# Introduction

Physics is one of my favorite topics. I get really excited whenever I get a chance to talk about it with someone who is curious about how things in our universe work. There is so much to talk about, it really can’t be covered in depth in a single article. I can, however, go over some of the high level concepts in different areas of Physics and give you a sense of what the different areas are. Here we go.

# Kinematics

The most basic area of physics is what we call kinematics, which is the science of motion in objects. Using kinematics, we aim to describe the path an object will take in the future (or the one it took in the past) based on things we know about it right now. For example, if I throw a ball in the air at a 45 degree angle at 2 feet per second, where will it land? What happens if I change the angle to 70 degrees? What if I increase the velocity to 10 feet per second?

Issac Newton was curious about these things and derived a bunch of equations that describe motion in all kinds of different scenarios. He had to consider things like acceleration (gravity), elastic forces (like a spring), and friction. His equations worked so well that he was able to describe things that weren’t incredibly well understood, such as the motions of the planets. It turns out, however, that his equations break down in some cases. I’ll talk about that later.

# Electricity and Magnetism

A lot of Physics involves forces, namely the four major forces that influence all matter in the universe: gravity, the strong nuclear force, the weak nuclear force, and the electromagnetic force. Gravity is a well known to most of us. The strong and weak nuclear forces only act on incredibly small distances, so most people aren’t even aware of them (and are somewhat advanced so I won’t talk about them here — if you are interested, you can read more about it on Wikipedia). People may not be aware of the electromagnetic force, but they are aware of its effects because it is what enables us to have things like cellphones and lights and cars.

The electromagnetic force (really two forces that are unified as one — the electric charges force and the magnetic force) is a force between charged particles such as protons and electrons. We say the protons have a positive charge and the electrons have a negative charge. Positive particles are attracted to negative ones and vice versa. This force is much stronger than gravity, but the positive and negative charges cancel out (every atom has an equal number of positive and negative charged particles).

In certain materials, such as metals, the electrons can flow around groups of atoms instead of single atoms. As they are flowing around, they carry energy that can be transferred to do work, such as heating up the filament of a light bulb or causing an electronic transistor to switch states. People learned to control the flow of electrons to provide electricity, and it is all powered by the electromagnetic force. James Clerk Maxwell came up with the equations that describe the forces behind this phenomenon.

# Special and General Relativity

Now we head into a deeper area of physics where things start getting weird. Physicists knew that Newton’s equations of motion didn’t quite predict the motion of some objects accurately, such as the orbit of Mercury around the sun. Einstein set out to come up with a better understanding of what was really going on, and he published some remarkable theories that have held up for over 100 years.

One of the things that Einstein postulated was that space and time are actually one and the same (Special Relativity) and that motion through space impacts motion through time. Imagine driving on the freeway in one direction, and you start getting onto an off-ramp. As you start moving sideways, your speed in the original direction decreases, and your speed in the sideways direction increases.

The same happens with space and time. As you increase your speed in space, you decrease your speed in time — you literally experience time flowing at a different rate than someone going slower or faster than you. This has been tested by putting atomic clocks on planes and flying them around and then later comparing them with clocks that stayed on the ground. The clocks that stayed on the ground are ahead of the ones that flew in the air.

One thing that Special Relativity didn’t account for was motion in an accelerated environment, such as gravity. Einstein came up with a separate theory (General Relativity), and one of the things he theorized is that gravity is caused by the mass of objects bending space. The more massive an object is, the more it bends space (and also time). If you are close to the earth where the gravitational field is strong, your clock will run slower than a clock high up in space where the gravity is much less.

These effects are so pronounced that they even effect simple things like GPS satellites. Because the satellites are in a lower gravitational environment and are moving much faster than us, they experience time at a much slower pace. We need to apply an adjustment to their prediction of where we will be because otherwise, it would be off by a significant amount.

# Quantum Mechanics

By now, most people have at least become aware of the fact that there is something called Quantum Mechanics, especially because we are starting to build Quantum computers. Understanding what this means, however, is much more difficult.

We study small things like electrons and quarks by hitting them with other particles (this is what particle accelerators are for). To see things more accurately (i.e., on smaller scales), we need to use higher energy particles. Unfortunately, the act of hitting one particle with another has unintended consequences.

Physicists realized that it isn’t possible to measure different state values, such as position and velocity, simultaneously. This is because of the fact that when we hit one particle with another, we change its velocity and position. The more we try to make position more accurate, the less accurate our velocity measurement is, and vice versa. This is known as the Heisenberg Uncertainty Principle.

Because of this uncertainty, we are forced to instead predict probabilities of these states. Equations were derived that described these probabilities, and one shocking result is that although particles like electrons have extremely high probabilities of being around their atom’s nucleus, the probability that they could be somewhere else in the universe is not zero. Even millions of miles away is a possibility, but an extremely unlikely one.

Experiments also showed that in some cases, particles act more like waves (now called probability waves) than point particles. The best example of this is the double-slit experiment (take a look at the Wikipedia article for more details). What makes the experiment so strange is that if we try to detect which slit an electron goes through, we see a different behavior than if we don’t detect which one it goes through — in the latter case, it appears to go through both at the same time!

This is where quantum computers comes in. The bits of a quantum computer can actually exist in both a 1 and 0 state at the same time (in analog computers, every bit is either a 1 or 0 but not both). When we run a program through the quantum computer, it is as if we try all the different keys to a lock at the same time (the probability wave collapses into a single point, the point being the answer we seek).

Quantum Mechanics has one more really strange phenomenon called entangled particles. Particles that have become entangled will both resolve to the same state (or complementary states— up and down, for example) when measured (measuring a wave particle causes it to collapse). This resolution will happen simultaneously even if the particles are separated by great distances. Physicists have yet to understand how this happens.

# String Theory

Quantum Mechanics has been able to tell us a lot about the world of the very small, but when Physicists tried to bring Quantum Mechanics and Relativity together (small particles in high gravity zones), the equations started giving nonsensical answers. This was important for understanding things like black holes, and despite years of research, no way of merging the two was discovered.

Physicists began to look in other directions and came up with a collection of theories that are collectively called String Theory. The idea of this group of theories is that matter is made up of incredibly tiny strings that exist in a multitude of dimensions (the three main physical dimensions, the time dimension, and other dimensions that small and curled up inside the strings). The basic elementary particles like quarks come into existence by different vibrational patterns of the strings.

Unfortunately, if the theory is correct, these strings are so incredibly small that we would need particle accelerators beyond our capabilities to build in order to see them. Without some other method of measuring particle states, these theories are unlikely to be confirmed any time soon. The tgeories have, however, allowed Physicists to better understand the world in places where things are both tiny and the effects of relativity are strong.

# Conclusion

I’m no physicist, and I strayed away from math as soon as I encountered differential equations, but the incredible things we have learned from Physics fascinate me. Physics has helped us understand the motion of objects such as the planets in our solar system. We have used physics to create electronic devices that we depend on every day. Advanced areas of physics have allowed us to perfect complex technologies such as GPS satellites. As we push the boundaries of our understanding of the universe, we will continue to reap the benefits of that understanding thanks to Physics.

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