Dark Energy
May. 1st, 2005 11:02 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
beccastareyesFor ![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
sssinder
Our story begins with a young Albert Einstein laboring over a hot set of equations. Now, Al was a bright guy and he realised his shiny new equations for gravity better explain the universe as a whole. Unfortunatly, his equations predicted that if you have a bunch of mass in the universe, and it's just showing random motions, it should collapse into a black hole. Al was bright enough to realise that no theory that said the universe should be a black hole would be accepted by physicists. So, he introduced a 'fudge factor' (called L the cosmological constant) which acted to counteract gravity, and called it good. From what Dr. Leung says about extragalactic astronomers, this is not unusual.
Enter Edwin Hubble. Ed had figured out that he could find pulsating variable stars (Cepheid variables) in those pretty spiral nebulae he saw all over the sky, and, because he knew that the time between peaks tells the real brightness, he could find the distance to the star (and, presumably the spiral nebulae). And, lo and behold, they were outside of the galaxy -- which meant they were as big as our galaxy, which meant that they were other galaxies.
Ed also decided to take some spectra -- essentially he ran the galaxy's light into a prism. Elements give off certain types of light that can be read by looking at spectra -- which is why a neon light is red-orange. Since we can't exactly get NASA to pick up a piece of a galaxy or star, this is useful. Another thing we can tell from spectra is if an object is heading towards or away form us -- if you go to a set of railroad tracks, you'll notice that train whistles sound higher-pitched when they are coming towards you, and lower as they head away from you. This is called the Doppler effect, and works with any sort of waves, including light.
So, Ed sat down and figured out the speeds and directions fo the galaxies he was looking at, and was surprised to discover that, with a few exceptions, they were all heading away from him. He did a plot (astronomers love plots) and discovered that, the farther away the galaxy was, the faster it was heading away -- he came up wiht a handy constant that describes this, and we call it the Hubble constant, because scientists like naming things after other scientist, in hopes that what goes around comes around. He thought about this a bit, and decided it was because space itself was expanding.
When Al read Ed's work, he decided to try an expanding universe in his field equations. And low and behold, the fudge factor was no longer needed. Al tossed the cosmological constant into the dumpster, and moved on with being a famous scientist. And I just threw in that last paragraph as I am on a Fullmetal Alchemist-induced euphoria.
Now, scientists figured out they could figure the age of the universe by working backwards using the Hubble constant, and they got a number that was about 11 billion years. Which was bad, as some of the stars they were looking at were older. In addition, the best value for the Hubble constant was 'somewhere between 50 and 100', mostly because galaxy random motions were messing with the data and we couldn't get believable distances far enough away that 'Hubble flow' could crush them. Astronomers decided to solve this the way they solve everything -- get someone to build them a better telescope.
So, the Hubble Space Telescope was launched, and, among other things, like taking pretty pictures, it was sent to look for a certain type of supernovae (type Ia), because they were always the same brightness (so they could tell us how far away a galaxy was). So, astronomers took the distances and speeds and tried to fit a Hubble constant to them. But, they couldn't get the line to quite fit right.
Then some bright person dusted off Al Einstein's old papers and wondered what would happen if you had an expanding universe with a cosmological constant. And, amazingly enough, this model could fit the data -- Hubble's 'constant' wasn't a constant. It was smaller in the past, meaning the universe was accelerating. Obviously this had to be due to some sort of repulsive energy in space. Only problem was that no one was quite sure exactly what it was -- they needed it for the models to work, but no explanation is really liked by everyone. So, since they couldn't see what it was, it was christened 'dark energy'.
sssinderOur story begins with a young Albert Einstein laboring over a hot set of equations. Now, Al was a bright guy and he realised his shiny new equations for gravity better explain the universe as a whole. Unfortunatly, his equations predicted that if you have a bunch of mass in the universe, and it's just showing random motions, it should collapse into a black hole. Al was bright enough to realise that no theory that said the universe should be a black hole would be accepted by physicists. So, he introduced a 'fudge factor' (called L the cosmological constant) which acted to counteract gravity, and called it good. From what Dr. Leung says about extragalactic astronomers, this is not unusual.
Enter Edwin Hubble. Ed had figured out that he could find pulsating variable stars (Cepheid variables) in those pretty spiral nebulae he saw all over the sky, and, because he knew that the time between peaks tells the real brightness, he could find the distance to the star (and, presumably the spiral nebulae). And, lo and behold, they were outside of the galaxy -- which meant they were as big as our galaxy, which meant that they were other galaxies.
Ed also decided to take some spectra -- essentially he ran the galaxy's light into a prism. Elements give off certain types of light that can be read by looking at spectra -- which is why a neon light is red-orange. Since we can't exactly get NASA to pick up a piece of a galaxy or star, this is useful. Another thing we can tell from spectra is if an object is heading towards or away form us -- if you go to a set of railroad tracks, you'll notice that train whistles sound higher-pitched when they are coming towards you, and lower as they head away from you. This is called the Doppler effect, and works with any sort of waves, including light.
So, Ed sat down and figured out the speeds and directions fo the galaxies he was looking at, and was surprised to discover that, with a few exceptions, they were all heading away from him. He did a plot (astronomers love plots) and discovered that, the farther away the galaxy was, the faster it was heading away -- he came up wiht a handy constant that describes this, and we call it the Hubble constant, because scientists like naming things after other scientist, in hopes that what goes around comes around. He thought about this a bit, and decided it was because space itself was expanding.
When Al read Ed's work, he decided to try an expanding universe in his field equations. And low and behold, the fudge factor was no longer needed. Al tossed the cosmological constant into the dumpster, and moved on with being a famous scientist. And I just threw in that last paragraph as I am on a Fullmetal Alchemist-induced euphoria.
Now, scientists figured out they could figure the age of the universe by working backwards using the Hubble constant, and they got a number that was about 11 billion years. Which was bad, as some of the stars they were looking at were older. In addition, the best value for the Hubble constant was 'somewhere between 50 and 100', mostly because galaxy random motions were messing with the data and we couldn't get believable distances far enough away that 'Hubble flow' could crush them. Astronomers decided to solve this the way they solve everything -- get someone to build them a better telescope.
So, the Hubble Space Telescope was launched, and, among other things, like taking pretty pictures, it was sent to look for a certain type of supernovae (type Ia), because they were always the same brightness (so they could tell us how far away a galaxy was). So, astronomers took the distances and speeds and tried to fit a Hubble constant to them. But, they couldn't get the line to quite fit right.
Then some bright person dusted off Al Einstein's old papers and wondered what would happen if you had an expanding universe with a cosmological constant. And, amazingly enough, this model could fit the data -- Hubble's 'constant' wasn't a constant. It was smaller in the past, meaning the universe was accelerating. Obviously this had to be due to some sort of repulsive energy in space. Only problem was that no one was quite sure exactly what it was -- they needed it for the models to work, but no explanation is really liked by everyone. So, since they couldn't see what it was, it was christened 'dark energy'.
