Although it is true that the universe is expanding at a rapid rate, this expansion of the universe does not affect our galaxy in the ways you might think.
How galaxies are affected by universe expansion
Our galaxy is made up of astronomical bodies, all of which orbit other objects and have a set path that has been the same for years. Galaxies will become distant from one another because they are expanding away from one another due to the universe’s expansion. But objects within a galaxy will not be affected in the same way.
This means that the distance between the earth and the sun will not be affected in the same way that the distance between our galaxy and other galaxies will be.
This is for the same reason that the distance between atoms will not be affected; so, there is no need to worry that your body will become stretched out or that your journey to work will become any longer thanks to the expansion of the universe.
What causes the expansion of the universe?
The expansion of the universe was initially caused by the Big Bang and further by dark energy. It can be difficult to wrap your head around the idea that the universe expanding is not about astronomical bodies flying away from each other, but actually most things are static.
When we say this, we mean that the stars, for instance, are static in relation to spacetime fabric which is expanding. Imagine a grid with two dots at two different intersections. If the whole of the grid is expanding and the squares are getting bigger, then it may seem that the two dots are getting further away from each other.
They are. But they are staying on the same intersection of the grid that they began. The grid is spacetime fabric, and the dots are stars.
Is it expanding from one area?
No. If the universe was expanding from one specific area, then we would be able to see a central point where all of the stars and galaxies are moving away from a specific point. But because the expansion is of space itself, there can be no logical center.
How does this work on the grid?
When you have the same grid which is expanding, imagine a page of grid paper getting bigger, there is still no center of expansion. You may choose to see the centre of the paper as the center of expansion, but this is not the case.
Because all of the dots that are drawn at grid intersections will be moving further away from every other dot, not just from one specific point on the grid paper.
What stops galaxies expanding?
The reason that a galaxy as a collective will not expand in the same way that the universe does, is mainly to do with the binding nature of gravity.
Take our own galaxy and our solar system for example; the reason that we orbit the sun and that our solar system in turn orbits a black hole like the rest of our galaxy, is due to the force of gravity.
This is a strong force when a great amount of mass is involved. So, the expansion of the universe does not affect galaxies because there are so many astronomical bodies in closer proximity to each other than there are in outer space. This close proximity causes more gravity.
How do we know that the universe is expanding?
The main reason we know that the universe is expanding actually proves that our own galaxy is not being affected by the expansion. This may seem like a confusing statement.
But imagine if all of our measuring equipment was expanding at the same rate that the universe is. We would not be able to note a difference inn distance against our own units of measurement.
Therefore, we can safely say that the universe is expanding, as well as saying that this expansion does not affect within our galaxy.
So, the main reason that the universe’s expansion does not affect the distance between earth and the sun, is because the expansion does not affect distances within a galaxy.
This is because spacetime around a large object will curve, this is gravity. In outer space, where this is more spaced out, spacetime is able to expand more freely.