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OtherRealms Issue 22 Part 11
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
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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
