Posted in Science & Nature

Centre Of The Universe

We often meet people who act as if they are at the centre of the universe. These egocentric people behave as if they are the most important people in the world and that their words and actions are more meaningful than they actually are, while assuming that they play an important role in other people’s lives. This is a common belief in children who are still learning to differentiate the world and other people from their own minds, but in adults, it is almost pathological.

Speaking of which, where is the centre of the universe?

In ancient times, the concept of “universe” was very different. Many cultures imagined the universe as consisting of the Earth where we lived, plus the heavens and the underworld (often supposedly where the good and bad end up after death respectively). These worlds would be connected by a central axis mundi, or world axis. An example of this is the mighty Yggdrasil, the World Tree, found in Norse mythology. It is said to be a gigantic tree that connects the Nine Worlds and is the centre of all life.

As the science of astronomy developed, we realised that we are not at the centre of the universe. Geocentrism – the model where Earth is at the centre of the world with the Sun, Moon and planets orbiting it – eventually gave way to heliocentrism – the modern model where the Solar System orbits around the Sun.

It took brave scientists such as Nicolaus Copernicus, Johannes Kepler and Galileo Galilei challenging the Church and Aristotelian science establishments to show that our understanding of the universe was wrong, despite pressure and punishment. Through scientific observation and inquiry, it was shown that we are not at the centre of the world, but the Sun is.

But as we discovered more about the heavens, we realised that the universe is far vaster than the Solar System. With the advent of the Big Bang Theory, we realised that the universe is expanding, with every object moving away from each other in all directions. This is an extremely difficult concept to visualise, but because the universe is expanding infinitely in all directions, it technically has no centre.

On a final note, the concept of the universe being infinite may not be relevant to us because we cannot observe the infinite universe. Instead, we often talk about the Observable Universe, which is the portion of the universe that we can physically observe with our eyes, telescopes and other instruments. The centre of the observable universe, like anything observable, is the observer.

Therefore, in some sense of the phrase, you are technically at the centre of the universe.

Posted in Science & Nature

Hammer And Feather

What would happen if you dropped a 1kg ball and a 10kg ball at the same time from a high building? Most people would think that the 10kg ball would obviously fall faster and thus hit the ground faster, but the truth is they would fall at exactly the same time. The reason for this is that the force that accelerates a falling object is gravity, which on Earth is constant at 9.81ms-2. This means that no matter how heavy the object is, they will always accelerate by 9.81 metres per second per second. This was hypothesised by Galileo Galilei, who came up with the thought experiment of dropping two balls of different mass from the Leaning Tower of Pisa (there is debate as to whether he actually performed the experiment). The theory was later solidified by a certain Isaac Newton, who devised the laws of universal gravitation and the three laws of motion.

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However, if the two balls were dropped from an extremely high place, they may land at different times as mass affects the terminal velocity – when the force of gravity equals the force of drag caused by air resistance, leading to a constant velocity. A heavier object will keep accelerating to a greater velocity than a lighter object, which would have reached terminal velocity before the heavier object.

One place where this will not happen is in a vacuum where there is no drag force. To prove that the hypothesis that two objects of different masses will fall at the same time in the absence of air resistance, Commander David Scott of the Apollo 15 moon mission took a hammer and a feather with him. Once he landed on the moon, he dropped the hammer and feather in front of a live camera, showing that the two landed at exactly the same time. He thus proved that Galileo’s conclusion from two hundred years ago was in fact correct.