Where do you live? It’s a question that for decades has plagued application forms, letters and now quite recently, online deliveries. It traditionally marks a new stage in a relationship and it invigorates trust between one another. When someone asks you for your address you generally tend to reply by disclosing things that make it easier for them to contact you.This usually involves things such as door number, post code (Or zip code-depends on where you are),city and street name. An example of an address could be:
10 Downing Street :The prime minister of the United Kingdom lives here. Or,
221B Baker Street : The residence of the famous fictional character Sherlock Holmes.
Although, whenever someone asks you for your address, we tend to overlook a lot of details. Your address may seem pretty straightforward, but in truth it’s way more complicated than you might think. What I’m talking about is not just the geographical location in which we eat and sleep, I’m not talking about our location in a specific country or a city, or even a continent. By address I mean our orientation in relation to the scale and grandeur of our universe. Now, you may think that telling the mailman what part of the universe we live in is unpractical and useless.And it is. Telling him those sorts of picky details won’t help him too much in locating your residence. Of course, he only needs a certain amount of information to find out where you live.
But knowing what part of the universe human beings as a species live in, is (In my eyes anyway) downright interesting. It traces back to the age old question of the scale of the universe and our place in it. Moreover, it is through and through, a humbling process.
Let’s start at the very beginning. In ancient times, people thought the Earth was the centre of the universe, and that the Sun, Moon, planets and stars rotated around us. Although some thought the Earth was flat, the ancient Greeks, like Plato, were convinced that the Earth was a sphere. They thought that each of the worlds and stars were in crystal spheres surrounding us. This idea is perfectly natural and intuitive. Anyone who stands outside and looks up can clearly see that the stars and the planets are turning around the Earth. But ancients astronomers such as Aristarchus who studied the heavens found a few problems that showed that some celestial bodies can’t be orbiting the Earth. This point was backed up hundreds of years on by scientists like Copernicus and Galileo. Galileo for instance saw that Jupiter had moons of its own, and that Venus went through phases like the Moon. This meant that Earth, all the other planets, their moons and everything else orbited the sun. In Galileo’s time this discovery was considered heresy as it opposed the beliefs of the church, and as a result Galileo narrowly escaped execution.
It took a few years for their ideas to catch on, and for the scientific establishment and the church to agree that yes, the Earth is just another planet, orbiting the Sun, and it’s not the centre of the Universe.
Great, so this meant that it took thousands of years just to prove once and for all that the earth wan’t at the centre of it all. That doesn’t tell too much about our place in the universe (Yet!) but it’s still a major discovery. It’s important to consider that knowledge of the Earth’s location in the universe has been shaped by centuries’ of curiosity plus another 400 years of telescopic observations ( kick started of course by our old friend Galileo), and it has expanded radically in the last century.
After this discovery, observations by the German-born British astronomer William Herschel and others showed that Earth’s sun lay within a vast, disc-shaped galaxy of stars, later revealed to be suns like our own.
A galaxy is a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Prior to this astonishing discovery, people thought that the extent of the universe reached from the sun to everything else that orbited it. The revelation that our sun is just one of many billions of stars was a fascinating and antagonizing fact. Astronomers also managed to roughly locate our position in this galaxy, which we know call-the milky way.
They discovered that our solar system, in all it’s vastness, is orbiting roughly near the outside of it.
By the 20th century, observations of spiral galaxies (a category of galaxy that our own milky way falls into), revealed that our galaxy was only one of billions in an expanding universe, grouped into clusters and superclusters of galaxies. Superclusters are among the largest known structures of the cosmos. They are so large that they are not gravitationally bound.
So where does this leave Earth? We’ve gone from being at the centre of the universe to becoming an insignificant ball of rock floating around the outside of an unimportant galaxy. Is there any way we can salvage some of our puny pride? Well, this is where it gets interesting.
Since there is believed to be no “center” or “edge” of the universe as it’s expanding. There isn’t any particular reference point which we can utilize to plot the overall location of the Earth in the universe.
Nevertheless, there is something about the Earth that makes it unique and special to us. The Earth is at the centre of the observable universe because its observability depends on it’s distance from earth. Let me explain. The observable universe just means the part of the universe that human beings can see from Earth. We’ve built quite a lot of complicated instruments for space observation. With existing technology we can look far beyond the deepest galaxies in the universe. Each swirly/shiny thing or speck is a different galaxy. Just like the milky way.
Whenever we look at something-anything – we’re essentially looking back in time. This is because the light that enables us to see something isn’t just there. It takes time for the light to reflect off an object and bounce back onto our retinas. The time the light takes could just be billionths of a second or it could take thousands of years. It depends on how far away the object is.
This means that you’re not seeing the cup of coffee on the desk in front of you as it is now. You’re seeing it as it was less than a billionth of a second ago, the time it took for the light from the coffee to reach your eyes.
So everytime an astronomer uses a telescope to look far back into the universe, they’re essentially looking far back in time. Owing to the fact that the time it takes for the light from those distant galaxies to reach Earth may take millions or billions of years. We know that the universe is approximately 14 billion years old, but we don’t know exactly how big it is because we cannot see all of it. If a Galaxy is so far away that the light from it takes around 14 billion years to reach us, than we know that that galaxy is one of the oldest in the universe.
But, you have to remember the fact that the universe is expanding. This means that the light from some galaxies may take more than 14 billion years to reach us. They could be as far as 50 billion light years away. So the observable universe just means that part of the universe that light and the age of the universe allows us to see.
This means that in a sense the Earth is at the centre of the universe. The centre of the observable universe anyway, because human beings can only observe the universe from Earth. If later on in the future, some astronomers could live on Mars and observe the universe from there, than Mars would be the centre of the observable universe for those astronomers.
But there is still so much of the Universe left to explore.
If you want to know more I highly recommend you watch this video, an excerpt from Carl Sagan’s Cosmos television series.
References and lot’s more information:
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