Much is unknown about the nature of the universe itself. It is the curiosity inherent in humans, leading to the search for answers to these questions, that drives science forward. We have already accumulated an incredible amount of knowledge, and the successes of our two leading theories - quantum field theory, which describes the Standard Model, and general relativity, which describes gravity - demonstrate how far we have come in understanding reality itself.
Many people are pessimistic about our current efforts and future plans to solve the great cosmic mysteries that baffle us today. Our best hypotheses for new physics, including supersymmetry, extra dimensions, technicolor, string theory, and others, have not been able to get any experimental confirmation so far. But this does not mean that physics is in crisis. This means that everything is exactly as it should be: physics tells the truth about the universe. Our next steps will show us how well we listened.
The greatest mysteries of the universe
A century ago, the biggest questions we could ask included some extremely important existential riddles such as:
- What are the smallest constituents of matter?
- Are our theories of the forces of nature truly fundamental, or is a deeper understanding needed?
- How big is the universe?
- Has our Universe always existed or did it appear at a certain moment in the past?
- How do the stars shine?
At that time, these mysteries occupied the minds of the greatest people. Many did not even think that they could be answered. In particular, they required an investment of so seemingly huge resources that it was suggested that we simply be content with what we knew at that time and use this knowledge for the development of society.
Of course, we didn't do that. Investing in society is extremely important, but it is just as important to push the boundaries of the known. Thanks to new discoveries and research methods, we were able to get the following answers:
- Atoms are made up of subatomic particles, many of which are subdivided into even smaller constituents; we now know the entire Standard Model.
- Our classical theories have been replaced by quantum ones, combining four fundamental forces: strong nuclear, electromagnetic, weak nuclear, and gravitational forces.
- The observable universe spans 46.1 billion light years in all directions; the observable universe can be much larger or infinite.
- 13.8 billion years have passed since the event known as the Big Bang that gave birth to the universe we know. It was preceded by an inflationary era of indefinite duration.
- Stars shine thanks to the physics of nuclear fusion, converting matter into energy according to Einstein's formula E = mc2.
And yet, it only deepened the scientific mysteries that surround us. With everything we know about fundamental particles, we are sure that there must be many other things in the Universe that are still unknown to us. We cannot explain the apparent presence of dark matter, we don’t understand dark energy, and we don’t know why the universe is expanding this way and not otherwise.
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We do not know why the particles are as massive as they are; why the Universe is overwhelmed by matter, not antimatter; why neutrinos have mass. We don't know if the proton is stable, if it will ever decay, or if gravity is a quantum force of nature. And although we know that inflation was preceded by the Big Bang, we do not know if inflation itself started or was eternal.
Can humans solve these riddles? Could the experiments we can do with current or future technology shed light on these fundamental mysteries?
The answer to the first question is possible; we don't know what secrets nature holds until we see. The answer to the second question is unequivocally yes. Even if every theory we have ever brought up about what is beyond the boundaries of the known - the Standard Model and General Relativity - is 100% wrong, there is a huge amount of information that can be obtained by performing experiments that we plan to run next. generation. Not building all these installations would be a huge folly, even if they confirm the nightmare scenario that particle physicists have feared for many years.
When you hear about a particle accelerator, you probably imagine all of these new discoveries that await us at higher energies. The promise of new particles, new forces, new interactions, or even completely new sectors of physics is what theorists like to blunder, even if experiment after experiment goes wrong and does not keep those promises.
There is a good reason for this: most of the ideas that one can come up with in physics have already been either excluded or severely limited by the data we already have. If you want to discover a new particle, field, interaction, or phenomenon, you shouldn't postulate something that is incompatible with what we already know for sure. Of course, we could make assumptions that would later turn out to be wrong, but the data itself must be in agreement with any new theory.
This is why the greatest effort in physics goes not to new theories or new ideas, but to experiments that will allow us to move beyond what we have already explored. Sure, finding the Higgs boson could be a big buzz, but how strongly is the Higgs related to the Z boson? What are all these connections between these two particles and others in the Standard Model? How easy is it to create them? Once created, will there be mutual decays that differ from the decay of the standard Higgs plus the standard Z boson?
There is a technique that can be used to investigate this: create an electron-positron collision with the exact mass of the Higgs and Z-boson. Instead of a few tens or hundreds of events that create the Higgs and Z boson, as the LHC does, you can create thousands, hundreds of thousands, or even millions of them.
Of course, the general public will be more excited about finding a new particle than anything else, but not every experiment is designed to create new particles - and it doesn't need to be. Some are intended to investigate matter already known to us and to study in detail its properties. The Large Electron-Positron Collider, the precursor to the LHC, has never found a single new fundamental particle. Like the DESY experiment, which collided electrons with protons. And so does the relativistic heavy ion collider.
And this was to be expected; the purpose of these three colliders was different. It consisted in exploring matter that really exists with unprecedented precision.
It doesn't seem like these experiments just confirmed the Standard Model, although everything they found was consistent with the Standard Model. They created new compound particles and measured the bonds between them. Decay and branching relationships were discovered, as well as subtle differences between matter and antimatter. Some particles behaved differently from their mirror counterparts. Others seemed to break the time reversal symmetry. However, others have been found to mix together, creating bound states that we weren't even aware of.
The purpose of the next great scientific experiment is not simply to search for one thing or to test one new theory. We need to collect a huge set of otherwise unavailable data, and let that data guide the industry.
Of course, we can design and build experiments or observatories based on what we expect to find. But the best choice for the future of science will be a multipurpose machine that can collect large and varied amounts of data that would not have been possible without such huge investments. This is why Hubble has been so successful, why Fermilab and the LHC have pushed the boundaries further than ever before, and why future missions like the James Webb Space Telescope, future 30-meter-class observatories or future colliders will be needed if we are to ever answer the most fundamental questions from all.
There is an old adage in business that also applies to science: “Faster. It's better. Cheaper. Pick two. The world is moving faster than ever before. If we start saving and don't invest in the “best”, it will be like giving up.
Ilya Khel