The cosmic time machine

Whenever you look up at the night sky, you are in fact peering into history. The stars that you see shining are as they were many years ago, from a few to many millions of years before our time, depending upon the distance they are from us. Indeed, there is no way of knowing whether the stars you see exist today some of them may have long perished, something that will only be known to our descendants in the distant future.

Light travels at a constant speed of 6 trillion miles per annum. The distance light travels in a year is commonly referred to as a light year. In the vast, lonely cosmos, our nearest stellar neighbour, Proxima Centauri, is 4 light years away, or 24 trillion miles. Through advanced telescopes, we are able to view stars which are more than 100,000 million light years away or, in terms of land miles, 100,000 million times 6 trillion miles. The point is, however, that if a star is located 2,000 light years away, we are seeing it today as it was 2,000 years ago, since it has taken that long for its light to reach us. To give an example nearer home, our own sun is 8 light-minutes away, which means that we can never see the sun without a time-lag. What we are seeing in the sky at this very moment is the sun as it was 8 minutes ago and, if God were to shut its power off at this instant, life would still continue on Earth for 8 minutes more and perish immediately thereafter.

It follows by logic, therefore, that the deeper we peer into the universe, the deeper we peer into time and therefore, history. If our star, located 2,000 light years away, were to suddenly explode before our eyes and become what is called a supernova, the event actually happened 2,000 years ago. In other words, it is an opportunity to see history being enacted live. It is for this reason that astronomers are building increasingly powerful telescopes to view what they believe to be the beginning of the universe, an event estimated to have occurred 15 billion years ago.

Imagine, now, that we are not entirely alone in the universe, but that we have fairly advanced counterparts living on our star located 2,000 light years away. Assume that they are able to clearly see Earth and the various events unfolding before them. What they would be witnessing is our history around 3 BC events such as the decline of the Roman and Egyptian empires, and the birth of Christ, and would already have observed Alexander the Great’s conquests. It would be tempting, therefore, for every historian to place himself on that star and, in effect, go back in time! To do that, however, he would have to travel faster than light to get there in under 2,000 years. But the speed of light is the limiting velocity of the universe, and nothing can travel faster than that. In short, therefore, we have to be content with viewing the histories of the other bodies in the universe around us and simply live in hope that our intelligent counterpart, whom we could meet some day, had the common sense to record the events in our history!