A Century of Paradigm Shifts in our Thinking About the Universe

Transcription

1 A Century of Paradigm Shifts in our Thinking About the Universe George R. Blumenthal Chancellor, UC Santa Cruz Professor of Astronomy and Astrophysics

2 Why start 100 years ago? Before 1910 there was no self-consistent model for the large-scale Universe. A foolish consistency is the hobgoblin of little minds --- Ralph Waldo Emerson

3 Despite Emerson s views, we would like models for the Universe to be internally consistent. We also want models that are predictive i.e. that can be tested. We want models that successfully meet observational tests.

4 Paradigm Shift No. 1 Einstein uses his new General Relativity theory to make consistent models for the Universe. -- But the damned model predicts that Universe is expanding!

5 Paradigm Shift No. 1 So back to the drawing boards for Einstein, who modifies general relativity to get a universe that doesn t expand. Einstein introduces his Cosmological Constant But his static universe is unstable. Not good!

6 Paradigm Shift No : Edwin Hubble discovers that the Universe is expanding! More distant galaxies expand away from us faster.

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10 Paradigm Shift No.2 (cont.) Einstein laments that his cosmological constant is his greatest mistake But is it really???

11 1948 Two Proposed Paradigm Shifts On April 1, Alpher, Bethe, and Gamow suggest the hot big bang model, which predicts a relic microwave radiation background. They thought that all elements heavier than H could be produced in the early universe. Efforts to discover the microwave radiation failed.

12 1948 Two Proposed Paradigm Shifts Bondi and Gold (and Hoyle) proposed the steady-state Universe, with accelerating expansion driven by continuous creation of matter. The battle between big bang and steady state raged for two decades.

13 1965: Paradigm Shift No.3 Penzias & Wilson discover the 3 degree microwave background radiation. The steady-state model is dead (or is it?)

14 1965: Paradigm Shift No.3 The hot big bang model correctly predicts all light element abundances in the Universe and the background spectrum. But a few loose ends still kept cosmologists up at night worrying.

15 1980: Paradigm Shift No. 4 Most of the matter in the Universe is invisible DARK MATTER. We detect dark matter through its gravity. Visible matter (which emits or absorbs light) is only about 15% of the mass in the Universe.

16 Dark Matter Evidence Vera Rubin showed that the speed of stars rotating around their parent galaxy requires much more mass than we see in stars.

17 More Dark Matter Evidence

18 Yet More Dark Matter Evidence Gravitational lensing of distant galaxies by clusters requires more mass than we see in the cluster.

19 Paradigm Shift No The dark matter is cold dark matter, which does not consist of protons, electrons, etc. Photinos?? to be seen LHC??

20 Paradigm Shift No This correctly predicts both the sizes of galaxies and the irregularities in the microwave background radiation.

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24 Paradigm Shift No. 6 The expansion of the universe is accelerating. An unexpected result from Keck. 73% dark energy 23% dark matter 4% ordinary matter

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26 Paradigm Shift No. 6 We really do need Einstein s cosmological constant (also called dark energy or quintessence.) Maybe Einstein gets the last laugh!

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29 The Past and Future of the Universe

30 Paradigm shift No. 7 (incomplete) Inflation At early times the Universe expanded by an enormous amount then reheated. Model has passed several observational tests.

31 Paradigm shift No. 7 (still incomplete) Quantum physics is responsible for galaxies and clusters of galaxies. Might even have eternal inflation, with continuing creation of big bangs like the steady-state Universe.

32 Eternal Inflation The Universe expands forever at an accelerating pace. New Big Bangs crop up all the time we are in one of those bubble big bangs. Our little bubble is our universe. Can this be tested? Is it science?

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34 Why is the Universe Matter Rather than Antimatter?? Is this Paradigm Shift 8?? We know there are about 10 billion photons for every proton of matter in the Universe. Why not antimatter? We can explain with GUTs but cannot predict number yet. This does predict the proton decays with lifetime greater than yrs

35 In Conclusion There are still many, many unanswered questions eg What is the dark energy? Why 73%? What is the dark matter stuff? Explaining the asymmetry between matter and antimatter in the Universe.

36 Finally The 21 st century promises to be just as interesting as the last one! Anyone for a new paradigm shift or two?