Europe leads the way in large particle colliders. What will my country’s future development look like?

When the Trisolarans learned that humans existed on Earth four light years away, they were both happy and scared. They were happy because human civilization was far inferior to the Trisolaran civilization, but they were scared because human civilization was evolving very quickly. If the Trisolarans used their fastest spacecraft at the time to reach Earth, it would take them four hundred years, and by the time they really got there, they might have been crushed by the technological level of humans.

So, they launched a preemptive attack by sending two proton computers at the speed of light to the earth first to cause damage secretly. But what bad things can two particles smaller than atoms do?

In addition to spying on the public intelligence of the earthlings, they also disrupted the particle physics research of human beings, affected the most cutting-edge particle acceleration collision experiments of human beings, created wrong experimental results, drove a group of the smartest physicists of human beings crazy, and finally locked the development of basic science of human beings. If human beings cannot discover new laws of physics at the microscopic level, there will be no higher level of science and technology, and naturally they will never be able to challenge the Trisolarans.

Isn’t it terrifying to think about it? We have to ask, is our physics now locked up by the Trisolarans’ sophons?

Not really, but basic physics seems to be "locked" by high R&D costs, because the cost of building such high-energy physics experimental machines is really a bit high.

On June 19 this year, the European Organization for Nuclear Research (CERN) unanimously passed the "European Particle Physics Strategy 2020" and planned to build a new high-energy physics experimental machine - the Future Circular Collider (FCC) to study the Higgs boson (the "God particle") and high-energy frontier exploration.

However, the construction cost of this 100-kilometer-long FCC circular collider is estimated to be 21 billion euros. The plan was able to pass thanks to the success of its predecessor, the Large Hadron Collider (LHC). This collider, which cost 5 billion Swiss francs and took 25 years to build and is 27 kilometers long, finally confirmed the existence of the Higgs boson in 2012, confirming a physics conjecture proposed 50 years ago.

It was this successful experiment that gave CERN great confidence, leading it to plan to build a super-large circular collider spanning Switzerland and France, with an area 13 times larger and a circumference 3.7 times larger, to discover deeper fundamental particles, such as the predicted supersymmetric particles, and thus verify those supersymmetric theories that can explain dark matter and dark energy.

Is it worthwhile to use such a large amount of resources to verify a physics hypothesis? In China, there is also a heated debate about whether to build the "Circular Electron Positron Collider-Large Proton Collider (CEPC-SPPC)".

So, what is the purpose of this large particle collider that Europe is going to build? Since Europe is already leading, is it necessary for my country to build a large particle collider?

Why build a large particle collider?

Particle colliders are the most important experimental equipment in modern high-energy physics research. If humans want to understand the microscopic level of the universe, that is, to understand the basic composition of cosmic matter and the basic laws of natural operation, they not only need to propose a series of scientific hypotheses, but also conduct physical experiments that can confirm or falsify these hypotheses. In this case, particle colliders are indispensable verification and measurement tools.

So how does a particle collider work? Just as we want to understand the internal structure of an object, we take it apart to have a look, physicists also use the same idea when dealing with microscopic particles. However, it is very difficult to break apart elementary particles smaller than atoms, so scientists have come up with the idea of ​​accelerating elementary particles and then letting them collide head-on. Only by colliding at speeds close to the speed of light and releasing the greatest energy can these particles be broken apart, and then humans can observe the more basic composition and various physical properties of particles.

(LHC lead ion collision experiment, produced a large number of new substances)

How to make two such tiny particles collide is a very complicated process. The only way that can be thought of is to accelerate hundreds of millions of particles at the same time. In the end, in a storm of particles, only a few lucky pairs of particles can collide head-on. What humans have to do is to measure the traces left by the particle collision in a flash (it is impossible to directly observe particle collisions), which also places extremely strict engineering requirements on particle colliders.

So, how did people find the Higgs boson in the LHC collider in 2012? Because the decay period of this God particle is only a short 10 to the negative 22th power of seconds, it is impossible for the detector to directly capture the God particle. Therefore, the signal recorded by the particle detector comes from the decay product of the God particle, that is, a pair of stable positive and negative electrons and positive and negative muons with a long life span. It is by measuring the correlation between these decayed particles that people indirectly deduce the existence of the God particle.

(Higgs boson)

What is the significance of discovering the "Higgs boson"? In the 1960s, scientists proposed the "standard model" of particle physics, which is a theory that describes the three fundamental forces of strong force, weak force and electromagnetic force and the fundamental particles that make up all matter. In this theory, the Higgs boson is considered to be the "source of mass". Other particles can only generate mass by interacting with the Higgs boson.

Therefore, the discovery of the "Higgs boson" has become the last piece of the puzzle to complete the "Standard Model". Since the puzzle of the "Standard Model" is complete, why do humans still need a larger-scale particle collider?

One is that scientists hope to conduct more in-depth research on the Higgs boson, but even if the LHC is continuously upgraded, that is, the energy level of the collision is increased, it is not possible to obtain enough Higgs bosons, so a larger collider device needs to be built.

Another thing is that the "standard model" cannot fully explain all the laws of physics. For example, it cannot explain the mass of neutrinos, the origin of dark matter and dark energy, the imbalance of matter and antimatter, and the grand unified theory that integrates the four forces. The feast of particle physics has just begun, and larger particle collision experiments are needed to verify it.

(European Particle Physics Strategy 2020)

Therefore, CERN is determined to make the study of the Higgs boson and the construction of a higher-energy particle collider "the highest priority in the future." So, what are the pros and cons of this huge scientific project in China?

The top confrontation in high-energy physics: Should we build CEPC?

Currently, there are three "Higgs factory" projects being planned around the world, which are capable of producing more Higgs bosons and measuring them with extremely high precision. The three projects are the Circular Electron Positron Collider-Large Proton Collider (CEPC-SPPC) proposed by Chinese physicists in September 2012, the International Linear Collider (ILC) that Japan is actively pursuing, and the Future Circular Collider (FCC) planned by CERN.

The CEPC-SPPC project proposed by my country in September 2012 is divided into two steps. The first phase is CEPC, which can be used as a Higgs factory; the second phase is SPPC, which will build a high-energy proton collider. The FCC roadmap determined by the European particle physics strategy proposed by CERN is actually highly consistent with our CEPC-SPPC concept. The total investment of FCC is 21 billion euros, while our investment scale is expected to be about 40 billion yuan for the first phase of the project, and the construction time is planned to be between 2022 and 2030; the second phase of the project cost is 100 billion yuan, and its investment scale is much smaller than CERN's investment plan, and the construction time is between 2040 and 2050.

(Guizhou Pingtang 500-meter Aperture Spherical Radio Telescope)

But in any case, the cost of the CEPC-SPPC large collider project is two orders of magnitude higher than that of existing large scientific projects. For example, the 500-meter Aperture Spherical Radio Telescope (FAST) in Pingtang, Guizhou, cost only 667 million yuan. The Jiangmen Neutrino Experiment is under construction with an estimated investment of 2 billion yuan.

Although this research and development cost is spent in batches over decades, it is still a huge sum for my country's current scientific research funding. On whether to support the construction of the CEPC-SPPC large collider project, my country's scientific community is also divided into two clear-cut factions.

In 2016, in response to the viewpoint of "China building a high-energy collider" proposed by the famous mathematician Qiu Chengtong, the well-known Chinese physicist Mr. Yang Zhenning published an article stating that "China should not build a super collider today", becoming an authoritative representative who openly opposed the construction of a large collider. The reasons given by Mr. Yang are as follows:

Firstly, the construction of a large collider and its subsequent detection projects are extremely costly and may be a "bottomless pit". The interruption of the Large Superconducting Collider (SSC) in the United States, which wasted $3 billion, is a lesson for us. Secondly, China is still a developing country and more financial funds should be invested in people's livelihood. Thirdly, it will inevitably squeeze other basic scientific research funds. Fourthly, the results of high-energy physics will have no practical benefits for human life in the short term.