Which is right? Silly question. It’s easy to see that history and geography are compatible but different. Much the same can be said for quantum mechanics and relativity. Relativity depends on measurement of time, and famously shows that time runs faster at the top of a mountain than at the bottom. Accurate atomic clocks can even show this at a height of a few centimetres. This kind of measurement just becomes too difficult when we are dealing with the tiniest objects we know about, which are the particles that make atoms. Here, centimetres are like thousands of miles. If the atoms in your fist were the size of a marble, your fist would be about the size of the earth. To make the nucleus of an atom the size of a small marble the atom would have to be as big as a football stadium. Most extraordinarily, atoms are mostly empty. It is a mind blowing fact that if you subtracted all the spaces between its atoms’ cores from the Empire State Building it would be about the size of a grain of rice. It is not hard to see why human scale measurement in this tiny world is just too crude. Even if we are dealing with a mountain, measurement has to be highly precise in order to detect any difference in time passing. The tiny scale of objects like atoms effectively obliterates such difference. And this is not just about scale. No apparatus exists which can measure atoms in this way, for the simple reason that the measurement tools interfere with the process. The measurer obliterates the measured. Detection is indistinguishable from result. For this reason quantum physics is a different discipline entirely. It abandons measurement and adopts instead a probabilistic approach. We can’t measure the movement or position of particles but we can work out what they probably do. This approach has worked spectacularly well. It makes technology work. So it is not the case that quantum mechanics and relativity are incompatible or contradictory. In fact that’s nonsense. Treating quantum mechanics as if its probabilistic calculations are objectively real has produced some outlandish conclusions. Objects are never in two places at once. Probability is kind of real but you can’t eat your dinner on it. Our two scientific tools are both useful. Just as measurement is unreliable at tiny scales, so probability becomes hugely complex at larger scales, as objects become more and more entangled with each other. Each science gives a different view. A bit like history and geography, they are different methodologies and are doing different things in different ways.