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Forces, page 2 Particle Physics - Structure of a Matter fundemental particle classification

In ancient times, people believed that all matter is a variation of earth, air, fire and water. Until early 20th century people believed that the basic building block of matter is an atom, visualized as a sphere. Nowadays, we know that atoms are made of even more fundamental entities. The diagram below show an increaing magnification of an imaginary microscope on an ordinary matter.

structure of matter

Beginning with bulk matter, this is the ordinary matter that we can see, down to the nanometer size which can be seen using an electron microscope. At higher magnification, atoms and molecules (atoms grouped into one entity) beginning to manifest, arranged in certain particlar order, which defines the shape of a solid. The range of scale size is large. This is because of different number of atom types and infinitely number of types of molecules of various sizes that made up different matter.

For a given atom, it is consisted of a nucleus occupies a very small volume of space, and a collection of electrons that are attracted to the nucleus by electromagnetic forces. The lump is called the nucleus of an atoms while the extension of electrons in space defines the size of an atom. The more number of electrons the larger the size of the atom. Electrons are incredibly small. No one knows the actual size, but it is estimated at the lower scale of 10-18 m, almost a point-like. Electrons are one of the most fundamental particles. In other words, they are not made of anything smaller (so we think).

However, the nucleus is made of a mixture of protons and neutrons. The size of a proton and a neutron are similar, in the order of 10-15 m. We now know that they are not the fundamental particles. Take, for example, a proton. It is now believed a proton is made of three fundamental particles called quarks. There are six different types of quarks, of which only up (u) quark and down (d) quark made up of protons: 2 up and 1 down. This is often written as 'duu'. On the other hand, a neutron is made of 'ddu': two down quarks and one up quark. Once again, to our current understanding, a quark is a fundamental particle. These quarks are held very tightly by the strong force carrier called gluon.

We now see that the present view of the nature of matter is very different since early 20th century. Notice also we use the word ordinary, indicating the type of matter structure we are describing. This is because there are different types of matters: (i) ordinary, as what we see around, (ii) cosmic, those originated from space, (iii) high-energy, those only stable (or exist) in a high energy environment (for example in a particle accelerator or the early Universe) and (iv) antimatter (no, this is not science fiction, antimatters are real).

Forces, page 2 Fundamental particles classification

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