Olbers Paradox In 1826 the astronomer Heinrich Olbers
Olber’s Paradox • In 1826, the astronomer Heinrich Olber’s asked, "Why is the sky dark at night? " By his time, physicists had learned enough to realize that, in a stable, infinite universe with an even distribution of stars, the entire universe should gradually heat up. • Prior to this, many believed the universe simply had existed for all time – a steady state model of the universe. Source: http: //www. arachnoid. com/sky/index. html
An Expanding Universe • The beginnings of theory… – Edwin Hubble – Astronomer • 1923 Proves that the universe extends far beyond the edges of the Milky Way galaxy • Notices that galaxies are “red-shifted” – moving away from us
An Expanding Universe • Hubble's Law: –The farther away a galaxy is from Earth, the faster it is moving away.
The Big Bang Theory • Where do cosmologists get the idea that the universe originated in a Big Bang? – Expanding Universe • Redshift – Cooling Cosmos • Cosmic Microwave Background Radiation – Abundance of Light Elements • Hydrogen, Helium, and Lithium
The Big Bang Theory • Where do cosmologists get the idea that the universe originated in a Big Bang? – Expanding Universe • Redshift – Cooling Cosmos • Cosmic Microwave Background Radiation – Abundance of Light Elements • Hydrogen, Helium, and Lithium
An Expanding Universe Redshift Source: image: http: //www. astrocappella. com/images/shifted_spectrum. jpg
Raisin Bread Dough Analogy
An Expanding Universe • In 1948, Russian-born physicist George Gamow took the next step by realizing that if all the galaxies are flying apart at high speed, the entire universe must have been concentrated in a single point at some time in the past. Source: http: //www. arachnoid. com/sky/redshift. html; Image: http: //www. astromia. com/biografias/fotos/gamow. jpg
Reverse Time The Primordial Atom
An Expanding Universe • During a radio interview, scientist, Fred Hoyle, coined the name "Big Bang“ – some say Hoyle was making fun of theory, he claims he was only trying to explain how it was different than his own “steady state” theory. • … but the term became popular, and has prevailed to the present day. Source: http: //www. arachnoid. com/sky/redshift. html; Image: http: //www. ananova. com/images/news/fredhoyle 350 x 531. jpg
The Big Bang Theory • Where do cosmologists get the idea that the universe originated in a Big Bang? – Expanding Universe • Redshift – Cooling Cosmos • Cosmic Microwave Background Radiation – Abundance of Light Elements • Hydrogen, Helium, and Lithium
A Cooling Cosmos - CMB • Cosmic Microwave Background Radiation (CMBR) – NASA projects • COBE (Cosmic Background Explorer) • WMAP (Wilkinson Microwave Anisotropy Probe) Source: http: //map. gsfc. nasa. gov/
A Cooling Cosmos - CMBR • 1992 COBE took a “picture” of the entire universe and its cosmic microwave background radiation • In February 2003, the WMAP data showed much greater detail Source: http: //map. gsfc. nasa. gov/
A Cooling Cosmos - CMB • As the electromagnetic wavelength is lengthened (stretched out by an expanding universe), gamma rays from the earliest stages of the big bang would turn to Xrays, UV, visible light, IR, and ultimately microwave Source: http: //map. gsfc. nasa. gov/
The Big Bang Theory • Where do cosmologists get the idea that the universe originated in a Big Bang? – Expanding Universe • Redshift – Cooling Cosmos • Cosmic Microwave Background Radiation – Abundance of Light Elements • Hydrogen, Helium, and Lithium
Hydrogen, Helium, and Lithium are only elements assumed to be produced directly from Big Bang, all others are synthesized in stars Elements heavier than Iron (Fe) are produced in the outer envelopes of super-giant stars and in the explosion of a supernova
The Big Bang How the Universe was formed…
A quick review of the life-cycle of stars…
Nebula ar e l c n Nu usio F th De a ity Grav Oxygen Boron Sodium Carbon Aluminum Nitrogen Argon ity Star Planetary Nebula Beryllium Grav & vity Gra clear Nu ion Fus Atom BANG. Elements #4 through 26 Nu c Fus lear ion BIG Primordial quarks, electrons, protons, neutrons Beginning of light Gr ity rav avi ty G Planetary Nebula ling coo Star Super-Giant ATOMS Elements #27 and higher Lithium ity av Gr Planets Nickel Zinc Copper Lead Xenon Gold Silver Cadmium Nuclea r Fusion Death Helium ty vi ra G Hydrogen Super Nova
How long did it take? BIG BANG 1 to 3 seconds 1 st Hydrogen Atoms 3 minutes Universe is 75% Hydrogen, 25% Helium 200 million yrs. Planets, Solar Systems, TODAY 13. 7 billion years Larger Elements nebulas, stars blackholes, galaxies
“Dark” Matter & Energy • Scientist think that the universe is made up of much more “stuff” than we can detect. The “ripples” indicate there must be more than we can see… Cosmic Background Radiation
Composition of the Universe The Cosmic Background Radiation shows us that only 4% of the universe is made of “stuff” we can see. 4% Atoms 23% Dark Matter 73% Dark Energy
“Dark” Energy • According to Newton’s 1 st law – an object in motion, remains in motion, at a constant speed and direction • Per Hubble’s law, galaxies in the universe are NOT moving at a constant motion, they are accelerating • Therefore, there must be some “Dark Energy” that is pushing galaxies apart – working the opposite of gravity
Inertia (Newton’s 1 st Law) explains the top galaxy’s motion – constant speed, straight line. Dark Energy is a theoretical explanation for the second galaxy's movement - acceleration.
- Slides: 31