# What are the differences between relict and relic?

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• KingGambit
KingGambit
Dear PF Forum,

It's been a while since I logged in PF Forum. And wish you a good health.

I'd like to ask a question concerning anti matter.
I read in Dan Brown's Angel and Demon that anti matter can be used as energy source.
A ha, I said to myself. There were you went wrong mr. Author.
The energy from matter/anti matter annihilation can't be greater than the energy that was used to create matter/anti matter pair, right.
What if we create pure anti matter, and smash it with matter, would it generate more energy than it was spent?

Perhaps if we take Einstein equation, E = MC2, and supposed that the speed of light is 300 millions m/s.
So, 90,000 tera joules is equivalent to 1 kg matter (or anti matter).
My question is this.
1. Is it physically possible to create say more than 500 gram of anti matter from 90, 000 tera joules?
2. Is it technically possible to create more than 500 gram of anti matter from 90,000 tera joules?

KingGambit said:
I read in Dan Brown's Angel and Demon that anti matter can be used as energy source.
A ha, I said to myself. There were you went wrong mr. Author.
The energy from matter/anti matter annihilation can't be greater than the energy that was used to create matter/anti matter pair, right.
Right.

KingGambit said:
What if we create pure anti matter
From what? You can't just create something out of nothing. You would have to find some nuclear reaction that produces antimatter particles, and that reaction would have to conserve energy; so the best you could do would be to capture all of the energy input in the antimatter particles that came out, and then you would get that energy back when you combined that antimatter with matter.

But that's at best; most nuclear reactions do not just produce one particle as output, so you would probably only be able to capture a portion of your input energy into antimatter particles. The rest would be taken away by reaction products that weren't useful to you.

KingGambit said:
1. Is it physically possible to create say more than 500 gram of anti matter from 90, 000 tera joules?
It should be obvious that the answer to this must be no. Otherwise you would violate conservation of energy.

KingGambit said:
2. Is it technically possible to create more than 500 gram of anti matter from 90,000 tera joules?
Obviously not, given the answer to 1. above.

vanhees71 and russ_watters
Antimatter as a source of energy is great if you find it in the wild and your acquirement costs are economical.

But there's another application: in theory it makes a very powerful, very compact fuel (which is not quite the same thing as a resource).

In other words: you make the anti-matter in your manufacturing plant (at great cost), then you take that tiny cannister and put it your your tiny starship (or whatever).
And it can go on very long trips without needing to return to port to refuel.
And you don't have to conserve energy; you have an unlimited supply.
And that includes your weapons and defenses.To summarize: the ways of using antimatter as a fuel are myriad (maybe you only carry the antimatter, and gather the matter on-the-road). But whatever way you might use it, the key point is that the initial cost of gathering or manufacturing the fuel is not the only consideration in whether or not it is cost-effective. The cost must be considered in the context of the expected application and its total cost/value.

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DaveC426913 said:
And it can go on very long trips without needing to return to port to refuel.
And you don't have to conserve energy; you have an unlimited supply.
These claims are highly questionable if you are talking about travel with a scope anywhere beyond a single solar system. You need to be much more specific about the distances and speeds you are assuming. Antimatter does not allow you to get around the rocket equation.

vanhees71
PeterDonis said:
Antimatter does not allow you to get around the rocket equation.
No, it allows you to substantially up the payload/fuel ratio, at least in theory.

I'm not trying to be specific about any particular journey. The only reason to mention spaceships at all is because it is the extreme example of needing a lot of power where you have no option to refuel. That's all.

PeterDonis said:
Antimatter does not allow you to get around the rocket equation.
And the energy density is low because it needs to be stored without touching anything, which means plasma.
Plus its not expensive like gold is expensive - it's expensive like the entire GDP isn't enough to make a macroscopic amount.
Plus its not the question asked.

Now if we had some dilithum....

vanhees71 and berkeman
DaveC426913 said:
it allows you to substantially up the payload/fuel ratio
To some extent, perhaps, compared to chemical rockets, since it allows a higher exhaust velocity/specific impulse to be reached. But fuel in the sense you are using the term is not the only thing that has to be carried besides payload. Reaction mass is also required. (Many treatments, such as the Usenet Physics FAQ article on the relativistic rocket equation [1], include reaction mass in "fuel".) And the amount of reaction mass you need doesn't care what kind of rocket you have; it's dictated by conservation of momentum.

From the FAQ article, the ratio of fuel mass (which, as above, includes reaction mass) to payload mass for the most fuel efficient kind of rocket possible, a photon rocket powered by matter-antimatter annihilation with 100% efficiency and perfect collimation, is

$$\frac{M}{m} = \gamma \left( 1 + \frac{v}{c} \right) - 1$$

where ##v## is the change in velocity relative to the starting point and ##\gamma## is the corresponding relativistic gamma factor.

But that is for just one rocket burn, i.e., one change in velocity. For a single trip you would need at least two burns, one at the start to get up to your chosen cruising speed and one to slow back down at the destination. But for the kind of trips you are talking about, you would need an indefinite number of burns. And each additional burn you add multiplies the mass ratio by the factor given above (with the appropriate velocity change for that burn), because for each burn the "payload" mass is the total payload + fuel + reaction mass for all previous burns. An antimatter rocket does not help with that at all.

The brutal math is even more apparent if you express it in terms of acceleration ##a## and burn time ##T##:

$$\frac{M}{m} = \exp \left( \frac{aT}{c} \right) - 1$$

Now it is clear that adding more burn time increases the mass ratio exponentially, making the payload a tinier and tinier fraction of the total. And again, an antimatter rocket does not help with that at all.

[1] https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html

jbriggs444, vanhees71, DaveC426913 and 1 other person
I think space travel may be taking this thread off topic, so i dont want to belabour it, so I'll tie it off with this:

I thought the idea behind antimatter propulsion is that all the matter gets converted to propulsion in the form of particles moving at c, so the amount of propulsion you get per unit of mass is the theoretical maximum.

But I am realizing by your excellent post above that i have been promulgating a pop-sci explanation of antimatter propulsion.

DaveC426913 said:
I thought the idea behind antimatter propulsion is that all the matter gets converted to propulsion in the form of particles moving at c, so the amount of propulsion you get per unit of mass is the theoretical maximum
That is correct as far as it goes; it just doesn't quite mean what you apparently thought it meant. A rocket of this type is indeed more capable than existing chemical rockets (if you assume that the storage requirements and other technical details can be solved). But yes, it's not as capable as many pop sci presentations like to portray.

vanhees71
KingGambit said:
Dear PF Forum,

It's been a while since I logged in PF Forum. And wish you a good health.

I'd like to ask a question concerning anti matter.
I read in Dan Brown's Angel and Demon that anti matter can be used as energy source.
A ha, I said to myself. There were you went wrong mr. Author.
This is a "mystery thriller" by a popular novelist. It has no pretentions to be scientifically valid.

You might as well analyse the physics of Alice in Wonderland.

phinds, russ_watters and KingGambit
I couldn't get farther than about p. 60. It's so full of physics errors that it's no fun to read anymore. I stoped at the moment, when he said the W- and Z-bosons were massless... In good science fiction for me the science should be right!

KingGambit
vanhees71 said:
I couldn't get farther than about p. 60. It's so full of physics errors that it's no fun to read anymore. I stoped at the moment, when he said the W- and Z-bosons were massless... In good science fiction for me the science should be right!
If we could just get rid of that pesky Higgs, the W's and Z would be massless. Now how could we do that? I think there is an inscription on the Chalice Well in Glastonbury...

-Dan

vanhees71
PeterDonis said:
Obviously not, given the answer to 1. above
I think the idea @KingGambit had here was using antimatter creation process substantially different from pair production - so that you don't 'waste' energy on creating the mundane matter component. If that were possible, you wouldn't violate conservation of energy as you'd only be transmuting half the mass-energy that is later used in annihilation.
Running such a process at full efficiency long enough would let you convert all the matter in the universe into radiative energy, but doing so wouldn't change the total energy content.
The question is essentially whether it's possible to create antimatter without the regular matter 'ash'.
Which I don't know, but I suspect there's a whole slew of other conservation laws to worry about here.

Looking at the problem of antimatter as fuel from another angle, one could always 'simply' capture antimatter from natural processes that require no energy input to initiate. E.g. anything involving beta+ decay. Herding all those positrons into a fuel cell would then be just an engineering problem, amirite?

Bystander
The SF answer would be one could harness solar energy in some orbital factory to make antimatter if there was some need / ability to use it as a fuel source for interstellar travel or whatever. But the containment issue is far from trivial - any breach and <boom>

vanhees71 said:
I couldn't get farther than about p. 60. It's so full of physics errors that it's no fun to read anymore. I stoped at the moment, when he said the W- and Z-bosons were massless... In good science fiction for me the science should be right!
D'accord. I read that in 2006,
actually I 'learned' some things from that novel,
That internet was created at CERN
That it was George Le Maitre that postulated the big bang theory,
But when it's said that anti matter as an energy source, I rather disappointed. I (think) knew that it was not true.

vanhees71 and PeroK
PeterDonis said:
Right.From what? You can't just create something out of nothing. You would have to find some nuclear reaction that produces antimatter particles, and that reaction would have to conserve energy; so the best you could do would be to capture all of the energy input in the antimatter particles that came out, and then you would get that energy back when you combined that antimatter with matter.

But that's at best; most nuclear reactions do not just produce one particle as output, so you would probably only be able to capture a portion of your input energy into antimatter particles. The rest would be taken away by reaction products that weren't useful to you.
It should be obvious that the answer to this must be no. Otherwise you would violate conservation of energy.Obviously not, given the answer to 1. above.

I mean instead of creating, say 300 gram anti matter and 300 gram matter from 90,000 tera joules.
Is it possible to create just 600 gram anti matter from 90,000 tera joules? It doesn't violate conservation of mass/energy I think.

Bandersnatch said:
I think the idea @KingGambit had here was using antimatter creation process substantially different from pair production - so that you don't 'waste' energy on creating the mundane matter component. If that were possible, you wouldn't violate conservation of energy as you'd only be transmuting half the mass-energy that is later used in annihilation.
Running such a process at full efficiency long enough would let you convert all the matter in the universe into radiative energy, but doing so wouldn't change the total energy content.
The question is essentially whether it's possible to create antimatter without the regular matter 'ash'.
Which I don't know, but I suspect there's a whole slew of other conservation laws to worry about here.

Looking at the problem of antimatter as fuel from another angle, one could always 'simply' capture antimatter from natural processes that require no energy input to initiate. E.g. anything involving beta+ decay. Herding all those positrons into a fuel cell would then be just an engineering problem, amirite?
Yes, yes, that's what I mean.

KingGambit said:
I mean instead of creating, say 300 gram anti matter and 300 gram matter from 90,000 tera joules.
Is it possible to create just 600 gram anti matter from 90,000 tera joules?
As has already been said, "create" is the wrong word; you're not creating antimatter out of nothing. You have to find nuclear reactions that produce the antimatter particle(s) you want.

If you are thinking of reactions that convert, say, 900 terajoules of photons directly into something, then there are no such reactions that only produce antimatter; any such reactions must produce matter and antimatter in equal quantities.

To produce just antimatter, you would need to find reactions such as, for example, bombarding appropriate atomic nuclei with neutrons or protons or something, that produced antimatter particles only. There might be such reactions in principle, but they won't be of the form "convert 900 terajoules of energy directly into antimatter".

KingGambit
Bandersnatch said:
I suspect there's a whole slew of other conservation laws to worry about here.
The obvious two to consider are conservation of baryon number and lepton number. Converting 900 terajoules of photons into antimatter only would violate one or the other (which one would depend on what kind of antimatter was produced).

vanhees71
It also violates the very generally valid CPT symmetry, i.e., you cannot make just "anti-matter" from photons, which are strictly neutral, i.e., you have to produce as much "matter" as "anti-matter".

PeterDonis
vanhees71 said:
It also violates the very generally valid CPT symmetry, i.e., you cannot make just "anti-matter" from photons, which are strictly neutral, i.e., you have to produce as much "matter" as "anti-matter".
What specifically are the CPT theoretical constraints as to what baryons can or cannot decay into, assuming you do violate baryon number conservation?
Does it mean that count of matter particles is separately conserved? If you must produce as much matter as antimatter then you cannot turn matter into antimatter and thus turning a proton into positron is forbidden by that separate conservation? Turning a proton into electron would be easier if you could get rid of the charge?

To add: there are actually three unobserved but widely popular processes violating baryon number conservation:
1. Proton decay. Never observed, despite several failed predictions. Remains a popular speculation.
2. Hawkins radiation. It is widely believed that black holes would evaporate disregarding the conservation of the number of baryons fallen into them
3. Big bang baryogenesis. World observably had a slight excess of baryons over antibaryons before the antibaryons annihilated leaving the baryons. (Mind you, we have no idea whether matter or antimatter prevails in the world. Electrons certainly exist in numbers matching the protons, but we cannot observe relict neutrinos, let alone ascertain whether relict neutrinos or antineutrinos are more common, and by how much). The initial state of the world is unknown, so there is no reason why the slight excess of baryons might not simply be the free initial state of world, with no natural laws distinguishing baryons for antibaryons; but there is the widely popular theory of baryogenesis claiming that the original numbers of baryons and antibaryons should have been exactly equal, and the observed excess of baryons should have been a result of some process embedded in natural laws.
So, how could you use antimatter as energy source?
Un-steered, 3) is not an energy source. If you invest energy to make a Small Bang and make a small excess of baryons again then this is the part of your energy investment you cannot get back.
But if you could steer it? Make a Small Bang which produces a big excess of antibaryons, in contrast to the Big Bang that produced a small excess of baryons? Then you could combine the excess antibaryons from Small Bang with excess baryons from Big Bang, and recover more energy than you put into Small Bang?

KingGambit
snorkack said:
relict
TIL a new word. And that snork did not merely mistype relic.

DaveC426913 said:
TIL a new word. And that snork did not merely mistype relic.
Checking up, the English do spell it as "relic". For some reason, "relic radiation" is not a common expression in English even for photons - "microwave background" is. Well, neutrinos are most definitely not "microwaves", and neither are antineutrinos.

snorkack said:
The English do spell it as "relic".
So who does spell it relict? It is in the Oxford dic, so it's a perfectly valid English form apparently.

PeterDonis said:
As has already been said, "create" is the wrong word; you're not creating antimatter out of nothing. You have to find nuclear reactions that produce the antimatter particle(s) you want.

If you are thinking of reactions that convert, say, 900 terajoules of photons directly into something, then there are no such reactions that only produce antimatter; any such reactions must
produce matter and antimatter in equal quantities.

To produce just antimatter, you would need to find reactions such as, for example, bombarding appropriate atomic nuclei with neutrons or protons or something, that produced antimatter particles only. There might be such reactions in principle, but they won't be of the form "convert 900 terajoules of energy directly into antimatter".

Thank you very much.

vanhees71 said:
I couldn't get farther than about p. 60. It's so full of physics errors that it's no fun to read anymore. I stoped at the moment, when he said the W- and Z-bosons were massless... In good science fiction for me the science should be right!
Wait. So my warp drive engine will work? hmmm......

DaveC426913 said:
So who does spell it relict? It is in the Oxford dic, so it's a perfectly valid English form apparently.
Relict and relic are two different words that are closely semantically related. When used in the sense above relicts are used for "groups" or concepts and relic is used for a specific "item". If I got this right (not a native English speaker) as an example the species Coelacanth is relict while an individual Coelacanth would be a relic.

KingGambit and Bystander
glappkaeft said:
Relict and relic are two different words that are closely semantically related. When used in the sense above relicts are used for "groups" or concepts and relic is used for a specific "item". If I got this right (not a native English speaker) as an example the species Coelacanth is relict while an individual Coelacanth would be a relic.
I find very little useful clarififying sources online, but one thing seems to be as suspected: relic is a noun whereas relict has an adjective form.

"That old thing is a relic; just one of the relict items in my collection."

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KingGambit

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