With Regrets

Hello Bloggers. Hohenheim here with some unfortunate news. My health has been acting up lately and I (and my health advisor) have decided that it would be best to temporarily discontinue the blog. Hopefully by summer I'll be in better condition and will be able to pick it back up again. Thanks for all the support.

Cosmo 101 (a bit of math included)

Oh here is another interesting property of Hubble’s law that I don’t think I talked about last time. You can use it to set a minimum on the age of the universe. So to review, Hubble discovered that the universe is expanding and he found that the rate at which stuff (stars nebula etc.) is moving away from us is proportional to the distance they are away from us. The further they are away the fast they are receding. And then he graphed his results and found a line. The equation goes something like this: (the speed at which something is moving away from us) = (the Hubble parameter) X (the distance from us to them). This Hubble parameter is sometimes called the Hubble constant but it’s not really constant. It changes with time, that’s why we use the word parameter. There is another really cool aspect of the Hubble parameter, we can use it to tell how old the universe it.

(the Hubble parameter)= (the speed at which something is moving away from us)/ (the distance from us to them)

In math terms this is

H=S/d so if we invert this we get

1/H=d/S

and if you take any distance (say the distance that a car has travel) and you divide it by the speed that it went at they you know the time it took to get there. So from the inverse of the Hubble parameter give you the time that it took the stuff (stars nebula etc.) to get where is at, thus putting a minimum on the age of the universe. The current accepted value for H is 70.8 ± 4.0 (km/s)/Mpc which give the age of the universe to be 13.8 billion years.

Suggestions?

Hello Bloggers! Well since we only have class on Monday, Wednesday and Friday we still haven't learned anything new this week so I still have nothing to report. But I do have a question for you all. We have to do a project and a presentation for the final exam in this class. So I was wondering if you guys have any suggestions? What do you want to know more about? What deep questions have to been staying up at night trying to solve?

GOD! ?

So we had a test today....I think it went well for the most part. But consequentially we didn't learn anything new so here is a GOD!? post.

So first up we have an Onion article with an interview from God:

http://www.theonion.com/content/node/28151

Next we have an entire website dedicated to the question: Does God Exist?

http://www.doesgodexist.org/

And look there, I added a video!

Cosmo 101 Cepheid Variables

Hey bloggers! We’ve now made the transition to cosmology! And I have a test on General relativity tomorrow oh no! Anyway we’ve already gone over a lot of the stuff that we are talking about in class but I noticed that while I talked about Hubbles law and all (you can read about it here), I didn’t mention Cepheid variable stars. These stars a very interesting in that they blink. Their luminosity literally varies periodically like a lighthouse. But the cool thing is that there is a very linear relationship between it’s period (how fast it’s gets light and then light again) and it’s luminosity (how bright it is). I’ve included a graph to show this relationship. The cool part is the since we know this, if we look out into the sky and see a variable star we can tell how far away it is. How? Well we can see measure it’s period and see how bright it comes across to us. If we know (from the graph) how bright it’s really suppose to be we can calculate how far it. Yay! You may have heard of these stars before but usually they are referred to as standerd candles.

lolfox?

I don't think I have anything to write about today. So I'm not going to write about anything. Here, have an lolcat...errr....fox.

Cosmo 101 Olber's Paradox

Hello bloggers! How are you all doing this fine day? Well I’m doing wonderfully. You know why? Because in my cosmology class we will actually start talking about cosmology and not just gravitation! (I will warn you now, some of this stuff we’ve already gone over in the background section of this blog). So first we’ve started off with Olber’s paradox. People before the 20^th century believed that the universe was infinite and static. And a consequence of an infinite universe was that if you looked out into the night sky any were you look you would see a star. So instead of being black and blotchy the night sky would be a uniform brightness. Like in the picture. But this is obviously not true. Why not? Well there are 3 main reasons quoted. Firstly is the finite speed of light. Secondly is the finite age of universe. Third is the fact that space expands. The first and second ones go together. If the universe was created a certain finite time ago then the light from the far away stars hasn’t reached us yet. The third one only adds to this effect because as the universe expands the light from really far away objects gets red-shifted into a wavelength we can’t see. So from all this we can concluded that the universe isn’t static or infinite.

Cosmo 101 Orbits (for that good clean feeling, no matter what)

Ok so what do general relativity orbits have to do with our solar system? Well for a long time the orbit of Mercury was a bit mystery. It doesn’t quite follow the prediction of Kepler’s laws. It is just a tad bit off. This issue was first observed in 1859. Scientist tried to account for it but they couldn’t figure it out. And then all of the sudden there was this other theory of gravity! So plugged all the numbers in for the orbit of Mercury and low and behold it explained the difference. And if you look at the graphs from yesterday you can see why. The Newtonian graph the Einsteinian graphs are rather different. And this accounts for the difference we see in the Mercury’s orbit. This was the first definitive test of the theory of relativity, and of course it came out positive. The moral of the story is that all of the gravity stuff we’ve been talking about doesn’t only apply to imaginary alien races that live on the surface of a black hole. It applies to our own solar system too.

Cosmo 101 Orbits (for that good clean feeling, no matter what)

Ok now that I’ve gotten that out of my system, back to black holes. There are a lot of different equations that I’ve not talked about here. They can get very complicated very fast and if I shared then it would be super confusing. But when you get an understanding of a certain number of equations it turns out that you can predict orbits around a black hole. And not just a black hole, one of the most famous applications of general relativity was an orbital prediction in our own solar system. Or bits in our own solar system?! you say. No! We already know those from Kepler and Newton, you say. But no! They are not quite right. I have a graphs here with two curved lines. They are both potential energy lines. Reading them is easy if you think about it right way. If you imagine putting a marble at the intersection of the straight line (the amount of energy in the system) and the potential energy curve and then letting it go then it’s going to go back and forth like a pendulum. But if we look at the horizontal axis we see that it is something corresponding to an orbital radius. From this we get a familiar looking orbit (the last picture). Now the first curve is what Newton and Kepler came up with, and the second curve is what general relativity predicts. You will notice there is a slight difference. When we get near the vertical axis the Newtonian curve just keeps going up. But when we get near the vertical axis in the general relativity curve we see that there is this sharp slope and the object falls off into the black hole. But the thing is that it doesn’t have to be a black hole. It can be any planet or star, including our own. Now, you say, what does this have to do with our own solar system? Well I shall explain that tomorrow!