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The universe cannot have existed for ever, otherwise it would have reached its equilibrium end state an infinite time ago. Conclusion: the universe did not always exist." [15] More recently though physicists have proposed various ideas for how the universe could have existed for an infinite time, such as eternal inflation.
Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true ...
The precise form of the Hartle–Hawking state is the path integral over all D-dimensional geometries that have the required induced metric on their boundary. According to the theory, time , as it is currently observed, diverged from a three-state dimension after the universe was in the age of the Planck time .
At the time the book was written, "superstring theory" had emerged as the most popular theory of quantum gravity, but this theory and related string theories were still incomplete and had yet to be proven in spite of significant effort (this remains the case as of 2021). String theory proposes that particles behave like one-dimensional "strings ...
On the Origin of Time is a 2023 book by physicist Thomas Hertog about the theories of Stephen Hawking. [1] Hertog is a Belgian cosmologist working at KU Leuven university, who worked extensively with Hawking. [2] He wrote the book at Hawking's request to popularize the top-down cosmological theory that they had developed together. [3]
Time Reborn: From the Crisis in Physics to the Future of the Universe is a 2013 book by the American theoretical physicist Lee Smolin.. Smolin argues for what he calls a revolutionary view that time is real, in contrast to existing scientific orthodoxy which holds that time is merely a "stubbornly persistent illusion" (Einstein's words). [1]
The book is divided into four parts and 15 chapters and has an appendix for the relevant math. Part one is entitled, "Time, Experience, and the Universe." Part two is named, "Time in Einstein’s Universe." Part three is called, "Entropy and Time’s Arrow." Part four is entitled, "From the Kitchen to the Multiverse." [6]
where t i is an initial time (τ i is the proper initial time), t f a final time (τ f is the proper final time), and H is the expansion parameter, also called the Hubble parameter. The BGV theorem states that for any spacetime where >, then the spacetime is geodesically past-incomplete.