now.
Then, Einstein assumed the universe was static -- creating a cosmological constant to make his math work. But then, Edwin Hubble came along… In 1925, Edwin Hubble was looking at galaxies. He was a lawyer by training, but loved cosmology and astronomy. He got time on a telescope in California, and began measuring the doppler shift of the light coming from galaxies. Doppler shift is why an ambulance or train sounds different coming at you than after it passes. That frequency shift is measurable, and he found every galaxy we could see was flying away from us. He realized space is expanding! He published his findings in the Proceedings of the National Academy of Sciences in 1929, and holy crap. Einstein called his cosmological constant his greatest blunder. Mathematician Georges Lemaître solved Einstein's equations in this expanding universe, and once we realized it was expanding, we could assume it started somewhere and thus, the Big Bang was conceived!
This was (and is) huge, and only getting bigger. Expansion pun! Okay, so, if all that's true, and our universe is expanding and isotropic what does that even mean? Think of our universe as baking raisin bread. If each of the raisins is a galaxy, as the bread bakes, the dough rises, and the raisin-galaxies expand away from each other along with the rise, in all directions at once! If this happens irregularly, the universe is anisotropic -- like the grain of a tree, it's stronger or tends to have layers, or striations where it might expand faster or slower. Isotropic universes, like ours, they don't have those. They're consistent, smooth, homogenous, and symmetrical… ours is all that. According to Astronomer Phil Plait, it's expanding at 74.2 kilometers, per second per megaparsec (plus or minus 3.6 kilometers) -- it's now called the Hubble Constant. A galaxy 10 megaparsecs away, Plait wrote for Discover Magazine, would be moving away from us at 742 km/sec Basically, every million years, galaxies are point-zero-zero-seven percent farther away from each other. Trust me. That's really really fast. And, thanks to dark energy, it's getting faster. But that's a whole other story. I'm sure you're thinking, okay cool, our isotropic, infinite universe is expanding. Fantastic. Expanding into… what? That's the complicated part. The universe, by definition is all existing matter, and space as a whole. If the universe is infinite and homogenous, then it's not expanding into anything, it's just… expanding. Think of it this way... You're an ant, standing on a balloon of incredible size. It's so big it seems flat from your perspective. As the balloon continues to inflate, it's expanding in every direction.
No matter which direction you look, the balloon is getting larger! No matter how fast or far you run, you'll eventually end up back where you started. Like a video game from the 1970s. You go off the screen, and you just come back on the other side. This is how astronomers look at the universe, but it's not a 2-dimensional surface of a balloon, it's a three-dimensional region, expanding in a 4-dimensional universe in every direction at once. No matter where you go, you'll eventually end up still in the universe, and back where you started. This is also why there's no center of the universe. Where would the center of the balloon's surface be? Knowing the universe is expanding, and how fast, and that it's isotropic, keeps cosmology, Einstein and hundreds of other scientists' theories safe, for now. But as we learn more, and measure deeper and deeper into the universe, who knows what we're gonna see.
Then, Einstein assumed the universe was static -- creating a cosmological constant to make his math work. But then, Edwin Hubble came along… In 1925, Edwin Hubble was looking at galaxies. He was a lawyer by training, but loved cosmology and astronomy. He got time on a telescope in California, and began measuring the doppler shift of the light coming from galaxies. Doppler shift is why an ambulance or train sounds different coming at you than after it passes. That frequency shift is measurable, and he found every galaxy we could see was flying away from us. He realized space is expanding! He published his findings in the Proceedings of the National Academy of Sciences in 1929, and holy crap. Einstein called his cosmological constant his greatest blunder. Mathematician Georges Lemaître solved Einstein's equations in this expanding universe, and once we realized it was expanding, we could assume it started somewhere and thus, the Big Bang was conceived!
This was (and is) huge, and only getting bigger. Expansion pun! Okay, so, if all that's true, and our universe is expanding and isotropic what does that even mean? Think of our universe as baking raisin bread. If each of the raisins is a galaxy, as the bread bakes, the dough rises, and the raisin-galaxies expand away from each other along with the rise, in all directions at once! If this happens irregularly, the universe is anisotropic -- like the grain of a tree, it's stronger or tends to have layers, or striations where it might expand faster or slower. Isotropic universes, like ours, they don't have those. They're consistent, smooth, homogenous, and symmetrical… ours is all that. According to Astronomer Phil Plait, it's expanding at 74.2 kilometers, per second per megaparsec (plus or minus 3.6 kilometers) -- it's now called the Hubble Constant. A galaxy 10 megaparsecs away, Plait wrote for Discover Magazine, would be moving away from us at 742 km/sec Basically, every million years, galaxies are point-zero-zero-seven percent farther away from each other. Trust me. That's really really fast. And, thanks to dark energy, it's getting faster. But that's a whole other story. I'm sure you're thinking, okay cool, our isotropic, infinite universe is expanding. Fantastic. Expanding into… what? That's the complicated part. The universe, by definition is all existing matter, and space as a whole. If the universe is infinite and homogenous, then it's not expanding into anything, it's just… expanding. Think of it this way... You're an ant, standing on a balloon of incredible size. It's so big it seems flat from your perspective. As the balloon continues to inflate, it's expanding in every direction.
No matter which direction you look, the balloon is getting larger! No matter how fast or far you run, you'll eventually end up back where you started. Like a video game from the 1970s. You go off the screen, and you just come back on the other side. This is how astronomers look at the universe, but it's not a 2-dimensional surface of a balloon, it's a three-dimensional region, expanding in a 4-dimensional universe in every direction at once. No matter where you go, you'll eventually end up still in the universe, and back where you started. This is also why there's no center of the universe. Where would the center of the balloon's surface be? Knowing the universe is expanding, and how fast, and that it's isotropic, keeps cosmology, Einstein and hundreds of other scientists' theories safe, for now. But as we learn more, and measure deeper and deeper into the universe, who knows what we're gonna see.
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