What is our universe made of? Whenever we talk about the universe, the first things that come to people's minds are images of galaxies, stars, lots of different colors, and all this in the midst of darkness. But only 5% of the universe is made up of visible matter, which is the matter you think of when you see galaxies and stars.
Most of our universe is composed of dark matter and dark energy, which are precisely things we don't know about exactly what they are. But our day-to-day life is that 5% of visible matter, which in physics we call baryonic matter, which affect our lives. Everything you do, from eating to watching a series on streaming or getting out of bed, involves interactions with visible matter.
Our body and basically everything we see around us is made up of a puzzle of atoms and particles, which we know as matter. And this puzzle of these components is extremely detailed and explained by the Standard Model of Physics, which I've even made a video about here on the channel. The Standard Model describes the fundamental particles that give rise to the atoms that fill everything we see and touch in our daily lives.
It is considered the most successful model in physics because all of its predictions have been confirmed sooner or later, such as the Higgs boson. But more than describing particles, the Standard Model also describes some of the possible interactions that these particles can have. can have with each other.
After all, you getting out of bed or opening the streaming app on your cell phone is a series of interactions between particles, almost like a quantum cordless phone. And all in all we know of four possible interactions that we see happening in the universe. The Model Standard Model explains three of them, and the last one left over is explained by general relativity.
And these are known as the four fundamental forces of the universe, and in this video we'll get to know each one of them. Just before I go on, I think this is the perfect time to talk about Lura, who made this video in partnership with me. Lura is the best place for you to learn new skills such as programming, video editing and company and team management.
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tv science bar every day or use the QR code that appears on the your screen now to subscribe to Lura with a special discount for those who follow Ciência Todo Dia. And now back to the video. The four fundamental forces or interactions are the gravitational force, the electromagnetic force, the strong force and the weak force.
Yours are quite famous and I'm sure you've studied or heard of them before at some point in your life. And the reason isn't just that they're more famous or better known, is that both the gravitational force and the electromagnetic force are the only forces that act on large scales, from us human beings to galaxies. So let's start with the gravitational force.
The understanding of gravity began when Isaac Newton published his Law of Universal Gravitation which we can summarize by the famous equation F equals g m1 m2 over e squared. Basically the law says that two bodies with masses m1 and m2 will have an interaction that is inversely proportional to the square of the distance between them. The further apart these bodies are, the less interaction there is between them.
And here was the first step towards understanding this fundamental force of nature. Another step was taken centuries later by physicist Albert Einstein while he was studying Newton's equations. Einstein was bothered by some problems that Newton's equations had and introduced the theory of general relativity as a solution.
For general relativity, gravity is the distortion of space-time caused by mass or energy of something. In other words, the Earth is gravitationally bound to the Sun because the Sun distorts the space-time with its mass. And we're stuck on the surface of the Earth because the Earth distorts the space-time with its mass.
Einstein's theory was so successful that, even after a century since its publication, to this day we haven't found any flaws in the scales on which it works. E it was thanks to Einstein that we came to understand gravity as part of the geometry of the universe itself, and not just as a force vector between two masses, which was Newton's view. But this doesn't mean that we need to leave Newton's universal gravitation behind.
It's perfectly acceptable to continue using Newton's equations for gravity, or even force terms, when referring to it on the right scales. The gravitational interaction, regardless of whether we are using Newton's or Einstein's approach, has some interesting characteristics. The first is that gravity is the weakest interaction of all four interactions fundamental interactions in the universe.
It is thousands of billions of billions of times weaker than the strong force, for example. And I swear that wasn't an attempt at a pun, it's a fact. And he second interesting feature is that it's not always the strongest that stands out the most, because although gravity is the weakest of the forces, it dominates the largest scales in the universe, as for example in the inevitable collision of the Andromeda and Vialactic galaxies, which is our galaxy.
And not only that. Since gravitational interaction is valid for very long distances distances, any body with mass anywhere in the universe is interacting with all the others bodies with mass. So yes, the supermassive black hole M87 star which is 55 million light-years away is interacting gravitationally with me.
But this interaction is so small that we can simply ignore it, as it will never make a difference to our lives. But remember, even though it's small, it's not zero. And this shows how powerful and important interaction is gravitational interaction.
The gravitational interaction also brings up some problems within physics, and questions which, as I said before, have remained open for centuries. But to be able to explain this, first we have to go to the second force on our list. The second force or interaction is the electromagnetic force, which is responsible for everything from our vision to the charger you use to charge the cell phone or computer you're watching this video on.
And not only that, the power electromagnetic force is also responsible for maintaining two components of atoms, which are the electrons and protons, interacting. And hence the possibility of atoms forming and chemical reactions take place. And one of the reasons for bringing this force now is that, apart from it being the second one that we know most about, it's very similar to the gravitational force when we put it into mathematical form, F equals K times q1 q2 over r squared.
This equation is called the Leide Coulomb equation, because it was first published by the physicist Charles Augustine de Coulomb at the end of the 19th century. 18th century. And if you take a good look at the equation, you'll notice that it has very interesting properties.
similar to the law of universal gravitation. The first is that it also falls with the square of the distance between the charges, so in principle it has a range of action similar to that of gravity. And that's true!
Two charged particles will interact independently distance, whether they are in the same atom or in another galaxy. And the interaction gets weaker as the distance increases until it reaches extremely low values that we can ignore, but it never reaches zero. But it's this fact that can begin to answer some questions.
Unlike gravity, electromagnetic interaction is already well explained by the standard model. We know the particles that interact with each other and also the particles that mediate the process. Wait a minute, what do you mean particles that mediate the process?
Isn't it just the proton and the electro interacting? So, in addition to the particles that participate, which are the protons and electrons, we also have the so-called messenger particles, or in a nicer way, the gauge bosons. All three interactions that are in the standard model have the gauge bosons associated with each of them.
An electromagnetic interaction is photons, more specifically virtual photons. Existence is temporary and only acts as a form of interaction. One way of imagining how these virtual photons act is as follows.
Imagine that you and I are sitting in front of each other with those office-type wheelchairs. I'm standing with a ball in my hand and you're standing with a ball in your hand. At one point I throw mine to you and you throw the yours to me.
We're both going to transfer momentum to each other, causing the chairs to become away from each other. That's basically what virtual photons do. They are responsible for the interaction between the two charged particles.
Repel in case of equal charges, or attract in the case of different charges. And still with the idea of the office chair to explain the attraction, we can do the same experiment, only throwing a boomerang in a way that it makes a half circle and reaches us. Physically speaking, virtual photons are the way charged particles find to return to the lowest possible energy state.
It's like if when two particles with equal charges are close together, they are in a state of greater energy state and need to move apart to return to the lower energy state. In the case of two particles with different charges, they need to approach each other to reach the lowest energy state. And who mediates this interaction are the virtual photons.
But there's another curious thing about them. Photons don't have mass, and mass has an interesting part when we consider the distance that these photons can travel. Both the existence of virtual photons and the lifespan they can have is described by Heisenberg's uncertainty principle, in the form of energy and time.
And when we analyze the distance through d equal to c times delta t, we arrive at the following formula. If we consider the mass to be equal to zero or set a limit of m tending to zero, the distance begins to tend to infinity. In other words, the interaction distance mediated by virtual photons is infinite, in the same way that we concluded through Coulomb's law.
And if you're waiting until now to explain what the problem with gravity is that I just commented on, here we can start to understand it. We've already come to the conclusion that the law of universal gravitation and Coulomb's law are very similar and have a similar range of action that is practically infinite. So the justification for this must be similar.
The gauge boson responsible for gravity has to have a range with the distance given by this equation tending to infinity. For this to happen, the mass of this boson must be zero, exactly the same as that of the photon. So this already gives us a direction on how to explain gravity and the distance of action of the characteristics of the gauge boson responsible for it.
And that boson even has a name, graviton. The problem is that we've never observed a graviton, so the existence is still uncertain. And besides, the theory of quantum gravitation is still not well established enough to begin to answer these questions and to be able to include the interaction gravitational interaction in the standard model through gravitons or something else.
But the explains well the electromagnetic force and two other forces called the strong force and the weak. I've just said that particles with the same electric charge repel each other and the closer they are they are, the stronger this interaction is. If you look at the nucleus of an atom you'll notice that it's basically a bundle of protons and neutrons packed together in a small space.
And how do these protons and neutrons stay together if their charge is equal? Shouldn't they just repel violently? And the answer to that is the strong force or strong interaction.
The strong interaction is responsible not only for keeping the protons and neutrons together but also for keeping the components of these particles together. Each proton and neutron is made up of three quarks. In the case of the proton two up quarks and one down quark and in the case of the neutron two down quarks and one up quark.
In addition, each quark can have a charge called the color charge which is not the same thing as the electric charge. The color charge comes in three types: blue, red and green. And the mixture of the three is called white.
And there's something like joining positive and negative charges and neutralizing. But an important thing is that when we talk about color we're not talking about these particles fundamental particles actually have colors. It's just an analogy to illustrate that putting the three colors you find a neutron.
It's the fault of physicists who lacked creativity in the 50s. Each proton and neutron must have all three colors, that is, each of the three quarks has one of these colors. And it goes even further.
Quarks can change color and indeed they do change color practically all the time. And responsible for this are the caliber bosons called gluons. Gluons also have color charges and they only interact with other things that also have color charges, namely quarks and other gluons.
They work more or less like rubber bands. If you've ever felt a rubber band being pulled tight and loose on your skin you know that how much more you stretch, the harder the rubber band pulls on your skin. The gluons create a kind of elastic band in the interaction between quarks and the change of colors.
If you try to pull one of these quarks that elastic will pull harder and harder until it reaches a point where the quark can no longer move away. And this interaction is called the strong force. It is different from the other forces because the farther away the quark is, the stronger it will be.
But there comes a point when the force is so great that the quark hardly leaves the particle and that's why protons are so stable. Because of this and the fact that gluons have charges, the strong force acts on a large scale. so small that it is not even comparable to gravity, even though it has a mass of zero.
Precisely because of what I said just now, gluons, because they have zero mass, could reach infinite distances like photons. Except that unlike photons, gluons have this charge and interact with each other, limiting their range. But if you manage to put in an absurd amount of energy into these quarks, for example the energy present in the nucleus of the sun, they can even get out of their particles.
And the energy needed to break the elastic that the gluons create is so gigantic that when a quark leaves, a quark and an antiquark are formed instead. The quark returns to its place inside of the proton or neutron and the antiquark forms together with the original quark a component called a meson or pion. And these mesons go from one neutron or proton to the other and will act as bosons of gauge in a very similar way to gluons.
They are responsible for keeping the atom together and for having mass. And when put into the equation you will find that they have a extremely small range which is practically the size of a proton. And it's thanks to these mesons and gluons that atoms are able to remain stable and that we exist.
And finally we have the last interaction, the weak force or weak interaction. The weak interaction is also present in protons and neutrons, but how can anything compete with such a great force? like the strong force?
Some even find it strange to call weak interaction a force, it works more as a kind of trick or power that protons and neutrons possess. A neutron can become a proton or a proton can become a neutron. And think what an incredible thing that is.
A particle can simply become another particle. And this exists because an up quark can become a quark down or vice versa. And well, protons and neutrons are made up of quarks.
You take a neutron that has two down quarks and one up quark and turn one of the down quarks into an up quark and voila, you have a proton. And those responsible for this change are the W gauge bosons which can have positive charges When a neutron's quark goes from down to up, it emits a negatively charged W boson. So, the particle that was neutral before, the neutron, is now a positive particle because it has lost a negative charge.
The W minus boson, in turn, is massive and unstable. So, in about 15 minutes, it decays into an electron and an antineutrino. And using our equation to get the range of this interaction, since the W boson has mass, its range is only 0.
1% of the size of a neutron proton. In other words, you need to be extremely close for this interaction to take place. starts in the first place, making it rare but still important.
And that's because weak force and the electromagnetic force have a very important relationship within physics, which is the electroweak interaction. Basically, the first unification discovered. But that's for another time next video, as well as the origin of these fundamental forces and how they are associated with the great unification of physics.
And finally, I think it's fair to comment that recently the collaboration Firm Lab, responsible for the particle accelerator in the United States, announced the possible discovery of a new force, the fifth force. That's because they re-ran an experiment this year and had the same result as before. Basically, mounds, which are particles similar to electrons, were accelerated and when they analyzed the frequency with which these mounds oscillated, they realized that it was as if there was another force pulling on them.
The experiment became known as muon g-2. The physicists in the collaboration argued in an article that there may be something new here, perhaps a A new particle or a new force. If confirmed, this could be the fifth fundamental force of nature.
The Firm Lab collaboration stated that they will redo the experiment in two years, as soon as they have more data and more sensitive data. So, who knows, in two years we might have an answer. So, if all goes well, in two years I will redo this video and the title will be updated to "The Five Forces of Nature Explained".
And besides, I know many of you must be curious about dark energy, as it is essentially the antagonist of gravity. We already know that on much larger scales gravity begins to lose because we now know it as dark energy. While gravity attracts, we see that very distant galaxies are moving away at an accelerated pace, almost as if there was a force pushing them and overcoming gravity.
Some scientists consider that yes, dark energy is another force of nature, but we still know almost nothing about it. So, it's still too early to say whether we are actually dealing with a new force or something different and that's why we call it dark energy. And since we're talking about mysteries, dark matter - don't confuse it with dark energy - only interacts with interactions still as a big question mark.
And I could make another video just with all the things that are still not explained using the four fundamental interactions, but unfortunately, my strength is running out. All four of them. That will be for the next video.
What a terrible joke. Thank you very much and see you next time.
