Physicists searching for the invisible hand that shapes our universe and its galaxies have focused their attention on the dark side.
In particular, a team searches behind every cosmic rock for so-called dark photons, which could transmit a hitherto unknown force of nature. These photons would mediate the interaction between all normal matter and the invisible stuff called dark matter.
But scientists have long understood that the nature of four known forces is stretched, pulled, torn and torn.So how could another force hide from us so long? These four known forces form the cornerstone of our everyday life: the tyrannical, but short-range, strong nuclear force that holds atomic nuclei together, the dark and whisper-quiet nuclear power that controls radioactive decay and speaks to the subatomic particles called neutrinos;bright electromagnetic force that dominates our lives, and the subtle gravitational force, by far the weakest in the Quartet. With these four fundamental forces, physicists can draw a portrait of our subatomic and macroscopic worlds.
There is no interaction in which one of these four characters is not involved. And yet, there are still many puzzles regarding the interactions in our universe, especially on the largest scale. When we zoom in on the scale of galaxies and beyond, something fishy appears, and we give that species the name of dark matter. Is dark matter simple and unadorned, or does it conceal a variety of previously unknown forces in its claws?
Now, an international team of physicists who have described their work online in the Preprint journal arXiv has used a data dump from the Large Hadron Collider – the world’s largest atomic destroyer – to search for such power.
At the moment their search is empty – which is good: it means that our well-known laws of physics still apply. But we still can not explain dark matter.
Lost in the dark
Dark matter is a hypothetical form of matter that accounts for about 80% of the total mass of the universe. It’s a big deal.
We do not really know what’s responsible for all those extra invisible things, but we know they exist and our biggest clue is gravity. By studying the motion of stars in galaxies and galaxies in clusters, as well as the evolution of the largest structures in the cosmos, astronomers have come to the conclusion almost everywhere that there is more than the galactic eye suggests.
A better name for dark matter could be invisible matter. While we can conclude from its gravitational influence (because Albert Einstein’s all-seeing eye escapes nothing), dark matter simply does not interact with light.
We know that because if dark matter had interacted with light (or at least if it had interacted with light like familiar matter), we would have seen the mysterious substance in the meantime.
But as far as we can tell, dark matter – whatever it is – does not absorb light, reflects light, breaks light, scatters light, or radiates light. For dark matter, light is simply a persona non grata, it just might not exist. So, there is a solid chance that legions of dark matter particles are flowing right through your body.
The combined mass of this endless stream can affect the fate of galaxies by gravity, but it goes through normal matter without a hello. Rude, I know, but that’s dark matter for you.
Bring the light
Since we do not know what dark matter is, we can think of all sorts of scenarios, both banal and imaginative. The simplest image of dark matter says it’s big and simple. Yes, it makes up most of the bulk of the universe, but it’s just a single, highly productive particle that does nothing but have mass. That is, the material can be felt by gravity, but otherwise never interacts with any of the other forces.
We will never catch a glimpse of dark matter if we do something else. The imaginative scenarios are more fun. When bored by theorists, they consider what dark matter could be and, more importantly, how we might recognize it. The next level on the scale of interesting theories of dark matter says that the substance can occasionally talk about the weak nuclear force with normal matter.
This idea motivates dark matter experiments and detectors around the world. In this scenario, however, it is assumed that there are only four natural forces left. If dark matter is a hitherto invisible type of particle, it makes perfect sense to point out (because we have no idea if we’re right or not) that it’s wrapped in a previously unknown force of nature – or maybe a couple, that This potential force could only make dark matter speak dark matter, or it could intertwine (and we do not understand) dark matter and dark energy, or it could open a new channel of communication between the normal and dark sectors of our universe
Rise of the dark photon
A proposed communication portal between the light and the dark area is a so-called dark photon, analogous to the known (bright) photon of the electromagnetic force.
We can not directly see, taste or smell the dark photons, but they could mingle with our world. In this scenario, dark matter emits dark photons, which are relatively massive particles.
This means that, in contrast to their light-flooded counterparts, they only have a short range. But occasionally, a dark photon can interact with a regular photon and change its energy and trajectory.
This would be a very rare event. Otherwise, we would have noticed a long time ago that something crazy is going on in electromagnetism. Even with dark photons, we could not directly see the dark matter, but we could detect the existence of the dark photons by examining the electromagnetic interaction fields.
In a tiny fraction of these gobs, a dark photon could “steal” energy from a regular photon by interacting with it. But as I said, we need a lot of interactions. It’s just that we built huge science machines to do just that, so we’re lucky. In the arXiv paper, physicists reported their findings after studying data from Super Proton Synchrotron, the second largest particle accelerator at CERN, for three years. For this experiment, the scientists smashed the protons against the subatomic equivalent of a wall and then examined all the pieces. In the rubble the researchers found electrons – many of them. Within three years scientists counted over 20 billion electrons with energies over 100 GeV.
Since electrons are charged particles and like to interact with each other, the high-energy electrons in this experiment also produced many photons. When dark photons exist, they should sometimes interact with one of the regular photons and steal energy, a phenomenon that is shown in the experiment as a lack of light.
This search for dark photons was empty – all normal photons were present and included – but that does not completely rule out the existence of dark photons.
Instead, the permissible properties of these particles are limited. If they exist, they would be low in energy (less than one GeV based on the results of the experiment) and would rarely interact with regular photons. However, the search for dark photons continues, and future runs of the experiment will continue to focus on this proposed creature of the subatomic world.