1. Origin & Evolution of the Universe
The Big Bang Theory
Origin & Evolution of the Universe

2. 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.
This made sense to Newton because the gravity of a finite number of stars would eventually cause the universe to fall together into a compact blob - clearly this isn’t/hasn’t happen[ing]/[ed]

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

4. 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.

5. But isn’t the sky dark at night…?
Something is wrong with Newton’s idea of a static, infinite universe.

6. 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.
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7. Special Relativity
Time and Space and their rates are intertwined and depend on the motion of the observer (1905).

9. 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).

11. 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.

12. 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.

13. 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.

14. 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.

15. Redshift vs Doppler Effect

16. 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.

17. 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).

18. 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.

19. 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.
Need segue - perhaps now that there is evidence that the universe is expanding, need an explanation/change to ideas for the origin of the universe.
Einstein dimissed lemaitre’s ideas, thinking that he did not understand the laws of physics properly.
After Hubble’s discovery that provided evidence of expansion, Lemaitre gave a lecture presenting his idea, and Einstein admitted his error (cosmological constant) - beautiful and satisfying interpretation

20. Origins of the Big Bang Theory
George Gamow (1948) suggested that if the universe was created with a “hot Big Bang”, then:
Various elements, such as H and He, would be produced for a few minutes immediately after the Big Bang due to the extremely high temperatures and density of the universe at this time.
The high density would cause rapid expansion.
As the universe expanded, H and He would cool and condense into stars and galaxies.
Today, due to continued cooling, radiation left over from the epoch of recombination, when neutral atoms formed (~380,000 years after Big Bang) should be about 3K.
Production of H and He during this time instead of just in H-burning in stars would explain why the H:He ratio of the universe is higher than what could’ve been produced by stars alone.
This paper was published as Alpher (student), Bethe (Gamow’s friend), and Gamow as a joke - referred to alpha beta gamma paper. Due to his sense of humour, much of gamow’s early work was forgotten.

21. 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.

23. 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.
Tried everything to get rid of this noise, including cleaning all of the pigeon droppings off of their antenna.

24. CMB Radiation
Detection of this radiation, called Cosmic Microwave Background radiation, won Penzias and Wilson the Nobel Prize for Physics in 1978.
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.

25. Expansion & Fate of Universe

26. Fate of the Universe

27. Research Today
Today, particle accelerators such as the LHC are trying to replicate conditions just after the Big Bang so that we understand how the universe formed.
Currently, all cosmic evolution after inflationary epoch can be modeled and described pretty accurately, but the time before this (10-15 sec) is basically unknown; understanding this time remains one of the greatest mysteries in physics.