Study Guide Review Everything! PDF

Key Terms Cosmology = The ultimate archaeological science that looks into the deepest realms of the Universe -​ Finite velocity of light is critical (this proves expansion happened?) Isotropic = The Universe looks the same from all angles, no matter where the observer is located Cosmological pr...

Key Terms Cosmology = The ultimate archaeological science that looks into the deepest realms of the Universe -​ Finite velocity of light is critical (this proves expansion happened?) Isotropic = The Universe looks the same from all angles, no matter where the observer is located Cosmological principle = The Universe is homogeneous and isotropic Cosmological constant = Λ (lambda) -​ Einstein’s biggest blunder because he would’ve been the first to discover the Universe is expanding if he had not factored this into his equation -​ Proves dark energy exists, which is the driving force behind the Universe expanding Omega Ω = Most important parameter! -​ Part of FRWL dynamics -​ Ω = 1 (critical density = Universe is flat) -​ Ω > 1 (closed Universe = Universe has a positive curvature) -​ Ω = 1 (open Universe = Universe has a negative (concaved) curvature) Redshift = The waves of light get stretched by the expansion of the Universe, so while the light is travelling through the Universe, the Universe stretches. When the wavelengths of light are stretched to become longer, they move towards the red of the spectrum, making it look redder than it originally was. Redshift helps astronomers figure out how fast objects in space are moving away from us, how far away distant galaxies are, and that the Universe is expanding (which supports the Big Bang theory.) Blackbody = A blackbody is a perfect object that absorbs all the light and radiation that falls on it, no matter the colour and type. It re-emits this energy as radiation (blackbody radiation) that depends only on its temperature. Also, a perfect blackbody doesn’t exist in real life, but some objects behave almost like blackbodies (so we were right). Dark matter = 25% of the Universe. Invisible and doesn't emit light but has gravity, helping galaxies stick together. Dark energy = Dark energy accounts for about 73% (according to my notes, 68% according to Wikipedia) of the Universe and causes the Universe to expand faster and faster over time. We don’t fully understand it but it might be the cosmological constant introduced by Einstein’s equations of general relativity, which describes the idea that space can have energy even when it appears empty. Baryonic matter = 5% of the Universe. The ordinary matter (stars, planets, you) we can see and touch. Concordance expansion = Globular cluster stars = rough spherical groups of 100,000-200,00 stars -​ radius of 20-50 pc -​ extremely high density -​ super old in the Universe -​ regular stars formed around the same time -​ color-magnitude diagram characteristic: accurate age determination on the basis of stellar evolution theories Parallax = apparent displacement of an object because of a change in the observer’s point of view (wobble?) Mousein = world’s first university with a library w/ 700,000 book scrolls and stored all knowledge in the ancient world Precession = chatgpt says it refers to the gradual change or "wobble" in the orientation of an astronomical body's rotational axis or orbital path over time. Star magnitude = star’s brightness Cosmology Timeline 2nd millenium BCE ​ Mesopotamian cosmology describes a flat, circular Earth enclosed in a cosmic ocean 12th cent. BCE ​ Rigveda has cosmological hymns Anaximander — 6th cent. BCE ​ The founder of scientific Astronomy and Cosmology and first to say that it was not the gods, but laws ​ ‘Earth floats free without falling’ ​ Aperion = boundless, infinite, indefinite is how the Universe originated Pythagoras — 6th cent. BCE (Samos, 570 - 495 BCE) ​ Geocentric worldview ​ Believed that Earth is a sphere with a central fire ​ Didn’t like gods, myths, or the divine, favored numbers instead ○​ Book of Nature: World can only be understood through numbers, musical harmony, harmony of spheres (planetary motion resembles music) ​ Found secretive school in Croton ○​ mathematikoi = learners extending and developing scientific and mathematical work ○​ akousmatikoi = listeners focused on religion and ritualistic aspects Democritus — (460-370 BCE) ​ Atomic theory (so no evidence, just a thought) ○​ Atomism = everything is made from atoms ○​ physically, not geometrically indivisble ​ All matter consists of invisible particles called atoms ○​ Atoms are indestructible ○​ Atoms are solid but invisible ○​ Atoms are homogenous ○​ Atoms differ in size, shape, mass, position, and arrangement, which decides what they are  ○​ Solids are made of small, pointy atoms, and liquids are made of larg, round atoms 470-385 BCE ​ Non-geometric cosmos ​ Philolaus of Croton ○​ Pythagorean school ​ First step toward hellenistic period ​ Central fire at cosmos center, everything revolves around the center w. a system of spheres (fixed stars, planets, Sun, Moon, Earth) Plato (428 - 348 BCE, 4th cent. BCE): ​ Geometric worldview (structured according to math) ○​ Geometry is the main principle ​ Key Ideas: ○​ In Timaeus, proposed the cosmos is crafted by a divine mathematician (Demiurge) who uses geometry as a blueprint for how the Universe was made. ○​ Introduced the Platonic Solids, associating them with elements of which the cosmos is made: ​ Tetrahedron: Fire ​ Cube: Earth ​ Octahedron: Air ​ Icosahedron: Water ​ Dodecahedron: Quintessence (the material of the heavens). ○​ Believed in an ideal, unchanging, and eternal world of forms, with the material world as an imperfect reflection. ​ Significance: ○​ His geometric view of the cosmos influenced both ancient and modern scientific thinking. ○​ Introduced philosophical methods for understanding the universe's structure. Aristotle 384-322 bce): ​ Geocentric worldview ○​ Earth at center of the Universe surrounded by 55 heavenly spheres ○​ Universe always existed (no creation) ​ Cosmos divided into two regions:  ○​ Earthly (earth, water, air, fire) ○​ Heavenly (made of perfect, unchanging substance called aether) ​ Movement in the heavens is circular and eternal, driven by a “prime mover” ​ 4 causes for why things happened: ○​ Material cause (what something is made of) ○​ Formal cause (its structure or design) ○​ Efficient cause (what brings it into being) ○​ Final cause (its purpose) ​ His cosmology dominated Western thought for over 1,800 years until Tycho Brahe found a new supernova and proved that the Universe was not eternal and unchanged ​ Put physics, metaphysics, and logic into one framework to understand nature Hellenistic Scientific Revolution Timeline Aristarchus (Samos, 310 - 230 BCE) — 3rd cent. BCE ​ Heliocentric worldview (basically ancient Copernicus) ○​ Earth rotates on its axis and revolves around the Sun, which is stationary ○​ Stars are distant (which is why their positions don’t seem to change, aka no observable parallax) ​ First attempt to measure the distance between Earth and Sun, which was the first attempt to scale the Universe Archimedes (287-212 BCE) — 3rd cent. BCE Eratosthenes (276 - 194 BCE) — 3rd cent. BCE ​ Hellenistic astronomer ​ Studied in Alexandria and Athens ​ Calculated earth’s circumference pretty accurately (39,690 km, 15% error rate) Apollonius — late 3rd cent. - 2nd cent. BCE ​ Epicycle theory for lunar and planetary motions Hipparchus (190 - 120 BCE) ​ trigonometric tables ​ precession of the equinoxes ​ motion of the moon (synodic, anomalistic) ​ solar and lunar eclipses ​ orbit of the moon: epicyclic theory ​ distance of the moon ​ star catalogue and celestial globe and farnese atlas ​ defined magnitude scale ​ invented astrolabe Seleucus — 2nd cent. BCE (190 -150 BCE) Antikythera Mechanism — 2nd cent. BCE (150 BCE) Ptolemy >:( — 2nd cent. BCE (100-170 AD) ​ The first geographer to use longitude and latitude to create coordinates ○​ Derived 21 latitude lines to be fairly accurate ​ Geografia → first geographer to use longitude and latitude to create coordinates ○​ Order of the planetary spheres → moon, mercury, venus, sun, mars, jupiter, saturn, sphere fixed stars ​ 4 projections??? “Modern” People Friedmann & Lemaître (Gravity) ​ Independently discovered the Universe is expanding, which is the solution to Einstein’s GR theory ​ Friedmann ○​ Says that the Universe is expanding based on 3 factors: ​ 1. density of matter/energy (p) ​ 2. curvature (k) ​ 3. cosmological constant (Λ) ​ Lemaître ○​ Proposed the Universe started as a primeval atom (hot and dense state) and that galaxies moved away from us (redshift), expanding and stretching space ​ Friedmann, Lemaître, Einstein, and De Sitter realized that in GR, the Universe cannot be static because the Universe either expands or contracts by a factor of a(t) ○​ a(t) = scale factor that describes how the Universe expands/contracts uniformly FRWL Universe: 1.​ The Universe is homogeneous, appearing the same everywhere (nowhere is special) 2.​ The Universe is isotropic (looking the same from all directions)  3.​ The Universe is dynamic, expanding/contracting by a(t) → cosmological principle: homogenous & isotropic (Newton believed the same!) FRWL Dynamics: describes how the Universe’s density changes over time -​ Ω = p/p crit (refer to “omega” term) Newton ​ Heliocentric worldview ​ 1687 → Philosophiae Naturalis Principia Mathematica ○​ One of the most important works in the history of science ○​ Newton’s laws of motion → forming the foundation of classical mechanics ○​ Newton’s law of universal gravitation → the discovery of the force of gravity ○​ Derivation of Kepler’s laws of planetary motion ○​ Integral and Differential Calculus ​ Laws of motion 1.​ An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force 2.​ A larger net force acting on an object causes a larger acceleration, and objects with larger mass require more force to accelerate (force = acceleration x mass = change in velocity x mass) 3.​ Action = reaction Kepler ​ Heliocentric worldview ​ Goal: to reveal the divine laws and plan dictating the motion of the planets according to Copernicus’s heliocentric system ​ Together with Galileo, Sun at the centre of our universe ​ Known for the laws of Kepler → derived them mathematically ○​ Intentions were different → had a mystical view → God made the universe ○​ Combined that idea with the idea that Copernicus was right ○​ With the motivations to find the mathematical rules of God, why the planets are ordered like they are, the reason for the radii of the orbits ​ Mysterium Cosmographicum, 1596 (book) ​ Laws of planetary motion → planets move in elliptical orbits ​ Music of the spheres came back like Plato and Pythagoras ​ Astronomia Nova, 1906 (book) → first two rules of Kepler were introduced  1.​ The orbit of a planet is an ellipse with the sun at one focus 2.​ A line segment joining a planet under the sun sweeps out equal areas during equal intervals (planets do not move with uniform speed along their orbit) 3.​ The square of the orbital periods of a planet is proportional to the cube of the orbit’s semi-major-axis ​ Following the motion of Mars in relation to Earth ​ His entire career was based on three questions: ○​ Why were there six planets back then? ○​ Why are they spaced around the sun as they are? ○​ Why do they move as they do? Kepler’s inference (earth & mars orbits): ​ kepler inferred that the planets orbiting are elliptical by studying mars and earth’s motion ​ collected mars’ oppositions ​ direction of the sun and the stars giving earth direction from the sun ​ gave directions and times of the orbit of mars ​ provided accurate determination of period of mars’s orbit Galileo Galilei ​ Heliocentric worldview ​ Showed how things worked → father of observational astronomy, modern physics, and scientific method ​ First to turn the telescope towards the sky ​ Developed his own telescopes → one with magnification of 3x and one with magnification of 30x ​ Evidence for sun at the centre was Galilei’s discovery of the phases of Venus Tycho Brahe ​ His knowledge of the sky was so big that he knew every star and also when a new star became visible ​ 1572 → found a new star in the constellation of Cassiopeia → was a supernova ○​ So the heavens did change, unlike Aristotle claimed → end of Aristotle’s cosmology ​ Geo-heliocentric model → disagreed with Copernicus ○​ Earth must be the centre, but the planets do rotate the sun and the sun rotates the Earth Copernicus ​ Heliocentric worldview ​ 1514 → commentariolus (‘Little Commentary’) 1.​ There is no center of all the celestial circles or spheres 2.​ The center of the earth is not the center of the universe, but only of gravity and of the lunar sphere 3.​ All the spheres revolve about the sun as their midpoint, and therefore the sun is the center of the universe 4.​ The ratio of the earth’s distance from the sun to the height of the firmament (outermost celestial sphere containing the stars) is so much smaller than the ratio of the earth's radius to its distance from the sun that the distance from the earth to the sun is imperceptible in comparison with the height of the firmament 5.​ Whatever motion appears in the firmament arises not from any motion of the firmament, but from the earth’s motion. The earth together with its circumjacent elements performs a complete rotation on its fixed poles in a daily motion, while the firmament and highest heaven abide unchanged 6.​ What appears to us as motions of the sun arise not from its motion but from the motion of the earth and our sphere, with which we revolve about the sun like any other planet. The earth has, then, more than one motion 7.​ The apparent retrograde and direct motion of the planets arises not from their motion but from the earth’s. The motion of the earth alone, therefore, suffices to explain so many apparent inequalities in the heavens ​ 1543 → publication of the Revolutionibus Orbium Coelestium (only year we need to know) ○​ ‘On the Revolution of the Celestial Spheres’ ○​ Presentation of a heliocentric model of the universe Einstein (1879 - 1955) ​ Father of GR (1915) ​ Special Relativity, pub 1905 ○​ no such thing as absolute space or time ○​ they are not independent, but together = spacetime ​ Principle of relativity: all the laws of physics are identical in all inertial reference frames ​ Constancy of speed of light ○​ Speed of light is the same in all inertial frames (independent of observer’s velocity and light-emitting source’s velocity) ​ Relativistic spacetime  ○​ Spacetime combines space (the three dimensions we move in) and time (the fourth dimension) into one single "fabric." In Einstein's theory of relativity: ​ Spacetime can be stretched, compressed, or bent by mass and energy. ​ Events in the universe (like the motion of planets or the ticking of a clock) happen within this spacetime. ○​ Think of spacetime like a flexible grid where everything exists and moves. Gravity, for example, happens because spacetime bends around massive objects. ○​ Speed of light constant = c = 3 x 10^8 km/s ○​ only possible if time and space are not absolute ​ Time dilation ○​ Time dilation means that time doesn’t flow the same for everyone. If you’re moving very fast (close to the speed of light) or near something extremely heavy (like a black hole), time will slow down for you compared to someone else. ○​ Example: if you're on a spaceship traveling at near-light speed, your clock will tick slower compared to someone’s clock on Earth. For you, only a few years might pass, but for someone on Earth, decades could go by. ​ Length contraction ○​ Length contraction means that objects appear shorter along the direction of motion when they move very fast (close to the speed of light). This effect only happens for the person observing the fast-moving object, not for the object itself. ○​ Example: if a spaceship flies past you at near-light speed, it will look squished or shorter from front to back. However, the people inside the spaceship wouldn’t notice this at all. Main Theories/Concepts Olber’s Paradox ​ In an infinitely large, old and unchanging Universe each line of sight would hit a star, so the sky would be as bright as the surface of a star ​ Yet the night sky is dark, so the Universe is not infinitely large, old or unchanging (at least one of these claims must be false) ​ The Olber’s Paradox proves the Big Bang Theory ○​ According to the Big Bang theory, the Universe is not static, but expanding, which causes the light of stars and galaxies to redshift ○​ According to the Big Bang theory, the Universe had a beginning, so a finite age General Relativity ​ Einstein figured out that gravity is the warping of space and time due to mass and energy ​ He made an equation that almost proved that the Universe because there’s curvature! ○​ Basically, when an object stretches spacetime, it creates curvature. This stretching implies the spacetime is getting bigger = expanding, and the act of this is gravity! Cosmic Microwave Background (CMB) ​ The CMB is a form of radiation (energy) that fills the entire universe. It’s made up of microwaves, which are a type of light with longer wavelengths than the visible light we see. It comes from all directions in space and is present everywhere. ​ The Big Bang theory states and predicts that the Universe expanded from a state of high density and temperature ​ 1965 → CMB was discovered accidentally in Bell Labs ​ Big Bang theory states ○​ Existence of Cosmic Background Radiation → The theory predicted that radiation from the early universe would still exist today, but its wavelength would be stretched (redshifted) as the universe expanded. This radiation should now be observable as low-energy microwaves, uniformly present in all directions. ○​ Blackbody Spectrum → The CMB should have a nearly perfect blackbody spectrum because the early universe was in thermal equilibrium. This means the intensity of radiation at each wavelength should follow a  specific curve described by Planck’s law. The temperature of this blackbody radiation was predicted to be a few Kelvin above absolute zero. ○​ Uniformity with Small Fluctuations → The CMB should be nearly the same in all directions (isotropic) because the early universe was homogeneous and isotropic on large scales. However, small temperature fluctuations (anisotropies) should exist, corresponding to tiny density variations in the early universe that later gave rise to galaxies and cosmic structure. 4 Fundamental Forces of Nature 1.​ strong nuclear force a.​ responsible for holding particles together inside nucleus b.​ the carrier particle in this force is called a gluon c.​ nuclear strong interaction has a range of 10^-15 m (diameter of a proton) 2.​ electromagnetic force a.​ responsible for electric and magnetic interactions, determines structure of atoms and molecules b.​ carrier particle is photon (quantum of light) c.​ interaction range is infinite 3.​ weak force a.​ responsible for beta radioactivity b.​ carrier particles are called weak gauge bosons (z, w+, w-) c.​ interaction has a range of 10^-17 m (1% of proton diameter) 4.​ gravity a.​ responsible for attraction between masses b.​ hypothetical carrier particle is graviton c.​ interaction range is infinite d.​ weakest force of nature > gravity’s range is infinite and not shielded, it’s cumulative as all mass adds up, and electromagnetic charges can be + or -, canceling each other out Adiabatic Expansion ​ The Universe sustains itself ​ Expansion is not driven by any outside energy forces ​ There is no loss of energy during expansion ​ There is no heat transfer during expansion ​ The gas cools during expansion because it uses energy to do work ○​ The Universe cools as a result of expanding ​ einstein, friedmann, and lemaitre’s universe expands adiabatically Big Bang ​ The Big Bang theory states that the Universe started with an extremely quick expansion of space itself around 13.8 billion years ago, which happened everywhere (so it is not an actual bang). This expansion is still going on till this day. ​ Basically, the Universe was just a hot soup of particles, and as it cooled down these particles began to form atoms. ​ The five points of evidence for the Big Bang are 1.​ Olber’s Paradox (the night sky is dark) 2.​ Hubble expansion ○​ The Universe expands because there is a relation between velocity and distance, so the Universe must have had a beginning 3.​ CMB (the leftover glow and the ‘ultimate’ evidence) 4.​ Helium abundance of 24% ○​ The Big Bang theory predicts that about 24% of the ordinary matter in the universe by mass would be helium and the rest would be mostly hydrogen. ○​ If the universe had been significantly older or younger at the time of nucleosynthesis, or if it had different physical conditions (e.g., different expansion rates, densities, or temperatures), the helium abundance would be vastly different. 5.​ The further you look into space, the earlier you look back into time ○​ If the Universe was infinitely old and didn’t change, you’d expect a universe far away to look the same as ours Epicycle Theory ​ The epicycle theory was an ancient and geocentric way of explaining the movements of the planets in the sky. It tried to explain the retrograde motions of the planets. ​ In a geocentric universe planets move on a small circle (epicycle), are superimposed and move on a large circle (deferent) → both epicycle and deferent rotate clockwise which explains the retrograde motion of planets in the sky. ​ Superior planets ○​ Planet moves through the night sky slower than the stars ○​ Each night planet appears to lag a little behind the stars = prograde motion ○​ Near opposition the planet would appear to reverse and move through the night sky faster than the stars for a time in retrograde motion before reversing again and resuming prograde ​ Inferior planets  ○​ Always observed to be near the sun and appearing only shortly before sunrise or shortly after sunset (Mercury and Venus) ○​ Apparent retrograde motion occurs during the transition between the evening star into morning star as they pass between earth and the sun ​ So, these people thought that the planets and the Sun were moving around the Earth like in the image below. Ptolemy’s Almagest — “The Great Book” -​ the great book -​ mathematical and astronomical treatise proposing complex motions of stars and planetary paths -​ written in 147-148 ad, inscription in canopus by ptolemaeus -​ 13 books -​ originally in greek (mathematike syntaxis, he megale syntaxis) -​ super influential scientific work syntaxis - almagest: “the great book” -​ ptolemy was the first scientist to use inductive method -​ models framed from preliminary facts -​ expand models by logical induction -​ testing hypothesis against reality -​ only surviving comprehensive ancient treatise on astronomy  -​ most important source of information on ancient greek astronomy -​ geocentric model, epicycle theory -​ models were presented in tables -​ dominated astronomy for about 13 centuries -​ roman (byzantine, western) world, arabic world -​ fairly accurate calculations for predicting solar and lunar eclipses -​ contains star catalogue (appropriated hipparchus) -​ 48 constellations, modern ones, not full sky cosmology of the almagest according to ptolemaeus’ cosmos: 5 main points: 1.​ the celestial realm is spherical and moves as a sphere 2.​ earth is a sphere 3.​ earth is at the center of the cosmos 4.​ earth in relation to the distance of the fixed stars has no appreciable size and must be treated as a mathematical point 5.​ earth does not move Copernicus’ Commentariolus ​ 1514 ​ theoretical treatise on heliocentric mechanism ​ 40 pages, 7 basic assumptions Kepler’s Laws of Planetary Motion/Kepler’s 3 Laws 1.​ The orbit of a planet is an ellipse w. the Sun at one focus a.​ Planetary orbits are not perfectly circular, and this dismantled previous beliefs that they were 2.​ A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time (planets don’t move with uniform speed along their orbit) a.​ Planets move faster when they’re closer to the Sun (perihelion) and slower when they’re away (aphelion), reflecting the conservation of angular momentum 3.​ The square of a planet’s orbital period is proportional to the cube of the length of the semi-major axis of its orbit a.​ Relationship between the size of a planet and the time it takes to complete one orbit Type 1a Supernovae ​ Two normal stars are in a binary pair → the more massive star becomes a giant which spills gas onto the secondary star, causing it to expand and become engulfed → the secondary, lighter star and the core of the giant star spiral inward within a common envelope → the common envelope is ejected while the separation between the core and the secondary star decreases → the remaining core of the giant collapses and becomes a white dwarf → the ageing companion star starts swelling, spilling gas onto the white dwarf → the white dwarf’s mass increases until it reaches a critical mass and explodes, causing the companion star to be ejected away ​ Chandrasekhar mass limit = the maximum mass at which a star near the end of its life cycle can become a white dwarf and above which the star will collapse to form a neutron star or black hole Inertial v.s. Gravitational Mass (Einstein) ​ Gravitational = a larger mass experiences a stronger gravitational force than a light mass ​ Inertial = a larger mass is more difficult to get moving than a light mass ​ Result = heavy mass falls just as mass as light mass → gravitational mass = inertial mass (hammer v feather)’ Equivalence Principle (Einstein) ​ Gravitational = a larger mass experiences a stronger gravitational force than a light mass ​ Imagine you're in a closed room, like an elevator, and you feel a force pushing you down. There are two possibilities: 1.​ The room is on Earth, and the force you feel is gravity pulling you down. 2.​ The room is floating in space, but it's being accelerated upwards at the same rate as Earth's gravity. ​ In both cases, you would feel the same force pressing you against the floor. From inside the room, you couldn’t tell whether it’s gravity or acceleration causing the force. ​ This principle leads to the idea that gravity isn't really a "force" pulling objects but instead the result of objects moving along curved paths in space-time, which is shaped by mass and energy. The equivalence principle bridges the concepts of gravity and motion and is a foundation for Einstein's revolutionary ideas about the universe. Curved Space (Einstein) ​ ChatGPT’s ‘easy’ explanation → Imagine space like a flexible rubber sheet. When you put something heavy, like a ball, on that sheet, it creates a dent or curve. The heavier the ball, the deeper the dent. In the universe, massive objects like stars and planets create similar dents in space, but in three dimensions instead of just two. This "denting" or curving of space affects how objects like planets, light, or comets move. Instead of moving in a straight line, they follow the curves, like a marble rolling around the dent in the sheet. So, curved space is just Einstein's way of describing how gravity works: heavy objects bend space and time, and this bending influences how things move around them. ​ Gravity and curved spacetime ○​ In gravity fields, light follows a curved path (= straight lines in curved spacetime) → like flightpaths of airplanes over the surface of the Earth ○​ Gravity is the effect of curved spacetime First three minutes after Big Bang 0 to 10⁻⁴³ seconds: The Planck Era ​ This is the earliest moment we can describe. ​ The universe was unimaginably hot and dense, and all forces (gravity, electromagnetism, and nuclear forces) might have been unified. ​ Physics as we know it doesn’t yet apply because quantum gravity dominates. 10⁻³⁵ to 10⁻³² seconds: Inflation ​ The universe expanded exponentially, faster than the speed of light (this doesn’t violate relativity since space itself expanded). ​ Tiny quantum fluctuations stretched out, becoming the seeds for galaxies and large-scale structures. 10⁻¹² seconds: Formation of Fundamental Forces ​ As the universe cooled, forces began separating:  ○​ Gravity split off first. ○​ The strong nuclear force and the electroweak force separated later. 10⁻⁶ seconds: Quark Soup ​ The universe was still extremely hot (about 10 trillion degrees). ​ Quarks (the building blocks of protons and neutrons) and gluons (force carriers for the strong force) existed in a hot, dense "soup." ​ Other particles like photons, electrons, and neutrinos also filled the universe. 1 second: Neutrino Decoupling ​ The universe cooled to about 10 billion degrees. ​ Neutrinos (tiny, nearly massless particles) stopped interacting with matter and began streaming freely through space, still detectable today as part of the "cosmic neutrino background." 3 seconds: Formation of Protons and Neutrons ​ Quarks combined to form protons and neutrons as the universe cooled further. ​ These particles made up the nuclei of future atoms. 3 Minutes: Primordial Nucleosynthesis ​ By this point, the universe was around 1 billion degrees. ​ Protons and neutrons started combining to form the first atomic nuclei, mostly hydrogen, helium, and a tiny bit of lithium. ​ Heavier elements couldn’t form because the universe cooled too quickly. Key Outcomes After 3 Minutes ​ The universe was a hot plasma of atomic nuclei, electrons, and photons. ​ It was too hot for atoms to form yet; they wouldn’t form until 380,000 years  later when the universe cooled further (releasing the cosmic microwave background). lecture 8 super quick overview: distance measurement = universe is too wide to measure everything -​ easiest way is to use apparent brightness (observed brightness of an object) and intrinsic brightness of an object (absolute brightness) -​ standard candles help determine distances in the universe when astronomers know the intrinsic brightness of an object cepheid stars are really bright and can help determine the distance to other galaxies henrietta leavitt = discovered period-luminosity relation of cepheid stars -​ hubble used this relation to establish distance of nearby galaxies and discover expansion measuring velocity = redshift/blueshift of radiation emitted by a source (galaxy or star) -​ if the light is going to us, it’s blue, if it’s going away, it’s red doppler effect!!!! ??? what is it??? ​ When the ambulance approaches you hear high pitch, when the ambulance passes you hear lower pitch. Sounds very weird. Works the same with light, because blueshift and redshift. spectrum = energy distribution of light (red = lower energy, blue = higher energy what the fuck is a spectral line!!! ​ The black lines in the colour spectrum and the coloured lines in the black thing/box ​ Like in the assignment with the little spectrograph thing we had to fold galaxy spectra = combined light of billions of stars slipher = first to measure redshift of galaxies hubble law = linear recession velocity - distance relation cosmic expansion manifests itself in a recession velocity which linearly increases w/ distance -​ no center of universe (would conflict w/ cosmological principle) results of expansion of universe: 1.​ distances get stretched 2.​ wavelength of light stretches = cosmic redshift z, related to a (t) a.​ redshift z = distance of observed object expanded by a (t) factor cosmic time dilation: -​ light curves supernovae -​ it’s a time interval over which the supernova rises then dims Summary (lecture 9) 1.​ Strong evidence accelerated expansion 2.​ Dark energy as cause cosmic acceleration 3.​ Independent evidence dark energy 4.​ Vacuum energy as dark energy a.​ Simplest explanation for dark energy is the energy associated with the vacuum IMPORTANT STUFF FROM LECTURE 10 universe expands adiabatically echo of the big bang = recombination, decoupling, last scattering yay light cmb recombination = protons and electrons combine to make hydrogen atoms decoupling = photons and baryonic matter are not friends anymore lost scattering = photons go bye bye cmb thermalization: 1.​ compton scattery 2.​ free-free scattering (what the FUCK) 3.​ double compton scattering = redistribute photon’s energy big bang cannot explain: 1.​ flatness problem = why universe is flat (FRWL DYNAMICS WITH OMEGA!!) 2.​ horizon problem = why universe is isotropic and homogenous 3.​ monopole problem why there aren’t any magnetic monopoles in universe 4.​ fluctuation problem = structure in the universe’s origin inflation of universe??