The Edge of the Universe

Where does the universe end? Is there really a boundary?

Nobody knows if by boundary you mean some sort of a wall that can’t be jumped across.

But there is another kind of a boundary. A point beyond which we can’t see or interact. In that sense, the boundary is set by our ability—or rather, inability—to look beyond.

Imagine a monkey on an island surrounded by an ocean that nobody can cross. If it can see up to 10 kilometers, the boundary of its universe is its horizon that far. Whatever lies beyond is practically non-existent for the monkey. We know how far our horizon in the universe is.

Here’s a law of our universe: Light travels at around 300,000 kilometers per second, and nothing can travel faster than the speed of light. When light from any object reaches our eyes—directly, or after being processed by machines—we can see that object.

We can see objects laying far away—very far away. Light from any object should reach us someday, although that ‘someday’ would be billions of years later for the very distant objects. And that day we will be able to see that object. Isn’t it?

No. There are places from where light isn’t able to reach us, because it is too slow.

The universe has been expanding since the big bang, when the existence came to existence 13.8 billion years ago. Galaxies are moving away from each other. Also, the farther the two galaxies are, the faster they are moving away from each other.

Think of a deflated balloon. Draw a few dots on that balloon. Now inflate the balloon. As you inflate it, the dots will travel farther from each other. The farther the dots are from each other, the faster they move away from each other.

The galaxies are moving away from each other similarly. As they move away from each other, the force trying to bind them together—gravity—gets weaker, which causes them to move away even faster. As they move away even faster, gravity gets even weaker, and so on… The galaxies that are distant enough are moving away from each other at speeds faster than the speed of light.

You might question that if nothing can travel faster than the speed of light how can distant galaxies—or anything for that matter—move away at higher speeds. They can because they are not traveling, but rather the fabric of space is expanding. The balloon is growing in size rapidly. No laws breached. You thought only advocates could bend the laws?

Coming back to the point, now we have galaxies moving away from us faster than the speed of light.

Think of a car moving away from you at 100 km/hour. If a man poking out from the sun-roof throws a ball towards you at a speed of 80 km/hour, the ball will never reach you. In the same way, the light from these distant galaxies will never be able to reach us. They are beyond our reach forever.

After tens of billions of years, all other galaxies would have crossed the boundary. Whoever would be living at that time in the Milky Way—assuming they will be smart enough—would think that there is nothing beyond the Milky Way. For them, the Milky Way will be the entire universe. They will never know about the other 2 trillion galaxies that we know about.

And since they would not be able to observe other galaxies moving away, they would never know that the universe is expanding. They would have no means to realize about the big bang. Those ignorant people would think of the universe as a small, static place. If you happen to tell them that time had a beginning, they’d laugh at you.

Consider this: Out of the 2 trillion galaxies that we can observe (our “observable universe”), about 94% have already gone beyond the edge. We see them today as they were billions of years ago (when they were inside the boundary) because their light is reaching us now. Since you started reading this (and thanks for reading), millions of stars have moved beyond the boundary.

Here’s something worth pondering about. What if some important clue crossed the boundary long ago and is already outside our Observable Universe? What if we are that someone who is not able to see that very important part of the cosmos where answers of our existential questions reside? What if we are the monkey trapped on the island?

Okay, let’s worry about the petrol price hike now.





Location: New Delhi, Delhi, India

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