1 The heavens declare the glory of God; the skies proclaim the work of his hands. Day after day they pour forth speech; night after night they display knowledge. There is no speech or language where their voice is not heard.” Psalm 19:1-3 NIV
“When I consider your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is man that you are mindful of him, the son of man that you care for him?” Psalm 8:3-4 NIV
“The Most Incomprehensible Thing About the Universe is that it is Comprehensible” Albert Einstein
COSMOLOGY Three Simple Questions.......... What is the nature of the Universe? What is its past? What is its future?
As long as men have been looking up to the skies at night and observing the panorama of the heavens, some men have been wondering about the origin and nature of the universe.
COSMOLOGY .......the study of the origin, structure, and evolution of the Universe
1914 Vesto Slipher was studying rotation of the Andromeda Nebula using the Doppler Effect could not observe any rotation did observe a large Doppler Shift corresponding to a “blueshift equiv. to 700,000 mph Observed a total of 12 “nebulae” or “fuzzy clouds” found all except Andromeda exhibited redshifts many receding from the earth at very high speeds • Modern Cosmology began in the early 1900’s
Edwin Hubble was grad student in audience and became interested in the project Hubble was a ex-lawyer turned astronomer By 1925 Slipher had measured 40 nebulae and found redshifts much more common than blueshifts At that time it was not known exactly what the “fuzzy” objects like Andromeda were local objects...in our galaxy? extra-galactic objects...outside our galaxy? • Slipher reported on work at American Astronomical Society meeting
General Relativity 1915 Albert Einstein introduced the ideas of General relativity accelerations in space-time cannot be distinguished from gravitation attraction gravitational forces are explainable as a curvature of space-time due to presence of mass
bending of light by strong gravitational fields movement of perihelion point of Mercury gravitational redshift of spectral lines Einstein’s GR made 3 testable predictions • All 3 have been experimentally confirmed • first 2 by early 1920’s
his solutions were unstable and dynamic, i.e. they implied that the universe is changing Einstein believe the universe was static added a “fudge-factor” to his equations to make the answer static • Einstein used General relativity to solve for the structure of space-time for the universe
Friedmann showed there were 3 stable solns and all were dynamic each different soln was characterized by a unique curvature of space spherically curved hyperbolically curved flat 1922 Russian mathematician Alexander Friedmann disc. error in Einstein’s calcs. (he had divided by zero at one point)
1917 Edwin Hubble began work at Palomar observatory and with help of Milton Humason (acknowledged as the best observational astronomer in the world - and totally self-taught!) expanded Slipher’s measurements and began to try to interprete their meaning
The nature of Slipher’s “fuzzy objects” or nebulae was being vigorously debated by astronomers…… were they galactic or extra-galactic? • 1920 Curtis-Shapley debate at the National Academy of Sciences over the nature of Nebulae...(inconclusive!)
At first even Hubble could not accept what an application of Henrietta Leavitt’s period luminosity relation for Cepheids implied.... a distance MUCH larger than any distance estimated for other “nebulous” objects • Using Palomar telescope, Hubble & Humason were able to resolve individual Cepheid Variables in Andromeda Nebula
Cepheid Variables in the Andromeda Galaxy......... identified by red arrows
Cepheid Variables are very large and bright stars with variable light output (due to pulsations in size). They are identifiable by their characteristic light curve.
Knowing the period gives one a measure of the star’s luminosity (actual total energy output of the star) and comparing this with its perceived brightness (from Earth), one can use the inverse square law and estimate the distance to the object.
Hubble soon discovered several Cepheid variables all implying the same result... Using the Period-Luminosity relation for Cepheids, they determined that the nebula was at least 2.2 million light years away and therefore EXTRAGALACTIC! This showed that many of the “fuzzy” nebulae were actually galaxies like our own
All of the distant galaxies in all directions were receding from the earth the velocity of recession was directly proportional to the distance of the galaxy • Hubble-Humason examined several dozen galaxies within 7 Million light years in which Cepheids could be resolved, and made an Astonishing discovery!
Redshift Data for 5 Representative Galaxies at increasingly larger distances
Hubble’s work was experimental confirmation of the theoretical predictions of General Relativity the universe was expanding the expansion was isotropic (same in all directions) • This is known as the Cosmological Red Shift • it is space-time itself that expands and NOT the objects in it
Expanding Cake Analogy Just as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies recede from each other as the universe expands.
Big-Bang Once Hubble’s Law was established simple matter to run the expansion backwards and conclude that all galaxies were originally at same point in space-time in fact all matter! the universe itself!, and space and time originated at this point point in space-time at which the universe began is known as the Big-Bang
Age of Universe Since Hubble’s Law can be written velocity of recession = (constant) x distance the constant is Hubble’s Constant H0 i.e. v = (H0 )(d) Running the expansion backwards H0 = velocity/distance 1/H0 = distance/velocity = time the “time” since the expansion began, i.e. the age of the universe
Using a value of H0 of 75 km/sec per megaparces or about 24 km/sec per million light years gives a time of about 13 x 109 or 13 billion years • The actual value of Hubble’s Constant has been a subject to intense debate with values as high as 100 km/sec/Mpc and as low as 50 km/sec/Mpc advocated. • this gives age of universe between about 9 to 17 billion years
Most of the very latest data presented within the last year or so has indicated that a value of 65 - 75 km/sec/Mpc, with a avlue close to 70 being favored. This gives a Hubble Age of about 13 Billion years.
Observable Universe As the universe expands, looking out in distance is thus equivalent to looking back in time a telescope is a sort of ‘time machine’ The observable limit of the universe is the distance that light could have traveled since the beginning of the universe for value of 75 km/sec/Mpc this is 13 Bly
Many astronomers did not accept the idea of a dynamic, expanding universe objections were primarily philosophical Big-bang implies an origin an eternal universe was desirable Plausible alternative was the Steady-State universe Objections to the Big-Bang Universe
Steady-State theory • Fred Hoyle (originator of the term big-bang!), Thomas Gold, and Hermann Bondi • could explain expansion and keep an eternal universe with no origin by allowing matter to be created at a rate to keep density of universe constant • This required violating the Law of Conservation of Energy
Steady State Universe Steady State Universe Enough matter appears to keep average density constant
Violation of conservation of energy would be small - less than 1 hydrogen atom per cubic meter per 50 million years • Much too small to observe!
Cosmic Microwave Background 1946 Physicists Ralph Alpher and George Gamov worked on the creation of elements in a big-bang (nucleosynthesis) disc. there should be a very cool residual radiation left over from the Big-Bang this diffuse radiation should be a blackbody radiation at about 5 K
The energy radiated by a Blackbody takes a special form when the relative brightness (or strength) of the radiation is graphed as a function of the wavelength
Calibrating antenna to eliminate noise With antenna set at 7.35 cm (4080 MHz) far from any galactic radio emissions kept getting peculiar static const regardless of time of day, season of year, direction in the sky 1964-65 Bell Labs scientists Arno Penzias & Robert Wilson were working on a microwave horn antenna for satellite communication
recalibrated antenna cooled their detectors removed nesting pigeons from horn cleaned antenna could not eliminate the static “Noise” in their Antenna
Realized they were seeing this residual radiation remnant from the Big-Bang Cosmic Microwave Background Radiation If a blackbody curve is assumed 7.35 cm corresponds to 3.5 Kelvin 1976 Penzias & Wilson received a Nobel Prize Contacted a group at Princeton University who were working on a design for a system to detect the residual radiation