This is one of my favourite questions simply because it just makes you feel so insignificant. In a good way. An average person spends much of their life deriving value from human constructs, that only seem to diminish the more you think about the “scheme of things”.
I suppose the most important definition when attempting to define concepts of distance in space is a light year; which really isn’t that complex at all. Light travels at a speed of 3 x 108 metres per second – which is really quite fast. A light year is a measure of how far a beam of light will travel in one (earth) year – which as it turns out is9.4607 × 1012 kilometers. A million million miles.
Most people know the universe started out with the big bang around 13.8 billion years ago – which is quite incredibly derived from the fact that astronomers can turn their telescopes in a multitude of directions and see light that is 13.8 billion lightyears away. But then we get into the question of size. What we have come to realise is that while the Earth may have been indeed 13.8 billion light years from this light we call the big bang, the Earth is not the centre of the universe. In fact that same spot is now 46 billion light years away (considering the expansion rate of the universe). Things are quickly getting larger.
If we now encapsulate the universe in a sphere (up to now we have been looking at lines) we get to an approximation of a sphere with a diameter of 92 billion light years. The problem with something that vast, is a human used to measuring in miles and kilometers cannot really comprehend. I mean does 91 billion and 92 billion light-years feel that different? Not really. But then a billion light years is still an incomprehensible distance. You have to remember these are all just approximations and they depend on many things.
Before we conclude – you have to question is it correct to model the universe as a sphere at all? Many NASA scientists have debated the shape of the universe, and they believe that the universe is flat. Well should they be right that means the universe in truth has no finite size. Most people can only think of finite things. How do you perceive something real with no end? It is also starting to feel a little bit spooky isn’t it? A large flat expanse we just so happen to be resting upon.
Today this is a brief post. For those interested the size and filling of the universe is a rich subject filled with all the exciting headline physical phenomena such as dark matter, hadrons, leptons and photons. Indeed the shape of the universe is a difficult one, from flat planes to bent brains. Discussion of these items will be broken into manageable chunks and reserved for future discussion, so as not to overload the post – and detract from my study time!