Science starts with curiosity...something that is born in all of us The starting point is to find patterns in the natural world
Seeing the Universe Visible light is a half-tone range where EM spectrum is full piano
10 8 16001700180019002000 Galileo Sensitivity Improvement over the Eye Year of Observation Telescopes alone Photographic & electronic detection 10 6 10 4 10 2 Huygens eyepiece Slow f ratios Short’s 21.5” Herschell’s 48” Rosse’s 72” Photography Mount Wilson 100”Mount Palomar 200”Soviet 6-m 10 Electronic Hubble Space Telescope Improving on the Eye 2012 10 11
The largest telescope can see 10 11 times (100 billion x) fainter than the naked eye WHERE DOES THIS GAIN COME FROM? The first factor is light gathering power A gain of 10m over 1cm (or 0.01m) squared, a factor of 10 6 A Factor of Ten Billion
The second factor is efficiency of detecting photons 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. For a gain of nearly 100% efficiency over 1% or so, or a factor of 100 WHAT IS THE LAST FACTOR OF 1000?
The Copernican Revolution The history of astronomy displaces us from cosmic importance
Estimation Scientists 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 exploratory calculations X 2 Accuracy For most numbers in cosmology 10% Accuracy For the best-measured parameters
DEDUCTION Deduction 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, algebra 2 + 2 = 4
DEDUCTION Induction 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
Science Limitations Uncertainty, imprecision, and error arise three different ways: CONCEPTUAL MACROSCOPIC MICROSCOPIC Making a false premise, confusing correlation with causation, inferring a pattern where none is present There is no such thing as perfect data. Every data set is limited and every instrument has limitations Heisenberg’s uncertainty principle sets a fundamental limit to precision for measurement of particle position and velocity, or energy and time
Evidence is: based on data reproducible quantitative not subjective never perfect Science is Evidence
The Importance of Evidence There is no science without evidence All assertions must be supported by data Every claim in science is subject to verification Science is data-driven, so progress is made by: 1. Gathering more data 2. Repeating the experiment 3. Someone else repeating the experiment GOOD! BETTER!! BEST!!!
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! Good Science : a model which survives repeated testing Theory
For 99.999999999999999999999999999% of the universe, including all stars and all galaxies, the evidence is indirect.
Distance Units 1 pc 1 Mpc 10 Gpc Typical distance between stars is 1 pc = 3.36 light years = 6 trilllion km, or 6,000,000,000,000 km. Typical distance between galaxies is 1 Mpc = 10 6 pc or 3 million light years. It’s an incredible 10 19 km. The size of the observable universe is about 10 Gpc = 10 10 pc, or 30 billion light years. That distance is an unimaginable 10 23 km.
Us Milky Way Earth THE UNIVERSE AND US Solar System UniverseMultiverse?
A Scale Model Set the Earth to the size of a walnut, or a 1:10,000,000 scale model = The Moon is a pea at arm’s length The Sun is a 3 m ball 100 m away Neptune is another pea 2 km away The nearest star is 50,000 km away
The Moon is a seconds walk away The Sun is 8 minutes walk away 10 hours to walk the Solar System A year to walk to the nearest stars And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any faster
Reduce the scale by a factor of 100,000,000 The Solar System is a grain of sand The distance between stars is 10 m The Milky Way is the size of India The MW has 100,000,000,000 stars
Now reduce by another factor of 100,000,000 The Milky Way is the size of a plate The nearest galaxy is 10 m away The universe is the size of India Billions of galaxies within this space
How Empty is Space? A one-inch cube of the air you’re breathing holds 10 20 atoms in it The average density of the universe is 10 22 times lower, about 1 atom per cubic meter
Lookback Time If 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.
How 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 time Moon1 second Sun8 minutes Sirius8 years Andromeda (M31)2.5 million years
How 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!
No Arrow of Time Arrow of Time Black Holes TIME SENSE Single Atoms Sentient Life Lots of Atoms
Speed of Light Size Time The Universe The early universe expanded much faster than the speed of light, so there are objects and large regions of space we have never seen. This violates no law of physics since the cosmic expansion is governed by general relativity, which sets no limit on the speed of expanding space.
Galaxy 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. Hubble Expansion
The redshift is not a Doppler shift; it is due to the expansion of space itself. Photons are stretched.
Galaxies 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.
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 curvature Photons in this 2D space have their wavelengths stretched or redshifted by the expansion as they travel Nature of the Expansion Galaxies are held together by gravity and do not expand, so imagine coins glued to the balloon
Dark matter binds galaxies and dark energy drives cosmic acceleration.
Nature 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.
A sand grain of diameter 0.5mm weighs about 3 grams. The sand is SiO 2, molecules 60 times hydrogen mass. 10 19 atoms
A normal monk, one who does not like “momos” too much, weighs about 50 kg. Monks are made of water, H 2 O, molecules 17 times hydrogen mass. 10 28 atoms 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 10 45 ATOMS, OR A SIZE ABOUT 100 KILOMETERS, GRAVITY BECOMES THE DOMINANT. SO GRAVTY DRIVES THE BEHAVIOR OF PLANETS, STARS, GALAXIES, AND THE UNIVERSE.
One solar mass is 2 x 10 30 kg. Which is an enormous factor larger than a hydrogen atom 2 x 10 -27 kg. Earth is 330,000 times less massive. 10 57 atoms
The typical galaxy contains 10 12 stars The whole universe contains 10 11 galaxies 10 69 atoms10 80 atoms
What is Dark Matter? THE SHORT ANSWER IS: WE DON’T KNOW. BUT SEVERAL LINES OF EVIDENCE INDICATE 10X MORE INVISIBLE THAN VISIBLE MATTER The rotation speed of galaxies does not decline with radius, violating Kepler’s law unless without a halo of unseen matter
Light 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.
Why are astronomer so confident that dark matter really exists? Because the law of gravity has passed so many tests, and if we put dark matter into computer simulations, we evolve structure that looks just like the universe. So far, we can only rule items out: Stars:(normal matter)census of stars does not allow it MACHOs:(sub-stars & planets)gravitational lensing rules it out Black holes:(dark, collapsed stars)no sign of preceding supernovae Dust:(dust up to rocks)re-radiation in infrared not seen Which leaves: weakly interacting particles, supersymmetric extension to standard model
Experiments 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.
This 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
Objects Atoms Universe TOP DOWN Dark Matter Molecules
String Theory String theory postulates dynamic 1-dimensional entities that are only noticeable on scales of 10 -43 meters, 33 orders of magnitude smaller than atoms!
In string theory, the smoothness and the emptiness of space are illusions. If we could imagine ourselves at the incredibly tiny Planck scale, 10 -43 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...
Atoms Strings BOTTOM UP Bosons Quarks Leptons Electrons
Four Forces Strength: 10 -38 10 -19 0.0073 1 Range: Long Subatomic Long Subatomic
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”
Energy is a very broad concept. It is anything that can make matter move or change Energy changes forms constantly but is not created or destroyed: this is a law of physics
Energy can be kinetic, the overall motion of an object Energy can be radiant, light or other electromagnetic waves Energy can be potential, stored in a number of ways Chemical bonds Electric fields Magnetic fields Gravity fields Elastic (materials)
Photons: they are “pieces” of light, each with a precise wavelength, frequency, and energy. Think of photons as tiny bullets, localized in space Photon energy is proportional to frequency of the wave Within the visible spectrum, blue light has higher energy than red light Within the electromagnetic spectrum, X-rays have the highest energy, followed by UV, visible light, IR, and radio Remember: Light is just one form of electromagnetic wave of energy, the kind we can detect with our eyes. Light is a Particle
If you pass white light through a prism, it separates into its component colors ROYGBIVROYGBIV spectrum long wavelengths short wavelengths
Emission Absorption Transmission Reflection or Scattering Terminology: Transparent: transmits light Opaque: blocks (absorbs) light Everything we know about the universe is a result of these effects Light Interacts with Matter
Electrons in every atom have distinct energy levels Each chemical element, ion or molecule, has a unique set of energy levels Atomic Energy Levels
Distinct energy levels lead to distinct emission or absorption lines Hydrogen Energy Levels Emission: atom loses energy Absorption: atom gains energy
Atoms, ions, and molecules have unique spectral “fingerprints” We identify chemicals in a gas by their spectral fingerprints With additional physics, we can figure out abundances of the chemicals, and often temperature, pressure, and much more. Chemical Fingerprints
Continuous Spectrum Hot/Dense Energy Source prism Emission Line Spectrum prism Hot low density cloud of Gas Absorption Line Spectrum Cooler low density cloud of Gas Hot/Dense Energy Source prism Types of Spectra
Anywhere 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 substance COOLER HOTTER
All the atoms and molecules in the universe are in constant (invisible) microscopic motion or vibration: Thermal energy As a result, every substance emits a smooth spectrum of radiation, mostly at invisible infrared wavelengths: Thermal radiation
E = mc 2 Mass-Energy Another 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 helium small number big numberhuge number
When 0.7% of the mass of a hydrogen atom is converted to radiant energy it is a huge amount relative to the mass involved The 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
What is Dark Energy? THE SHORT ANSWER IS: WE DON’T KNOW. BUT ONE OBSERVATION OF DISTANT SUPERNOVAE POINTED TO A COSMIC ACCELERATION
Redshift cz (km/s) Riess et al. (1998) Perlmutter et al. (1999) Constant or faster in past (expected) Slower in past (big surprise!) Riess, Press, & Kirshner (1996) 30,000 300,000 3,000 100 1,000 10,000 Distance (Mpc) Farther in the past Expansion History of the Universe
Einstein’s Theory: General Relativity Riess et al. 1998 Perlmutter et al. 1999 Accelerating Decelerating No Big Bang 0 1 2 3 12 Closed Open Strength of matter Strength of cosmological constant, x If the acceleration is caused by Einstein’s cosmological constant, HST data on 8 SN Ia have increased our cosmology knowledge by a factor of 7 Riess et al. 2004 Tonry et al. 2003 8 HST SN Ia z > 1
Dark energy is much more mysterious than even dark matter. It’s existence rests on the unexpectedly faint distant supernovae, and a few less direct arguments. The direct detection of dark energy is very challenging. Physics provides no assistance. The vacuum of space could have energy in quantum theory, but it would be 10 80 times larger than is observed! Dark energy is a repulsive force that counter gravity. It does not change its strength with time (Einstein’s gravitational constant “blunder”) The density of dark energy and dark matter are roughly equal, this is the only time in the history of the universe that is true: is this a coincidence?
First instant after the big bang event Most of the history of the universe The underlying unity suggested by string theory and the unification of forces is only realized in the big bang itself
A few dimensionless parameters govern the behavior of the universe: Matter Density Energy Density Fine Structure Constant Entropy per Baryon Dielectric Constant Number of Space Dimensions A few pure number occur over and over through mathematics
The 92 stable elements in the periodic table lead to almost infinite complexity. Life uses only about 20.
Cosmological The universe was initially very smooth; over time complex structures grew by the action of gravity
Quantum fluctuations are a mechanism for multiple realizations of the universe …leading to the concept of the “multiverse”
More 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 properties LEVEL 3: indeterminacy, and quantum variation LEVEL 4: mathematical forms, multi-dimensional space-times, 10 preferred
String Theory Landscape Perhaps 10 different vacua 500 de Sitter expansion in these vacua create quantum fluctuations and provide the initial conditions for inflation. String theory provides context for the “multiverse”
Knowing 1 Space 2 Time 3 Matter 4 Energy 5 Structure 6 Life 7 Meaning 8
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?
In 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?
Brandon Carter presented the “anthropic principle” in 1973 in Poland during the 500 th 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. Anthropic Principle
Stars of the right type for sustaining life supportable planets only can occur during a certain range of ages for the universe –stars of the right type only can form for a narrow range of values of the gravitational constant Living 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 values But 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. Conditions for Life
Gravitational force –Attractive force between all objects with mass –Weakest, long range Electromagnetic force –Attractive and repulsive –Long range, 10 39 times stronger than gravity Nuclear Weak force –Cause neutrons to decay into protons –Range <10 -17 m, 10 28 times stronger than gravity Nuclear Strong force –Holds the nucleus together –Range <10 -15 m, 10 41 times stronger than gravity Fundamental Forces
Some 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. Coincidences
Gravitational force –A bit stronger, and stars have rapid, unstable lives –A bit weaker, no supernovae, so no heavy elements Electromagnetic force –A bit stronger, no shared electrons, no chemistry –A bit weaker, atoms cannot hold their electrons Nuclear Weak force –A bit stronger, neutrons all decay, no heavy elements –A bit weaker, all hydrogen converted to inert helium Nuclear Strong force –A bit stronger, nuclear reactions too efficient, H to Fe –A bit weaker, electrical repulsion splits apart nuclei Fine-Tuning of Forces
0 X The following incredibly precise tweaking of the Universe is known as the flatness-oldness problem The critical density is the matter density just required to eventually overcome the expansion of the big bang If 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 universe Only a value relatively close to the critical value leads to an old and flat universe Cosmological Fine-Tuning
The 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…. OPEN FLAT CLOSED –If the density is much below critical, early expansion is too rapid for stars and galaxies to form, so no life –If 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 life
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. Multiverse Redux 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.
Is 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 existence 2. We should be surprised not to see features of the universe that are incompatible with our existence 1 is true, but 2 does not follow from it This 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” The odds of double six are always 1 in 36, so the supposition above doesn’t explain it A double six will occur eventually in a long sequence of throws, sequential or parallel This is the “inverse gamblers” fallacy Applying Logic
Let’s look at the strange conceptual journey we have just followed We can only observe a universe that is capable of creating observers like us Some features of the universe are very finely-tuned around the existence of life But is this an unduly anthropocentric view of life based on stars and carbon? Quantum creation and string theory give the context for the multiverse ensemble Fine-tuning might be due to happenstance, providence, or self-selection in a multiverse And how to assign likelihood or probability on an infinite set of hypothetical universes? But these theories are not yet well-tested and other universes are unobservable Epistemology
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. Sentience and mortality define the human condition