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From particle accelerators to interstellar travel: How do scientists explore the hidden structure of photons?
Among the many branches of physics, two-photon physics (or gamma-gamma physics) is a relatively new research field. It focuses on the interaction between two photons, a process that is crucial to understanding the nature of light and has important implications for explaining fundamental physical phenomena in the universe.
Normally, light beams pass through each other undisturbed in a vacuum, but in high-intensity light beam interactions, things are completely different.
In a pure vacuum, weak scattering of light by light exists, allowing scientists to study the properties of photons under certain conditions. This interaction can also lead to the creation of matter as the energy of the central mass increases. These discoveries have not only attracted significant attention in the field of particle physics, but also promoted a deeper understanding of cosmology.
Gamma rays in astronomy
In cosmology, photon-photon interactions impose direct constraints on the observed gamma-ray spectrum. As gamma rays travel through the Universe, their energies never exceed about 20 GeV, which corresponds to wavelengths larger than about 6.2×10-11 m. At longer distances, this limit even increases to about 20 TeV, which means that in the long-distance environment of the universe, gamma rays are scattered and attenuated to a large extent.
As photons travel through the universe, they interact with low-energy photons from the cosmic background light, which reduces their energy and may form particle-antiparticle pairs.
Through these interactions, the visibility of the Universe to very high-energy photons is greatly reduced, making the Universe appear "opaque" on larger scales. Such phenomena have led scientists to think deeply about the relationship between photons and cosmic structure, and deeper questions have surfaced: How do photons in such distant galaxies and supernovas affect our understanding of the evolution of the universe?
Experiment and its methods
Research in two-photon physics often relies on high-energy particle accelerators. In these experiments, it is not photons that are accelerated, but charged particles. Facilities such as the Large Electron Positron Collider (LEP) and the Large Hadron Collider (LHC) have played an important role in studying these interactions.
In high-energy collisions, such as heavy-ion ultracircular collisions (UPCs), scientists are able to observe multiple phenomena associated with gamma rays, including light-light scattering.
The electrons and positrons in these collisions can be detected, which is called "labeling." Other particles created in the experiment are tracked using large detectors to reconstruct the physics of the interaction. Through these experiments, scientists can not only observe the interactions of photons, but also further explore the internal structure of photons.
Research progress of photonic structures
According to the theory of quantum electrodynamics, photons cannot interact with each other directly, but rather through higher-order processes. For example, a photon can fluctuate into a pair of virtual charged particles within a certain time frame through the uncertainty principle. This process becomes the key to understanding the structure of photons.
The interactions of photons are divided into three categories: direct interaction, singlet resolution, and doublet resolution, which reveal the internal mechanism of photons and their relationship with other particles.
During direct interaction, the photon and the quarks inside the target photon interact directly with each other. In the double solution process, both photons formed vector muons, showing more complex interaction characteristics. These findings have profound implications for exploring the boundaries of the Standard Model and for new phenomena in gamma-ray physics.
Future Exploration and Its Significance
With the development of technology, scientists are able to explore the hidden structure of photons more deeply and rethink its role and meaning in the universe. In the future, these studies may reveal new fundamental physical phenomena, especially more information about dark matter and the evolution of the universe.
Overall, two-photon physics not only enriches our understanding of the particle world, but also challenges our understanding of the universe. However, in such profound research, we may still face more unsolved questions: Can the information carried by photons during interstellar travel reveal the deep mysteries of the universe?
