This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Where Did the Universe Come Where Did the Universe Come From ? The traditional answers: “God created it” (Plato) or “It always existed” (Aristotle) are not acceptable for scientists. Not because scientists are not religious but because scientists want a more complete answer. An acceptable scientific answer: Although the Universe is not eternal it has neither a beginning nor an end. (Hawking and the Superstrings Theory) Another correct scientific answer is: The Universe started as a microscopic quantum fluctuation , possibly in a previously existing Universe. The possibility that the Universe eternally recreates itself does not necessarily resolve the problem of creation, but pushes it back to indefinite past. SelfReproducing Universes SelfReproducing Universes Andrei Linde introduced the selfreproducing Universes in his chaotic inflationary theory. His quantum fieldsbased theory introduced waves of quantum fluctuations which are stretched by an inflation process. Quantum “kicks” occurring every 1035 sec. can be accumulated and sometimes they can double in size. In some places these waves become stationary and lead to the formation of galaxies. But occasionally “eternal inflation” can occur, which leads to the formation of a “pocket Universe”. A multitude of types of Universes can form, each giving birth to others and although some Universes can crush themselves out of the existence, the cosmos would go on forever. In Linde’s theory various Universes can have different physics laws. They can probably be inherited from the previous Universe and mutations can happen. In our Universe these laws allow the creation of life, while in others their laws might not permit life. The Inflationary Multiverse The Inflationary Multiverse Where Did Matter Come From ? Where Did Matter Come From ? Virtual particles become real Particles from change of dimensions Quantum uncertainty principle allows for virtual pairs of particlesantiparticles. In the Inflationary Model quantum fluctuations add up in the same place and the particleantiparticle pairs become real. 1981 H.Pagels and D.Atkatz at Rockefeller U. propose that the Universe might have began with a sudden change in the dimensionality of space. They showed that a 10dimensional space could create particles during its transition to a 4dimensional space time (similar to the Higgs mechanism related to a change in symmetry). MassEnergy in the Universe MassEnergy in the Universe The accounting of massenergy deals with bodies and forces Bodies have positive massenergy Their gravitational attraction corresponds to negative massenergy The sum of all contributions to the mass energy of the Universe gives ZERO That is the reason why creating a new Universe is not difficult Hawking’s “Baby Universes” Hawking’s “Baby Universes” The selfreproducing Universes theory is complementary to Hawking’s “Baby Universes” model, associated with the study of black holes. Hawking proposed that the particles go through the black hole into a small selfcontained universe which branches out of ours. It can join later our region of spacetime and evaporate returning the particles. Although not good for space travel, these baby Universes can influence observations in our Universe. There might be an astronomical number of baby Universes and they might influence the value of Einstein’s cosmological constant. MTheory Cosmology MTheory Cosmology The picture for the Multiverse based on the MTheory (detailed discussion in the last lecture): Our Universe is a 4dimensional brane on a vibrating 5dimensional bubble. We see only a part of our Universe because of the bubble geometry. There are other Universes on other 5dimensional bubbles which can be very close to ours (fractions of a milimeter) Big Bangs are associated with collisions between these bubbles. No need for quantum fluctuations to justify them ! Are There Parallel Universes ? Are There Parallel Universes ? The work of Linde, Hawking and the Mtheory all point to possible parallel Universes, but where are they located ? A Stanford group in 1998 showed that a 5th dimension might be curled with a macroradius (about 1mm). They explained that gravity is weak at subatomic scale because it spreads in 5 dimensions. So far, experiments showed that Newton’s gravity theory is valid down to fractions of a mm. The simplest version of the MTheory based model assumes a 1030 cm gap between the 4dimensional parallel branes on 5dimensional bubbles. These branes interact only gravitationally and therefore we cannot see a “shadow” brane, but we can feel it gravitationally. This might explain some “missing mass” in the Universe. The Evolution of the Definition of The Evolution of the Definition of our Universe Greek philosophers: Earth, Sun, planets were the Universe 17th century: Sun at the center of our system and other stars Beginning of 20th century: Milky Way is our Universe and there are other “Universes” corresponding to other galaxies Today we speak about our Universe containing 1011 galaxies and we started studying the possibility of parallel Universes outside our 4 dimensional spacetime. Current pictures of the Universe see it as part of a Multiverse. The two current competing models are the Inflationary and the MTheory based “brane” model. Does God Really Play Dice ? Does God Really Play Dice ? Einstein’s famous comment “God does not play dice”. But the Universe is clearly indeterminist at micro level and current theories about the creation of the Universe talk about either about quantum fluctuations, or about the M Theorybased Multiverse. Our Universe becomes deterministic at macro level because at this level systems suffer external interactions (bombardment with cosmic particles). But without these particles the reality would be indeterminist. Even when we described the evolution of life through chemical and then biological processes (again) randomness was a key feature. ...
View Full Document
- Spring '10