Well, we actually sort of know that something is different far away, since the rotation profile of galaxies do not match theoretical predictions. There are curr

Well, we actually sort of know that something is different far away, since the rotation profile of galaxies do not match theoretical predictions. There are currently two different resolutions, either postulating new particles (dark matter and energy) or change of fundamental laws (MOND theories). Since we didn't manage to detect either in our solar system we know that something is different.