lecture 1: intro and welcome
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SCIENTIFIC THEORY: !
• consist of one or more hypothesis based on observations. !
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eg) big bang theory!
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• theories have varying levels of confidence. !
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eg) bad theory “0” = sun will not rise tomorrow!
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good theory “100” = sun will rise tomorrow!
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• use theories until they don't explain or predict observations, then start cycle over again. !
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observation -> hypothesis -> theory -> repeat!
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STRUCTURE OF EARTH !
atmosphere: nitrogen, oxygen, co2!
crust: oxygen silicon aluminum iron calcium sodium potassium magnesium!
upper mantle 700 1300 degrees!
lower mantle: !
outer core: liquid iron sulfur nickel oxygen 3200 degrees!
inner core: solid iron and nickel 4500 degrees!
lecture 3: fate of universe
• “observable universe” - sphere that can only see to the point where we run out of light!
• due to light taking finite speed to get to us !
• can only see to when the universe started producing light - cant see further as light hasn't
got to us yet. !
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WHERE DID IT ALL COME FROM !
• universe began with the appearance of space time and mass!
• before everything began, there was on space time or mass - there was no “before”!
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big bang theory: - 1.37 billion years!
• at some point in past when universe began, everything in universe was squeezed into smaller
area than green pea!
• everything exploded out from that point!
• imagine sultana bread rising - move out from each other at same rate - expansion!
• time starts at point when explosion begins - mass and space also!
• 1/100 second after universe consists of sea of light + small amount of matter!
• 3 min 46 sec later atoms created !
• initial inflation of universe is exponential from 10^-35 seconds to around 10^-32 seconds. (fast
then slows to current expansion rate) !
• expands in that time to 10^30 times original size !
• expansion is lumpy - density varies !
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10^30 SECS TO 10^10 SECS!
• dark matter created - holds structure of the universe together (theoretical) !
• matter dominates over antimatter (opposite of matter) !
• at this point the universe could have been either antimatter or matter !
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10^2 SECONDS!
• 100 billion degrees Kelvin, Super high density!
• photons neutrinos and electrons mixed with small numbers of protons and neutrons !
• starting to get hydrogen made!
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THREE MIN 46 SEC AFTER!!
• 900 million degrees Kelvin!
• fusion of the nuclei of helium and hydrogen atoms !
• the seeds of galaxies and other structures are formed and shaped by dark matter !
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A BIT LATER!
• the universe cools down and gas condenses to form infant nebula and galaxies, inflation stops
and expansion slows. !
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INFLATIONARY ERA !
• from the big bang to around 300000 years !
• initial exponential acceleration followed by slowing !
• for the past 6 billion years Universe accelerating again, but at a much slower pace!
• really fast, slows a bit, speeds up again!
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THE DARK UNIVERSE!
• for the first 380000 years after BB no light - as photons couldn't escape into Universe!
• microwave radiation “visible” at about 380000 years - first radiation that can escape!
• background microwave radiation from explosion predicted to be visible everywhere you look
in space !
• theory was tested in 1992 by Cosmic Background Explorer !
• visible light at about 400 million years!
• the lumpy nature of satellite images was unexpected - could explain dark matter - evidence for
colliding universes!
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WHAT IS THE UNIVERSE MADE OF? !
• 70% dark energy!
• 26% dark matter!
• 4% everything else (stars planets etc) !
• not really sure of what dark energy and dark matter are,!
• dark energy appears as a property of space or new type of energy field or fluid !
• dark matter - not visible not ordinary matter not antimatter would be WIMPs (weakly
interacting massive particles) !
• can predict what effect it has on galaxies - can predict motion of stars and galaxies and see if
they match looking for dark matter in dwarf galaxies where the motion of the stars cant be
explained by the mass of the stars alone!
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IS THERE ANY OTHER EVIDENCE!
• evidence of age of universe can come from!
• ages of stars - life cycle!
• ages of stars - radiometric dating!
• hubble constant - initial evidence of accelerating
universe !
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age of stars - life cycles!
• measure luminosity of stars that burn H and He = main
sequence stars!
• luminosity decreases with temperature and time - is
measure of age!
• universe age from life cycles = 12.1 billion years with 95%
confidence - minimum age - between 8.5 and 14.6 billion
years old. !
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radiometric dating!
• some elements are radioactive and can be used for
dating archaeological cities rocks and the universe!
• can use many elements !
• eg) decay of carbon 14 to carbon 13!
• only good to 70000 years!
• universe is older than this!
• need to find slower decay rates!
• measures slow decaying isotopes !
• measuring radiometric decay indicated in light from stars!
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hubble constant:!
• Edward hubble noticed that the further away a galaxy cluster was to us the faster it moved!
• 1920’s published results!
• V=Hr !
• V- velocity, r is the distance to the cluster (megaparsec), H is the hubble constant (can have
value from 50 - 100)!
• reverse distance and time = all goes back to one point on graph - big bang !
• age can be calculated by 1/H!
• best estimate of H - 67.15 +- 1.2 = 13.82 billion years !
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WHAT HAPPENS NEXT? !
• in 4 billion years the Andromeda galaxy and our galaxy will collide!
• there will be flooded with light - no night\!
• this may all change as observations are made. !
• the universe will have 3 options depending on the mass of the universe - which depends on how
much dark energy and dark matter there is!
• big rip: if dark energy increases, acceleration will increase, size of everything will increase
which will tear apart everything - until rate of movement is so fast not even atoms can hold
together!
• constant dark energy: if dark energy is constant, acceleration will continue and universe will
expand forever, this means that galaxies and stars will go so far apart that light from adjacent
galaxies light will disappear and the universe will become dark and cold. !