Quantum Physics and Beyond

Transcription

1 Physics 120 Today Lesson 3: Dark Matter & Dark Energy, Problems with the Big Bang, Cosmic Inflation John Harris 1 Physics 120 Now posted on homepage Announcements Homework 1-2 Solutions Homework 3 Reading and Questions Quiz in two weeks Monday Feb minutes, 6 8 questions similar to those in homework Questions require short answers (no more than 2-3 sentences unless noted) Discussion session on Wednesdays (here 3:30 4:20 PM) Reminder Class grade based on: reading/homework assignments (total 20% of grade) 2 in-class quizzes (total 20% of grade) mid-term examination (20% of grade) participation in class discussion (15% of grade) a final paper (total 25% of grade) John Harris 2 1

2 Today s Class Topic Remaining from Last Class Dark Matter Dark Energy After the Big Bang: Picking up the pieces! Problems with the Big Bang Big Bang and its Epochs/Eras Inflation (quantum tunneling) & the Big Bang Gravity - the Force We Think We Know John Harris 3 Physics 120 Reading for next class 1) Echoes from the Big Bang (link) good overview although re-discovery of gravitational waves! 2) Pop Goes the Universe, Sci. Am. Feb. 2017, (link on webpage) alternative view of inflation! 3) Einstein's gravitational waves found at last, Nature News: 4) Gravitational Waves read the 3 subheadings What are gravitational waves?, Why detect them? and Sources and Types of Gravitational Waves in 5) LIGO - A Gravitational-Wave Interferometer read the 4 subheadings What is LIGO?, About LIGO, What is an interferometer?, LIGO interferometer but not the last on LIGO technology in 6) Look Deeper read only the lead page on Why gravitational waves? ook-deeper 7) LIGO Virgo announces observation of four more black-hole mergers hole-mergers/ 8) LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars. Discovery marks first cosmic event observed in both gravitational waves and light. Read the article (no need to view press conference video). View video Ripples of Gravity and Flashes of Light after the article. John Harris 4 2

3 Topics Remaining from Last Class John Harris 5 The Concept of Gravitational Lensing Example of how lensing by (dark) matter along the line of sight affects observations: N. Kaiser Yale Physics 120 1/18/2019 John Harris 6 3

4 Dark Matter Yale Physics 120 1/22/2018 John Harris 7 Some of Your Questions on Dark Matter Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos. What was the reason for the change in composition of the universe and whether we can infer from this particular properties of dark matter and dark energy? Weakly Interacting Massive Particles (WIMPs) are a good explanation for Dark Matter, but what could they be made of? What particles or elements that existed at that time could have fused to form WIMPs? What we currently do not know about dark matter and dark energy may solely be due to a lack of appropriate technology. Interested in what dark matter actually could be, and how we could study it in laboratories (i.e., with particle accelerators). Could we clarify the definition of dark matter? It takes up more content than anything else in the universe but where is it stored? In stars and clusters? What does its presence mean? Is there a chance that we are misinterpreting dark matter and that it is indeed no different from baryonic matter (i.e., brown dwarfs)? Is there a chance that, in say 30 years, we will look back on these findings and declare them inaccurate? John Harris 8 4

5 Some of the Evidence for Dark Matter! Over many years, evidence has mounted: Baryonic matter in Universe too low! Motion of galaxies in clusters Odd rotation of spiral galaxies Stability of disk galaxies Gravitational Lensing (distortion of star-light due to unseen masses) Large-scale structure Cosmic Microwave Background fluctuation studies Visible effects through gravity! Yale Physics 120 1/22/2018 John Harris 9 Dark Matter! Most persuasive evidence for dark matter is Bullet Cluster a pair of galaxy clusters that collided. Collision did not affect the galaxies stars (visible image), because they present small targets on these scales. Interstellar gas clouds rammed into each another and emitted x-rays (magenta). Dark matter (blue) visible because its gravity distorted the light of background objects. It remained aligned with the stars indicating that the particles that make up dark matter are highly unreactive. Yale Physics 120 1/30/2017 John Harris 10 5

6 What is Dark Matter? Visible through gravitational effects Possible it is matter that does not emit or absorb light! It could still interact via the weak nuclear force???? Weakly Interacting Massive Particle or Super-WIMP with not even a weak interaction We do not yet know! There are active searches ongoing: Large neutrino detectors (search for its decay): Underground & outer space Direct detection (search for its interaction) Large Hadron Collider (produce and detect it) Yale Physics 120 1/22/2018 John Harris 11 Back to Your Questions on Dark Matter Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos. What was the reason for the change in composition of the universe and whether we can infer from this particular properties of dark matter and dark energy? Weakly Interacting Massive Particles (WIMPs) are a good explanation for Dark Matter, but what could they be made of? What particles or elements that existed at that time could have fused to form WIMPs? What we currently do not know about dark matter and dark energy may solely be due to a lack of appropriate technology. Interested in what dark matter actually could be, and how we could study it in laboratories (i.e., with particle accelerators). Could we clarify the definition of dark matter? It takes up more content than anything else in the universe but where is it stored? In stars and clusters? What does its presence mean? Is there a chance that we are misinterpreting dark matter and that it is indeed no different from baryonic matter (i.e., brown dwarfs)? Is there a chance that, in say 30 years, we will look back on these findings and declare them inaccurate? John Harris 12 6

7 Dark Energy Yale Physics 120 1/22/2018 John Harris 13 Some of Your Questions on Dark Energy Dark energy is intriguing considering we have no real idea what it is. I would be interested to discuss it in the context of the scientific method. We do not know what to expect beyond the horizon of the universe, yet we hypothesize that dark energy composes of 72% of the universe. Is it some manifestation of energy or a property of the vacuum? When described, it seemed as if Dark Energy was only the scientific explanation given for the supposed accelerated expansion of the universe, or a property of the vacuum itself. Does the negative pressure of dark energy have a directional component, as in, is it pushing out on space, stretching space, or is it exerting some other form of influence that has caused the observed expansion of the universe? If the expansion of the universe is speeding up, then dark energy must somehow have a negative gravitational pull. What kind of matter could have negative gravitational pull? How does dark energy explain why the universe can be flat while still experiencing accelerated expansion? What properties of dark energy allow for this? I would like to know what has caused the increase in dark energy over time and how, if at all, it is created. What exactly is the cosmological constant term? It s a leading candidate for dark energy and accelerated expansion, but it was a constant Einstein dreamed up to account for a stagnant universe? John Harris 14 7

8 Evidence for Dark Energy Cosmic Micro-wave Background Large scale supernova searches Yale Physics 120 1/22/2018 John Harris 15 Expansion of Universe with Dark Energy Yale Physics 120 1/18/2019 John Harris 16 8

9 Our Future! Significance of Dark Energy? Yale Physics 120 1/22/2018 John Harris 17 Again we do not yet know! What is Dark Energy? Cosmological constant in Einstein s theory of gravity? A property of space - empty space is not a void! - See next slide! Yale Physics 120 1/22/2018 John Harris 18 9

10 Empty Space Is Not a Void! e.g. the QCD Vacuum Quantum Chromo-Dynamics Vacuum of space (at the level of quarks & gluons) Theory of the strong interaction on the scale of the size of nucleus quarks and gluons come into and out of existence Lattice QCD based dynamical vacuum visualization, Adelaide Group Yale Physics 120 1/22/2018 John Harris 19 Again we do not yet know! What is Dark Energy? Cosmological constant in Einstein s theory of gravity? A property of space (empty space not a void!). A fluid of energy filling all of space? Repulsive effect, opposite that of gravity! A new type of field (force!) that creates cosmic acceleration? Either Einstein s theory of gravity is not correct or incomplete a new type of force? Many extra-terrestrial studies, is there a relation between dark matter & dark energy? Yale Physics 120 1/22/2018 John Harris 20 10

11 Scenarios for Expansion Rate of Universe Orange curve a closed, high density universe expands for several billion years, then turns around and collapses under its own weight. Green curve flat, critical density universe expansion rate slows down curve becomes ever more horizontal. Blue curve open, low density universe expansion slowing down, less than the previous two because the pull of gravity is not as strong. Red curve large fraction of Universe is in "dark energy causes expansion rate to speed up (accelerate). Growing evidence that our universe is following the red curve. Yale Physics 120 1/18/2019 John Harris 21 Back to Your Questions on Dark Energy Dark energy is intriguing considering we have no real idea what it is. I would be interested to discuss it in the context of the scientific method. We do not know what to expect beyond the horizon of the universe, yet we hypothesize that dark energy composes of 72% of the universe. Is it some manifestation of energy or a property of the vacuum? When described, it seemed as if Dark Energy was only the scientific explanation given for the supposed accelerated expansion of the universe, or a property of the vacuum itself. Does the negative pressure of dark energy have a directional component, as in, is it pushing out on space, stretching space, or is it exerting some other form of influence that has caused the observed expansion of the universe? If the expansion of the universe is speeding up, then dark energy must somehow have a negative gravitational pull. What kind of matter could have negative gravitational pull? How does dark energy explain why the universe can be flat while still experiencing accelerated expansion? What properties of dark energy allow for this? I would like to know what has caused the increase in dark energy over time and how, if at all, it is created. What exactly is the cosmological constant term? It s a leading candidate for dark energy and accelerated expansion, but it was a constant Einstein dreamed up to account for a stagnant universe? John Harris 22 11

12 Gravity Yale Physics 120 1/22/2018 John Harris 23 Gravity - the Force We Think We Know Gravitational force equation What we can see and feel Everyday life, solar system What we can see but cannot imagine Black Holes, Pulsars, Quasars, etc. Gravity Yale Physics 120 1/18/2019 John Harris 24 12

13 Gravity - the Force We Think We Know Gravitational force equation What we can see and feel Everyday life, solar system What we can see but cannot imagine Gravity Pulsars etc. What we cannot see Gravitons (or gravitational waves) The Force We Want to Get to Know Better Yale Physics 120 1/18/2019 John Harris 25 Gravity Gravity - the Force We Think We Know Gravitational force equation What we can see and feel Everyday life, solar system What we can see but cannot imagine Pulsars etc. What we cannot see Gravitons (or gravity waves) The Force We Want to Get to Know Better A Problem with Gravity Instantaneous Action of Newtonian Gravity (film clip) Yale Physics 120 1/18/2019 John Harris 26 13

14 Gravity - the Force We Think We Know Gravitational force equation What we can see and feel Everyday life, solar system What we can see but cannot imagine Gravity Pulsars etc. What we cannot see Gravitons (or gravity waves) The Force We Want to Get to Know Better A Problem with Gravity Instantaneous Action of Newtonian Gravity (film clip) What is gravity? Is it a force? If not, what might it be? Yale Physics 120 1/18/2019 John Harris 27 Problems with the Big Bang Yale Physics 120 1/22/2018 John Harris 28 14

15 First A Few Things to Point Out Principle of Relativity Laws of physics are the same in all inertial frames Some Rules of the Game according to Trefil! Basic Rule 1 Laws of Nature are the same throughout time, and can be understood by theories tested by experiment. [counter to it s always possible to explain a fact by tailoring a theory to fit it! ] Basic Rule 2 No special conditions at the creation. John Harris 29 What Are the Problems with the Big Bang Theory Anti-Matter Problem Horizon Problem Flatness Problem Galaxy (Structure) Formation Problem John Harris 30 15

16 What Are Plausible Solutions to the Problems of the Big Bang Theory? Anti-Matter Problem Horizon Problem Flatness Problem Galaxy (Structure) Formation Problem John Harris 31 Anti-Matter Problem Anti-Matter Problem Why is matter dominant in our Universe? Anti-Matter Plausible Answer(s) from Trefil Big Bang started with an imbalance of matter over antimatter. Antimatter became segregated or -? John Harris 32 16

17 Horizon Problem Horizon Problem How can regions causally disconnected have the same temperature? Horizon Problem Plausible Answer(s) from Trefil Some process before particle era (unknown) that precludes our assumptions Universe created in thermal equilibrium John Harris 33 Galaxy Formation Problem Galaxy (Structure) Formation Problem How did the large scale structure of the Universe come about? Galaxy (Structure) Formation Problem Plausible Answer(s) from Trefil Some process (unknown as yet) that aggregated matter before atoms form. Universe created with matter clumped enough to allow galaxy formation. John Harris 34 17

18 Flatness Problem Flatness Problem Will Universe continue to expand or end in a collapse or? Flatness Problem Plausible Answer(s) from Trefil Requires deeper understanding and experimental guidance! John Harris 35 A Few Things to Discuss from the Reading Trefil states at the time of his book: There are problems that are presently unsolved, but should be solvable with our present knowledge. Horizon Problem Galaxy Problem Antimatter Problem There is a problem that requires a much deeper understanding of physics than at present. Flatness Problem John Harris 36 18

19 Thing You Should Know about the WMAP Results (review these slides from last class on your own!) Yale Physics 120 1/22/2018 John Harris 37 The WMAP Signal and What it Means! Transformation (into spherical harmonics) gives Details of clumpiness on different size scales John Harris 38 19

20 More on the WMAP Results John Harris 39 MAP Results Like Sound Waves in a Pipe John Harris 40 20

21 WMAP Results Acoustical Oscillations in the Early Universe John Harris 41 John Harris 42 21

22 Conclusions from WMAP Observations WMAP harmonic analysis gives info on basic parameters of Big Bang density and composition of Universe baryonic vs non-baryonic matter Non-baryonic matter properties Interactions Amount Universe today WMAP Universe is ~ flat! Mean energy density equals critical energy density = 5.9 protons / m 3 Energy/Matter breakdown to right Universe 380,000 years old John Harris 43 Dark Matter and Dark Energy Review Questions What do you think dark energy is? What characteristics would you give to dark matter? When and how in the evolution of the Universe is dark matter important? When and how in the evolution of the Universe is dark energy important? What force(s) would you expect each of them to interact with/through? How do they appear to be distributed (e.g. smooth, lumpy,..?) in the Universe? John Harris 44 22

23 Quantum Tunneling & Inflation Yale Physics 120 1/22/2018 John Harris 45 Tunneling A Quantum Mechanical Phenomenon Particle in a potential well Seeks lowest energy state could be a vacuum state Classically will be at bottom of well Can be in higher states (excited) Quantum Mechanics Probability to be at different places Probability distribution shown Note can be outside well Origin of Tunneling Has been observed But probability extremely small John Harris 46 23

24 False Vacuum Real vacuum state in early Universe? Energy minimum False vacuum state? Local minimum Tunneling From false to real vacuum state Quantum probability John Harris 47 Symmetry Breaking John Harris 48 24

25 Inflation A Few Things to Discuss & Know from the Reading Trefil s use of the Higgs Field, it should be read as Inflaton Field Not the Higgs as we now know it Similar properties creates mass in the Universe (more later when we study the Higgs that has been discovered at CERN!) Energy tied up in the Higgs Field meaning Inflaton Field Inflationary Universe Radius of curvature expands exponentially Inflationary Universe doubles size 70 times in seconds: 270 size expansion No inflation doubles size 8 times in seconds: 23 size expansion Most of the mass of the Universe is created after tunneling out of the False Vacuum! John Harris 49 Inflation John Harris 50 25

26 Cartoon Cosmic Inflation Explained (Read outside of class!) ons-cosmic-inflation-explained Yale Physics 120 1/22/2018 John Harris 51 John Harris 52 26

27 John Harris 53 John Harris 54 27

28 John Harris 55 Epochs of the Big Bang Yale Physics 120 1/22/2018 John Harris 56 28

29 Things to Know About the Big Bang & its Epochs/Eras Time Temperature s Planck Time Which Force(s) Freeze? GUT Era s Freezes s Freeze Quark Era Electroweak Era Which particles? 10-5 s 3 minutes 380,000 yrs Freeze Particle Era Form Form John Harris 57 Things to Know About the Big Bang & its Epochs/Eras Time Temperature s s s 10-5 s 3 minutes 380,000 yrs Quarks freeze into particles Particle Era particles Nuclei form Atoms form Weak & EM Forces Freeze Quark Era GUT Era X particles, (fermions, bosons) Strong & EW Forces Freeze Electroweak Era Quarks, leptons, photons Vector bosons Planck Time John Harris 58 29