Why do physicists want to build particle colliders on the moon?

BEIJING, June 11 (Xinhua) — As the exploration of how the universe works becomes more and more in-depth, particle physics experiments are becoming more and more complex, according tomedia reports. To uncover the mysteries of the tiniest subatomic particles, physicists must keep the colliders and detectors as low as possible and remove as much excess air as possible to keep them stationary for reliable results.

Why do physicists want to build particle colliders on the moon?

NASA recently launched the Commercial Lunar Payload Service Program (CLPS), which aims to find the best payloads to be delivered to the lunar surface in the future, including instruments for basic scientific research. Shown here is lockheed Martin’s concept map for a commercial lunar lander

So, physicists have suggested, what if we skip these and experiment directly with particle physics on the moon? A paper published earlier this year in the preprint database arXiv argues that the moon is actually a good place for high-energy physics research.

First of all, the moon is very cold and the temperature can be very low. There is no atmosphere or water, so there is no medium to transfer the heat of sunlight from one place to another. At night, when the sun falls below the moon’s horizon, the temperature drops to minus 73 degrees Celsius , within the typical low temperature experiment setting on Earth. During the day, the moon’s temperature will rise a little, reaching more than 38 degrees Celsius. But just as water ice is hidden in the shadow of the moon’s craters, you only need a little shade to cool yourself down;

Physicists need such low temperatures for a reason. In particle accelerators, low temperatures ensure that superconducting magnets do not melt on their own. The role of superconducting magnets is to throw particles into the accelerator so that they reach speeds close to the speed of light. Second, the higher the detector’s temperature, the more noise it will process when it filters out tiny signals from subatomic particles – more heat is equivalent to more molecular vibrations, or more noise.

In addition to the cold temperatures, the fact that the moon has no atmosphere is also an important advantage. On Earth, physicists have to pull out all the air in accelerators and detectors, because before the experiment begins, you don’t want particles close to the speed of light to crash into a wandering nitrogen molecule. The lunar vacuum environment is more than 10 times better than anything physicists make in the lab, and it is natural and requires no effort.

Finally, because the tides are locked, the moon’s rotation cycle is the same as its rotation around the Earth, so the moon always points at the Earth on the same side. This means that the moon’s beam of particles points to the Earth’s exploration laboratory, which does not require very hard adjustment of the settings to take advantage of long distances.

Moon Neutrino Factory

Perhaps the most promising use for physics experiments on the moon is to serve as a source of neutrinos. Neutrinos are ghostly tiny particles with no charge and little mass. This allows them to pass through normal matter with little or no notice – hundreds of billions of neutrinos are passing through your body every moment, and you can’t feel anything.

Because of this characteristic, neutrinos are difficult to study and understand. These particles are produced in large quantities in nuclear reactions, so we can build a nuclear power plant on the moon, and the resulting neutrinos will fly quickly to Earth, where physicists on Earth can collect them for research.

An annoying and mysterious feature of neutrinos is the ability to change types during flight (in physics parsing the three “tastes” of neutrinos are electro-neutrinos, neutrinos, and neutrinos). By separating the generation and detection of neutrinos over long distances, we have given more neutrinos a chance to change their “taste” to better understand this behavior. The moon can be a perfect source of neutrinos: it is far enough away from us to separate long distances, but at the same time close enough to capture enough neutrinos for practical research (or, if anything, to troubleshoot equipment).

Who needs the earth?

If we can set up a physical experiment on the moon, we can also send objects other than neutrinos to Earth, such as cosmic rays. Even the most powerful particle colliders today do not reach the energy that naturally produces and emits cosmic rays (if the estimates are accurate, we can’t even reach one-billionth of that energy). Every now and then, a large number of high-energy subatomic particles from outer space whizz into the Earth’s atmosphere, pounding gas molecules and releasing large numbers of particle by-products before reaching the ground.

Cosmic rays come from some of the most powerful sources in the universe (such as supernovae), but they are not yet known. Physicists are thinking of a real device that can be used — a cosmic ray gun. We can make these high-energy particles elsewhere and then launch them into the Earth’s atmosphere so we can do research. How about putting this device on the moon? By producing large numbers of high-energy particles on the moon and then shooting them into the Earth’s atmosphere, we can observe the resulting effects on the ground to better understand the high-energy side of the universe.

But why stop there? Why not put the probe on the moon, too? Setting up a complete particle physics experiment on the moon, including launch sources, accelerators and detectors, has advantages over similar systems on Earth. On Earth, the primary bottleneck facing physicists is how to obtain a highly controlled vacuum, and experiments on Earth become relatively compact. But on the moon, you can get a vacuum for free. This vacuum works better than the one used in particle collider experiments. Physicists can build experimental equipment to the size they want without worrying about investing in gas pumps. This is a huge advantage.

Of course, landing on the moon and building complex experimental devices on the moon may present a significant technical challenge, but once this problem is solved, physics may be a big breakthrough.