Thread: Matter-antimatter annihilation

Hello everyone

I have a question regarding antimatter

If you had a propulsion system based on annihilation of matter and antimatter, with pions and gamma rays coming out of the exhaust (and later pions turning into radiation too) , how would this event visually look like in space? Would there be any light emmited on the exhaust?

It depends on exactly how the engine works. Most “realistic” antimatter engine designs use a small amount of antimatter to super-heat a large amount of water (or some other liquid), which is then shot out the back of the ship. Depending on exactly what sort of fuel you were using and how hot you got it, that might look pretty impressive. If you have a more exotic scheme where you’re ejecting the pions etc. directly into space, I don’t think you would be able to see it.

This whole matter anti-matter annihilation engine stuff sounds like the warp engines in Star Trek. I'm pretty sure they were based on that idea. Cool stuff.

Originally Posted by Scifor Refugee

It depends on exactly how the engine works. Most “realistic” antimatter engine designs use a small amount of antimatter to super-heat a large amount of water (or some other liquid), which is then shot out the back of the ship. Depending on exactly what sort of fuel you were using and how hot you got it, that might look pretty impressive. If you have a more exotic scheme where you’re ejecting the pions etc. directly into space, I don’t think you would be able to see it.

So the reaction itself is invisible? I mean if you could take a peek into the reactor and observe the annihilation, you would only see darkness?
(unless the reaction heated some nearby object which start to glow)

Originally Posted by Kosta

This whole matter anti-matter annihilation engine stuff sounds like the warp engines in Star Trek. I'm pretty sure they were based on that idea. Cool stuff.

Actually the most realistic ideas of antimatter propulsions, are simple Newtonian rockets , using force to push the ship, warp engines are a much more far out concept, much less realistic

Anti-matter/matter ahhnialation is the energy which far surpasses any. Newtonian rockets are not the way forward. Trillions of gigawatts of energy are wasted when a rocket takes off, and even more would be wasted if there were a matter/anti-matter reaction, in terms of ideas, not many have come up with one since Newton, and those who have have pretty pathetic ideas, no offense. Warp Drive would be feasible if you understand the theory. Like and great scientist will tell you, it only becomes a reality if you beleive it is. You'll see quotes from Newton through to Darwin on this idea. Modern scientists lack that passion, that umph to do so, afraid to put their neck on the lines for the greater good. As more and more fall to greed of money/repuation etc, the more science suffers. It is time for real heroes of science to return with new fresh ideas and that is why I salute the youth of today-bold cocky and arrogant, but with intelligence capabilities far surpassing ours. We need people who have not accepted-oh thats the way it is to give us new technologies and wonders-after all the audastity of youth is the only thing that keeps the age old question going-what if?

Well don't get me wrong, I didn't mean to say warp drives are impossible, I'm not really qualified to say either way, I'm just saying, before that happens we are probably going to see force-rockets driven by antimatter, as a step between. Perhaps not beam core rockets, but maybe something including a separate propellant as someone mentioned here already.
But even more likely, fission and later fusion powered Newtonian ships, before any warp drives.

Matter-antimater reactions don't emit visible light, rather gamma rays. Then if gamma rays strike matter, this may produce visible light as lower energy reactions occur and emit smaller quantums, visible light included.

One of the reasons of the impracticality of matter-antimatter reactions as energy source is that as they produce basicly gamma rays, obtaining energy form them is quite difficult as gamma rays just ricochet through matter and you need really a lot of matter to stop them and get some usable energy, namely heat. It's a bit like pushing a bicycle by shooting at it with a machinegun, bullets would likely ricochet through it leaving only minimal thrust behind...

(The other big problem, one which ST never accounted for, is that antimatter doens't exists in our universe and so you must create it by a ideal proportion of m(antimatter)=(e/c^2)/2. Now, if you have such amount of energy at your disposal, why waste it manufacturing anti-matter? And where does such enormous energy come from in the first place?)

Originally Posted by Trilex

Hello everyone

I have a question regarding antimatter

If you had a propulsion system based on annihilation of matter and antimatter, with pions and gamma rays coming out of the exhaust (and later pions turning into radiation too) , how would this event visually look like in space? Would there be any light emmited on the exhaust?

Have you met my sister yet?

My point is, get to your point........

I have have obviously been told that already.

Well antimatter is the best possible way of storing energy for later usage.
In order to reach certain relativistic speeds, you need to convert a large part of your ships mass into pure energy, and the only way to do that is to use antimatter.
The problem is, you can never reach near light speed, unless the MOST of your rocket mass is antimatter+matter fuel, and considering how much a current penning trap weighs, I seriously doubt we will have a penning trap that is going to weigh considerably less than its content.

You'd need tons of antimatter+matter, contained in maybe kilograms of machinery holding it, which is I think impossible.
That's the real problem of antimatter propulsion that I can see.

Not to mention that we probably won't be making tons of antimatter within this century.

But you can't reach relativistic speeds with any other kind of power, like fusion or fission, simply because it doesn't convert most of ships mass into energy.

I played around in Matlab with this, and came up with a solution that
in order to reach v speed, expressed as a fraction of c (between 0 and 1),
you need to have square of v fraction (also between 0 and 1) of your ships mass convert into energy (be antimatter fuel in other words) , that is if you had a perfect way of converting all the energy you get into motion, which is another almost impossible obstacle.
Of course from this, it is obvious that the only way to reach speed of light is to have all of your ships mass turn into kinetic energy, so as your
desired speed reaches speed of light, so does your mass fraction of ship mass reach square root of v/c

Originally Posted by streamSystems

Originally Posted by Trilex

Hello everyone

I have a question regarding antimatter

If you had a propulsion system based on annihilation of matter and antimatter, with pions and gamma rays coming out of the exhaust (and later pions turning into radiation too) , how would this event visually look like in space? Would there be any light emmited on the exhaust?

Have you met my sister yet?

My point is, get to your point........

I have have obviously been told that already.

I'm not sure I understand you there

Originally Posted by Trilex

Originally Posted by streamSystems

Originally Posted by Trilex

Hello everyone

I have a question regarding antimatter

If you had a propulsion system based on annihilation of matter and antimatter, with pions and gamma rays coming out of the exhaust (and later pions turning into radiation too) , how would this event visually look like in space? Would there be any light emmited on the exhaust?

Have you met my sister yet?

My point is, get to your point........

I have have obviously been told that already.

I'm not sure I understand you there

Ok, sorry, who is going to fund our next 'big idea"?

Matter_antimatter.
We should ask ourselves.....who's the godfather.

You mean godfather of the marriage of matter and antimatter?
God-Father, perhaps?
lol, this is out of topic

Yes.

I mean anyting that makes a conversation.....


Ok: what type of conversation can emit some type of mathetical juice?\\

hmm...still not following you

Hmmmm....likewise

Originally Posted by Trilex

The problem is, you can never reach near light speed, unless the MOST of your rocket mass is antimatter+matter fuel, and considering how much a current penning trap weighs, I seriously doubt we will have a penning trap that is going to weigh considerably less than its content.

Even worse, for any real space mission you will presumably want to stop when you reach your destination...so you actually need enough fuel to go through all that acceleration twice. Once to speed up on the way there, and again to slow down when you arrive.

That so makes sense.

Thank you.

Originally Posted by Holytide

Warp Drive would be feasible if you understand the theory.

Do you actually have any reason for believing this to be true, other than that you want it to be true? I mean, warp drive might or might not be possible. It's not necessarily automatically possible just because you want it to be. It’s not like the laws of physics give a damn about what we want to be true.

i guess you'd have to start decellerating half-way. otherwise you would be subjected to insane g-forces. I read somewhere that about 4 g's is the most we could handle confortably for an extended period of time, so no matter what propulsion system we have, for the moment, it would still take a very long time to get anywhere. To make it viable, there would have to be major leaps in hibernation technology or cryogenics. (Wish the inertia dampers on Star Trek were a possibility)

Maybe I should say someting you'se can follow?

Originally Posted by Scifor Refugee

Originally Posted by Trilex

The problem is, you can never reach near light speed, unless the MOST of your rocket mass is antimatter+matter fuel, and considering how much a current penning trap weighs, I seriously doubt we will have a penning trap that is going to weigh considerably less than its content.

Even worse, for any real space mission you will presumably want to stop when you reach your destination...so you actually need enough fuel to go through all that acceleration twice. Once to speed up on the way there, and again to slow down when you arrive.

Yea, lol, I didn't even consider that

That makes reaching light speed and decelerating to initial speed using own energy of any body, impossible even in theory.

Originally Posted by KALSTER

i guess you'd have to start decellerating half-way. otherwise you would be subjected to insane g-forces. I read somewhere that about 4 g's is the most we could handle confortably for an extended period of time, so no matter what propulsion system we have, for the moment, it would still take a very long time to get anywhere. To make it viable, there would have to be major leaps in hibernation technology or cryogenics. (Wish the inertia dampers on Star Trek were a possibility)

Well, you could have a constant acceleration of 1g (by increasing thrust as your speed increases, to compensate for growing mass as it reaches relativistic speeds) and "walk" on walls, as if on earth.

Any question on something like antimatter requires the "you might win a lottery"....

Don't you reckon?


Aren't I that lucky?

Well if cost is what you have been trying to steer attention to all along, then the answer is, this is all a hypo situation, in some distant future, where
making antimatter would be so cheap that it would reach near 0.5 efficiency

Well, you could have a constant acceleration of 1g (by increasing thrust as your speed increases, to compensate for growing mass as it reaches relativistic speeds) and "walk" on walls, as if on earth.

Thats what i mean. But I heard we should be able to tolerate 4g acceleration while still awake and walking around. the space ship would be like a skyscraper lying on its side. then you could change the orientation to face the other way once the halfway mark is reached for deceleration.

Still.

I need to explain some type of thing, right?

U will tell me what that is, right?

Well, there are a couple of ways to go about it. It takes about a year at 1 G acceleration to reach light speed. If you get close enough to light speed, time will slow down for you enough that the trip will hardly seem to take any time at all. So you might only spend a few days coasting along at near C going from one star to another (while tens or hundreds of years pass for the rest of the universe), then flip back around and spend another year decelerating.

Or, if you’re in a hurry, you can submerge yourself in a tank of fluid that has almost the same density as the human body – then you should be able to handle 10-20 Gs of acceleration, and the speeding up/slowing down will only take a few weeks (which you will have to spend in the tank). Of course you’ll want to be drugged unconscious while you’re in the tank, but that wouldn’t require any exotic hibernation technology.

Originally Posted by Scifor Refugee

Well, there are a couple of ways to go about it. It takes about a year at 1 G acceleration to reach light speed. If you get close enough to light speed, time will slow down for you enough that the trip will hardly seem to take any time at all. So you might only spend a few days coasting along at near C going from one star to another (while tens or hundreds of years pass for the rest of the universe), then flip back around and spend another year decelerating.

Or, if you’re in a hurry, you can submerge yourself in a tank of fluid that has almost the same density as the human body – then you should be able to handle 10-20 Gs of acceleration, and the speeding up/slowing down will only take a few weeks (which you will have to spend in the tank). Of course you’ll want to be drugged unconscious while you’re in the tank, but that wouldn’t require any exotic hibernation technology.

that's true, but time dilation is not a linear function. It takes to get REALLY close to light speed in order to start having serious benefits from it.
If you could shorten your trip 10 times that would be great, but you could never reach that kind of speed in order to shorten it so much , and still have
enough energy to stop the ship.

Originally Posted by KALSTER

Well, you could have a constant acceleration of 1g (by increasing thrust as your speed increases, to compensate for growing mass as it reaches relativistic speeds) and "walk" on walls, as if on earth.

Thats what i mean. But I heard we should be able to tolerate 4g acceleration while still awake and walking around. the space ship would be like a skyscraper lying on its side. then you could change the orientation to face the other way once the halfway mark is reached for deceleration.

Well you can tolerate as much as 9g , but the question is for how long.
We are talking about months here, any kind of increased gravity would have negative effects on the body, even if it's under 2g.
The heart would have a lot of stress trying to pump blood to the head at 2g, simply because it evolved and grew under 1g

Originally Posted by streamSystems

Still.

I need to explain some type of thing, right?

U will tell me what that is, right?

Ok, now this is getting real close to Yoda meets Oracle

Originally Posted by Trilex

that's true, but time dilation is not a linear function. It takes to get REALLY close to light speed in order to start having serious benefits from it. If you could shorten your trip 10 times that would be great, but you could never reach that kind of speed in order to shorten it so much , and still have enough energy to stop the ship.

It's just a matter of making a larger and larger fraction of your ship be fuel. If you have a "perfect" antimatter rocket that completely converts all your matter/antimatter fuel into kinetic energy, you would need your rocket to be about 90% fuel and 10% ship/cargo by mass if you wanted to accelerate close to C and then slow back down.

If you did have 90% of your mass as fuel, you could go
to nearly 0.95 of speed of light, using a one way ticket only

If you wanted to slow down, you couldn't go anywhere near that speed.

That's the problem.

At 0.95 speed of light, time would be about 10.5 times shorter, which is a good time saving, but not that much if you want to really "travel the galaxy".
It would be possible to reach a certain speed at which you could get to another galaxy in a matter of days, from the perspective of a ship (being millions of years outside), but you would have to have 0.9999999999 or more of your mass to be fuel, and you could never stop the ship.


I'm going to see if I can come up with a "point of no return" speed for
a given fuel mass/ ship mass ratio

Originally Posted by Trilex

If you did have 90% of your mass as fuel, you could go
to nearly 0.95 of speed of light, using a one way ticket only

Or you could get up to about 90% and slow back down, without much time dilation. Or, if you want to 10x time savings, go with 99% fuel by mass.

It seems my hunch was wrong, I just put it all down on paper, and it seems that slowing down is not as restrictive as I assumed.

Here is what I came up with:

2* v^2 - v^4 = mf

where v is the desired fraction of light speed (0 to 1)

and mf is the fraction of mass taken by fuel


It actually makes sense if you think about it for a second

in extreme case, which is an unattainable limit , where desired speed is speed of light (v=1), you don't need ANY energy to slow down because
you wouldn't have any mass at all. Which is all insane, because neither can you reach c, nor can you be without mass, nor can you slow down without energy, but that's the limit.
Everything larger than 1, gives negative fuel fractions, which is outside of the realistic domain.

So if you wanted to reach 0.95 speed of light AND slow down to your initial speed (which is a zero if your reference frame didn't change)
you would need a little more than 0.9904 of your ships mass to be
fuel, which is actually pretty good, because considering how much energy you spent accelerating, you are decelerating almost for free.
If you compare it with the same speed with a one way ticket only, it would
take 0.9025 mass of the ship to be fuel.

That's not a very big difference, about 0.9 for one way, and 0.99 for both acceleration and deceleration, that's pretty good.

At first I assumed that decelerating would be a huge problem, but the trick is to (with the above equation) plan your trip so that no matter how much you accelerate the loss of mass of ship and loss of mass of fuel are such that in the end you end up with the same fuel/ship mass ration as the ration of the fuel you spend vs. mass you had, meaning you have the same energy potential as when you started the trip, meaning you can decelerate to the starting speed

Here is how the function looks like:



x axis is desired fraction of light speed to reach


y axis is required fraction of ship mass to be fuel in order to reach the speed AND decelerate


as you can see there is no "point of no return" speed, as I assumed

Did you remember to take relativistic mass increase into account? Remember, it actually takes almost as much energy to get from 90% C to 95% C as it does to get from zero to 90% C.

Originally Posted by Scifor Refugee

Did you remember to take relativistic mass increase into account? Remember, it actually takes almost as much energy to get from 90% C to 95% C as it does to get from zero to 90% C.

of course, that's where I actually started from

I didn't post the whole math here, but the formula I started from was relativistic kinetic energy, which takes into account mass increasing into infinity

I took into account both relativistic growth of mass , and gradual decrease in "static" mass as fuel is being consumed.

The reason why this graph is near-linear is because relativistic increase in mass most of the time is compensated by decrease in mass , as fuel is being converted into energy.
So when mass grows 10 times, it just turns out that the rest mass decreases nearly as much times, it is a pretty convenient sideffect of having most of your ships mass as fuel

The only thing I didn't take into account is efficiency of the drive.
This is a hypothetical drive which converts all of reaction energy into motion, meaning that even the exhaust tube should stay perfectly cold, which is impossible.

Originally Posted by Trilex

The reason why this graph is near-linear is because relativistic increase in mass most of the time is compensated by decrease in mass , as fuel is being converted into energy.

Ahhh, okay. That was why I thought it looked odd...I wasn't taking that into account.

The only thing I didn't take into account is efficiency of the drive.
This is a hypothetical drive which converts all of reaction energy into motion, meaning that even the exhaust tube should stay perfectly cold, which is impossible.

Photon drive? I think there are some light sources (like free-electron lasers) that are close to 100% efficient.

Well having a 100% efficient source of radiation is not the problem in this case, because you already do have a 100% efficient source making gamma rays from antimatter, the problem is, converting that radiations or any other kind of propellant energy into motion.

Even with a 100% efficient laser, the part of the energy of photons would probably go into heating the reflective material

Converting 100% of energy into kinetic motion of the ship would mean
all of your machinery involved would actually not change in temperature once the engine is turned on.
Which , I think think is even possible, even if you use your cold finger to push a ball, you are converting a fraction of energy into heat, and not just kinetic energy.

With some kind of antimatter reaction tube (that would emit radiation and particles through the exhaust), I think a considerable portion of energy would go into heating that tube, and that portion of energy would not end up speeding the ship.

Whenever there is some kind of collision, there is loss in total kinetic energy, due to change in temperature.