By Ryan Ridden 05/02/2016 1

The universe is immense. All too often we are reminded of how large the Universe is; it is 150 million km or 8 light minutes to the Sun, 30,000 light years to the galactic centre, 2.5 million light years to the Andromeda Galaxy (the closest galaxy to the Milky Way) and 46 billion light years or 4.2×10²³ km (42 followed by 22 zeros) to the edge of the observable Universe. These distances are indisputably large. In fact they are too large.

Distances in the Universe don’t make any sense to our brains. This isn’t the brains fault, it has evolved on a world where, before the advent of vehicles, distances of kilometers were large. So when confronted by a distance like 4.2×10²³km, the brain simply has no innate understanding. The fact that it is in km is almost meaningless, it’s a unit but not as we know it.

Pondering Worlds Unknown

The view outside the window on my flight to Christchurch, as I crossed the Tasman Sea 10,000m in the sky.

As an astronomer I have grown used to the large numbers and thought I had a decent grasp on what the numbers mean. That thought changed over the weekend.  As it happened I was flying across the Tasman Sea at sunset and when I gazed out the window I was struck by two things. The first was of course, how magnificent it was seeing the sunset from 10,000 meters in the sky and the second was how immense the Universe is.

Out the window there was a sunset. Something beautiful. Something filled with more complexities and information than we could possibly imagine. But that patch of sky was only a tiny fraction of the Earth, a minuscule part of reality. I found myself imagining a sunset in the enormous cloudy skies of the gas giant Jupiter.  In that moment I began to appreciate the grandeur and size of these magnificent worlds, along with the physical laws which govern them.

My next moment of realisation followed soon after. I reminded myself that the Earth and Jupiter are only two planets in a single star system. In the expanses of the cosmos there lies trillions upon trillions of planets, each governed by the same physics, each with just as much information and each with sunsets.

Limitations of Imagination

The sunsets on the planets of my imagination, renewed my wonderment for the complexities, the rules and of course the size of the Universe. But of course the planets are only tiny specks compared to stars, which are specks to a galaxy, an object too large for my imagination. In that brief moment as I looked out to the Earth and saw sunsets on countless worlds, I realised that distances in astronomy were not only incomprehensible because of the large numbers, but also because of what they contain.

The Universe is immense.

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