Thursday, June 30, 2011

The Universe is really, really big.

I love pondering over the size of the universe, and coming up with different calculations to try and grasp just how big it is. When I look around me on this planet in everyday life, I feel like a lot of people aren’t actually aware of how massive it is. So, please join me as I attempt to present numbers and analogies in a graspable way.
First of all, as I’m sure a lot of you know, our sun is 93 million miles from earth. Uranus, which is the most distant planet in our solar system, is 1.59 billion miles away. It would take 17.7 years to fly to the sun in a fast jet plane, and 302.5 years to fly to Uranus.
The speed of light is 186,000 miles per second, 669.6 million miles per hour, or 5.86 trillion miles per year. Light is 1,116,000 times as fast as a jet plane, meaning it travels 211 miles for every 1 foot the plane travels.
At the speed of light, the sun is only 8.33 minutes away, and Uranus is 2 hours and 22 minutes away. Imagine that. Traveling at a speed of 186,000 miles every second (7.44 entire loops around the equator of the earth in each second), it takes 2 hours and 22 minutes to reach the farthest planet in our solar system. That’s a very long time for such a speed. But remember, it would take 302.5 years to cover the same distance in a plane.
So, now that we have a concept of how large our solar system is, and how fast the speed of light is, let’s begin to look out at the rest of our galaxy. If you set up a miniature solar system in Seattle, WA, and placed the sun about 60 feet from the earth, the nearest other star to us would have to be put in Boston, MA, for the scale to be in proportion. This star is called Proxima Centauri, and it is 4.2 light years from the earth. Light years. Remember how it took 2 hours and 22 minutes to reach Uranus at 186,000 miles per second? Well, it takes 4.2 years to reach Proxima Centauri at the same speed, and that is the nearest star to us other than our sun. It is 24.6 trillion miles away. 264,902 times the distance of the sun.
Betelgeuse is another nearby star, about 640 light years from the earth. Traveling at the speed of light (669.6 million miles an hour, 186,000 miles a second) it would take 640 years to reach Betelgeuse. Why do I say this is nearby? Because the galaxy is 100,000 light years in diameter, and 1,000 light years in thickness. If you put a model of the milky way galaxy covering all of the state of texas, our sun would be 0.2 millimeters from earth. That’s right. To fit our galaxy within the borders of texas, our sun has to be a fifth of a millimeter from the earth.
There are 200-400 billion stars in the milky way galaxy, and approximately 50 billion planets. So, with the galaxy being 100,000 light years across, Proxima Centauri and Betelgeuse, lying 4.2 and 640 light years from us, do turn out to be merely our close neighbors, even though Centauri is 264,902 times the distance of the sun, and Betelgeuse is 40.4 million times the distance of the sun. 40.4 million times the distance. This is approximately 5.05 miles from the earth and sun on our texas scale.
So, we have a concept of the size of the milky way galaxy now, and you can imagine how, if it were the entire universe, it would at least be a theoretically plausible proposition to wrap one’s head around the size of it. But the actual reality is truly ungraspable. We can lay out mathematical analogies and know theoretically what the distances are, but there is no way for the human mind to really comprehend it or imagine it clearly.
The milky way galaxy is just one out of about 200 billion galaxies in the observable universe.
Our neighbor galaxy, Andromeda, is 2.5 million light years away, and is one of the closest other galaxies to us. There are some others that are slightly closer, but Andromeda is considered our main neighbor galaxy because it’s a spiral galaxy, just like the milky way, and it looks cool.
Think about this. We’re still talking about that pace of 186,000 miles per second. How could it take 2.5 million years to get somewhere at that speed? Can you imagine the distance? For 2.5 million years you’re moving 186,000 miles every single second. See why I said it’s ungraspable?
2.5 million light years is only twenty five times the diameter of the milky way. So if we made a 10 square foot model of the milky way, Andromeda would be 250 feet away from it. Not very far. Hence why it’s our neighbor galaxy. However, keep in mind that the milky way galaxy is actually 586 quadrillion miles across (100,000 light years), not 10 feet. The galaxies are only close if you’re thinking in terms of those sizes.
So, where are the rest of the 200 billion galaxies? (Take a minute to remember how big the milky way galaxy is, from the distances to Uranus and the sun, to the nearby stars, etc. There are 200 billion galaxies, all in the general size range of the milky way). They’re spread out throughout the observable universe, which is about 13.7 billion years old, and 93 billion light years in diameter.
Until now we’ve talked about light seconds (186,000 miles each), light minutes, light hours, and even light years on massive scales, from the 100,000 light year diameter of the milky way, to the 2.5 million light year distance to our neighbor galaxy Andromeda.
Now, we’re talking about the universe being 93 billion light years in diameter. Traveling at 186,000 miles every second, 11.1 million miles every minute, 669.6 million miles every hour, 16 billion miles every day, and 5.86 trillion miles every year, it would take you 93 billion years to span the universe. 93 billion light years is 37,200 times the distance between us and Andromeda. So, if you somehow travelled at the speed of light, and somehow lived to be 2.5 million years old, and made it to Andromeda, it would be like starting off on a journey from Seattle to Boston, and covering a couple blocks.
One last image: If the universe was the size of the earth, the earth would be 1.17 femtometers in diameter. A femtometer is one quadrillionth (or one millionth of a billionth) of a meter. There are one trillion femtometers in a millimeter.
The Universe is really, really big.

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