How big is the universe? Since the universe is growing constantly, one easy answer to this question is ‘infinite'. But the answer is not satisfying for many people. We understand infinity, but how are we to feel it? In fact feeling it is not even possible. Some sense of it can be had, though, and today I will try to give you a little of that sense.
The infinity of the universe
Let's assume that at this moment the boundary of the universe is x kilometres from where I stand. Cross those x kilometres and I will reach the edge of the universe. Let's assume I can cross that distance in 1 second. I board my spacecraft and cover x kilometres in that last second. But what is this! I see the edge of the universe further away still — because the universe keeps growing. In the very second in which I reach the edge, the universe has become vaster. And yes, that is infinity: something that has no boundary or edge, or whose boundary we cannot measure.
What is a light-year?
Now let's get some sense of how big the universe can be. What is the fastest-moving thing in this universe? Everyone knows the answer: the particle of light, the photon. Its speed is what we call the speed of light. Light, or the photon, travels 3×10⁸ metres in 1 second. The number may look small, but it really is not. First write 3 on a piece of paper, then put eight zeros after it. A very large value, is it not?
Now let's get to know a new unit. We have learned how far light travels in one second. Now we will learn how far light travels in one year. Multiplying the speed of light by 60×60×24×365 — the number of seconds in a year — we get 9.46×10¹⁵ metres. That is how much distance light covers in a year. This is called 1 light-year, and it is used to measure distances in astronomy, because the kilometre is far too small a unit there. That is why I introduced this unit at the start of the discussion. Astronomy uses some larger units too, but for now let's explain with this one.
Alpha Centauri
We have just seen that light travels at a tremendous speed. Even at that tremendous speed, light from our nearest star — Alpha Centauri — takes 4.37 years to reach this Earth! Imagine: if the nearest star is that far away, where are the distant ones? Now let's reach out towards the far distance and see how far the universe can tell us about! 😮
The Milky Way galaxy
The Milky Way galaxy
Everyone has more or less an idea of our solar system. Many solar systems like ours together make up a galaxy. Every solar system has a star, around which countless planets like the Earth revolve. If we take our own galaxy, the Milky Way, the distance from one edge of it to the other is 200,000 light-years! Which means that even travelling at the speed of light it would take two hundred thousand years just to go from one side of the Milky Way to the other. Now think how many tens of millions of light-years it would take to go round the whole Milky Way 😮
The Local Group and superclusters
Alarmed? No, it does not end there. Such an enormous galaxy is a very small part of the universe. Fifty-five galaxies including ours come together to form the Local Group, and the Local Group spans 10 million light-years! Then more than 100 local groups together form an immense cosmic cluster of galaxies named the Virgo Supercluster, whose diameter is about 110 million light-years!
The Laniakea Supercluster
But there is nothing to be troubled about here either. This supercluster too is a small part of the universe! 😁 Another 20 to 30 superclusters like it come together to form a huge cluster of galaxies called the Great Laniakea Supercluster, which holds more than 100,000 galaxies like our Milky Way! The diameter of this Laniakea is about 520 million light-years! And, to disappoint you again, this cluster of galaxies called the Great Laniakea is a very slight and utterly tiny thing compared with the whole universe! 😱
The largest supercluster
The largest supercluster discovered so far is the Hercules-Corona Borealis Great Wall! It was discovered in 2014. It is so large that going round it would take 10 billion light-years! 😰 And yet the age of our universe is only 13.8 billion years! There ought to be superclusters larger than this, but they lie outside the observable part of our universe.
Dark matter
The unobservable part
All that we have discussed so far, science has been able to observe. But the extent of the universe is far greater, and science has not yet been able to observe it at all. That is called the unobservable universe. Because the Big Bang happened about 13.8 billion years ago, light from anything further away than that has not yet reached us. So we cannot form an idea about those parts.
Dr Mihran of the University of Oxford and his colleagues have estimated that the size of our actual universe is about 250 times larger than our observable universe! Can you imagine?
Not only that: NASA has said we know only 5% of the universe. The remaining 95% we cannot know! And yet even knowing this 5%, the universe is beyond fathoming. So think what the scale of its unknown part must be. It is therefore assumed that within this 95%, 27% is dark matter and 67% is dark energy. We will discuss dark matter and dark energy another day.
The existence of a creator
Now — if superclusters this enormous are like tiny dots in this universe, then how much are we? It would not be wrong, I think, to call ourselves nothing at all. If, as such nothings, using brains smaller still than ourselves, we set out to prove by science whether the creator of this vast universe exists, then in my view nothing could be more absurd.
From the discussion above we see that a mere 13.8 billion light-years is our boundary. Beyond it we cannot observe. We can know only 5% of the universe. And yet the creator may have made an infinite number of universes like this one and be sitting there. And we will bring that creator down with the formulas of our physics? Will he appear under the microscope of our biology laboratory and say, “Here, the proof of my existence!”? Certainly not. The interesting thing is that, being inhabitants of a three-dimensional world, we are not capable of comprehending any world above it. That does not mean those worlds do not exist. They exist, but beyond the limits of our knowledge. So for science to go looking there for a creator who is above all dimensions is plain foolishness.
In fact anyone who sees so finely regulated a universe will be bound to accept that a creator exists. He must exist; otherwise the creation of the universe would be utterly impossible. No, these are not my opinions. The first rank of scientists have agreed on this.
The prince of physics, Sir Isaac Newton, said,
“Gravity explains the motions of the planets, but it cannot explain who set the planets in motion in their places. God governs all things and knows all that is or can be done.”
And the Nobel-winning physicist Albert Einstein said,
“The more I study science, the more I believe in a creator”
The father of microbiology, Louis Pasteur, said,
“A little science takes you away from God, but more of it takes you to Him.”
Werner Heisenberg, one of the originators of quantum mechanics, said,
“The first gulp from the glass of nature will turn you an atheist, but at the bottom of the glass God is waiting for you.”
In the end this much remains to be said: there has never been a dispute in science about the creator. Science does not even prove that there is no creator, nor does science have the capacity to prove it. So it would not be wrong to call it entirely uncalled-for to drag science in to prove the existence of the creator.