Hi /sci/! How do I convince my flatmate that a scientific theory is not a the layman's 'theory' ie. a theory has hard evidence like the 'theory of gravity' or the 'theory of evolution', rather than a 'theory' as in an opinion. They also do not understand that it is incorrect to say 'I believe in this theory'. Does a scientific theory not have hard evidence and is therefore the truth?
A theory can have evidence. But you generally can't prove a theory right. You can prove it wrong though. Supporting evidence plus the lack of a proof against a falsifiable theory usually counts as "this is more or less true".
Too see why you would need to believe in a theory, take the most fundamental version of the theory of gravity, which can be summed up as: "things fall downwards".
("down" being the direction that things fall in, so basically your theory would be that all things fall in the same direction, at least when they are in the same place.)
You can't check that everything in the whole universe actually falls downwards, so you'd have to take it on faith. However you can gather evidence by dropping loads of things and see which way they fall, and also there will never be any proof of the opposite. Thus your theory is "true".
>Is there any way of describing someone that only accepts that which has hard evidence? i.e in your example someone who has seen the hard evidence on dropping things?
I'd call such a person "reasonable"
Mostly because if you believe things that you don't have evidence for, you are unreasonable
Only if it's a hard contradiction, which almost never is the case.
Example: the "stuff falls downwards" theory, above, is impossible to deal with this way. There is no hard contradiction. No matter how many times you drop an object and say "hey look, this one doesn't fall upwards", it's not a contradiction of the assumption that the theory is wrong because something else might fall upwards.
The only thing we have, and the only thing we ever CAN have, is evidence plus lack of proof to the contrary.
The "theory" of the sun orbiting the earth was found to be false despite being widely believed.
A theory is something which has been thought up; usually has some evidence in order to support it. However it isn't exactly (at least always) the whole truth and nothing but the truth.
You can't prove anything about the physical world, only about our mathematical models of it. We can predict the trajectory of a projectile, and then launch projectiles every day for years, but we still don't know that they will *always* follow a parabolic trajectory.