After the discovery of the Higgs particle, is physics done? In this last lesson, we will be discussing that there is much more to learn of our universe and particle physics. Another way of saying is that we, mankind, are like fish swimming in an aquarium and that we discovered that we are swimming in water, and the water is then the Higgs field. And how as fish did we discover that? Well, by observing the ripples at the surface of the water. And the water is in this analogy, the Higgs field, and the ripples are then the Higgs particle. With this Higgs mechanism, the standard model is complete, and it's able to describe particles that have mass. And so, is now everything solved particle physics? Well, certainly not. The standard model has a number of features that are impossible to understand. First, the Higgs field corresponds to an energy in the vacuum. But energy means mass itself, E equals MC squared. It is like space is filled with a large mass throughout the whole universe. So why don't we see the effects of this large mass at large scales in the universe? Now, usually it would mean that the universe would have to be shrinked to the size of a football, a huge cosmological constant, which clearly is not the case. And further, we don't understand why the Higgs particle, and this is a bit more abstract, itself has the mass of 125 GeV. As we have observed at the LHC, it would have been much better explained if the Higgs particle would have a mass many orders of magnitude larger. Really many orders, like 10 to the 19 GeV would be much better to explain. So why actually is the mass of the Higgs particle very light? These are fundamental questions that we do not have an answer to, and every particle physicist in the world therefore believes that the standard model is not the end of the story. A large number of models are constructed to explain these difficulties of the standard model. And they go under the names of supersymmetry, extra dimensions, new Higgs particles, and all other names that you have. And all of these models solve parts of the problems that were mentioned before, sometimes more elegantly, sometimes more specific. But all of them have one feature in common. They predict the existence of new yet undiscovered fundamental elementary particles. So you can imagine that the true quest is ongoing to find new particles that don't fit in the framework of the standard model. None of them have been observed yet. Where the Large Hadron Collider at CERN is perfectly able to find them, if they exist up to a certain maximum mass of the order of 5000 GeV. And after that, we need a bigger machine, a bigger accelerator to explore even higher masses. Remember, energy equals mass times C squared. And now, let's move to the other side of the spectrum, the extremely large structures of our universe, because there is a very intriguing coincidence in the understanding of our cosmos. Many observations of the universe, the formation and behavior of galaxies, the gigantic interactions between the galaxies, and the very detailed information of the cosmic background radiation all show one thing in common. They actually show and predict the existence of a vast amount of matter and energy that we don't know the identity of. In total, 96% of our universe is built of stuff, particles, that we don't know what it is, energy that we don't know where it comes from. We simply call it dark matter and dark energy, and the naming already shows that we don't have a clue what it is. Is dark matter actually the particles that explain the shortcomings of the standard model as it is guided by supersymmetry or other new models that I discussed before. Particle physics stands for a large challenge. The standard model cannot be the end of the story and new particles have to be discovered. It may be that world of the extremely small explains the very large structures of dark matter in our universe. And this is the area where particle physics and cosmology joined forces with identical questions for our universe. A worldwide network of experiments have been set up to try to create or detect the dark matter particles. And there are so many more questions that are unanswered in this field. For example, we concluded in a previous lesson that in the collisions, equal amount of matter and antimatter are produced. These collisions happened during the early stages of our universe. But where did all the antimatter go? We don't observe any antimatter in our universe. Are there maybe tiny differences between matter and antimatter that can explain this? We don't know. Maybe neutrinos play a role here. You have to realize that after the discovery of the Higgs particle, a whole new set of challenges for particle physics have appeared. The challenges link the cosmology to that of particle physics. And any new discovery in one of these two extreme areas of research has direct consequences for the other one. Elementary particles fill the universe and determine the evolution of it where there are so many aspects that don't know how it works and what it is.