the challenging Universe outline Einstein vs Newton and the solar eclipse of 1919 The missing mass problem Seeing the invisible: gravitational lensing Dark matter hunting Dr Roberto Trotta The challenging Universe: a critical view Imperial College London & Royal Astronomical Society Albert 1 2 3 4 Sir Isaac Einstein Vs Newton ECLIPSE SPLENDID. Deflection of light THROUGH CLOUD. HOPEFUL. May, 29th 1919 5 6
GRAVITY CENTRIFUGAL Observations Newton Seeing the invisible The Andromeda Galaxy (M31) Fritz Zwicky (1898 1974) 7 8 Seeing the invisible 9 10 11 12
13 14 Why Hubble? The Hubble space telescope An orbiting telescope the size of a school bus, Hubble goes around the Earth 15 times a day 15 16 The einstein ring distant galaxy Lens galaxy Strong gravitational lensing Earth 17 18
Visualizing Dark Matter Distant galaxy (original shape) Lens galaxy Distant galaxy (lensed shape) 19 20 200 million years after the Big Bang 1 billion years after the Big Bang 21 22 5 billion years after the Big Bang 13.7 billion years after the Big Bang 23 24
Weak lensing: everything is lensed The Millennium Simulation The Dark Matter Universe 25 But life is not always easy... How do we do it? In an ideal Universe: distant galaxies 26 The real Universe: the distant galaxies are randomly oriented and have ellipticities, too observed (lensed) galaxies distant galaxies Lensing (vastly exaggerated) 27 28 Image credit: Catherine Heymans Hunting for Dark Matter Sky (1 mile above) 29 Astronomer 30
the Big Bang machine E=mc2 31 32 the challenging Universe Cosmology is an observational science: we cannot make experiments! The frontier of physics It relies on (among other things): 1. The laws of physics are the same everywhere for all times 2. The cosmological principle: we are not in a special place 3. Einstein s theory of gravity is correct 33 A critical view 34 A critical view 1. The laws of physics are the same everywhere for all times 2. The cosmological principle: we are not in a special place Indications from quasar spectra that the fine structure constant was smaller in the past (note: now the observations are in doubt) But we are! We could not live in intergalactic space or immediately after the Big Bang (selection effects) The early Universe was very different from the modern Universe: inflation, unification of forces, quantum gravity The Multiverse hypothesis: we must inhabit a patch that is hospitable for life 35 36
A critical view 3. Einstein s theory of gravity is correct We should not forget that gravity has been tested only on a limited range of scales. The extrapolation is huge!? tested extrapolation scale 1 mm 10 13 m 10 23 m 10 26 m lab tests Solar system Large scale structures visible Universe 37 38 cosmology marches on Cosmology is the dot com of the sciences. Boom or bust. It is about nothing less than the origin and evolution of the Universe, the all of everything. It is the boldest of enterprises and not for the fainthearted. Cosmologists are the flyboys of astrophysics, and they often live up to all that image conjures up. Prof Mike Turner, Theoretical Cosmologist, University of Chicago Some healthy skepticism [...] Some of the recent claims for cosmology are grossly overblown. Cosmology rests on a very small database: it suffers from many fundamental difficulties as a science (if it is a science at all) whilst observations of distant phenomena are difficult to make and harder to interpret. It is suggested that cosmological inferences should be tentatively made and skeptically received. Prof Mike Disney, Astronomer, Cardiff University 39 40 rutherford had his own views... Don t let me hear anyone use the word Universe in my Department! Attributed to Ernest Rutherford, Nobel Prize in Chemistry 1908 41