Is the universe infinite? How big is it really? These are the central questions that I try to answer in this article, based on current research in observational astronomy. Though this question seems quite plain and simple, the answer to it is definitely not. Let us see why it is so.
Our world is a small dot in the vastness of space, revolving around another brighter and larger dot, the Sun, which revolves around the galactic center of the Milky way. Our galaxy is one of the billions of galaxies that exist in the universe. These galaxies form clusters and clusters form supergalactic clusters. The scale of complexity keeps on growing to gigantic proportions. Perhaps, it has no end.
Universe is the totality of space, time, matter, and energy. It includes every physical entity that exists. Being a part of it, it is difficult to understand how large it actually is. Trying to answer the question about the size of our universe, is questioning if the vast expanses of space and time have an edge or an end. Where does it end? Does it keep going on and on (infinite) or does it have a finite boundary? Let us try to find an answer to this question. Its size cannot be compared with anything else, as it encompasses everything.
There was a time when people had no idea about how vast our planet Earth was. People debated about what shape it was and whether it had an edge. To put an end to these questions, adventurers like Magellan underwent sea voyages and circumnavigated across the great oceans, to finally see for themselves.
However, attempting to answer the question will not yield a solution through a human voyage. The distances are gargantuan and billions of generations would have been born and died, even before one would get halfway across, to the nearest galaxy. The reason is that our spacecrafts are not fast enough for exploration of the universe. So, we try to measure the expanses of the universe indirectly, through the fastest traveling entity, that is light.
Size of the Observable Universe in Light Years
There is no way we can understand how vast it is, unless we have a way of measuring large distances and observing the farthest known objects. Light is the fastest way of transferring information in the Universe. In fact, the speed of light (roughly 3x108 m/s) is unattainable, for any physical object.
The unit of measurement, used to determine the distance of far away objects in the universe, is a 'Light Year'. It is the distance that a ray of light would travel unobstructed, in one year. One light year is roughly 9.46 trillion kilometers. (Trillion is a thousand billion or 1 followed by 12 zeroes after it). The nearest galaxy to our own galaxy, the Andromeda, is about 2,500,000 light years. Light from the Andromeda would travel 2.5 million years before it would reach us. So, all that we see is the past, as light takes a lot of time to reach us.
So, the only way one can know the size, can be through observing light, from as far as we can. The Hubble space telescope is the eye that can see the farthest for us and what it sees are things that happened long ago.
That is because, light reaching us, started traveling from there, millions or billions of years ago. Just being able to observe light from afar, is not enough, one needs some way in which, we can estimate the distance from where it started. This is achieved through the use of cosmic candles, that are objects for which, astronomers have a calibrated relation between distance and brightness.
Using such cosmic candles, the farthest reaches of our universe, have been explored. Still, one cannot predict its size, but one can safely say that the observable universe extends for 93 billion light years. It is a number up to which you may not be able to count in a lifetime.
What lies beyond that observable horizon? There is no way we can know that currently, as light from farther, has not yet reached us. According the prevalent theory of origin of the universe, the big bang theory, spacetime is expanding constantly and at an accelerated rate. The very spacetime, which is the fabric of the universe, is expanding. So, we have no idea about how vast it is today. Neither can we say anything about whether it's finite or infinite. Whatever theories you hear about, are all pure speculation. Only thing that can be said is that it's really really big and getting bigger by every passing second. Bigger than anything you can think of and full of surprises, yet to be discovered.