Lecture 2 Big Bang Time Line The Birth of the Quantum Max Planck –The energy contained in...
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Transcript of Lecture 2 Big Bang Time Line The Birth of the Quantum Max Planck –The energy contained in...
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”
nhfE
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
43210
4hf3hf2hf1hf0
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.
HeliumArgon
NeonKrypton
Bright Line Emission Spectra
Hydrogen
Wavelength
Kirchoff’s Laws• 1st law: A luminous solid or
liquid, or a sufficiently dense gas, emits light of all wavelengths and produces a continuous spectrum of radiation.
• 2nd 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 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 BackgroundType 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=HoR
The Hubble Law
• Improved data showing that the Hubble law holds to much larger distances
= 75km/s/Mpc0H
v=HoR
6 61 10 3 10Mpc pc x light year
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
1010 Light years
1010 Light years 108 Light years
5x107 Light years 106 Light years 1000 Light years 120 Light years 100 Light years light minutes
Stellar Parallax
Parallax 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.
𝑑=𝐴 .𝑈 .𝑝
Parsec
An object with a parallax of 1 arcsecond is located at the distance of 1 parsec.
1 pc = 3.26 light-years = 3.09 1013 km
1d (in parsecs) = -------------------------- p (in arcseconds)
Parallax
A.U.
Earth
Sun
2x Parallax (p) in arcsecs
BackgroundStars
A.U. = Astronomical Unit = Earth-Sun Distance = 1.5x1011mParsec = pc = distance when parallax is 1 arcsec:
2 radians in circle = 360 deg ==>
161 . . 1 . .206000 . . 3.1 10
11 sec206000
AU AUd AU x m
arc rad
360deg1 57deg 57 60 min
257 60 60 sec 206000 sec
rad x arc
x x arc arc
The Hubble Law
·
dR
RdHV == 0
= 75km/s/Mpc0H
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
12
3
1
2
3
Like raisins in rising raisin cake, galaxies move awayaway from each other in our expanding universe.
Cosmology
• Hubble Time• The age of the universe if the expansion has been
constant.• t = 1/Ho = ?
• The expanding universe probably originated in an explosion called the Big Bang between 12 and 18 billion years ago.
91 10billion
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.
0W and Z 12(10 )s
210 s
Big Bang Timeline
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 915 10x years