2Science starts with curiosity ...something that is born in all of us The starting point is to find patterns in the natural world
3Seeing the UniverseVisible light is a half-tone range where EM spectrum is full piano
4Sensitivity Improvement over the Eye Improving on the Eye201210111010Photographic & electronic detection108Telescopes aloneElectronicSensitivity Improvement over the Eye106PhotographyHubble Space Telescope104102Short’s 21.5”Rosse’s 72”Mount Wilson 100”Mount Palomar 200”Soviet 6-mHerschell’s 48”HuygenseyepieceSlow f ratiosGalileo16001700180019002000Year of Observation
5A Factor of Ten Billion The largest telescope can see 1011 times (100 billion x) fainter than the naked eyeWHERE DOES THIS GAIN COME FROM?The first factor is light gathering powerA gain of 10m over 1cm (or 0.01m) squared, a factor of 106
6The second factor is efficiency of detecting photons For a gain of nearly 100% efficiency over 1% or so, or a factor of 100WHAT IS THE LAST FACTOR OF 1000?The eye must “read out” every 1/10 of a second, like a movie camera, to give the illusion of motion. On the other hand, a CCD can integrate for hours before the image is read out.
7The Copernican Revolution The history of astronomy displaces us from cosmic importance
8X 10 Accuracy For most exploratory calculations EstimationScientists often use estimation or order of magnitude calculations in their work. Often it is not possible, or necessary, to derive very accurate numbers. This is particularly true in astronomy where the objects under consideration are usually very faint and very far away.X 10 Accuracy For most exploratorycalculationsX 2 Accuracy For most numbers incosmology10% Accuracy For the best-measuredparameters
9DEDUCTIONDeduction combines statements or premises and combines them to reach a conclusion.The conclusion is valid only if the premises are justified and the logical construction is correct.Deduction preserves truth but doesn’t always expand knowledge.i.e. symbolic logic, arithmetic, algebra2 + 2 = 4
10DEDUCTIONInduction involves a generalization from a limited amount of data to a broad conclusion.Induction cannot yield certainty, but backed by a lot of data, gives reliable conclusions.Induction can expand knowledge so is a basic tool of science.i.e. data is always finite so theories are always subject to verification.INDUCTION
11Science LimitationsUncertainty, imprecision, and error arise three different ways:Making a false premise, confusing correlation with causation, inferring a pattern where none is presentCONCEPTUALMACROSCOPICThere is no such thing as perfect data. Every data set is limited and every instrument has limitationsMICROSCOPICHeisenberg’s uncertainty principle sets a fundamental limit to precision for measurement of particle position and velocity, or energy and time
12Science is Evidence Evidence is: based on data reproducible quantitativenot subjectivenever perfect
13The Importance of Evidence There is no science without evidenceAll assertions must be supported by dataEvery claim in science is subject to verificationScience is data-driven, so progress is made by:1. Gathering more data2. Repeating the experiment3. Someone else repeating the experimentGOOD!BETTER!!BEST!!!
15Theory Good Science : a model which survives repeated testing Science seeks robust explanations for observed phenomena that rely solely on natural causes.Science progresses by creating and testing models of nature that explain the observations as simply as possible.Occam’s Razor (there may be more than one explanation for any particular data set)A scientific model must make testable predictions that may force us to revise or abandon the model.Plus, the role of luck and persistence: Science is a very human enterprise!Theory: a model which survives repeated testing
16For % of the universe, including all stars and all galaxies, the evidence is indirect.
18Distance UnitsTypical distance between stars is 1 pc = 3.36 light years = 6 trilllion km, or 6,000,000,000,000 km.1 pc1 MpcTypical distance between galaxies is 1 Mpc = 106 pc or 3 million light years. It’s an incredible 1019 km.The size of the observable universe is about 10 Gpc = 1010 pc, or 30 billion light years. That distance is an unimaginable 1023 km.10 Gpc
19THE UNIVERSE AND USUsEarthSolar SystemMilky WayUniverseMultiverse?
20A Scale ModelSet the Earth to the size of a walnut, or a 1:10,000,000 scale model=The Moon is a pea at arm’s lengthThe Sun is a 3 m ball 100 m awayNeptune is another pea 2 km awayThe nearest star is 50,000 km away
21And at this scale, light is reduced to very slow walking speed And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any fasterThe Moon is a seconds walk awayThe Sun is 8 minutes walk away10 hours to walk the Solar SystemA year to walk to the nearest stars
22Reduce the scale by a factor of 100,000,000 The Solar System is a grain of sandThe distance between stars is 10 mThe Milky Way is the size of IndiaThe MW has 100,000,000,000 stars
23Now reduce by another factor of 100,000,000 The Milky Way is the size of a plateThe nearest galaxy is 10 m awayThe universe is the size of IndiaBillions of galaxies within this space
24How Empty is Space?A one-inch cube of the air you’re breathing holds 1020 atoms in itThe average density of the universe is 1022 times lower, about 1 atom per cubic meter
25Distant Light = Old Light Lookback TimeIf the speed of light were infinite, light from everywhere in the universe would reach us at exactly the same time and we would see the entire universe as it is now.But it is not, so we see distant regions as they were in the past.Distant Light = Old Light
26How can we know what the universe was like in the past? Light travels at a finite speed (300,000 km/s).Thus, we see objects as they were in the past:The farther away we look in distance,the further back we also look in time.DestinationLight travel timeMoon1 secondSun8 minutesSirius8 yearsAndromeda (M31)2.5 million yearsPoint out how fast the speed of light is: could circle Earth 8 times in one second….Also note that the speed of light is always the same…
35How do our lifetimes compare to the age of the universe? The Cosmic Calendar: a scale on which we compress the 13.7 billion year history of the universe into 1 year.This is a time scale model that used a scale factor of 14,000,000,000:1.Our lives would scale similarly, so 80 years goes down by a factor of 14 billion too.In the scale model, a human life lasts about 2 tenths of a second!Our favorite way to present the scale of time: a modified version of Carl Sagan’s Cosmic Calendar. Worth noting:Since we are compressing the 14 billion-year history of the universe into one calendar year, 1 month represents about 1.2 billion real years, 1 day represents about 40 million years; 1 second represents about 440 years.the universe already 2/3 of the way through its history before our solar system even formed.dinosaurs arose the day after Christmas, died yesterday.All of (recorded) human history is in the last 30 seconds.You and I were born about 0.05 seconds before midnight, Dec. 31.
36TIME SENSEBlack HolesArrow of TimeSentient LifeLots of AtomsSingle AtomsNo Arrow of Time
37The early universe expanded much faster than the speed of light, so there are objects and large regions of space we have never seen.SizeThe UniverseSpeed of LightTimeThis violates no law of physics since the cosmic expansion is governed by general relativity, which sets no limit on the speed of expanding space.
38Hubble ExpansionGalaxy spectra show redshifts, where all the spectral features shift to longer wavelengths. The amount of the shift increases with growing distance: more distant galaxies are moving away faster.This linear relation was discovered by Edwin Hubble back in 1929.
39The redshift is not a Doppler shift; it is due to the expansion of space itself. Photons are stretched.
40Galaxies are all moving away from each other, so every galaxy sees the same Hubble expansion, i.e there is no center.The cosmic expansion is the unfolding of all space since the big bang,i.e. there is no edge.We are limited in our view by the time it takes distant light to reach us,i.e. the universe has an edge in time not space.
41Nature of the Expansion Space really does expand, like the material of the balloon. The balloon surface area is finite but unbounded. The universe is close to flat so imagine a large balloon with little curvatureGalaxies are held together by gravity and do not expand, so imagine coins glued to the balloonPhotons in this 2D space have their wavelengths stretched or redshifted by the expansion as they travel
42Dark matter binds galaxies and dark energy drives cosmic acceleration.
43Nature of the Expansion Early expansion is rapid, driven by radiation. It slows as dark matter begins to dominate and more recently has begun to accelerate due to dark energy.
47A sand grain of diameter 0. 5mm weighs about 3 grams A sand grain of diameter 0.5mm weighs about 3 grams. The sand is SiO2, molecules 60 times hydrogen mass.How Many?1019 atoms
48A normal monk, one who does not like “momos” too much, weighs about 50 kg. Monks are made of water, H2O, molecules 17 times hydrogen mass.NOTE: EVERYTHING THAT HAS MASS EXPERIENCES THE GRAVITY FORCE, INCLUDING ATOMS. HOWEVER, THE BEHAVIOR OF ALL SMALL OBJECTS, SUCH AS MONKS AND MOUNTAINS, IS GOVERNED BY THE FAR STRONGER ELECTRIC FORCE BETWEEN ATOMS. FOR ANY OBJECT WITH MORE THAN ABOUT 1045 ATOMS, OR A SIZE ABOUT 100 KILOMETERS, GRAVITY BECOMES THE DOMINANT. SO GRAVTY DRIVES THE BEHAVIOR OF PLANETS, STARS, GALAXIES, AND THE UNIVERSE.How Many?1028 atoms
49One solar mass is 2 x 1030 kg. Which is an enormous factor larger than a hydrogen atom 2 x kg. Earth is 330,000 times less massive.How Many?1057 atoms
51What is Dark Matter?THE SHORT ANSWER IS: WE DON’T KNOW. BUT SEVERAL LINES OF EVIDENCE INDICATE 10X MORE INVISIBLE THAN VISIBLE MATTERThe rotation speed of galaxies does not decline with radius, violating Kepler’s law unless without a halo of unseen matter
52Light from distant galaxies is bent by an intervening cluster to form little arcs. The amount of bending indicates a lot of unseen matter in the cluster.Light from all distant galaxies is very slightly distorted and bent as it travels through the “sea” of dark matter. With the best images, these distortions of 0.1% in shape can be seen.
53X X X X Why are astronomer so confident that dark matter really exists?Because the law of gravity haspassed so many tests, and if weput dark matter into computersimulations, we evolve structurethat looks just like the universe.So far, we can only rule items out:Stars: (normal matter) census of stars does not allow itXMACHOs: (sub-stars & planets) gravitational lensing rules it outXBlack holes: (dark, collapsed stars) no sign of preceding supernovaeXDust: (dust up to rocks) re-radiation in infrared not seenXWhich leaves: weakly interacting particles, supersymmetric extension to standard model
54Experiments in the 1960’s and 1970’s showed that, just as atoms are not simple and fundamental, so protons and neutrons are made of much smaller particles that were named quarks.
55This scheme has multiple generations of particles and their anti-particles, so it is not very elegant or simple. This has led physicists to suppose that there may be an even deeper level of sub-atomic structure
57String TheoryString theory postulates dynamic 1-dimensional entities that are only noticeable on scales of meters, 33 orders of magnitude smaller than atoms!
58In string theory, the smoothness and the emptiness of space are illusions. If we could imagine ourselves at the incredibly tiny Planck scale, meters, we would see a chaotic version of space-time. At every point, the six hidden dimensions that are not apparent in the everyday world would be manifested...
60Four Forces Strength: 10-38 10-19 0.0073 1 Range: Long Subatomic Long Subatomic
61The forces are associated with particular families of particles The forces are associated with particular families of particles. But just as these particles are secondary manifestations of strings, the individual forces are manifestations of a single underlying “superforce”
63Energy is a very broad concept Energy is a very broad concept. It is anything that can make matter move or changeEnergy changes forms constantly but is not created or destroyed: this is a law of physicsUse this figure to define the nucleus; protons, neutrons, electrons; scale of atom and “electron cloud.”
64Energy can be kinetic, the overall motion of an object Energy can be radiant, light or other electromagnetic wavesEnergy can be potential, stored in a number of waysChemical bondsElectric fieldsMagnetic fieldsGravity fieldsElastic (materials)
65Light is an electromagnetic wave Use this slide to define wavelength, frequency, speed of light.
66Light is a ParticlePhotons: they are “pieces” of light, each with a precise wavelength, frequency, and energy. Think of photons as tiny bullets, localized in spacePhoton energy is proportional to frequency of the waveWithin the visible spectrum, blue light has higher energy than red lightWithin the electromagnetic spectrum, X-rays have the highest energy, followed by UV, visible light, IR, and radioRemember: Light is just one form of electromagnetic wave of energy, the kind we can detect with our eyes.
67Our first key idea is that visible light is only a small part of the complete spectrum of light. You may wish to spend some time explaining the various things shown in this figure… You may also want to repeat this slide at various points to summarize other ideas.
68If you pass white light through a prism, it separates into its component colors long wavelengthsROY G B I Vshort wavelengthsspectrum
69Light Interacts with Matter EmissionAbsorptionTransmissionReflection or ScatteringEverything we know about the universe is a result of these effectsBriefly explain the 4 major interaction processes.Terminology:Transparent: transmits lightOpaque: blocks (absorbs) light
70Atomic Energy LevelsElectrons in every atom have distinct energy levelsEach chemical element, ion or molecule, has a unique set of energy levelsThis slide represents the first introduction to quantized energy levels.
71Distinct energy levels lead to distinct emission or absorption lines Hydrogen Energy LevelsEmission: atom loses energyAbsorption: atom gains energy
72Chemical Fingerprints Atoms, ions, and molecules have unique spectral “fingerprints”We identify chemicals in a gas by their spectral fingerprintsWith additional physics, we can figure out abundances of the chemicals, and often temperature, pressure, and much more.
73Types of Spectra Hot/Dense Energy Source Continuous Spectrum prismContinuous SpectrumprismHot low density cloud of GasEmission Line SpectrumHot/Dense Energy SourceprismCooler low density cloud of GasAbsorption Line Spectrum
74Anywhere in the universe, atoms and molecules are always in constant, microscopic motion Temperature is a measure of the average kinetic energy of the particles in a substanceStudents sometimes get confused when we’ve said there are 3 basic types of energy (kinetic, potential, radiative) and then start talking about subtypes, so be sure they understand that we are now dealing with subcategories.COOLERHOTTER
75All the atoms and molecules in the universe are in constant (invisible) microscopic motion or vibration:Thermal energyAs a result, every substance emits a smooth spectrum of radiation, mostly at invisible infrared wavelengths:Thermal radiation
77Mass-EnergyAnother way to think about this is that the energy that holds the helium nucleus together has a tiny amount of equivalent mass, and that energy gets released going by fusion from hydrogen to heliumE = mc2big numbersmall numberhuge number
78When 0.7% of the mass of a hydrogen atom is converted to radiant energy it is a huge amount relative to the mass involvedThe mass-energy in the ink in the dot at the end of a sentence in a book could power a typical family home for an entire year
79What is Dark Energy?THE SHORT ANSWER IS: WE DON’T KNOW. BUT ONE OBSERVATION OF DISTANT SUPERNOVAE POINTED TO A COSMIC ACCELERATION
80Expansion History of the Universe 30,000300,0003,0001001,00010,000Constant or faster in past (expected)Redshift cz (km/s)Riess, Press,& Kirshner (1996)Slower in past (big surprise!)Farther in the pastRiess et al. (1998)Perlmutter et al. (1999)Distance (Mpc)
81Einstein’s Theory: General Relativity 3Riess et al. 1998Perlmutter et al. 1999No Big Bang2Strength of cosmological constant, LRiess et al. 2004Tonry et al. 20038 HST SN Ia z > 1If the acceleration is caused by Einstein’s cosmological constant, HST data on 8 SN Ia have increased our cosmology knowledge by a factor of 71AcceleratingI also had a chance to recalculate constraints in the omega_M,omega_l spaceThe new constraints are about 5 times more precise than the ones either team published in 1998There is a lot more we can do with this data and more like it in the future to understand the nature of dark energyxDeceleratingClosedOpen12Strength of matter
82Dark energy is much more mysterious than even dark matter. It’s existence restson the unexpectedly faintdistant supernovae, and afew less direct arguments.The direct detection of darkenergy is very challenging.Dark energy is a repulsive force that counter gravity. It does not changeits strength with time (Einstein’s gravitational constant “blunder”)Physics provides no assistance. The vacuum of space could have energyin quantum theory, but it would be 1080 times larger than is observed!The density of dark energy and dark matter are roughly equal, this is theonly time in the history of the universe that is true: is this a coincidence?
90First instant after the big bang event Most of the history of the universeThe underlying unity suggested by string theory and the unification of forces is only realized in the big bang itself
91A few dimensionless parameters govern the behavior of the universe: Matter DensityEnergy DensityFine Structure ConstantEntropy per BaryonDielectric ConstantNumber of Space DimensionsA few pure number occur over and over through mathematics
92The 92 stable elements in the periodic table lead to almost infinite complexity. Life uses only about 20.
93CosmologicalThe universe was initially very smooth; over time complex structures grew by the action of gravity
94Quantum fluctuations are a mechanism for multiple realizations of the universe …leading to the concept of the “multiverse”
95More than just this… LEVEL 1: regions we can not see in big bang model LEVEL 2: many bubbles of space-time, unobservable by us, different propertiesLEVEL 3: indeterminacy, and quantum variationLEVEL 4: mathematical forms, multi-dimensional space-times, 10 preferred
96String Theory Landscape 500Perhaps 10 different vacuade Sitter expansion in these vacua create quantum fluctuations and provide theinitial conditions for inflation. String theory provides context for the “multiverse”
98Knowing Meaning Space Life Time Structure Matter Energy 1 8 2 7 3 6 4 5StructureMatterEnergy
99? ? ? ? ?As creatures who occupy a tiny portion of time and space we have learned much about our universe. But many important questions are still answered.WHAT IS TIME?WHAT IS SPACE?WHAT IS MATTER?WHAT CAUSED THE BIG BANG?IS THE UNIVERSE UNIQUE?ARE WE ALONE?
100In the universe with ten thousand billion billion stars, and a likely myriad of life forms, we’re special in some ways yet we are not in a cosmic sense. This leads to another big question:WHY ARE WE HERE?
101Anthropic PrincipleBrandon Carter presented the “anthropic principle” in 1973 in Poland during the 500th birthday of Nicklaus Copernicus. The idea seems to subvert the sense that we are not special, by elevating the role of intelligent observers in the universe to central importance.The weak form of the anthropic principle states that we can only observe a universe with properties such that intelligent observers exist. This is self-evident and little more than a tautology.The strong form of the anthropic principle states that the universe has to be the way it is because intelligent observers exist. This is much more audacious because it implies a special role for life.
102Conditions for LifeStars of the right type for sustaining life supportable planets only can occur during a certain range of ages for the universestars of the right type only can form for a narrow range of values of the gravitational constantLiving cells consists of light and heavy elements (hydrogen, carbon, oxygen, and metals such as iron, copper, etc.)To make both the light and heavy elements in the correct proportions, the strengths of the various fundamental forces must lie within a very narrow range of valuesBut does this place too specific a requirement on life? Perhaps life just needs disequilibrium chemistry and an energy source, not necessarily carbon and a star.
103Fundamental Forces Gravitational force Electromagnetic force Attractive force between all objects with massWeakest, long rangeElectromagnetic forceAttractive and repulsiveLong range, 1039 times stronger than gravityNuclear Weak forceCause neutrons to decay into protonsRange <10-17 m, 1028 times stronger than gravityNuclear Strong forceHolds the nucleus togetherRange <10-15 m, 1041 times stronger than gravity
104CoincidencesSome physical coincidences are noteworthy and so beg for an explanation. All the seemingly arbitrary, unrelated constants in physics have one strange thing in common – they have just the values that would create a universe capable of sustaining life. In other words, our universe could have quite different values of the fundamental forces and it would be physically sensible, but it would contain no carbon-based life forms.
105Fine-Tuning of Forces Gravitational force Electromagnetic force A bit stronger, and stars have rapid, unstable livesA bit weaker, no supernovae, so no heavy elementsElectromagnetic forceA bit stronger, no shared electrons, no chemistryA bit weaker, atoms cannot hold their electronsNuclear Weak forceA bit stronger, neutrons all decay, no heavy elementsA bit weaker, all hydrogen converted to inert heliumNuclear Strong forceA bit stronger, nuclear reactions too efficient, H to FeA bit weaker, electrical repulsion splits apart nuclei
106Cosmological Fine-Tuning The following incredibly precise tweaking of the Universe is known as the flatness-oldness problemThe critical density is the matter density just required to eventually overcome the expansion of the big bangIf X is critical density, what is the actual density?It could have any value, but the matter density has a huge impact on the evolution of the universeOnly a value relatively close to the critical value leads to an old and flat universeX
107OPENFLATCLOSEDIf the density is much below critical, early expansion is too rapid for stars and galaxies to form, so no lifeIf the density is much above critical, the universe will recollapse quickly, with not enough time for stellar evolution to create carbon, and once again, no lifeThe matter density is only ¼ critical; the other major component affecting the expansion is dark energy, which leads to another issue related to fine-tuning….
108Anthropic Principle Multiverse Redux Our universe emerged from a quantum space-time foam at the Planck epoch. Other universes may have been spawned this way, with physical properties that are randomly different.Most of the past, present and future universes in the multiverse would be inhospitable to life. Ours is just a mediocre member of the ensemble.Anthropic Principle
109Applying LogicIs there really a logical basis for anthropic arguments about life?1. We shouldn’t be surprised to see features of the universe that are compatible with our existence2. We should be surprised not to see features of the universe that are incompatible with our existence1 is true, but 2 does not follow from itThis universe has special features, like a double six thrown with dice. The multiverse hypothesis is akin to speculating that there are many possible outcomes, ours is “double six”A double six will occur eventually in a long sequence of throws, sequential or parallelThis is the “inverse gamblers” fallacyThe odds of double six are always 1 in 36, so the supposition above doesn’t explain it
110Scientific Method? Epistemology Let’s look at the strange conceptual journey we have just followedWe can only observe a universe that is capable of creating observers like usSome features of the universe are very finely-tuned around the existence of lifeBut is this an unduly anthropocentric view of life based on stars and carbon?Fine-tuning might be due to happenstance, providence, or self-selection in a multiverseQuantum creation and string theory give the context for the multiverse ensembleBut these theories are not yet well-tested and other universes are unobservableAnd how to assign likelihood or probability on an infinite set of hypothetical universes?Scientific Method?
111Sentience and mortality define the human condition The physical parameters of nature and the universe are tuned to values that allow carbon-based life.The big bang allows for other universes and other realities but most of these might be devoid of life.The universe is “built for life” in a profound way, but this begs the question of the definition again.Is it self-selection, coincidence, or evidence of design?We share a planet with other sentient life forms, and it’s very likely there is sentience elsewhere.Our power carries moral responsibility and obligation.