A Brief History of Time (Stephen Hawking)

Albert Einstein (1905)

Albert Einstein theory of relativity, laws of science should be same for all freely moving observers no matter their speed (E=MC squared, energy-mass-speed of light); time not completely separate from / independent of space, but combined with to form space-time; but what about gravitational pull?

General Theory of Relativity

Albert Einstein's description of gravity that was published in 1915. This theory explains the relationship between the geometry of space and the flow of time in our Universe. Describes the force of gravity and large-scale structure of universe (on scales from few miles to million million million million miles, size of observable universe)

Galileo (1609)

Aristotelian / Ptolemaic theory received deathblow when Galileo started observing w/ telescope (just invented) and saw Jupiter was accompanied by several small satellites or moons that orbited around it (implied everything didn't orbit around earth)

Aristotle (340 BC)

Aristotle said earth was round not flat b/c 1) eclipses of moon were caused by earth coming b/w sun and moon and shadow on moon was round, and 2) Greeks knew North Star was lower in the sky when viewed from the south (they traveled extensively); Aristotle also thought earth was center of universe

Expansion of Universe (before 20th century)

Before 20th Century, nobody suggested universe was expanding or contracting; universe had simply existed forever in unchanging state or created at finite time in past

Black Holes: Event Horizon

Black holes have an event horizon that light cannot escape that circulates around black hole (light has parallel paths so it doesn't collide and fall into black hole); black hole and event horizon can't emit particles so particles emitted from empty space outside of event horizon

British Expedition in N. Africa (1919)

British expedition, observing eclipse in W. Africa, showed that light was deflected by sun (gravitational pull), so star's actual position in sky may be different than what we see; theory of relativity got rid of absolute time

Quantum Mechanics

Deals w/ phenomena on small scale, millionth of millionth of inch; cannot be consistent w/ theory of relativity - both cannot exist and be correct; search for a new theory is underway to incorporate both relativity and quantum mechanics; called quantum theory of gravity (complete unified theory)

Edwin Hubble (1929)

Edwin Hubble observed wherever you look distant galaxies are moving rapidly away from us (universe is expanding); there was a time when they were all in one place (10 or 20 thousand million years ago); suggested there was a time, big bang, when universe was infinitesimally small and infinitely dense; in unchanging, static universe you can imagine that it had to be imposed by a being outside of universe (God), but if universe is expanding, may be physical reasons for beginning

Albert Einstein (1915)

Einstein's GENERAL theory of relativity = gravity is not a force like other forces, but consequence of fact that space-time is not flat...it is curved or "warped" by distribution of mass and energy in it; bodies like earth aren't made to move on curved orbits by gravity, instead they follow nearest thing to straight path in a curved space (geodesic); geodesic = shortest (or longest) path b/w two nearby points (example: surface of earth in 2D curved space, a geodesic on earth is called a great circle and shortest route b/w two points...think air travel)

Newton's Laws

First law: a body not acted on by any force will move in a straight line at constant speed Second law: body will accelerate, or change its speed, at a rate proportional to force

Good Scientific Theory

Good scientific theory: 1) accurately describes large class of observations, and 2) make definite predictions about results of future observations; eventual goal is to provide single theory that describes whole universe; two major theories today are general theory or relativity and quantum mechanics

Four Categories: Force-Carrying Particles

Grouped into 4 categories: gravitational force (weakest), electromagnetic force, weak nuclear force, strong nuclear force (strongest)

Heinrich Olbers (1823)

Heinrich Olbers objected to infinite static universe b/c an infinite static universe would demand that nearly every line of sight would end on surface of star (whole sky would be bright as sun); counter argument was that light would be absorbed by intervening matter (but intervening matter would eventually heat up until it glowed like a star); only way to avoid that would be to assume stars hadn't been shining forever but were turned on at finite point in past (light from distant stars may not have reached us yet)

Werner Heisenberg (1926)

Heisenberg formulated uncertainty principle; you can't predict future position and velocity of particle b/c when you shine light on it to see present position and velocity (at least one quanta), the velocity will be disturbed in a way that can't be predicted; fundamental inescapable property of the world, and signaled end to "theory of science" (completely deterministic model)

Edwin Hubble (1924 and 1929)

Hubble discovered ours is not only galaxy and there are many others w/ empty space b/w them; 1929: Hubble stated that the further a galaxy is, the faster it is moving away (Doppler effect: wavelength of light waves is longer as things move away from us)

Immanual Kant & St. Augustine (1781)

Immanuel Kant's Critique of Pure Reason said there were equally compelling arguments that universe had a beginning or that it existed forever; whether a beginning or not, infinite amount of time prior (same argument for both); time goes back forever; St. Augustine said time had no meaning before creation of universe (time was property of universe God created, didn't exist before universe)

Isaac Newton (1687)

Isaac Newton published Philosophiae Naturalis Principia Mathematica (single most important work published in physical science); Newton put forth theory of how bodies move in space and time and put together math to analyze motions; postulated law of universal gravitation: each body in universe was attracted to every other body by a force stronger the more massive the bodies and closer they were to each other (same force that caused objects to fall to ground...gravity); gravity causes ellipses; the reason stars don't fall was b/c there must be an infinite number of stars on each side of every star (infinite) so center point to fall to; now disproven (impossible to have a infinite static model of universe where gravity is always attractive)

Kepler (early 1600s)

Johannes Kepler modified Copernicus by suggesting planets moved in ellipses not circles; Kepler was not happy w/ ellipse hypothesis b/c he couldn't reconcile that w/ idea that planets made to orbit sun by magnetic force

Isaac Newton

Known to be a jerk; wrote Principia Mathematica (most influential work in physics); sought revenge on anybody that withheld data or claimed they had made same discovery prior...ruthless

Max Planck (1900)

Max Planck suggested light, x-rays, and other waves couldn't be emitted at arbitrary rate, but only in certain packets called quanta; each quantum had a certain amount of energy (greater the higher the frequency of the waves, so at high enough frequency the emission of a single quanta would require more energy than available)

James Clerk Maxwell (1865)

Maxwell predicted that radio or light waves should travel at certain fixed speed; Newton had gotten rid of absolute rest theory, so if light traveled at fixed speed, fixed speed would need to be measured relative; so "ether" postulated to be present everywhere, even in "empty" space; Einstein later said theory of ether unnecessary

Copernicus (1514)

Nicolas Copernicus (Polish priest) proposed a simpler model that sun was stationary at center and Earth and planets moved in circular orbits around sun; not taken seriously for a century; two astronomers (Johannes Kepler and Galileo Galilei) started to support this theory

Ole Christensen (1676)

Ole Christensen observed that moons didn't pass behind Jupiter at evenly spaced intervals (not a constant rate); proving that light travels at a finite speed (he measured this speed too); eclipses of Jupiter appeared later that farther we are from Jupiter

Quarks

Particles of matter that make up protons and neutrons

Ptolemy (2nd Century AD)

Ptolemy created model of the universe w/ Earth at center w/ spheres of (in order) moon, Mercury, Venus, sun, Mars, Jupiter, Saturn, "fixed stars" radiating out (adopted by Christian Church)

Heisenberg, Shrodinger, Dirac (1920s)

Reformulated mechanics into new theory called quantum mechanics, based on uncertainty principle; particles no longer had separate, well-defined positions and velocities that couldn't be observed; instead had quantum state (combination of position and velocity randomness)

Albert Einstein

Sicked by WW1 (waste of lives) and very pacifist; Zionist, especially as anti-semitism spread throughout Europe before WW2; was in U.S. by WW2 but ended up encouraging development of nuclear bomb b/c Germany would likely get there (different than prior stance on bomb); wanted, however, for nuclear weapons to be controlled internationally; offered presidency of Israel in 1952 but declines (not a politician)

Black Holes

Star that is massive and compact has such a strong gravitational force that light cannot escape (light has finite speed but is impacted by gravity); light wouldn't reach us so it would appear to us as a black void

Twins Paradox

Twin living at top of mountain will age faster than twin living at sea level (albeit very small difference at that scale...), but only if you believe in absolute time; if you believe in relativity, everybody has own personal journey through space and time!

Galileo Galilei

Was in conflict w/ the Catholic Church b/c of his adherence to Copernican views (planets orbit sun) and insistence of moving man forward by observing the natural world; Catholic Church declared Copernicanism "false and erroneous" in 1616 under pressure from Aristotleian professors; Galileo's friend became Pope and let Galileo write book w/ Aristotleian / Copernican viewpoints w/o taking sides ("Dialogue Concerning the Two Chief World Systems," a popular masterpiece); the pope regretted his decision, brought Galileo before Inquisition and sentenced him to life of house arrest