Lecture 2 Big Bang Time Line

The Birth of the Quantum Max Planck –The energy contained in radiation is related to the frequency of the radiation by the relationship n is a positive integer called the quantum number f is the frequency of the oscillation –A discreet packet of energy, later to become known as “a photon”

Implications of Planck’s Law The energy levels of the molecules must be discreet Only transitions by an amount E=hf are allowed The implication is that light is discreet or quantised These quantum levels are known as number states hf 3hf 2hf 1hf 0 energy n

Spectroscope

Three Types of Spectra

Spectral Analysis of the Elements Continuous Spectrum: a collection all possible wavelengths/ frequencies of light Studying the light emitted by an object in order to know something about that object!

Emission Spectra Pattern of bright spectral lines produced by an element.

Absorption Spectra Pattern of dark spectral lines where light within a number of narrow frequency ranges has been removed.

Helium Argon Neon Krypton Bright Line Emission Spectra Hydrogen Wavelength

Kirchoff’s Laws 1st law1st law: A luminous solid or liquid, or a sufficiently dense gas, emits light of all wavelengths and produces a continuous spectrum of radiation. 2nd law2nd law: A low-density hot gas emits light whose spectrum consists of a series of bright emission lines which are characteristic of the chemical composition of the gas. 3rd law3rd law: A cool thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place superimposed on the continuous spectrum.

Spectra and Background Type of spectrum seen depends on the temperature of the thin gas relative to the background temperature. TOP: thin gas cooler than background, absorption lines seen. BOTTOM: thin gas hotter than background, emission lines seen.

Studying the Stars: Analyzing the light from a star can tell us: 1. The composition of the star. 2. The relative motion & rotation of the star. 3. The star’s temperature.

Shows limited Range of Light Energies Reaching Earth’s Surface

Hubble’s Discovery of the Expanding Universe (1929) Spiral nebulae known to have redshifted spectra Hubble and Humason carry out quantitative study Hubble shows velocity of recession is proportional to distance

Instrument of Discovery: Hooker 100” Telescope Mount Wilson Observatory

The Hubble Law Hubble’s original data showing the galaxy velocities to be propor- tional to their distance v=H o R

The Hubble Law Improved data showing that the Hubble law holds to much larger distances = 75km/s/Mpc v=H o R

Cosmic Distance Ladder Radar METHOD Supernovae Britest Galx. In Cluster Rotation Velocity Period-Lum. Relat. Color-Mag Rel. Stat. Parallax Moving Cluster Parallax Objects Remote Galax. Remote Clusters Spiral Galaxies Cepheid Var. Stars Star Clusters Hyades Star Cluster Planets & Stars Nearby Planets Useful Distance Light years 10 8 Light years 5x10 7 Light years 10 6 Light years 1000 Light years 120 Light years 100 Light years light minutes

Stellar Parallax ParallaxParallax is the annual shift in a star’s apparent position in the sky due to the Earth’s orbital motion. The parallax angle is half the annual shift. The parallax angle of the nearest star, Proxima Centauri, is 0.77 arcseconds.

Parsec An object with a parallax of 1 arcsecond is located at the distance of 1 parsec. 1 pc = 3.26 light-years = km 1 d (in parsecs) = p (in arcseconds)

Parallax A.U. Earth Sun  2x Parallax (p) in arcsecs Background Stars A.U. = Astronomical Unit = Earth-Sun Distance = 1.5x10 11 m Parsec = pc = distance when parallax is 1 arcsec: 2  radians in circle = 360 deg ==>

The Hubble Law  d R R dHV  0 = 75km/s/Mpc

The Expansion of the Universe: One should consider the galaxies located on the surface of the sphere which expands with time. As the sphere expands all lengths, including that of light increase. That means all the photons redshift. The redshift increase with the distance. The Expansion of the Universe

Raisin Cake Model Like raisins in rising raisin cake, galaxies move away away from each other in our expanding universe.

Cosmology Hubble Time The age of the universe if the expansion has been constant. t = 1/H o = ? The expanding universe probably originated in an explosion called the Big Bang between 12 and 18 billion years ago.

Big Bang Timeline We are here

Big Bang Timeline GUT period -age of quarks and gluons: Dense concentration of matter and antimatter; gravity a separate force, more quarks than antiquarks Inflationary period: rapid expansion, strong force separate from electroweak force

Electroweak era; age of leptons: Leptons distinct from quarks; bosons mediate weak force ; Particle era: Age of nucleons and antinucleons: quarks bind together to form nucleons and antinucleons; energy too low for nucleon- antinucleon pair production at. Age of nucleosynthesis: stable deuterons; matter 74% H, 25% He, 1% heavier nuclei Age of ions: expanding, cooling gas of ionized H and He. Big Bang Timeline

Recombination era: age of atoms; neutral atoms form, pulled together by gravity; universe becomes transparent to most light. Age of stars and galaxies Thermonuclear fusion begins in stars, forming heavier nuclei Present era