Saturday Morning Physics

1. 12/15/01 Saturday Morning Physics 1 Lectures on String Theory Music of the spheres � Lectures on string theory; Lecture 3 : M stands for MysteryMusic of the spheres � Lectures on string theory; Lecture 3 : M stands for Mystery

2. 12/15/01 Saturday Morning Physics 2 Outline of the series Outline of Saturday morning lecturesOutline of Saturday morning lectures

3. 12/15/01 Saturday Morning Physics 3 Summary last week

4. 12/15/01 Saturday Morning Physics 4 Interacting strings Only approximately known through �tube� diagrams Strength of interactions determined by the string coupling and only when this number is smaller than 1 can we use our approximate description in terms of �tube� diagrams Strong string interactions roughly correspond to strong gravity, in which case the �tube� diagram approximation is no longer under control

5. 12/15/01 Saturday Morning Physics 5 String theory vs. quantum field theory

6. 12/15/01 Saturday Morning Physics 6 Superstrings and the correspondence principle If the length scales under consideration are much larger than the string length a point-particle description should be a good approximation At low energies we therefore approximately obtain supersymmetric quantum field theories including gravity ; supergravity

7. 12/15/01 Saturday Morning Physics 7 Introducing D-branes D stands for Dirichlet; a mathematician A surface on which open strings end; Dirichlet boundary conditions Think of it as an open string soap-bubble (membrane) Embedded in a closed string theory They have charge Q, mass M and p extended directions No force between N parallel D-branes ! We can use our string �tube� diagram approximation when gravity is weak, so when the mass M of the D-brane is small Think of open string (soap) bubbles; square soap bubble demoThink of open string (soap) bubbles; square soap bubble demo

8. 12/15/01 Saturday Morning Physics 8 Black hole physics Created when nothing can stop the gravitational attraction Space-time singularity, black hole horizon surrounding the no escape zone (Schwarzschild radius) Elementary particle�s uncertainty in position is usually larger than its Schwarzschild radius No longer true when Planck scale energies are involved! Black holes have mass, charge and can rotate, but that�s it Rubber sheet demo; from a lead ball to a black hole Sun R_g = 3 km (radius sun=700000 km), electron�s R_g = 10 �25 cm Temperature black hole: extremely small; Hawking radiation; fast for small bh�s but extremely slow for large bh�s.Rubber sheet demo; from a lead ball to a black hole Sun R_g = 3 km (radius sun=700000 km), electron�s R_g = 10 �25 cm Temperature black hole: extremely small; Hawking radiation; fast for small bh�s but extremely slow for large bh�s.

9. 12/15/01 Saturday Morning Physics 9 Black hole �quantum� physics Black holes emit black body Hawking radiation (tiny) Can be assigned a temperature and entropy Entropy is a measure of disorder or randomness We lack a microscopic understanding

10. 12/15/01 Saturday Morning Physics 10 Black p-brane solutions Extended generalizations of black hole solutions Classical solutions of supergravity; General Relativity plus generalized electromagnetic fields Sources have a mass M, a charge Q and p extended directions (p=0: black hole); �heavy objects� What do they correspond to in string theory? Supergravity and black p-brane solutions; Rubber sheet, the heavy cylinder.Supergravity and black p-brane solutions; Rubber sheet, the heavy cylinder.

11. 12/15/01 Saturday Morning Physics 11 From D-branes to black holes D-brane picture valid at weak gravitational coupling; small # of D-branes A black hole appears at strong gravitational coupling; large # of D-branes Understanding of black holes in terms of D-branes and open strings! Add area law and Hawking radiationAdd area law and Hawking radiation

12. 12/15/01 Saturday Morning Physics 12 String dualities Strings are very useful objects to consider at weak coupling We like strings because they can deal with graviton exchange Degrees of freedom can change; e.g. consider water and ice Something similar happens in string theory; at strong coupling new (weakly coupled) degrees of freedom can be used in an approximate description This phenomenon is generally called a duality Particle/wave duality Strong/weak coupling duality (electric/magnetic) Electric and magnetic field lines demo!Electric and magnetic field lines demo!

13. 12/15/01 Saturday Morning Physics 13 The hidden eleventh dimension Highest dimension for supergravity theories Gives a ten-dimensional supergravity (IIA) when wrapped on a circle and the radius turns out to be related to the string coupling ! Small string coupling = 10 dimensions Strong string coupling = 11 dimensions Strings turn into Membranes Wrapping the rubber sheet around the cylinderWrapping the rubber sheet around the cylinder

14. 12/15/01 Saturday Morning Physics 14 What is M-theory? Membrane, Mystery, Mother, Magic, �

15. 12/15/01 Saturday Morning Physics 15 What about experiments? Never say never, we are working on it One ongoing single big �experiment� is very promising (in my humble opinion)

16. 12/15/01 Saturday Morning Physics 16 Summary of today�s lecture String theory, using D-branes, has given us some clues about the constituents of some black holes Five superstring theories are approximate corners of a more fundamental structure called M-theory We do not yet know what M-theory is Involves membranes, eleven dimensions and more

17. 12/15/01 Saturday Morning Physics 17 Credits: The internet in general, but in particular: www.particleadventure.org www.superstringtheory.com The highly recommended book: �The Elegant Universe� by Brian Greene The SMP crew: David Gerdes, Carol Rabuck Demos: Angela Plagemann, Mark Kennedy, Warren Smith Sponsor: Dr. M. Lois Tiffany