Dark Matter
esiegel | November 17, 2010"I've been noticing gravity since I was very young." -Cameron Diaz
Yesterday, I told you about one of the simplest arguments for dark matter. We look out at the fluctuations in the microwave background on all the different angular scales we can measure -- from about 0.2 degrees all the way up to the whole sky -- and look at what the temperature fluctuations are doing.
We also look at the large-scale structure in the Universe, and try to correlate how mass clumps together.
We are only allowed -- by the laws of physics -- a few parameters to play with to try to fit this massive data set. We…
esiegel | November 16, 2010"What makes the universe so hard to comprehend is that there's nothing to compare it with." -Anonymous
If I were brand new to theoretical cosmology, I might be skeptical of a whole bunch of "dark" things that I'd heard of. "Dark matter?" "Dark energy?" Come on; you've got to be kidding me! You're telling me that 95% of the Universe is not made of protons, neutrons, and electrons, like all the matter we know?
After all, I look out at the Universe, and this is what I see.
Stars, galaxies, gas and dust... normal matter, all of it. Yet all I need to do is start with two very well-supported…
esiegel | July 23, 2010"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light." -Plato
Imagine, if you will, the year 2200. Forget about the flying cars and robotic exoskeletons, though. I'm thinking about the incredible scientific tools we'll have at our disposal, as well as the huge set of information we'll have available about the Universe.
One day, the latest telescope project gets completed, and we're finally able to make detailed measurements of an extra-solar planet's surface!
We'd already been able to learn much about this planet, including…
esiegel | July 21, 2010He was a dreamer, a thinker, a speculative philosopher... or, as his wife would have it, an idiot. -Douglas Adams
When I started writing about science online in January of 2008, I put the word out that I would accept questions from my readers. After all, I knew that there was a lot of misinformation out there, as well as the more insidious "technically correct but misleading" information about science.
In particular, I want to get the actual information that we know out there. As far as what I can contribute, I'm confident that I can add an expert voice for my specialties (physics, astronomy…
drorzel | July 14, 2010With the rumors of a Higgs Boson detected at Fermilab now getting the sort of official denial that in politics would mean the rumors were about to be confirmed in spectacular fashion, it's looking like we'll have to wait a little while longer before the next "Holy Grail" of physics gets discovered.
Strictly speaking, the only thing I recall being officially dubbed a "Holy Grail" that's been discovered was Bose-Einstein Condensation (BEC), first produced by eventual Nobelists Carl Wieman and Eric Cornell in 1995. Somebody, I think it was Keith Burnett of Oxford, was quoted in the media calling…
esiegel | June 30, 2010"I have given them the last rites, now you do what you will. You are stronger than us, but soon I think they be stronger than you." -Dawn of the Dead
Here at Starts With a Bang, one of the things I'm passionate about is putting forth all sorts of different pieces of evidence for dark matter, and trying to help you piece together a coherent picture of how the Universe works.
But every once in a while, something comes along to derail me. I'm not going to let that happen today, though. From showing you how two colliding galaxy clusters interact, separating the majority of protons, neutrons, and…
esiegel | June 28, 2010The task is not so much to see what no one yet has seen, but to think what no body yet has thought about that which everyone sees. -Arthur Schopenhauer
Most of you who've been reading Starts With A Bang for a while have seen this picture come up many, many times.
Why do I keep putting it up, and why is it so important?
Let's go back to the 1960s for a little bit. Back then, there were two major rival theories about the origin of the Universe: the Big Bang theory and the Steady-State model of the Universe. The Big Bang contended that the Universe was hotter and denser in the past, and thus of…
esiegel | June 24, 2010"The Universe is made mostly of dark matter and dark energy, and we don't know what either of them is." -Saul Perlmutter
When I was starting out as a graduate student, one of the most exciting (and daunting) tasks facing me was to piece together a scientifically accurate and useful picture of the Universe, including its composition, structure, and history. (And I owe a huge shout-out to my PhD advisor, who helped me immeasurably in that task.)
The big question facing me, as far as I was concerned, was deciding whose ideas were right, and which were the ones I should spend my time and energy…
esiegel | June 12, 2010"If we lived on a planet where nothing ever changed, there would be little to do. There would be nothing to figure out. There would be no impetus for science. And if we lived in an unpredictable world, where things changed in random or very complex ways, we would not be able to figure things out. But we live in an in-between universe, where things change, but according to patterns, rules, or as we call them, laws of nature. If I throw a stick up in the air, it always falls down. If the sun sets in the west, it always rises again the next morning in the east. And so it becomes possible to…
drorzel | May 6, 2010There's a minor kerfuffle at the moment over the XENON experiment's early data (arxiv paper) which did not detect any dark matter in 11 days of data acquisition. This conflicts with earlier claims by the DAMA experiment and recent maybe-kinda-sorta detections by the CoGeNT and CDMA experiments.
As a result, a couple of members of other collaborations have posted a response on the arxiv saying, basically, that they don't believe the sensitivity claimed for the XENON detector in the energy range in question, and that their result can't really be said to rule out the possibility of dark matter…
esiegel | April 9, 2010"Cosmologists are often in error, but never in doubt." -Lev Landau
I've been telling you about the Big Bang, the greatest story ever told, and the entire natural history of the Universe. Let's remind you -- historically -- of how our conception of the Universe changed as we learned more about our surroundings.
Maybe the first astronomical observation ever made was that the Sun rises in the East, passes overhead, and sets in the West. And it does this day after day, every day. It's no wonder that our first "cosmological model" of the Universe was that the Earth is stationary, and the Sun…
esiegel | March 26, 2010"No matter how dark things seem to be or actually are, raise your sights and see the possibilites -- always see them -- for they are always there. -Norman Vincent Peale
Dark matter. I talk about it a lot here for a number of reasons. These include:
the fact that it makes up about 85% of the mass of the Universe,
the only way (so far) that it appears to interact with anything is gravitationally, and
from our observations, we've learned that it's made up of slow-moving, massive particles.
You put what we know about dark matter into a simulation, and it tells you what type of structure you…
esiegel | December 18, 2009One of the reasons I write here on ScienceBlogs is because of our associations with the New York Times, a journalistic news source that I'm proud of on most days.
Today is not one of those days.
It isn't just the Times, either, the BBC is busy botching this story, so is the Telegraph, the Daily Mail, and pretty much everyone else, except for TG Daily, which got it right.
If you go down to the bottom of Soudan Mine in Minnesota, you'll see an usual site for a mine: a group of giant physics experiments! Why? At the bottom of mineshafts, you have up to hundreds of feet of Earth protecting you…
edyong | December 18, 2009Exciting hints that scientists had finally discovered the existence of dark matter - the mysterious substance thought to make up a quarter of the Universe - were dashed last night as researchers realised their equipment had detected a dark mattress instead.
The premature announcement was blamed on faulty software. "Apparently, someone left an errant ampersand in our code," said an embarrassed physicist, before weeping slowly into a whisky glass.
The Cryogenic Dark Matter Search (CDMS) laboratory, buried half a mile underground in an iron mine, announced last night that they had found traces…
esiegel | December 14, 2009Trying to squash a rumor is like trying to unring a bell. -Shana Alexander
Around the internet, blogs are all abuzz that an experiment searching for dark matter, CDMS, has cancelled all of their upcoming announcements and will be holding a special press conference on the 18th (this Friday!) to release their latest findings.
Here's what you can expect. First off, here's how it works. They take a bunch of hockey-puck shaped detectors,
shield them at the bottom of a mine shaft deep beneath the Earth (in Soudan, MN),
and try to measure these very rare events of dark matter particles (which can…
esiegel | October 26, 2009Perhaps you've been following my ongoing series on dark matter. Perhaps, like many, you're still skeptical. After all, it's not like we've gone and made it in a lab or discovered it in an experiment. 15 years after David Weinberg composed the Dark Matter Rap, we still don't know exactly what dark matter is.
But there's a whole lot that we do know about it just from looking out at the Universe.
You see, there are a whole bunch of scales we can see, from galaxies to clusters to superclusters and the large-scale structure of the Universe as a whole.
And-- since the big bang happened just under…
esiegel | October 13, 2009
Barney: Next they're gonna show my movie.Bart: You made a movie ?Barney: I made a movie? I wonder why there was a picture of me on the cover of Entertainment Weekly.
Earlier this year, a documentary film challenge was issued internationally. The goal was to make a movie about one of this year's two themes: hope or fear.
A group of Oregon filmmakers, The Cingulate System, called me up at work and asked if they could interview me for their film about Dark Matter. The challenge was to make a documentary, from scratch, in under a week. The film premiered April 8th right here in Portland…
esiegel | October 8, 2009Earlier this week, I wrote about an article that appeared in Nature, New Scientist and other places. The article -- and especially the popular writeups -- talked about a problem with dark matter and how MOND (MOdified Newtonian Dynamics) solves those problems.
And I'm livid about it. Another physicist/scienceblogger thinks my anger is misplaced, and left me the following in my comments section:
Ethan - this is not a creationism debate.
Hong Sheng is a top dynamicist and he knows perfectly well what the issues are.
The whole point of science at this level is to test models and propose…
esiegel | October 6, 2009You're sweet as a honey bee
But like a honey bee stings
You've gone and left my heart in pain
All you left is our favorite song
The one we danced to all night long
It used to bring sweet memories
Of a tender love that used to be
Now it's the same old song
But with a different meaning
Since you been gone --The Four Tops
Those of you who've been with me since the start of our current series on Dark Matter, including parts I, II, III, and 3.5, know that I'm a big proponent of dark matter. I think, based on everything that we know, that it is the simplest, easiest, and most likely explanation for…
esiegel | September 30, 2009Many of you saw the pictures I posted Monday of colliding galaxy clusters. These pictures were spectacular, because they not only show galaxy clusters less than 200 million years after a collision (which is short, cosmically), they also show where the mass lies (traced in blue) and where the X-ray emitting areas are (pink). You get pictures like this one from the Bullet Cluster:
This one from MACS J0025:
And this one from Abell 520:
This is what happens when clusters collide, the normal matter gets separated from the dark matter! Let's tell you how.
Some normal matter is packed together in…