* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Time From the Perspective of a Particle Physicist
Modified Newtonian dynamics wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Theoretical astronomy wikipedia , lookup
Astrobiology wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Shape of the universe wikipedia , lookup
Dark energy wikipedia , lookup
Hubble Deep Field wikipedia , lookup
Geocentric model wikipedia , lookup
Outer space wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Extraterrestrial life wikipedia , lookup
History of astronomy wikipedia , lookup
Observational astronomy wikipedia , lookup
Ultimate fate of the universe wikipedia , lookup
Expansion of the universe wikipedia , lookup
Flatness problem wikipedia , lookup
Non-standard cosmology wikipedia , lookup
Fine-tuned Universe wikipedia , lookup
Stellar kinematics wikipedia , lookup
Observable universe wikipedia , lookup
Lambda-CDM model wikipedia , lookup
Hebrew astronomy wikipedia , lookup
Physical cosmology wikipedia , lookup
Time From the Perspective of a Particle Physicist David Hedin Department of Physics August 8, 2001 Outline • Time in our everyday lives • Looking back in time examples from Astronomy • Looking back in time examples from high energy accelerators Markers of Time DAY: Sun at maximum height MONTH: length of time it takes for the moon to make an orbit around the Earth (repeats phase every 29.5 days) Most early cultures use the day and month to mark time moon-month-measure-man same root may all have the Length of Day and Month are changing • Friction between the Earth and the Moon (seen daily in tides) • Day becomes .002 seconds longer each century • Moon receeding from the Earth by 4 cm each year 500,000,000 years ago there were 22 hours in a day 400 days in a year Billions of years in the future there will be 1 “day” = 47 present days 1 “month” = 1 “day” Earth-Moon frozen into a pair with no additional spin for the Earth alone The Year Two Indicators • Due to the Earth’s tilt the Length of the Day and Sun’s path through the sky vary. One year = returns to the same spot More dramatic further north (Stonehenge) • Which stars are overhead changes with seasons. Gives passage of year Passage of time at night also given by stars’ apparent motion Stars = Calendar and Clock Star Wheel • Stars “move” East to West over the course of one Night (in circle about the North Star) • Stars “move” East to West by 2 hours per month and “return” to the same position after one Year • just Earth’s daily spin and yearly orbit about the Sun What Year Is It? • Almost all societies agree - 2001 • But where should time really start? Formation of Earth 4.5 billion years ago Formation of Sun 5.0 billion years ago Sun will continue as a star for another 5 billion years and then transform into a Red Giant and then a White Dwarf. The Sun orbits the center of the Milky Way galaxy every 250 million years So now in the 20th “galactic year” Formation of Universe 13 billion years ago 365.242 days in a year • “Ancient” calendars were Lunar Babylon - 12 months 6 with 29 days and 6 with 30. Add 13th month occasionally (also used in India and similar in China) Egypt - 12 months each 30 days plus 5 extra Polynesia - 13 lunar months drop 1 occasionally • Priests would determine when to add extra months and day • Very tempting to have 360 days in a year and 12 months of 30 days. “nice” numbers Lack of correlation between day-monthyear “bothered” philosophers and theologians. Understanding this “random” motion (and the planets were even worse) by Copernicus, Kepler, Galileo, Newton gave us modern science 365.242 days in year • If normal year has 365 days need extra 24 days/century and extra 2 days/millenium • 46 BC Julius Ceaser (really Sogigula an Egyptian) - Julian calendar with leap day every 4 years. But 8 too many days every 1000 years so…. • Gregorian calendar adopted Spain and Catholic Europe 1582 England 1751 Russia 1918 which immediately skipped 10 days (in 1582). No leap day on century years 1700,1800,1900,2100,2200 (just those divisible by 400) Time in Astronomy • Lives of Stars stars are born in interstellar gas clouds and “die” once they have exhausted their nuclear fuel more massive stars burn their fuel faster and may only exist for 1 million years while stars like our Sun (or smaller) will exist for 10 billion years or longer • Clusters of Stars stars are formed in groups with some massive and some small. The size of the largest stars in the cluster tells us how old all the stars in that cluster are. The oldest clusters are formed from the primordial material of the Universe (before stars existed) and their atomic composition is a fossil record from the first few minutes after the Universe was created Galaxies • Stars come in groups of 200 billion or more like our own Milky Way Galaxy • as they are so bright galaxies can be seen if if extremely far away - 5 billion light years • as light takes time to travel to us, looking at galaxies very far away means we are looking back in time. Soon the latest telescopes will have study more and more galaxies from the time when they (and the stars they contain) were first formed Galaxies and Hubble’s Law • It has been observed (first by Hubble in the 1920’s) that galaxies are moving away from us and that the further away they are the faster they are moving (v=Hd) • Indication that the Universe is expanding, and it has been ever since it was created in the Big Bang about 13 billion years ago • Understanding how the expansion rate changes with time tells us about the inherent mass and energy which makes up the Universe, a more precise values for its age, and what its fate will be • Current data is perplexing: most of the mass is “missing” and due to some unexplained new types of matter and there is “vacuum” energy which is acting like a kind of anti-gravity and accelerating the expansion More on Hubble’s Law • As the Universe expands it cools down. At its earlier times it was much, much hotter. • If the Universe keeps on expanding forever everything will come to a cold end, the stars will all end there lives and no new ones will be formed • if the expansion stops and a contraction begins the Universe will heat up as it returns to a state similar to when it was formed • Not unambiguously known what fate will be Fire and Ice Robert Frost - 1923 Some say the world will end in fire, Some say in ice. From what I’ve tasted of desire I hold with those who favor fire. But if I had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice. Exploring Very Early Times • “Fossil” evidence available to astronomy are remnants from the first few minutes after the Big Bang • To explore back to earlier times we use our understanding of physics • The earlier you go in time the hotter was the Universe. Particle accelerators can briefly reproduce those conditions. The highest energy machine is equivalent to about 1 picosecond (.000000000001) after the universe began • Even earlier times can be understood by extrapolating symmetries in Nature but going back to the moment of Creation needs a complete knowledge of gravity and a more complete understanding of time itself Fermilab • World’s highest energy particle accelerator (2 TeV = 2 trillion electron volts = 2,000,000,000,000 eV = total energy) • collides protons with antiprotons • located in Batavia - take I88 (or Rt 38) to Kirk Road (just east of toll booth then a few miles north on Kirk) VISITORS WELCOMED • self-guided tour plus videos in main building • Education center • Nature trails and fishing • Buffalo herd Fermilab Accelerator - 2 TeV Energy Tevatron Ring(1 km radius) CDF D0 Main Injector Ring Matter-Antimatter Asymmetries • We live in a world which is dominated by matter such as protons and electrons (but antimatter is readily made at accelerators and has some medical applications) • But the very early universe had equal amounts of both matter and antimatter. After most annihilated with each other a very, very, very small excess of matter was left over to make everything including us WHY???? Matter-Antimatter continued • Matter-antimatter differences have also been observed in the decay of the strange quark (1964) and the bottom quark (2001) • the underlying math which describes quarks shows that if there are at least 3 generations of quarks then you can have an asymmetry (which is why we are all very happy that the top and bottom quark exist!!) • Still missing is a “Theory of Everything” which explains why there are three generations. (Carl Albright of NIU is working on it.) This “ToE” probably also explains mass differences • Ongoing experimental efforts (including neutrino studies) gives constraints which theorists like Albright use as a guide in selecting models of the “ToE” Why is Gravity so Weak? • The Weak, Strong, and Electromagnetic Forces all have about the same strength at Fermilab’s energy (though not at “room” temperature) and are well described by complete relativistic quantum mechanical theories • Gravity is much, much weaker. 37 orders of magnitude weaker than EM. Only dominates at larger distances as EM has both positive and negative charges and others are short-ranged • No complete theory of gravity exists. Einstein tried for one and this is Stephen Hawking’s primary work. Will be necessary to understand the very, very early universe when all 4 forces had the same intrinsic strength Weakness of Gravity II • Need new theories, two of which are Supersymmetry and Extra Dimensions Supersymmetry (SUSY) • postulates the existence of extra particles, which are partners to existing (selectrons partner to electrons, etc) • All particles produced similarly in the very early universe. All forces also the same at that time • As Universe cools during first picosecond SUSY particles “freeze” out as they are heavier. Their existence helps to explain gravity’s weakness (though not completely) • SUSY particles could explain “missing mass” observed in astronomy Weakness of Gravity III Extra Dimensions • Let’s assume (for fun) that we live in an 11-dimensional world time normal 3-D position space 7 extra dimensions which are “small” (compactified is the physics term) less than 1 mm • Only gravity can “communicate” to the extra dimensions (all other particles and forces are confined to the normal 3D space) • Fairly simple geometry explains why gravity appears weak - it has to spread its force fields over a larger space which thereby dilutes them in the normal 3D space itself CONCLUSIONS • The understanding of the motion of the Sun, moon, and planets - which are day-today indicators of time - lead to the development of first astronomy and then physics • By both studying the “fossil record” in stars and elsewhere and actually looking back in time by analyzing distant objects, astronomers have mapped out most of the Universe’s history from the Big Bang to today. Though the ultimate fate is still uncertain. • To understand the first instances of time requires an understanding of Nature’s underlying particles and forces. There is not yet a Theory of Everything but we are working on it.