It’s generally assumed that at some level, gravity will be quantum, just like the other forces. But it’s possible that gravity is inherently classical, and that there are important ways that quantum processes, even involving the other forces, feed back (or backreact) onto spacetime, affecting gravity itself
It’s generally assumed that gravity is quantum, but it’s possible that gravity is inherently classical. Gravity is one of the universe’s four fundamental forces, along with electromagnetism, the strong nuclear force, and the weak nuclear force. However, gravity is the only one of these forces that lacks a “quantum” description
Quantum gravity (QG) is a field of theoretical physics that attempts to describe gravity using the principles of quantum mechanics. However, there is currently no quantum model of gravity. Current models of gravity are classical, so they break down in environments where quantum effects can’t be ignored.
Some physicists have proposed a number of theories to solve this problem. Zurek says that string theory is the best description to date. Physicists originally proposed string theory in the late 1960s.
Newton’s law of gravitation states that every particle in the universe attracts every other particle with a force. The force is:
- Directly proportional: To the product of their masses
- Inversely proportional: To the square of the distance between them
Newton’s law of gravitation provides insight into the relationship between mass and force.
Newton also developed three laws of motion:
- First law: An object will not change its motion unless a force acts on it
- Second law: The force on an object is equal to its mass times its acceleration
- Third law: When two objects interact, they apply forces to each other of equal magnitude and opposite direction
Newton’s laws of motion, along with Kepler’s Laws, explain why planets move in elliptical orbits rather than in circles.
Quantum entanglement does not cause gravity. However, some physicists have suggested that gravity and spacetime may emerge from quantum entanglement.
Quantum entanglement is a phenomenon where the properties of one atomic particle depend on the properties of another particle, even if there is no physical connection between them.
Some researchers believe that spacetime is built up of quantum entanglement. They think that gravity and spacetime may emerge from the entanglement of particles on a 2-D surface.
Here are some predictions for the future of gravity:
- Gravitational wave detections: Future gravitational wave detections from space could reveal new fundamental fields and shed light on unexplained aspects of the universe.
- Quantum gravity: Predictions can be made for quantum gravity for low-energy phenomena.
- Gravitational wave energy spectrum: The Chern–Simons -essence gravity model predicts two signals that can be verified by future gravitational wave experiments.
Einstein’s theory of general relativity predicted many phenomena before they were observed, including:
- Black holes
- Gravitational waves
- Gravitational lensing
- The expansion of the universe
- The different rates clocks run in a gravitational field
Einstein’s theory of general relativity also predicts that time passes more slowly where gravity is stronger. This is called time dilation.
Albert Einstein’s theory of general relativity (GR) describes gravity as the curvature of spacetime. This curvature is caused by the uneven distribution of mass, which causes masses to move along geodesic lines.
Entropic gravity, also known as emergent gravity, is a modern physics theory that describes gravity as an entropic force. This force has macro-scale homogeneity but is subject to quantum-level disorder
Quantum gravity (QG) is a field of theoretical physics that describes gravity using quantum mechanics. It deals with environments where quantum and gravitational effects can’t be ignored, like near black holes.
In QG, space-time behaves in new ways. Instead of creating particles, it creates universes. Entanglement may create connections between distant regions of space-time.
Some theories of QG include:
- Loop quantum gravity: Merged two lines of research to solve each other’s difficulties
- String theory: Describes a universe with 10 dimensions, six of which are unseen
Some preparatory knowledge for studying QG includes:
- Nuclear physics
- Quantum mechanics
- Special relativity and electrodynamics
- Introduction to the structure of matter(full article source google)
Universe discoveries 