Physics is riddled with puzzles, and in a way, that’s what sustains the field. These puzzles that bend the mind they nurture the race for truth. But of all the dilemmas, I would say that two undoubtedly fall under Priority A.
First, when scientists look at the sky, they constantly see stars and galaxies traveling farther from our planet, and from each other, in all directions. The universe in a way looks like a bubble blowing, which is why we learned it was expanding. But something doesn’t make sense.
The universe doesn’t seem to have enough things floating in it — stars, particles, planets, and everything else — to inflate so quickly. In other words, the universe is expanding much faster than our physics says it can, and even accelerating as you read this. Which brings us to problem two.
According to the best calculations by experts, galaxies spin so incredibly fast as everything revolves around that we would expect the spirals to behave like out-of-control carousels throwing metal horses off the ride. There doesn’t seem to be enough things in space to put them together. However, the Milky Way is not moving away.
So what’s going on?
Simulation of dark matter filament across space.
Zarija Lukić / Lawrence Berkeley National Laboratory
As complete terms, physicists refer to “missing” things that push the cosmos out of dark energy, and pieces that hold galaxies together – probably in a halo-like shape – of dark matter. Neither interacts with the light or matter we can see, so they are essentially invisible. The combination of dark matter and dark energy makes up an incredible 95% of the universe.
Focusing on a piece of dark matter, the authors of a recent review, published in the journal Science Advances, write that “it may consist of one or more types of fundamental particles … although part or all may consist of macroscopic clumps of some invisible form of matter, such as are black holes. “
Black holes or not, dark matter is completely elusive. In an attempt to decipher its secrets, scientists have selected several suspects from the cosmic line, and one of the most sought-after particles is a strange little spot called an axion.
The wide-eyed hypothesis about axions
You may have heard of the Standard Model, which is a pretty holy grail, a growing particle physics manual. She describes how each single a particle in space works.
However, as the Science Advances review points out, some “particle physicists are restless and dissatisfied with the standard model because it has many theoretical shortcomings and leaves many urgent experimental questions unanswered.” More specifically for us, this leads right into a paradox regarding a well-established scientific concept called CPT invariance. Yeah, the physical puzzles continue.
Galaxy and related halo of dark matter, illustration.
Mark Garlick / Science Photo Libra
Basically, CPT invariance says that the universe must be symmetrical when it comes to C (charge), P (parity) and T (time). For this reason, it is also called CPT symmetry. If everything had the opposite charge, was left instead of right-handed and traveled through time backwards instead of forwards, it is said that the universe should remain the same.
For a long time, CPT symmetry seemed unbreakable. Then came 1956.
In short, scientists have found something that breaks the P part of CPT symmetry. It’s called weak force and dictates things like neutrino collisions and fusion of elements in the sun. Everyone was shocked, confused and scared.
Almost every fundamental concept of physics relies on CPT symmetry.
About a decade later, researchers also discovered a weak force that violates C symmetry. Things were falling apart. Physicists could only hope and pray that even if P is violated … and CP is violated … maybe CPT is not yet. Perhaps weak forces only need a trio to maintain CPT symmetry. Fortunately, this theory seems correct. For some unknown reason, a weak force follows the overall CPT symmetry despite C and CP flashes. Ugh.
But here’s the problem. If weak forces violate CP symmetry, you would expect strong forces as well, right? Well, they don’t, and physicists don’t know why. This is called a strong CP problem – and right where things get interesting.
Neutrons – uncharged particles inside atoms – are subject to strong force. In addition, by enabling simplification, their neutral charge means that they violate T symmetry. And “if we find something that violates T symmetry, then it must also violate CP symmetry in such a way that the combination of CPT is not violated,” the paper states. But … that’s weird. Neutrons do not work due to a strong CP problem.
And so the idea of an axion was born.
Neutrons are uncharged particles in the central group of atoms.
Getty / iLexx
Many years ago, physicists Roberto Peccei and Helen Quinn proposed adding a new dimension to the Standard Model. This included a field of ultralight particles – axions – which explained the strong CP problem, thus relaxing neutron conditions. Axions seemed to fix everything so well that the duo’s idea became “the most popular solution to a strong CP problem,” the paper said. It was a miracle.
To be clear, axions are still hypothetical, but think about what just happened. Physicists have added a new particle to the standard model, which outlines the spots the whole universe. What could that mean for everything else?
The key to dark matter?
According to Peccei-Quinn’s theory, axions would be “cold” or would move very slowly through space. And studije researchers of the study say “existence [dark matter] it is inferred from its gravitational effects, and astrophysical observations suggest that it is ‘cold’. “
The paper also states, “there are experimental upper limits as to how strong [the axion] interacts with visible matter. ”
So, basically, it seems that the axions that help explain the strong CP problem also have theoretical properties that are in line with the properties of dark matter. Extremely good.
The European Council for Nuclear Research, better known as CERN, which manages the Large Hadron Collider and leads antimatter research, also emphasizes “one of the most suggestive properties of axions is that they can be produced naturally in huge numbers soon after the Big Bang. This population of axions would still be present today and could make up the dark matter of the universe. “
One area of SLAC research reconstructs the formation of the universe. We are familiar with galaxies, but this simulation shows the threads of dark matter that connect the cosmos. Galaxies form in brighter nodes where the density is highest.
SLAC National Accelerator Laboratory
There you go. Axions are among the hottest topics in physics because they seem to explain a lot. But once again, these sought-after parts are still hypothetical.
Will we ever find axioms?
It has been 40 years since scientists started looking for axions.
Most of these searches “mostly take advantage of the interaction of the action field with electromagnetic fields,” the authors say in a recent review published in Science Advances.
For example, CERN developed the Axion Search Telescope, a machine designed to find a hint of particles produced in the Sun’s core. Inside our star there are strong electric fields that could potentially interact with the axions – if they are really there, that is.
NASA’s rocket probe mission reveals a stunning view of superheated magnetic filaments in the solar atmosphere.
University of Central Lancashire
But the quest has faced several rather big challenges so far. First, “particle mass is not theoretically predictable,” the authors write — that is, we have very little idea of what an axion might look like.
At the moment, scientists are still looking for them, assuming that they are broad masses. However, researchers have recently offered evidence that the particle is probably between 40 and 180 microelectron volts. That is unimaginably small, about 1 billion mass of electrons.
“In addition,” the team writes, “the axion signal is expected to be very narrow … and extremely weak due to very weak connections to the particles and fields of the Standard Model.” In essence, even if miniature axioms try their best to signal their existence to us, we could miss them. Their signs can be so faint that we can barely notice them.
Despite these obstacles, the axion search continues. Most scientists claim that they must be there somewhere, but they look too good to be true when it comes to a complete explanation of dark matter.
“Most experimental experiments assume that axions make up 100% of the halo of dark matter,” the study authors emphasize, suggesting that there may be a way to “look at axion physics without relying on such an assumption.”
Although they may be the stars of the series, what if the axions are just one chapter in the history of dark matter?