Antimatter

Next I will talk about antimatter.  When antimatter comes in contact with matter, they explode. Antimatter is composed of positrons (anti-electrons, or electrons with positive charges), and antiprotons.  Both of these, among other antiparticles are routinely created at certain particle accelerators.  in 1995 they created the first anti-atom , anti-hydrogen at CERN.

Unfortunately it currently costs about $100,000,000,000 to create a milligram of antimatter, which is far more than needed for current experiments, but is about the amount needed for large scale use.  In order to be used commercially, that price would need to decrease to about $10,000,000.  Also it takes more energy to create anti-matter than the reaction creates.

  • My first question regarding antimatter is approximately how long do you think it will be before we launch the first antimatter propelled spacecraft, or do you think we ever will?
  • My second question regarding antimatter is how much energy does the reaction creating antimatter need, and how much energy does the matter-antimatter reaction give off?
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2 thoughts on “Antimatter

  1. Eoin Butler, ALPHA Experiment, CERN says:

    It’s very hard to answer your first question, because the answer could well be NEVER. I don’t think that we’ll see it in our lifetimes.

    CERN uses around 200 megawatts of energy (http://home.web.cern.ch/about/engineering/powering-cern) when it’s running ( not _all_ of that is used for antimatter, but let’s imagine that it’s 10%). The Antiproton Decelerator creates something like 4×10^7 (40 million) antiprotons per 100s. So the rate at which you’re storing power is, at best, 2 * (4 x10^7) * (mass of the proton) * (speed of light)^2 / (100 seconds), or 0.1 milliwatts. That’s roughly one hundred billion times less. Huge number.

    Another thing that you have to think about is how to store all that antimatter in your spaceship. If you store antiprotons, they’re electrically charged, and push each other away. The more antiprotons you add, you need to use very strong electric fields to cancel this repulsion and it makes construction very difficult. You can get around this if you use neutral antimatter, like antihydrogen atoms, but creating antihydrogen atoms from antiprotons is very inefficient.
    At ALPHA, we were able to store 1 atom of antihydrogen for roughly every 10^8 antiprotons we received from the Antiproton Decelerator.

  2. Tim Tharp says:

    I can try to address your second question, “how much energy does the reaction creating antimatter need, and how much energy does the matter-antimatter reaction give off?”

    In a perfectly engineered system, we can calculate the energy required to produce antimatter. Particles tend to be produced in pairs, so let’s say we want to create an anti-proton and a proton from nothing. From Einstein’s equation, E=mc^2, we can calculate the required energy to create these two new particles, and it comes out to (mass of proton + mass of antiproton)*(speed of light)^2 = 1.8 billion electron volts.

    (An electron volt is a unit of energy which is very small compared to energy units most people are used to. For example, 1 electron volt = 4.5 x 10^(-26) kilowatt hours. It might seem odd that I’m telling you that antimatter contains such a tiny amount of energy, but that is because here I am talking about the energy contained in one particle or atom, not the energy per gram or kilogram which would contain vastly more energy.)

    How much energy is then released in the matter/anti-matter reaction in a space ship? Exactly the same amount, 1.8 billion electron volts, every time an anti-proton and a proton collide. Therefore, anti-matter is not a source of energy. Rather, even in a perfect system, antimatter can at best be used as a way to store and transport energy, much like a rechargeable battery.

    Since antimatter contains more electron volts of energy per kilogram than any other known fuel, this makes it an attractive idea for propelling spacecraft in science fiction. However, the practical issues of working with antimatter make it very unlikely to be used any time soon. As Eoin points out, a real system takes much, much, MUCH more energy than 1.8 billion electron volts to produce the antimatter, because the production of antimatter is very inefficient. This and the storage issues he mentioned make antimatter a very unlikely candidate for space propulsion in our lifetimes.

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