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  • 1. St Benedict’s School 2013 January 29 GEORGES LEMAITRE: Life, Science, and Legacy Simon Mitton Vice President, Royal Astronomical SocietyDepartment of the History and Philosophy of Science, University of Cambridge Fellow, St Edmund’s College, Cambridge Website www.totalastronomy.com 1
  • 2. Goals of the Talk» To describe some of the evidence and history for why astronomers believe that the universe is expanding» To describe what Fr Georges Lemaître proposed 85 years ago to explain these observations.» To show how he followed science and faith as two roads to the truth. 2
  • 3. 3
  • 4. The Nature of the Universe What kind of universe do we inhabit? What is its history? What was the Big Bang? How did galaxies form? How do we know what we know? 5
  • 5. Heart of Darkness: Unraveling the Mysteries of the Invisible Universe Jeremiah P. Ostriker & Simon Mitton Cloth | 2013 | $27.95 / £19.95 | ISBN: 9780691134307 288 pp. | 6 x 9 | 16 color illus. 40 halftones. "If you want a clear and fair assessment of the astonishing recent progress in understanding the cosmos--and of the mysteries that remain to be addressed--then this is the book for you. Ostriker and Mitton write with authority, and with style as well."--Martin Rees, Master of Trinity College, University of Cambridge, and Astronomer Royal Available now at AmazonHeart of Darkness describes the incredible saga of humankinds quest to unravel the deepest secrets of theuniverse. Over the past thirty years, scientists have learned that two little-understood components--darkmatter and dark energy--comprise most of the known cosmos, explain the growth of all cosmicstructure, and hold the key to the universes fate. The story of how evidence for the so-called "Lambda-ColdDark Matter" model of cosmology has been gathered by generations of scientists throughout the world istold here by one of the pioneers of the field, Jeremiah Ostriker, and his coauthor Simon Mitton.
  • 6. Newton’s PrincipiaQuick QuestionWhat did the other personon the title page write? 7
  • 7. Andromeda galaxy - our nearest neighbour 8
  • 8. Looking through Space and TimeA light year – the distancelight travels in one year Galaxy 50(10,000,000,000,000 km) millionlight yearsaway It looked like this 50 millionyears ago A telescope is a time machine! 9
  • 9. 100,000 light years Dark matter haloSolar system Disc of the Galaxy 10
  • 10. Voyage to the centre of the Milky WayREAL Photographs, not a simulation 11
  • 11. Coma cluster of galaxies40 million light years 12
  • 12. Einsteins Theory of General Relativity •In 1916, Albert Einstein published his Theory of General Relativity. •It replaced Newton’s clockwork universe. Einstein’s described gravity as a geometric property of space and time. This was a truly revolutionary idea about the universe. 13
  • 13. Step 1 to a Great DiscoveryIn 1915 Einstein published theGeneral Theory of Relativity, atheory of gravity that includes the“time” dimensionArthur Eddington in Cambridge understands that Einstein’smaths can be used to figure out the properties and behaviourof the entire universeAt the Total Eclipse of the Sun in 1919 Eddington confirmsEinstein’s theory, which thereafter is how mathematicians workout what’s Einstein and Eddington, The Observatories what in the universe 14
  • 14. The Static Universe Model •One hundred years ago, astronomers thought: •The universe was unchanging through time. •The stars of our galaxy (the Milky Way) made up the whole universe •The galaxy was nearly motionless •Physicists trying to create a model for the universe had to match these "facts". •The challenge to these facts started in Cambridge as early as 1917 15
  • 15. Lemaître in Cambridge 1923 - 24 •Arthur Eddington, mathematician and astronomer at Cambridge, having proved the Theory of General Relativity in 1919, and became the world expert on Einstein’s theory •Georges Lemaître, the priest with a doctorate in theology,worked with Eddington on finding solutions to Einstein’s equations. Their aim was to find what properties of the universe were allowed by Einstein. In other words, answer the question “What type of universe are we living in?” A BIG question! 16
  • 16. Step 2 to a Great Discovery1923-24. Georges Lemaître and ArthurEddington in Cambridge work together onEinstein’s models of the universe1924 Lemaître the theorist goes to the otherCambridge (Boston, USA) to work at Harvardand MIT. He meets astronomers who uselarge telescopes to view the distant universe:Vesto Slipher and also Edwin Hubble, withboth of whom he discusses model universes 17
  • 17. The Fate of the Universe •There are many possible answers to Einsteins equations. Each solution implies a possible ultimate fate of the universe. •Alexander Friedman in Russia proposed a number of such solutions in 1922, as did Georges Lemaître in Belgium in 1927. •Both of them published in obscure journals (a mistake!). The remarkable fact about their answer was this: •The Universe is Expanding (a big shock!) 18
  • 18. Step 3 to a Great Discovery about the UniverseIn 1912, far away in Arizona, a youngastronomer had clocked the speed of a galaxyfor the first timeBy 1917 Vesto Slipher discovered that a dozennearby galaxies are racing away from the MilkyWay (redshifted)What could this mean?For certain it meant that galaxies were farbeyond our own Milky Way Galaxy 19
  • 19. Discovery of Galactic Redshifts •In 1912, Vesto Slipher was the first to observe the shift of spectral lines of galaxies, making him the discoverer of galactic redshifts. •Redshifts are analogous to the Doppler effect – think racing cars or trains passing you at speed. •An observed redshift due to the Doppler effect occurs whenever a light source moves away from an observer. •Conversely, light sources moving towards an observer are blueshifted. 20
  • 20. Step 4 to a Great Discovery1927 Lemaître has an explanation for Hubble’s results.Publishes in 1927 a paper on the expansion of theuniverse in which he demonstrates that the model isconsistent Einstein’s mathsEinstein regards this as “preposterous” but Eddingtonsupports his former student, and promotes hispreposterous theory!1930 Lemaître speaks on the expanding universe at theRoyal Astronomical Society. He publishes the Primeval Atomconcept Lemaître called his model the “Fireworks Universe”. The expression “Big Bang” came later, in 1948, courtesy of Fred Hoyle. 21
  • 21. A Primeval "Cosmic Egg"? •In 1931, Georges Lemaître published a model of the universe suggesting that the expansion of the universe might have originated when a primeval "cosmic egg" exploded in spectacular fireworks, creating an expanding universe. •Published in the journal Nature, it wasnt taken seriously at the time. But now, his contribution is highly valued. 22
  • 22. Cosmology… …in a cinema!In World War II these three mathematicians researchednaval radar for the Admiralty (British Navy)When they returned to Cambridge University in 1946 theyworked on theoretical astronomyThey went to the cinema once a week. They saw a movie Gold, Bondi, and HoyleDead of Night in which the main action centres on several Rome IAU 1952recurrent nightmares.Gold (on the left of this 1960s photograph) joked “What ifthe Universe is like that? Note that Hoyle is on the frontrow - his favourite location!This led to the concept of a Steady State Universe, anotion that the three of them enthusiastically promoted.Astronomers had to decide:Big Bang (sudden start) promoted by Lemaître, or,Steady State (has existed for ever) promoted byCambridge mathematicians 23
  • 23. “Big Bang” or Steady State? There were two primary explanations put forth for the expansion of the universe: » Lemaîtres “Big Bang” theory, advocated and developed by George Gamow. » A Steady State model, proposed in 1948 by Hermann Bondi, Thomas Gold, and Fred Hoyle, in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time. 24
  • 24. Lemaître and Pius XII •Pius XII, found Lemaître’s Fireworks Universe attractive. The Big Bang taught that the universe exploded into existence with a burst of light.He said that the apparent order in the universe was a sign of divine reation •Georges Lemaître was shocked in 1952 when Pius XII was to speak at the General Assembly of the International Astronomical Union in Rome on creation and the Big Bang. Lemaître interrupted a trip to South Africa in order to visit the Vatican and advise the Holy Father against connecting Divine Creation with the Big Bang. This echoed Aquinas who taught that theology and natural philosophy are two roads to the truth 25
  • 25. Finding the Big BangThe difference between the rival theoriesIn the Steady State version the universenever changes its appearance: The far awayuniverse looks more or less the same as thelocal universeIn the Big Bang version the universe changesits appearance over time. The distantuniverse is younger than the nearby universe… 26
  • 26. Looking through Space and TimeA light year – the distancelight travels in one year Galaxy 50(10,000,000,000,000 km) millionlight yearsaway It looked like this 50 millionyears ago A telescope is a time machine! 27
  • 27. Finding the Big BangIn the Steady State version the universe neverchanges its appearance: The far away universe looksmore or less the same as the local universeIn the Big Bang version the universe changes itsappearance over time. The distant universe is youngerthan the nearby universe …By the mid-1950s there was good evidence that theuniverse has evolved. Lemaître’s concept slowlygained groundIn 1963 there was fundamental breakthrough … 28
  • 28. The proof in favour of the BigBangthe whole universe is filled withradio waves1964. This strange radiotelescope accidentallydiscovered that the entire skyemits a weak microwave signalThe microwaves are a formof radiant heat at a very lowtemperatureWhat had been discovered washeat energy, in the form ofmicrowaves, released by the HotBig Bang Arno Penzias and Bob Wilson 29 1978 Nobel Prize Physics
  • 29. Heart of Darkness: Unraveling the Mysteries of the Invisible Universe Jeremiah P. Ostriker & Simon Mitton Cloth | 2013 | $27.95 / £19.95 | ISBN: 9780691134307 288 pp. | 6 x 9 | 16 color illus. 40 halftones. "If you want a clear and fair assessment of the astonishing recent progress in understanding the cosmos--and of the mysteries that remain to be addressed--then this is the book for you. Ostriker and Mitton write with authority, and with style as well."--Martin Rees, Master of Trinity College, University of Cambridge, and Astronomer Royal Available now at AmazonHeart of Darkness describes the incredible saga of humankinds quest to unravel the deepest secrets of theuniverse. Over the past thirty years, scientists have learned that two little-understood components--darkmatter and dark energy--comprise most of the known cosmos, explain the growth of all cosmicstructure, and hold the key to the universes fate. The story of how evidence for the so-called "Lambda-ColdDark Matter" model of cosmology has been gathered by generations of scientists throughout the world istold here by one of the pioneers of the field, Jeremiah Ostriker, and his coauthor Simon Mitton.
  • 30. Dark Matter & Dark Energy •Over the past 35 years or so, cosmologists’ and physicists understanding of the universe has been turned on its head. •It is now generally accepted in the scientific community that ‘normal matter’ — the matter that we experience in our everyday lives, and that scientists have been studying since the time of the ancient Greeks — comprises only about 4% of the matter in the universe. •So, what is the other 96%? 31
  • 31. Dark Energy •Evidence for Dark Matter and Dark Energy has accumulated, and it is now estimated that only about 4% of the matter/energy in the universe is ordinary matter. •In other words, we have no real clue what the other 96% consists of! •This is most embarrassing! 32
  • 32. Dark Energy and Lemaître • Lemaître’s concept is now central to our present understanding of the universe • The expansion is propelled by dark energy • The dark energy is a fundamental property of the universe •Lemaître is now referred to as ―The father of the Big Bang‖ 33
  • 33. Faith and ReasonWhen asked by professional astronomers how an astronomer priestcould believe in both Divine Creation and the Big Bang, Lemaîtrefollowed the philosophy of Thomas Aquinas: There are two roads tothe truth and we should not expect them to be in agreement becauseour knowledge is always incomplete 34
  • 34. Heart of Darkness: Unraveling the Mysteries of the Invisible Universe Jeremiah P. Ostriker & Simon Mitton Cloth | 2013 | $27.95 / £19.95 | ISBN: 9780691134307 288 pp. | 6 x 9 | 16 color illus. 40 halftones. "If you want a clear and fair assessment of the astonishing recent progress in understanding the cosmos--and of the mysteries that remain to be addressed--then this is the book for you. Ostriker and Mitton write with authority, and with style as well."--Martin Rees, Master of Trinity College, University of Cambridge, and Astronomer Royal Available now at AmazonHeart of Darkness describes the incredible saga of humankinds quest to unravel the deepest secrets of theuniverse. Over the past thirty years, scientists have learned that two little-understood components--darkmatter and dark energy--comprise most of the known cosmos, explain the growth of all cosmicstructure, and hold the key to the universes fate. The story of how evidence for the so-called "Lambda-ColdDark Matter" model of cosmology has been gathered by generations of scientists throughout the world istold here by one of the pioneers of the field, Jeremiah Ostriker, and his coauthor Simon Mitton.