So many people seem to misunderstand the basic concept of a scientific theory, I thought I would write a bit about it.
Science is not the direct search for truth; it is rather the search for understanding which often leads to truth. Scientific theories are formed for a single purpose - to make accurate predictions. If it does this successfully, it is a worthy theory regardless of whether or not it is true. That is what I think people fail to realize: theories which are false can be valid useful theories. So are theories which are true. So are theories which have unknown truthiness, so long as the mathematical predictions that they make are accurate. This is best explained via example...
Imagine it is thousands of years ago and you and I live in a small village, probably somewhere in arabia. An argument breaks out concerning the shape of the world. Someone displays a map of the village on a flat papyrus scroll and proposes:
The Earth is flat.
Just as the papyrus the village is drawn on is flat, so is the earth under the village. Is this an accurate theory? To test it, we plan an imaginary trip on the map. We decide we will walk exactly 1 block north, then 1 block east, then 1 block south, and then 1 block west, and according to the map we should end up right where we started. Then we test the theory by actually taking the walk and I am sure you can guess, we do in fact end up exactly where we started. We have proved the validity of this theory. The Earth is flat. This is a valid theory and produces accurate mathematical results within the village where it was tested.
But wait, what if the earth isn't flat, but actually cube-shaped, with our village on one side? The trip around the block still works with the cube theory just fine. Now we have an interesting problem, because we have two different theories that both work, but both can't be true. What can we do? Well, within the village we can use the simplest one, the flat one, and we will be just fine. But how can we know which one is actually true? Keep testing. We will make the same square walk, but very very large. Lets say we walk exactly 2,000 miles north, then 2,000 miles east, then 2,000 miles south, then 2,000 miles west, using a compass to keep us on track. If the flat model is true, we should come back to where we started. If the cube model is true, either we will come to an edge of the cube, or we will end up back where we started.
So what happens? This time the result is much more interesting. We do not find an edge of the cube, but we also do not end up back where we started. How can this be? Neither theory works on this scale, so we need an entirely new theory.
The Earth is spherical.
Science always looks for simple explanations, and a sphere is the simplest shape that can be used to make accurate predictions that match our experimental data. When we finished our square we were right on target to our starting point but fell short. This means that our east-ward leg took us much farther in longitude than our west-ward leg, which is to be expected when a square is projected onto a sphere using our system of latitude and longitude. Now we can discard the cube theory and use our two existing theories:
On small scales, the Earth is flat.
On large scales, the Earth is spherical.
Remember, we still don't know which one is true, just that both work under different circumstances.
Fast-forward to today. This is the situation we find ourselves in with Newtonian and Einsteinian physics - we have no way of knowing which is 'true', just that they both work under different circumstances.
Now having sent men into space who could turn around and take pictures of the Earth, we know the truth that the Earth is round. So we can finally discard the whole Earth is flat theory right? No way! If we did that, we would have to calculate spherical chord lengths using sines and cosines just to get around the block! It is still much easier to use the Earth is flat theory when working on small scales and all the mathematical numbers will work out to be more than accurate enough.
This is how scientific theories are used. None of them attempt to establish truth directly, only a method to predict outcomes; with the standing challenge for anyone else to propose a better one. Anyone who has an idea that contradicts established scientific theory must be able to use their theory to make just-as or more accurate predictions about whatever the theory concerns. Otherwise, it is not a scientific theory.
The point here is that scientific theories cannot be used to argue about what is true or not. To understand them correctly, it takes some humility to admit that one does not, and at this point can not, know the truth. The theory is simply the closest thing to the truth that we do know.