Self-study
Because no other theory has been able to predict it so simply and accurately, the advance of the perihelion of Mercury is sometimes cited as evidence in support of Einstein's theory of general relativity. ████████ ████ ██████████ ███ ███████ ████ █████ ████ ████████ █████████ ███ ███████ ███ ██ █████ ████████ ████████ ███ █████████ ██ ████████ ███ ███████ ███████ ███ ███ ██████████ ████████ ██████████ ██████████ ███ ████ ███████ ██████ ███ ██ ███████ ██ ████████ ██ ███████ ██ ██████████ ███████
Summary
The accuracy with which Einstein’s theory of relativity predicts Mercury’s orbit is not evidence that the theory is correct. This is because Einstein already knew Mercury’s orbit while making his theory, and he adjusted his theory so it would correctly predict the orbit.
Notable Assumptions
The author’s argument makes sense on the surface—Einstein’s theory didn’t actually predict Mercury’s orbit; he just adjusted his theory so it output the correct numbers. But the author is still assuming this means predicting Mercury’s orbit is not good evidence that the theory is correct. We want a rule that clearly outlines this assumption:
If you adjust a theory to predict a phenomenon, then the theory’s accurate prediction of that phenomenon is not good evidence that the theory is correct.
17.
Which one of the following ███████████ ██ ██████ ████ █████ ██ ███████ ███ ████████ ██████
a
Unless a phenomenon █████████ ██ █ ██████████ ██████ ██ ███████ ██ ███ ████ ███ ██████ ██ ██████████ ███ ██████ ██████ ███ ██ ████████ ████ ███ █████████ ██ ████ ███████████
(A) leads to the wrong conclusion. We aren’t trying to prove whether Einstein’s theory discovered Mercury’s orbit. We just want to know if predicting it is evidence that the theory is correct.
b
A phenomenon that ██ █████████ ██ █ ██████████ ██████ ██████ ███ █████ ██ ████████ ██ █████ ██ ████ ██████ ██████ ███ ██████ ███ █████████ ████ ████ ██████████ ██ █████
Wrong trigger. (B) translates to—if a theory is not developed with a phenomenon in mind, then predicting that phenomenon is not good evidence that the theory is correct. We know that the theory was developed with Mercury’s orbit in mind, so we can’t use this conditional statement.
c
Unless a theory ███ ██████████ ███████ ███ ███ ████████ █████████ ████ ███ ███████ ████ █████ ██ ███ ████ ██ ███ ████████████ ██ ██████ ██ ████████ ██ ████ ██████████
Wrong trigger and wrong conclusion. We don’t know whether Einstein’s theory was able to accurately account for phenomena other than Mercury’s orbit, so we can’t use this conditional statement. We also aren’t trying to prove that Einstein’s theory as a whole isn’t well supported, just that its prediction of Mercury’s orbit does not constitute support.
d
If a theory ██ ████████ ████████████ ██ ███████ ███ ████ ██████████ ███████████ █ █████ ███████ ████ ██████ ███ ████ ██████████ ██████ ███ █████ ██ ████████ ██ █████ ██ ███ ███████
We know from the premises that Einstein adjusted his theory to match the orbit of Mercury. (D) tells us this means the theory’s prediction of Mercury’s orbit is not evidence that the theory is correct, which justifies our conclusion.
e
If a theory ██ ████████ ██ ████████ ███ ███████ ███████████ ███ ████ ██████████ ████ ██ ███████ █████ ██ ███ █████████ ██████████ ███ ███████ ███ ██████ ██████ ███ ██ ███████ ██ ██████████ ████ ███████████
(E) leads to the wrong conclusion. We want to prove that predicting Mercury’s orbit is not evidence that the theory is correct, not that the theory didn’t predict Mercury’s orbit.