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+ | {{indexmenu_n>10}} | ||
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+ | ~~NOTOC~~ | ||
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====== Open Problems ====== | ====== Open Problems ====== | ||
- | <nspages open_problems -h1 -textPages=""> | + | <WRAP group> |
+ | <WRAP half column> | ||
+ | Our present understanding of nature is far from complete. | ||
+ | |||
+ | Real problems are things related to **unexplained observed phenomena**, like dark matter or dark energy. | ||
+ | |||
+ | In addition, there are things that we can describe but do not understand. These are not really problems but rather **[[http://jakobschwichtenberg.com/problems-vs-puzzles/|puzzles]]**. Examples are the [[open_problems:flavour_puzzle|still not understood masses and mixing angles]] of the elementary particles or also the [[open_problems:hierarchy_puzzle|hierarchy puzzle]] and the question why strong interactions [[open_problems:strong_cp_puzzle|do not violate]] [[advanced_notions:cp_symmetry|CP symmetry]]. | ||
+ | |||
+ | |||
+ | </WRAP> | ||
+ | <WRAP half column><nspages open_problems -h1 -textPages=""></WRAP> | ||
+ | </WRAP> | ||
+ | |||
+ | ---- | ||
+ | |||
+ | **The 5 Great Problems** | ||
+ | |||
+ | - __The problem of quantum gravity.__ This is the problem of combining general relativity and quantum theory into one theory. Such a theory would be able to describe all known interactions of nature. | ||
+ | - __The problem of quantum theories.__ This is the problem of understanding quantum such that it makes sense and solve its fundamental problems. | ||
+ | - __The unification of the particles and forces.__ Still no theory exists that unifies all known particles and interactions into a single fundamental entity. | ||
+ | - __Explain the constants of nature.__ The standard model of particle physics has 20+ free parameters that need to be inferred from experiments. It is an open problem to understand how these values are "chosen" by nature. | ||
+ | - __Explain dark matter and dark energy.__ If they really exists, as suggested by experiments, we need to understand what they consists of. In addition, the constants of the standard model of cosmology need the be explained. | ||
+ | |||
+ | For more information, see the chapter "The Five Great Problems in Theoretical Physics" in the book "Time Reborn" by Lee Smolin. | ||
+ | |||
+ | ===== Lists of Open Problems ===== | ||
+ | |||
+ | |||
+ | * [[https://arxiv.org/abs/1804.08730|Life, the universe, and everything - 42 fundamental questions]] by Roland E. Allen, Suzy Lidström | ||
+ | * http://math.ucr.edu/home/baez/physics/General/open_questions.html | ||
+ | * https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics | ||
+ | * Chiral Fermions, see https://arxiv.org/pdf/hep-th/0102028.pdf | ||
+ | |||
+ | ---- | ||
+ | |||
+ | ===== Quotes ===== | ||
+ | |||
+ | |||
+ | <blockquote>The laws of physics seem to be composed out of five | ||
+ | fundamental ingredients: | ||
+ | |||
+ | * 1 Identical particles. | ||
+ | * 2 Gauge interactions. | ||
+ | * 3 Fermi statistics. | ||
+ | * 4 Chiral fermions. | ||
+ | * 5 Gravity. | ||
+ | |||
+ | The question is whether one can find a “deeper structure” | ||
+ | that gives rise to all five of these phenomena. In | ||
+ | addition to being consistent with our current understanding | ||
+ | of the universe, such a structure would be quite | ||
+ | appealing from a theoretical point of view: it would | ||
+ | unify and explain the origin of these seemingly mysterious | ||
+ | and disconnected phenomena. | ||
+ | The U(/1)xSU(2)xSU(3) Standard Model fails to | ||
+ | provide such a complete story for even the first four | ||
+ | phenomena. Although it describes identical particles, | ||
+ | gauge interactions, Fermi statistics, and chiral fermions | ||
+ | in a single theory, each of these components are introduced | ||
+ | independently and by hand. For example, field | ||
+ | theory is introduced to explain identical particles, vector | ||
+ | gauge fields are introduced to describe gauge interactions | ||
+ | Yang and Mills, 1954, and anticommuting fields | ||
+ | are introduced to explain Fermi statistics. One | ||
+ | wonders—where do these mysterious gauge symmetries | ||
+ | and anticommuting fields come from? Why does nature | ||
+ | choose such peculiar things as fermions and gauge | ||
+ | bosons to describe itself? | ||
+ | |||
+ | <cite>Colloquium: Photons and electrons as emergent phenomena Michael Levin and Xiao-Gang Wen https://journals.aps.org/rmp/pdf/10.1103/RevModPhys.77.871</cite></blockquote> | ||
+ | |||
+ | ---- | ||