In 2017, physicists again did not find dark matter, and many of them lost patience. This note is designed to explain to the general public why they are so nervous because of this
First the facts. In October of last year, the results of the XENON1T experiment, conducted at the Italian Gran Sasso laboratory, and a similar project by Chinese physicists PandaX were published. For some years physicists (or rather, invented by them detectors) were on duty near huge tanks with liquid xenon. Physicists expected that now a particle of dark matter would fly in there, cut into the core of xenon and cause a flash of light. But in vain: there were no flashes.
And this is not the only experience with a negative result: such experiments have been conducted for three decades already. The only encouraging result was obtained in the same mountains of the Gran Sasso, and we wrote about it, but this experience was not reproduced. In November of this year, another ray of hope flashed: earlier in cosmic rays, there was an excess of positrons, about which they thought that it could be from the annihilation of dark matter, or maybe just debris ejected by a couple of near pulsars. So, it turned out that this excess can not be written off for pulsars. According to the principle «If not Shmutin, then who» should be attributed to his dark matter. However, everyone understands the extent to which such interpretations are written by forks on the water by the method of exclusion — maybe the real candidate simply was not allowed to vote?
Thus, the verdict is this: it’s time to find dark matter long ago, but it’s not as yet.
The author of these lines is a physicist, perhaps on a diploma, and therefore it is especially easy for him to place himself in the place of the ignorant or, let us call him so, the sincere reader. For such a reader there is nothing more boring than some kind of excess positrons or even flares in a vat with liquid xenon. It is interesting to him (that is, to me and to you): how does this dark matter — or the fact that it’s all there and not — change my conception of the world? We will now try to understand this together.
On the insidiousness of nature
Let us recall in a few words the prehistory: that in addition to ordinary matter there is also «dark», astronomers guessed first. They noticed that the galaxies are five times heavier than the total amount of all visible matter in them (that is, stars, gas, dust, black holes, etc.). At first glance, it is easier to explain such a light: there are, then, some particles that never interact with anything other than through gravity. Of course, because of gravity, they will gather in a bunch around each piece of ordinary matter, like galaxies, so that any invisible mass will be added invisible. But there is no other way to observe them in principle. Since, by definition, they «do not interact with anything», then «anything» includes any conceivable devices. Why not simply assume the existence of such particles and not move on to more interesting cases?
In the time of Newton, nothing prevented it from doing so. In those golden years, the laws of physics seemed to be something like a jewelery decorating frame: insert any stones you want into it, and they must obey the pattern. But since then everything has become much more complicated: it turned out that the stones and the frame do not exist independently of each other. The «laws of physics» and «matter obeying them» are one and the same thing. So, it is necessary to assume the existence of such and such a particle — and it is necessary to change all physics for the sake of it.
It started, probably, in 1928, when Paul Dirac realized that if there is an electron in the world, then there simply must be a positron. The theory is complex, but the underlying logic is just as banal as in the argument: «If there is a ball flying to the right, there can be a ball flying to the left.» Since then it turned out that this kind of symmetry in nature is complete. In a symmetric composition, it is impossible to add something by own will, and the more complex the symmetry, the more limited the possibilities of the decorator. It was the symmetry of the overall picture, incidentally, that required the existence of the Higgs boson, which had been searched for half a century, but still found.
Thus, we can not simply add a new particle to the picture of the world: we must find its place in the symmetry of things. The same can be said in other words: it is necessary to explain exactly how this particle was formed from the vague high-energy mash of the Big Bang and why these particles are now exactly that much, and not any other arbitrary quantity, including «zero.»
About thick stools
In physics, there were not so many places where you could painlessly stick particles of dark matter, and even in such quantities that they accounted for 4/5 of all things. One of these places is «weakly interacting massive particles», or WIMPs. The name is offensive (it’s also called the thick and harmless American ochkariki, who are all teased and beat), but assuming these two properties are massive and weakly interacting, a miracle happens: it turns out that as a result of the entire evolution of the universe from the Big Bang up to now, these hollows should have remained exactly as much as there is dark matter.
We have here not without reason mentioned the «general picture», for the completion of which physicists to such a degree needed the Higgs boson, that humanity was threatening billions for its discovery. This picture is called the Standard Model, it includes all the known particles, and there really was no place for the «WIMPs» in it. But the Standard Model can be slightly extended without affecting the overall logic. One such continuation is called supersymmetry, and it is important to know about it, that it is in it that the «WIMPs» fit irreproachably. How supersymmetry explains everything at once, you can read in Gordon Kane’s charming book «Supersymmetry», read on to health. And here we mentioned it because it is on the hypothesis of «Wimp» and most likely supersymmetric «WIMPs» that most of the attempts to find dark matter are based. These superfluous positrons, which we mentioned at the beginning of the note, should just appear under these assumptions. And those flashes in liquid xenon, which did not wait for the Italian and Chinese physicists, either. And at the Large Hadron Collider, a «super-supersymmetric partner» should have been open long ago.
And since all this is not open, perhaps the world is arranged in a completely different way.
On desperate physicists
Desperate physicists gathered at a conference at the University of Maryland back in March 2017 — six months before the Italians and the Chinese officially announced their failures. They discussed there the following: if the most natural expansion of the physics borders is supersymmetry, nothing is confirmed by anything, perhaps a place for dark matter should be sought not there. Perhaps, instead of expanding the boundaries of the old suburban site, it is necessary to develop a completely new allotment, on cutting in a dense forest. Physicists called this hypothetical place «dark» or «shadow sector» (it seems, you will still hear this nickname). Theorists quickly figured out how it could be. There, for example, could be a massive photon, which sometimes «mixed» with an ordinary photon … A simple person in such things can not understand, but then it follows that the dark matter was looking for is not there.
And most importantly: its particles should be much easier than they thought. Not thousands of masses of a proton, but of the order of one. In such particles, vats with liquid xenon cause only contemptuous laughter. If you like billiards (or its highest snooker version), you should know that the ball transmits the most ball of the same mass with the frontal impact, most of all the energy (namely, the whole). But from the much larger mass — from the side of the table, for example — it is likely to bounce off with all its original energy. Therefore, light particles of dark matter should be caught not in xenon, but, for example, in liquid helium. And literally immediately after their conference the desperate — no, again intoxicated by a crazy hope — the physicists proposed an experiment that allows this.
It remains to find money for this, and it’s in the hat. If, of course, the new assumptions about the «shadow sector» are indeed true. Yet do not forget that they look insanely enough not only for us, ignorant profane, but for most of the scientific community.
Our story about the adventures of scientists in the dark matter world will be incomplete, if not to mention Erica Verlinde. In search of an escape from this physical labyrinth, Eric Verlinde went the farthest: in his opinion, there is simply no dark matter, there is nothing to look for. And what about the whole century of astronomical observations of the motion of stars in galaxies ?! It’s more than simple, Eric says: they are based on the assumption that everything must obey Einstein’s laws of gravity, and these laws are nonsense.
Believe us or not, the world is full of half-trained idiots who consider Einstein a slut. They, in fact, form a rather thick malignant layer between scientists and the public, which prevents them from communicating normally with each other, drowning out the conversation with meaningless cries. It was this layer in its time, with enthusiasm, adopted a theory called MOND — «Newton’s modified dynamics», which is supposed to completely disprove Einstein. The trouble with this theory is that it does not follow from anywhere.
But Dr. Verlinde is not an ignorant madman, but a famous string theorist from the University of Amsterdam (I hope everyone understands the difference). He did not suck his version of MOND out of his finger, but derived from those very frozen equations (we wrote about them many times), which allow striders to easily abolish gravity by jumping into the world with a different number of dimensions. «For me, gravity does not exist,» Dr. Verlinde said seven years ago. And since there is no gravity, there is no single argument that forces physicists to search for dark matter.
About Eric Verlinde and his revolutionary (or crazy) ideas we recommend reading here. The superficial reader (as well as the superficial author, like your humble servant) is allowed to confine himself to the following thesis: if dark matter is not found anywhere, here and nowhere, the most insane theories, including Verlinde’s ideas, will have to be considered more seriously than on they are watched now. Probably, there will come a holiday and in the street of madmen discussing in facebook, what Einstein is silly.
I would not want to, but what if that is the logic of the development of science?
Why is 2017 the year of dark matter?
The real year of dark matter will come when it is finally discovered. But until this happened, the 2017th is the best candidate. Last year, physicists, it seems, thought seriously about the fact that not always everything is going well as it happened with the Higgs boson. Sometimes like all the signs should be so, but it’s rrraz! — and that’s it. This consideration, of course, will not prevent them from asking taxpayers more and more money for expensive experiments, but, perhaps, will open new horizons for understanding the world. Or at least an understanding of the fact how wrong they all have understood so far.
And we, the ignorant public, will not gloat, but on the contrary, we applaud them. Such dashing turns of knowledge teach the humility of not only scientists, but us, the ignorant public. Although we, unlike scientists, in any case, there are enough reasons for humility.