Bang-Bang and Steady State Cosmologies, 6 December 2013!To review: In the last lecture, we discussed the straight big bang theory and 1.the accelerating universe bing bang theory. !The evidence for the accelerating universe is challengeable, but Berkeley A.has a big stake in it. !It is on the cutting edge, which means that no one has a good grasp on it a.yet. !The decelerating universe: a competing theory in the 60s-70s in which the 2.expansion of the universe is slowing down. !It was a leading theory until evidence starting going against it. !A.This may just be an awkward time in gathering data which shows that a.the universe is decelerating. !In this cosmology, the weight of the universe is so much that its B.gravitational pull overcomes the outward momentum of the big bang. This causes the universe to slow down expansion, stop expansion, and then start contracting. !SIZETIMENOWwhat astronomersknowEXTRAPOLATIONFUNDAMENTAL GRAPH OF COSMOLOGYSIZETIMENOWwhat astronomersknowEXTRAPOLATIONFUNDAMENTAL GRAPH OF COSMOLOGYstraight big bangaccelerating universeHere is what cosmologists will see at certain points in this cosmology:!a. Orange: At the place where expansion has reached it widest, but there b.is no more outward momentum, cosmologists will see the farthest things moving outward quickly, nearer things moving outward slowly, and close things are not moving at all. ! Purple: A bit after, cosmologists will see far things moving away, but not c.as fast. They will see near things not moving, and close things slowly approaching. !Explaining this would be tough. !1. Green: At the rightmost point, cosmologists will see that everything is d.strongly shifted toward the blue end of the spectrum. This means the universe is coming down on their heads. !The sky will no longer be as dark as it used to be, and temperatures 1.would rise.!A good science fiction series about this is The Restaurant at the End 2.of the Universe by Douglas Adams. !Eventually, all matter and energy in the universe will shrink down into e.complete cosmic collapse, with everything in 1 place at 1 time. This is called the big crunch. !Physics cannot tell you what is happening here because physics breaks 1.down in singularities like this.!The Bang Bang/Oscillating Universe cosmology: If history repeats itself after C.the big crunch in a decelerating universe, the big bang will reoccur, recreating the universe again. !This is the ultimate recycling: everything good and bad accomplished in a.the lifespan of the universe will be converted into pure hydrogen and helium for star formation. !There is no way to send a message from this incarnation of the universe b.into the next incarnation of the universe. !No information can get through a universe sized black hole. !1.SIZETIMEEXTRAPOLATIONFUNDAMENTAL GRAPH OF COSMOLOGYThere is no way to know if there was a previous incarnation, or how 2.many. !Astronomers have no idea how this could occur, or if it even occurs.!3.The only thing contrary to this theory is present observations which c.show that expansion is accelerating rather than slowing down. !However, this could be an artifact of measuring distance today 1.(especially when it comes to type 1a supernovae brightness).!The lifespan of the universe in the Bang Bang cosmology is the shortest:!d.It is theorized the the time between each crunch was 70 billion years. !1.Since our universe is 13.7 billion years, we would still have 4/5 of A.the time left. !The Steady State cosmology!3.This theory was hatched just after WWII At Cambridge University by Fred A.Hoyle (1914-2001), Herman Bondi (1919-2003), and Thomas Gold (1920-2004). !They didn't like the big bang for astrophysical, theological, and a.philosophical reasons. !For theological reasons, they did not like that the big bang was 1.created by Lemaître to be consistent with the Bible. They wanted a theory that was consistent with astrophysics, but not the Bible. !Fred Hoyle was the leader. !b.He was a polymath that wrote science fiction and did astrophysics. !1.He never finished his phd, but was a professor of great distinction 2.anyway. !He was one of the most creative people in the history of astronomy. !3.He created part of the theory of how stars generate heavier A.atoms, which was partially right.!Herman Bondi and Thomas Gold were grad students that worked with c.Hoyle. !Bondi later became a straight physicist and did not participate in the 1.SIZETIMEFUNDAMENTAL GRAPH OF COSMOLOGYcosmology argument. !Gold was another extremely creative person with a different 2.approach to things. !He wasn't right in all of them, including this one (though when he A.and the others had this idea, there was no counter evidence).!Unlike the other cosmologies, the universe in this theory is expanding, was B.expanding, and always will be expanding.!The universe still has constant density throughout because new matter is a.created atom by atom to fill the gaps formed by the universe's expansion. !The blue lines on this graph represent the new matter that fills the 1.expansion, and you can draw as many as you want (they are infinite). !People did not like this theory because it was the physics version of C.spontaneous generation in biology. !The theory of spontaneous generation was the idea that life came from a.nonliving things, such as flies from garbage or germs from dust. This theory was disproven and firmly rejected after advances in germ and cell theory. !To recreate in physics what was rejected in biology seemed incorrect.!1. The proponents of the steady state theory had some defense: !b.You would only need to create 1 atom of hydrogen in the volume of a 1.sports stadium to maintain the constant density of the universe. !The creation of new matter is so slow that you wouldn't notice it, A.and the reason it is not noticed is that it is slow. !The Big Bang was the spontaneous creation of all the atoms in the 2.whole universe, so the argument is not about whether there is spontaneous generation, it is about the rate at which it occurs. !SIZETIMENOWFUNDAMENTAL GRAPH OF COSMOLOGYThis cosmology is so entirely different that there isn't a generally agreed upon way to graph it. This is a possible way.This defense was more effective in hushing the opposition than the A.previous one. !Problems with the steady state theory: !D.Counter evidence first arose in the mid 60s when radio astronomers a.found the embers of the bing bang. !If you have the embers of the big bang, there must have been a big