Five Problems in theoretical physics

From: http://limiao.net/155

 

Jon shock received Lee Smolin's "The trouble with physics" from the publisher and showed it to me after reading it.

At the beginning, I saw five major problems listed by Lee in theoretical physics. The problem is as follows:

1. combine quantum theory and general relativity into a complete theory of nature.

2. solve the basic problem of quantum mechanics, or make the theory meaningful through re-understanding, or re-invent a theory.

3. Determine whether different particles and interactions are uniform.

4. Understand how free parameters in the particle physics standard model are determined.

5. Explanation of dark matter and dark energy. If they do not exist, they determine how gravity is modified on a large scale. More broadly, explain why parameters in the standard cosmic model take these values.

Everyone has five major problems in his mind. Lee is talking about five common problems. From this point of view, Lee doesn't want to be different at all. As he said in his book, he is a person who does not like conflict.

Recently, I have become a more pragmatic school. I believe that the real progress does not come from who solved a major problem at once, for example, any of the above problems, but from the work that seems to be done. Let alone the example in the past one hundred years. Planck tries to combine the formula of the lie-jeans and Wien into a complete law to discover quantum. Bohr finds his quantization rule in order to explain the Balmer formula. Einstein's work seems a little like a big theory, or a big problem, but he is also a step by step. The special theory of relativity is established after Lorentz's electronic theory and Poincare work, the general theory of relativity came out step by Einstein. So if I need to make a list and paste it on the wall of my office, my problem will be very different from Lee's.

I will first comment on the five problems listed by Lee, and then list my five problems.

1. combine quantum theory and general relativity into a complete theory of nature.

This is undoubtedly a central issue. Neither string theory nor loop gravity can claim to solve this problem. Logically, the string theory solves this problem under certain circumstances, such as the divergence of the disturbance theory. In some cases, the implementation of string theory even involves non-disturbance, such as ADS/CFT. The biggest problem of string theory at present is how to implement it without the supersymmetry, and how to combine it with cosmology.

Another very practical problem of quantum gravity is how to find a computing solution when the quantum fluctuations of gravity become very important. The black hole problem is such a problem.

The Schwarzschild black hole problem, whether it is string theory or loop gravity, is not truly solved.

2. solve the basic problem of quantum mechanics, or make the theory meaningful through re-understanding, or re-invent a theory.

I don't think quantum mechanics needs to be modified. If quantum mechanics seems hard to understand in a "realist", it may be that we do not really understand the meaning of a considerable measurement. For example, many people think that if quantum mechanics only gives a probability of a particle at a certain position, this theory is incomplete. In my opinion, to what extent is the concept of particle "reality" that we don't understand. Let me give two examples to illustrate my point of view. The first one is the full equality of particles. in quantum mechanics, this is a assumption or "principle ". In quantum field theory, this is an inference. In our field theory, we assume that only stable particles will appear in the gradual state, and the scattering amplitude between the gradual states is a considerable measurement. This makes it impossible to define the relative local volume, including a particle at a given time. This example shows that we do not really understand the so-called "reality" of the particle, or we do not have a better understanding of the particle except for the progressive state. The second example involves general relativity. The Unruh effect tells us that the concepts of particles and even events are related to the observer.

If we do not have a "reality" object for the moment, how can we feel that quantum mechanics is incomplete from the perspective of a realist? Maybe we still lack a deeper understanding of quantum mechanics, but this understanding will not come from quantum mechanics itself, nor from modifying quantum mechanics, instead, quantum mechanics can be obtained after being understood in a larger framework. For example, how quantum mechanics is implemented in quantum gravity and how quantum mechanics is used to implement quantum cosmology.

Feynman's views on quantum mechanics are still the best: I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem.

3. Determine whether different particles and interactions are uniform.

I personally think the real decision is in the hands of the experimenters.

4. Understand how free parameters in the particle physics standard model are determined.

This issue is related to the previous issue.

5. Explanation of dark matter and dark energy. If they do not exist, they determine how gravity is modified on a large scale. More broadly, explain why parameters in the standard cosmic model take these values.

The existence of dark matter, especially dark energy, tells us that it is no longer possible to separate the so-called basic theory from cosmology. Dark energy is the biggest problem of quantum gravity. In the past, I thought that black hole entropy is applied to quantum gravity as a black body radiation to quantum theory. Now I think dark energy is the question of black body radiation of quantum gravity.

Take a rest and write it at night.

My five problems:

1. What is the most common physical representation of the holographic theory of quantum gravity?

We may not yet have a complete theory of quantum gravity, but black hole quantum physics clearly tells us that there is a holographic principle there. ADS/CFT is a specific implementation of holographic principles.

To implement holographic principles, on the one hand we need ry, This is the side of gravity, and on the other hand we need field theory. In extreme circumstances, the gravity side may completely disappear, for example, an analyticdb with a small radius. What replaces ry when ry disappears? Or is there nothing. The theory of reliability is just the field theory?

Is there a universal holographic principle in cosmology? If so, what is the relationship between the implementation of this holographic principle and quantum cosmology?

The specific implementation of a holographic principle can directly explain the entropy of the black hole and whether the evolution of the black hole fully complies with quantum mechanics.

2. What is dark energy?

Is dark energy only a constant of Einstein's cosmology? Or variable? If it is variable, how long does it take for cosmic observation to clearly tell us that it is variable?

Does the existence of dark energy reflect the relationship between infrared and UV of quantum gravity? Or is it because landscape scenario tends to be a random number that is related to the principle of human choice?

3. What is the first experiment capable of reflecting quantum gravity?

I hope that the theoretical practitioners can come up with more experiments that can be achieved in the near future or in the far future. No matter which kind of quantum gravity theory (string theory, loop gravity, and so on), a reliable quantum gravity effect cannot be calculated so far, this reliable quantum gravity effect is not the High-Energy Scattering in string theory, nor the quantization of the volume and area in loop gravity, but the effect that can be seen in relatively low-energy fields. For example, the brown movement represents the physical effect of an atom long before we can "directly see" it.

The small black hole we have discussed previously is undoubtedly a possibility, although it is very unlikely.

I personally am particularly interested in the Trans-Planckian effect in inflation. It is of course very exciting to see the quantum gravity effect in CMB power spectrum, so we don't have to wait until the human civilization can reach the Planck energy.

Apart from inflation, is there any other observation or experiment that may reflect the quantum gravity effect in the field of cosmology?

4. What are the physical parameters of a particle?

This is a big question, but I think it is easier to ask if there is a uniform tag for all interactions. Recently, Tegmark and Wilczek have studied the relationship between the physical constants of particles, cosmic parameters, microscopic physical limitations, and selection effects:

Dimensionless constants, cosmology and other dark matters

Is it possible to study which constants are random from the perspective of the model independent of quantum gravity? Of course, the final decision is experiment. However, it is the theoretical responsibility to tell the experimenters what kind of experiment is related to this issue, so we need to carefully sort it out. I stress that model independence is very important. I don't believe in any conclusions drawn from a specific, sometimes very hand-Waving Model.

5. Is there any physics beyond the standard model in particle physics?

Of course, the neutron quality is not counted.

LHC may bring us unexpected things. If so, we don't have to sit here, as Lee Smolin laments that there has been no substantial progress in the past few decades in high-energy physics + gravity theory.

The five questions above are too big. They are not just pot-filling tasks, but they are five questions that I really want to answer.

Appendix:

1. Lubos's list of top twelve results of string theory

2. Warren Siegel's top 10 string theory questions

3. Sabine hossenfelder's top ten

4. David mermin's top ten

5. John Baez's open questions in physics

Because the second issue among the five questions of Lee Smolin is most likely to be controversial, I suggest you take a look at meimin's third issue. Meimin has a unique understanding of quantum mechanics and has also written related science. Therefore, I think his statement on this issue is very interesting. It can be seen that there is no problem with quantum mechanics, opposite to Smolin. I think people with strong philosophical tendencies usually think that there is a problem with quantum mechanics, and Lee's philosophical preferences have always been strong. I mentioned Feynman'sFamous saying: Shut up and calculate, which is my attitude towards this issue. Let's take a look at meimin's third question:

3. are fundamental theories still based on superpositions of States that evolve unitarily, or have the basic principles of quantum mechanics been replaced? If quantum mechanic has implements ved, have people reached a consensus on the solution to the interpretive problems, or have they simply ceased to view them as problems needing a solution? If quantum mechanics has not attached ved, has the theory that replaced it clarified these puzzles, Or do people find it equally or even more mysterious?

We can see that meimin emphasizes the most important feature of quantum mechanics, that is, the linear superposition principle and the normal evolution. Zheng evolution is related to time. If the concept of time is replaced, it may not be so basic. Therefore, the principle of linear superposition is the most basic.