Pang Xuelin chatted with Catherine Murphy all afternoon.

This woman is worthy of being a senior reporter for Time magazine, and she is very good at controlling the rhythm of chatting.

From mathematics to life, from life to career, it was not until half past four in the afternoon that the interview, which lasted more than three hours, ended.

Subsequently, Pang Xuelin cooperated with the photographer of Time Magazine to pose for more than half an hour to complete the pose.

"Mr. Pang, thank you very much for your cooperation today, can I have the honor to treat you to a meal in the evening?"

Murphy got up and shook Pang Xuelin's hand, scratched his little fingertips on Pang Xuelin's palm without a trace, and looked at Pang Xuelin with a smile.

Pang Xuelin quietly withdrew his hand, and was about to say no, when Edward Witten hurriedly walked in at the door of the café.

"Mr. Pang, I'm sorry I didn't bother you, right?"

Edward Witten looked eager.

"Professor Witten, it's okay, I just finished the interview, what's wrong?"

Pang Xuelin wondered.

Witten said: "About Ponzi geometry, I want to talk to you, I don't know if it's convenient for you now?" ”

Pang Xuelin shrugged his shoulders at Catherine Murphy and said with an apologetic smile, "Ms. Murphy, it's a pity that I can't have dinner with you in the evening." ”

Murphy raised his eyebrows, brushed and wrote down a string of numbers in his notebook, tore off the page and handed it to Pang Xuelin, and said with a smile: "This is my mobile phone number, I will stay at Princeton for a few days, if you have time, welcome to me!" ”

With that, Murphy picked up the recorder and backpack, winked at Pang Xuelin, and said to Edward Witten: "Professor Witten, I won't disturb you and Teacher Pang. ”

This woman......

Pang Xuelin shook his head and smiled, and said to Witten: "Professor Witten, do you have anything to do with me?" ”

Edward Witten looked around and said, "Mr. Pang, let's find a quiet place to talk." ”

Pang Xuelin said: "Okay, go to my room!" ”

Coming to the executive suite where Pang Xuelin lived, the two sat down in the office area.

Geng Huan brought a cup of coffee to each of them, and then quietly exited the room.

Witten took out a stack of manuscript paper full of formulas from the small bag he carried with him, and said, "Mr. Pang, do you know the superstring theory?" ”

Pang Xuelin was slightly stunned, and his eyes narrowed slightly.

The most important reason why Edward Witten has such a famous name in the field of theoretical physics is that in 1995, he proposed the M theory on the basis of superstring theory, which unified the five superstring theories and the supergravitational theory of 11-dimensional space into a single mathematical structure.

This work set off the second superstring revolution, and in later generations, M theory was considered the ultimate theory with the most promising solution to the essential interaction between matter and energy.

But at this time, Edward Witten should not have completed the research work on M theory, could his own Ponzi geometry give him any inspiration?

Pang Xuelin said: "I probably know that in physics, one of the basic problems to be solved is how to realize the quantization of gravity and unify gravity with the other three basic interactions in nature (electromagnetic force, strong interaction, weak interaction), and superstring theory is the only theory that can achieve the above requirements." ”

Witten was a little surprised: "Great, Pang, I think you also know that although superstring theory seems to be able to describe the ultimate unity between the interactions of nature, there are also several problems. First, there are five self-consistent perturbation string theories in the sense of quantum mechanics in physics, which are two IIA and IIB, a hybrid string theory with a gauge of Apin(32)/Z2, a hybrid string theory with a gauge group of E8×E8, and a type I string theory with a gauge of SO(32). They are physically equivalent, and we cannot theoretically choose one of them to exclude the existence of the other four superstring theories. ”

"Second, the self-consistency of the five perturbation strings all requires ten-dimensional space-time and space-time supersymmetry, and their natural standard energy is 10^19 GeV, and it is impossible for us to build such a high-energy accelerator for direct testing of string theory in the foreseeable future. Therefore, the minimum test requirement is that some kind of perturbation string theory can give observable physics in four-dimensional space-time, such as the Standard Model of particle physics......"

"The third question, for an ultimate theory that describes all the physical laws of nature, the quantities should be determined by the dynamics of the theory, except for some possible fundamental constants such as the speed of light, Planck's constant, chord tension, and possible initial values or boundary conditions. In particular, the vacuum state of the theory should be determined by its kinetics. ”

"But perturbation string theory assumes from the outset that space-time is flat, and requires that string interactions be minimal in order for string perturbation to be effective. These assumptions are contrary to the ultimate theoretical requirements. Therefore, the five existing perturbation string theories are all limit theories and are unlikely to be the ultimate theories. ”

"Fourth, from the perspective of perturbation string theory, the eleven-dimensional supergravitational theory seems to have nothing to do with describing the real world, and we know that the low-energy limit of the five perturbative string theories gives the corresponding supergravitational theory, while the lower-dimensional supergravitational theory corresponds to the compacted superstring low-energy theory. If perturbation string theory is really the ultimate theory, then we cannot explain the existence of 11-dimensional supergravitons. ”

But if we look at the one-dimensional spatial dimension of the eleven-dimensional space-time as a very small circle, then the eleven-dimensional supergravity gives one of the low-energy valid theories of superstrings. The radius of this small circle is proportional to the strength of the interaction of this string theory. From this we can see that the eleven-dimensional supergravity should be related to the low-energy theory of the non-perturbation theory of such strings. In other words, we can only explain the eleven-dimensional supergravity if we understand the non-perturbative nature of string theory. ”

Pang Xuelin said with interest: "Professor Witten, what do you mean ......?" ”

Edward Witten's eyes sparkled, and he said: "I have been seeking a completely new theory for several years, unifying the five superstring theories and the eleven-dimensional supergravitational theory, but I have never been able to find the right mathematical tools to describe it, but through the study of Ponzi geometry in the past two days, I vaguely feel the dawn of a new theory." But my research on Ponzi geometry is still quite superficial, and I need your help, or maybe we can work together to find a new ultimate theory, what do you think? ”

Pang Xuelin looked at Edward Witten's eyes, pondered for a moment, stretched out his hand and smiled: "Happy cooperation!" ”