![]() “Stephen himself said that this work was the area he was most proud of,” said Malcolm Perry, a colleague of Hawking’s at Cambridge University. In string theory, reality is described through the interactions of one-dimensional objects known as cosmic strings. The new theory takes work that Hawking and the US physicist James Hartle published in the 1980s and updates it with the more powerful, modern mathematical techniques used in string theory. It gives us hope that we can arrive at a fully predictive framework of cosmology.” Stephen would say that, theoretically, it’s almost like the universe had to be like this. “It reduces the multiverse down to a more manageable set of universes which all look alike. ![]() “This paper takes one step towards explaining that mysterious fine tuning,” Hertog added. “The mystery was why do we live in this special universe where everything is nicely balanced in order for complexity and life to emerge?” “In the old theory there were all sorts of universes: some were empty, others were full of matter, some expanded too fast, others were too short-lived. While the consequences of the proposal may not be obvious, the theory may provide some comfort to physicists who wonder how, given all the hostile variations thought possible, we find ourselves in a universe well-suited to life. Instead of space being filled with pocket universes where radically different laws of physics apply, these alternate universes may not actually vary that much from one another. “The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes separated by an inflating ocean,” Hawking said last autumn.īut in the latest work, Hawking and Hertog challenge that view. This bound would become significantly lower if the probability of intersection is less than 85%.03:09 Cosmology's brightest star Stephen Hawking dies aged 76 – video (G is Newton’s constant.) This is slightly smaller than the values (≳2× 10 − 6) predicted for the cosmic-string theory of galaxy formation. By assuming that the probability of self-intersection is less than 85%, as the comparison with the results of Albrecht and Turok indicates, an upper bound on the string tension is obtained: Gμ < 10 − 6. If the string tension μ is too large, then the gravitational radiation will be so copious that it interferes with primordial nucleosynthesis. A comparison with the numerical simulations of Albrecht and Turok indicates that the probability of self-intersection is indeed large enough to allow the energy density in strings to stabilize at a small fraction of the radiation density, but there is a potential problem with the gravitational radiation that is produced by the strings. The strings can be prevented from dominating the energy density of the Universe only if there is a large probability (≳50%) that a closed loop will intersect itself and break up into smaller loops. It is shown that, in a radiation-dominated universe, the fate of the string system depends sensitively on the fate of the closed loops that are produced by the interactions of very long strings. ![]() ![]() The evolution of a system of cosmic strings is studied using an extended version of an analytic formalism introduced by Kibble.
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