1. Goal: To understand the big bang. Objectives: 1)To explore the History of the Universe 2)To understand How we know it exists 3)To learn about What the big bang tells us

2. Hints at the big bang By the 1950s it was pretty well established that our universe was expanding. But what did that mean? Was it possible everything was once all together (just like our conga line)? However, what this meant for our universe in the past was not known yet. There were many theories around.

3. “Big Bang” coined One of the theories was that the universe started at a point as a single atom. In a radio show in 1949 Fred Hoyle coined the term “Big Bang”. However, support was half towards this theory and half towards the other. We needed evidence to show who was right!

4. Cosmic Microwave background Was first predicted in 1948 (although done very incorrectly). In 1965 Arno Penzias and Robert Woodrow Wilson were attempting to construct a radio telescope but kept finding a 3 degrees K excess temperature.Arno PenziasRobert Woodrow Wilson At first they though it was the equipment.

5. However By testing every possible orientation they discovered that this 3 degrees came from every direction! They had inadvertently found the cosmic microwave background! This proved that the hot big bang model was the correct one.

7. Where it comes from? Lets hit the rewind button for a minute here. Instead of galaxies flying away from us they now come towards us. All the galaxies would meet in 1 region of space (all the ones we can see anyway). As that happens the temperature of the gas would be higher (simple gas law). If the gas gets too hot the atom becomes ionized. What that means is that the electron and proton are seperated.

8. Oops I rewound too far If everything is ionized all the light gets scattered because there are now an infinite amount of energy levels for the electron. So, the electrons scatter all the available light. However, as the universe expands, the gas will cool, and therefore reach a point where the electrons combine with the protons. This is called recombination. Once this happens, the resulting photons are free to travel through the universe undisturbed until they reach us.

9. Proof is in the (why would it be in pudding?) So we have a blackbody spectrum – CHECK! But it is at 2.7 degrees K not the 6000 K that recombination come out at. So, why the difference? Well, because of the expansion of the universe. So, the light is Doppler shifted so that it seems cooler. And we have our big bang!

10. Big bang unveiled

11. What can we learn? We can start to see the structure of the universe as we have it today. We can also see other things such as how much mass the universe has (but more on that next week). Finally, we get to see how OLD it is!

12. How age? Well if we know how fast things are moving away from us based on their distance then we know how long it took to get there. Back to the conga line analogy suppose the closest person to you was 5 m away. If they go 1 m per song then you know the age of the conga line is 5 songs. In astronomy if you know Hubble’s constant you have some idea of the age of the universe.

13. Hubble Constant V = Ho * D (or D = V / Ho) Ho is currently estimated to be 71 km/s / Mpc (with an error bar of about 3). So, if D = 1 Mpc then the velocity is 71 km/s. How long does it take to go 1 Mpc at a constant velocity of 71 km/s? T = D/V (basic physics) = 1 / Ho If Ho is 71 km/s / Mpc then T is 13.7 billion years.

14. Conclusion The universe expands, so that means everything once started at the same point. This point and time was the big bang. From the universe know we can retrace the steps to the big bang. One of the major steps is the time of recombination which created the cosmic microwave background which is now “cooled” to 2.7 K. From the structure of this we can find other cool stuff – but that is a lesson for next week!