Dark matter is a real pain in the neck.
The term dark matter refers to a hypothetical substance which seems to interact only with the rest of the universe via gravity and serve as scaffolding for galaxies and other massive cosmic structures. However, real particles of dark matter have never been found – despite decades of intensive efforts to discover them. Certain criticisms therefore reject the concept as a simple factor of fudege that physicists use to support their incomplete theories of the functioning of the universe. But that dark matter is a “real” thing or a useful fruit of the imagination of theorists, there is simply too much evidence to wish that the problem disappears.
Call that what you want, there is obviously something very strange in the universe. The stars on the outskirts of galaxies in orbit too quickly. The galaxies buzz in clusters far too quickly. The rich components of the cosmic web are too quickly melted. And there are so many other examples.
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Each attempt to relegate the dark matter to the basement of physics ideas thrown away, such as the modification of the gravity force to adapt to all the associated observation quirks, failed. If it is impossible to exclude such approaches – you never know what an intelligent theorist could cook tomorrow – half a century of culture has not yet given satisfactory fruit.
Decades of evidence have largely excluded obvious black matter candidates who have been inspired by high energy physics. But high energy physics is not the only game in town. There are other areas, including the physics of condensed materials, the branch of physics which examines the properties of large material collections, such as the way in which all atoms in a glass pane conspire to make it transparent. This area of physics has its own strange corners, as the strange world of superconductivity. And these corners are strange enough to provide a potentially useful inspiration for understanding the puzzle of dark matter.
Our best supposition as to the nature of dark matter is that there is a form of matter which does not interact with light – or really many others or even itself. (Admittedly, this is not a good assumption, but it is the best we have.) This case occupies the major part of almost all the galaxies and the larger structure, and it is right there, existing, being known only by its gravitational tractions on visible matter.
Each cosmological survey line underlines the humiliating realization that only a thin fraction of the case in the universe lights up. After centuries of effort, by developing the periodic table, the particle zoo, the standard model of particle physics, the forces of nature and all the others, we now know that we have barely scratched the surface.
But science is only a trip for the humble, so we have only one choice in front of us: forward.
We have many powerful tools at our disposal in our trips through the dark corners of the universe. A tool is our continuation of observations, from the measures taken at galactic scales to the cosmic which extend over the extent of the observable universe and the depth of deep time. All these observations inform and ultimately judge any theory of candidates. We can be in darkness on dark matter East, But we have a very good sense of what he do. If you have your own idea of explaining dark matter, it must go through the crucible of intact observations. If an idea fails anywhere along the way, we continue and try the next one.
The other powerful tool is physics itself, our mathematical exploration of the world. We do not completely understand the dark matter, its identity or its characteristics or its interactions with the rest of the universe. But we know, to various degrees of trust, what the rest of the universe does. The dark matter is like a missing piece in a puzzle; We don’t know what the room is, but we roughly know the shape it has to take.
Whatever the dark matter, it must obey the laws of physics (even if we do not yet know all these laws).
For example, when the universe had less than a minute, dark matter must have somehow disconnected from normal matter (a process called “freezing”) to obtain the right current amount that we deduce from observations. This is how we found our main candidate for dark matter, the mauviet or the massive particles weakly in interaction. We had hypothetical particles generated in the theories of physics which, if they were active and abundant and generally around the universe, would have naturally done that exactly.
But we have not yet detected a wimp directly, and its theoretical foundations have turned out to be on thin ice.
So we are going.
There is also the axion, another hypothetical particle from high energy physics and another of the billions of times lighter than the mauviet. If the axion exists and has the right properties, it could also do everything we know that we need dark matter to do.
But we have not yet detected directly an axion – although, to be fair, we have not looked for axes almost as largely as we did for the Wimp, simply because the Wimp were considered a shoo -in for dark matter.
So we are going.
In May Guanming Liang and Robert Caldwell, both at Dartmouth College, published an article in Physical examination letters in which they offered their own candidate for dark matter. A pessimist could look at this study and ride his eyes: “Oh, joy, yet another proposal for a candidate particle, probably the umpteenth this month, which is almost certainly erroneous – just another random blow in the dark, another touch of spaghetti launched against the refrigerator of cosmology.”
This answer would be right. This model is probably – no, almost certainly -. But it is because most models are bad most of the time. If we knew the answer in advance, we would not need to do science. We cannot find the right answer by passing through all the bad ones, choosing the wheat of the straw, trying again and again until we find something worthy.
But we only know when we try.
And admirably, the Liang and Caldwell model tries not only but really tries something new. Instead of drawing inspiration from high energy physics, with hypothetical particles derived from this interaction or this exotic interaction, the authors turn to the physics of the condensed matter and in particular the bizarre nature of suprrrriscectivity.
In a regular driver, the electrons wear electricity, but they also offer resistance. At sufficiently low temperatures and in the right materials, however, the electrons condense – or, if you want, frozen – being made in pairs in a configuration with the lower energy. This eliminates electrical resistance and makes the magic of superconductivity.
By analogy, the Liang and Caldwell model considers dark matter as a soup of exotic particles born a few moments after the Big Bang, in the bizarre era before the arrival of protons and neutrons. This soup does not interact with normal matter but also does not have mass in itself. As the cosmos expands and cools, the particles of dark matter condenses and aggregate, forming massive “droplets” which continue to have their own separate evolution, disconnected from the rest of the visible matter in the universe, except by their gravitational influence.
The calculations are complex and temporary but promising. The main advantage of this approach is that it allows a new mechanism to create dark matter in exhilarating conditions in the first minutes after the Big Bang which does not depend on the same steps as the usual WIMP procedure follows. And this model does not only summarize the existing evolution of dark matter. If the exotic particles have a certain mass, then only some of them condense to form dark matter. The others lock in place as a background which saturates the universe, potentially playing the role of dark energy, the mysterious force which seems to accelerate the expansion of the universe. Above all, in this model, dark energy can vary over time, which aligns with temporary results from surveys in galaxy.
Studies like these are only the first step: a plausibility control which obtains roughly the right amount of dark matter roughly at the right time. It remains to be seen if this can explain the absolute mountain of evidence that we have for dark matter: can it simultaneously explain the wide range of behaviors that we attribute to dark matter, from the first epochs of the cosmos to the modern universe filled with stars?
And can he take the ultimate test of everyone? Can it predict the existence of a particle – or a droplet of condensation of dark matter – which we could one day see directly by ourselves?
The search for the true nature of dark matter is indeed frustrating because the obstacles that any model must erase is at least numerous. We will not believe this model, or any other hypothesis, until it can succeed where so many others have failed.
So we are going.
