The Big Bang Theory: Origin & Evolution of the Universe

Newton’s Static Universe Universe is static and composed of an infinite number of stars that are scattered randomly throughout an infinite space. Universe is infinitely old and will exist forever without any major changes. Time and Space are steady and independent of one another and any objects in existence within them.

Newton’s Error If universe is as how Newton describes, then why is the sky dark at night?

Olber’s Paradox If space goes on forever with stars scattered randomly throughout, then in any line of sight in any direction will eventually run into a star. Using this logic, the sky should be the average brightness of all of these stars; the sky should be as bright as the sun, even at night.

But isn’t the sky dark at night…? Yes, of course - that is what we observe now and have always observed. Something is wrong with Newton’s idea of a static, infinite universe.

Einstein’s Relativity Einstein overturned part of Newton’s theory with his theories of special and general relativity - time and space were indeed related, as were the objects existing within them.

Special Relativity Time and Space and their rates are intertwined and depend on the motion of the observer (1905).

General Relativity Gravity bends the fabric of space time - the matter that occupies the universe influences the overall shape of space and the rate of time (1916).

Implications of Einstein’s Ideas Based on the general relativity equations, the structure of universe is either always expanding, always contracting, or always static. To agree with the ideas of the time (Newton’s), Einstein added a “cosmological constant” which yielded a static universe.

Cosmological Constant Represents the pressure that allows the universe’s expansion to directly balance gravitational collapse due to the objects existing within the universe, thus yielding a static universe. Without this idea of a “cosmological constant”, Einstein could’ve been the first to predict that the universe is not static.

Hubble’s Discovery Edwin Hubble’s observations of remote galaxies, and the redshift of their spectral lines (1924). Hubble noticed that the further away the galaxy, the greater the redshift of its spectral lines. This linear relationship is called Hubble’s Law.

Redshift The wavelengths of the light emitted by distant objects is elongated as it travels to earth. Longer the light travels, the more it gets redshifted.

Hubble’s Law v = H 0 d v = recessional velocity of the galaxy H 0 = Hubble constant D = distance of galaxy to earth Galaxies are getting farther apart as time progresses, therefore the universe is expanding.

Hubble’s Constant Expansion rate measured using Type 1A Supernovae. The age of the universe can be derived from Hubble’s constant: T 0 = d →  T 0 = 1 H 0 d H 0 For example, if H 0 = 73 km/s*Mpc, then T 0 = 13.4 Billion years old

Age of Universe Currently, after taking into account differences in expansion rate over time and our movement through space: T 0 ~ ± 0.2 byo Age of stars: ~13.4 byo ± 6% Therefore, oldest stars are younger than the age of universe.

How the Universe Expands The space between galaxies expands, not the galaxies themselves; objects held together by their own gravity are always contained within a patch of nonexpanding space. Example: raisins in a loaf of bread. –As the dough rises, the overall loaf of bread expands; the space between raisins increases but the raisins themselves do not expand.

Center of Universe? There is NO CENTER to the universe –Expansion looks the same regardless of where you are in the universe. –Every point appears to be the center of the expansion, therefore no point is the center. –The universe is infinite.

Evidence for Expansion The light from remote galaxies and other objects is redshifted. This redshift is called cosmological redshift because it is caused by the expansion of the universe, not by the actual movement of the object (doppler redshift).

Observable Universe Olber’s Paradox is solved: due to the finite speed of light, the observable universe does not include the entire universe. Radius of the observable universe depends on the age of the universe and the speed of light: ~47 billion lightyears. Result: Sky is dark at night with points of light (stars, galaxies, etc.) scattered throughout.

Origins of the Big Bang Theory Georges Lemaître (1927) expanded on idea of expanding universe, realizing that the universe was smaller yesterday than today, and so on until a “day that would not have had a yesterday”: the moment of creation. –The moment of creation would be the sudden expansion that started the expansion of the universe as we know it today. This idea wasn’t widely accepted at first: Fred Hoyle dismissed “this hot Big Bang”, noting that there wasn’t any record or remnants. He argued for a “steady state” universe.

Evidence for the Big Bang Theory Gamow’s theory was revisted in the 1960’s by Bob Dicke and Jim Peebles of Princeton University. –Believed that this cooled radiation would be redshifted to the microwave region of the electromagnetic spectrum. –Made a receiver to detect this radiation, but were unsuccessful.

Evidence for the Big Bang Theory The radiation, so far undetected by the Princeton team, was posing a problem for NJ Bell Telephone Labs, where Arno Penzias and Robert Wilson were developing a new microwave-satellite technology for phone calls. –Puzzled by steady hiss that they received no matter where in the sky they pointed their antenna. –This faint background noise they were trying to get rid of was exactly what the Princeton team was trying to detect: evidence of the Big Bang.

CMB Radiation Detection of this radiation, called Cosmic Microwave Background radiation, won Penzias and Wilson the Nobel Prize for Physics in CMB radiation can be detected by your tv as well - 1% of static seen on a channel that your tv doesn’t receive is from the birth of the universe.

CMB Radiation Intensity of CMB Radiation reveals origins of universe. –However, difficult to detect intensity from Earth- the atmosphere is opaque to wavelengths 10  m to 1 cm (CMB ~ 1 mm). COBE (Cosmic Background Explorer) 1989: detector outside the atmosphere: –Measured the blackbody spectrum of CMB radiation to be at T = K - consistent with theory. –CMB radiation almost entirely isotropic; CMB is slightly warmer in direction of Leo and slightly cooler in direction of Aquarius. WMAP (Wilkinson Microwave Anisotropy Probe) (2002) improved picture of CMB Radiation.

CMB Radiation Radiation appears to be mostly smooth, but there are slight variations in temperature that show that matter had started to clump in the early universe - clumps of matter formed the galaxies and stars see today. Sound waves in early universe are recorded in this radiation; by studying the characteristics of these sound waves, we can find out about the conditions of the early universe.

Horizon Problem Despite all of the success with the Big Bang Theory so far, the horizon problem was still yet to be solved. –The temperature of the CMB radiation was the ~same no matter where you look in the sky, indicating that some how information linking all parts of the sky was traveling faster than the speed of light. –Also, information from one side of the sky at 100,000 years old (horizon is 100,000 light years in diameter) differed from the other side of the sky by 10 million light years times the diameter of the horizon. How is this possible?

Inflation Theory Alan Guth (1970s) had a solution: –The universe must have expanded exponentially very early for a short period of time. –This would account for the clumping of matter.

Evidence for Inflation Theory Guth predicted that the average density of the universe should be equal to the critical density (6 protons/m 3 ) –This was confirmed by powerful telescopes. Evidence from WMAP shows that the clumping of matter is consistent with the amount of accelerated expansion during inflation.

Extent of Inflation Today, evidence and theory show that: At T = sec, universe d = cm Between T = sec and T = sec, the universe expanded exponentially by a factor of For the briefest moment, the universe expanded faster than the speed of light.