When was the quantum field in the universe first formed?

 According to foreign media(hermes Scarves On Sale) reports, no matter how we observe the universe, whether it is at low temperatures or extremely high energy, near the earth or the farthest part of the observable universe, we will observe the same laws of physics. The fundamental constants are the same, the gravitation is the same, and the quantum transformation and relativity effects are also exactly the same. At any point in the observable universe, the application of general relativity (dominating gravity) and quantum field theory (dominating other known forces) seems to be the same as on Earth. But has this always been the case? Could the quantum field in the universe have ever been different? Even once there was no quantum field at all? Chris Shaw, a supporter of the crowdfunding website Patreon, wanted to know the answers to these questions, so he asked:

　　 "When did the first batch of subfields in the universe form? Have they existed since the Big Bang? Will they form even earlier than this, before the Big Bang expansion period?"

　　 Quantum fields may exist even under unexpected conditions. For quantum fields, we currently have the following information.

When it comes to "field", most people's cognition may be the same as that of scientists in the 19th century: if there is an electric charge or a permanent magnet, it will form a field around itself in all directions in space. This field exists regardless of whether other particles are affected by it. But you can detect the existence of the field (and the objects and ways that the field can affect) through the interaction of various charges and the field.

　　 For example, iron powder can be arranged in a magnetic field in accordance with the direction of the magnetic field. Charges in an electric field (or when moving in a magnetic field) are accelerated by force, depending on the strength of the field.

In the conceptual system of Einstein and Newton, even gravity can be described as a field. Any form of matter or energy will be affected by the cumulative gravitational effect on its position in space, which determines its future motion. Track.

However, although this kind of visual description is very useful and common, it can only be established in a non-quantum setting. It well reflects the operating mechanism of the classical field, but the reality we live in is closely related to quantum. According to our perception of the classical physical world, the field is smooth and continuous, and on the "spectral line" from the theoretical minimum to the theoretical maximum, the characteristics of the field exist at any point. However, in the quantum universe, none of this will work.

　　 Quantum fields not only exist around the source (hermes outlet), but are everywhere. If there is mass (corresponding to gravity), electric charge (corresponding to electromagnetism), a particle with a non-zero weak supercharge (corresponding to a weak nuclear force), or a color charge (corresponding to a strong nuclear force), they will behave as an excited state of the field , But regardless of the existence of these field sources, the existence of the field is not affected. Not only that, the field is quantized, and its zero-point energy (or the lowest energy level it can have) can be zero.

In other words, what we understand as a "vacuum" without electric charge, mass or any field source is not really empty, but possesses the aforementioned quantum field. This means that the space is also full of quantum fluctuations generated by the combination of the quantum nature of the field and the Heisenberg uncertainty principle, occupying every possible quantum mode and quantum state (the probability of these quantum states being occupied is specific , And can be calculated theoretically).

You may be skeptical about this and think: "So what? Quantum field theory is just a calculation method, and it cannot verify whether these quantum fields exist in a vacuum." But in fact, we can use it. It comes to experiment. Take two parallel conductive plates and place them in the most perfect vacuum you can create. There is no matter and any kind of field source, only the quantum field that comes with the vacuum, including the most basic quantum electromagnetic field.

　　 Outside these two conductive plates, all possible states of these quantum fields can exist, and there are no restrictions on quantum modes. But inside the conductive plate, only a part of the quantum field can exist, because some boundary conditions prevent the generation of specific electromagnetic waves, so that part of the excited state of the quantum field cannot exist. Even if there is no source of electromagnetic waves, these excited field states are different inside and outside the plate, resulting in a resultant force called Casimir force on the plate.

The Casimir force was first predicted by Hendrik Casimir in 1948, but it was not confirmed and detected in experiments until 1997. The physicist Steve Lamoreaux successfully completed the experiment and the result was within 5% of Casimir's prediction. These quantum fields are indeed everywhere in space. This experiment not only proves the existence of quantum fields, but also shows the strength of these fields.

　　 One concept that physicists want to figure out is whether the quantum fields in vacuum are all composed of quantum fields as we know them (that is, quantum fields that belong to the Standard Model and are related to gravity), or whether they also contain other quantum fields. For example, the following sources may also produce quantum fields: the source of dark matter, the phenomenon or field that produces dark energy, the residual field during the expansion of the universe, the new field or new interaction formed by the unified theoretical system, or any other than the standard model New physical phenomena (including but not limited to new forces or particles, etc.).

Although the laws of physics will not change under the conditions we observe, whether in the particle accelerator or in the earliest observable stage of the Big Bang, the nature of the quantum field ensures the strength of quantum coupling (with particles in the quantum The force felt in the field is consistent) will change as a function of energy and temperature.

　　 In physics, we call this "running of the coupling constant". You can understand it this way: these virtual quantum particles occupy more excited state modes than low-energy ground state modes. Although this does not mean that in the early high-energy period of the universe, the quantum field that dominates the universe is different from today, but it also shows something: these coupling constants may have been unified at some point, indicating a strong nuclear force , Weak nuclear force and electromagnetic force may all originate from the same unified theory. Under this theory, all forces are unified.

This framework not only provides the possibility of the existence of other quantum fields and exposes the influence of these quantum fields under high energy, but also shows that there may be a set of "ultimate unified theory" or "theory of everything" in the universe. If this state really exists, you can imagine it as the ultimate form of restoring symmetry, like putting a ball on the top of the highest mountain on the planet.

　　 If the symmetry is broken, the ball will roll down the hill and fall into the lowest point of a valley encountered along the way. But if you put the ball back to the top of the mountain, try a few more times, try to balance the ball as much as possible, the ball may not roll down the same path every time, depending on the following factors: small differences in initial conditions, small, Even quantum-level fluctuations, the rate of expansion or cooling of the universe, and the existence of new field coupling.

When the symmetry is restored (yellow ball at the top), everything is symmetrical, and each state has the same priority. But when the symmetry is broken at low energy (the blue ball at the bottom), the degrees of freedom in all directions are no longer the same. In different quantum fields, the "lowest point" the ball rolls into may also be different.