Antimatter production, storage, control, annihilation applications in propulsion
sciencedirect.com
sciencedirect.com
Surprisingly, antimatter can be stored for months. They built a 2.5 ton storage box, ultra high vacuum and magnetic trap and a loading mechanism. In a first trial they loaded 70 protons and drove around the campus on a truck.
Impressive that this is even possible. But with 2.56 * 10^-15 Wh/kg still orders of magnitude from current batteries.
The article says 1000 kilograms, that is 1 ton.
Sounds like someone (LLM) then treated lbs like KG to turn that into tonnes again?
Dumb. Easy to do if not paying attention.
In theory, could you use mc^2 energy to create a mass m of antimatter, combine it with m matter (which is rather more readily available), get 2mc^2 energy back out, and repeat, effectively consuming matter to make energy?
(I’m sure there are other things that would also hinder the 2x outlook you are asking about)
This is more a theoretical question of whether any law of physics makes this impossible (e.g. you can't create unpaired particles), or whether this is theoretically possible but it's difficult to get enough efficiency to make it net positive.
(We currently haven't even gotten fusion to be reliably net positive; practicality is as always a set of concerns all its own.)
It's theoretically impossible, with the slight problem that there seems to be more matter than antimatter in the universe today and nobody really knows why.
Either the theory is wrong (and it being a conservation rule, then by Noether's theorem there's an equivalent symmetry* you'd have to violate if the conservation doesn't hold), or the initial value that's getting conserved wasn't ever zero.
* the wikipedia page says this is specific to continuous symmetry; but integers aren't continuous, so has this been generalised, or is it just assumed?
Baryon and lepton number are almost conserved, which would require you to produce (or consume) equal numbers of particles and antiparticles, unless you can figure out a way to make nonconservation happen outside of a black hole or whatever.
(Feeding matter to a black hole and using the Hawking radiation as an energy source would probably do what you describe, but there are practical difficulties)
There’s just the wee problem of getting or making a black hole and then grabbing it and controlling its spin.
Charge alone doesn't seem like it'd be a fundamental limitation here, considering that (for instance) antineutrons exist.
> Baryon and lepton number are almost conserved
Is the "almost" here something other than the Hawking radiation "one half falls in a black hole and the other half doesn't"?
There are others such as isospin, lepton number…
These types of conservation laws are what limits the possible particle interactions.
Therefore there is no path to generate antineutrons in which you do not have pairs of electrically charged particles with opposite charges that are generated or annihilated.
The annihilation and pair generation reactions are electromagnetic interactions between electrically charged particles and antiparticles with opposite electric charges, which are otherwise identical, in order to satisfy all conservation laws.
Only the neutrinos do not have electric charge and about them it has not been proved beyond reasonable doubt that the antineutrinos are different from the neutrinos (in other ways except opposite spin). Neutrinos do not participate in annihilation and pair generation reactions.
Neutrinos may appear and disappear in similar reactions that are mediated by weak interactions (i.e. by the heavy bosons), like the inter-conversions between protons and neutrons (actually between u and d quarks), but in these weak-force based reactions the energy that is produced is much less than in annihilation reactions and frequently much of it is lost by being carried away by neutrinos. It is possible to make electric generators with beta-radioactive isotopes, where this kind of reactions happen, but the only advantage of those is the extremely long lifetime, because otherwise the power density and energy density are low.
So when talking about using antimatter for energy storage purposes, that refers exclusively to generating electrically-charged particle-antiparticle pairs, separating and storing the antiparticles, then annihilating the antiparticles with their corresponding particles, resulting in extremely intense gamma radiation, which carries the reaction energy.
When the annihilation is done inside matter, which includes annihilation between nucleons (where there may be multiple annihilation events between the component quarks) the gamma photons interact with the surrounding matter or sub-nucleon components, producing a cascade of various accelerated particles, including many new particle-antiparticle pairs, which will cause later other annihilations. So from a single initial annihilation a great number of accelerated particles and gamma photons may result, but the first stage is always the generation of a pair of gamma photons.
Does this mean neutrons are (or can be) polarized like a water molecule (but much weaker)?
https://en.m.wikipedia.org/wiki/Neutron_electric_dipole_mome...
Which interactions exactly are possible depends on the particles & forces involved, and further conservation laws for quantum numbers (e.g. charge) that the force obeys.
TL;DR Turning a single massless particle into a single massive one is not possible, you always need at least two.
(What conservation law would it violate?)
I think other than this, there are no known ways to even create more antimatter than matter in a process. But it is believed that more processes must exist, in order to explain the predominance of matter over antimatter in our universe.
[1] https://ars.els-cdn.com/content/image/1-s2.0-S26662027240045...
[2] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
https://www.centauri-dreams.org/2012/07/20/medusa-nuclear-pu...
[1] https://en.wikipedia.org/wiki/Nuclear_lightbulb
[2] https://en.wikipedia.org/wiki/Direct_Fusion_Drive
[3] https://en.wikipedia.org/wiki/Fission-fragment_rocket
[4] https://en.wikipedia.org/wiki/Pulsed_nuclear_thermal_rocket
A fun collection of articles!
So where do you get that energy in the first place? Everything leads back to solar power. In this case, since we're talking about far-future tech, we return to what I consider the most likely path for humanity: the Dyson Swarm. This is the sort of thing you can do with a truly mind-bogglingly large energy budget.
And this matters because the energy budget, regardless of the energy source, for interstellar travel, is so ridiculously large.
Zipping around the galaxy at 0.95c, stopping at destinations and then zipping off again will require carrying a lot of antimatter with you.
EDIT: Thanks to Wolfram Alpha I was able to see that it the kinetic energy of 1 kg at 0.87c is very close to the mass energy of 1kg of matter.
Now I have read that it may be possible to use a powerful magnetic field to assist with slowing down by braking against the interstellar medium, which helps.
The Avatar films have (in spite of very derivative plots) fairly realistic (at least physics wise) interstellar ships. They accelerate using beamed laser propulsion from the Sun and use antimatter rockets to decelerate, then repeat this in reverse to come home. One assumes they somehow recharge at their destination but this is not shown. Too bad all that cool tech is in service to humans who decided to be the bad guys from War of the Worlds.
Still traveling that close to c brings up tons of other problems. Collision with a micrometeorite would be like an atomic explosion, and blue shifting of incident and cosmic background radiation would blast you in the head with x-rays and gamma rays. Those problems would demand more mass for active or passive shielding, and you’re already mass constrained.
All things considered it’s way more practical to go slower — which could still be insanely fast e.g. 0.25c — and figure out how to cryosleep or become an AI that can just turn yourself off for the trip. Cryosleep for humans is a brutally hard biomedical problem but way easier than trying to approach the speed of light. There are other multicellular animals that can do it, albeit much simpler ones, so it’s probably possible.
0.25c allowing for acceleration and deceleration gets you to Centauri in around 25 years and to further star systems with promising exoplanets in hundreds of years.
Then there’s generation ships, but that’s the kind of thing Mormons would do. :)
I'd imagine it would take them 10,000 years or so to make it to the next star system but they might not care if they can live a comfortable lifestyle in the great dark.
The first problem is a big challenge as they're cold, dark, and small. Just finding them to begin with is a giant problem. Accurately charting them is another order of magnitude increase in difficulty. Even tiny error bars in the measure of their proper motion means your spaceship can miss them by millions of miles. Even missing them by a dozen miles is the difference between life and death.
Even with a huge catalog of extremely accurate interstellar fuel-capable objects they don't do you any good if they're not on the way to where you want to go. A meandering route to a destination in order to visit refueling stops adds tons of extra complexity and points of failure.
Heck, you have to get better than 5 nines to even compress a year into a day, .9999963c, which would take a freakish amount of energy to accelerate a KG to (3.3 × 10^19 J).
What medical ethics board is going to approve a research project "put healthy experimental subject in coma for 5 years, observe what they are like when they wake up?"
Reminds me of https://en.wikipedia.org/wiki/Deep_sleep_therapy and https://en.wikipedia.org/wiki/Chelmsford_Royal_Commission
I think this is an example of a technology which, if it is ever developed, is most likely to be developed by some kind of totalitarian regime which has no ethical qualms about human experimentation.
Inducing torpor would have major medical uses in surgical and emergency medicine, it's not just useful for passing the time.
We do know how to inefficiently create and store antimatter, we don’t have any idea how to cause human hibernation.
To me getting two dozen of orders of magnitude better at something is clearly hard, but that still beats trying to do something we don’t have a clue how to start. For human hibernation step 1 is probably serious genetic engineering and there’s going to be other steps.
World ending doesn't begin to describe what that looks like.
Do the same thing over a year in many different devices and you’re basically dealing with a normal nuclear power plant’s output.
Hell, we can't even store hydrogen without leakage issues and with anti-hydrogen any leakage is very bad.
They've put pigs into suspended animation for an hour or two, I'm not sure what the upper bound is on that or how much further it's possible to go with it. Ditto organ deep-cooling. So while it's not feasible now, it feels like we need "only" 100x or so improvement to make it viable.
In the interstellar medium, matter is primarily in molecular form and reaches number densities of 10^12 molecules (mostly composed of) hydrogen, then helium, oxygen, nitrogen) per cubic meter (1 trillion molecules per cubic meter).[1]
So, what, about a picogram per cubic meter.
If your ship has a cross-sectional area of one square meter, and Alpha Centauri is 40,000,000,000,000 meters away [2] (and you thought it was a long way to the shop if you want a Chiko Roll), you’ll have to manage with 2.62^23 tonnes of mostly hydrogen in the way.
The interstellar medium is also about 1% dust, so about 2.6^21 tonnes of solid matter.
Someone check my mass maths.
1. https://en.m.wikipedia.org/wiki/Interstellar_medium
2. Google Search AI Overview
Dust is a concern but again the typical dust particle size would be about the power of a gun shot of a small caliber rifle. A problem to deal with but a rarer event still. Of course another challenge would be larger dust particles which while improbable are still possible which largely rules out humans in these craft. But that goes without saying since the acceleration to get to that speed would be unlikely something humans could withstand anyway.
Even interstellar/stellar wind would have enough molecules of gas to cause some crazy erosion/damage.
Impact seems to have a timelined meaning, starting with destruction, then following up with conquering, and exploration coming somewhere before constructive applications at the far end.
As apes we just can't keep holding back till we can build houses or something with it, when we also could just throw that stone at something. Especially before someone else does :)
[1] https://www.reddit.com/r/dataisbeautiful/comments/s4tbry/oc_...
EDIT: here's a small discussion: https://physics.stackexchange.com/a/196171 There's a whole PBS SpaceTime episode about this, but I can't find it, rn.
- Burma Shave
It's why some kind of generation ship, that is basically a colony, is really the only conceivable method of traveling between stars.
Also remember that whatever energy is produced by antimatter, you need more than that to produce the antimatter to begin with. Where are you getting that energy? I believe it's from solar power from a Dyson Swarm.
In addition to the ark-ship colony, or the cryosleep slow ship:
1. Assuming it's a stream of robotic probes doing flybys, without decelerating, we have the Breakthrough Starshot approach. Maybe there's a way to use the target system's sun for solar sail braking? Send smart enough robots that have agency, that can do the exploring for us.
2. For human travel - it could just be a bunch of frozen embryos with a robotic nursemaid, accelerated via external propulsion and decelerated via nukes / high-g aerobraking... (Raised by Wolves had a cool introduction like this in the first episode - then went quickly downhill)
3. ...
As for cryosleep, this curently seems unlikely but not impossible. For one thing, the decay of radioactive elements in your body (primarily Carbon-14) would give you about a lethal dose of radiation after about a century. Some organisms have natural antifreeze and other means of surviving low temperatures. We do not. Freezing water tears our cells to shreds.
Cryobabies and artifical wombs are another vector. This is nontrivial too but also, woould you trust the automation? Some AI might have to raise humans hundreds or thousands of years in the future without any context of what's happened in that time. We might be able to communicate with such a ship and update it but should it trust such updates?
You're also creating a whole bunch of people who haven't consented to never see Earth. Generation ships have this problem too to some degree. That has questionable ethics.
As for using the target star to decelerate, that's entirely possible. It's just a solar sail. And that might be the only way we could do interstellar travel anyway because of the reaction mass problem. But solar sails can only accelerate so fast. Travel too fast and you might not have time to decelerate as well. So you're still looking at hundreds of years most likely.
It really seems like we need radical life extension while maintaining quality of life to make these time frames reasonable (relatively). That actually does seem doable.
For stop and go; we'd be looking at something that could deploy a dyson swarm, generate and contain its own antimatter and then go again right?
I should play universal paperclips again.
Yes, it's called the relativistic rocket equation.
https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/...
So you would need at least (and with the efficiency loss of production, much more than) 1.5 Little Boy atomic bombs worth of energy to make a single gram of antimatter.
Only a tiny amount reaches the Earth, and we use only a tiny amount of that. But if we could capture even a small percentage of the total energy of the Sun we could produce antimatter by the ton.
Is there something I'm missing here? Proxima Centauri is 4+ light-years from us and firmly out of the solar system.
How about this one though:
At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years.
https://en.wikipedia.org/wiki/Space_travel_under_constant_ac...
However, a key part of relativity is that the laws of physics are the same in every reference frame. If you're on a ship with sufficient fuel, you can keep accelerating forever and cover vast distances. You'll never reach a point where the universe prevents you from accelerating. If it were otherwise, then relativity wouldn't be true - because there would be special rules that apply to people traveling at a certain speed. That's the whole point of relativity is there can't be such laws because there isn't a preferred reference frame in the universe!
However, the more you accelerate away from the earth the longer time will have passed on earth if you turn around and come back.
Here's a calculator you can play with: https://spacetravel.simhub.online
As an example, if you could accelerate at 9.8 m/s (same as gravity - so you could walk around the 'back' of the ship as if in earth gravity), then you could travel 50 light years in 7.7 'ship years'. However, if you turned around and went back to earth 102 years would have passed there, even though you would only be ~15 years older.
Not with antimatter rockets, it's not. Even though antimatter is extremely energy dense, the rocket equation still applies. You need reaction mass.
If you use laser beams as your rocket exhaust, then you get maximal efficiency (exhaust velocity is C), but very low thrust. That's not going to get you anywhere in days or weeks.
If you use stored matter (hydrogen, say) as your rocket exhaust, then you'd get better thrust, but all sorts of other issues come into play. Radiating all that waste heat. Running out of reaction mass. Again, there's not a practical design that could get you anywhere near a nearby star in "days or weeks", even if you assume "perfect" materials, efficiency, etc.
> If you're on a ship with sufficient fuel, you can keep accelerating forever
Um, no.
That's pretty mind boggling and quite different from "you can never reach the speed of light therefore you could never travel across the Milky Way in a human lifetime".
If you could carry sufficient fuel to accelerate at 9.8 m/s for 12 years you could travel across the Milky Way galaxy (112000 light years). You would be 12 years older but 112000 light years away from where you started. That's amazing to me.
It's a given that this is impractical.
For static objects, I'm not sure how you'd get past the constraint that at some point you want mass somewhere else, and it needs to be moved.
I wouldnt want to work at the IAA right now.
Countries on a budget do not have the resources to create a CERN-like accelerator. In a relative sense, building a nuke with enriched uranium is the "cheap" option compared to amassing enough antimatter for even a kiloton yield.
> Thanks russia, thanks china, thanks usa - one world locked in a eternal Mexican standoff it is
We've been in this spot since the 60s. Nukes got the ball rolling and ICBMs hammered in the idea that you cannot escape nukes if your enemy doesn't want you to.
> Future generations are going to look at the collapse of Assads regime as the last "downfalls" without nail-biting.
Perhaps if they all live under rocks. The past 10 years of the Syrian revolution were absolutely a nailbiter, with Assad torturing, systematically executing and mass-burying his own citizens and political opposition. There were stockpiles of chemical weapons, underground concentration camps and Putin could launch an missile attack or airstrike with a phone call and enough money offered.
Syria's citizens only knew they were safe when Assad ran out of money. They suffered under Russia's oppression for 10 long years and thousands of people died horrific and unjust deaths. If anything, the fact that Assad was allowed to keep Syria this long is a condemnation of western diplomacy as a whole.
There's some possible ideas for how to do it out there, but obviously we kind of lack enough antimatter to go experimenting.
Antimatter is the opposite of matter, with the same mass but opposite electric charge. It's considered the rarest, most expensive, and potentially most dangerous substance on Earth. One gram of antimatter costs around $62.5 trillion
Sounds like we won’t be using antimatter for anything practical for a long time.
With fission nuclear propulsion you run out of reaction mass long before you're out of energy. It's a few times better than chemical fuels, but not 10x better.
Those electromagnets would need power too, so I guess a battery or RNG (nuclear) solution could be used.
What concerns me most is the radiation risk of travelling close to light speed. Surely we'd pass by some ionising radiation, or weakly-interacting neutrinos.
I suppose the only way to be sure is to build a prototype and try it.
Not in our planet's back yard. Maybe behind the moon.
It's much worse than that. At those speeds, the cosmic background radiation would get blue-shifted to the point that you'd be constantly bathed in x-rays and gamma rays.
The main use of antimatter is to heat reaction mass. The advantage over nuclear rocket is that the "temperature" of antimatter is really high so the specific impulse can also be high. One advantage is that can change the amount of reaction mass to get more thrust or better efficiency.
I remember reading a Robert L Forward book where he described all this in great detail.
EDIT: I think the book was "Indistinguishable from Magic" which was interesting science-wise but not compelling as a science fiction book.
He also seems to have written about antimatter directly: "Mirror Matter: Pioneering Antimatter Physics"
And imattwr is at the end of a tech tree that we have not started
The energetic efficiency of producing antimatter in order to store energy in it is well approximated by zero.
Storing antimatter requires a huge volume and mass per the energy stored and it also requires a continuous power consumption, so long term storage would degrade the energetic efficiency even more.
There are methods of producing energy that nobody knows how they could be done, like nuclear fusion without producing neutrons (aneutronic fusion), but which nonetheless have a chance to be realized that is much, much greater than discovering a method of producing antimatter with high efficiency and also solving the problems of long term storage and of harnessing the energy produced by annihilation as intense destructive radiation.
For now, the only realistic research target for improving space propulsion in the next few decades is the use of nuclear fission reactors, which could allow travel inside the Solar System with much more acceptable durations.
> A general conclusion was drawn that antimatter technology and its development for propulsion is still in its theoretical stages.
Sometimes we think of these as philosophical questions, but in many ways they are questions for science that we don't know how to tackle.