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New Directions

New Directions. o r Everything Your Know Is Rong. This logo denotes A102 appropriate. At the End of the 19 th Century, a certain scientific smugness was in the air. Munich physics professor Philipp von Jolly advised his student Max Planck against going into physics:

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New Directions

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  1. New Directions or Everything Your Know Is Rong This logo denotes A102 appropriate

  2. At the End of the 19th Century, a certain scientific smugness was in the air • Munich physics professor Philipp von Jolly advised his student Max Planck against going into physics: • “…in this field, almost everything is already discovered, and all that remains is to fill a few holes.” • Lord Kelvin,1900: • “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”

  3. Albert Michelson, America’s first Nobel Prize winner: • “The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote . . . Our future discoveries must be looked for in the sixth place of decimals.”

  4. In 1899, the head of the United States Patent Office, Charles Duell, allegedly argued to close the Patent Office because "everything that could have been invented, has been invented.“ • This could be apocryphal, but it illustrates the mood • A recurrent theme • Resurfaced at the end of the 20th century • Hubris, hubris, hubris "Flight by machines heavier than air is impractical and insignificant, if not utterly impossible." -- Simon Newcomb, Director, U.S. Naval Observatory, 1902

  5. Clouds • There were a few unresolved issues, however • 1900: Lord Kelvin gave a lecture to the Royal Institution of Great Britain titled “Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light” • He was talking about the null result of the Michelson-Morley experiment and the problems of blackbody radiation • Where was the ether? • Why are there discrete spectral lines? • Also, what the heck is Brownian Motion?

  6. The Luminiferous Aether • Proposed by Aristotle and again almost 2000 years later by Descartes • 1881: Albert Michaelson, along with Edward Morley, set out to find it • The idea is this: if light is a wave, then it must travel through a medium, like water waves • Therefore waves will be different going with the “current” than across it It’s still here!

  7. Null Result • Michaelson and Morley found no evidence of any aether • Then how could light be a wave? • Recap: • 1670: Huygens; light is a wave • 1699: Newton; light is a stream of particles • 1801: Thomas Young; light is a wave • So now what?

  8. And then there’s Discrete Spectra • If light comes from accelerated electrons and light carries away energy from the electrons, why doesn’t all matter collapse as energy is lost?

  9. Resolutions circa 1910 • Energy isn’t continuous but comes in discrete packets called quanta • The death of continuum physics and the birth of quantum physics • Max Planck (a converted continuist); his “kludge” from the Spectra PPT was a major instigator • Light is neither a particle nor a wave but has the qualities of both • And therefore requires no aether to propagate • Demonstrated by Einstein and later by Compton • Both denied ‘common sense’ • Both required new ways of thinking

  10. Einstein vs Newton

  11. Newton’s Universe • Objects attract each other with a force proportional to their masses and inversely proportional to the square of the distance between them • There is an absolute state of rest • “Law” for almost 200 years, but with a cause for gravity

  12. Albert Einstein (1879-1955) • Life/Career • Achievements • Important Publications • 1905 papers • 1915 papers • 1921 Nobel Prize • 1935 EPR

  13. Einstein’s Universe • General Theory of Relativity, 1915 • Mass curves space • *There is not absolute state of rest • i.e. there is no perfect place from which to view the Universe • *All motion is relative, but the speed of light is fixed for everyone • BTW, Einstein explained Brownian Motion in a 1905 paper *Special Theory of Relativity, 1905

  14. William Wallace Campbell • Director of Lick Observatory 1900-1930 • Pioneer of the astronomical spectroscopy; catalogued radial speeds of stars. • Tried to confirm Einstein’s theory with eclipse viewed in Kiev • Clouds! • Tries again in 1918 in WA • Bad gear, no confirmation • Goes to London to report negative result

  15. Sir Arthur Eddington • An English pacifist during WWI • Felt kinship with German pacifist Einstein • Wanted to show science was above politics • Also, first to propose a fusion-like process for the Sun’s energy • Journeyed to island of Principe off Africa for the best view of 1919 eclipse • Results nebulous, but Eddington wires London with confirmation

  16. Confirmed • 1922, WWC goes to Australia for eclipse viewing, confirms GT with 92 stars

  17. Modern Testing • Cassini Spacecraft sends back radio signals from Saturn • The curvature of spacetime near the Sun is tested • Einstein is correct!

  18. Gravitational Lensing

  19. Microlensing • Used for: • Additional magnification of distant objects • Evidence of dark, intervening objects • Space-time curvature data

  20. In other words: • “Mass tells space how to bend and space tells matter how to move” • GR predicts many things that were heretical at the time • Stars, under certain conditions, can shrink to nothing with infinite density • It is unlikely that the Universe is static

  21. 1914-1918: WWI • Karl Schwarzschild (1873-1916) • Child prodigy • Published a paper on orbits at age 16 • His son Martin also became a famous Astrophysicist • Member of Prussian Academy of Sciences up until the war • Joined the German army at age 41 • Submitted papers while serving in Russia

  22. 1915: found a solution to GR that allowed stars to collapse into zero volume and infinite density • Later named “Black Holes” by John Wheeler • KS was not the first mathematician to conceive of such things • Einstein verified the solution but didn’t like the consequences

  23. Massive Stars • If a giant star at the end of its giant phase has > 1.4 Msun, it will collapse suddenly and then violently explode as its materials rebound off a superdense core • There is about 1 SN every century in our galaxy, 1 every second in the Universe • In a few weeks they emit more energy than the Sun does in a century

  24. However, if the giant star has > 3 Msun at the end of its giant phase, the explosion stalls due to the overwhelming gravity, and the star continues to collapse to an infinitely tiny point, or singularity • Space is so tightly curved around it that nothing can escape

  25. To sum up GR (a little):

  26. But he realized that his equations wouldn’t permit this stability • Remember Poisson’s equation? • It says that the condition of no acceleration (e.g. no gravitational force) can only exist in an empty Universe • Introduced a cosmological constant, L (lambda), into GR to counteract any acceleration that would change his static model

  27. The Steady State Model • One assumption that underlay the discussion of the shape of the cosmos was that the Universe was eternal and unchanging • SSM formally posed in 1948, but its demise was already present in GR • The idea was hard to bury, despite being a source of paradox

  28. Kepler’s *Paradox (AKA Olber’s Paradox) • If the Universe is eternal and infinite, why is the sky dark at night? • In Kepler’s words: “If [this] is true, and if they are suns having the same nature as our sun, why do not these suns collectively outdistance our sun in brilliance?” *Ryden’s Law of Misonomy – Olber actually saw no paradox, stating that the universe soaks up a little light from every star

  29. Not So Steady • 1692: Newton receives a letter from theologian Richard Bentley • Asks Newton how would the Universe change with time if all matter was initially distributed perfectly symmetrically • Newton replies that it would be static • But perfect symmetry is as likely as “an infinite number of needles standing on their tips on a mirror” • Bentley replies that isn’t that the same likelihood as an infinite number of fixed stars?

  30. Learning to Love L* • Einstein himself held that the Universe was static and homogeneous with spherical geometry • Remember, in 1915 when he produced GR, 5 years before The Great Debate, the scope of the Universe was not known • He therefore looked at only stars in the MW and saw that there was no obvious expansion or contraction *With a nod to Dr. Barbara Ryden

  31. Alexander Friedman 1888-1925 • Russian Mathematician and Cosmologist • Like Schwarzschild found a solution to GR • His 1922 solution showed that GR predicted an expanding Universe • 1929 Hubble data confirmed this

  32. Edwin Hubble’s work, circa 1925 • His observations helped settle the Great Debate • But they also posed a new question: • Why is practically everything in the Universe moving away from us?

  33. Bigger and Bigger • Hubble’s data suggests that the Universe is expanding • Not only that, more distant objects are moving away faster • Hubble determined these distances and velocities using red shift

  34. Blunder • With Hubble’s discovery Einstein removed L and called the constant his “greatest blunder” • “Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder of his life”. -- George Gamow, My World Line, 1970 • Ironically, he was right: L is back in modern cosmology • If only he had stuck by his guns!

  35. Georges Lemaître 1894-1966 • Belgian Roman Catholic Priest and (!) Cosmologist • 1927 submitted a paper that independently arrived at Friedman’s solution • Primordial atom • Einstein read both and, at the time, dismissed them

  36. Expansion of the Universe • A tricky idea • What is not happening: • Objects are getting bigger • The space in atoms is increasing • Proper motion is not part of the expansion • Expansion means that space is stretching, like polka dots on the surface of an inflating balloon with conditions

  37. Regardless of how, Hubble showed, and Einstein agreed, that the Universe was indeed expanding • This implies: • The Universe is not static • The Universe is not infinitely old • The Universe had a beginning • However, at first, Hubble’s equation was good but his measurements were off, causing the Universe to be too young at 2 Gyr.

  38. And this explains it all, right?  • Called the Robertson-Walker metric (AKA FLRW) • Shows how space and time scale with expansion • For the curious: • Distance: s • Cosmological scale factor: a • Time: t • Curvature: k • Radial distance: r • Azimuth angle Q • Altitude angle: f • In a way, it’s like measuring distances on the surface of the Earth

  39. It’s not that everything in the Universe is expanding in a big box, it’s that the box itself is expanding • How it expands is the subject of Cosmology • The so-called Big Bang is just a part of the subject • (details to follow later)

  40. Still there were doubters • Sir Frederick Hoyle 1915-2001 • Respected Astrophysicist • Postulated stellar nucleosynthesis • Proponent of Steady State Theory • Dismissed Friedman’s idea of a “Big Bang” • Cited 2 Gyr cosmos

  41. SSM • Hoyle and his camp agreed that the Universe was expanding • But to avoid a “beginning” he had the Universe constantly creating matter between the galaxies

  42. Karl Jansky 1905-1950 • 1931: discovered radio waves emanating from the Milky Way • A clue!

  43. George Gamow • With colleagues *Ralph Alpher and Robert Hermann pictured the early Universe as a nuclear oven in which light elements were cooked, backing up the Big Bang theory • They posed that the earliest temperatures would be staggeringly high ~ 100 billion K • During the late 1940s and early 1950s they made predictions that the cosmos would have cooled like a blackbody radiator to a temperature ranging from 5K to 50K • Evident as microwave radiation • Hoyle actually backed them up on this while maintaining his SSM! *GG’s grad student, the mathematician of the group

  44. Blackbody Radiation • Hot objects (T > 0K) emits a spread of “heat’ radiation • Peak occurs ~ 1mm

  45. CMB • Cosmic Microwave Background • First observed in 1940 by Andrew McKellar • Cyanogen excitation (0 -> 1) corresponds to 2.4K • These data were not recognized for what they were at the time, or even in an important paper in 1950

  46. Hissssssssssss • 1965: Arno Penzias and Robert Wilson, worked for Bell Labs in NJ • Used an ultra-sensitive microwave receiving system to study radio emissions from the Milky Way • Found an unexpected background of radio noise • They consulted with Princeton physicist Robert H. Dicke who had predicted that if the Big Bang theory was correct, a background radiation at 3-degree Kelvin would exist • This and better Hubble measurements in 1949 verified BB Wilson explaining the noise

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