Willelm said:
Well, there are things like the number of electrons of each element and the speed of light and sound, that are set randomly without any rule. Why physicists are interested in such randomly facts?
It's all about perspective. I don't find these thing to be random; they are what they are. You may find these physical traits to be random and unrelated, but physicists try to make sense of these facts and relate them.
For example, the permeability of free space ( the μ
0 constant within the equation for magnetic force ) was defined a relatively simple value, but its sister constant, the permittivity free space, ( the ε
0 constant within the equation for electric force ), had an experimentally determined value. These funky numbers seemed unrelated mathematically, but physics experts had a hunch that they were based on the nature of the forces involved. After many investigations, a beautiful relation was discovered. Behold:
$$c=\frac{1}{\sqrt{ \varepsilon_0 \mu_0}}$$
( c ) represents the speed of light. Now the constants don't seem as random. Speaking of the speed of light, does it's value ( 2.9979x10
8 m/sec ) seem random or are our metrics for measuring space and time ( commonly the meter and second, respectively ) truly the cause for such speed's randomness? Since this question asks for subjective answers, it belongs in a philosophy forum. Nevertheless, most physicists redefine the metric for space and time so that the speed of light is simply$$c=1$$
No units, no powers of ten, no infinite decimal places, just one. The speed of light is so fundamental and natural, physicists treat it as if it were a natural number; it's easy to deal with.
Now for the number of electron in an element, it doesn't seem random or arbitrary to me. Quantum mechanics clears that up nicely.
The speed of sound is not random; it depends on temperature and its medium material. The speed of sound is much faster in solids and liquids than in gases.