Gravity
Einstein’s Approach to Gravity
In the introductory material, we read that Einstein resolved some discrepancy within Mercury’s orbit. Well, he did, while providing the most accurate understanding we have of gravity, and being at the forefront of hair modeling.
What did Einstein add to gravity, anyway?
What if, instead of thinking of the masses as just sitting there on a (flat, constant) 3-dimensional grid of spatial coordinates, we imagine that the masses can warp the fabric of space itself? It’d be like putting bowling balls on a trampoline. That’s what happens to spacetime when stuff with mass exists in it: it warps.
This idea is shown below with a two-dimensional coordinate plane, stretched into three dimensions.
The more massive the object is, the deeper and steeper the space “funnel” it creates. Other nearby objects “roll down” the gravity funnel made by our original object. This “warped grid” view of gravity explains the warping of spacetime that occurs near black holes, and any other massive object. Light even bends around our own Sun.
Newton explained the planets’ motion around the Sun using an invisible, attractive force called gravity. Einstein revolutionized this idea by saying the planets were following their paths in the fabric of the Sun’s general warping of space-time. Both claims lead to the same orbital motions observed in planets, etc. Einstein’s claims provide greater accuracy than Newton’s.
It’s a mind-boggling concept, but it works great on paper. Not so much on fabric. Once Einstein makes an appearance rather than writing equations of motion for the objects, we change the mathematics so that they describes the space in which these objects exist itself. This way of thinking allows us to visualize what a singularity of infinite mass, known as a black hole, can do to the space around it. We’ll bring this up again later in physics, but for now, just imagine Aunt Gertrude ripping a hole in the trampoline. There’s no coming back from that. Fun time is over.
Einstein’s Theory of General Relativity allows us to trace the evolution of space itself. It almost single-handedly gave birth to the science of cosmology, the study of the origin of the universe. Not to be confused with Cosmetology (the science of hair cutting), cosmology is a subject to which Einstein could have added to our understanding in addition to spacetime and relativity, two subjects he’s most known for. .
Looking ahead of Newtonian physics, we point out that while gravity plays a central role in modern astronomy, astrophysics, and cosmology, it’s far too weak of a force in comparison with the electromagnetic and nuclear forces to be of any consequence in the world of quantum mechanics, another area of modern physics. However, don’t take that as a personal suggestion to ignore gravity when determining theories of skate boarding or skydiving baking.
And don’t ignore Einstein’s general relativity and ideas on spacetime when accounting for our next planet’s orbit.