Electronic OtherRealms #22 Fall, 1988 Part 11 Copyright 1988 by Chuq Von Rospach All Rights Reserved OtherRealms may not be reproduced without written permission from Chuq Von Rospach. The electronic edition may be distributed or reproduced only in its entirety and only if all copyrights, author credits and this notice, including the return addresses remain intact. No article may be reprinted, reproduced or republished in any way without the express permission of the author. Interview Joel Davis This interview was held on the Delphi Timesharing service by Sysop Mike Banks and other Delphi members. It was held on July 16, 1988. For information on joining the Science Fiction group on Delph, get your local access number from 800-544-4005. Log onto Delphi with account JOINFICTION and password URANUS. This will qualify you for a special discount. Mike> We are pleased to welcome Joel Davis, co-author (with Dr. Robert L. Forward) of Mirror Matter! Pioneering Antimatter Physics. Published by John Wiley & Sons, Mirror Matter! is a pop-science book on the development of a future antimatter technology that will lead to cheap solar system travel within 25-50 years. For a first question, I'd like to ask you to synopsize for us just what antimatter is. (Or is not) Joel> Antimatter is not "dark matter" or "shadow matter." Antimatter is, in a sense, matter which is the "mirror image" of ordinary matter. Mass is the same, but other properties such as electrical charge and direction of spin are opposite. For example: the electron has a negative electric charge but the positron (antielectron) has a positive electric charge. Same for the antiproton -- the charge is negative instead of positive, but other properties are the same, such as mass. Mike> In normal matter, then, electron (-) , proton (+), but antimatter reverses? Does the direction of electrons in their orbits reverse? Joel> Yes on the first, not necessarily to the second. The idea of "orbits" around nucleus is really just a fiction of the Bohr imagination. It isn't really like that in there at all. What it IS like, is mysterious. We are talking about the properties of the subatomic particles themselves, not the direction of their orbits in an atom, or a nucleus. Ralph> The thing Mike said about solar system travel in 25-50 years intrigues me. How can this be when we can't even keep a shuttle on the launch pad? Who's developing it? Joel> Good question. First, more background. When matter and antimatter meet you have total annihilation of matter into energy. Everything basically cancels out and you get pure E=Mc2. Theoretically, anyway, this could be a superb source of propulsive energy. As to who is working on it: (1)Not NASA. It's too "far out" for our space agency. (2) The Air Force is very interested in it. Bob Forward's been working with them for about 5 years now on a consultant basis. USAF sees antimatter as a definite possibility for earth to orbit propulsion and for in orbit propulsion, at least to start with. Mike> What kinds of energy can be expected? Hard radiation? Joel> To start with, a first-generation antimatter space propulsion engine would use a very small amount of antiprotons (nanograms to micrograms) to heat a large amount of "working fluid" like liquid hydrogen. You get several thousand seconds of specific impulse, which is a hell of a lot more than the shuttle. Hard radiation. This kind of reaction with antiprotons produces as a byproduct about 1/3 gamma rays. Hard ones. But 2/3 of the byproduct of the annihilation event is pions, which are subatomic particles with mass. Some are charged. So magnetic fields can direct them for more thrust.... You do have to shield for the gammas, but the thrust and specific impulse is so huge that the weight penalty is not that serious. Mike> You seemed to imply by "working fluid" in alluding to liquid hydrogen that the liquid hydrogen would be used for boost mass? Or am I wrong in my inference? Joel> No you are correct. The working fluid is heated up to a plasma (you can use liquid methane, or water, or whatever) and that is your boost mass. You have a ratio of a few micrograms of antimatter to a few metric tonnes of working fluid. Mike> Great. I love it. Heinlein's torch ships. Joel> Exactly. Warren> How can the conversion be controlled , i.e., rate? Joel> This is, as we say, "just an engineering problem...." Actually, it is a big engineering problem. However, antimatter has been made and controlled for decades now in particle accelerators by physicists. The trick is to construct small and compact magnetic bottles which can hold micrograms to milligrams of antihydrogen ice flakes. Also, the flakes are kept slightly charged with an electron gun (simple stuff) and levitated in the bottle. Such bottles exist now, called Penning traps, but they are the size of a refrigerator. But the engineering is not impossible. Mike> Then the real engineering problem is how to release the flakes selectively? Joel> Right. The flakes must be sent down a tube to the thrusters where they mix with the large amounts of normal matter. Mike> The tube must somehow be isolated...magnetically? Joel> Yes. Magnetic fields, for sure. Also cooled to a fraction of a degree above absolute zero to keep the antihydrogen flakes as flakes. Damon> Really more of a matter of metering out the stuff atom by atom, or nearly so. I think it would be similar to existing particle accelerator guideways, but more compact. Joel> Much more compact. And different design, too. Not circles but straight. This is one place where the warm temperature superconductor technology will make a big difference.. Mike> Has anyone written to say they're using Mirror Matter! as source info for a novel, yet? Joel> Yes, Greg Bear has told me he is already stealing ideas from the book. I should also note that Jack Williamson wrote a nice blurb for the book, and he's the inventor of antimatter SF. Mike> Can you briefly highlight applications involving antimatter other than spacecraft/aerospacecraft propulsion? Joel> Sure. Antimatter, especially antiprotons, can be used for imaging the interior of a human body in much more detail than current PET scans and CAT scans by building up pictures pixel by pixel, like Voyager 2. Also, antiproton beams can be used to cauterize tumors that are otherwise inoperable. Some people at the University of Syracuse in NY are working on this. The same technology can be used to image/anneal the interior of solid objects. Mike> What about weapons? Joel> Weapons? Well, not bombs. Too expensive, and antimatter/matter annihilation tends to be fizzle and not boom. Antiproton beam was considered by SDI people, but shelved as "too expensive." Actually it was too far down the road, after Reagan administration so they were not interested. Damon> I've seen a proposal for room temperature storage of mirror matter in ring molecules. Any thoughts on that? Joel> That sounds interesting. The problem with room temperature storage, as I see it is the presence of air molecules. Now, if this is room temperature storage in a very hard vacuum, then you got something interesting. Damon> The idea is to capture positrons in a ring of molecules so it'd be relatively isolated from outside influences, such as stray molecules. I point out that this is still theoretical as far as I know. Joel> Ah. The problem there is (1) won't the positrons annihilate on contact with the ring molecules, and (2) positrons are not as good for antimatter propulsion as antiprotons. Hey, ALL of this is theoretical, right now.. Damon> It's not a great answer for all applications, but provides a possible means of storage somewhat like a small battery, as an analogy. Joel> That might be very good for some nonpropulsion applications, such as medical uses or metallurgical uses. Do you know who is doing that research? Damon> This was from a letter in Aviation Week and Space Technology. And the author was proposing tank-killing rifle bullets, for example, more as hypervelocity rounds than semi-nuclear explosives, I think. Joel> Forget that. Very expensive antitank weapon. Antimatter costs hundreds of millions to billions of dollars per milligram. But that would be a good storage method for other uses. Such as in a high school or college physics lab.. Think of the experiments you could do. Mike> Do you see any "spinoff"-type applications or discoveries associated with near -- future antimatter research? Joel> The first spinoffs, I think will be in the area of physics research, since storage of large (nanogram) amounts of matter will make possible some very interesting new experiments. Like, does antimatter have the same gravitational force as matter? Other spinoffs may show up 10-15 years down the road, in those medical applications. Mike> What's your opinion on that? Joel> On the gravity thing? I think it's the same for antimatter as matter. At this point there is no reason to think otherwise. Though I wonder about the 5th and 6th force experimental results.... Interesting. Perhaps an antimatter component there? Mike> Antimatter could, among other things, promote "hands-on" research into some currently-neglected areas. Joel> Yes. Bob Forward calls it "low velocity nuclear physics" since all the current antimatter physics experiments are done with high velocity antimatter beams. Clay> I read in Scientific American, that antimatter is "heaver" than matter - because of gravitons & antigravitons and all that stuff. Joel> We assume gravitons exist (and therefore antigravitons) but no one's ever detected them. A physicist at Harvard is currently doing experiments at CERN to determine exactly that, Clay. Dropping antiprotons down a tube to see if they fall at the normal rate in a 1g field. Joel> Right, He's first using protons, then antiprotons. The first step was last year, when he captured individual antiprotons in a penning trap and played with them. Mike> You mentioned/described briefly the penning trap earlier. This is a true magnetic bottle? (Or electron-beam "levitation?") Joel> Yes. It uses magnetic fields to capture and then trap a subatomic particle in a container, and keep it there. Mike> What is the "incidence" of antimatter particles, antiprotons, say, when compared with normal matter? i.e., how many ppm (or billion, trillion?) Joel> Theoretically there should be equal amounts of matter and antimatter in the universe, since this is a symmetrical production thing. For every matter particle produced there would be an antimatter particle.... However, there is almost no antimatter naturally found in the universe... Mike> Indeed, Joel. Any theories on that? Joel> The theories are pretty complex, and currently are tied up in the Alan Guth idea of the inflationary scenario of the universe's creation. Some very tiny imbalances at that point lead to a slight preponderance of matter over antimatter and the stuff all annihilates except for the left over matter. And that IS US. And the galaxies, etc..... Damon> Either production wasn't symmetrical after all, or we just haven't seen it yet. Joel> Damon, we have been looking for a long time and there are characteristic radiation signatures to antimatter/matter annihilation, which are not seen in the universe. Damon> Does our current understanding of nuclear physics (such as it is) suggest that interactions of matter and antimatter might be significantly different between different elements and antielements? I.E., would the generated subatomic particles and various radiation be different, as in fission and fusion reactions? Joel> No. The proton is a proton is a proton (apologies to Gertrude Stein) no matter what atom it's in, and the same is true of antiprotons, etc. The by-products of antimatter-matter annihilation is pretty well known for antiprotons and positrons. It might get more complex for large clusters of them. But not really different. Joel> Yeah, everything eventually cancels out. Even the pions eventually decay to gamma rays and positrons and electrons, which annihilate to gammas. Brandon> You mentioned experiments concerning 5th and 6th forces. Like most other people, I've only heard of the "Four Forces". What are these experiments? Joel> Recently some physicists have found tentative evidence for the existence of variations of gravity on a short range. Gravity is infinite in its expanse. But the fifth and sixth forces would act at short distances a few hundred meters to a kilometer or so. One is attractive, one repulsive, and no one is sure that they are real at this point. But some of the evidence is intriguing. Mike> Are these analogous to gravity, strictly speaking? Joel> I believe so yes.... The main thing about them is that they would explain some discrepancies in the measurements of gravity forces that have been found over the years, and also win someone a Nobel Prize. Warren> What about inverse process - energy to matter and antimatter? Joel> Oh yes. That is VERY true. E=Mc2 again. That is how the first antiparticle was discovered. By Carl Anderson of Cal Tech. Found electrons and positrons appearing in a cloud chamber when a cosmic ray hit a particle of some atom in the chamber and it was photographed. Warren> Then antimatter can be manufactured? Joel> YES. Interesting consequences. That is what physicists do today in particle accelerators. Make antimatter, namely antiprotons, and keep them in a beam, then slam the antiprotons into a target and get a spray of quarks. So the key to antimatter technology is to make A LOT of antimatter and learn how to store it. Making it is not hard. Just energy consuming. Susan> Joel, how do they contain it? Joel> They keep it in a vacuum tube bent into a circle about 10-15 km. in diameter, which runs under Switzerland and France. Magnets keep it circling around in the tube. Susan> So if they make a mistake, there goes Europe? Joel> No. The stuff is so minuscule in amount (femtograms or less) that all that happens if the magnets cut out is that there is a blip on some radiation counter. Damon> Has antihydrogen actually been manufactured, even in single-atom quantities? Joel> Yes it has, at least in nuclear form -- since that is just antiprotons. But also antideuterons, antitritons, and some isotopes of antihelium. But antihydrogen with an antiproton circled by a positron: not yet. But not difficult to do, either. Damon> Why not? Just no need for it yet? Joel> Well, the reason why not is that most physicists consider making real antihydrogen just "a trivial chemistry experiment." And they are not interested. Just another "engineering problem." ---- End of Part 11