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  1.  
    "Time is an illusion. Lunchtime, doubly so." - Douglas Adams, The Hitchhiker's Guide To The Galaxy
    http://arxiv.org/pdf/1307.6167.pdf
  2.  
    I thought time was what kept everything from happening at once.
  3.  
    Why does half time pass so quickly?

    It's the only time you can get a man's attention on Sunday.
  4.  
    I protest against the implied trivialisation of getting a woman's attention, any time.
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      CommentAuthorAngus
    • CommentTimeJul 25th 2013
     
    Posted By: magic momentWhy does half time pass so quickly?

    It's the only time you can get a man's attention on Sunday.


    Well, duuuuh. It's only half as long as the whole time. Are you blonde or something?
  5.  
    Better blonde than never.
  6.  
    harumph.


    Seen on blonde's t-shirt: "You can't be first, but you can be next."
  7.  
    I dreamed of superconductors spinning at 15 Krpm with Dremmel motors in cans with LN2, and something about a tetrahedron. Weird.
    • CommentAuthorLakes
    • CommentTimeJul 27th 2013
     
    Posted By: Andrew PalfreymanI dreamed of superconductors spinning at 15 Krpm with Dremmel motors in cans with LN2, and something about a tetrahedron. Weird.
    SpinDizzy?
  8.  
    Ah the old spindizzy. I have The Seedling Stars somewhere I think.
  9.  
    Frank Wilczek has a new paper about, well, everything: "Multiversality"
    http://arxiv.org/abs/1307.7376
  10.  
    (moved from elsewhere)

    Hmmmmm....It had never occurred to me to use Hawking radiation as an energy source. There's a thought. See you in a few centuries when I've figured this out. We already have enough energy to make nano-holes, so....(wanders off mumbling)...

    https://en.wikipedia.org/wiki/Black_hole says

    A stellar black hole of one solar mass has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole needs to have less mass than the Moon. Such a black hole would have a diameter of less than a tenth of a millimeter.[87]

    If a black hole is very small the radiation effects are expected to become very strong. Even a black hole that is heavy compared to a human would evaporate in an instant. A black hole the weight of a car would have a diameter of about 10−24 m and take a nanosecond to evaporate, during which time it would briefly have a luminosity more than 200 times that of the Sun. Lower-mass black holes are expected to evaporate even faster; for example, a black hole of mass 1 TeV/c2 would take less than 10−88 seconds to evaporate completely. For such a small black hole, quantum gravitation effects are expected to play an important role and could even—although current developments in quantum gravity do not indicate so[88]—hypothetically make such a small black hole stable.[89]


    So we can't keep a little one around, and we don't want, for propulsion, to have to accelerate a Moon mass. That means that we can only use a Moon mass stable black hole as a source of antiparticles. But that's very useful, because then we can build antimatter drives. Yay. The damn thing just sits there, carving up the vacuum virtual particles and feeding our storage devices. It is continually replenished via the CMB. Sounds like the ideal fuel generator. And, guess what - we already have a moon...

    Just a couple of engineering details to be worked out.
  11.  
    Antimatter holds the promise of liberating space travel from dumb old rocketry with its big dumb mass of dumb fuel. Less than a nano-gram of positrons contains sufficient energy to lift 1 kg of payload beyond the gravitational pull of Earth. It will not only enable us to launch to space more efficiently, but also to travel our solar system faster and indeed to get us to the stars within the lifetime of a man. We need to solve the problems of production, storage, and engine design. State of the art storage is a Penning-Malmberg trap. Large numbers of antiparticles may be stored there.

    If we use a captive black hole to produce antimatter, production rates can be increased by using a smaller mass black hole, and continually pumping in energy to stabilise the Hawking radiation efflux. Conveniently, this would be focussed direct (incoherent) solar, or focused coherent radiation from solar-powered laser or microwaves.Multiple collectors orbit elliptically, shaving the event horizon as they scoop up their cargo. The whole thing is relatively lossless. CMB makes great fuel.

    What might be useful is a small black hole that can be stabilised by a GW-level continuous energy influx and positionally stabilised by the same laser tweezers that feed it. It's fail-safe - turn off the lasers and it evaporates instantly. This would produce a high rate of antimatter production, but the problem is to get hold of the hole in the first place.

    I don't know whether the production rate for an equilibrium black hole could exceed our other techniques, which yield a current best rate of about 5 nano-gram/year. I suppose that depends on whether we can marshal a sufficient number of black holes.

    http://iopscience.iop.org/1742-6596/443/1/.../1742-6596_443_1_012081.pdf‎ describes state of the art positron production.
  12.  
    "State of the art storage is a Penning-Malmberg trap. Large numbers of antiparticles may be stored there."

    For certain values of "large".

    How many positrons are there in a nanogram? How long can you store them in a PM trap?
  13.  
    Posted By: alsetalokin"State of the art storage is a Penning-Malmberg trap. Large numbers of antiparticles may be stored there."

    For certain values of "large".

    How many positrons are there in a nanogram? How long can you store them in a PM trap?
    You'll find the answers at the link above. me is 10-27gm; mp is 10-24gm
    •  
      CommentAuthoralsetalokin
    • CommentTimeAug 5th 2013 edited
     
    I don't want answers, I just want to ask stupid ignorant pointed questions, to make you think about the answers. Answers are useless, they tend to stop speculation.

    Do we even know if antimatter responds normally to gravity?
  14.  
    Do we even know if antimatter responds normally to gravity?
    Good question. There's an experiment ongoing to determine that right now. At CERN I believe. Yeah..
    http://www.pbs.org/wgbh/nova/next/physics/cern-details-precursor-to-anti-gravity-experiments/

    The questions are great. At the moment, I'm noodling the numbers to which you're referring.
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      CommentAuthoralsetalokin
    • CommentTimeAug 5th 2013 edited
     
    Right. So a nanogram of antimatter might fall up instead of down. If you emit a nanogram per second of antimatter in a beam, do you expect a thrust reaction in the opposite direction, or a pulling, tractor-type reaction in the same direction?
  15.  
    And what are you doing up this early? Isn't it like 2:30 AM in the sillycon valley?
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      CommentAuthoralsetalokin
    • CommentTimeAug 5th 2013 edited
     
    Current production is at a rate of 5 nanograms/year. What is the energy cost in Joules (A) for us to produce 5 whole nanograms of antimatter? How much energy is emitted (B) when all this antimatter participates in total annihilation events with ordinary matter? Is A>>B, A>B, A=B, A<B, or what?

    (Neglect storage costs, of course.)