1 All but 4 percent: Dark Matter and Dark Energy

2 Our story begins in 1933…

3 The Coma Cluster of Galaxies and Astronomer Fritz Zwicky Slow down – You move too fast!

4 The Coma Cluster of Galaxies and Astronomer Fritz Zwicky Why don’t you fly apart?

5 The Coma Cluster of Galaxies and Astronomer Fritz Zwicky If the Stars don’t weigh enough…

6 The Coma Cluster of Galaxies and Astronomer Fritz Zwicky Then something else does! Dark Matter!

7 40 years later, Vera Rubin shows galaxies spin too fast to hold together… Stars and gas rotate with speed V around the center of NGC 3198 (Image from Begeman 1989) Measuring spectra of galaxies to infer velocity from Doppler shifts (c. 1970)

8 …unless held together by dark matter! Although diffuse, dark matter is crucial for galaxy formation Credits: Left: J. Kormendy (NGC 4216). Right: K. Begeman (NGC 3198) and K. Freeman GM(r)=rV c 2 (r) Dark matter Luminous galaxy Embedded in cloud of dark matter

9 Recipe for our Universe! Credit: NASA/GSFC Photons: 0.03% Neutrinos: 0.3% Atoms: 4% Dark Matter: 23% Dark Energy: 73%

10 4% does not gain admission to this show!

11 What is the dark matter?

12 What is the dark matter? Not electrons, protons, or neutrons, even if they do not “shine” as stars (nuclear fusion in the early universe would drastically overproduce Helium)

13 What is the dark matter? Not known elementary particles or combination thereof

14 Our best guess for the dark matter since 1977: A new elementary particle generically called a Weakly Interacting Massive Particle, or WIMP

15 How will we test this hypothesis? Produce it in high-energy particle physics collisions Simulated production of neutralino WIMP at a future International Linear Collider (c. 2025) Credit: Norman Graf, SLAC

16 How will we test this hypothesis? Watch it annihilate with anti-matter NASA/DOE Fermi Gamma- Ray Space Telescope and other satellite and balloon experiments looking for this now! Image credit: Sky & Telescope/ Gregg Dinderman

17 How will we test this hypothesis? When it hits us, we will know it (or will we?) Many laboratory experiments are searching for atomic recoil from WIMP collisions. Image credit: Discover/ Michael Attisha

18 When a WIMP hits me, I’ll know it… Cryogenic Dark Matter Search detector element in deep freeze (0.1 K), ½-mile underground in Soudan, MN This experiment has not seen WIMPS yet, but has placed the best current limits on their properties if they exist. See Technology Review May/June 2009!

19 But wait, there’s more!

20 A Strange Universe Why are distant galaxies accelerating away from us?

21 How to describe the expanding universe Galaxies rushing apart on their own Stretching of space

22 Imagine a repulsive force that grows with distance between every pair of atoms What would happen?

23 Co-Discoverer of Cosmic Acceleration Johns Hopkins Professor MacArthur Award Winner Adam Riess MIT SB 1992

24 A cancer has taken over the cellular machinery of space! Linder 2008 Scholarpedia

25 What is the cosmic carcinogen? 1. Einstein’s Cosmological Constant added to his theory of gravity – revoked, and… …resurrected by modern physics as quantum fluctuations of the vacuum.

26 What is the cosmic carcinogen? 2. Exotic new forms of energy, Dark Energy, behaving similarly to the quantum vacuum.

27 What is the cosmic carcinogen? 3. Maybe Einstein’s theory of gravity is wrong. Phillip Zukin, physics graduate student

28 What is the cosmic carcinogen?

29 How can we find out?

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32 Study the growth of cosmic structure after the big bang – gravity writes history.