How I Stopped Worrying and Learned to Love the Universe

1. How I Stopped Worrying and Learned to Love the Universe Marilena LoVerde Columbia University Hubble Deep Field, NASA seven sisters 2005

2. How I Stopped Worrying and Learned to Love the Universe • Evidence for Dark Energy • Models of Dark Energy • Methods of detecting Dark Energy seven sisters 2005

3. The Expanding Universe • Matter Dilutes • Radiation redshifts seven sisters 2005

4. Data Sets Galaxy surveys 1-13 Billion yrs Photons decouple t ~ 300,000 yrs Supernova data 7 -13 Billion yrs NASA/WMAP Science Team SDSS Supernova Cosmology Project LBNL seven sisters 2005

5. What we find With accelerating expansion! Flat, homogeneous, and isotropic universe seven sisters 2005

6. What could cause accelerated expansion? Einstein’s Equations + First Law of Thermo. Fluid equation of state: pressure = w * energy density has w  -1/3 Weird, the energy of this stuff increases with volume, like a stretched rubber band. seven sisters 2005

7. What is this “Dark Energy”? • Vacuum Energy pressure = - energy density • Quintessence pressure = w(t) energy density • Modified gravity ? • . . . seven sisters 2005

8. Quantum Theory: Vacuum Energy? General Relativity: Gravity couples to absolute energy so we have to include this Ground state has a non-zero energy seven sisters 2005

9. Do we expect Vacuum Energy? We can calculate this from field theory: Standard Model particle physics predicts: vac~MEW4~1044eV4 Supersymmetric particle physics predicts: vac~MSUSY4~ 1048 eV4 But we observe: vac~ 10-11 eV4 A disagreement of 1059!!! seven sisters 2005

10. Another problem: Why now? We are here matter vacuum radiation seven sisters 2005

11. V()  Quintessence Scalar field, potential dominates over kinetic energy Can solve the coincidence problem Quintessence can also cluster seven sisters 2005

12. Modified Gravity Extra dimensions? seven sisters 2005

13. How can we learn more about dark energy? • From Earth we measure: radiation fluxes, redshifts, and angular sizes of things flux  1/d2flux, z dL(z) size   d  , z dA(z) z redshift~ time These are exactly what we need to infer the expansion history seven sisters 2005

14. Type Ia supernova Intrinsic luminosity can be determined from light curve: European Southern Observatory Flux  luminosity/d2 Saul Perlmutter Standard Candle seven sisters 2005

15.  x d(z) Baryon Oscillations Matter Power Spectrum Acoustic oscillations “bump size” can be calculated M. White astro-ph/0507307 “Standard Ruler” seven sisters 2005

16. In an accelerating universe: grav(t2) grav(t1) Another Probe: Integrated Sachs-Wolfe Effect seven sisters 2005

17. My Research • Can we distinguish between vacuum energy and quintessence? • How can experiments be optimized? • Have we taken everything into account? seven sisters 2005

18. Conclusion • Cosmologists have learned a lot but mostly we have learned we know very little • Determining the nature of dark energy is of great importance in cosmology and particle physics • There’s lots to be done to help! seven sisters 2005

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20. Life of graduate physicists seven sisters 2005

21. Graduate Life Typically 2 years of courses and teaching, research first summer and during second year. ~4 years of full-time research, attending seminars, and journal clubs Also get sent to workshops and summer schools - good fun, free travel Living stipend (~$22,000/year), basic health insurance and tuition is paid by university for ALL PhD students seven sisters 2005

22. Is there time for anything else? Graduate study does take a lot of time more time than a regular job, but your schedule is more flexible. Plus, research, teaching, and learning physics can be very rewarding. In addition to work I have time and money for dinners, movies, and concerts with friends. Also bit of time to do volunteer work/outreach and I go biking or running daily. seven sisters 2005

23. Do you want to go? Most important thing I can say: DO research as an undergrad! Determine whether or not you like it. Also, attend colloquia, talk to your professors and search the internet to learn about different fields of research Other options: take time off : full-time research, Peace Corps, Teach for America, Cambridge Part III. . seven sisters 2005

24. What field? • Theory or experiment? • Large or small collaboration? • Do you mind/want to travel? seven sisters 2005

25. Applying (I) Apply to dream schools, realistic schools, and schools that will be very happy to have you. Find schools that are active in a variety of fields of research Contact professors and graduate students working on projects that interest you Apply to fellowships - really great practice writing essays, and fantastic if you get them: NSF, Hertz, DOE, DoD, NPSC . . . http://cuinfo.cornell.edu/Student/GRFN/ seven sisters 2005

26. Application (I) ~3 letters of rec, ask 6 weeks early if you can. Provide envelopes, forms, and due date. Ask people who know you beyond your grades in their course. Don’t feel bad about asking, it is part of your professor’s job. Do ask directly if they feel comfortable writing you a good letter. GRE, practice but don’t worry too much physicists have the highest average score! Physics GRE, ugh, take practice exams under timed conditions. Dimensional analysis and physical arguments can often eliminate 1-2 answers seven sisters 2005

27. Application (II) -Transcripts -Statement of interest: discuss previous research, what you did, what you learned from the experience. Start and end are the most important parts - make them strong. If you are interested in a specific group say so. Schools are interested in students who are able and likely to complete the program, demonstrate this in your essay. Also discuss your contributions to the community, experiences that solidified your desire to become a scientist seven sisters 2005

28. Decisions (I) Once you’re accepted schools will fund a visit to their department. Talk to the graduate students, ask them the best and worst things about the department. Are they happy? Does the department care about them? What percentage of students pass the qualifying exams? Is there more emphasis on teaching or research? Are you comfortable with the number of women in the department? seven sisters 2005

29. Decisions (II) Pick a school with several professors you are interested in working with Can you communicate with the professors you are interested in working with? Will they be able to take a student from your year? Consider the location, can you imagine yourself being happy and productive living there? Do you like your potential classmates? seven sisters 2005

30. Being there • Coursework is demanding, make friends to discuss your work with • Know that international students arrive more prepared - don’t feel bad about this! • Try to make some friends outside of the department so you don’t go nuts • Attend journal clubs, or suggest one • Initiate interactions potential research groups seven sisters 2005

31. Women in physics • Yes, mostly male • You are easy to remember • Can form community with other women seven sisters 2005

32. ….qualifying exams Most schools have some kind of qualifying exam. You will be tested on core topics (eg mechanics, E and M, quantum, stat mech.) at an advanced undergraduate or beginning graduate level. Most schools give you two chances to pass. Beware of schools that fail a fixed percentage of students. Quals are a pain, but think of it as a chance to solidify your knowledge, after all the next time you see the material you may be teaching it! seven sisters 2005

33. Reading • First Three Minutes by Steven Weinberg • Introduction to Modern Cosmology by Liddle • wikipedia.org surprisingly good physics reference • Modern Cosmology by Scott Dodelson • Early Universe by Kolb and Turner • xxx.lanl.gov - free archive of scientific publications, often very technical • Email me! marilena@phys.columbia.edu seven sisters 2005