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NASA Researching Antimatter Engines
dbolger writes: "CNN has a story about how scientists at NASA's Marshall Space Flight Center in Huntsville, Alabama are researching ways to use antimatter to fuel missions to Mars and beyond within the next 50 years. It very light on technical details, but does give an interesting look at current and future potential uses of antimatter."
There is something definately wrong with the picture on cnn.com. This picture looks very wrong someone must have been thinking bad thoughts at the time.
You can weigh antimatter?
(i seriously don't know, im asking...)
is anyone else concerned about mass manufacture of antimatter? they could potentially induce a teraton size explosion if the kinds of amounts they are talking about come into contact with matter.
I've never understood exactly how you would contain antimatter until it is used...Is it contained in some kind of electromagnetic field, or is this all still theoretical? I thought that antimatter was immediatly annilihated due to its inherently volatile nature when it is produced.
Anyone know any more details on how one would actually build up a gram of isolated antimatter?
There's an older (1999) article on nasa's site with a bit more technical detail.
Hogsback
I go to school at UA in Huntsville. There's lots of research in propulsion here - from the linear accelerators posted earlier to launching lasers, ion drives, and this stuff. I just want to know when they start playing around with large quantities so that I can move. The last thing I need to live next to is a very large bomb.
I thought you needed a reactor core with dilithium crystal to make a matter-antimatter reaction possible. Can NASA produce dilithium crystals yet ? and visors for the reactor core technicians ?
All the more reason to get our asses into space, so we can set up automated plants to manufacture anti-matter far away from inhabited areas...
Besides, free power (solar), free reaction mass (with sufficient heat, we can liberate volitiles from moon rock, asteroids, etc), and we're already outside of the gravity well... lots of advantages to doing space-related research, while actually in space. We just have to make like we want to stay there, instead of making very expensive vists all the time.
I was at MSFC on a business trip a while back, and talked to the guys working on Gen2, Gen3 and later RLV design. Basically what the lead engineer told me they do is "assume we have really cool technology that meets certain specifications" and work backward from there to figure out how the rest of the vehicle be designed.
While I'm sure there might be one or two people actually doing research into antimatter, most of the work they do is just assuming *someone* will come up with the necessary technology by the time they have to build something.
When a matter particle comes into contact with an antimatter particle, they annihilate each other and produce kinetic energy.
Why bother with antimatter? I had the same effect with my last marriage.
Cell phones = communicators
Babelfish = universal translator
Taser(tm) = Phaser on stun
2-way videophone = Screen on the bridge
PC = Enterprise computer terminal
Now antimatter propulsion.
Was this guy good or what?
Computer Science is no more about computers than astronomy is about telescopes. --E. W. Dijkstra
There are two problems with anti-matter as fuel:
1 - the cost of production is insane! One raisin worth may be enough, but that raisin could cost as much as the space shuttle to produce and concentrate.
2 - storage. You let this stuff touch anything and boom! You'll need to use some sort of electromagnetic containment field that will likely take energy to produce and be a complicated aparatus that may offset antimatter's one benefit: it is extremely compact.
The sad thing is that these hurdles probably won't be bridged until we have some sort of major war and the military finds some burning need to be able to destroy the world with one bomb instead of thousands.
I say, good luck to NASA, but don't hold your breath.
BlackGriffen
Is antimatter really being used for medical imaging? Considering the trouble it is to make, it seems like antimatter wouldn't be cost effective for this kind of use, and would be overkill for the cancer treatment proposed in this article. I could use a reference link here if anyone knows of one.
I can see the advantage in propulsion since so much of the weight of our current rockets is fuel, and most of that fuel is spent lifting other fuel.
However, if we have to create our own antimatter from scratch, the amount of fuel needed to travel to the nearest star (a common goal for which anti-matter is often considered a solution) would probably overtax our planet's energy resources. (This is presuming we don't just find a huge supply of antimatter hiding behind Saturn or something -- which isn't likely from what we think we know about the universe.)
So antimatter, like wormholes, would probably become just a plaything for the rich. I predict it will be used for the ultimate in opulent jewelry.
Am I the only one thinking antimatter costs more energy to produce than you get out of it?
Secession is the right of all sentient beings.
Physicist Robert L Forward wrote a popular science style book, Indistinguishable From Magic
The first chapter is titled Antimatter, discussed what antimatter is, how we storeit, produce it, how we could produce it econmonically, how to use it more space travel and more mundance applictions.
He also write science fiction, I remember enjoying Rocheworld and Camelot 30K
That's the least of your worries. Live anywhere near a gas storage facility? Toxic dump? Or even a gas filling station? How about within several states of a nuclear power facility?
The slightest thing going wrong with the containment at any of these places and you can kiss your ass goodbye.
Now we all know that these things don't blow up every day but - broadly speaking, scientists in a lab type environment take far more sensible precautions over the storage, use and containment of potentially hazardous materials than people in the real world.
That's because the scientist's priority will invariably be safe, repeatable research carried out in baby steps whereas the real world corporations will always weigh risk against profit.
And, personally speaking, I don't think that a bean counter focused on the fiscal bottom line is the best person to trust when it comes to safety.
"Accept that some days you are the pigeon, and some days you are the statue." - David Brent, Wernham Hogg
And we very light on verbs.
I'd rather have someone respond than be modded up.
Containment depends on what form it's in. Slashdotters have been referring to Penning traps here. Well, a Penning trap only works for charged particles, not neutral atoms, and it only traps one sign of charge -- you can't trap both + and - particles in the same Penning trap. Therefore, I don't think a Penning trap would be suitable for storing even microgram quantities of bulk matter; if you have matter or antimatter in bulk quantities, it has to be electrically neutral. I think the posters were confused between containment of plasma and containment of antimatter.
Containing antimatter, if you had it in bulk quantities, would be much easier than containing a plasma, since it doesn't have to be superhot like a plasma. You have to have an extremely good vacuum, however, because any matter that finds its way in will annihilate with the antimatter. I doubt that even the vacuum of interplanetary space would be good enough.
Find free books.
I would be rich... (this abused phrase notwithstanding).
/. readers) would consider archaic. I mean, 16 bit processors are finally being used for many missions and 8 bit processors are still common.
Seriously, there are so many futuristic NASA research projects (most of them in the $10,000 to $100,000 range). They cover everything from anti-gravity to blowing bubbles (liquid soap bubbles).
I personally think this is what NASA does best, and the results from these research grants are quite interesting. It is also very unlikely that NASA will ever do anything with most of these research projects.
{Rant Mode On}
Just for an example, there hasn't been a new propulsion technology for manned spaceflight since the 1970's (mainly due to politics... including internal NASA stuff too), and even the robotic probe missions are using what most geeks (and
I would consider myself to be a major NASA supporter, and I do vote for congressmen that are supportive of the space industry. I would also say, however, that I think the days of NASA are numbered and I wouldn't mind the complete dismantling of the entire agency. They are too stuck in the past (reliving the glory days of Apollo), and are actually doing more harm than good now for giving me or my children the opportunity to work and live in space.
As a percentage of the US Federal budget, NASA is now totally inconsequential. During the 1960's NASA was second only to the Department of Defense. Now, NASA doesn't even show up except on a list of miscellaneous agencies, and even the Department of Defense now comes in third of fourth (it is grouped with the Department of Veteran Affairs and the State Department to show it as a bigger piece of the federal budget in the 2001 tax booklet from the IRS).
I'm not advocating a renewal of NASA funding to 1960's funding levels (which was about 10% of the Federal Budget), but I am suggesting that it certainly is no longer a national priority, as defined by the United States Congress and the President of the United States.
Unfortunately, with much of the space infrastructure in Texas and strong Republican states (like Alabama, Utah, or swing states like Florida and California), I highly doubt that it could be cut with the current administration either.
{Rant Mode Off}
Nuclear efficiency is in between. While there is not complete conversion, there is some mass going to energy, unlike in chemical rockets. However, nuclear physics is practical and well understood. A system would probably not work just as a bunch of bombs going off(though research was done on that, see The Binding Curve of Energy), instead liquid fuel, possibly liquid hydrogen or ammonia, would be sent through a nuclear core, then expelled. This would allow radiation release to be kept in check pretty easily, and a highly efficient super-heated plasma would propel the ship. In addition, unlike normal rockets the plasma could be controlled with magnetic fields.
While nuclear certainly holds a great stigma to many people, and is not as sexy as advanced antimatter/space warp/whatever systems, it is here and could be turned into a drive with minimal fuss. I could see a single nation/group(of sufficient economic strength, aka US, EU, possibly Japan) or coalition of nations getting behind this and making a ship to do it. The others will be needed, and research should continue, but if we want to go to other planets in the next couple of decades, this is probably the technology to do it with.
First off, I think this is a project and think it'd be great to hear about a 2 week mars mission in my lifetime... but I must play devils advocate
OK, so assume that NASA gets a containment vessel built, presumably with an electromagnetic field, and they make enough antimatter to conceivably power a test vehicle or something. How do you transport the thing? I can see politicians and reactionaries screaming NIMBY when they attach it to a test vehicle. Even assuming that the test vehicle fails in say, a nice safe place like outer space, how do you convince the intelligent citizens of Florida (Motto: "Where's my Medicare Card?") that the transport of the container into outer space will be safe?
The ultimate goal is to send an automated craft to the sun and convert heat energy into order, stored as crystalline structure. The crystals can then be broken down to generate massive amounts of energy, stored in a magnetically based containment system as heat and light. This reaction can be used to initiate a form of hyper-fusion reaction with electrodes to separate matter from antimatter within the byproduct.
This will spontaneously generate tons of matter in a very small space. Some of this matter and antimatter will be expelled in order to produce locomotion, while the rest is simply to compress the space surrounding the vehicle. After this, the matter-antimatter will be recombined, to once again, expand space. The operation of expanding/shrinking space will be repeated continuously in order to allow faster than light travel without breaking the laws of relativity. NASA has deemed this mode of transport "Warp travel," since space is warped in the locomotion process. Since this is the major breakthrough that allows for extra-solar exploration, it is theorized that it may attract the attention and diplomatic relations of any nearby space-traveling civilizations.
Well...maybe its just to have a source of energy that is extremely easy to use and very portable.
But we can always dream, can't we?
Mod me down and I will become more powerful than you can possibly imagine!
Every known matter particle has an antiparticle which has identical mass, but opposite charges (for every kind of charge, including electrical). We don't know why, they just do. There doesn't seem to be much antimatter out there; again, for reasons unknown.
Antiparticles still have positive mass, like every other known particle, and are not repelled by gravity.
When a particle meets its antiparticle, they are converted into their combined mass worth of energy in accord with: E=mc^2 (where E is the energy, m is the combined mass, and c^2 is a ludicrously large number). Hence, antimatter is the most compact form of energy storage theoretically possible.
In other words, pretty good rocket fuel. Antimatter bombs would be rather unpleasant, and any contained antimatter is a potential bomb (there's nothing "potential" about uncontained antimatter for very long).
There is no reliable, efficient way of making antimatter, and no place to just pick it up for free. However, if you smash protons together hard enough with huge particle accelerators, they occasionally spit out highly energetic photons that decay into matched matter/antimatter particle pairs. With luck, you can catch a few in a magnetic field and hold them for a little while. This is about as cost-effective as it sounds.
If you ever meet your anti-self, and he hasn't exploded yet, either he or you will before you have a chance to shake his hand, so don't worry about it.
Despite this title, and the potential benefits of effective antimatter storage, antimatter can not be contained by a nutshell. Don't try.
Now I'm wondering if there's anti-matter in between my sofa cushions.
Maybe some background information would be helpful here. Antimatter is matter, but with the opposite charge. So, an anti-electron has the same mass as an electron, but with a positive charge. An anti-proton has the same mass as a proton, but with a negative charge.
Scientists have been able to create antiprotons for some time now, I believe several years. For example, they generate antiprotons at CERN in Switzerland, and can store them, as others have mentioned here, in Penning traps. Basically, this is a magnetic confinement trap, where the charge of the antiprotons (negative) is used to keep them in a very cool (like 2 Kelvin) container, away from the walls, and away from matter. The antiprotons are pulled off from the main accelerator loop, and in the center of the Penning trap, a bath of cold electrons slow them down (because they were traveling at v approx c, remember). Like a bowling ball being slowed down by a bath of ping-pong balls, the antiproton eventually loses enough energy and sits still in the middle of the trap.
Now, these antiprotons can be carried around in the trap just like anything else. They just have to be kept cold, and in the magnetic field. In fact, antiprotons were delivered from Switzerland to Stanford (their linear accelerator) this way.
The next big puzzle is to create anti*matter*. So far, it's been just antiprotons, which you recall, are charged. If they could combine antiprotons with antielectrons, to generate anti-hydrogen, this would be very exciting.
Certainly it takes a whole lot of energy to create antimatter, but the great benefit from the perspective of space travel, for example, is that you can get orders of more energy out of the same mass, and you don't have to waste fuel sending so much fuel mass up into space.
Hope this helps!
Of the amount of energy created by matter/animatter annialation, consider the amount of energy that goes into creating the antimatter in the first place. The size of the accellerators and all the energy it takes to operate, just to produce a single particle of antimatter.
What you get out of this, is the energy potential equivalent of accellerating a single particle to near the speed of light. Thats a LOT of energy and it can be stored within two particles. Its no wonder that we need a very small amount of it to accomplish great things.
However, its extremely costly and time consuming to create, and without drastically improving the effiency of the creation process, this is not going to change anytime in the near future.
Also, don't forget about the potential arms race here. Antimatter doesn't occur naturally in nature like nuclear elements (such as uranium) do (at least not in a form that can be collected easily). Right now nobody has the capability of creating enough antimatter to do any significant damage. But if we are able to create enough to be useful, a few grams of antimatter could be used to make a weapon that is significantly more powerful than a nuclear weapon. And although tactical nukes come in briefcases, imagine a bomb of equal power that fits inside a watch.
Another issue to consider is that antimatter needs to be stored. If a chemical fuel tank leaks, no big deal. If a nuclear fuel tank leaks, you might get radiation poisoning, but the effect will be limited. If a gram of antimatter gets loose. WATCH OUT.
Still, if we plan to travel great distances, its a necessary step.
-Restil
Play with my webcams and lights here
We could use it to deflect asteroids. All you need is a small spacecraft carrying a particle accelerator. The craft would fly into space, to within range of the asteroid, then fire up it's particle accelerator. The particle accelerator would create a beam of high speed high energy antimatter aimed at the surface of the asteroid. The resultant explosion would be equivilant to a very large thermonuclear explosion and would deflect the asteroid.
:-P
I would recommend the spacecraft be manned and have enough computer capabilities to be able to simulate the motion of the asteroid itself and determine the best location to hit. It should be able to orbit at any distance from the earth between LEO and the moon. It would also need an VASMIR drive to allow it to easily change it's orbit.
Shields against such a weapon would be simple. Just detect the charge of the beam being fired at you and produce a large electric field of the same charge. This system would be ideal for defending earth from asteroids and the borg.
"The energy you get from the anti-particle particle annihilation is about ten billion times that of chemical combustion," Schmidt said.
You definitely wouldn't like to see a terrorist organization get control of this stuff. With a kilo of anti-matter, you might take out NYC, never mind the WTC. Of course I'm sure the explosive applications (as this technology developed) would be thoroughly explored by the major military powers long before it could trickle down to that level. So before anti-matter could be used on a widespread basis, we will need to develop methods of ensuring that uncontrolled explosions can't occur by chance or by design.
Side note: one of the more offbeat theories about the Tunguska explosion was that it was a chunk of antimatter, not an asteroid.
Side note 2: It was in 1928 that British mathematician and physicist Paul Dirac suggested the existence of antimatter.
The job of a rocket is to create a stream of really fast particles moving in a particular direction. The faster, the better. Newton's Third Law and all that.
Those particles could be gas, accelerated with good old heat, ions accellerated with an electric field, or plasma.
Here's the rub: matter-antimatter reactions produce really energetic particles. Gamma rays, like. They kind a whiz right through the fuel you want to heat up. And the "combustion chamber." And the crew, and . . .
I read up on antimatter and fusion propulsion at grad school. (There's a suprising amount of good material out there; do not rely solely on the word of popularizers like Robert Forward!) The most-fully-realized antimatter rocket was kind of clunky. In the middle of the "combustion" chamber would be a cylinder of dense tungsten alloy full of tubules. A slow but steady stream of antiparticles are shot into the cylinder, which heats up. Hydrogen in pumped into the tubules; it heats up and "whoosh."
The disappointed bit: The specific impulse would "only" be about 5,000 seconds. This is about ten times what a liquid-fueled motor is capable of, and about 50% better than the little ion motor tested out on Deep Space One, but it's not amazing.
The most promising use for animatter: Using it as part of a fusion drive. A antimatter-catalyzed fusion drive described in the text I read was predicted to have a total impulse of something like 130,000 seconds. THAT is impressive. The thrust wouldn't be high, but you could keep it up for months and months.
What we might see are ships that use the direct-thermal sort of antimatter motor for getting a ship going (e.g., reaching escape velocity out of the Earth / moon system), then the fusion drive would be used to provide constant acceleration to speed up the trip.
Stefan
I really doubt this is is something we'll see any time soon. I mean, we don't have inertial dampeners. Or structural integrity fields. What about the ODN lines or EPS taps? Can NASA vent drive plasma yet? I don't want anything leaving the ground until we can reroute warp power through the main deflector, recalibrate the phase discriminator, and backflush the bussard collectors. Do we have deuterium purge vents, final stage magnatomic flux contrictors, impulse syncrotron units, impulse-deflection crystals, isolinear chips, Jeffries tubes, LCARS displays, matter/antimatter mix chambers, navigational deflector grids, power transfer conduits, RCS thrusters, tractor beam emitters, biomatter resequencers, duotronics, interphase generators, isomagnetic disintegrators, replicators, or SELF SEALING STEM BOLTS? My god, how could we get by without the SELF SEALING STEM BOLTS? Do we have doppler and heisenberg compensators or pattern enhancers and buffers? Do we have phaserbanks or photorps do defend ourselves? Do we have ablative armor or regenerative and metaphasic shielding? If we had shielding, could we rotate the frequency? Do we have PADDs, tricorders, hyperspanners, hyposprays and multispatial probes as tools? NO! We are NOT ready for this.
Error: PANTS NOT FOUND. Press <F1> to continue.
I'd rather only have to pack a kilogram of antimatter on my space ship than a moderately sized inland sea's worth of chemical fuel.
You could probably engineer something like a constant inflow of anti-matter to make for continous thrust. The only problem is the back flow on the fuel lines. this would be a lot easier than having a continous atomic fission explosion for thrust.
Strangely enough, this also works as a method fo moving asteroids around, since you could have atomic fuel lines running to a convenient crater. A trickle feed would create a continous nuclear reaction that would push the asteroid to a new course.
Alot of this stuff would need to be NOT engineered in low earth orbit, for obvious reasons.
"It is a greater offense to steal men's labor, than their clothes"
The problem that's not addressed in the article is that sure, antimatter is small, light, and excellent for storing energy with little mass, but what does that energy get you? Every spacecraft we've ever designed uses a reaction drive (and yes, solar sails are reaction drives too. They just use external sources as propellant.). The article doesn't address how we tackle the problem that for reaction drives to work we need to have something to throw behind us at high speed.
Not to say NASA isn't working on it. I'm sure they're looking at Bussard Ramjets or some other mechanism for using this tremendous energy to snare interstellar particles and throw them behind the ship. In fact, NASA has a few projects on the books for exploring exactly where the barriers between stellar and interstellar wind lay, and what the particle densities are really like. I guess this sort of detail is just too much for the average CNN reader.
The article, as is, doesn't provide any reason for being written now, other than a 'gee whiz the future's out there' fluff piece.
Hey, at least it's not about Afghanistan or weapons development.
Kevin Fox
I saw a presentation about this use of antimatter at Dragon Con in 2000. I wish I had a URL to go with it.
"Luncheon meats make the sawdust in your stomach explode."
... it gives a whole new meaning to the term "vaporware."
Robert L. Forward covers the topic of antimatter and some of its uses in his book Indistinguishable From Magic. You can find some information online about him and get some links to his ideas at his website.
Sapere aude!
Um, how the hell are they going to store all the antimatter (It needs to be standing still, not being slung around a particle accelerator), and how the hell do they make all the antimatter that will power these spacecraft?
.5 grams of antimatter met up w/ .5 grams of normal matter, then you'll end up with 8.99 x 10^13 J (lots and lots of power). However, this also kinda means that to get .5 grams of antimatter, you have to put in a slew of energy, because there has to be a conservation of energy. How NASA scientists will get around this will be interesting to see.
E=MC^2 : that's a very commonly known formula, and it means that even if a very tiny amount of matter was turned into energy, there would be a whole lot of that energy made. For example- if
Am I the only one thinking antimatter costs more energy to produce than you get out of it?
It's not about cost to produce. It's about how much usable energy you get per pound of fuel that you have to carry with you. It's worth it to spend the energy up front in order to make the trip through space feasable.
On the contrary, the gamma-rays (even when they are not energetic enough to cause fission) will merely be absorbed by the high-Z nuclei, knocking them loose to rattle around the spacecraft (kinetic energy), or alternatively raising them to an excited state, after which they will relax by emission of one or several gamma-rays in random directions (isotropic distribution). Since you will have absorbed the momentum of a gamma-ray that was going in the wrong direction, you will end up with a net loss.
If it were that easy to "reflect" gamma-rays, believe me, gamma-ray astronomers would have been doing it a long time ago...
-Renard
If you make anti-hydrogen you are able to store it in normal gas storage cyclinders. Same goes for any anti-atom. anti-matter only annihilate's when if touch's its couterpart. Simply(in theory) keep them apart. If true full scale production was to happen, it would logicly be done in space, on a asteroid or the moon. Not that logic means that it WILL happen there. Im looking for the discover mag article i read on this but it must be in storage. Crackers`n`Soup
I'm unaware of any principle of physics which says that mass must always be positive. Look at either Newton's or Einstein's laws of motion, for instance--in F=ma, you can plug in negative numbers for mass just as easily as positive numbers. You get answers which are self-consistent (if sometimes counterintuitive) and which maintain the beauty of the mathematical system. These are tantalizing hints--and that's all they are, hints--that negative mass is permitted by the universe.
:)
We have no idea how to make it, but we know what it would look like, how it would interact with positive mass, and how forces would act upon it.
Since I am the only geek I know to have failed high school maths, I ask this in all seriousness.
Given that the minimum distance between the Earth and Mars is 54.5 x 10^6 kilometres, are the acceleration pressures (G's) that humans would be subjected to in such a quick trip going to make us black out and/or die before we get there? Do we need to develop some kind of technology -- I hesitate to use the Trek term 'inertial dampeners' ;) -- before it can be of practical use, except for automated probes?
"If you create user accounts, by default, they will have an account type of Administrator with no password." KB Q293834
i really have no knowledge of all this, but the first thing that comes to mind after reading the only the main article is: what ever happened to the theory of matter never being created or destroyed??? the word annihilation hits me as destructive....
Going through the replies to this article, I noticed quite a disturbing trend: nearly all responses referencing Star Trek or its technologies have been modded 0 and off topic, and have been otherwise ignored (i.e. left without reply). Why?! This site is a self-admitted purveyor of "News for Nerds". And, one of the cornerstones of obsessive worship of various things, one of the most common of these being Star Trek. Are the readers of Slashdot too ashamed of their true natures, too terrified of fitting the nerd (arche/stereo)type to show even the slightest amusement or appreciation of those few who are either brave enough to break or ignorant of the almost taboo status of being a trekkie, and their attempts at humourous (whether successful or not) comments?! For shame, for shame.
The clue here is efficency. Here on earth energy exists in massive amounts compared to in space, the problem is bringing it up there.
Lets say anti-matter has a 1:10 efficency (with engines and all, just as an example). Say you want to send 1 ton of payload into space. This takes 100kg of fuel. But in order to make room for those 100kg, and fuel to put that up there, you need another 10kg. And to put those up there you need even more room and fuel, say 1kg and so on, a total of 1111,11... kg. Only 1/9th of the payload.
Now take a conventional rocket at 9:10 efficency, still 1 ton payload. But now you need 900kg fuel to get it up there. And to make room and bring fuel for those 900kg fuel you need another 810kg. To make room and bring fuel for those 810kg you need 729kg more and so on. In total, you need to send up a rocket weighing in at 10 tons, 90% of which is fuel, fuel tanks, engines and other costly but not value-adding components. All together it's 9 times the payload.
So a 9:1 improvement in efficency is a 81:1 improvement in size of the non-valueadding parts. Parts of it will be fuel, part fuel tanks, part engines, none of which are cheap and that all take a lot of energy to produce and use.
Kjella
Live today, because you never know what tomorrow brings
Does anyone have any ideas about how it will be designed?
As far as I know, when matter and anti-matter anhillate, it produces two gammas going in opposite directions. So this engine will have to have some type of water tank or other shielding in order for those gammas to ionize atoms and create heat, and then some type of engine to transfer that heat to the fuel to be exhausted. It seems to me that it isn't going to be as easy as tossing some antimatter into the engine and holding on for the ride.
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
Star Fleet entrance exams may say this is a "trick question," but you really don't want to use a 1:1 matter/antimatter mixture.
The core issue is that energy, per se, is irrelevant in spacecraft propulsion. What matters is momentum transfer.
Kinetic energy scales as mv^2/2. Momentum scales as mv. So the "ideal" system would make a lot of mass move slowly... but that would require you carry around a lot of mass so you can throw it overboard.
Matter/antimatter is on the other extreme. Lots of energy, very little momentum transfer. If it were a sports car, the driver would be spinning his wheels and burning rubber, but barely moving because the tires aren't gripping the road.
I vaguely recall ideal matter/antimatter ratios being something like 10:1 to 20:1. If you assume the amount of junk thrown out goes up by a factor of 16 or so, the velocity will drop by a factor of 4. However the momentum transfer will be bumped by a factor of 4. You have to carry more reaction mass, but if you're talking about a less than an ounce of antimatter, a 16:1 ratio means a whopping pound of reaction mass.
A more advanced version of this gives you variable thrust engines. If you're in a deep gravity well, you toss in more mass so you burn more consumables but have better momentum transfer where it's critical. When you're in deep space, you use less reaction mass for the same amount of fuel.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
It's funny you say that, because antimatter was predicted to exist solely on the force of negative energy solutions of the Dirac equation (the Dirac equaction is the relativistically correct "version" of the Schroedinger equation).
Essentially what you say is correct though, in that resolving the negative energy problem forced a change in the sign of the charge.
There is nothing magical about anti-electrons (say) they're identical to 'normal' electrons
Along with the charge sign change, there is also a change in a quantity known as "lepton number" (for a given system the lepton number is, surprisingly, the number of leptons;-). Basically, the lepton number of a system is invariant, so when you make an electron and a positron (both of which are leptons) the positive and negative lepton numbers cancel [1+(-1)], so there is no change in the lepton number of the system.
So it isn't really accurate to say that they are identical.
"We have an equivalent amount of energy in just one gram or about a raisin-size worth of antimatter,". Whenever I read an article about a new/improved form of power, the first question that lends itself to mind is always: "what devastating weapon could the government create from this?". Proportionally, if you consider the possibilities:
With current technology, we are able to wipe out massive amounts of land with, say, a hydrogen bomb. The weight of a hydrogen bomb is, however, massive. But, with our current fighter-bomber jets, this is no issue.
However, (provided antimatter could be used for weapons of mass destruction), a anti/matter-bomb of the _same weight_ would have a massively greater impact. To such a degree, that it would probably be unthinkable for us to use one of that size/weight. So, most likely, we would compress them into a smaller size, but of equal power. The reasoning for this? Consider: if one fighter-bomber can carry 2 hydrogen bombs being a total of 50 tons, then - similarly - you could carry a greater number of anti/matter-bombs (total of 50 tons), each being as powerful as one hydrogen bomb. The result? Blanket bombing just got a lot more devastating. I'm not looking forward to that day.
I think, therefore, I'm smarter than our president.
Funny coincidence, that.
Felt kind of nostalgic and was just watching Nadia again this afternoon.
mis
sorry to reply to an AC, but antimatter isn't really !matter. it takes the form of anti-protons and the like, ie protons with a negative charge (really big protons) that when they combine with a proton they cancel out, kind of like you and your computer, you cancel out, leaving the rest of us free to actually breed and better humankind.
"You have to have an extremely good vacuum, however"
no, that's what's surprizing about penning traps, you don't have to have a VERY strong vacuum, only that you will not have many exposed neucleons.
IIRC the thing that keeps the anti-protons and the protons in outside matter to anihilate are the orbiting electrons in the atoms. the vacuum is needed for the electromagnetic traps to keep the anti-protons from escaping.
BTW, why shouldn't you INJECT the trap with negatively charged ions (say Cl-)? these will balance your electrostatic charge. until you'll turn the matter to plasma (or inject it with protons) you will have practically no anihilations ?
Working for necessity's mother.
What is below is a post from about 5 years ago I made to the sci.space.tech newsgroup. After 5 years of development it is still relevent as we don't have free (or even cheap enough) consumer energy. Of course humanity might still make it, but I wouldn't bet on taking all of your "flesh and blood" with you.
:)
:-)
:-)
--article starts--
Many moons ago ('bout 200) Ares magazine had an article title "The 1
Billion dollar bottle of wine" or something similiar. Ares is/was(?) a
gaming magazine. The article aimed to show the ridiculous cost of
interplanetary space travel and why humans might have trouble leaving
the solar system, even if we want to. The article is lost in the shed
but from memory what follows is the rough jist of it. I read this
article before I did Uni physics so didn't question it's truth that
much.
Question is: How close to the mark is it?
Please, please this is not super-serious!!!
Please excuse any slight math rounding and total disregard for
relativistic effects , I have similiarly misplaced Einsteins
equations. If necessary we'll assume the ship gets up to 10% speed of
light and then coasts if need be.
Argument goes like such.
Energy to accelate ship is 0.5*m*((ato)^2 - (ati)^2)
m is mass, say 10 ton
a is acceleration, assume constant 1g
to,ti time
with to - ti = 1 second above simplifies down to
Power = 0.5 ma^2
= 500kW (to accelerate 10 tonne ship at 10m/s^2)
Now assume it uses 100% efficient matter/ antimatter drive
(ok,ok this is a mighty big assume)
Power costs roughly $0.12 per kW/hr in Oz
This will be the cost in electricity of generating anti-matter
(ignores rather severe capital investment and assumes 100% efficient
process, this is even bigger assume)
So cost for power is 3.3e-5 $/kWHr per second of
manufacture/consumption in drive
Seems cheap so far!
But at 500kW this turns out to be $15/second.
So if we accelerate for one year turn around for one year
decaccelerating, also at 1 gee.(someone else work out distance
travelled? aiming for 4.7 light year )
Total cost to make anti-matter we used is very roughly (at best!)
$15 * (60*60*24*365) * 2 = $1000 Million
Summary: I don't know how much useful "stuff" one could send to
nearest star but I wouldn't mind betting 10 tonne doesn't supply much
life support system! Which led to the reference of a bottle of wine
once drives and controls are taken into account.
The idea is not to produce kilograms of antimatter and use it directly. That is far beyond our present production capacity (picograms a year!), impossible to store, and very difficult to use. The idea is to use very, very tiny amounts of antimatter as a trigger device for fission, fusion, or both.
A large particle accelerator would be used to generate a few nanograms for storage on the spacecraft. (Note that this quantity is quite safe) The spacecraft would spit out tiny pellets of fissionable materials, possibly with a deuterium core, and "ignite" it using a small fraction of the stored antimatter. The result is a small explosion, and hence, thrust. The system is easily controlled, safe, and very efficient. Most importantly, it can be done using present technology, and with a modest budget.
" ..We don't know why, they just do ..."
wrong, see any elementary quantum field theory book, the reason is because charge is a result of your fields being complex, and your measured quantities being real (C-symmetry).
there are real-field (=> neutral) particles , they don't have anti-particles.
(actually C-symmetry may sometime be broken but thats another story.)
Working for necessity's mother.
I wonder what cnn reporters smoke.
Gentlemen, you can't fight in here, this is the War Room!
"... makes only one billionth of a gram a year at a cost of $80 million.
At that rate, it would take one million years and $80 quadrillion (80,000 trillion) to produce one gram."
Seems to me it would take a thousand times longer than 1 million years to produce 1 gram. And yet, they were able to get the price right. You would think that a "reputable" news source would do some sort proof reading.
Any mistakes in the above post are my own. I am not reputable.
Antihydrogen would be completely useless as fuel anyway. Unlike the hydrogen atom, antihydrogen is _very_ unstable. Your space trip would have to last for fractions of a second, before all fuel breaks up into positrons and antiprotons ;) (those particles could, of course, be used anyway, but what would the point be of the antihydrogen?).
Opinions stated are mine and do not reflect those of the Illuminati
Only NASA would try to invent something as incredible as a anti matter engine and still use it in the worst, inefficient way possible, as a rocket. The rocket concept is too simple, and must be abandoned if you really want to go fast, it just has too many limits on it to achieve what we want.
Haven't we learned enough by how horrible cars are? Why do we have to go copy them?
What about the theoretical exotic matter?
Antimatter is matter with a reversed charged.
When matter meets antimatter, both are annihilated and energy is released (a lot of it, based on E=mc^2).
Exotic matter, which isn't generally considered possible under Newtonian physics but which might be possible under quantumn physics, is matter that has a negative mass, and negative energy density. It has the opposite gravitational effect in relation to normal matter. A body of exotic matter would repel other bodies of both exotic and normal matter, AFAIK. Exotic matter, if it could really exist, would probably spread out equally across space, since it repels, rather than attracts other matter. If it came in contact with normal matter, it would annihilate it, but, unlike antimatter, it would release no energy whatsoever.
In general, the idea of exotic matter is very appealing, because it allows:
1.) The stabilisation of Einstein-Rosen gates, allowing an effective portal to another universe, should one exist. An Einstein-Rosen gate can be created by a spinning black hole, but is extremely unstable, to a point where even a boson would cause it's collapse.
2.) Construction of wormholes. (You need a great deal of exotic matter for this one, probably more than is practically attainable, even with very advanced technology)
One design suggests a wormhole that creates it's own exotic matter, eliminating the need for it's production.
3.) Construction of 'warp drives'. Alcuberre's warp drive (do a search on Google if you want to know what that is) violates certain conditions of quantumn physics and required an absurdly large quantity of energy. However, Chris van den Broeck, suggested an alteration of the design, whereby the 'warp bubble' would be extremely small (smaller than a proton) and the starship/object to be warped would be in another bubble which a larger internal volume than it's external volume. In principle possible, perhaps, but it's not known if the idea would work in reality, especially since the author of the paper has since published another paper listing problems with his proposal.
Still, the idea is kind of interesting.
Nobody knows if exotic matter is possible at all, let alone whether it's mass production is feasible.
Everyone knows you can't make a warp drive work until you have mastered the structural integerity field!
From the article and comments, I have deduced that AM is the same thing as matter, except with charges reversed.
Does that mean that there is an AM counterpart to hydrogen, oxygen, etc?
If so, what would happen if hydrogen AM mixed with helium matter?
H(am)+He= [E+H] or [E+He(fragments)]?
I realize that the above reaction is not possible with conventional chemistry.
1+1=10
NASA Marshall is funding the work of Prof. Gerry Smith, formerly of the PSU Physics Dept. (where I got my Ph.D. a while back) and who has gone to NASA MSFC
/. here.
This was posted previously on
You can seen the PSU antimatter propulsion page here.
He also has tried to sell folks on anti-matter assisted fusion energy at the NASA fusion propulsion workshop that was held in 2000.
I haven't the slightest idea how far any of this will get under the current NASA budget woes.
-- Mycr0ft
Me physicist. Me make rockets.
Don't you hate the fact that slashdot is usually second in the line of whatever the discussion is?
/ ms ad12nov97_1.htm
Well, now it's third.
Here's the original:
http://science.msfc.nasa.gov/newhome/headlines/
I know because I'm there.
"Yeah...it was the numbers that were irrational, not the murderous cult of vegetarians...." -- Hippasus of Metapontum
Antimatter is the most efficient energy storage possible. 'E = mc^2' tells us that annihalating it with an equal mass of matter produces 9*10e16 joules of energy for every kilogram of mass thus reacted.
That's the instantaneous production of 90,000 terajoules - on the order of the amount of energy expended by all the world's industry in a day. Impressive? Certainly.
However... to accelerate a mass to the near-light speed necessary to take advantage or relativity (very useful in an interstellar voyage if you want to get there in a reasonable fraction of a human lifetime), you need... E = mc^2!
That means that to get to near-light speed with a 100%-efficient antimatter engine, you need to have almost as much matter/antimatter fuel as the 'dry weight' of the vessel, including storage tanks. The dry weight of the Space Shuttle orbiter is about 80 tons... so to get a shuttle to those kinds of speeds would take 40 tons of antimatter and 40 tons of ordinary matter.
AND... you have to slow down again at the other end. So you have to take the 160 tons of your decel mass, and get THAT up to light speed with another 160 tons of fuel (again, half matter, half antimatter). So the launch breakdown on your itty bitty 80-ton eight-person spacecraft is: 80 tons spacecraft, 120 tons matter, 120 tons antimatter - 320 tons!
It's just like rockets and gravity. Most of your launch mass is wasted on fuel. And we can't beat these numbers with our current physics.
None of this would be a problem if we could make a LOT of antimatter... like a ton a day. But that has its own problems. Like, where to put it.
Let's assume that breakthroughs in nanotech and fusion physics allow us to build reactors that are one millimeter across and turn hydrogen into antiprotons at the rate of 1 particle per microsecond. To produce just 120 tons of antimatter per year, the factory would form a cube 200 meters on a side (Borg, Anybody?). I don't know what such a thing would be made of, but an equivalent volume of water would weigh 8 million tons.
The 4H2 -> He2 fusion reaction releases approximately 1/140th the mass-energy of the original hydrogen as a side-affect of the fusion reaction (go ahead, look up the relative masses of H and He on your periodic table and plug it into E = MC^2, you'll see what I mean). That means that a 100% efficient 'factory' would burn 140 times the mass of hydrogen to produce one unit of antimatter... or 16,800 tons of hydrogen per year.
So is it impossible?
No.
IF we had the fusion physics and the nanotech, we could put a self-assembling factory into orbit in the upper atmosphere of a gas giant. Feed it a large iron asteroid for raw materials, and allow it to grow slowly, adding a 1mm layer of fuel reactors at a time. The size of the thing would grow at cubic rates (since it grows in three dimensions) and even though the initial fuel output of the thing would be trivial, it would quickly grow to a size where it was producing tons of fuel a year.
And THEN we can start sending people to the stars on a regular basis. First a dozen, then hundreds, then thousands, at a rate that grows as fast as we can produce the fuel.
Like JFK said... We choose to do these things 'not because they are easy, but because they are hard.'
Actually no. Kinetic energy is an abstraction related to momentum. When matter and anti-matter collide they produce photons, gamma particles, according to the formula E=MC^2.
It's not that it's lost and nobody knows where to find it. Anti-matter is pretty uncommon, at least in our pocket of the Universe. Anti-matter in tiny quantities is always being produced by nuclear decay, but since it's surrounded by regular matter, it annihilates very quickly producing gamma rays.
I know it's CNN, but c'mon -- if you're doing a piece on antimatter, at least have a scientist look it over before you publish it.
As I write this, an electron gun is spewing streams of electrons directly at my face. Yet I don't feel the slightest urge to duck. Nor do I hear little clicking sounds as the electrons impact on my monitor screen. I don't expect any of the things that happen when matter is about, because electrons aren't matter. They're a constituent of matter.
The anti-electrons used in PET scans are the same, only more so. Nothing remarkable about having them around, but they're extremely transient entities. So accumulating them in large quantities is a lot harder than this article, in the gee-wiz style NASA PR bozos are so fond of, suggests.
That's a circular argument. "All particles have antiparticles with all charges opposite" is the essense of C-symmetry. Adding more twists and terms (and math) to a circular argument doesn't make it less circular. Actually, stating the more precise form of C-symmetry (which would claim that the particle is identical except for the opposite form) introduces an innaccuracy, since, as you say, C-symmetry is broken in some situations, and a larger symmetry is actually followed (antiparticles should behave identically in a mirror image universe with time going backwards, IIRC; what was it called... CPT-symmetry?).
Who was it who said, "Do not express yourself more clearly than you think."?
My point was that the existance of antiparticles is inseperable from a fundamental principle, which doesn't have a mechanism of simpler components to explain it.
I wonder if NASA has even began to consider how they will contain the reactions? Nuclear particles (electrons, protons, muons, positrons ect.) are a defined entity. An electron of an iron atom is no different that one from a water atom. This means that particles from the hull of the ship and the nickel that they plan to annihilate have equal probability of colliding with an antimatter particle. When one collision between an anti and true particle take place, the resulting energy could send trillions upon trillions more particles into similar collisions. The entire ship could be converted into pure energy.
I once shot a man who posted too many, "Imagine a beowulf cluster of these"
Yes but you use the antimatter beam to destroy their ship. The shields would be impractical to protect the entire earth, they only protect the ship.... :-P
This is an on-topic post.
First, you seem to have the misconception that NASA is entirely devoted to the manned exploration of space, and that moreover, they haven't done anything new since Apollo.
You are simply misinformed. You're just plain wrong.
Take a look at some of the projects that NASA has been up to recently, and then see if you can still claim they are "living in the past" :
Space Observatories
Chandra X-Ray Observatory
Hubble Space Telescope
Earth Observatories
Advanced Spaceborne Thermal Emission and Reflection Radiometer"
Solar System Missions
Mars Rovers
Astrophysics Research
Origins Program
And a sampling of the slate for future missions :
The Terrestrial Planet Finder
Deep Impact Comet Mission
Dawn Asteroid Flyby"
As you can see, NASA is not just about flying shuttle missions. They are actively sponsoring research in the space sciences and astrophysics across the board... from the study of our own planet, to the solar system, other stars and galaxies, and the cosmos as a whole. Their missions support the development of new technologies (which, unlike the previous poster seems to believe, are not limited to propulsion technologies, but include a wide array of telescopes and detectors across the entire spectrum). And NASA also actively supports scientists at all levels -- from graduate students through postdocs and faculty.
I think we live in a unique time where we as a species are really beginning to understand what makes up the universe, and how it works. I'm quite
confident that when the history of science of the 20th and 21st centuries is written, NASA will have played an enormously significant role in that process of discovery.
Bob
Science, like Nature, must also be tamed, with a view turned towards its preservation.
They voted down the extra asteroid sheilding at the front.
Table-ized A.I.
Antimoney
-----------------
Chance of joke already thot of: 68%
Change of being funny: 32%
Change of being modded down: 62.5%
Table-ized A.I.
one-hundred
Table-ized A.I.
It was also used in the drop tests. The very first flights were on top of the 747 to test basic aerodynamics, later tests used explosive bolts to separate from the 747 and simulate the final stages of reentry.
Remember - up until this time every spacecraft went "splat" when it landed. Americans landed in the water, Soviets landed in farm land... and according to the standards boards Yuri Gagarin was *not* the first man to pilot a spacecraft in orbit since he bailed before the capsule even got back to earth. (The standards require the pilot remain with the craft from stationary start on ground to stationary stop on ground.)
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
I haven't been following it closely, but apparently some early experimental work has shown some exotic particles with imaginary mass!
You find yourself in this rather unusual state of affairs because the mass isn't measured directly. What you can measure works out to m^2 and it's always been a positive number. Until recently, when the number works out as a negative number. Hence negative numbers.
This would mean that gravity is repulsive between two objects of the same imaginary mass. But what's the attraction/repulsion between normal mass and imaginary mass?
Newton's laws get even weirder. Negative mass is annoying - if I push on it, it doesn't push back. It actually pulls me towards it. Push on imaginary mass and you get... what? Maybe it only responds to imaginary accelerations... and that answers the questions about gravitational attraction as well.
This is probably some subtle experimental error, even if the results have been verified at several sites. More data will show positive m^2. Or a subtle error in the design of the instrumentation.
Yet....
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
If you liberate H2 from H2O, you spend more energy than you get back by burning H2 and O to make water. If you convert a Proton, for example into an Anti Proton, and then introduce it to another Proton, then since you are Converting the 2 Protons from matter to energy, the energy out is not just the energy that was used to convert the Proton to an Anti Proton. Does converting a Proton to an Anti Proton take more energy than you get when you anilhate a Proton with an Anti Proton ? If so Anti matter is a good very dense storage medium for energy. If not matter (converted to antimatter) becomes a source of energy. Think about the possibility of turning matter into energy. Energy Crisis ? What energy crisis. Also as the earth looses mass, we start to orbit further and further out from the sun, so the greenhouse effect of the 20th C. is mitigated ;-)
NASA has also revealed that it is researching ways to use magic as the next generation spacecraft propulsion. One scientist was quoted as saying: "With magic we could, for example, twitch our noses and *wish* the spacecraft to be at it's destination" "However," he cautioned, "magic is not known to exist. Nor may it ever". NASA has reportedly employed a young new scientist by the name of Harry Potter to aid in its newest research project.
It's 10 PM. Do you know if you're un-American?
first, please lets not make this personal or impolite (regarding the "Umm... Dude.." title).
regarding cyclicity:
"All particles have antiparticles with all charges opposite is the essense of C-symmetry"
only if you accept QFT axioms; among them symmetry (C, P, T , whatever your lagrangian holds), locality and lorentz invariance (which , IIRC implies CPT )
the existance of anti-particles IN SOME FORM does not have to be inseperable from the above principles , i.e. there may be (I doubt anyone proved otherwize) other models (with no regard to experimental evidence) with some kinds of anti-particles without the theoretical base of QFT and above axioms.
this is what I mean by an explanation of some phenomenon:
there exists a model which is more "basic", i.e. applicable to and implies a wider class of phenomena then the "explained" observation, within which the phenomenon fits.
e.g. "all apples fall to the ground" is explained by Newton's model of gravity. It is not inseperable from newton's model or a different way of expressing it (hence this is not a cyclical argument).
correct me if I'm wrong
Working for necessity's mother.
Just this weekend I've finished reading The Engeneer' series of books by James Doohan - aka Scottie of Star Trek (co-auther S.M. Sterling).
They use antihydrogen as the fuel for their star ships. In fact they are fighting a war over control of the antihydrigen fields and the fuel run their entire society.
zenray
from the article:
The world's largest maker of antimatter...
I never thought I'd read this sentence in my lifetime!
https://www.accountkiller.com/removal-requested
That's what you'd need to do a teraton blast in TNT (by definition). We've got bombs in the megatons - what, maybe 5 megatons?
200,000 of those together would generate a teraton blast.
Unless we find an "antimatter mine", antimatter is a storage medium, NOT an energy source.
I don't have the numbers, but i'm guessing we'd have to build an elliptical Dyson sphere, polished on the inside, orbiting so as to hold the sun at one focus, collecting the energy at the other one.
For this purpose, though, if we can get the conversion efficiency up to where the weight advantage beats the conversion loss, we might have something. We'd still have to take along some reaction mass, though.
My apologies; I thought you were arguing that negative energy cannot exist, which is what I was taking exception with. :)
... because although its observable behaviour would be opposite, the effects on spacetime curvature would be exactly the same as positive mass
:)
:) Keep in mind that it's a first approximation meant to illustrate the point, nothing more.
So therefore it is always some positive value somewhere in the system right?
Not necessarily. The system is allowed to be at a zero-energy state. A lot of people believe that, from whatever point within the cosmos that you observe the cosmos, the net energy of the cosmos is zero. I'm not certain I buy this, but not because the idea is bad--just because I haven't seen evidence to directly suggest this.
My arguement is that "negative" energy, as you put it, would have the same effect within the universe as positive "energy"
You seem to be conflating mass and energy here. An equivalency exists between the two, but they're not strictly speaking identical to each other. A photon, for instance, has no mass--but due to its energy level, it can be treated as if it possessed mass. Discussing this more would quickly get extremely arcane, but a good astrophysics text should explain it much better than I can.
First, in many instances you're right. Whenever you see an energy-squared term, the cosmos doesn't care whether the sign is negative or positive--the squaring means the result is always positive.
But that doesn't mean in all instances you're right. As a very quick and primitive example, look at E = mc**2. Let's say you're watching a spacecraft zoom by at relativistic speeds. Its energy content is equal to its mass times the square of c.
Now let's say you slow down that spacecraft somehow. You reduce its kinetic energy content by applying an acceleration opposite to its direction. You're diminishing the energy--or, not to be too mathematical about it, applying negative energy to the system. You apply so much energy that you bring the spacecraft to a crashing halt. Before, it had E energy, and now you've applied -E energy.
Well, how do you get -E energy? -m times c**2, of course. So as you apply negative energy, you also confer a negative mass... so as the spacecraft slows down, its relativistic mass vanishes (negative mass applied) and it returns to its conventional rest mass.
Professional physicists will undoubtedly want to crucify me for this example.
Short version: negative energy levels are known to exist. Negative masses are necessary in order to make some of the equasions work out properly, but we don't know whether (a) negative masses can exist on their own, or (b) whether it's just an illusion created by the mathematics we use to describe the system.
As an illustration of (b), imagine a square-shaped yard that's a hundred square meters. How long is each side? Well, ten meters, of course. But the square root also means negative ten meters would give us the same answer. In this instance, the negative result is discarded as an illusion of the mathematics. The same basic principle might apply to negative mass--necessary to make equasions work, but doesn't really exist.
I suspect the answer is (b), but I'm not willing to make any wagers on it. The cosmos can be a really weird place.
poo poo hello