Gravitational Waves as a Probe of the Early Universe

1. Gravitational Waves as a Probe of the Early Universe Scott Dodelson, AAAS Meeting

2. Consider the United States in 1790 • Over-densities of order 50 • Concentrated in East • Vast Voids with low density Scott Dodelson, AAAS Meeting

3. Consider the United States Today • Over-densities of order 10,000 • Concentration in coasts • Traces of primordial density (Boston-Washington; East > West) • Vast Voids Scott Dodelson, AAAS Meeting

4. The story of this evolution is the story of the United States • When we understand the evolution from one map to another, we can understand • the sociological, economic, and political forces acting on the US • the people, or the constituents, of the US Scott Dodelson, AAAS Meeting

5. Less parochially, we rely on cosmic maps This map of the Cosmic Microwave Background (CMB) shows that the photon/baryon distribution was smooth to one part in 10,000 at t=400,000 years. WMAP Today, there are huge overdensities: the density in this room is 1030 larger than in an average spot in the Universe Sloan Digital Sky Survey Scott Dodelson, AAAS Meeting

6. Less parochially, we rely on cosmic maps This map of the Cosmic Microwave Background (CMB) shows that the photon/baryon distribution was smooth to one part in 10,000 at t=400,000 years. Modern Cosmology quantitatively explains this evolution: Gravitational Instability WMAP Today, there are huge overdensities: the density in this room is 1030 larger than in an average spot in the Universe Sloan Digital Sky Survey Scott Dodelson, AAAS Meeting

7. Quantifying Cosmic Evolution has led to great Discoveries Dark Sector Cosmic Web Galaxy Formation Kravtsov et al. Scott Dodelson, AAAS Meeting

8. Lingering Question Who/what planted the seeds of structure? Scott Dodelson, AAAS Meeting

9. Was it even possible? How are these two spots correlated with one another? Hubble Radius(Distance light travels as the Universe doubles in size) at t=400,000 years Scott Dodelson, AAAS Meeting

10. The Horizon Problem Distance between 2 spots in CMB Distance Hubble Radius t = 400,000 yrs Time Scott Dodelson, AAAS Meeting

11. The Horizon Problem Distance between 2 spots in CMB Distance Hubble Radius t = 400,000 yrs Time Scott Dodelson, AAAS Meeting

12. The Horizon Problem Distance between 2 spots in CMB Be careful extrapolating backwards … Distance Hubble Radius t = 400,000 yrs Time Scott Dodelson, AAAS Meeting

13. Expansion is Governed by the Constituents of the Universe • Early times correspond to large energies • The Standard Model of Particle Physics has been tested up to ~100 GeV • Higher energies/earlier times might bring new particles/forces Scott Dodelson, AAAS Meeting

14. Probe Unification of Physics at High Energy LHC Seeds of Structure Tevatron George Rieke Scott Dodelson, AAAS Meeting

15. Inflation Solves the Horizon Problem Distance between 2 spots in CMB Distance Hubble Radius Inflation t = 400,000 yrs Time Scott Dodelson, AAAS Meeting

16. The Seeds of Structure Einstein’s Theory of General Relativity associates over-dense regions with distortions in the fabric of space-time. What was distorting Space-Time during Inflation? Scott Dodelson, AAAS Meeting

17. Quantum Mechanical Fluctuations Ubiquitous on the sub-atomic level … Inflation stretches them to astronomical sizes Scott Dodelson, AAAS Meeting

18. Seeds of Structure • Quantum mechanical fluctuations generated during inflation • Perturbations freeze out when distances get larger than horizon • Evolution when perturbations re-enter horizon Distortions in Space-Time Scott Dodelson, AAAS Meeting

19. Sealing the Deal & Identifying the Physics Einstein’s theory allows for different types of distortions in the fabric of space-time. Seeds of structure are scalar or density perturbations. There are also tensor perturbations or gravitational waves. Scalar/Density Tensor/Gravitational Waves Scott Dodelson, AAAS Meeting

20. Gravitational Waves are Produced, e.g., in Collisions of Black Holes But they are also produced microscopically due to quantum mechanics … just like density perturbations. Scott Dodelson, AAAS Meeting

21. How can we detect Primordial Gravitational Waves? Measure Polarization of Cosmic Microwave Background Backer, Jaffe, Lommen 2003 Primordial Signal Scott Dodelson, AAAS Meeting

22. Compton scattering of unpolarized anisotropic radiation produces polarization • Require Quadrupole (small before t=400,000 yrs) • Require Compton scattering (rare after t=400,000 yrs) • Signals factor of 10 smaller than temperature anisotropies Scott Dodelson, AAAS Meeting

23. Polarization field decomposed into E- and B- modes Mission Concept Study: Theory 2008 Scott Dodelson, AAAS Meeting

24. Polarization field decomposed into E- and B- modes Density perturbations produce only E-modes Mission Concept Study: Theory 2008 Scott Dodelson, AAAS Meeting

25. Polarization field decomposed into E- and B- modes Density perturbations produce only E-modes Mission Concept Study: Theory 2008 Gravity waves produce E- and B- modes Scott Dodelson, AAAS Meeting

26. Results E-modes have been detected: their spectrum agrees with theoretical prediction Samtleben, Staggs, & Winstein 2008 Scott Dodelson, AAAS Meeting

27. New QUAD Results Pryke et al. 2008 Scott Dodelson, AAAS Meeting

28. Scientists are voting with their feet Scott Dodelson, AAAS Meeting

29. Scientists are voting with their feet Scott Dodelson, AAAS Meeting

30. We have sharpened questions that have been asked for millennia … “Who Created These?” Isaiah 40:26 What physics drove inflation in the early universe, thereby producing the seeds of structure? … and we have real hopes of answering them over the coming decade. Scott Dodelson, AAAS Meeting