Of all the fundamental forces, Gravity is the most fundamental to our experience on this planet. We’ve always known that what goes up must come down, though we never really knew why.
Aristotle believed that objects fell toward Earth because they wanted to move toward their “natural state”. Because Aristotle was wrong about everything.
Galileo proved that objects fall at the same rate regardless of how heavy they are, and that they fall at a constant acceleration of 9.8 meters per second squared.
Sir Isaac Newton was the first to grasp that gravity was an attractive force between objects with mass and was able to devise the equations around gravity that we still use today.
Then Einstein redefined our understanding of gravity as a curvature in space-time caused by objects with mass.
Now, a common misconception is that gravity doesn’t work in outer space because we always see astronauts in zero gravity.
And if you’re anything like me, you grew up seeing this and just thought that the further you get away from the earth’s surface, the less gravity affects you, and that’s why astronauts get to float around all cool up there like that.
But that’s not how it works. That’s not how any of this works.
The reason these astronauts are floating is because they’re in orbit around the planet. And orbit is basically a state of always falling.
So being on the ISS is basically like constantly being in an elevator that’s plummeting toward the ground.
Some people, myself included, originally mistook the higgs boson as the force carrier for gravity because when you look at the standard model of particle physics, the other three fundamental forces all have force carrier particles called bosons.
Specifically, photons, gluons, and w and z bosons.
But the higgs boson is the force carrier of the higgs mechanism, which is a totally different thing. So I was wrong. I know, go figure.
But because all the other forces have force carrier particles, it was assumed that gravity would as well, which scientists called the graviton.
The graviton, if it exists, would be massless, because it works over unlimited distances, and would be a spin-2 boson, also known as a tensor boson.
It’s been theorized a massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do.
Gravitons also pose a problem with a mathematical issue called renormalization.
These issues have spurred some researchers to look for answers outside of quantum field theory like in string theory.
Some have tried to merge the supersymmetry found in string theory with general relativity in what they call Supergravity.
In the 80’s a theory called Modified Newtonian Dynamics, or MOND was introduced which tries to explain the movement of stars in galaxies without the use of Dark Matter.
Later, in 2004, MOND got modified further to create tensor-vector-scalar gravity which relies on a relativistic lagrangian density that maintains the law of conservation of energy.
Another popular idea is Erik Verlinde’s entropic gravity, which argues that gravity is an emergent force that arises from entropy itself and not a fundamental force at all.
And who can forget the chameleon particle theory, which has a variable effective mass that is an increasing function of the ambient energy density, meaning the particle’s mass changes to cause different effects on the particles around it.
So strangely, the first force we were aware of has become the last to be fully understood. And the one that, if we do ever fully understand it, would unlock the secrets of the universe.