Our life is full of mysteries, unexplained events and problems that we’ll probably never manage to solve. Usually, strange events and legends are connected with night and darkness, since it’s the period of the day in which nothing is clear and the sunlight, that lights up everything, is absent. Historically, darkness is linked with horror stories, with the unknown, which is maybe the most scaring thing ever.
Well, now it may be obvious why scientist decided to use the definition “dark matter” for a strange substance that permeates the entire universe but is almost invisible, impossible to detect through usual methods. This mysterious matter cannot be seen with telescopic observations and it might explain several things about the rotation of remote galaxies.
But what is the nature of dark matter? When was it firstly discovered? And how? What are the consequences of its existence? When did dark matter formed?
These are just some of the questions we’ll try to answer, so, if you are interested, stick with me and prepare to an epic journey through the nature of dark matter.
(roll intro)
When talking about dark matter we are dealing with one of the most important problems modern physicists are trying to solve. To understand what dark matter is, we firstly need to give a proper definition of matter.
Matter is any substance with a mass. Everything that we can touch around us has its own mass, since it’s made by molecules, that are composed by atoms. However, in physics we must get deeper into this definition to understand why dark matter is something that is totally different from what we are used to know. In the last two centuries, we have discovered that atoms are not indivisible, but they are composed by smaller particles. Most of you surely knows that they are made of protons, neutrons and electrons; but physicists have discovered something more. They understood that protons and neutrons are made of smaller particles called quarks. What a shocking result! And why do they have a different charge and behavior? This is a brilliant question and here is the answer. Quarks are characterized by a spin can have six different “flavors” (they differ for electrical charge): up, down, charm, strange, top and bottom. We have found out that the most common ones are the first two and they combine in different ways to form the particles of our atoms: the proton is made of two quarks up and one quark down, whereas the neutron is composed of two quarks down and one quark up. Quarks and electrons are some of the so-called fundamental particles.
Everything in our world is made out of these tiny objects. More precisely, we define as hadrons all particles composed of quarks, and if the number of these last ones is odd, we call them baryons. We’ve reached the answer to the previous question: what we commonly call as matter is everything that is made of baryons.
So what is dark matter? Probably, dark matter is not baryonic and the reason why it’s really difficult to detect is that it doesn’t interact with electromagnetic radiation. What does it mean? Well, differently from baryonic matter, it doesn’t absorb, reflect or emit light or other types of electromagnetic radiation like X and UV rays or microwaves. You can easily understand that it’s almost impossible to detect something in the night sky if it doesn’t emit any type of signal or light detectable from our telescopes.
Ok, we have a brief idea of what is dark matter, but why is it so important for physicists?