From: mk_thisisit
String theory is a concept that has intrigued many physicists, though it has also faced significant challenges and criticisms, leading some, including the speaker, to abandon it as a path to a grand unified theory [00:19:09].
Initial Appeal and Mathematical Elegance
Initially, the speaker found the idea of string_theory appealing when he first heard about it from Leonard Suskind [00:20:21] [00:22:27]. The core concept involved replacing lines in Feynman diagrams with “little tubes” or “strings” [00:22:32] [00:22:38].
The Problem of Infinities in Quantum Field Theory
In quantum field theory, calculations performed using Feynman diagrams often lead to infinite solutions, particularly with diagrams that include loops [00:21:11] [00:21:20]. These infinities make the solutions technically “useless” [00:21:44]. Physicists employ “tricks,” such as renormalization, to work around these infinities and obtain good solutions [00:21:51] [00:22:02]. The speaker, however, felt uncomfortable with these tricks, preferring to understand why answers were correct rather than relying on methods he didn’t fully believe in [00:22:15] [00:22:21].
String Theory’s Proposed Solution
string_theory offered an elegant solution by replacing point-like particles (represented by lines in Feynman diagrams) with strings forming “little tubes” [00:22:32] [00:22:58]. These tubes, being smooth and without sharp edges, theoretically resolve the infinities in calculations, making the model “beautiful” and mathematically complete [00:23:03] [00:23:06].
Challenges and Criticisms
Despite its initial appeal, the speaker eventually became a strong critic of string_theory.
The Dimension Problem
A major challenge for string_theory arose with the realization that it “doesn’t work unless space-time has 26 dimensions” [00:23:21]. This was part of what was called the “first string revolution” [00:23:36]. Later, attempts were made to get a “better version” with only 10 or 11 dimensions [00:23:48] [00:23:51]. However, the speaker found this combination of dimensions (10, 11, and 26) to be a “mess” [00:24:01]. The idea of introducing these extra dimensions as “little loops” or “knots” in spacetime also did not work for him [00:24:10] [00:24:17]. M-theory, for instance, involves 11 dimensions [00:25:52].
Lack of Physical Contribution
The speaker contends that string theory has not contributed meaningfully to understanding fundamental physics, despite its mathematical interest [00:19:40] [00:20:00]. He believes it is a “dead end” for the path towards a grand unified theory [00:26:44].
”Fashion, Faith, and Fantasy in the New Physics of the Universe”
He wrote a book titled “Fashion, Faith, and Fantasy in the New Physics of the Universe,” suggesting the title himself, with string_theory being categorized as a “fashion” in physics [00:24:36] [00:24:52] [00:25:00]. He emphasizes the danger of prioritizing mathematical beauty over physical correctness: “just because you have a theory that says and I think it’s a very beautiful theory doesn’t mean it’s physics” [00:25:32] [00:25:37]. He even questions its mathematical beauty, finding it “clumsy in many ways” and a “mix of dimensions” [00:25:47] [00:25:50].
Grand Unified Theory
The ultimate goal of a grand unified theory is to unify all fundamental forces: electromagnetism, weak interactions, strong interactions, and gravity (general relativity) [00:26:50] [00:27:41]. While string_theory claims to achieve this, the speaker asserts that it is not the correct path [00:26:44] [00:27:36].
Alternative Perspective: Twistor Theory
In contrast to string_theory, the speaker developed twistor_theory, which attempts to combine relativity and quantum mechanics in a different way, without changing the number of dimensions (sticking to three spatial dimensions and one time dimension) [00:36:32] [00:36:43]. Instead of points, it considers light rays as fundamental elements [00:37:43] [00:37:46]. He believes twistor theory has the potential to revolutionize physics [00:37:59].