Why there cannot be anything outside the universe
The Sunday Nation
Nairobi,
11 September 2011
Vincent Onoka from Kisumu wants to know “why we do not feel the earth moving”. There is a straightforward answer to that: it is because we are moving with the planet. The only way we can tell that we are in motion is by looking “outside” the Earth. That is, observing the stars in the sky.
This principle ties up well with another question from Jomondi Giuseppe
of
If the fly was slower, you would overtake it. And if it was faster, it would overtake you. Simple, isn’t it?
Things, however, are not always that straightforward. Albert Einstein wondered about that problem and in the process came up with an interesting “thought-experiment” that went like this:
Suppose you were inside a space ship that can move at the speed of light (one billion kilometres per hour). If you faced forward and held a mirror in front of your face, would you see your image?
Conventional reasoning says that to see your image, light must travel from your face to the mirror and then bounce back to your eyes. But since you and the mirror are moving forward at the speed of light, then the light from your face will never catch up with the mirror. So you cannot see your image!
But Einstein said no! He insisted that the disappearance of the image would break the fundamental principle that the only way you can tell you are moving is by looking outside. Therefore, he argued, the image must remain on the mirror no matter what speed the space craft is moving.
Vincent had another question: “what is there beyond the earth and other planets (stars, space, and ‘universe’ included)?” The answer is nothing!
In fact, we can confidently say that nothing CAN exist “outside” the universe. The reason being that the word ‘universe’ means ‘everything’. Thus, if you discover something farther away than the farthest known object, your new discovery will still be part of the universe!
If you start from the earth and travelled outwards in a random direction, it is very unlikely that you would come across anything any time soon. Even though Venus lies between 50 and 250 million kilometres away, the probability that your random trajectory will lead you towards it is extremely small! My guess is that you would travel for several hundred trillion kilometres before seeing another object of any kind.
Eventually, 100 billion trillion kilometres later, you would come to the end of the known universe; but if you saw other objects farther away, they would also be in the universe! All you would have done is proved that the universe is not as “small” as we have been assuming.
 |
 |