# Left side of the Universe

This was a phrase I thought of this afternoon, then realised it was impossible.

The Universe is apparently infinite, so you can’t have a centre, you can’t have a top, bottom, side, front or back?

Obviously we know that stars are a certain distance away, and if you look at star maps you can identify individual stars. But did you know they move? Stars move around the centre of the galaxy. Some faster than others. The distance to a star is measured by parallax. Hold your hand out at arms length, look at the tip of your thumb with one eye, then the other. Notice how the background seems to move. That’s because each eye is at the base of a very long thin triangle and your thumb is at the tip. Now think of the stars. How do you measure their parallax.? The answer is take the measurements at opposite sides of the Earth’s orbit, six months apart.

What was found was the stars are not fixed. They are moving due to the matter around them and their relative speeds. So stars in one position a thousand years ago might have moved quite a distance.

That’s not all, the Galaxies that contain the stars are moving too. Some, like our galaxy, the Milky Way, and the Andromeda galaxy are due to collide in the next few billion years. We won’t be around to see it, but it has been modeled.

Then looking further out Galaxies seem to be flying away from each other at a rapid rate. You would think gravity would hold them together, but something in the Universe, (dark matter, dark energy) is pushing it apart.

This was measured by noticing the galaxies light from further away appears redder ( red shifted). In other words travelling away from us.

To explain, if you hear a fire engine siren it sounds different moving towards you than moving away. That is because the sound waves get squashed up as they move towards you, and stretch as they move away. Light does the same thing, as an object moves towards you it squashes up and changes to a bluer colour. As it moves away it stretches and we see a redder colour.

I’m not a scientist, so I can only hope what I’ve written makes sense. All I know is that something might be in an exact place now but because everything is in constant motion you just can’t say where the ‘left side of the universe’ actually is!