### The Four Fundamental Forces

- The four fundamental forces include: gravity, electromagnetism, strong nuclear force, and weak nuclear force.
**Gravity:**Sir Isaac Newton was the first person to discover gravity when an apple fell from a tree and landed on his noggin'. Gravity is very weak and acts between objects with mass. It's the reason we don't fall through the center of the earth or float into mid air.**Electromagnetism:**Is much smaller and acts between electrically charged particles. It gives off electromagnetic fields and includes electricity and magnetism.**Strong nuclear force:**Keeps nucleus together by binding protons and neutrons together. Strong nuclear force is the strongest out of the four forces. The main purpose of this force is to hold particles together at the subatomic level.**Weak nuclear force:**Responsible for radioactive decay. It is stronger than gravity but only effective at very short distances.

### Einsteinâ€™s General Relativity

- The theory was published in 1915.
- Einstein explains that the universe is like a giant sheet stretched out, like a trampoline.
- The more massive the object, the greater the dent in the sheet. The less massive, the smaller the dent.
- Gravity is found from the steepness of the dent.
- The theory means space and time are formed into one which is called the space time continuum.
- Relativity influences space and time. When space-time is bent it affects space and time.
- Black holes are nearly infinite, bending space time, so it doesn't let light escape.

### Quantum Mechanics

- The quantum world is much different than the real world, it is very small and we can't see it.
- Nobody can know the outcome of something, just the probability of the outcome.
- It describes the way the world works at a microscopic level.
- Quantum mechanics is very hard to experiment but we do know that it doesn't equal relativity.

### Unification

- Unification was Einstein's quest for everything in the universe to be explained into one equation.
- A common problem that occurred during the quest for unification was anomalies.
- Anomalies are when an equation ends up not symmetric / doesn't equal each other.
- In 1984 however two physicist proved anomalies weren't present anymore and proved unification correct.
- All four forces haven't been unified yet because they haven't incorporated gravity.
- The overall theory hasn't been reached yet, but may be someday.

### String Theory

- The discovery of string theory was an accident and is difficult to find results for because it can't be tested.
- String theory states that there are 11 dimensions with parallel universes.
- String Theory is an idea in which the particles of physics are replaced by one-dimensional objects that are referred to as strings.
- Along with unification, string theory is an attempt to unify the four fundamental forces into one unified theory.