The Beginning and the End

Transcription

1 The Beginning and the End Encompassing material from Seeds, Chapter 18 A Brief History of Beginnings Non mythological beginnings, that is Georges Lemaître and his primordial atom Vatican Astronomer Alexander Friedman: Big Bang Russian Mathematician He didn t name the beginning The Big Bang It wasn t remotely big and it didn t go BANG! A pejorative term given by Sir Frederick Hoyle Einstein wasn t comfortable with either theory, although he did verify the correctness of Friedman s mathematics N.B. We will have to think in very, v-e-r-y short times scales here! The Evidence 1

2 Hubble s Law Edwin Hubble found that, the more distant the galaxy, the faster it was receding from us H o is the slope of this line Currently is thought to be ~ 73 H o is in units of km/sec/mpc Ultimately units of time Gives us the age of the Universe! / Gyr The Rationale: According to the Red Shift of distant galaxies, the Universe is expanding If the Universe is expanding, we can run the clock backwards and find the starting point (whatever that means) Important! Wrap your minds around this: By the beginning we don t mean that all the matter and energy exploded into an existing space. We mean that all matter, energy, SPACE and TIME all began at this singular point. Definitions 123rf.com Homogeneous The same everywhere at a certain scale Isotropic The same in every direction 2

3 A way to plot space and time It tells you how much information you can have at a certain time, limited by the speed of light The x-y plane represents space and the z axis represents time Now is 0, past is -, future is + Not far in the past (white arrow) only nearby events can be known Events that happened long ago (gold arrow) can be known even if they were far away Light Cones String-Theory Stems from the transition from continuum Physics to quantum Physics at the turn of the 20 th C Starting in the 80 s the notion arose that strings were a better model for the basic constituents of matter Strings were on the Planck length scale m Since we can t see detail at that scale, particles would naturally be the first approximation First applied to describe strong interaction, but the theory generated gravitons, much to everyone s surprise And strings demanded 10 dimensions! 3

4 Feynman diagrams too convoluted to incorporate these extra dimensions Branes are introduced to explain interactions Dimensions M-Theory String theory required 9+1 dimensions However, this produced 5 equally valid variations! Unacceptable! A lesser known theory, Supergravity, postulated 10+1 dimensions Merging the two ideas resolved the 5 variations However, the addition of the 11 th dimension caused the strings to weave into Membranes 4

5 Insane in the (mem)brane A theory of the trigger Multidimensional Universe or multiverse Gravity is the weakest force because it stretches between branes and is diluted Intersection of branes initiates a BB So time didn t have to begin with the BB Other Dimensions Flatland, a Romance in Many Dimensions Edwin Abbott Abbott, 1885 A square and his wife in Flatland An introduction to greater dimensions Lisa Randall Astrophysicist at Harvard Leading Brane proponent Warped Passages: Unraveling the Universe's Hidden Dimensions See also David Deutsch, Hugh Everett 5

6 How the Universe Got Its Spots Jenna Levin and others propose a more topological description of cosmology than String Theory However it started Epochs We divide the early history of the Universe up into epochs: Planck Era: unknown by present theory t <10-43 sec GUT Epoch < t < sec Inflationary Epoch < t < sec Electroweak Epoch < t < sec Particle Epoch < t < 1 second 6

7 Continued Nucleosynthesis Epoch 1 sec < t < 3 min Nucleii Epoch 3 min < t < 380,000 years Atom Epoch 380,000 < t < 1 Gyr Galaxy Epoch 1 Gyr until now and beyond All times approximate Planck Epoch No Physics exists to describe the cosmos previous to this time: seconds (unless M-theory bears out) Impossibly high temperatures (10 32 K), inconceivably tiny universe (10-35 m) at the end of this brief epoch All four fundamental forces strong, weak, electromagnetic, and gravity- were expressed as one. Unified by the high energy/temperature into a single force GUT Epoch GUT stands for Grand Unified Theory It was during this epoch that the electro magnetic* force and gravity separated from the strong force Also known as symmetry breaking during a phase transition, (like water to ice) K Ending around seconds *AKA the electroweak force 7

8 TOE: Theory of Everything GUT: Grand Unified Theory Inflation occurred here, when gravity split from the other forces. Inflationary Epoch As the name implies, a period of enormous expansion The Universe grew from m to m To put this in perspective, think of the size of a proton compared to a parsec! The Universe cooled, as any expanding system of particles would, then reheated shortly after inflation ended. The energy used to push the Universe outward was released as heat A Note About Inflation Proposed by Alan Guth of MIT in the early 1980s, Inflation does a good job of explaining the Universe as we see it today During this era the early Universe expanded faster than the speed of light Not a violation of SR since nothing is actually moving > c It solves the flatness problem, the horizon problem, and the monopole problem Flatness: why (total energy density of the universe) is so close to crit Horizon: why the CMB varies so little Monopoles: N or S magnetic pole w/o the other 8

9 You are here Where Inflation Comes From Current theory holds that a different value of the cosmological constant, inflation, was present during this epoch This formed an inflaton field, a type of scalar field You can think of a scalar field like gravity near the ground the higher you go the more potential for falling fast you have Invoking a scalar field is common in theoretical physics, and perfectly legal, but it doesn t make a theory true. For that, real evidence is required And from observation, the Universe is in a period of inflation now, with the current scalar field being dark energy (whatever that is) 9

10 BICEP2 has found Primordial B-mode polarization CMB photons polarized by intense gravitational waves rapid inflation at s, earlier than thought How Inflation Fixes Flatness The Flatness problem: the ratio of the current energy density ( ) of the Universe to the critical density is 1 Doesn t seem like much, but when you allow for expansion and run the clock backwards, the ratio differs from 1 (perfectly flat) by one part in 10 60! This is about as likely as everyone in the world winning the California lottery every time in a row!! Inflation fixes this by essentially flattening all the bumps in the Universe, much like inflating a balloon smoothes out all the wrinkles is currently very close to zero; 0 means flat Better than COBE WMAP The red regions are where CMB photons, losing energy as they climb out of a gravitational potential, are red-shifted And the reverse, of course VERY small differences in T, a result of inflation The CMB predates stars and galaxies, but shows the boundaries of gravitational potentials where they can be expected to form 10

11 Dark Matter/Energy Horizons and Flatness are inter-related The geometry of the Universe is determined by the amount of dark energy* Left: the scale of the CMB fluctuations in the WMAP picture indicate curvature Open if the fluctuations < 1 / o 2 Flat if ~1 o, closed if > 1 o Ultimately determines the fate of the Universe *perhaps it s Vacuum Energy, the energy allowed in an empty void by quantum mechanics A More Familiar Negatively- Curved Shape WMAP Tells the Tale If the Universe is flat, the angle is 1 o If it is curved inward (closed) the angle is > 1 o If it is curved outward (open) the angle is < 1 o 11

12 How Inflation Fixes Horizons The temperature of the Universe is remarkably uniform on a large scale Planck Supersedes WMAP 2.5x WMAP resolution, measurements at 10 9 positions Latest age of the Universe: Gyr Horizons Think of a horizon as the furthest distance than can be seen for which there is time for light to travel If an event happens in one region that would affect another region, then there must be sufficient time for the effect to travel that distance Remember the light cone! Run the clock backwards. It turns out that, given the short time scales involved, there was insufficient time for energy to travel from one region to another, a necessary condition for a near-uniform temperature 12

13 The same smoothing function that inflation provided to solve the flatness problem also inhibited any thermal inhomogeneities that may have existed by pushing the horizon father away In other words, regions flew apart too fast and could not communicate with each other Events that occurred before inflation were wiped from the cosmic record You can almost say the Big Bang started with inflation! What Physicists call Initial Conditions How Inflation Fixes Monopoles A monopole is like a single-pole magnet, only as a North pole or a South pole, not a pair Quantum Mechanics predicts their formation from topological defects in the divergence of the four forces as the Universe cooled, part of the phase transition mentioned before Because inflation pushed the Universe to be so big so quickly, the few monopoles that may have formed are e-x-t-r-e-m-e-l-y rare. You may find 1 monopole in Mpc 3! The Universe is only Mpc 3 in volume Electroweak Epoch: after inflation During this time the Universe cooled enough for so-called symmetry breaking This is when the four forces fully divided Strong Nuclear Force Weak Nuclear Force Electromagnetism Gravity Epoch sometimes called quark soup 13

14 You are here Particle Epoch Quarks cool and form more massive particles Two up and one down = p+ Two down and one up = N Interactions abound m N > m p so more p than N Heavy decays to lighter 6p for 1N Too hot for nuclei to form Universe has cooled to 10 9 K by end of era The Freeze Out ; baryons cease to perish in the high temperature You are here 14

15 Nucleosynthesis Era Universe cools to 3000K 1s < 3 min Atoms formed (ionized): N half-life ~ 15 minutes By 3 minutes, 14p for 2N Some neutrons had decayed into protons 2p + 2N = He So out of 16 nucleons, 1 He for 12 H Hydrogen, including deuterium (75% by mass) Helium (25% by mass) Lithium (10 9 < He) Atom Epoch 3 min < t < 380,000 years Universe cools enough for electrons to attach to atoms Down to 18 K by end of era Universe becomes transparent, photons free to travel The Last Scattering CMB starts now! ½ of 1% of radio noise is CMB Stelliferous Era From about 380,000 years A.B.B (after the Big Bang) until now Galaxies at about 1 billion A.B.B Average temp = 3K The era of stars, galaxies, and us What we ve talked about most of the semester! Top down vs. bottom up Did massive clouds of gas form first, generating the stars (top down) or did stars form first, collecting into galaxies (bottom up)? Probably a combination Where gas was dense enough, stars formed first Where gas was rarefied, dark galaxies formed, later yielding stars Era will continue until the year 100 trillion A.B.B Youngest object ever 800MYr A.B.B 15

16 The First Stars The Universe at 2 Gyr Old Hubble Ultra Deep Field 1 million second exposure Red shifts allow for dating and therefore 3D imaging Looking back to 700 million years A.B.B. The last image shows a red galaxy, the earliest object ever imaged 16

17 And here we are today What will happen in the distant future? Fate 17

18 Vacuum and/or Dark Energy Very low energy density 1X10-8 ergs/m 3 If the whole Earth volume were V.E. it would be about 1 day s worth of electricity for 1 person The Quintessence ( ) is B-A-C-K! If true, then constants evolve Current Mix of Cosmological Stuff is very close to crit Or, if you prefer, CMB fluctuations very nearly 1 o Small changes in the proportions will change the shape of the Universe just might be Dark Energy A constant density Part of space-time itself, not residing within The Friedmann Equation A way to predict the future! See H, the Hubble parameter? is the average density of the Universe a is the scale factor, in essence, the distance scale is the curvature of the Universe (-1,0,1) is Einstein s revived cosmological constant: 18

19 Entropy vs Gravity (curvature) Entropy: a thermodynamic law dictating the inevitable march to disorder Simple disorder, like breaking glass Thermodynamics disorder: concentrations of energy, as in a star The arrow of time Gravity (curvature) pulls together (order), entropy corrupts (disorder) over time Expansion The Universe continues to expand Expansion occurs from dark energy Where matter is closely spaced, gravity (curvature) overwhelms Elsewhere wins And ultimately will win! The Future: The most likely* outcome will be the open Universe AKA The Big R.I.P. The actual density of the Universe is less than the critical density / c ~ 1 *Actually too small to ever measure accurately for proper prediction The Universe will expand forever Three Foreseeable Epochs (after the Stelliferous Era): The Time of Degeneracy The Time of Black Holes The Time of Photons 19

20 But first A way to get a handle on these massive time scales Remember from our first lectures, the idea of powers of 10? 10 1 = = = 1000, etc Let s define a cosmic decade, 10 t years 10 1 years is the first cosmic decade, 10 2 is the second, and so on The decade is t Like stairs where every next step is 10X the height of the last We are in the 10 th cosmic decade The Stelliferous Era will last to the 14 th cosmic decade The Time of Degeneracy Not about deplorable behavior: how matter behaves Quantum Claustrophobia From cosmic decade 14 to 37 How do we know? From the mean half-life of a proton, years Few stars, only when two Brown Dwarfs collide producing a red dwarf Once in a while, two White Dwarfs may collide and produce a supernova Pop quiz: which type? If not, all WDs will shine away all their energy The End of Structure The Time of Black Holes Cosmic Decade 37 to 100 How do we know? Steven Hawking determine the rate of black hole evaporation, now know as Hawking radiation Particle pair production near the event horizon Due to the stretching of space-time One particle falls in, the other escapes Radiation follows blackbody curve Cooling time can be calculated 20

21 The Time of Photons Cosmic Decade 100 until??? Very long wavelength photons Cold, dark Entropy wins Or does it? Very difficult to make predictions years in the future Could be that new complexity begins From other branes Via processes we can t imagine But this will all happen after the final exam THANK YOU FOR YOUR INDULGENCE! 21