I came up with this idea for a space-based weapon and I'm wondering how viable it actually is. The weapon is made possible using portals.

The Portals

The portals are a clarketech produced by a portal generator. This generator consumes relatively little energy, and has a limited range (in order to prevent teleporting a bomb into your enemy's ship being the dominant form of warfare). The portals themselves are 2-dimensional circles that, in pairs, connect two points in space. The portals will have two primary functions to facilitate antimatter particle accelerators.

Small Linear Accelerators

Placing one portal in front of a linear accelerator and one behind it will allow particles to repeatedly pass through the accelerator, constantly gaining speed and effectively giving that accelerator infinite length. When the particles reach the desired speed, the portals can be (very precisely) disabled, allowing the particles to shoot out the front of the accelerator. This allows incredibly short linear accelerators to produce particles moving at similar speeds to those found in much larger circular accelerators.

Antimatter Production

By placing a pair of non-orientable wormholes right outside the exit of the accelerator, the accelerated particles will have their chirality reversed, reversing their charge and turning them into the antimatter versions of whatever particles they are. As this is a clarketech, this process somehow does not draw much additional power from the portal generator (this could probably be used to create a perpetuum mobile, but such is sci-fi). I imagine the issue of some of the particles annihilating right outside the accelerator could be mitigated with strong electric fields clearing the entrance.

The Question

With that provided information, how effective would these antimatter weapons be in space warfare? If the answer is "not effective at all", how could they be improved to increase their viability?

In this question I am assuming space warfare to mean 'large manned spaceships shooting at one another from great distances'.

Please note that while such a weapon may not be completely realistically practical, this is sci-fi, and as such I am looking for answers that are constructive rather than destructive.

  • 2
    $\begingroup$ Have you considered that a target ship could deploy a linked pair of portals just outside its own hull, one on the side facing an enemy ship and one on the other side? Any particles, antimatter or otherwise, that are shot at it will simply enter the portal facing towards the enemy and skip to the portal on the other side, not affecting the target ship in between at all. Which makes this an almost perfect defensive system, rather than an augmentation to an offensive system. $\endgroup$ Jul 7, 2023 at 2:32
  • 1
    $\begingroup$ One thing to consider: To accelerate particles, they must be charged. Charged particles are easily deflected by magnetic fields. $\endgroup$ Jul 7, 2023 at 10:47
  • 2
    $\begingroup$ IIRC an object starts packing its own intrinsic mass-energy in kinetic energy when moving at 87-88% c. At 99.9999% c (gamma of like 700), whether it's antimatter or not matters very little. $\endgroup$
    – BMF
    Jul 7, 2023 at 12:45
  • $\begingroup$ @BMF, past ~0.95c the amount of Energy added by antimatter vs the kinetic energy alone becomes irrelevant. Of course, it kind of depends on if you are just talking about an antimatter charge or the entire projectile. But just fyi $\endgroup$
    – ErikHall
    Jul 7, 2023 at 14:29
  • 1
    $\begingroup$ @KlausÆ.Mogensen the problem with deflecting charged beams is Bremsstrahlung radiation. Especially the very relativistic ones. You just end up dumping the beam energy into your spacecraft armor in a different form: x-rays. $\endgroup$
    – BMF
    Jul 7, 2023 at 14:38

2 Answers 2


Its like i was born to answer this one

Render of a Interstellar Spaceship of mine, which uses a linear accelerator for thrust (And interstellar refueling)

On the Portals

This is a nitpick but a circle is 1 dimensional, what you mean is a disk.

On the Linear Accelerators

The portal stuff is a bit useless. Like, you dont need a long accelerator to get up to speed. A 1 meter long Wakefield accelerator can induce $10 GeV$ into a particle. Which translates to $0.99631042638c$. Following this equation;

$$v_p = c*\sqrt{1-\left(\frac{1}{\frac{E_P}{m_P*c^2}+1}\right)^2}$$

Where $E_P$ is the Energy in Joule and $m_P$ is the mass of the particle.

If you spice it up a bit to $100 GeV$ the "muzzle" velocity is already $0.999956747967c$. And that is a 10 meter long tube. What big accelerators like the LHC are after is hardly speed. You can make a 100 meter long accelerator that rivals the speed of the LHC. But you know what your 100 meter tube cant match ? The number of particles. Because that is where the issue is. One particle moving at close to the speed of light is fairly useless. You need a lot of them to do much of anything. To accelerate a lot of particles, you need big boy magnets. So even with your portals, a weapon capable accelerator will not be small. It cant be, otherwise you cannot physically accelerate the sheer number of particles fast enough to make anything funny happen.

On the Question

You know, pretty useless. If you are shooting a weapon that fires at almost the speed of light, that little bit of additional energy from Antimatter annihilation really doesn't matter anymore.

To illustrate the point, lets consider the ship from above. That Thruster induces $400 GeV$ per particle. And fires ~$6.5x10^{23}$ particles per second. Which translates to about $0.001 \frac{kg}{s}$. Moving at $0.999997258692c$ or about $299791636.177 \frac{m}{s}$. The Kinetic energy of this exhaust, cannot be estimated with $\frac{1}{2}mv^2$ anymore. Instead we need;

$$E_k = m_0*c^2\left(\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}-1\right)$$

Which works out to $4.2x10^{16} Joule$ Which is about $10 Mt$ of TNT equivalent. And this is why children we are assuming the magical total system efficiency of 99.9999% xD

But, just how much more energy would we get if we converted this Beam into Antimatter ? Well, that is just $E = mc^2$ assuming 100% conversion bla bla bla. Which works out to $0.02 Mt$ of additional energy ON TOP of our $10 Mt$ beam.

As you can see, thats just not worth it. You are significantly better off just making the gun a bit longer and push the energy to say $500 GeV$. That gives you way more bang for your bug.

The Real Weapon

The render above is deceptive. It makes the exhaust look like a tiny baby girl flame. Where as in reality this exhaust would be several light seconds long before you couldn't see it anymore. The colors and apparent shortness is just relativistic effects.

Obviously, standing in such a beam reduces your life expectancy rapidly. Its a bit like the Titan, one moment you exist the next you dont. But this is not the main danger from such a Drive / Weapon. Its the radiation. Particle accelerators like the LHC, my drive or your Portal Gun produce radiation at the end of the day. And this radiation does not stop being angry until it hits something. So unlike normal rocket exhaust, these kinds of weapons are deadly potentially across a solar system depending on the exact numbers.

Its a bit hard to illustrate just how much radiation the weapon you propose would generate. But this radiation is your actual weapon. You can very realistically irradiate an entire planet in a few minutes with anything that powerful. And if you get close enough you can just cause the Atmosphere to undergo thermonuclear fusion. (Hyperbolic).

This is also why this scene from Avatar 2 is so god damn dumb. If you enter an Atmosphere with an Antimatter rocket Engine, the Atmosphere would explode. I did the math a while ago but each of the ISV´s thrusters would produce the equivalent of 100 Mt per second.

enter image description here

More In Depth

So, why do i think you can ditch most of the idea and just use a particle accelerator on its own like the Thruster in the render ?

First, the exhaust would literally be a few Billion degrees hot. So hot that normal matter just cannot exist within it. Which makes it really handy because it is quiet literally impossible to stop. Even a Magnetic field will struggle if the beam hits it perpendicularly.

Second, unlike a normal weapon this remains deadly for a long time. Even if you are light seconds away, the particles are still moving. They are just so far away that the beam has diffused and not really has a temperature anymore. Its just a bunch of really angry particles. Essentially Cosmic rays. These will not only irradiate anything they touch but also physically degrade the matter. In Fusion reactors, something known as Neutron-Induced Transmutation happens. Where Neutrons enter the atoms of the containment chamber and change the atom. Usually this does not happen with charged particles to the same extend. But if the Charged particles move this fast they overcome nuclear binding / repulsion forces and can Transmutate matter. Which weakens materials very quickly and makes them screamingly radioactive.

Your core idea is not bad, and really imo all you need to do is ditch the Antimatter part. With a pure particle accelerator virtually all of the Particles and as such the Radiation moves away from you. So you yourself do not get turned into a mutant. But the moment you interduce Antimatter some of that will Annihilate before it hits the target. Annihilation produces Gamma / X-Rays omnidirectional. So you get hit as well. The dosage might be low but it is just another point against Antimatter for this application.

Powerful enough particle accelerators are perfectly fine long distance weapons on their own.

  • $\begingroup$ Does this: "You know, pretty useless." not contradict this: "But you know what your 100 meter tube cant match ? The number of particles. Because that is where the issue is."? Surely portals would allow you to have a much smaller accelerator fire a relativistic beam with many more particles than without said portals? And regarding the fact that turning the beam into antimatter doesn't actually make it all that much more energetic, would the beam being made of antimatter not significantly affect how it would interact with a target? $\endgroup$
    – M S
    Jul 7, 2023 at 13:51
  • $\begingroup$ Actually, considering the non-orientable wormhole is pretty much a free energy generator, would it not just make more sense then to shoot out a very large number of particles at relatively low speeds (e.g 80% SOL)? That seems like it would be more energy and space efficient than using a much larger and more powerful accelerator without the wormholes. $\endgroup$
    – M S
    Jul 7, 2023 at 13:53
  • $\begingroup$ Not really. My argument was that doing the Antimatter part is useless. The portals themselves are fine. But it just wont be as small as you want, you still need space for the magnets. Otherwise there aint no accelerator. As for particle density. The 100 tube cant match it because you cant induce that much energy in there. You either have to make the beam waist larger or the tube longer. Generally you want a longer tube because of the inverse square law. In my case a 1 meter waist @800 meters works for 0.001 kg/s. $\endgroup$
    – ErikHall
    Jul 7, 2023 at 13:55
  • $\begingroup$ @MS as for the interaction with matter, not really. The Antimatter will just annihilate and release energy according to E = mc². And that just is not a lot of energy compared to the beam. And it only makes the accelerator more complicated. $\endgroup$
    – ErikHall
    Jul 7, 2023 at 13:56
  • $\begingroup$ @MS as for the low velocity thing. Nah, thats not worth it. You want to exploit the fact the Kinetic energy rises exponentially. 400 GeV is not a lot of energy for this kind of stuff. 800 isnt either. But a 800 GeV Beam is gonna do a lot more damage than a idk 0.001 GeV one. $\endgroup$
    – ErikHall
    Jul 7, 2023 at 13:57

Frame challenge: Less Clarketech required

Let's look at what this is weapon is doing, as stated. First, it is accelerating a particle up to super-high speeds without being the size of the Large Hadron Collider (LHC). Then it is converting said particle into antimatter at the instant that it leaves the muzzle and hurtles towards the enemy ship.

If the particle is accelerated to extraordinary speed (eg 0.999999 c, comparable to the LHC) then it gains immense kinetic energy due to special relativity increasing its mass, with this energy dissipated into the enemy ship it is shot into. If it is turned into antimatter then, when it interacts with an equivalent particle of normal matter, it will convert itself into a burst of gamma rays. The problem with doing both is that, all things being equal, damage output is much less than doing just one of them.

Let's look at the speed first. An old cathode ray tube, as found in pre-LCD TVs and monitors, shoots its electrons out at 0.1 c. It is not especially hard to get something that will shoot a particle out at 0.98 c without any need for extremely lengthy hardware or repeating-loop portals, and it will consume many, many orders of magnitude less power than accelerating a particle up to LHC speeds. (Feel free to work out the maths if anyone feels like it - I'm going to be really conservative and figure it will require about a million times less energy to reach 0.98 c vs 0.999999 c, but I suspect it's more like billions.) In terms of targeting a distant enemy ship, 0.98 c is practically as good as 0.99 c or 0.999999 c. The huge advantage is that by accepting an infinitesimally lower "muzzle velocity", your rate of fire for a given power input will be at least a million times greater. Which means that you get a million times more particles hitting the enemy ship.

Without the second piece of Clarketech, this would not be especially useful - a million times more low energy particles will do less damage than a single super-high-energy one. However, these are not normal particles, due to the second piece of Clarketech these are antimatter particles. (Yes, this second piece of technology, unless it has truly obscene power requirements, is a source of effectively infinite energy.) Bombard anything with a million particles of antimatter and it will have a very bad day, much worse than it would have with one super-high-energy antimatter particle.

In summary - pick your favourite piece of Clarketech and ditch the other one, so your weapon is either relying on kinetic energy or matter/antimatter annihilation but not both. You may wish to consider that the portal generator, as written, is a near-perfect defensive shield, as I mentioned in the comments on the question. (If you do not want it to be a defensive shield then you need to make the maximum portal diameter very small and specify a handwavium reason why non-linked portals must have some minimum separation that prevents an array of them being used as a shield.) On the other hand, the matter-to-antimatter gizmo blatantly violates conservation of energy.

  • $\begingroup$ Could having the particles accelerate at a very minor angle relative to the portals not give you the best of both worlds? That way the particles pass through the accelerator X number of times before passing by the side of the exit portal. That would let you fire a constant stream of high-velocity antimatter, without the reduction in fire rate. $\endgroup$
    – M S
    Jul 7, 2023 at 11:22
  • $\begingroup$ And yeah I don't really like the idea of portals being OP shields. I'd probably say then that the energy costs scale drastically as portal surface area increases, meaning you could only cover a small amount of your ship in defensive portals, with precise placement and movement being used to reflect the most damaging incoming projectiles. $\endgroup$
    – M S
    Jul 7, 2023 at 11:24
  • 1
    $\begingroup$ @MS You said you wanted energy costs to scale drastically with size. If they scale any more drastically than the square of the radius, you're better off with multiple small ones. If they scale less than quadratically, you should go for one large portal instead. There is mathematically no way you can tweak the scaling to make it harder to defend a ship with these portals than your "regular" quadratic scaling. $\endgroup$
    – biziclop
    Jul 7, 2023 at 13:45
  • 1
    $\begingroup$ @MS Until someone invents the idea of using two generators. There is no mathematically sensible way to enforce this via energy cost tweaking. Even worse, the target could use a pair of portals to redirect the beam back to its source. $\endgroup$
    – biziclop
    Jul 7, 2023 at 21:52
  • 1
    $\begingroup$ @MS So hang on, this generator that, and I'm quoting you here, "consumes relatively little energy", is somehow simultaneously also very expensive? And nobody in the whole universe has gone "hang on, energy is just energy, why don't we use a steam turbine?" My disbelief would be very far from suspended if I read this in a story. $\endgroup$
    – biziclop
    Jul 8, 2023 at 9:35

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .