The Ultimate Structure of Matter Chapter 13 Great Idea: All matter is made of quarks and leptons, which are the most fundamental building blocks of the universe that we know.
Chapter Outline Of What is the Universe Made? Discovering Elementary Particles The Elementary Particle Zoo The Four Fundamental Forces
Of What is the Universe Made?
The Library Superficial description Fundamental building blocks Basic Books Rules for organization Words grammer Ultimate description Letters Spelling
Reductionism Reductionism Ultimate building blocks How simplicity gives rise to complexity True nature Thought, experiment, observation
The Building Blocks of Matter Fundamental building blocks Changed over time Atom Nuclei and electrons Elementary particles
Discovering Elementary Particles
Cosmic Rays Cosmic Rays Particles emitted by stars Used to understand nucleus Found new elementary particles
Particle Accelerators: The Essential Tool Particle Accelerator Artificial cosmic rays Ernest O. Lawrence cyclotron Synchrotron Linear accelerator
The Elementary Particle Zoo
Leptons, Hadrons, and Antimatter
Quarks and Leptons Quark Fundamental building blocks of hadrons Fractional electrical charge Only six kinds Leptons Six kinds Outside nucleus
Quark Confinement Individual quarks No experimental isolation of a quark Elementary particles Difficult to isolate
iclicker Question Which of the following are the fundamental building blocks of matter in the universe: A atoms and molecules B quarks and leptons C planets and stars D energy and waves
iclicker Question The quest for the ultimate building blocks of the universe is referred to by philosophers as: A reductionism B science C atomism
iclicker Question Which of the following lists has the items listed correctly from smallest to largest? A B C D E atom, quark, nucleus, neutron, molecule neutron, quark, nucleus, atom, molecule quark, neutron, nucleus, atom, molecule nucleus, quark, neutron, atom, molecule molecule, atom, nucleus, neutron, quark
iclicker Question The main working part of a synchrotron is: A a large ring of magnets B a nuclear fusion generator C a flux capacitor D a diode
iclicker Question True or False: Moving charged particles are not affected by magnetic fields. A True B False
iclicker Question Which elementary particle does not take part in holding together the nucleus? A antiparticle B hadron C lepton D All of the above take part
iclicker Question Which type of elementary particle exists inside the nucleus? A Electron B Hadron C Lepton D All of the above exist in the nucleus
iclicker Question True or False: For every particle in the universe, it is possible to produce an antiparticle. A True B False
iclicker Question What does PET (as in PET scan) stand for? A patient electrocardio torture B positron emission tomography C patient electro transmission
iclicker Question Which of the following is made from quarks? A hadrons B leptons C electromagnetic
Reviewing Subatomics
Reviewing Subatomics
Reviewing Subatomics
Reviewing Subatomics
Reviewing Subatomics Neutrinos are produced in the Weak Interaction, for example Neutrinos from the earth natural radioactivity Man-made neutrinos accelerators, nuclear power plants. Astrophysical neutrinos Solar neutrinos Atmospheric neutrinos Relic neutrinos left over from the big bang.
Neutrino Factoids The earth receives about 40 billion neutrinos per second per cm 2 from the sun. About 100 times that amount are passing through us from the big bang. This works out to about 330 neutrinos in every cm 3 of the universe! By comparison there are about 0.0000005 protons per cm 3 in the universe. Our body emits about 340 million neutrinos per day from 40 K. Neutrinos don t do much when passing through matter. Remember, it is very difficult to observe neutrinos.
Neutrino Detection The neutrino is observed by detecting the product of its interaction with matter. ν e ν μ Electron Muon
iclicker Question True or False: Quarks have actually been isolated and observed in the laboratory. A True B False
The Four Fundamental Forces
The Four Fundamental Forces
Force as an Exchange Forces cause matter to accelerate Gauge particle Produce fundamental forces
Unified Field Theories Unified Field Theories Fundamental forces seen as different aspects of one force Four fundamental forces may be different aspects of a single force Electroweak force Standard model Theories of Everything
iclicker Question How many fundamental forces are there? A 2 B 4 C 6 D 11 E 21
iclicker Quesiton Which of the four fundamental forces is the strongest? A strong force B weak force C gravity D electromagnetic
iclicker Question Which of the four fundamental forces is the weakest? A strong force B weak force C gravity D electromagnetic
iclicker Question True or False: The search for a theory of everything will be accomplished in my lifetime. A True B False
String Theory: the idea All matter consists of small onedimensional objects (strings). Strings look like particles when not resolved closely enough All particle types are different normal modes of the string.
String Theory: the interactions All interactions consist of the splitting and joining of these elementary strings. This is currently the best description of the scattering of gravitational waves at very high energies! Looks like General Relativity plus other interactions at low energies. No parameters: string length sets units.
Possible Downsides At first sight there appeared to be a number of different kinds of string theories. Open, closed, heterotic, Type I, Type IIA,... Predicts we live in 10 spacetime dimensions! Experimental update: number of (large) dimensions = 4 Very difficult to experimentally test so far. Strings are so short that once the symmetries and spectrum are gotten right, most of the details are usually also right. Calculation gets known masses right, but.. experiment m exp = 0.00. 005 theory m th = 0.00000000
D-Branes Polchinski String theory is bigger than previously thought. Normally, open strings satisfy Neumann boundary conditions, string ends move at light speed. Dirichlet boundary conditions also make sense string ends live on a surface. This surface is interpreted as a large massive object, a D- brane, in spacetime, much like a monopole.
Why Do This? Good Things Happen if the theory has both strings and D-branes: Previously-hidden duality symmetries emerge, with all known string theories dual to one another under these symmetries! Some weakly-interacting string theories are the duals of the strong-coupling limit of others! Led to discoveries of similar symmetries amongst ordinary particle theories. Conjecture: all known string theories are different solutions to a more fundamental (11-dimensional) theory (M Theory).
String Length and Gravity Arkani-Hamad, Dvali & Dimopoulos Could strings be as big as they can be: l s = l w? Non-gravitational physics is characterized by the weak scale: G F = l w2 = (10-3 fm) 2 If so, strings may be experimentally discovered tomorrow! If so, does this explain why l w is so much larger than l p = 10-19 fm? ie: Why is gravity so weak? Why are stars so big? Gravity would be weak because the extra dimensions are large: If n = 2 then l s = l w requires a ~ 0.1 mm!! If n = 6 then l s = l w requires a ~ 10 5 fm, a = α effl s l pl 2/n l s
Intermediate-Scale Strings CB, Ibanez & Quevedo Q: Can l s and a be similar in size? A: Yes. l s / a = 0.01 works if: I: l s = (l w l p ) =10-11 fm. l w = l 2 s / l p naturally arises if supersymmetry breaks on another brane, and is transmitted to our brane by gravity. II: n = 6 extra dimensions. No heirarchy need be dialed in. Other nice things also happen if so: String axions can solve strong CP problem, neutrino masses similar to experiments, etc l pl l w α eff = l s a = 0.01 = l 2 pl 2 l s = α eff 2 l s a n
String Summary String theory is the only known theory where gravity and quantum mechanics co-exist at high energies. Major Lesson of the 20 th Century: Relativity and Quantum mechanics are almost inconsistent, and so together impose extremely strong self-consistency conditions. The string length is likely much longer than the Planck length. Size Matters: much better prospects for comparison with experiments. The intermediate scale is well motivated on particlephysics grounds: l s = (l w l p ) =10-11 fm. We may all be Brane bound.
iclicker Question I find the idea that there might be 10 or 11 dimensions: A exciting B interesting C confusing D scary E nonsense