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Unformatted text preview: Recap the Fate of our Universe Recap the Fate of our Universe Describe how various models of the Universe appear on the Hubble diagram. What is the current favored model ? What is dark matter ? What is dark energy and how do you explain it ? What is Einstein’s cosmological constant and what is its variation with time ? Big Bang and Inflation Model Big Bang and Inflation Model The homogeneity problem: according to WMAP after 1 second the Universe was a few lightyears across. Explained by the inflation theory which corresponds to doubling in size 100,000 times in 1030 seconds ! The inhomogeneity problem: how did the variations in density (which lead to galaxies and clusters) appear ? Explained by the decay of the inflationary energy into radiation with various rates in various places. WMAP confirms it. Einstein’s general relativity cannot explain the moment of creation and new theories were needed. Linde’s chaotic inflationary theory is a solution. We call it (shortly) the Inflation Model. In addition one needs the dark energy mechanism to explain the current accelerated expansion Superstring Cosmology Superstring Cosmology The Superstrings theory has gravity included and therefore can be useful in cosmology: KikkawaYamasaki showed that a contraction of the Universe to the world of superstrings would bounce it back BrandenbergerVafa showed how superstring antisuperstring annihilations can lead to some of dimensions to expand while others stay wrapped together Veneziano Gasperini showed how quantum fluctuations in the supertstrings theory leads to the formation of new Universes M Theory Cosmology M Theory Cosmology M Theory offers a new look at our Universe – a “brane” member of the Multiverse A 5th macrodimension separates various Universes, which are 4 dimensional “surfaces” on 5 dimensional bubbles. In the Cyclic Model developed by Steinhardt and Turok the Big Bang is triggered by the decay of the dark energy and the process is repeated for ever. Stage 1 in the Cyclic Model Stage 1 in the Cyclic Model Big Bang does not require infinite temperature and density. Before the bang space is flattened and filled with a smooth distribution resulting from the decay of the dark energy. Interbrane gravitational force draws branes together amplifying quantum wrinkles. Branes engage in a cycle of collision, rebound, streching, collision etc. Stage 2 – Radiationdominated stage Stage 2 – Radiationdominated stage A microsecond after the bangs the branes reach maximum separation but continue to strech rapidly. At this stage the branes are filled primarily with radiation. The radiation converts into pairs of particles and antiparticles but they decay quickly into radiation. Stage 3 – Matterdominated Stage 3 – Matterdominated stage About 75,000 years after the bangs as the branes cool off radiation and ponderal matter (particles) separate. The first atoms form 380,000 years after the bangs. The branes becomes transparent Stage 4 – Dark energy dominated Stage 4 – Dark energy dominated After about 56 billion years the dark energy becomes dominant. Galaxies, stars, dust, molecules and atoms thins out and the brane approaches an empty, uniform state with few traces of the previous stage Our brane has been for about 89 billion years in this stage, which will continue for 1 trillion years. Stage 5 – the Contraction Epoch Stage 5 – the Contraction Epoch A key assumption in the cyclic model is that dark energy can decay slowly and smoothly. At some stage of this decay the expansion of the brane stops and it is replaced with a brane contraction. Stage 6 – Big Crunch stage Stage 6 – Big Crunch stage The brane contraction leads to some of the highpressure form of the dark energy to suddenly convert into hot matter and radiation. The brane remains smooth and flat. Like in the inflationary model, inhomogeneities are result of quantum fluctuations. Like the inflationary model, the cyclic model agrees with WMAP. Cyclic vs Inflationary Model Cyclic vs Inflationary Model The Inflationary Model of the Multiverse deals with time by saying that an infinite number of Universes were and continue to be formed all the time. Our Universe will expand for ever. The Cyclic Model also assumes an infinite number of Universes but the life of our Universe is cyclic. The Inflationary Model uses both the inflationary energy and the dark energy, while the Cyclic Model uses only the dark energy. The Cyclic Model can describe the evolution of our Universe through the Big Bang, while the Inflationary Model creates a new spacetime through each Big Bang. These two cosmological models complement each other. The question is which describes best our own Universe ? At this stage of experiments both models are able to explain WMAP measurements. Future Experiments Future Experiments Both Inflationary and Cyclic models explain the WMAP data. A new experiment is the European “Planck” satellite experiment in 2009, which will obtain a much higher resolution than WMAP. More challenging is the direct observation of the gravitational in the Universe. Indirect observations were related to pairs of pulsars (TaylorHulse 1993). First direct observations will come from the Laser Interferometer Gravitationalwave Observatory (LIGO), which uses the interference of two 4 km long laser beams. Local interference is avoided by synchronizing two experiments in distant areas. Next the Laser Interferometer Space Antenna (LISA) will consist of a triangle of lasers mounted on spacecrafts. In more than 20 years scientists hope to launch the Big Bang Observer (BBO) which will observe directly the background gravitational waves of the Universe. Modern Cosmology Modern Cosmology Einstein’s general relativity offered the first scientific approach to cosmology, but it did not offer an answer to the creation question. Quantum Cosmology uses the Feynman’s “alternative histories” explanation of quantum phenomena (for ex. the doubleslit experiment) The M Theory describes an almost infinite (10500) number of Parallel Universes (the Multiverse) distinguished from each other by the way in which the 7 microdimensions are curled up. These Universes have different apparent laws. The Topdown Approach (I) The Topdown Approach (I) In the bottomup approach to cosmology the Universe evolves in time on the basis of the a set of laws In the topdown approach the probability that a Universe is in a certain state is arrived at by adding up the contributions from all possible histories related to what is being measured. The Topdown Approach (II) The Topdown Approach (II) M Theory does not explain why our Universe has the properties that it has. It will only explain those properties in terms contribution probabilities from other parallel Universes. M Theory does not explain why we see only 4 macro dimensions M Theory does not explain why we observe the standard model of particles and forces, the mass and charge of an electron etc. The Weak Anthropic Principle The Weak Anthropic Principle The “weak” anthropic principle refers to the rules that select the environment which allows life: A single star system. Little planetary orbit eccentricity (2% for Earth). Age of the Universe at least 10 billion years to create the Carbon needed for life (longer for silicon but there are chemical reasons against siliconbased life). Protection from large asteroids to create a “quiet” place in which the natural selection allowed for the evolution of over 1 billion species. The Strong Anthropic Principle The Strong Anthropic Principle The “strong” anthropic principle relates to the constraints on the laws of nature The need to have the electron charge exactly equal to that of the proton The strength of fundamental forces must be such that carbon can be formed. Recent calculations show that 0.5% change in the strength of the color force, or 4% change in the strength of the electromagnetic force would destroy all carbon and all oxygen nuclei. The Grand Design The Grand Design Both anthropic principles state that our habitat is one of the many possible cosmological situations. There is nothing special about our planetary system or about our Universe (other that we exist in it). Many planetary systems and many Universes can be similar. Darwin explained the existence of various forms of life. The M Theory explains the existence of a huge number of Universes with different sets of laws. There is no purpose in the evolution of life forms or Universes. Exactly as Darwin’s selection laws explained the evolution of the Earth life species, M Theory – based models should explain the evolution of Parallel Universes. ...
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This note was uploaded on 05/03/2011 for the course NATS 1740 taught by Professor Hall during the Spring '10 term at York University.
- Spring '10