An invisible civilization may exist right under your nose. Although we know that ordinary matter is responsible for only 1/20 of the energy of the Universe and 1/6 of the energy carried by matter (and everything else goes to the expense of dark energy), we consider ordinary matter to be a very important component. With the exception of cosmologists, almost all people concentrate on ordinary matter, although from an energetic point of view, it is not so important.
Ordinary matter is more dear to us, of course, because we are made of it - like the entire tangible world in which we live. But we are also interested in her because of the rich variety of her interactions. The interactions of ordinary matter include electromagnetic, weak and strong - they help matter to form complex dense systems. Not only stars, but stones, oceans, plants and animals exist thanks to the non-gravitational forces of nature responsible for interactions. Just as the reveler is more influenced by alcohol than the other components of beer, so ordinary matter, although it carries a small part of the energy density, affects itself and the environment much more noticeably than something just passing by.
The visible matter familiar to us can be considered as a privileged percentage - more precisely, 15% - of matter. In business and politics, 1% of people influence decisions and rules, and the remaining 99% of the population provide infrastructure and support - maintain buildings, keep cities running, and deliver food. Likewise, ordinary matter influences almost everything that we observe, and dark matter, in its abundance and ubiquity, helps to create clusters and galaxies, ensures the formation of stars, but has little effect on our immediate environment.
The structures close to us are governed by ordinary matter. She is responsible for the movement of our bodies, for the energy sources that feed our economy, for the computer screen or paper on which you read this, and for almost everything you can imagine. If something interacts in such a way that it can be measured, it is worthy of attention because it can influence our environment.
Usually, dark matter doesn't have this interesting influence and structure. It is assumed that dark matter is the glue that holds galaxies and their clusters in amorphous clouds. But what if it isn't, and it is only our bias - and ignorance, the root of bias - that causes our misconceptions?
In the Standard Model, there are six types of quarks, three types of charged leptons (including an electron), three types of neutrinos, particles responsible for all forces, and the newfound Higgs boson. What if the world of dark matter, maybe not so much, but also diverse? In this case, the interactions of dark matter will be negligible, but a small part of it will interact with forces that resemble the forces of ordinary matter. The rich and complex structure of particles and forces of the Standard Model is responsible for many interesting phenomena. If dark matter has an interacting component, it can also be influential.
If we were creatures consisting of dark matter, it would be wrong to believe that all particles of ordinary matter are the same. Perhaps people made of ordinary matter make the same mistake. Given the complexity of SM particle physics, which describes the simplest components of matter known to us, it seems strange to assume that all dark matter consists of only one kind of particles. Why not assume that some part of it is subject to its own interactions?
In this case, just as ordinary matter consists of different types of particles, and all these fundamental constituent parts interact through different combinations of charges, dark matter will also have different constituent parts - and at least one type of such particles will participate in non-gravitational interactions … SM neutrinos are not affected by electrical force or strong interactions, unlike the six types of quarks.
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Likewise, it is possible that one type of dark matter particles weakly or does not interact with anything except through gravity, but some 5% of the particles experience other interactions. Based on the study of ordinary matter, we can say that this option is more likely than the usual assumption about the presence of one weakly interacting particle.
It is a mistake for foreign public relations people to try to bunch up the culture of another country and ignore the fact that there may be diversity in it that is obvious to their own country. Just as a good negotiator does not assume the predominance of one sector of society over another when trying to compare different cultures, so an unbiased scientist should not assume that dark matter is not as interesting as ordinary matter, and it lacks a variety of matter, similar to that what's in ours.
Popular science writer Corey S. Powell, reporting our research in Discover magazine, began his article by saying that he was a "light-matter chauvinist" - and that we are all too. He meant that we think that the matter we know is more important, and therefore more complex and interesting. Very similar views were overturned by the Copernican revolution. But most people insist that their point of view and belief in our importance correspond to the real world.
Many components of ordinary matter interact in different ways and affect the world in different ways. So maybe dark matter has different particles with different behaviors that affect the structure of the universe in a measurable way.
When I first started studying partially interacting dark matter, I was surprised that almost no one thought that the assumption that only ordinary matter exhibits a variety of types of particles and interactions is an arrogant delusion. Some physicists have tried to analyze models such as "mirror dark matter", in which dark matter repeats everything that is typical of ordinary. But such examples are exotic. Their consequences are difficult to combine with what we know.
Several physicists have studied more communication models of the interaction of dark matter. But they also assumed that all dark matter is the same and undergoes the same interactions. No one admitted the simple possibility that, although most of the dark matter does not interact with ordinary matter, a small fraction of it can do so.
One of the reasons for this is understandable. Most people believe that a new type of dark matter will not affect most of the observed phenomena if it is only a small fraction of dark matter. We have not even been able to observe the most important component of dark matter yet, and it seems premature to deal with its small component.
But if we remember that ordinary matter carries only 20% of the energy of the dark, while most of us notice only it, we can understand where this logic is wrong. Matter interacting through more powerful non-gravitational forces may be more interesting and more influential than most weakly interacting matter.
This is true with ordinary matter. It is overly powerful, despite its small number, as it shrinks into dense disks from which stars, planets, Earth, and life can form. The charged component of dark matter - although there may not be that much of it - can also shrink and form discs, such as the visible disc in the Milky Way. It can even condense into objects that look like stars. In principle, such a structure can be observed, and, perhaps, it is even easier to do than ordinary cold dark matter scattered in a huge spherical halo.
Thinking this way, the number of possibilities grows rapidly. After all, electromagnetism is just one of several non-gravitational interactions experienced by particles in the Standard Model. In addition to the force that binds electrons to nuclei, SM particles experience weak and strong nuclear interactions. In the world of ordinary matter, other interactions can also exist, but they are so weak at the energies available to us that no one has yet observed them. But even the presence of three non-gravitational interactions hints that non-gravitational interactions can also be present in the dark sector in addition to dark electromagnetism.
Perhaps, in addition to forces similar to electromagnetic ones, dark matter is also influenced by nuclear forces. It is possible that dark stars can form from dark matter, in which nuclear reactions take place, due to which structures are formed that behave in a way more similar to ordinary matter than the dark matter that I have described so far. In this case, the dark disk may contain dark stars, surrounded by dark planets consisting of dark atoms. Dark matter can have the same complexity as ordinary matter.
Partially interacting dark matter provides fertile ground for speculation and inspires us to explore possibilities that we would not otherwise have looked at. Writers and filmmakers may find all these additional forces and consequences lurking in the dark sector very alluring. They might even suggest the existence of a dark life parallel to ours. In this case, instead of the usual animated creatures fighting with other animated creatures, or, in rare cases, working with them, creatures of dark matter could march across the screen, which would drag the entire action onto themselves.
But it wouldn't be so interesting to watch. The problem is that filmmakers would have had a hard time filming a dark life that is invisible to us. Even if there were dark beings, we would not know about it. You may not know how cute a dark life could be - and you almost certainly won't.
While it is fun to speculate about the possibilities of dark life, it is much more difficult to figure out how to observe it - or at least detect its existence by circumstantial evidence. It is rather difficult to find life, consisting of the same components as we are, although the search for extrasolar planets is underway. But proof of the existence of dark life, if it exists, will be even more elusive than proof of the existence of ordinary life in distant worlds.
More recently, we have been able to observe gravitational waves emanating from huge black holes. We have practically no chance of detecting the gravity of a dark creature or an entire army of dark creatures, no matter how close they are to us.
Ideally, I would like to somehow communicate with this new sector. But if this new life is not influenced by the forces we know, this will not happen. Although we share gravity with them, such an influence from a single object or life form would be too weak to detect. Only very large objects, such as a disc in the plane of the Milky Way, can produce the observed effects.
Dark objects or dark life can exist very close to us - but if the total mass of dark matter is small, we will not know about it. Even with modern technology, or whatever technology we can imagine, only very specific capabilities can be tested. “Shadow life,” as exciting as it is, is unlikely to have tangible consequences and can be a seductive but unattainable opportunity. But the dark life is a very loose assumption. Scientists will have no problem creating it, but the Universe has many more obstacles for this. It is not clear which of the variants of chemical interactions are capable of supporting life, and we do not know what kind of environment is needed for those variants that are capable of doing so.
Nevertheless, in principle, dark life can exist, right under our noses. But without stronger interactions with the matter of our world, it can have fun, fight, be active or passive - and we will never know about it. Interestingly, however, when there are interactions in the dark world, whether or not life is involved, they can affect structure in a measurable way. And then we can learn much more about the dark world.