Transcript

MARCUS DU SAUTOY

So, Newton assumed space and time were uniform in nature, and that gravity is a direct force that acts on objects due to mass. Einstein said space and time are curved, and that gravity isn’t even a force.

In reality, matter tells space how to curve, and curved space tells matter how to move. If you think of it this way, suddenly it makes more sense that a massive planet can have an effect on something very far away. It’s not a direct force called ‘gravity’, it’s the way that time and space curves around such a massive object.

Hmm. Hang on a minute. Does that mean that gravity as a concept is useless, and we should stop using the word? Well, no. Because Newtonian physics works really well most of the time on Earth, and so you can still use the calculations for gravity. You know it’s not totally correct, but it gives you the kind of results that work for most situations, and avoids the complicated maths of Einstein’s formulation. Obviously, if you get a job planning space probe trajectories, then Newtonian rules aren’t going to cut it for you, and you’ll need to take curved spacetime into account. But for everyday stuff, most physicists still refer to gravity, even though our understanding of its cause has changed.