The development of science and technology is endless. No matter how much progress we have made, we should know that this is only a short stage, and mankind still has a long way to go in the future. Therefore, scientists are still actively exploring and putting forward their own opinions. For example, on the issue of whether to build a collider, two famous Chinese physicists, Wang Yifang and Yang Zhenning, have had a dispute. The Large Hadron Collider (LHC) is the world's largest particle collider: a marvel of modern particle physics that allows researchers to probe the depths of reality. In 2012, the 16.5-mile (27-kilometer) underground ring on the border of France and Switzerland, a huge atom smasher, enabled researchers to find evidence of the famous Higgs boson, leading to many other discoveries. 1. What is the Large Hadron Collider? The origin of the Large Hadron Collider can be traced back to 1977, when Sir John Adams, former director of the European Organization for Nuclear Research (CERN), proposed the construction of an underground tunnel to house a particle accelerator capable of reaching extremely high energies, according to a 2015 historical paper by physicist Thomas Schörner-Sadenius. The project received official approval 20 years later, in 1997, and construction began on a ring under the Franco-Swiss border, which could accelerate particles to 99.99% of the speed of light and smash them together. According to CERN, inside the ring, 9,300 magnets steer packets of charged particles in two opposite directions at 11,245 times per second, eventually bringing them together for head-on collisions. The facility can produce about 600 million collisions per second, spewing out incredible amounts of energy, and every now and then, an unprecedented strange heavy particle. The LHC operates at 6.5 times the energy of the previous record-holding particle accelerator, Fermi National Accelerator Laboratory's decommissioned Tevatron in the United States. Before it started operating, there were fears that the new atom smasher would destroy the Earth, perhaps by creating a black hole that would swallow everything. But any reputable physicist would say such fears are unfounded. Data from previous runs of the LHC have been used to discover ghostly neutrinos inside the machine, mysterious primordial "X" particles from the dawn of time, and a strange pattern in the universe that we cannot currently explain. 2. The dispute between Wang Yifang and Yang Zhenning The idea that China should build a large collider was first put forward by Shing-Tung Yau, a famous Chinese mathematician. He believed that China now has the ability to lead the world in a certain field of science and technology. If so, why not increase investment to take the lead in mankind, invent a large collider that can refresh the mathematical community and promote the development of mathematics and physics? It was this speech that triggered a fierce academic discussion, especially between Wang Yifang and Yang Zhenning, who argued for years about whether China should build a large collider. Wang Yifang is a famous physicist in China. He is not only gifted with a smart mind suitable for scientific research, but also hardworking and dedicated to academic research. At the age of 27, he was entrusted with an important task and became the youngest leader of the "New Particle Search Group". At that time, all the leaders were much older than him, and he was not only young, but also inexperienced and even just a student. Many people did not think highly of him because of his youth and inexperience, but he proved his strength to everyone with his research results. At that time, none of the leaders in his experimental group thought that the experiment of measuring the polarization of tau leptons could be done, but Wang Yifang believed in it and successfully measured it through unremitting efforts. He has made great contributions to the world of physics, achieving many "firsts" in the field of physics. Among them, the most remarkable one is undoubtedly the Daya Bay Neutrino Experiment, which was selected as one of the top ten scientific breakthroughs of the year by *Science*, and Wang Yifang has thus become the most promising future Nobel Prize winner in the academic circle. Wang Yifang holds a firm positive attitude towards the construction of a large collider, because he believes that the concept of the collider proposed by Europe around the same time is extremely similar to the principle of the collider proposed by Chinese scientists. This shows that the construction method proposed by China is feasible, so we should rush to develop this technology before them. Of course, a scientific research project must be supported by national financial resources. Wang Yifang calculated that building a large collider would require an initial investment of about 36 billion yuan, which is no small investment for China. Although the investment is large, if it can be successfully developed, it will be of great significance to China's scientific community, and can be said to be a leap forward in China's science. Based on this, Wang Yifang believes that a large collider should be built. However, Yang Zhenning, also a scientist, holds an opposite view. Yang Zhenning is a well-known physicist whose main research fields are particle physics and statistical mechanics. After becoming a physicist, he kept researching and made great contributions to the scientific community. He won the Nobel Prize in Physics, the highest honor, for his paper on the theory of parity non-conservation co-published with Li Zhengdao. As a physicist, Yang Zhenning has broken through the boundaries of existing physics and brought new progress to it. As such a physicist who is dedicated to scientific research and pursues innovation, Yang Zhenning should have supported the construction of a large collider, but he has always opposed this issue and thus argued with Wang Yifang for years. Why? In fact, Yang Zhenning's opposition to the construction is mainly based on the following considerations. First, the cost is too high. Second, because of the funding issue, Yang Zhenning believes that compared with the illusory new large collider, there are many areas in China's scientific field that are in need of money. Therefore, instead of putting money into the large collider that is far away and may not be accessible for a long time, it is better to first solve the urgent problems at hand. Finally, Yang Zhenning raised a key question: whether the large collider can really play the key role that people imagine. Scientists want to develop a large collider to find supersymmetric particles, but this research has been going on for many years, and it is still an unsolved mystery whether such particles exist, how to find them, and whether a large collider can really find them. Without any solid basis, rashly investing a huge amount of money and a lot of human and material resources in research is not only a very impulsive act, but also irresponsible to the scientific community and the country. 3. Three reasons why the Large Hadron Collider cannot make particles move faster 1) Magnet strength. If we could increase our electromagnets—the "bending" magnets that keep particles in circular motion—to arbitrarily high field strengths, it seems we could continue to accelerate these particles to faster and faster speeds. Each lap around the largest circular track, an electric "kick" would bring you to a higher speed, while a corresponding increase in magnetic field strength would bend your particles more severely. As long as your magnets can keep up, you can keep increasing the speed of the particles, making them get closer and closer to the speed of light. For particles like protons, their mass is large compared to their charge, which is a difficult task for magnets. Stronger magnets are needed to keep high-mass particles in a circular orbit of a specific radius than low-mass particles, and protons are about 1836 times more massive than electrons, while electrons have the same charge. For the LHC's magnets, their maximum strength is about 8 tesla, roughly four times that of the previous record-holding Tevatron's magnets. Unfortunately, it's not just about reaching that field strength, but precisely controlling it, maintaining it, and using it to fully bend these particles as needed. The current generation of electromagnets in the LHC simply cannot maintain stronger field strengths than this, although research at the National High Magnetic Field Laboratory has achieved and maintained field strengths of up to ~45/75/101 tesla for short periods (depending on the setup and magnet), and up to 32 tesla for long periods, a new record set earlier this year. Even with liquid helium cooling, which makes the electromagnets superconducting, there is a physical limit to the field strength that can be achieved and maintained for long periods. Equipping an accelerator with a new set of electromagnets is expensive and labor-intensive: any such upgrade would require specialized manufacturing facilities designed to produce the magnets needed for the accelerator. A whole new set of supporting infrastructure is also needed. This advancement was the major upgrade that led to the discovery of the top quark at Fermi National Accelerator Laboratory—when a new generation of electromagnets was installed, creating the Tevatron—but with the technology installed on the current LHC, higher field strengths are simply impossible. 2) The charge-to-mass ratio of protons. If you could manipulate the nature of matter, you could imagine reducing the mass of a proton while keeping its charge the same. Although we are talking about relativity here, Newton's famous equation F=ma is sufficient to show that with the same field and same force but smaller mass, you can get greater acceleration. We have a particle with the same charge as a proton but much lower mass: the negatively charged electron and its antimatter counterpart, the positron. With the same charge but a mass of only 1/1836, it can be accelerated faster and more easily. Unfortunately, we have already tried experiments accelerating electrons and positrons in the same ring where the LHC is now: it is called LEP, which stands for Large Electron-Positron Collider. Although these electrons and positrons can reach faster speeds than the protons in the LHC—299,792,457.992 m/s compared to about 299,792,455 m/s for protons—these correspond to much lower energies than the protons in the LHC. The limiting factor is a phenomenon called synchrotron radiation. When you accelerate a charged particle in a magnetic field, it not only bends perpendicular to the magnetic field and the particle's original motion; it also emits electromagnetic radiation. This radiation carries energy away from the fast-moving particle, and: the faster the particle moves, the greater its charge, the lower its mass, and the stronger the magnetic field, the greater the energy of this synchrotron radiation. For particles like protons, synchrotron radiation is still negligible, while for particles like electrons or positrons, it is already a limiting factor for current technology. A better solution would be to find a particle with a mass between that of an electron and a proton but with the same charge. We have one: the muon, but the problem is that it is unstable, with an average lifetime of only 2.2 microseconds. Until we can create and control muons as easily and successfully as we do protons and electrons (and their antimatter counterparts), the heavy mass of protons or the synchrotron emission of electrons will be a limiting factor. 3) The (fixed) size of the ring. All else being equal, you can always get higher energy by increasing the size of the particle accelerator. A larger radius means that particles with the same magnet strength and same charge and mass can achieve higher energy: double the radius, and you can achieve double the energy. In fact, the main differences between the Tevatron (reaching ~2 TeV per collision) and the LHC (reaching ~14 TeV) are: their magnetic field strengths (from ~4.2 tesla to ~7.5 tesla), and the circumference of their rings (from ~6.3 km to ~27 km). The larger your ring, the higher the energy you can probe the universe with. This means more energy available for particle creation (via Einstein's E=mc²), a higher chance of observing rare processes that are suppressed at lower energies, and a higher chance of discovering something completely new. While theorists often debate what may or may not lie beyond the currently known boundaries, experimentalists know a more fundamental fact: nature is what it is, and often defies our expectations. If we want to know what's out there, the only way to find out is to observe. If any of these three obstacles can be overcome—if we can increase the maximum strength of electromagnets, if we can increase the charge-to-mass ratio of protons (but not too much), or if we can increase the size of the circular trajectory followed by particles—we can achieve higher energies in particle collisions and push the frontiers of experimental physics beyond current explorations. For now, our best hope of finding new physics at the LHC will come from collecting more data, by increasing the collision rate of particles and running at the increased collision rate for a long time. We hope that more data will reveal a subtle effect, hinting at something new beyond current expectations. Conclusion: If we really want to achieve the highest energy with the particle accelerators we build, we must start building them on a scale larger than entire planets; perhaps going to the solar system scale should not be ignored. For now, perhaps unfortunately, these will remain dreams of physics enthusiasts and mad scientists. In reality, particle accelerators on Earth, limited by size, magnetic field strength, and synchrotron radiation, simply cannot compete with the astrophysical laboratories provided by our natural universe. Science is endless. We should not be surprised by the disputes among scientists; instead, we should be gratified and grateful. Because only when scientists always have curiosity and ambition can China's science be promoted and achieve more exciting breakthroughs. Sources: Liyu Popular Science, Zhengdao Observation, Hongchen Huajuan