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Here is a simple introduction to physics for non-scientists.
What does the common person think the world is made of? One possible list of things would be: "different people, animals, plants, earth, sky, rocks, water, cars, televisions, telephones, ghosts, gods, spirits, minds,..."
One of the main fields within physics is the study of what the universe is made of, that is to say, the study of what exists. You can take a rock, break it up, and see that it is made up of smaller rocks. Each one of these tiny rocks is generally different. In the same way you can take a plant and break it up and find out that it's made up of tiny little plant cells, each one generally different. These cells are made up of organelles, proteins and other smaller matter. Physicists keep breaking things apart to find out what they are made of, and have reached a stage that is orders of magnitude more interesting and important than knowing that a plant is made up of tiny plant cells.
One of the most amazing discoveries in physics is that the whole universe is made up of a very small and simple set of things: 3 space dimensions, 1 time dimension, and not much more than a few tens of fundamental particles types. I'll call these things the "elements of the universe".
If we restrict ourselves to those particles that make up the bulk of the stuff around you, we have only 3 particles: electrons, protons, and neutrons. People are made up of just different combinations of those 3 kinds of particles. So are animals, plants, rocks, the sky, cars, and televisions; they are all made up of different combinations of those 3 kinds of particles. Another particle which is very important in your daily life is the photon, which makes up light, as well as all the radio waves that your mobile phone uses to communicate with others.
There are many particles of each kind, but one thing that is of great significance is that every particle of the same kind is perfectly identical. It differs only by a few very simple variables, such as its shape, position, velocity and so on. The important thing to remember is that if you take an electron away from a human body, you can take absolutely any electron from anywhere in the universe to replace it, and the human body will behave in exactly the same way regardless of which particular electron you took. This is due to the fact that every electron is identical.
So physics has taken the long and complex list of things in the universe, and has discovered that everything is made up of a very short list of particles types. Compare this perfectly valid yet simple description of what exists in the universe with the invalid yet complex description given by a common person who does not know any physics.
The fact that the universe is made up completely of a very small set of particle types is a very intriguing fact. Somebody who is used to thinking of the universe as being made up of all sorts of completely different and unrelated things should be pleasantly surprised to find out how simple the universe really is.
So now we have learned that what exists are just 3 space dimensions, 1 time dimension, and a few tens of particle types. Not much. Another important part of what physicists do is study these elements of the universe. We measure the different properties of each particle, such as its mass, its charge, its spin, and various other properties they have. It turns out that not only is the universe made up of a very simple set of elements, but the properties of these elements are also very simple. This makes it quite easy to understand the elements of the universe. The kinds of things that are discovered by such understanding will be talked about in the following chapters.
If we take a proton and combine it with an electron, we get a hydrogen atom. If we take 8 protons and 8 neutrons, pack them together tightly, and add 8 electrons, we get an oxygen atom. If we take an oxygen atom and bond it with 2 hydrogen atoms, we get a dihydrogen monoxide molecule. What are the properties of this molcule? What is its color? What happens if we put a whole lot of these molecules into a jar? Physicists can make calculations that will predict all of this substance's properties. It turns out that all those properties are in perfect agreement with the properties of what people call "water". It turns out, water is made up of dihydrogen monoxide molecules.
What happens if we create atoms using 47 protons and 60 neutrons each, with 47 electrons. Physicists can perform a calculation that shows this to have a white color. In fact, this is what silver is made of. What about using 79 protons, 118 neutrons, and 79 electrons? Physicists can calculate that this has a yellow color. In fact, this is what gold is made of. Because we understand how the elements of the universe work, we can understand how everything made up of these elements work by simply doing some calculations.
As you can see from the above simple examples, everything is made up of particles. Just change the way in which you combine the protons, neutrons and electrons, and you get all sorts of different matter. This includes water, gold, silver, your skin, your eyes, computers, spacecrafts, the sun, the stars, the moon, and yes, even you. One of the things physicists do, is study the different ways in which you can combine particles to create new kinds of matter.
Notice that I only needed to give the number of protons, neutrons and electrons for a physicist to be able to calculate the color of the substance. This is in stark contrast to what has to be done without physics. Without physics, you'd have to actually take those protons, neutrons and electrons, and combine enough of them so that you can actually see the color with your eye or a camera. Because physicists know almost everything about protons, neutrons and electrons, they don't need to actually build the atoms to discover their properties, they just need to think about it, or do some calculations. You want to invent a new substance with a particular density, color, softness and sexiness? No problem; just do some calculations. There is no need to randomly mix chemicals in the lab anymore for every new combination you think of... you just need to do some calculations on the computer.
Since time is one of the elements of the universe, it is also something a great deal of physicists study. How does time work? What are the relationships between the past, present and future? How do particles and combinations of particles evolve as time passes? These are the kind of questions physics answers.
Let's say you start with a set of particles at the present time. Where will those particles be in the future? Physicists study the relationship between the past and the future. If we start with particles arranged in the way that a tv is, what will they be like a few seconds later after somebody presses the power button? We already know that the future state of the particles after the power is turned on is in a kind of state in which a picture is displayed on the screen. In fact, physics is what was used to invent the television. We knew that the world is made up of particles, and we knew how particles acted. We then asked the question: "How should those particles be arranged, so that after somebody presses a power button, we have a moving picture on a screen?" The answer was calculated using physics, and after enough calculations were done, we set out to actually build a tv. And now many people are enjoying the comfort that the television provides.
In order for physicists to calculate the properties of combinations of matter, and behaviour of matter with time, they use language, logic, and mathematics.
Physicists need language to make statements, and to define the meanings of words and statements. At least one natural human language is needed, and most advanced languages, such as english, are sufficient. In addition to the natural human language, logic and mathematics are languages themselves that extend the natural human language.
Logic provides the means to make sound arguments using the english statements in physics. Everybody uses some logic in their everyday lives, and the way in which physics requires it, is very similar, except that it is used with much more precision and rigour.
Mathematics serves as a very efficient language to help describe the properties of the elements of the universe. A simple example is the way mathematics defines the multiplication operation to simplify a very long and cumbersome set of addition operations. The most complex properties of the elements of the universe are described using mathematical formulas. Mathematics is also used to make calculations that start from the formulas describing the properties of the elements. The color of gold, for example, is calculated through a very long operation made up of thousands of simpler mathematical operations. Another example is the calculation of what would happen in the future if I press the power button on a television. Physicist execute many mathematical operations to figure out that a television designed in a particular way would display a moving picture.
There are two major ways in which computers are related to physics. First, physics is used to design and create computers. Second, computers are used to help physicists perform calculations.
Just like your television, physics is required to design and create computers. The properties of the elements of the universe are used to figure out how we can build a machine that will behave like a computer. This includes, for example, figuring out the properties of semiconductors, such as those made from billions of silicon atoms bonded into a large crystal lattice. Silicon atoms can each be made by combining 14 protons, 14 neutrons, and 14 electrons. One of the goals in designing a computer is to create a machine that we can control, communicate with, and which can execute mathematical calculations much more quickly than a human can.
Although a human can perform at most a few additions per seconds, most desktop computers found in people's homes can perform over a billion additions per second. Calculations that would take a lifetime for a human to do without a computer can be done in less than a second using computers. Computers are currently used to make many calculations to figure out the properties of very complex combinations of matter, like the proteins in your body.
Since everything in the universe is made up of the elements of the universe, and physicists understand the elements of the universe, using physics, computers and effort, we will eventually be able to understand everything in the universe. With effort, we will be able to explain the operation of every particle in your brain that causes you to think and believe in your own existence. You can imagine all the fields of science as subfields of physics. For example, biology can be a considered a subfield of physics, in which you study the properties of matter made up of the elements of the universe, that happen to take the shape of living beings.
Historically, physics was completely disconnected from other fields of science, such as chemistry, biology, and medicine. With time, everything in the other fields of science will be understood in terms of physics. The main obstacle in achieving this is the large amount of computing power we need to be able to make the calculations for all the particles studied in large objects. Medicine, for example, deals with human bodies. A human body has over 10,000,000,000,000,000,000,000,000,000 particles. Calculating the behaviour of all those particles, even with extreme simplifications and approximations, takes a lot of computing power. The main obstacle remaining for being able to understand the complete human body, including a human's complete thoughts, is the power of our computers. With time, as we build more powerful computers, we shall be able to explain all the functions of the human body using physics. The limited power of today's computer is the only reason medicine is still highly disconnected from physics. Only a small subset of current medical knowledge has been derived using physics.
The ability for physics to explain all scientific knowledge, is one of the things that attracts many people to study physics.
I hope this was an interesting introduction to physics. If there is anything else about physics that you would like me to explain, send me a comment!
Introduction to Physics, by The Humanoid