SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond

1. SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond Lecture 13 24 March 2014 Science Center Lecture Hall A

2. Outline: Disjoint Topics 1. Cosmological inflation (popular email demand): Big news from last week 2. Continental drift and plate tectonics: - Brief overview of geology of 19th century - Wegener and idea of continental drift: Fight to death (Wegener’s) - Plate tectonics: Evidence, largely magnetic, developed; near complete acceptance by late 1960s (may not get to until Wed.)

3. Cosmological Inflation: Why Excitement? Background: Big Bang was intense, hot collection of (ionized) matter and radiation. Resultant universe (now) shows space-time very close to being “flat”: no curvature. (What does that mean?) But universe expanded enormously since Big Bang. Hence, exceedingly close to being flat initially. Coincidence (or anthropomorphic argument) or physical reason for it? Called “flatness problem” by those who need reason. Question: Is either anthropomorphic (c. 1974) or physical (1981)reason good enough? Or must it be latter?

4. Enter Inflation Inflation to rescue in 1981 (gave reason): Postulated field, which caused exponential expansion of universe, near start, for ≈ 10-34 sec Universe expanded by ≈ 1050 or so during inflation. Solves flatness problem: balloon analogy. But inflation just a theory

5. Evidence For Inflation? So far little: Solves existing problems; what about prediction of something observable, but not yet observed? Especially important since inflation physics so far beyond anything have had contact with, e.g., enormous energies so soon (≈ 10-32 sec) after Big Bang. There is something – involving CMB - but very difficult to detect Look at prediction sequence (alas, we must use Black Boxes = BB, so labeled)

6. Prediction Sequence (BB) • Quantization of gravitational field, coupled to inflation, produces primordial background of gravitational waves (IGW = Inflationary Gravitational Waves) with characteristic spectral shape • IGW induce anisotropies in the CMB, within “last scattering surface,” yielding polarization in the CMB of a special sort (“B-mode”) at degree angular scales • Note length (and complexity) of chain: Recall Lecture 1

7. Paydirt: BICEP2 Results • B-mode signal detected, in accord with expectations. Strength of signal encapsulated in parameter “r,” the ratio of the IGW effect to others of a different character: r = 0.16 ± ≈ 0.06 • Noise level under 0.1 μK. “All” sources of systematic error investigated and found negligible • Caution: Other, upper limits, seem to provide conflicting results as yet unexplained • Stay tuned

8. Change Of Pace And Of Subject We switch from modern test of inflation model of Big Bang cosmology back to study of problems on earth: What do we know about earth’s surface and its possible evolution?

9. Underlying Theme Largely 20th century collaboration, in detective investigation, of specialists in geology, physics, chemistry, and astronomy yielded special fruit: apparent solution to age-old problem of evolution of earth’s surface -- illustrating by example at least one aspect of unity of science

10. Status of Geology Before This General Period In first half of 19th century, geology was prestigious; by end of century, geology had lost its luster to physics, chemistry, astronomy, and later biology Geology had plodding connotation; Rutherford likened it to postage-stamp collecting and described it as consisting of “making maps by identifying and locating rocks and fossils” Revolution we’ll be discussing changed all that!

11. Quick History of Geology: I 1795: Scottish James Hutton proposes first scientific theory of geology: land worn by erosion is replenished by volcanism; “the present is key to the past.” “The result, therefore, of our present enquiry is that we find no vestige of a beginning–no prospect of an end.” Cornerstone is study of rocks and strata; not theories. 1830s: British uniformitarians (unending cycles) victorious over French catastrophists (but not by force of logic)

12. James Hutton (1726 -1797)

13. Quick History of Geology: II Later in 19th century: Permanentistsformed with rallying cry: “once a continent, always a continent; once an ocean, always an ocean.” Example of supporting evidence: shallow seas appear and disappear over continents explaining sea fossils found on land (and none from denizens of deep sea) Contractionists: earth’s history not history of cycles, but of development and decay; interior of earth shrank, crust wrinkled, folded, and subsided. “Motor” was earth’s contraction

14. Problems With Contractionist Theory Mountain ranges too extensive for any reasonable estimate of contraction Radioactivity (early 20th century) argued strongly against contraction theory. (Heating from radioactivity causes expansion.) Contractionist’s motor had overheated!

15. An Iconoclast Surfaces Alfred Wegener, with PhD in astronomy and chosen career in meteorology, in 1912 takes up cudgels for earlier proposed theory of continental drift (see, also, next slide plus two); he was prompted by casual observation of apparent closeness of fit between west coast of Africa and east coast of South America

16. Fit Between South America & Africa

17. Alfred Wegener (1880-1930)

18. Two Of Drift-Theory Precursors 1844: fit between West African coast and east South American coast noted and published; apparently noted much earlier (1596!), from first maps of both coast lines 1882: Moon thought to have been ripped from Pacific Ocean (now discredited); Atlantic opened as Africa and South America moved apart to fill in depression

19. Encapsulation of Wegener’s TheoryI: Background and Overview First published in 1915 (94 pages): “Origin of Continents and Oceans.” Fourth edition published in 1929 -- his last word (he perished in 1930 in Greenland). When drift lost its most vocal champion, it drifted to back burner among concerns of geologists. Had been sort of a standoff between opponents and proponents

20. Wegener & Villumsen(In Greenland)

21. Encapsulation of Wegener’s Theory II: Continents Present continents originally joined in supercontinent, Pangaea. Pangaea broke into pieces, due to stresses within earth; these pieces drifted apart. Later some regrouping, such as via collision of India with Asia, resulting in Himalayas. Motor??

22. Pangaea

23. One View Of Continental Drift Through Time

24. Encapsulation of Wegener’s Theory III: Other Evidence Radioactivity increases temperature; made movement of continents over surface easier Distribution of species and fossils on different continents explained naturally (e. g., see next slide), as well as subtropical Spitzbergen and glaciated Australia, which occurred at same time in past Wegener concluded: “One chance in a million that drift idea is wrong.” (Basis for number in different “coincidences.”)

25. Some Fossil Evidence For Drift

26. Encapsulation of Wegener’s Theory IV: Final Evidence Geodetic evidence shows westward drift of Greenland at rate of ≈10 m per year (turned out later to be error)

27. Wegener Attacked None of Wegener’s arguments was impregnable; each and every one of them was attacked. Some critics were mostly sarcastic: “One truly sews a rotten bag with gold thread.” “It is easy to fit the pieces of a puzzle together if you distort the shapes, but when you have done so, your success is no proof that you’ve placed them in their original positions. It is not even a proof that the pieces belong to the same puzzle or that all of the pieces are present.” “ I found half a fossil in Newfoundland and the other half in Ireland.”

28. Wegener Defends While alive, he fended off each attack, for example in his defense of inductive reasoning and his analogy with Kepler and Newton. More pointedly: He tackled sunken land-bridge arguments for intercontinental exchanges of flora and fauna After his death, others, sporadically, continued to battle, some with fervor. Arthur Holmes, a committed drifter, noted, “proving Wegener wrong [on many details] is by no means equivalent to disposing of continental drift” Note: Wegener argued that motion was clear and that it was up to others to come up with a cause (the motor). He proposed that isostasy made it easier, as well as radioactivity (noted above)

29. Typical Controversy Arthur Holmes defends drift and proposes that continents are carried on backs of convection cells (see next two slides), driven by heat of radioactivity. This proposal solved theory puzzle: How could soft rock of continents push through ocean floor of hard rock? It would be like stick of butter pushing through steel plate Harold Jeffries, a consummate mathematical geophysicist, dramatically disagreed with Wegener and Holmes How possible? Different assumptions about the unknown (and then partly unknowable)

30. Holmes’ Model Of Earth Convection

31. Convection Demonstration Model of convection cell in operation

32. Sir Arthur Holmes (1890-1965)

33. Typical Reaction to Drift Proposal “If we are to believe Wegener’s hypothesis, we must forget everything which has been learned in the last 70 years and start all over again.” R. T. Chamberlin (1928)

34. Typical Reaction To New Ideas Opposition to Wegener’s ideas on continental drift were illustrative of opposition to new ideas that “upset” established views of how Nature behaves, as in Chamberlin’s comment

35. Winter Weather Warning Please check your email Wednesday morning before coming to class: A blizzard is predicted to start on Tuesday and continue until mid-day on Wednesday; if it materializes, I may have to once again postpone class and to make it up at a later date