I seem to have learned more about the world in 6 years in Japan than in 27 years in Singapore. That’s what I like about Japan. Even their variety shows are very educational.
It might be just me, but I always had the idea that gravity is what holds the planets together in the solar system. I remember that being told to me, that for example, Venus pulls the earth on one side while Mars pulls in on the other side, that’s why it is held in its place. It didn’t make much sense since the planets are not always in a line. But a recent trip to the planetarium made me realize how wrong that understanding was, and either I had a really bad teacher or I’m just really dumb.
If you’re as dumb, let me share with you what I learned. And if you’re much smarter (as most of the world is), please let me show off what little I now know.
So Newton discovered that gravity exists. But if you think about it, it’s ludicrous how gravity is strong enough to pull planets of such huge mass together in the solar system. Gravity is in fact a very weak force, because if it really were that strong a pulling force, you shouldn’t even be able to lift your finger easily. When Galileo discovered that objects fall at a constant speed regardless of its mass, an experiment was also carried out to find out if objects fall at different speeds if their velocity differ. It was then discovered that, cannon balls hit the ground at the same time when dropped from a stationary height and when fired from a cannon. Which means that, since the earth is round, if you fire something at a really high speed such that it can travel to the end of the earth before it hits ground, it will continue dropping forever since it can never hit ground. In other words, it will orbit earth forever.
So, of what use is this concept?
This concept is the very basis of how satellites work.
You would also have heard of Einstein’s (special) theory of relativity and maybe this thing called gravitational time dilation. Simply put, time passes faster at altitude. The weaker the gravitational force, the faster time passes. Another of Einstein’s theory called the “twin paradox” posits that time passes slower at higher speeds. So if you take a twin and send them to space in a rocket traveling close to the speed of light, they will return younger than the twin left on Earth.
Again, what is the use of this concept?
If you think about it, satellites in space are traveling at extremely high speeds in order to make it round the earth. This quick speed and high altitude means that time is different on the satellites than on Earth. At the distance it is from land, every deviation however minute means a loss of accuracy on ground. While driving, your GPS would probably tell you to turn left after you pass the junction. The theory of relativity provides the basis on regaining GPS accuracy.
Going back to the solar system, if it isn’t gravity, what then holds the planets together? Put simply, gravity is the reason for the planets’ alignment and orbits. But instead of holding them in place, gravity simply does what it does best (i.e. pull). I know I sound like I’m contradicting my first paragraph, but let me finish. Einstein’s general theory of relativity states that gravity curves space and time. And that is what holds the planets, us, and everything else in their place. Confusing?
Imagine a trampoline. Place a tennis ball near the sides of the trampoline and what happens? Nothing really happens. But if you place a bowling ball in the middle of the trampoline, the trampoline sinks and what happens? The ball rolls toward the bowling ball because of gravity and because the trampoline is curved. Our galaxy is like the trampoline, but invisible. Every object in this world bends space and time affecting other objects around us. The sun bends the space and time in a certain way such that other planets “roll” towards it. But why don’t the planets hit the sun?
Have you ever seen one of this in science centers? If you roll a ball in one direction (not down!) really quickly, it will circle the concave bowl continuously until it loses speed and gradually goes down. At the high speeds planets are traveling, they end up circling the sun forever instead of rolling closer and closer towards it.
I hope the term “space-time continuum” now makes a tiny bit more sense.
If you already knew about this, thank you for sparing your time to watch me expose my embarrassing lack of knowledge.