What do we look like from the other side of the universe?

 by Zoë Gamble

This blogpost has been inspired by Dr Chris North who delivered an engaging talk on this topic at Cardiff University’s Department of Physics and Astronomy Sixth Form Conference 2013

Space is big. Really, really big!

The earth, and all of it’s 7 billion human inhabitants would fit inside Jupiter over 1000 times. Jupiter would fit inside our sun about 1000 times (or it would hold over a million earths!)

Distances between things in space are huge too.

The distance from the earth to the sun is about 150,000,000,000m. But what about objects outside our own solar system? The distance to our next nearest star, Proxima Centuri is about 39,900,000,000,000,000m. Instead of having to write lines and lines of zeroes, we can use light years.

Light year

A light year is the distance travelled by light in one year. Light travels at 299,792,458 m/s, so can get really far in one year! In light years, the sun to Proxima Centauri is about 4.24 (much easier to think about than 39,900,000,000,000,000m).

Looking at the past

What this means is, to a person next to Proxima Centauri looking back at us, they are actually seeing us in the past by over 4 years, as that’s how long it takes the light from earth to get there.

This might sound a bit strange – over small distances on the earth we don’t notice this it all. But the light that we see from the sun is actually 8 minutes old, because that’s how long it takes the light to travel from the sun from the earth. Because of this ability to ‘look into the past’, we can actually find out a lot about the universe.

I’m going to imagine you are 16 years old…

…and someone is looking down at you on the earth from different points in the universe.
What would you look like?


Fromthe sun




Galactic Centre sounds pretty far away, but in universe terms is still in our neighbourhood. Looking back from the Perseus Cluster of galaxies, about 250 million light years away, would reveal dinosaurs walking the earth. How about ‘El Gordo’, a galaxy cluster about 7 billion light years away? This is way before the particles that would one day become the earth have even started to join together!

But is it true?

Would a person on Kepler 186f right now (with an amazingly powerful telescope) really be able to see Henry VIII ruling England? In theory, yes they would! Currently though, we can’t know for certain. Along the way, the light could have been blocked by a supernova between us. We wouldn’t know for sure until 500 years in the future, if a message were to come back saying ‘liking the red and gold fashion guys!’

What can we learn?

What if we were to consider this situation the other way round? From our point of view on earth, looking out into the universe? Astronomers are able to gather key information by studying stars and galaxies at different distances from us. By observing distant objects, we can build up a picture of how the universe was formed and much, much more.

It’s exciting to think about – when we observe a galaxy far, far away, and we can see stars and planets in the early stages of their existence – what is really there now? Has a civilisation emerged, looking out into the universe, looking at a spiral galaxy just beginning to form? Will we ever know?

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