## Tuesday, January 30, 2018

### Gravity & Time

When we study how the universe behaves, we observe four forces (interactions): electromagnetic force, gravity, strong nuclear force, and the weak nuclear force.

### Strong & Weak Nuclear Forces

The strong and weak nuclear forces are not directly observable by us since they operate on the atomic and sub-atomic scale, respectively.

The strong nuclear force is the strongest of the four forces and it's the force that holds matter together. It is approximately 137 times stronger than electromagnetism, a million times stronger than the weak nuclear force, and 1,038 times stronger than gravitation.

The weak nuclear force takes place over a distance of less than the diameter of a proton. It is the mechanism of interaction between sub-atomic particles.

### Electromagnetism

Electromagnetism is a universal force we interact with and manipulate. This force travels as wave-particles (photons) and it includes light, heat, microwaves, x-rays, radio waves, etc. Since one of its properties is that it travels as waves, we can constructively and destructively interfere with it. Magnetism, which is part of this force, provides a great example of how this force works when playing with magnets. A north pole and south pole are attracted to each other, while like poles repel each other.

Being able to attract and repel electromagnetism, along with the ability to block it, is a key principle of this force. We pull down a window shade to block out light; we look into a mirror and it reflects (repels) light back at us.

### Gravity & Time

Gravity is simply a force that brings all matter together. What prevents the entire universe from lumping together into one big ball of matter is gravity's interaction with the other forces. When climbing a tree and sitting on a limb, I can fell gravity pulling me down while the other forces overcome gravity's pull and keep me (and the tree limb) from falling to the ground.

Time, on the other hand, isn't an actual force. Rather, it's a dimension which can be measured, along with the three spatial dimensions (length, width, and height). Specifically, time is measured by the passage of events. But, on an absolute scale, time can vary which is clearly observed when traveling at speeds close to the speed of light. When a person travels at close to the speed of light, their immediate perception of events seems normal, but their surroundings will be sped up, like watching a time lapse movie. This isn't an illusion. The twin paradox is a thought-experment that illustrates the differences in the passage of time. If one identical twin travels on a rocket at close to the speed of light, they will return to find that their twin, who remained on Earth, has aged more. This phenomenon has been verified by flying a highly accurate atomic clock on an airplane and noticing the time difference when it has returned.

While time slows down as matter approaches the speed of light, there's an asymptote where matter can never reach the speed of light without requiring an infinite amount of energy. Light, on the other hand, is massless and it always travels at the speed of light which, in theory, means time has stopped for a photon of light.

What's interesting about gravity, as well at time, is it only acts in one direction or dimension. There seems to be no anti-gravity at any level. This makes it hard to measure since it can't directly react or be absorbed with a measurement device like, say, a light meter that measures brightness. While we can measure the passage of time, we can't measure its force, especially because that depends of its frame of reference.

In other words, there's no way to block gravity or travel through time. Perhaps neither one truly exists as a fundamental quality, but rather as a consequence?