IB Astrophysics - cosmology - Flippingphysics by nothingnerdy
presentsa production COSMOLOGY based on the IB Astrophysics option 1
COSMOLOGYWhere did the universe come from? Olbers’ paradox Red shift Expanding universe The Big Bang Open universe CMBR International space research
Olbers’ paradox Why is the night sky dark? If the universe is infinite and ageless (according to Newton’s model), the night sky should be uniformly bright since there will be stars in every direction. If stars are further, away they will be less bright but more numerous.The brightness decreases according to the inverse square law, but the number of stars is proportional to distance cubed.SOLUTIONSThe universe is not infinite in size.The universe is not infinitely old. Some light has not yet arrived.The universe is expanding so some of the light has beenstretched (red-shifted) outside the visible spectrum.
Red shift An application of the Doppler effect The wavelength of light from an object which is receding willincrease (and the frequency decrease). This means that theknown absorption lines in the hydrogen spectrum will be foundnearer the red end of the electromagnetic spectrum. From this wecan calculate the speed of the object.For an object which is approaching, the emitted light will be blue-shifted (shorter wavelength and higher frequency).
Expanding universe In the 1920s, Edwin Hubble realised that thespectra of all distant galaxies show a redshift,which means that they are all moving awayfrom Earth. This lead to the conclusion that thespace-time of the universe is expanding. At some time in the past, all of the matter in the universe originated at one point. Space and time were created when it began to expand.
The Big Bang13.7 billion years ago, the universe, space and time werecreated and the universe began to expand. Before this,according to the theory, there was NOTHING.
CMBR Cosmic Microwave Background RadiationModels of the early universe suggest that after 300thousand years, it became transparent for the firsttime (at 4 000 K) and high frequency photons couldpass through it. As the universe has expanded, thisradiation has been red-shifted until it has becomemicrowave radiation. This represents a temperatureof 2.7 K.The existence of the CMBR was predicted in 1948,but at that time it had not been detected.
Detection of the CMBR In 1964, Penzias and Wilson were working with a microwave aerial and found that no matter in what direction they pointed the aerial it picked up a steady, continuous background radiation. The COBE and WMAP satellites measured tiny ripples in the CMBR, the seeds of the first stars and galaxies.
Fate of the Universe There are different ideas about the future of the universe depending on how much mass it contains. Flat universe has a critical density so that its expansion will slow down due to gravity but never stop. Closed universe has higher density, gravity will halt its expansion and it will contract.Open universe has lower density and it will expand forever.
Measuring density To predict the fate of the universeThe mass of the matter in the universe can be estimatedby measuring stars and interstellar gas, but we find thatthe mass of observable matter is far too small to holdgalaxies together.To solve this problem, astrophysicists have suggested andobserved dark matter (5 times more abundant thanmatter), but they do not know what it is made of.In 1996, the expansion of the universe was measured tobe increasing. To explain this, dark energy has beensuggested (3 times more abundant than dark matter) butwe do not know what it is. CONCLUSION: the universe is open
The universe is made ofHeavy elementsNeutrinosStarsFree hydrogen and heliumDark matterDark energyDark matter could be Weakly Interacting Massive Particles(WIMPs) - preliminary observations have been made.Or Massive Compact Halo Objects (MACHOs) - normal matterwhich doesn’t emit light such as black holes, neutron stars,brown dwarfs have also been suggested, but theory rules thisout; the Big Bang did not make enough normal matter.
Space Research Many modern space projects are the result of international cooperation.Examples: Hubble Space Telescope; International Space Station;International X-ray Observatory; Very Large Telescope in Chile 12
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