Nothing much in the way of stories published today, so instead I will focus on the second part of my series about Dark Matter.
An earlier blog described the concept of dark matter. Now, I'm going to go into some detail about the article I've written that just got final approval today. It talks about how scientists are trying to prove what dark matter really is, and the techniques they are using.
First, particle accelerators create mass. When the particles are smashed together, so much energy is released, that new mass forms by Einstein's famous equation of E=mc^2. So the more energy you have, the more massive particles you can create, which is why the LHC will be able to probe deeper into the depths of matter than any experiment before.
If any new particles are created by the LHC—remember that everything is still technically theoretical, nobody knows for sure what will happen—they will almost instantly decay into more stable particles. Scientists can not "see" the new particles, but they can see what they decay into.
When the particles are created, they fly out of the event in every direction. And when they do, their momentum, or energy, must be balance. That is to say, the energy from one side of the collision has to equal the energy from the opposite side. When they don't, it means there is a particle shooting out carrying energy that scientists can not see.
Now, detecting a new particle like this does not necessarily mean it is what dark matter is made out of. It could be a brand new particle that has nothing to do with dark matter. To find out, scientists must first detect dark matter in the "real world," that is, outside of a particle accelerator.
To do this, scientists are studying the skies looking for gamma rays, positrons, or anti-protons that don't seem to be coming from anywhere. If found, these sources could mean that there are invisible particles colliding on their own in outer space. Meanwhile, here on earth, or rather under it, scientists are trying to detect a dark matter particle striking a regular particle. By shielding the experiments deep beneath the ground, other types of particles are blocked from the experiment. So if something hits a particle in the experiment, it can only be an invisible particle that made it through thousands of feet of solid rock.
When all of the data finally comes in, and scientists get lucky enough to spot new particles both in the accelerator and outside of it, they must be compared. If their properties are the same, then scientists will have found dark matter.
Do I sound like I know what I'm talking about yet? What was confusing about that whole rant? Let me know so I can do better next time…
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2 comments:
How do they know that dark energy and dark matter are both out there? Couldn't it be one or the other? How do they know 2/3's is dark energy?
Hey Randy, glad to see you figured out how to leave comments, especially since it seems nobody else is interested enough in this stuff to ask any questions...
But your question is a good one, and I had to do some research to answer it. It's really complex and long, so you'll just have to take my work for a few things, or visit some sites I can recommend.
The amount of matter and dark matter in the universe has been confirmed through two different studies. One involves taking an area of space and calculating how much mass is there based on how much mass we can see and the gravitational effects that the dark matter has on it. Once this is determined, it's assumed the universe if fairly uniform, and the mass is extrapolated to include the whole universe.
The second way is through the Cosmic Microwave Background, background noise caused by the Big Bang. Detailed observations of this phenomenon result in the same numbers for the ratio of regular to dark matter.
But this doesn't answer the question of dark energy.
Dark energy permeates the universe and acts like an anti-gravity. Through more calculations using the Cosmic Microwave Background, it has been determined that the universe is flat. This requires a very specific density of the universe. So once this density is calculated, and they have calculated how much regular and dark matter exists, the remaining "missing mass" must be dark energy.
Additionally, studies of how galaxies are moving have proven that the expansion of the universe is accelerating. If gravity were working alone, it would be decelerating, or even coming back together towards a "big crunch." But since scientists can calculate how fast it's expanding, and how much mass/gravity exists, they can guesstimate the amount of dark energy needed to counter-act gravity.
So how confusing is that?
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