When do we have to give up on an old theory and try to come up with a new theory?
Would it be when the old theory under goes changes?
Also, how would I compose my answer to this question into a paragraph?
This happens when we suspect that the theory is not perfect. E.g., the Standard Model of particle physics has not been falsified experimentally (except for the fact that neutrinos are not massless, but that can be repaired), but we know that it cannot describe Nature correctly, because it doesn't include gravity (and it cannot be changed to include it in a trivial way).
Also there are are some other technical problems with this theory, but so far no experimental violations. But this is enough for physicists to search for new theories.
If, on the other hand, there are no good reasons to believe that a theory is false, then you won't see many physicists searching for alternative theories. A good example is quantum mechanics. It is believed by almost all physicists that the principles of quantum mechanics are exactly true. There are only a handful of physicists who work on alternatives to quantum mechanics.
Thanks!
To compose your answer to this question into a paragraph, you can start by explaining that the decision to give up on an old theory and propose a new one typically occurs when there are indications that the old theory is not perfect or complete. For example, in the case of the Standard Model of particle physics, although it has not been experimentally falsified except for certain minor issues that can be addressed, it is known that the theory cannot correctly describe nature because it does not incorporate gravity in a straightforward manner. Additionally, there may be other technical problems with the theory, even if experimental violations have not yet been observed. These reasons are sufficient for physicists to start looking for new theories that can better explain the phenomenon at hand.
On the other hand, if there are no substantial reasons to doubt the validity of a theory, then there is typically no need for scientists to actively search for alternative explanations. A prime example is quantum mechanics, which is widely accepted by the scientific community as an accurate description of reality. Only a small minority of physicists explore alternative theories to quantum mechanics.