THE DARK MATTER

If someone tells you they know what dark matter is, they must be lying: nobody knows anything about it for sure, all we know is that there is something out there. With the improvement of telescopes, distant cosmic objects arouse ever more interest among the public. In the 20th century, people started observing faraway galaxies; by now, we are used to the idea that the Milky Way is just one of many galaxies in our Universe. At first, however, this was a novel idea, and observing other galaxies seemed like an exotic thing to do. Isn't it amazing that who knows how far from us space objects and huge clusters of them live the same life and obey the same laws as we do - only in a slightly 'wrong' way! This revelation shocked the scientific community. How can that be? Does it mean that all our calculations were wrong?

Well, our calculations cannot just be wrong: if I throw a ball applying little force, it will fall on the ground. If I put all my strength into it (that is, if I am very, very strong and there is no ceiling above me), it will overcome the Earth's gravity and fly off straight into space. But if I calculate the force of the throw exactly, considering the mass of the ball, I will be able to send it on a orbit around the Earth. This is called the first cosmic velocity, and the fact that we have satellites orbiting our planet proves that we have learned to calculate it correctly. However, the total mass of cosmic objects that gather into clusters doesn't necessarily have to be great enough to keep those objects together. When I throw a ball, I know that it will fall, I know why it will fall and the reasons for it; however, we do not know what gives rise to the gravity that keeps whole galaxies and their clusters together, preventing thim to fly off in all directions. In order to make the processes we observe possible, galaxies must contain much more - many times more - mass than the total mass of the objects contained in them.

It is that missing mass that we call dark matter. For decades, physicists have been trying to discover its invisible particles experimentally. But it is hard to see what cannot be seen. When in 2012 the Large Hadron Collider allowed scientists to discover Higgs' boson, it basically repaired the last remaning hole in the standard model by finding this previously missing particle. Everyone has been expecting that the LHC could also help explain the nature of WIMPs (weakly interacting massive particles) - the most probable building block of dark matter. WIMPs have always attracted scientists' interest. Supposedly these particles emerge in hot dense plasma, which was abundant right after the Big Bang. WIMPs would have been so numerous as to constantly collide with each other, giving rise to normal particles that we can observe today. But as our Universe keeps getting larger and colder, these procecces become weaker and last remaining WIMPs move slower. If we theoretically calculate how many WIMPs exist at present, we will get a number that exceeds the amount of all normal matter fivefold! 'Well, that's just what we've been looking for!' thought the scientists in the 70s. The picture seemed just perfect, but with every decade and with each failed experiment, the researchers' enthusiasm waned. Numerous failures do not prove that such particles do not exist; they simply force us to re-evaluate the cause. What if there is no dark matter in our Universe at all?

Our Universe is the key phrase here. The hypothesis that could explain the source of extra gravity is based on the multiple universe theory; and now this idea, which could help unite all these disparate theories into one theory of everything, seems much more objective.

Let us talk about four-dimensional space for a moment (eventually we will post an article dedicated to the subject). Massive objects warp the fabric of space-time, extending it, forcing various objects to attract to each other; it is all going on inside the Universe. But let us take a look from the outside, taking a flat, two-dimensional universe as an example. In order for two universes not to intersect, to be mutually independent, they have to be parallel - and in a two-dimensional case, it is easy to imagine.

In our three-dimensional case, we need to use more imagination. We have a flat universe on top, and somewhere below there is another one, parallel to the first. These universes do not intersect - that is, their inhabitants cannot interact in any way, but a massive object inside the top universe can warp it to such an extent that it will touch the bottom universe. This will not give rise to any new objects or matter in the bottom universe, but it will create additional gravity - and that's exactly what we've been searching for. Now the second universe has an immaterial source of gravity. Whole new galaxies and galactic clusters can form around such a source. And here's one more point in favour of this hypothesis: in the presence of gravity and in the absence of mass, 'dark matter' of our Universe may turn out to be nothing other than normal matter of another universe. Isn't that cool?

Even though dark matter has no effect on you and me personally, it is everywhere, and there are lots of it; moreover, it is thanks to the presence of dark matter that life has appeared in our Universe in the first place. If there was no dark matter, almost all large-scale processes taking place in our Universe would either not occur or follow completely different paths.