The strong interaction is, as suggested by its name, the strongest of all interactions. It is about a hundred times stronger than electromagnetism (and about a hundred trillion trillion trillion times stronger than gravity). How is it possible that we almost never hear about this interaction if it has such an immense strength? The problem is that its range is just billionth of a millionth of a meter. It may seem that a force with such a short range would never be able to influence our universe in a significant way, but the truth is that without the strong interaction, humans would never be able to exist.

As already mentioned, the universe was flooded with elementary particles right after the Big Bang. Those then started clumping together to create composite particles – quarks started forming protons and neutrons. But what caused them to attract? Why were quarks so keen on creating more complex particles? As you may already suspect, the attraction between individual quarks was provided by the strong interaction.

It does not end here, though. The strong interaction is to blame for another crucial phenomenon of our reality – the existence of atoms. We already know from the previous chapter that the same electric charges repulse each other. However, this means that protons in the nuclei of complex atoms should repulse and escape into all conceivable directions. But the strong interaction ensures that protons remain together. If electromagnetism were just a tiny bit stronger than the strong interaction, the existence of atoms would simply be impossible.

The final force, the weak interaction, may be the least known and the least interesting of all interactions. However, this is not to say it is not important. The weak interaction has the power to turn a neutron into a proton. Why would it do that? Within some atoms, there is an unstable ratio between the number of electrons and the number of protons in the nucleus. And the weak interaction is here to make sure that this instability is eliminated. When there are too many neutrons in a nucleus, the weak force simply turns one of them into a proton. This phenomenon is called the beta decay.

As we know from the first chapter, the number of protons in the nucleus determines what atom we are dealing with. But this means that any time an atom undergoes beta decay, which adds one proton into its nucleus, the whole atom changes into a different element. The weak interaction can therefore turn carbon into nitrogen or hydrogen into helium just by turning neutrons into protons.

And that is all. We have reached the end of the story of interactions. They make sure that our universe functions the way it does and without them, we would have never existed – perhaps with the exception of the weak interaction, which is the only one that does not affect the course of the cosmos in a significant way. Now, we can focus our attention on another fascinating element of our universe – huge fusion factories which are making billions of photons each moment.

https://play.google.com/store/apps/details?id=brychta.stepan.universe

Electromagnetism might be the best-known interaction to us. However, we mostly speak about two separate entities. First of them, electricity, is a force our entire modern society is based upon, since it propels possibly all modern devices, from the most primitive calculators to the fastest supercomputers. Without electricity, we would never have televisions, the internet, computers, and a lot more. There is no doubt that electricity is crucial for the proper functioning of today’s society. But what about the other of the two entities? Magnetism is mostly known for being an endearing force, due to which we can attach various objects to our fridges. But is electromagnetism really like that?

It turns out that electricity and magnetism are very closely related. So related, in fact, that one could not exist without the other. If you move an electrically charged particle (electron, for instance), a magnetic field is spontaneously formed around it. Conversely, anytime you move a magnet, an electric field is created. This phenomenon is exploited in power stations. Nearly all power stations are built on the principle of electromagnetic induction – a magnetic field is placed to the vicinity of an electrical conductor and spins perpetually (here, different types of power plants come into play – each type achieves the spinning of the magnetic field in a different way), which causes electric current to form in the conductor.

Just like gravity, electromagnetism has an infinite range. Unlike gravity, however, it does not affect every single object in the universe but only objects with electric charge (opposite charges attract each other, same charges repel). Nevertheless, electromagnetism can be observed all around us. Let us now describe individual manifestations of electromagnetism one by one. And we are going to start somewhat unexpectedly – with sight.

Sight is the most important of human senses. More than three quarters of all sensory perceptions our brain receives to process are provided by our eyes. Eyes that have been through hundreds of millions of years of evolution, so that they can function properly. All the various organs of sight, from the simplest of eyespots inside the bodies of minuscule organisms, to the most perfect eyes in the animal kingdom, have the same mission – to detect a specific part of the electromagnetic radiation which we like to call light.

As the name itself implies, electromagnetic radiation has something to do with electromagnetism. Its creation and propagation occur quite simply – a moving electric field generates a magnetic field, which in turn again generates an electric field, and so on. These repeating fields travel through space-time (at the speed of light, of course) until they reach an impediment that would absorb them.

For example, the electromagnetic radiation sent by the screen of the device on which you are reading these words travels into your eye, where it is absorbed and transformed into electric signals leading right to your brain. Once there, the signals are processed and consequently decoded as an image. If electricity and magnetism were not a conjoined entity, light would not be able to exist.

Now let us move to the subatomic level. Focus on any object in your field of vision. Positively charged protons attract the negatively charged electrons, which ensures the existence of the atoms your chosen object is made of. If we move a level up, we quite likely encounter molecules (collections of atoms) of the object. These molecules are formed due to diverse chemical bonds, which again are a manifestation of electromagnetism. In short, if this mesmerizing interaction ceased to exist, all objects around you – including yourself – would immediately break up into individual subatomic particles.

As we have just demonstrated, electromagnetism is, just like gravity, crucial for the existence of the cosmos as we know it. The manifestations of this interaction could be discussed much longer. However, we are going to move to the next, no less important force – the strong interaction.

https://play.google.com/store/apps/details?id=brychta.stepan.universe