1To Do TodayGuided writingClass discussionOverview: The Quantum World & SUSYPeer-led discussionReadings for next time10 minute guided writingWhat do you think about dark matter? What kind of evidence would you like to see cosmologists present to the public?to 3:052Let’s make a list . . .What questions would you like to see answered about dark matter if you were visiting a planetarium?Think about: parents, children, teachers, typical adults . . .to 3:10Class discussionIs it more "radical" to 'invent' a new form of invisible matter, or is it more radical to replace Newton's and Einstein's theory of gravity?If you think “dark matter” is more radical, come sit in the back two rows on the right side of the room (near the door).If you think “changing gravity” is more radical, come sit in the front two rows on the right side of the room.One volunteer from each group3Let’s make two lists . . .Dark matter PRO and CON (including questions you/we don’t know the answer to)Modified gravity PRO and CONDiscuss in your groups and then we’ll share on the boardto 3:20Overview: The Quantum WorldWhat is a “quantum”?to 3:404MACHOSto 3:40MACHOSThere cannot be enough stars, planets, comets, asteroids, etc. to make up the dark matter. We’re focusing the hunt for dark matter on the quantum world!to 3:405WIMPs: Weakly Interacting Massive ParticlesOverview: The Quantum WorldThese particles belong to the quantum world, so they have strange properties. Quantum “stuff” is both a wave AND a particle.to 3:40The Bohr atom vs. the electron cloud model6Overview: The Quantum World QM isn’t “deterministic” – instead it deals with probabilities. For example, a particle has a “wavefunction” that describes the probability of it being in each possible location. In a sense, the particle is in all of those locations.to 3:40The Bohr atom vs. the electron cloud modelInterpretations of Quantum Mechanicsto 3:40The Copenhagen Interpretation (Bohr and Heisenberg): the measurement process “collapses the wavefunction” or “picks one state.”7What is Schrodinger's Cat Paradox? (in his own words)"One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small that perhaps in the course of one hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid." -- Erwin SchrodingerTranslation by John D. TrimmerInterpretations of Quantum Mechanicsto 3:40 The Copenhagen Interpretation (Bohr and Heisenberg): the measurement process “collapses the wavefunction” or “picks one state.” The Many Worlds Interpretation: for every outcome with a nonzero probability, there is some world where that outcome occurred. All the “worlds” exist at the same time, as though they are in layers. Objective Collapse: wavefunctions will be collapsed by something objective, i.e. some physical threshold is reached. No tests can tell the difference between these scenarios! So they are philosophical questions (“metaphysics”), not scientific theories.8QM and Philosophyto 3:40Einstein: “God does not play dice with the Universe.”Bohr: “Stop telling God what to do!”The role of the “observer” as actually telling the Universe what to do is unsettling for many.QM and the “Standard Model” When QM was developed, we only knew about: Protons Neutrons Electrons Photons Discoveries of new particles: 1937, 1947, 1948, 1951, 1952 . . . We began to realize that these were not fundamental particles. They were made of smaller building blocks, called quarks. By the 1970s, we’d combined this information into the Standard Model of particle physicsto 3:409Fundamental Particles The Fermions are matter. Leptons and quarks cannot be broken down, but they can be converted to pure energy, and the heavy ones can decay to the light ones.  Bosons are responsible for “communicating the forces of nature between Fermions.” to 3:40Fundamental Particles Each Fermion has an “antiparticle” with the same properties but the opposite charge. If antiparticle pairs run into each other, they annihilate, releasing their energy to the Universe. This means that there must have been fewer anti-quarks and anti-leptons in the early Universe than quarks and leptons. Otherwise the Universe would be empty!to 3:4010to 3:40Interactions and Conservation Particles interact when they: Bump into each other, exchanging kinetic energy Gravitate towards one another Exchange photons (interact electromagnetically) Collide to produce new productsto 3:4011u+⅔u+⅔d-⅓Interactions and Conservation After an interaction, the Universe will have the same: Mass, energy, and electric charge “Colour” charge (quarks can have red, green, or blue colour charge, and the results must always have one of each. Example is a proton!)to 3:40u+⅔u+⅔d-⅓Interactions and Conservation After an interaction, the Universe will have the same: Mass, energy, and electric charge “Colour” charge (quarks can have red, green, or blue colour charge, and the results must always have one of each. Example is a proton!) The Universe ends up having a nice symmetry Every particle has an antiparticle with the same mass and an opposite charge This “principle of opposites” is important later! The totals always balance out!to 3:4012Fundamental Particles The photon “mediates” the electromagnetic force. The gluon is responsible for the strong force (it “glues” the Universe together) The W,Z bosons are responsible for the weak force What about gravity? We don’t know! If the Higgs exists, then particles that interact with the Higgs boson are permitted to have mass through that interaction.to 3:40How does this relate to dark matter?There are three “flavors” of neutrinos, very low-mass particles that interact with matter very rarely.If each of them had 1/100,000ththe mass of the electron, that could make a LOT of dark matter!If you want to find them, you need either a lot of neutrinos (i.e. a nuclear reactor) or a really big detector (i.e.