On The Debate On Einstein And Newton

Recently, I read an article on NBC news which had a very catchy title – ‘Einstein proved Newton was wrong about gravity. Now scientists are coming for Einstein’. The title itself set off alarm bells in my head, it’s not exactly accurate. The article itself was more unbiased and told a good tale, but I just wanted to write about the debate and how theories work in physics.

So the thing is, Newton was neither wrong nor was he completely right. Newton proposed that the force of gravity varied with the inverse of the square of the distance between two bodies that have mass, and directly proportional to the product of the masses of the bodies. The force of gravity was defined as a consequence of mass and the further away the two bodies were, the lesser would be the strength of gravitational attraction between the two bodies.

The following experiments substantiated this claim. It helped Kepler calculate the orbits of the planets. It worked when a torsion balance was used to test it. The thing is, this was a perfectly fine theory for certain energy scales. At very low energy scales, Newton’s Laws are a perfectly good description of gravity. Now, there is one glaring issue with Newton’s theory. It does not talk about how gravity works but just tells us how to calculate the force of attraction and figure out how the matter will move under the influence of gravity.

Now, when we observed the orbit of Mercury, we realized Newton’s theory was not the complete truth. There was an unexplained precession in the orbit of Mercury that the inverse square law was not able to predict. According to Newton, the orbit should have been stable, with no precession. This issue, however, was resolved by Einstein’s Theory of General Relativity. His theory has a very accurate description of the precession and gave meaning to gravity. Gravity, he said, influenced the very fabric on which our entire cosmos was built on. An important point to be noted here is that one of the first tests of General Relativity was that whether we could recover Newtonian gravity at large distances, and Einstein’s theory passed this test with flying colors.

Now, moving on, physicists have been having a go at Einstein for decades. Einstein’s theories are also not a complete description of reality. It describes gravity at certain energy scales. It fails inside a Black Hole, and especially when we start asking questions about the singularity and the nature of spacetime itself within the Black Hole.

Many potential theories want to try and figure out what gravity does at those scales. These are theories like Quantum Gravity, Loop Quantum Gravity, String Theory, Shape Dynamics and many more. If any of these theories are going to be an accurate and absolute theory that describes gravity universally, it has to recover Einstein’s theory at the appropriate energy scales.

The thing about modern theories is that it is becoming more and more evident that we cannot figure out a so-called Theory of Everything from scratch. What we are doing now is coming with theories of forces that are valid at some energy scales. The future step may be to try and piece all these together into one equation that talks about everything but that might not be possible. We will probably have bits and pieces of theories, each of which will work at specific energy scales. Right now, we are trying to test Einstien’s theories at extreme energy scales and hoping that shows some cracks which will give us a good starting point to see where we can go. But then again, given how Einstein’s theory worked every time we tried to crack it, there is not much to look forward to. The best we can do is wait and hope.