Question #420d4
1 Answer
Normally, this is a result of a model which is consistent with some observations we do have which can be extended to describe something that we have very little evidence of.
Explanation:
This is a great question! Normally, this is a result of a model which is consistent with some observations we do have which can be extended to describe something that we have very little evidence of. (That didn't really help, did it!)
Let's take an extreme example - black holes. I've never seen one, but I believe that they exist. How is this science? It sounds more like faith! In reality, it is an example of a model which has been extended to a situation that we can't directly measure.
In this case, the model is that of gravity, more specifically, general relativity which was famously described by Einstein and which replaced the previous model which was due to Newton.
The new model was created to describe measurements wherein light is "bent" by the presence of a mass. But if light is weightless, according to the previous model, it shouldn't be affected. General Relativity treats gravity not as a force, but as the curvature of space. Therefore, the apparent bending of light is actually light taking a straight line through curved space - cool!
A side-effect of the new model is that if one has enough mass in one place it can prevent light from ever leaving - a black hole. For a long time, physicists argued whether this was sensible or was it a flaw in the model. As time went on, people thought of ways to measure whether any black holes were out there, and eventually, the evidence gathered in favour of them existing.
In your example, there is a similar process at work. We look around us at the galaxies in our neighbourhood. We create models of the universe (like the big-bang) that explain what we see. Then we extend that model to a bigger scale than we can observe.
