What does the Universe look like?
Our cosmos is so huge we can’t see it all
Look at the large-scale structure of the Universe today and countless galaxies are strung out on endless filaments in a cosmic web. It seems that tiny variations in density in the very early Universe acted as seeds from which this structure eventually blossomed. Over-dense regions drew in more and more material to create galaxy-filled superclusters and leave behind supervoids.
Except the Big Bang theory says that the early Universe should have been completely smooth. How come it had tiny imperfections of just a few parts in one hundred thousand, but which created the Universe as we see it today?
One explanation is a modification to the Big Bang, called inflation. It argues that the Universe underwent a period of super-rapid expansion in the first miniscule fraction of a second. The cosmos went from considerably smaller than an atom to about the size of a grapefruit in a trillionth of a trillionth of a trillionth of a second.
Before this, the Universe was so small that it was dominated by minute quantum variations. The ensuing explosion in size blew up those variations. It’s worth saying that currently there’s no evidence that inflation really happened, although it does help solve other problems with the Big Bang too. Nor do we know the Universe’s true size. Astronomers speak about the observable Universe – a spherical region 13.8 billion lightyears in all directions where light has had time to reach us since the Big Bang. However, there could well be things beyond this cosmic horizon that are so far away the light hasn’t arrived at Earth yet.
This also makes it difficult to determine what shape the Universe is. Astronomers currently believe the 4D fabric of spacetime is flat, but it could simply be that inflation has smoothed out the billions of lightyears we can see, and beyond that the Universe is actually curved.