The Early Universe: The Early Universe The Big Bang is the name given to our current understanding of the early universe. The essential feature of the theory is that the early universe was extremely hot and dense and that the expansion of space cooled it and allowed structures (protons, neutrons, nuclei, and atoms) to form. Time t = 0 to 10-35 seconds is not included in the theory because the temperatures and density during that time are beyond our current understanding of physics.


Slide2: The first step toward our understand of the early universe came with the discovery of Hubble’s Law and its interpretation as empirical evidence that space is expanding, consistent with Einstein’s general theory of relativity (a theory of gravity). From this, it was hypothesized that the universe must have had a beginning in time and that the early universe was extremely hot and dense. This hypothesis led to several predictions about the present universe that have turned out to be correct.


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Slide4: Edwin Hubble with his cat Nikolus Copernicus. (Colliers Magazine, 1949) Hubble’s Law: For distant galaxies, the redshift in their radiation (the amount by which the wavelength of the radiation is increased) is directly proportional to the distance to the galaxy. Published in 1929.


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Slide6: Einstein lecturing on the GTR in Pasadena, California, 1932. Einstein developed the general theory of relativity (GTR) in 1915. It predicted that space had to be either expanding or contracting. Einstein believed this to be incorrect and changed his theory.


Expansion of Space: Expansion of Space 1916 - Einstein’s general theory of relativity predicts that space must be either expanding or contracting. Einstein does not believe this and tries to 'fix' the theory. 1920s - Other astronomers and physicists show that all versions of the GTR require either the expansion or contraction of space. 1929 - Hubble’s Law. 1930 - Arthur Eddington explains Hubble’s Law as the expansion of space as described by the GTR. 1930 - Einstein calls his not accepting his original theory 'the greatest blunder of my scientific career.'


Expansion of Space: Expansion of Space Using Einstein’s GTR and the assumption that the universe is homogeneous and isotropic, we can calculate the relationship between the distance to an object and the redshift in its radiation. Without the cosmological constant, the rate of expansion must be slowing down due to the attractive force of gravity. Supernovae type 1a are standard candles. In 1998 two teams independently measured the apparent brightness (distance) to several very distant SN 1a and found that they were much more distant than theory predicted. Expansion of space must be accelerating! There is an anti-gravity force acting on the large-scale of the universe. This is called dark energy.


The Balloon Model of Expanding Space: Clusters of galaxies are represented by pieces of paper on the balloon. As the balloon is blown up its surface area (space) increases with time. The clusters of galaxies do not increase in size. They get further apart but do not move through space. The Balloon Model of Expanding Space


Slide10: 1920s - shows that GTR, even with the cosmological constant still requires that space either expand or contract. 1930s - reenters cosmology. First to develop a model based on GTR of what the universe would have been like in the past. Father of Big Bang. Most scientists are skeptical in part because LeMaitre is a priest and there are many similiarites between the Big Bang and Genesis. Abbe George LeMaitre


Slide11: George Gamow Gamow with Wolfgang Pauli 1948 - Gamow used new knowledge of nuclear physics along with the GTR to describe the early universe. He assumed (like LeMaitre) that the early universe was much hotter and denser than it is today and that the expansion of space cooled it and allowed structures to form. He intended to show how the hot, dense conditions of the early universe could produce all the chemical elements present in the universe today.


Predictions of the Big Bang model: Predictions of the Big Bang model The early universe contained only hydrogen and helium. Because of the expansion of space and its cooling effect, nucleosynthesis only occurred between 3 to 4 minutes after the big bang (A.B.B.) and essentially stopped after helium. The universe is filled with a background radiation whose temperature is a few degrees above absolute zero. When neutral atoms formed (about 500,000 yrs A.B.B.), the electromagnetic radiation essentially stopped interacting with matter. The expansion of space cooled the radiation from its initial value of about 3000 K to its present low value.


Slide13: Burbidge, Burbidge, Fowler, and Hoyle show that elements heavier than helium can be produced in the interiors of stars. The explosive deaths of these stars scatter the elements into the space between the stars and make them available for later generation stars (like our sun).


Slide14: Arno Penzias and Robert Wilson Bell Labs’ radio telescope. Early 1960s - Penzias and Wilson are hired by Bell Labs to evaluate the performance of the new radio telescope to be used in trans-Atlantic telephone communications. They find a small, unexplained signal regardless of the direction the telescope is pointed. It is not enough to be a problem, but they are curious. 1964 - They become aware that the noise in their telescope is the cosmic background radiation predicted by the Big Bang theory.


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2006 Nobel Prize in Physics: 2006 Nobel Prize in Physics John Mather was PI on the COBE project and also had primary responsibility for the experiment that revealed the blackbody form of the microwave background radiation. George Smoot had main responsibility for measuring the small variations in the temperature of the radiation.


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Time = 0, the Big Bang: Time = 0, the Big Bang The early Universe was extremely hot and dense. Space was expanding which cooled the contents of the Universe. Initially the temperature was so high that no structures could exist. As the Universe cooled, structures formed.


Formation of protons and neutrons: Formation of protons and neutrons At t = 10-6 sec ABB, the Universe was cool enough for quarks to combine to form protons and neutrons. Proton Neutron photons Electron


Formation of hydrogen and helium nuclei: Formation of hydrogen and helium nuclei At t = 3 to 4 minutes ABB, the universe was cool enough for protons and neutrons to stick together. Protons outnumber neutrons. Helium-4 nucleus, 6% Hydrogen-1 nucleus, 94% Electrons Photon


Formation of hydrogen and helium atoms: Formation of hydrogen and helium atoms At t = 300,000 years ABB, the universe was cool enough for electrons to stick to hydrogen and helium nuclei. Helium-4 atom, 6% Hydrogen-1 atom, 94% Photons


Formation of the cosmic background radiation: Formation of the cosmic background radiation When atoms formed, the Universe went from charged matter to neutral matter. This caused photons to decouple from matter. Those photons are still in the Universe today except that they have been cooled by the expansion of space. The temperature at the time of formation was 3000 K. Today it is 2.73 K.


Early History of the Universe: Early History of the Universe T = 0 - Big Bang beginning of a hot, dense universe in expanding space. Expansion cools the universe. T = 10-35 sec A.B.B., Temp = 1027 K - Inflationary period. Matter dominates antimatter. Temperature is too hot for any structure to exist. Elementary particles - leptons (electrons) and quarks in a sea of photons. T = 10-5 sec, Temp = 1012 K - Formation of protons and neutrons from quarks. T = 3 to 4 min, Temp = 109 K - Formation of helium nuclei from protons and neutrons. 94% protons (H nuclei) and 6% He nuclei. T = 300,000 yrs, Temp = 3000 K - Formation of atoms from electrons and nuclei. Universe becomes neutral and the background radiation is released.


Early History of the Universe: Early History of the Universe T = 0 - Big Bang beginning of a hot, dense universe in expanding space. Expansion cools the universe. T = 10-35 sec A.B.B., Temp = 1027 K - Inflationary period. Matter dominates antimatter. Temperature is too hot for any structure to exist. Elementary particles - leptons (electrons) and quarks in a sea of photons. T = 10-5 sec, Temp = 1012 K - Formation of protons and neutrons from quarks. T = 3 to 4 min, Temp = 109 K - Formation of helium nuclei from protons and neutrons. 94% protons (H nuclei) and 6% He nuclei. T = 500,000 yrs, Temp = 3000 K - Formation of atoms from electrons and nuclei. Universe becomes neutral and the background radiation is released.