When objects which have mass are attracted to each other, then the force between them is known as Gravitational force.
Gravity is all around us. It keeps the planets in our Solar System, for example, in orbit around the Sun. The Moon stays in orbit around the Earth also because of gravity.
The person most credited for discovering gravity is Sir Isaac Newton. As the legend states, he observed a falling apple while thinking about the forces of nature.
He realized that some force must be acting on falling objects, like apples, for example, because otherwise, they would not start moving from rest. Gravity governs the motion of planets, holds galaxies together, and determines the structure of the Universe.
There are four fundamental forces of nature, gravity, electromagnetism, weak force, and strong force. All that aside, here are some gravitational force facts.
Gravity is the weakest force
Though it may seem odd, gravity is actually the weakest force we currently know of. It only attracts and doesn’t have a negative version of the force to push things apart.
Though gravity is powerful enough to hold galaxies together, it is also so weak that we overcome it every day. When you pick out an object, you’re counteracting the force of gravity from all of Earth.
In comparison to other forces, the electric force between an electron and a proton inside an atom is around one quintillion times stronger than the gravitational attraction between them. Though we presume gravity to be weak, we don’t actually know how weak it is.
Gravity isn’t weight
When we see astronauts float on a space station, we sometimes say that they are in zero gravity. However, this isn’t true. An astronaut experiences the force of gravity by about 90% of the force they would experience on Earth.
They are indeed weightless, but since weight is the force of the ground, it exerts back on them on Earth. For example, in an elevator, weight fluctuates, and we feel the elevator accelerating and decelerating.
However, the gravitational force is the same, but in orbit, astronauts move along with the space station. Nothing pushes them against the side of the spaceship to make weight. Einstein turned this idea, along with his particular theory of relativity, and came up with general relativity.
Gravity makes waves
These waves move at the speed of light; Einstein’s theory of general relativity also predicted this. When two stars or black holes are locked in mutual orbit, they slowly get closer as gravitational waves carry energy away.
Earth also emits these gravitational waves as it orbits the Sun, though the energy loss is too minuscule to notice. A consequence of relativity is that nothing can travel faster than the speed of light in a vacuum. This also applies to gravity. If something happened to the Sun, the gravitational effect would reach us at the same time as the light from the event.
Microscopic behavior of gravity
Except for gravity, the other fundamental forces of nature are described by quantum theories at the smallest of scales, namely, the Standard Model.
We still don’t understand much about gravity, thus the lack of a quantum theory of gravity. However, researchers strive to unfold it. One of these researches called the loop quantum gravity uses techniques from quantum physics to describe the structure of space-time.
The prime idea is that space-time is particle-like on the tiniest scales, just like matter. Matter would be restricted to jump from one point to another on a flexible, mesh-like structure. This allows loop quantum gravity to describe the effect of gravity on a scale far more minuscule than the nucleus of an atom.
Another approach is called the string theory. It states that particles, even gravitons, are vibrations of strings that collide in dimensions too small for experiments to reach. However, both theories, or any others for that fact, can provide testable details about the microscopic behavior of gravity.
Massless particles – Gravitons
In the Standard Model, all particles interact among themselves via other force-carrying particles. As an example, a photon is the carrier of the electromagnetic force.
These hypothetical particles in quantum gravity are called gravitons. Scientists have recently begun to unveil how they work from general relativity.
Like photons, gravitons are massless particles in which gravity might be carried upon. To date, experiments haven’t detected any mass, but they don’t rule out a minuscule tiny mass as being present.
Quantum gravity appears at the smallest length
Though gravity is weak, it becomes stronger as two objects come closer and closer. In this event, it ultimately reaches the same strength as the other fundamental forces at a very tiny distance called the Planck length. This distance is many times smaller than the nucleus of an atom.
This is where quantum gravity’s effects will be strong enough to be measured. However, due to the small size, no experiment can accurately probe this.
Though different theories tried to postulate and come up with some answers, they weren’t successful. Observations continue, however, and hopes are high.