Core Points - The article discusses the concept of dimensional reduction in physics, illustrating how theories evolve from higher dimensions to lower dimensions, ultimately affecting human understanding of the universe [1][2][3] Group 1: Dimensional Reduction Theories - The first layer is M-theory, which operates in 11 dimensions and reduces to string theory through various projections [4] - The second layer is string theory, which exists in 10 dimensions and includes 3D space, 1D time, and 6D Calabi-Yau manifolds, influencing the types of fundamental particles and physical constants in the universe [5][6] - The third layer is General Relativity, which reduces from string theory in low-energy limits and connects to the concept of gravitons [9] Group 2: Further Reductions - General Relativity can further reduce to Special Relativity under conditions of flat spacetime and no gravity [10] - Special Relativity reduces to Newtonian mechanics when objects are moving at speeds much lower than the speed of light [11] - Newtonian mechanics is described in a 3+1 dimensional framework, emphasizing the complexity of truly understanding it [12] Group 3: Quantum Field Theory - Quantum Field Theory, considered a fourth layer, is composed of Quantum Yang-Mills theory, Higgs mechanism, and fermionic field theory [14] - Under certain conditions, Quantum Field Theory can reduce to Quantum Electrodynamics [15] - Quantum Electrodynamics can further reduce to Maxwell's equations in low-energy and non-relativistic limits [16][17] Group 4: Historical Context and Challenges - The article highlights the historical significance of Yang-Mills theory and its revival after being initially dismissed, showcasing the complexity of applying classical theories to quantum contexts [18][19] - It also discusses the contributions of mathematicians like Hilbert and their impact on the development of theories in physics, contrasting them with physicists like Einstein [20][21]

Group 1 - The concept of parallel universes is not merely a creation of science fiction but is derived from scientific observations and theories [1] - There are various theories regarding parallel universes, some of which are simpler to understand while others are more complex, particularly those related to string theory [3][32] - The observable universe is limited to a sphere with a radius of approximately 41 billion light-years due to the finite speed of light and the expansion of the universe [5][12] Group 2 - The concept of the observable universe suggests that regions beyond our observable limits are completely independent and cannot be influenced by us [7][11] - The universe's expansion has been accelerating since about 7 billion years ago, which means that some galaxies currently within our observable universe may eventually move beyond our reach [12] - If the universe is infinite, there could be countless parallel universes with identical arrangements of particles, leading to the existence of duplicates of ourselves in different scenarios [14][16] Group 3 - The inflationary universe theory addresses the uniformity of cosmic microwave background radiation by proposing a rapid expansion of the universe shortly after the Big Bang [18][22] - This rapid inflation occurred approximately 10^-36 seconds after the Big Bang and expanded the universe by a factor of 10^26 [22] - The concept of eternal inflation suggests that while our local universe may have stopped inflating, the overall universe continues to expand indefinitely, creating numerous "pocket" universes [26][31] Group 4 - String theory introduces the idea of multiple dimensions and membranes, suggesting that our universe exists on a three-dimensional membrane among many others [32] - Quantum parallel universe theory posits that when a quantum event occurs, the universe splits into multiple branches, each representing different outcomes [57][61] - The double-slit experiment illustrates the wave-particle duality of electrons, leading to the conclusion that they can exist in multiple states simultaneously until observed [40][49]