I have a stupid question, and I have an intuitive feeling that the answer to this question is yes. In making antimatter, is the amount of energy required to produce it equal to the amount of energy that is released when it comes in contact with matter?
No. Matter and antimatter particles can form spontaneously from a gamma ray photon, for instance, but they annihilate very quickly, yielding the gamma ray again. It’s possible to use powerful electromagnets to pull them apart, but that takes lots of energy. And if you sat around with some humongous magnets waiting for vacuum fluctuations and gamma rays to yield the antimatter you need, you’d be waiting for a very long time, and using up gobs of energy in the process.
The standard method is to fire charged particles that have been accelerated to nearly light speed at a heavy metal target. The energy from the collision produces lots of stuff, including the particles that you want. If you want antiprotons, you shoot a beam of protons at said metal target, and you get a tiny number of both protons and antiprotons being produced, which are collected using magnets, to put it in a massively oversimplified way.
Considering that you need to use the worlds biggest particle accelerators to get micrograms/per year of the stuff, it’s a massively inefficient process in termes of yield. Fermilab, presently the best anti-proton factory we’ve got has an efficiency of about one part in ten million. That means to get one watt of antiproton power, you’ve got to put ten million watts in.
I read a one sentence statement once that said, “There’s some evidence that anti-matter is simply ordinary matter that is traveling backwards in time.” No other details offered in the piece, so I’ve no idea if it’s legit info or not, nor if it offers any clues towards easier methods of production or utilization.
I see. 
I guess that pretty much precludes making a large amount of the stuff anytime in the near future. Well, is there any way (theoretically, of course) to produce a large amount of antimatter? And could you point me to a website that can explain antimatter in simple terms that even a person who gets a headache from high school algebra can digest?
I think it’s safe to say we should be able to improve our antimatter output in the (reasonably) near future by a couple orders of magnitude, maybe a little more. That’s still a pathetically inefficient way to generate a fuel, and puts antimatter propulsion of any kind well out of the realm of practicality. It’s just too expensive. So unless we come up with a source of energy that vastly improves on the cost part of the equation (in terms of extractability, environmental impact, and total supply, among I’m sure a number of other variables), antimatter is probably a no-go.
But if we do come up with such an wonderful new energy source (say practical fusion power generation), then even if your antimatter yield is crap, it doesn’t matter. You just keep running the factory until you get the amount you want. It may take a long time to get the mass of antimatter you need, but I figure if you’re planning to build a ship that will take centuries, if not millenia, to get to its destination, sitting around for a few years waiting for the antimatter to build up might not be a big deal.
All of this assumes we can store and manipulate the antimatter safely. If large amounts of antiprotons, which are a good potential fuel, get loose, the result is the explosive production of huge amounts of gamma ray energy, as well as a cascade of both matter and antimatter decay products (starting with particles called pions) that will yield something very much like a thermonuclear fireball. Being anywhere near a couple of pounds of spilled antiprotons would really, really mess up your day. I’m sure this will be a daunting engineering problem, but I’d be willing to bet we’ll develop all the needed technology to work with antimatter with an acceptable level of safety.
I’m in the same boat. 
How about this?
My understanding of this is rudimentary at best, but what I gather is that particles can be thought of as going backwards in time to become their own antiparticles for very brief periods; but this looks exactly the same as a particle and an antiparticle bursting into existence, arcing inexorably toward one another from the point of creation in space, and annihilating at a very short interval, in terms of both space and time, away and in the future, respectively. I’m not sure if it’s really meaningful to think of, say, a “real” antiproton in a storage ring as being a proton going backwards in time. It has the basic properties of such a beast, so I suppose it doesn’t matter to a certain extent; but its also going to observe the second law of thermodynamics in precisely the same way as a normal particle, so is it really moving forward in time?
Better minds must answer…(and correct my inevitable mistakes…)
What’s rigorously true is that the maths of quantum field theories are such that any antiparticle going forward in time is mathematically equivalent to a particle that’s going backwards in time. This is therefore a very handy way for theorists to describe antiparticles: you can think of them as particles, but at the expense of having to worry about stuff going backwards. In many cases, being able to do so can help simplify calculations and explanations.
On the other hand, as in Loopydude’s example, you probably wouldn’t think of a bunch of antiprotons going round the LHC as being protons going backwards in time. You certainly could, but in practice that’d just be, well, inconvenient.
Whether you then think antiparticles are actually going backwards in time - rather than this just being a useful way of thinking about them in some circumstances - is largely a philosophical issue.
You know, I’m thinking that the Moon would make a real safe place to set up this kind of operation. That way if it went BOOM we wouldn’t have to worry about too many people being killed.
Don’t be silly—that would be far too expensive and impractical. :smack: Just put your antimatter factory in a nearby handy-dandy third world country like Guatemala. If it blows, all you have to do is deny all responsibility, and convince everybody that they had it coming to them anyway.
Yes, but if we put it in Guatemala, then how are we going to get Moon Base Alpha started on their way? I mean, we’re already five years behind schedule of getting them sent off in the first place, and we can’t have aliens showing up who’ve followed the historical documents we’ve been beaming into space, with the Moon still up there in the sky, now can we? They’d think we were all frauds! We’d be the disgrace of the galaxy! Is that really what you want? Aliens stopping by and turning up their noses at us, simply because we refused to blow the Moon out of orbit like we said we did? I know I don’t want to spend the rest of my life hanging my head in shame.
Seems reasonable that if anybody is going to be working with large masses of antimatter, it’s a safe bet they won’t be doing it anwhere near large numbers of people. The moon might be a good place, as there’s a fair amount of fusionable (helium 3) material that can be gotten there.
I imagine once they hollow out a small planetoid or whatever to build the colony vessel, and install the antimatter containment and delivery facilities, it will be a fact of life for anyone on board that if something goes wrong, everybody is going to die in a really spectacularly big way. Given that they’re all going on a one-way trip, and will likely die of old age en route, all the while knowing their descendants of whatever degree could find the destination insurmountably hostile, which would lead to the torturous extinction of the entire colony, loss of proper antimatter containment might rank pretty low on the list of worries.
Well, it’s not a given that they’d just point the thing and launch it at a star in hopes that it’d have an inhabitable planet. NASA’s got plans on the drawing board to build telescopes which could detect Earth-type worlds using current technology for the most part, so the lucky folks that got launched into space could be assured that they’d have a decent shot at finding an inhabitable planet at their destination. Of course, the problem then becomes that there might already be intelligent life on that planet when they get there…
For their sake, they had better be as technologically advanced as we are. Because if they’re not, and they have anything that we deem to be of value to us, they will rue the day they met H. sapiens.
Incidentally, once you have managed to get your matter-antimatter source into space and you actually start the reaction, all you have is a lot of energy. As I said originally, energy does not of itself make spaceships move: such a reaction in space would simply be a very very bright light.
You would still have to convert that energy into some kind of propulsion. I don’t know about the energy to momentum transfer characteristics of ion drives, but the orion craft sprays a huge graphite plate with small polystyrene discs which expand under the heating effect of the nuke/antimatter thingy, and it is this which actually causes the ship to accelerate.
I liked this link. However, something bothers me. On the 12,5 LY radius map, a little more than 20 stars appear. In the 250 LY radius map, 20 times the diameter, only something like 40 stars (plus the 20 previous ones, I assume) are displayed. There should be vastly more than that.
So, is the 250 LY map incomplete, or is there an exceptionnally high density of stars in our immediate neighborhood? I assume the former, but if it’s the later, then why are we situated in a cluster of stars?
Has the concept of solar sails, which used to be quite trendy, been ruled out for some reason? It wouldn’t require fuel, except for manoeuvers.
I would suspect it’s earth like in composition/size, as opposed to Jupiter/ Neptune like, not earth like as in “inhabitable”. So, the only thing they would be assured to find could be as hospitable as, say, Venus.
Yes, only well known/bright stars appear. As it says under the map:
One final, serious problem we haven’t covered here yet is “Once you’ve reached your Earth-like planet, travelling at 0.1c or whatever, how the heck do you slow down?” An orion craft would need another million nukes to do so. This, I suspect, is where solar sails and the like on tiny craft come in handy.
The thread seems to have moved on to anti-matter, but if you wish to know about ion propulsion, you need to check into the resounding success of the Jet propulsion Laboratory’s Deep Space 1, one of NASA’s least famous but most significant recent missions. It was launched to test a bunch of newer technologies, including the first ion engine on a space probe, and an automatic stellar navigation system (you tell it where to go, and it figures out how to get there by the arrangement of the stars).
Here’s their FAQ on the subject, written before the results were back in.* The ion engine performed at least as well as anticipated, and the next generation of the technology may be used on the future Jupiter Icy Moons Orbiter.
*BTW, This is the only other reference I can find to the “Deep Space 4” project mentioned in the FAQ. I can only assume the mission was renamed or scrapped. It’s name does not appear in the missions that make up the New Millennium Project technology testing program, but then again, it would not be testing the technology, but applying it.
We will know soon if solar sails live up to their hype.