April10

Announcements Today is the last chance to pick up and to deal with corrections to Assignment 2! ● The final exam is coming! Today and Thursday after class are Q&A Sessions: MP203 w/ the TAs, and Thursday here with me or with the TAs in MP203. ● ● Thursday is a review class Exam Format: ● 40 multiple choice: (Similar to, and in some cases the same as the Weekly Quizes) 8 Short Answer questions – chose 6: ● One may bear striking resemblance to one of the assignment questions ● The cover the whole semester, with more weight on the 2nd half. Very similar in format to the midterm.... ● Era of Galaxies (Now) Galaxies form at age ~ 1 billion years Era of Atoms (era of just gas) From the cooling of the primordial plasma at age ~ 380,000 yrs to the formation of stars and galaxies. Era of Nuclei (era of the primordial plasma) Universe is filled with an ionized Hydrogen/ Helium plasma. CMB released at the end of this era. Era of Nucleosynthesis Universe hot enough for nuclear fusion. This is when most of the Helium in the Universe is formed! 0.001s to 3 min after the Big Bang! Particle Era Different elementary particles freely change into each other (photons, Protons, antiprotons, Electrons, etc..) Nearly equal amounts of Matter and Antimatter. Proton Annihilation Photons Antiproton Particle Era ends... when T gets too low to make protons and antiprotons out of photons. there was 10-7% more matter than anti-matter... So.. we have something left! Why? This is another one of the great unsolved problems in physics... Electroweak Era Radiation and matter are essentially indistinguishable. The end of the electroweak era is approximately at the highest temperatures that have ever been studied... GUT and Planck Eras... Eras of speculation... We know that we do not understand the physics of whatever happens during these periods. General relativity and Quantum mechanics both matter – and we can't merge them yet. Nature of the Universe.... Content Normal Matter ie, Stars, dust, cheesburgers Dark Matter ???? ie, ???? ie, neutrinos, Star Trek particles Expansion of the Universe: Accelerating Age of the Universe: 13.8 billion years Geometry of the Universe: Flat/Euclidian Nature of the Early Universe: very smooth Confirmed by multiple observations: cmb, supernova, large scale structure, light element abundances.... WHY IS IT LIKE THIS??? COBE All Sky Map The Early universe was very very very uniform! The other effect of density: Geometry. Critical Density Universe (W=1) High Density Universe (W>1) Low Density Universe (W<1) Closed W>1 Flat W=1 Open W<1 Measured density W=0.25 Computer Simulations: Nature of the Universe.... Content Normal Matter ie, Stars, dust, cheesburgers Dark Matter ???? ie, ???? ie, neutrinos, Star Trek particles Expansion of the Universe: Accelerating Age of the Universe: 13.8 billion years Geometry of the Universe: Flat/Euclidian Nature of the Early Universe: very smooth Confirmed by multiple observations: cmb, supernova, large scale structure, light element abundances.... WHY IS IT LIKE THIS??? Inflation: an idea that may shed some light on these observations. Geometry of the Universe: Flat/Euclidian Nature of the Early Universe: very smooth Inflation: a neat idea.... Maybe, at very early times, back in the era of speculation, the universe went through a period of very rapid expansion. (a factor of 1030 -36 in only 10 s!) Things in contact no longer are after inflation... This produces smoothness. Inflation flattens out the curvature... If it started closed, it will still be closed, but will be very very close to flat... If it started open, it will still be open, but will be very very close to flat... As an added bonus, Inflation predicts there should be some (small) density fluctuations in the early universe... Quantum mechanics produces random fluctuations. These get inflated to the scale where they form the seeds of structure today. The properties predicted from inflation match observations of the CMB (eg, BOOMERANG, WMAP) Spider: Gravitational waves from Inflation Inflation should also produce gravitational waves. These might distort the CMB in a measurable way. Spider is a balloon borne telescope designed to measure this... We are building it right now.... Fine Tuning: Is the Universe Special? ● strong nuclear force constant if larger: no hydrogen; nuclei essential for life would be unstable if smaller: no elements other than hydrogen weak nuclear force constant if larger: too much hydrogen converted to helium in big bang, hence too much heavy element material made by star burning; no expulsion of heavy elements from stars if smaller: too little helium produced from big bang, hence too little heavy element material made by star burning; no expulsion of heavy elements from stars gravitational force constant if larger: stars would be too hot and would burn up quickly and unevenly| if smaller: stars would be so cool that nuclear fusion would not ignite, thus no heavy element production electromagnetic force constant if larger: insufficient chemical bonding; elements more massive than boron would be unstable to fission if smaller: insufficient chemical bonding ratio of electromagnetic force constant to gravitational force constant if larger: no stars less than 1.4 solar masses, hence short and uneven stellar burning if smaller: no stars more than 0.8 solar masses, hence no heavy element production ● ● ● ● Selected from www.reasons.org, a Christian motivated science/religion web page. The author, Hugh Ross is a UofT Graduate Fine Tuning: Is the Universe Special? ● ratio of electron to proton mass if larger: insufficient chemical bonding if smaller: insufficient chemical bonding ratio of number of protons to number of electrons if larger: electromagnetism dominates gravity preventing galaxy, star, and planet formation if smaller: electromagnetism dominates gravity preventing galaxy, star, and planet formation expansion rate of the universe if larger: no galaxy formation if smaller: universe collapses prior to star formation entropy level of the universe if larger: no star condensation within the proto-galaxies if smaller: no proto-galaxy formation mass density of the universe if larger: too much deuterium from big bang, hence stars burn too rapidly if smaller: insufficient helium from big bang, hence too few heavy elements forming ● ● ● ● Selected from www.reasons.org, a Christian motivated science/religion web page. The author, Hugh Ross is a UofT Graduate Fine Tuning: Is the Universe Special? ● velocity of light if larger: stars would be too luminous if smaller: stars would not be luminous enough initial uniformity of radiation if smoother: stars, star clusters, and galaxies would not have formed if coarser: universe by now would be mostly black holes and empty space ● fine structure constant (a number used to describe the fine structure splitting of spectral lines) if larger: no stars more than 0.7 solar masses if smaller: no stars less than 1.8 solar masses if larger than 0.06: matter is unstable in large magnetic fields ● ● mass excess of the neutron over the proton if greater: neutron decay would leave too few neutrons to form the heavy elements essential for life if smaller: proton decay would cause all stars to rapidly collapse into neutron stars or black holes initial excess of nucleons over anti-nucleons if greater: too much radiation for planets to form if smaller: not enough matter for galaxies or stars to form ● Selected from www.reasons.org, a Christian motivated science/religion web page. The author, Hugh Ross is a UofT Graduate Fine Tuning: Is the Universe Special? ● ratio of the mass of exotic (dark) matter to ordinary matter if smaller: galaxies would not form if larger: universe would collapse before solar type stars can form number of effective dimensions in the early universe if smaller: quantum mechanics, gravity, and relativity could not coexist and life would be impossible if larger: quantum mechanics, gravity, and relativity could not coexist and life would be impossible number of effective dimensions in the present universe if smaller: electron, planet, and star orbits would become unstable if larger: electron, planet, and star orbits would become unstable big bang ripples if smaller: galaxies will not form; universe expands too rapidly if larger: galaxies will be too dense; black holes will dominate; universe collapses too quickly uncertainty magnitude in the Heisenberg uncertainty principle if smaller: oxygen transport to body cells would be too small; certain life-essential elements would be unstable if larger: oxygen transport to body cells would be too great; certain life-essential elements would be unstable cosmological constant (dark energy) if too large: universe will expand too quickly for solar type stars too form ● ● ● ● ● Two BIG Questions: ● How did the Universe Begin? ● Why does the Universe appear to be 'fine tuned' to allow life? Two Answers: 1) An Intelligent Designer (eg, God) A Creator, who exists outside of knowable physics, created the Universe according to some plan or desire. Explains existence and fine tuning ? Requires big (though popular) assumption  (the existence of God) ? Does not seem to make testable predictions Two Answers: 2) The Anthropic Principle Imagine there are an infinite number of different 'Universes', each with different physical laws. Regardless of how unlikely 'observers' are, they will exist, but only in very special (rare) Universes capable of supporting them. Explains apparent fine tuning ? May make testable predictions.... ? Requires a big assumption  (the existence of infinite Universes) Note: answers 1 and 2 are not mutually exclusive... Other 'Answers'.... Maybe: Physics will eventually explain it all – fine tuning will go away, and it will all become clear.... Consciousness creates itself.... We live in The Matrix.... (what does this mean?) Evaluations: Prof A: C.B. Netterfield (Me) Prof B: Ray Jayawardhana Do not evaluate TAs on this form! Use Pencil or Black/Blue ball point pens. Do not use Red Ink or felt tip markers