THE UNIVERSE AND COSMOLOGY

1. THE UNIVERSE AND COSMOLOGY • Cosmology is defined as the study of the entire Universe, including its origins and evolution with time. • Cosmology has been the most difficult field of Astronomy to study observationally, because of the vast distances and correspondingly faint and/or small apparent sizes of the individual objects of study. • Cosmology involves not only the study of individual galaxies and other objects, as a function of their apparent distances, but also the characteristics of diffuse background radiation, over the entire ranges of distances and of the electromagnetic spectrum. • Because of the expansion of the Universe, distant objects appear to be moving away from us, as first realized by Edwin Hubble, at speeds (to first order) proportional to their apparent distances (as based on other observational evidence). • This motion results in “red-shifts” of the apparent wavelengths of radiation received from these objects, indicating speeds comparable to the speed of light (and other forms of electromagnetic radiation). • This recessional red-shift, therefore, provides a means for determining the distances to these very distant objects.

2. THE UNIVERSE AND COSMOLOGY • The age of the Universe, until very recently, was not well established, but is now believed to be about 13.7 billion years, or about 3 times the age of our Solar System. • The Universe is thought to have originated in a point-like concentration, which began expanding outward in a “big bang” at the speed of light. • Over very large distances, the expansion velocity and other properties of the Universe are such that the theory of general relativity must be used for quantitative descriptions. • The Hubble Constant H0 = v/R, indicated that the apparent recession velocity of an object, v, is proportional to its distance, R, to the distances accessible until recently with ground-based telescopes. • However, with the advent of more powerful space- and ground-based telescopes and instrumentation, there are now indications that H0 is not constant, but changes with apparent distance (redshift). • Accurate determinations of H0 are needed in order to determine the age and evolution of the Universe.

4. THE UNIVERSE AND COSMOLOGY • Establishment of values for H0 requires measuring the recession velocity of objects for which other means (other than redshift) of determining the distance, R, are available. • One such means is to observe Cepheid variable stars, whose periods of variation are a known function of absolute luminosity. • Another method, applicable to greater distances, is observations of Type I supernovas (exploding white dwarfs) which are much brighter than Cepheid variables (but unpredictable in advance). • The Hubble Space Telescope has provided the capability to observe Cepheid variables and other distance indicators to much greater distances than has been possible previously. • The self-gravitation of the Universe acts to slow down the expansion with time since the Big Bang (characterized by the deceleration parameter q0); hence it is presumed that the most distant objects would appear to be receding at a faster rate than in direct proportion to apparent distance. • However, recent observations with HST and other instruments has indicated that the expansion of the Universe is increasing with time!

5. Globular Cluster in M31 Star in Our Galaxy This very deep-exposure HST image of the halo of the (relatively) nearby Andromeda Galaxy (M31) also reveals, in the background, a large number of very distant galaxies.

8. Great Observatories Origins Deep Survey (GOODS)

9. THE UNIVERSE AND COSMOLOGY • Determinations of distance require not only measurements of redshift, but also indicators of the absolute brightnesses of distant galaxies (for comparison with observed brightnesses). • The rate of expansion, and its variation with time, are dependent on the total mass of the Universe. • If the total mass is greater than a certain critical mass, the expansion of the Universe eventually ceases, and then reverses. • If the total mass is less than the critical mass, the expansion of the Universe continues indefinitely, and may proceed at an increasing rate with time. • The most recent measurements, using the Hubble Space Telescope and large ground-based telescopes, appear to indicate that the expansion of the Universe is accelerating with time. • This also appears to indicate the presence of “dark energy” and “dark matter”, which cannot be detected directly with currently available instrumentation.

10. Previous Models of the Expanding Universe (Most Recent Results indicate negative value of q0!)

11. RELATIVITY AND COSMOLOGY • The distances and velocities involved in the study of cosmology are so great that the laws and relationships involved in classical (Newtonian) physics must be replaced with the relationships described by Einstein’s Theory of Relativity, often broken down into the Special and General theories of relativity. • An important feature of the theory of relativity is that no material object or information can travel faster than the speed of light, which is about 300,000 km/sec (or 186,000 miles/sec). • Special relativity deals with unaccelerated motions (moving in a straight line at constant velocity) whereas general relativity deals with accelerated motions. • The more comprehensive General Theory of Relativity also includes a theory of gravitation. • Relativity requires four dimensions (three space dimensions, and time) to display (called “spacetime”), and so is somewhat difficult to conceptualize pictorially.

12. RELATIVITY AND COSMOLOGY • The history of the theory of relativity dates back to the late 19th and early 20th centuries, when experiments by Michelson and Morley were unable to determine a reference position of rest from which the speed of light could be determined. • If light waves were analogous to sound waves, their velocity should be higher when approaching the light source, and lower when receding from the light source. • They found that the speed of light they measured was the same regardless of the direction or motion of the measuring apparatus (including Earth’s rotation on its axis and revolution around the Sun). • Einstein’s theory of relativity states that the speed of light is the same for all observers, regardless of their relative motions; however, the observed wavelength of light changes with motion toward or away from the light source.

13. RELATIVITY AND COSMOLOGY • Einstein’s theory also postulated that: • No material object can travel at or faster than the speed of light • The energy equivalent of matter is given by the equation E = mc2 • The classical expression for kinetic energy of a material object, KE = 1/2mv2, is replaced, at speeds comparable to (but still less than) the speed of light, by a relationship that increases more rapidly than the square of velocity, and becomes infinite at v=c. • The energy equivalence of matter is the basis of the nuclear reactions that produce energy by fission or fusion of atomic nuclei, which power the Sun and stars, as well as nuclear reactors (and weapons) utilized on Earth. • An important factor in this theory is that there is no preferred point of reference in the Universe (it does not have a “center” or an “edge”). • A feature of the general theory, proven by astronomical observations, is that massive objects (such as our Sun) can bend the paths of light rays coming from more distant stars behind them.

14. SPEED LIMIT – STRICTLY ENFORCED Captain Kirk, pull over!

15. Effects of Special Relativity on Views of Fixed and Moving Observers Moving observer at B sees A moving to the left between A’s sending and receiving the (reflected) light, and so finds a longer path length of travel. If the speed of light is c, the time also has to be longer. Stationary observer at position A sends flash of light to observer and mirror at position B, moving at velocity v. Time to send and receive is 2a/c.

16. RELATIVITY AND COSMOLOGY • An important aspect of Einstein’s special theory of relativity, is that the apparent speed of light is the same, to an observer, regardless of the differential velocity of the light source toward or away from the observer. • There is also no standard reference for determining whether the observer or the light source is the moving object. • Although this may appear to be contradictory, if the same light source is observed simultaneously by another observer at rest relative to the light source, it is actually compensated by apparent time dilation (as viewed by the moving observer), and/or apparent contraction of the length of a meter stick carried by the moving observer, as observed by the stationary observer (“Lorentz-Fitzgerald contraction”): and

17. RELATIVITY AND COSMOLOGY • According to the equivalence of matter and energy, specified by Einstein’s equation, E = mc2, the mass term in the classical relationship for kinetic energy, KE = ½mv2 is replaced by the relationship which approaches infinity as v approaches c. • Likewise, the relativistic Doppler effect varies not directly with line-of-sight velocity,  =0 (1+ v/c) (applicable for v << c), but according to Note, the apparent speed of light is the same, regardless of velocity of the observer toward or away from the light source, but the apparent wavelength of the light shifts to shorter or longer wavelengths per the above equation.

18. OBSERVED EFFECTS OF SPECIAL RELATIVITY • One of the well-observed phenomena that provides direct support of relativity theory, is the lifetime of muons (a type of sub-atomic particle) that are produced when cosmic rays (mostly very high energy protons) collide with the nuclei of Earth’s upper atmospheric atoms. • The half-lifetimes of these muons, as measured in the laboratory, are extremely short (about 1.5 x 10-6 second), so even if they were traveling close to the speed of light they would travel only 450 meters in this half-lifetime. • However, the muons that are observed travel distances much larger than this, about 1800 meters, in this lifetime. • This is a manifestation of “time dilation”- time runs slower for the high-velocity muon by a factor of 4 or more, vs. the time recorded by observers on (or at fixed locations above) Earth. • Another (as yet untested!) manifestation is that of the “traveling twin”. If one twin takes a flight at nearly the speed of light to another solar system, and returns (after the visit) at the same speed, he or she will have experienced (by their clock) a shorter elapsed time, and will appear physically younger, than the stay-at-home twin.

19. RELATIVITY AND COSMOLOGY • According to the principle of relativity, there is no preferred location in the Universe, and hence no absolute reference point for a coordinate system (such as the Sun provides for our solar system, or the center of our Galaxy provides for the stars within it). • The speed of light, as witnessed by an observer, is the same regardless of position in space, or velocity relative to the observed object. • The concept of spacetime is a 4-dimensional coordinate system, consisting of three spatial dimensions and time. • An observer can only detect “events” that occur within his or her “light cone”, whose boundaries correspond to velocities equal to the speed of light. • Time can change only in one direction (forward, in the light cone diagram). Distance (3 dimensions) Velocity = Speed of Light Time Observer

20. THE COSMOLOGICAL PRINCIPLE • The cosmological principle states that the Universe is isotropic (homogeneous in its structure, and distribution of galaxies), on a scale greater than 200 Mpc. • From this principle, we infer that there is not (to our current knowledge) a “center” or an “edge” of the Universe. • Therefore, no matter where we are located in the Universe, it will appear that we are at the center of the expansion, with generally uniform distributions (in direction and distance) of galaxies as seen from our location (there is no “preferred” location in the Universe). • The large-scale structure of the Universe, as determined from surveys of galaxies over wide ranges of distance (out to about 750 Mpc) and in all directions in the sky, appear to show randomly distributed structures in their distribution, in the forms of “voids”, “walls”, and “bubbles”. • However, there appear to be no large-scale structures (greater than about 200 Mpc) in the distribution of galaxies.

21. THE COSMOLOGICAL PRINCIPLE • A two-dimensional analog to the three-dimensional expansion of the Universe is given by placing adhesive paper dots on the surface of a partially-inflated balloon. • As the balloon is further inflated, the dots will appear (to an observer, such as an ant, on any one of the dots) to move outward, in all directions (in the 2-dimensional space of the balloon’s surface), at a velocity proportional to distance. • Therefore, no matter where on the balloon the observing ant is located, it will have the impression that it is at the center of the expansion. • Likewise, no matter where we are located in the Universe, we will see uniform expansion away from our apparently central location; in the (apparently) three-dimensional Universe, time serves as a fourth dimension for the general expansion. • As mentioned previously, detailed analysis of this process requires use of Einstein’s general theory of relativity, which treats time as a fourth dimension.

22. THE “BIG BANG” AND THE ORIGIN OF ELEMENTS • The current hypothesis concerning the origin of the Universe is that it started out from a point (or very compact) object, composed of pure energy, which exploded outward in a “big bang” at the speed of light, and has continued to expand outward at this speed ever since. • Currently, the Universe consists of matter, as well as energy in the form of heat, kinetic energy, and electromagnetic radiation, and (hypothetically) “dark energy”. • Energy and matter can be interchanged, according to Einstein’s equation E = mc2, where E is energy, m is mass, and c is the speed of light (300,000 km/sec). • Currently, in our Universe, the matter which it contains far exceeds (in energy equivalence) the electromagnetic radiation (in the form of starlight and the cosmic microwave background radiation) and so is considered to be matter-dominated.

23. THE “BIG BANG” AND THE ORIGIN OF ELEMENTS • Stars (including our Sun) generate most of their energy by converting matter into energy, by means of thermonuclear reactions (such as fusion of hydrogen to make helium and other, heavier elements). • In the early Universe, the opposite process was at work, in which energy was converted into matter (elementary particles such as electrons, protons, and neutrons) which in turn were converted into the light elements, hydrogen and helium (and a small amount of lithium). • An example of this process is the interaction of two high-energy gamma-ray photons to produce an electron and a positron (the process of “pair production”), the inverse of the reaction which we observe in the laboratory at present. • To produce electron-positron pairs requires photons of about 1010 K; however, to produce proton-antiproton pairs requires energy equivalent temperatures above 1013 K!

24. THE “BIG BANG” AND THE ORIGIN OF ELEMENTS • For reasons as yet unknown, there was a dominance of protons and electrons over antiprotons and positrons in the early Universe; the former (along with neutrons) constitute the entire mass of the objects in the current Universe. • No significant amount of new matter is thought to have been created since the first minute of the “Big Bang”! • It is thought that the Universe was “radiation dominated” for the first few thousand years of its existence, following which it was “matter dominated”. • The first atoms are thought to have been created (by combination of electrons with protons and neutrons) about 106 years after the “big bang”. • The creation of neutral atoms (by combination of free electrons with positive nuclei) also resulted in de-coupling of the electromagnetic radiation from matter. • This made the Universe much more transparent to the electromagnetic radiation, which previously was strongly scattered by the free electrons.

25. THE EARLY EVOLUTION OF THE UNIVERSE • The first element to be produced (by combination of electrons with protons) was hydrogen, followed by deuterium (by combination of neutrons with protons, and addition of an electron). • The next element, helium, was produced by fusion of deuterium with hydrogen (1H + 2H  3He, and 3He + neutron  4He). • A small percentage (about 2 x 10-5 atoms per proton in the Universe) of lithium was also created at this time. • This primordial process was essentially the entire source of the lithium in the current Universe! • The observed abundance of lithium in the present-day Universe can be used to estimate the current total density of the Universe (based on extrapolation, backwards in time, to the period when the lithium was being created). • This calculation indicates that the current density of the Universe is only a few percent of the critical density (above which the Universe will eventually reach a maximum size and then re-collapse).

26. THE EARLY EVOLUTION OF THE UNIVERSE • However, studies of the motions of galaxies in clusters and superclusters indicate that the total mass (based on gravitational interactions) of the Universe is about 1/3 of the critical density. • This, in turn, implies the existence of “dark matter” which has gravity but is invisible (also implied from the rotation velocity vs. central distance curves of individual galaxies). • This also implies that this “dark matter” is not made up of protons and neutrons (and so cannot be in the form of brown or white dwarfs, neutron stars, or black holes). • Although the energy equivalence of matter in the current Universe far exceeds that of the cosmic background radiation, the latter still exceeds the energy content of starlight due to all of the currently existing stars and galaxies. • The recent determination that the expansion of the Universe is accelerating, not decelerating as previously hypothesized, also indicates the presence of a currently unknown “dark energy”.

27. THE UNIVERSE AND COSMOLOGY • The HubbleSpace Telescope (HST) and new large ground-based telescopes have allowed imaging and redshift measurements of galaxies at much greater distances from Earth than previously possible. • Observations of very distant galaxies are required to determine the time /distance variation of the expansion rate, and whether the total mass of the Universe is less than, equal to, or greater than the critical mass. • However, recent observations appear to indicate a less than perfectly linear increase in velocity with distance, which would indicate that the rate of expansion has increased with time since the “big bang”. • The planned Next Generation Space Telescope (NGST), recently re-named the James Webb Space Telescope (JWST),will extend our observations of galaxies to much greater distances than currently possible, by the use of a much larger aperture than HST, and by observing farther into the infrared (corresponding to larger redshifts).

28. THE UNIVERSE AND COSMOLOGY • The intense radiation field which accompanied the Big Bang is still evident today, as the cosmic background radiation. • This background radiation was first detected in ground-based microwave measurements by A. Penzias and R. Wilson in 1965. • The Cosmic Background Explorer satellite (COBE), launched in 1989, had as a major objective the detailed measurement of this microwave background radiation. • This radiation, initially characteristic of multi-million degree temperatures, has been red-shifted by the expansion of the Universe so that it now corresponds to black-body radiation characteristic of a temperature of 2.73 K. • Small variations in the intensity of this background radiation over the sky may indicate the initial fragmentation of the material into clumps capable of condensing to form galaxies. • The recently launched Wilkinson Microwave Anisotropy Probe (WMAP) mission is now obtaining much more detailed mapping of the cosmic background radiation over large regions of the sky.

30. All-Sky Map of the Cosmic Microwave Background Radiation Obtained by the Cosmic Background Explorer (COBE) The color variations are due to our solar system’s (and Galaxy’s) proper motion relative to the Universe and the background radiation (which otherwise appears nearly uniform in distribution).

31. All-Sky Map of the Cosmic Microwave Background Radiation Obtained by COBE, after Local Background Variation Subtraction and Contrast Enhancement

32. Wilkinson Microwave Anisotropy Probe (WMAP)

33. Wilkinson Microwave Anisotropy Probe (WMAP)

34. WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) • The WMAP mission, successor to the COBE mission, is the most recent to observe the cosmic background radiation and the overall structure of the Universe. • WMAP is providing much higher resolution imagery and other information about the cosmic background microwave radiation, as revealed by very slight, small-scale temperature fluctuations. • These and other, related data are both verifying and strengthening theories of the origin and early evolution of the Universe, such as the Big Bang and Inflation theories. • The WMAP map of the sky in the 2.73 K background radiation corresponds to a view of the Universe when it was only about 380,000 years old! • These (and other) measurements have also refined and more accurately determined our previous estimates of the age of the Universe, now indicated to be 13.7 billion years (with 1% accuracy!).

35. ALL-SKY MAP OBTAINED BY THE WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP)

37. COSMIC EVOLUTION

38. FUTURE RESEARCH OBJECTIVES IN COSMOLOGY • The recent WMAP (and other) space missions, in combination with ground-based observations and theoretical research, have greatly advanced our knowledge of our Universe and its history, in recent years. • However, they have also revealed new and unexpected mysteries, which will provide much to investigate in the foreseeable future. • Among the most important of these, are the realization that previously unknown “dark matter” and “dark energy” are major components of our Universe, for which the laws of physics, as we know them, have no immediate explanation! • The current observations indicate that matter, in the forms we know (protons, neutrons, and electrons), constitute only a few percent of the total! • In addition, we still do not have direct information about the events and time scales of the origin of the Universe (in the time period 0 to 380,000 years) - much less, about what happened prior to that!

39. THE MORE WE DISCOVER, THE MORE WE FIND WE DON’T KNOW! • Perhaps the most important result of our most recent observations of the distant Universe, is that many of the aspects of cosmology we set out to prove, have been proven false! • In particular, observations of the redshifts of very distant galaxies have shown that the rate of expansion of the Universe is increasing with time, instead of decreasing with time, as previously assumed. • This can be explained only by the presence of previously unknown dark energy which uniformly permeates the entire Universe. • In addition, and even prior to this, a previously unknown cold dark matter was required to explain the rates of revolution of stars around the center of our Galaxy, and of external galaxies. • These previously unknown contributions to the total mass and energy of the Universe constitute more than 95% of the total! • Clearly, there is still a great deal that needs to be done, by both observational and theoretical research, to complete our understanding of our Universe, its origins, and its future.

40. Inventory of Matter and Energy in the Universe

41. THE JAMES WEBB SPACE TELESCOPE • The James Webb Space Telescope (JWST, previously known as the Next Generation Space Telescope, NGST) is planned as the follow-on to the Hubble Space Telescope, particularly in the research areas of distant galaxies and cosmology. • The JWST is designed to study the earliest galaxies and some of the first stars formed after the Big Bang. • The JWST will have a larger collecting mirror than the HST, and will be optimized for studies in the infrared wavelength range. • It will also be placed in a very distant orbit from Earth (as was the Spitzer space telescope) to avoid heating and infrared radiation interference by Earth and its atmosphere. • Because of the very large mirror size (6.5 meters in diameter) and sunshield, the JWST is launched in a “folded up” configuration, and deployed only after launch into space. • The JWST is currently planned for launch in August, 2011.

42. THE JAMES WEBB SPACE TELESCOPE • JWST science objectives involve finding answers to the following questions: • What is the shape of the Universe? • How do galaxies evolve? • How do stars and planetary systems form and interact? • How did the Universe build up its present elemental/chemical composition? • What is dark matter? Artist’s Concept of JWST in Solar Orbit