For a month, the physicist Gorham and his colleagues have been observing a giant balloon floating high above the ice, carrying a series of antennas. This balloon scans the frozen landform of Antarctica over 1 million square kilometers, looking for high-energy particles from space.
Except for the strange background noise signal, the results of the balloon’s first flight experiment seemed lackluster. The results of the second flight experiment more than a year later were just as unflagging. When the balloon was scanned for the third time, the scientists decided to review its past detection data, especially those signals that were previously ignored as noise. This decision is really important. After further examination, the scientists discovered a signal that appeared to be an indication of high-energy particles. But it was not the target they were looking for, and it was an “impossible signal”-the particle did not come from space, but burst out of the ground.
This strange discovery was made in 2016. Since then, scientists have proposed various theories based on known physics to explain this strange signal, but all these explanations have been ruled out. However, the important meaning of this signal is lingering. To explain this signal, we need to create a parallel universe that is upside-down with our universe in the Big Bang that created our universe, also known as the mirror universe. Or anti-universe. In our view, the positive things in our universe are all opposite in this mirrored universe, the left is right, and the time flows backward. This may be the most puzzling view emerging from the Antarctic ice, but it may be correct.
An amazing signal
This ambitious balloon experiment is the “South Pole Pulse Transient Antenna” (also known as “Anita”). It is not an exaggeration to say that it is ambitious. why?
The earth is often bombarded by cosmic rays. Cosmic rays are particles that come from the deepest part of space. Some of them have energy 1 million times that of the best particle accelerators. Scientists hope to understand the composition and source of these ultra-high energy cosmic rays, but these questions are difficult to answer. First, the trajectory of cosmic rays is distorted by countless magnetic fields in the Milky Way, so it is almost impossible to trace the origin of cosmic rays.
Anita experimental scene.
Fortunately, no matter what source produces ultra-high-energy cosmic rays, it will certainly produce a more useful “beacon”-neutrinos. Because they are not charged, neutrinos are not affected by the magnetic field, but travel in a straight line in space. In this way, only the source of a neutrino can be traced to the source of the cosmic rays accompanying the neutrino. Tracing the source of a neutrino is simple-just reverse its trajectory from the point where it hit the earth. Anita’s mission is to find the origin of cosmic rays. Isn’t it very ambitious?
When a high-energy neutrino falls into Antarctic ice, the rain of charged particles produced by it will generate radio waves. If Anita detects such radio waves emitted from the surface, scientists can calculate the location of the neutrino and determine the source of the cosmic rays that accompany the neutrino. The main participant in Anita’s experiment and experimental particle physicist at the University of Hawaii, Gorham, said that the reverse process is simple and straightforward.
However, this process cannot explain the strange signal (anita signal for short) that scientists identified in 2016. Since this strange high-energy particle did not fall from the sky, but jumped out of the earth’s surface, it can be inferred that it entered the earth from the other side of the earth, passed through the interior of the earth and then flew out of the earth’s surface. Low-energy neutrinos can accomplish this kind of travel because they can easily penetrate matter. But whether it is high-energy neutrinos or cosmic rays, it is impossible to encounter an entity like the earth unhindered.
There are three types of neutrinos: electric neutrinos, mu neutrinos and tau neutrinos. They can’t travel at high speed, but tau neutrinos occasionally transform into another kind of particle-leptons, and then return to tau neutrinos. The possibility cannot be ruled out: a high-energy tau neutrino undergoes this deformation after entering the earth to complete the journey through the earth. But this explanation is controversial, after all, it is just a conjecture.
In 2018, the mystery of the Anita signal became more difficult to understand. At that time, Anita discovered another massive particle signal bursting from the ground. University of Pennsylvania scientist Fox and his colleagues said that Anita would never have seen two such events in such a short period of time, because their calculations showed the probability that a tau neutrino would cross the earth freely twice during the Anita mission. Only one part per million. In this way, τ neutrinos cannot be used to explain the Anita signal.
Because the Anita signals are too difficult to understand, some scientists even explain them with knowledge other than known physics. For more than 40 years, particle physics has been dominated by the Standard Model. The so-called standard model refers to a set of particles and forces, which are very accurate in explaining the natural world. But whenever Anita finds a strange signal, scientists often break the rules. For example, Professor Eastbourne from the University of Barcelona in Spain pointed out that the strange particles observed by Anita may be axons. Scientists first proposed the hypothetical particle of axons in the late 1970s. The purpose is to explain why CP is conserved in strong interactions (that is, the problem of strong CP). The Anita signal may be changed when interacting with the earth’s magnetic field. Produced by the axon of the photon.
Super symmetry (schematic).
Fox and his colleagues used supersymmetry to explain the Anita signal. Supersymmetry theory is a great extension of the standard model. According to this theory, every known elementary particle has a twin particle with a larger mass. Fox and others believe that the particles that pass through the earth and generate the Anita signal are supersymmetric tau neutrinos. But the problem is that other experimental devices designed to detect supersymmetric particles (such as the Large Hadron Collider near Geneva, Switzerland) have not detected such particles at all. Therefore, many physicists disagree with the supersymmetric interpretation of Anita’s signal.
An amazing explanation
According to Turok, a scientist at the Canadian Institute of Circumstantial Theoretical Physics, all the foregoing explanations are too complicated. He believes that in order to explain the Anita signal, one does not need to invent a series of imaginary particles, but only by studying what is known. Many people believe that particle physics has gone from the simplest to the most complex prediction theory. But Turlock didn’t think so.
It may be Turlock’s preference for “simply explaining things” that made him propose an extraordinary explanation for the Anita signal. Turlock’s initial focus had nothing to do with Antarctic ice, but the most direct consequence of the Big Bang. In order to study this period, there is not much guide information. One of the theories is symmetry-under certain changes, the laws of physics remain unchanged.
We use shorthands to refer to these symmetries. For example, C symmetry represents charge conjugate symmetry, which means that replacing the charge of a particle with the antimatter charge of the particle will not affect the basic behavior of the particle. P symmetry represents the symmetry of the odd-even transformation, which means that the physics in a situation is the same as the physics in the mirror image of the situation. T symmetry represents time reversal symmetry, which means that the process of turning back time does not violate any laws of physics.
Anita balloon lifted off, scanning the Antarctic.
Several processes involving elementary particles are known to violate one of C, P, and T symmetry, that is, there is a deviation, but if they also violate the other two, the deviation can be corrected. From this point of view, on the whole, CPT symmetry can never be broken. Turlock said that everything in nature cannot avoid CPT symmetry.
In 2018, Turlock and his colleagues began to explore the subject: If CPT symmetry existed in the earliest period of the universe, what does CPT symmetry mean today? They found that their calculations had strict limits on the type and number of particles ejected from the Big Bang. One of the particles is a right-handed neutrino. This is contrary to Turlock’s desire to explain the Anita signal with imaginary particles. But the physics community generally believes that right-handed neutrinos are necessary to balance the mass of known neutrinos, left-handed neutrinos (named for their direction of rotation). CPT symmetry requires the existence of a sufficient number of right-handed neutrinos, and Turok and his colleagues found that if they set the mass of a right-handed neutrino just right, they can match the most elusive matter in the universe—— The quality of dark matter. Physicists have been searching for dark matter for decades, but have not found it. Turok and others can’t believe that right-handed neutrinos are the best candidates for dark matter—the mass of right-handed neutrinos calculated by Turok and others exactly matches the mass of the particles that generate the Anita signal! Of course, Turlock and others did not know this coincidence.
An amazing coincidence
Louis, a theoretical physicist at the City University of New York, and his colleagues first pointed out this coincidence. They proposed that for millions or even tens of millions of years, the right-handed neutrinos in the universe have been captured by the earth’s magnetic field and have stayed inside the earth ever since. They also speculated that these dark matter particles sometimes decay into Higgs boson and tau neutrino pairs, thus generating Anita signals. Luis said that what Turlock’s team predicted was the energy of Anita’s signal, which was simply amazing. After all, this is a specific quantitative prediction, and it is supported by experimental results, which is really rare in particle physics.
But if the Anita signal particles are really right-handed neutrinos, really dark matter particles, then there will be trouble explaining the universe as we know it. A direct inference of CPT symmetry is that there are the same amount of matter and antimatter in the universe immediately after the Big Bang (ie our universe). But the two cannot coexist peacefully, but immediately annihilate each other, leaving only energy. The fact is that the amount of matter in the universe today greatly exceeds the amount of antimatter. This makes many cosmologists believe that the universe does not always conform to CPT symmetry. In order to restrain such doubts, the Turlock team needs to answer such a big question: How does our universe exist?
The answer lies in CPT symmetry itself, and the answer is very puzzling. In order to understand this answer, one needs to consider one of the most fundamental particle processes we know: the production of electrons and their antimatter forms, positrons, in the presence of a strong electric field. However, in order to strictly follow the CPT symmetry, the answer to the question “how does our universe exist” needs to be viewed in another way: before the electric field is generated, the positron is an electron that goes back in time, and after the electric field is generated, the electrons no longer time. Backflow. Although it sounds weird, the considerations of the aforementioned two methods should be completely equivalent, and it is impossible to find out which one is “correct”.
Turlock’s explanation of the Anita signal is extraordinary because it requires that similar situations also occur in our universe. The traditional view of the Big Bang is: at the moment of the Big Bang, a single universe was created, and there was almost no antimatter in this universe. In order not to violate the CPT symmetry, the Big Bang must produce two parallel universes. Most matter enters one of the universes (our universe), and most antimatter enters the other universe. In this other universe, everything is upside-down and opposite in our universe. All stars and planets in the other universe are made of antimatter rather than matter. What’s amazing is that this anti-universe shrinks backwards in time toward the point of the Big Bang instead of expanding forward from the point of the Big Bang.
The Anita team is working.
Expect amazing discoveries
At least, from our perspective, the anti-universe is like this. Just as CPT symmetry stipulates that a positron that moves forward in time is equivalent to an electron that moves backward in time, so our universe is also equivalent to an anti-universe in which everything seems to us to be the opposite of ours. For the inhabitants of the anti-universe, our universe is turned upside down and backward, full of “errors.” In fact, it is impossible for us to know whether we live in the “positive universe” or the “anti-universe”. We only know that the other universe is anti-universe in our eyes. In the cosmic sense, time is not an arrow imposed by an external observer, but more like a personal weather vane pointing to the direction of expansion of the universe where the person is. In short, time can be forward or backward. As for the definition of time forward or backward, it depends on the universe where the person lives. In one universe, another parallel universe-the mirror universe is the anti-universe, and vice versa.
This view is far from the existing cosmological view. Turlock was the first to admit that his “avant-garde” view still had some loopholes to plug. But he believes that he and others who agree with him in this regard can plug these loopholes without introducing new particles. Once the loopholes are closed, their views are definitely better than other views in this regard.
Regarding the views of Turlock and others, there is indeed a potential measuring device at work. If Anita does catch the right-handed neutrino predicted by the anti-cosmic view, then other neutrino observatories should also catch it. However, by the end of 2019, the IceCube experiment adjacent to Anita (which continues to observe the flashes produced by the decay products of neutrinos that travel through 1 cubic kilometer of Antarctic ice) team announced that they had not found the signal claimed by the Anita team Any high-energy neutrino in the direction.
But this is not a death sentence for anti-cosmic theory. Lewis pointed out that the trajectories of high-energy tau neutrinos may be mistaken for low-energy mu neutrinos. This statement is still controversial, but it also implies that Anita and the IceCube team may have found evidence that may indicate the existence of parallel universes.
There are many other ways to support the anti-cosmic view (also called anti-cosmic theory). The theory predicts that the Big Bang should not produce primitive gravitational waves (the ripples in space and time that cosmologists have been searching for but have not been able to find). The theory also predicts that the lightest of the three neutrinos actually has no mass. Turlock believes that this will be confirmed within 5 to 10 years. But if these predictions are eventually overturned, then the anti-cosmic theory will also collapse. Although he was a little worried, Turlock was still confident in his theory.
At the same time, the focus of attention of scientists once again returned to Antarctica. They hope to capture more massive particles erupting from the ground. Three years have passed since Anita’s fourth soft landing, and the analysis of its detection data is still in progress. Gorham is not willing to comment on the content of the analysis. He just said: “We don’t know how to describe it (referring to Anita’s detection results), but we found something.”