Antimatter energy from a small amount of mass

  • #1

Main Question or Discussion Point

If an object's energy is proportional to its mass, how can a gram of antimatter produce more energy than 80 kilotons of TNT? Where does all this energy come from such a small amount of mass?


Skip to 5:19 of the video where he says this:

Please explain this in the most simplest way possible.
 

Answers and Replies

  • #2
Vanadium 50
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It is what it is.

You seem to think this number is too large. What number do you think it should be?
 
  • #3
It is what it is.

You seem to think this number is too large. What number do you think it should be?
No idea. But I just feel like there isn't enough mass to produce that much energy. Unless, it just depends on how efficient the energy transfer process is. Maybe the way TNT reacts and produces energy is a very lousy way which doesn't mirror its mass content, so there's tons of mass left behind, and not much energy produced 🤷‍♂️.

But I don't know haha, I still think a gram of something should not produce ridiculous amounts of energy that seem disproportionate to its qualities. Like, the amount of space a gram of antimatter occupies wouldn't fill the amount of space its energy occupies :oldconfused:
 
  • #4
Bandersnatch
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While one can say that object's (rest) energy is proportional to mass, it doesn't mean that all of this energy is always released in whatever process we're thinking about.

In chemical reactions (such as in TNT explosions) or nuclear reactions, only a small fraction of the initial mass is converted into other forms of energy that we call explosion (i.e. heat, radiation, kinetic energy of the products). Most of the mass is retained in the reaction products. E.g. burning hydrogen in an oxygen atmosphere produces a H2O molecule, which is almost as massive as the initial components. It's only the difference in the binding energies before and after the reaction that is released.

For some materials, that difference is larger, which makes them better explosives. In nuclear reactions, the forces involved are much stronger, which means the difference is much higher - but still only a small fraction of the total mass.

In a matter-antimatter annihilation, all of the mass of the material is converted to other forms of energy.
 
  • #5
While one can say that object's (rest) energy is proportional to mass, it doesn't mean that all of this energy is always released in whatever process we're thinking about.

In chemical reactions (such as in TNT explosions) or nuclear reactions, only a small fraction of the initial mass is converted into other forms of energy that we call explosion (i.e. heat, radiation, kinetic energy of the products). Most of the mass is retained in the reaction products. E.g. burning hydrogen in an oxygen atmosphere produces a H2O molecule, which is almost as massive as the initial components. It's only the difference in the binding energies before and after the reaction that is released.

For some materials, that difference is larger, which makes them better explosives. In nuclear reactions, the forces involved are much stronger, which means the difference is much higher - but still only a small fraction of the total mass.

In a matter-antimatter annihilation, all of the mass of the material is converted to other forms of energy.

Oh my god, of course! I deserve a big fat facepalm. I guess it does have to do with how efficient the mass-energy conversion is. It still amazes me though that such a small amount of mass can produce ungodly amounts of energy. Really puts things into perspective. Like who knew a gram of something you can fit into your hand could blow up an entire city? It really doesn't take much to produce lots, I guess. Mindblowing!
 
  • #6
In a matter-antimatter annihilation, all of the mass of the material is converted to other forms of energy.
Which also begs the question... Does this mean that annihilation is more efficient than fusion? Since in the fusion process, some of the mass is contained as a new element forms (say, hydrogen into helium), while of course the vast majority is emitted in photons and such? Could this also mean that annihilation would be a much cleaner source of energy than fusion, because it's 100% efficient, while fusion is not?
 
  • #7
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Which also begs the question... Does this mean that annihilation is more efficient than fusion?
Yes, by more than a factor 100.
If you fuse deuterium p;us tritium to helium plus neutron (the most useful fusion reaction) you convert 1 kg of fuel to ~995 g of products, only ~0.5% of the mass is released as energy.
If you annihilate 500 g of antimatter with 500 g of matter most of it ends up as radiation. Some fraction ends up as neutrinos which escape without further interaction.
 
  • #8
Yes, by more than a factor 100.
If you fuse deuterium p;us tritium to helium plus neutron (the most useful fusion reaction) you convert 1 kg of fuel to ~995 g of products, only ~0.5% of the mass is released as energy.
If you annihilate 500 g of antimatter with 500 g of matter most of it ends up as radiation. Some fraction ends up as neutrinos which escape without further interaction.
Very interesting! Thank you, and everyone else for your insights!
 
  • #9
DaveC426913
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It still amazes me though that such a small amount of mass can produce ungodly amounts of energy.
Look at it the other way around.
It took a lot of energy - compressed into a very tiny space - to make a particle with mass.

That energy is there, locked up in the particle.

All that a M-/AM reaction does is release that energy.
 
  • #10
ZapperZ
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Which also begs the question... Does this mean that annihilation is more efficient than fusion? Since in the fusion process, some of the mass is contained as a new element forms (say, hydrogen into helium), while of course the vast majority is emitted in photons and such? Could this also mean that annihilation would be a much cleaner source of energy than fusion, because it's 100% efficient, while fusion is not?
But you are forgetting something else... the cost of energy to produce the equivalent amount of antimatter. Just because when they meet, they can annihilate one another and produce a lot of energy, doesn't mean that there was no cost to get them there in the first place. Production of antimatter is inefficient, and requires a lot of energy, more energy than we get out in return. You need to consider the overall efficiency here, not just at the end stage.

Otherwise, we would have had matter-antimatter power generator already.

Zz.
 
  • #11
DaveC426913
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Thus:
Production of antimatter is inefficient, and requires a lot of energy
 
  • #12
phyzguy
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It's interesting to look at Einstein's reply to the OPs question. He was asked:

"You're saying there's more horsepower in a lump of coal
than in the whole Prussian cavalry," they complained. "If this
were true, why hasn't it been noticed before?"

And Einstein replied:

"If a man who is fabulously rich never spent or gave away
a cent," Einstein replied, "then no one could tell how rich
he was or even whether he had any money at all. It is the
same with matter. So long as none of the energy is given off
externally, it cannot be observed."
 
  • #13
Look at it the other way around.
It took a lot of energy - compressed into a very tiny space - to make a particle with mass.

That energy is there, locked up in the particle.

All that a M-/AM reaction does is release that energy.
That makes so much sense! I guess literally everything that exists is just compressed energy into a space. And it takes lots of energy to contain that energy in a small mass, therefore it takes lots of energy to release it. Wow!
 
  • #14
It's interesting to look at Einstein's reply to the OPs question. He was asked:

"You're saying there's more horsepower in a lump of coal
than in the whole Prussian cavalry," they complained. "If this
were true, why hasn't it been noticed before?"

And Einstein replied:

"If a man who is fabulously rich never spent or gave away
a cent," Einstein replied, "then no one could tell how rich
he was or even whether he had any money at all. It is the
same with matter. So long as none of the energy is given off
externally, it cannot be observed."
That's almost ironic. Einstein saw what most humans didn't; he saw a universal secret that couldn't be observed externally. Simply genius!
 
  • #15
Orodruin
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Could this also mean that annihilation would be a much cleaner source of energy than fusion, because it's 100% efficient, while fusion is not?
The reason fusion is viable is that you can find or produce fusile materials at low cost (economically as well as ecologically), whereas there is practically no antimatter around. Producing the anti-matter would be running the annihilation process in the other direction, meaning you would have to put in as much energy as you would get out in the end. After accounting for energy losses in the process, you have anet loss of energy.
 
  • #16
The reason fusion is viable is that you can find or produce fusile materials at low cost (economically as well as ecologically), whereas there is practically no antimatter around. Producing the anti-matter would be running the annihilation process in the other direction, meaning you would have to put in as much energy as you would get out in the end. After accounting for energy losses in the process, you have anet loss of energy.
Hmm.. I see now. So basically antimatter in theory is 100% efficient. But at the stage we're at now, it would take more energy to produce and contain it than actually using its effects. I appreciate your insight!
 
  • #17
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It's not just "the stage we're at now", it's a fundamental limit. If you convert X to Y then you need at least as much energy as you can release when converting Y to X. "At least" because your conversion will come with some losses, apart from that is a consequence of conservation of energy.
 
  • #18
It's not just "the stage we're at now", it's a fundamental limit. If you convert X to Y then you need at least as much energy as you can release when converting Y to X. "At least" because your conversion will come with some losses, apart from that is a consequence of conservation of energy.
Well that is unfortunate then. I hope one day we will have clean, readily available energy then, because interstellar travel using antimatter seems very promising! Thanks again.
 
  • #19
Orodruin
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Hmm.. I see now. So basically antimatter in theory is 100% efficient. But at the stage we're at now, it would take more energy to produce and contain it than actually using its effects. I appreciate your insight!
It is not about technological development. The problem is that there is no anti-matter and producing it will require more energy than you would get out.

Conpare to coal burning. In that case, there is a lot of the fuel in the ground. Extracting that fuel and making it ready to be burned is going to require less energy than what you get out of burning it. Therefore, burning coal is a source of energy.
 
  • #20
Vanadium 50
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Conpare to coal burning. In that case, there is a lot of the fuel in the ground. Extracting that fuel and making it ready to be burned is going to require less energy than what you get out of burning it. Therefore, burning coal is a source of energy.
And `compare that to sodium burning. There isn't any free sodium in the ground so you can't mine and burn it.
 
  • #21
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Unless, it just depends on how efficient the energy transfer process is. Maybe the way TNT reacts and produces energy is a very lousy way which doesn't mirror its mass content, so there's tons of mass left behind, and not much energy produced
That is pretty much what’s going on. If we were to gather up all the hot gases and other combustion products from the explosion of one kilogram of TNT, we would find that they weighed slightly less than one kilogram: .99999999999906 kg if I typed the right number of nines. This explosion is releasing only the energy of chemical bonds in the TNT molecule, and that’s just a tiny fraction of the total energy present.
 
  • #22
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That is pretty much what’s going on. If we were to gather up all the hot gases and other combustion products from the explosion of one kilogram of TNT, we would find that they weighed slightly less than one kilogram: .99999999999906 kg if I typed the right number of nines. This explosion is releasing only the energy of chemical bonds in the TNT molecule, and that’s just a tiny fraction of the total energy present.
And, just to beat this to death, that is why nobody noticed this until 1905 -- and it was a man with paper & pencil who figured it out, not an experiment. I would guess even the best scales today probably couldn't measure this small difference.
 
  • #23
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The best "scales" I found (gravimeters) are a factor 10-100 away from measuring mass differences from non-nuclear reactions. It's a difficult experiment, but I guess once the scales get sensitive enough someone will do it.
 
  • #24
scottdave
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It's unlikely we will see matter/antimatter generators powering our cars or homes any time soon.

But this type of reaction can be useful, such as in a PET scan. Isotopes emit positrons (anti-electrons) which annihilate with nearby electrons, emitting gamma rays, which are detected by the scanner.
 
  • #25
scottdave
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Here is another interesting video, related to PET scans. I found it interesting because it talks about how they make the radioactive material, then combine it with different molecules to target different parts of your body. Also, it goes into how they detect the gamma rays to get 3D images.
 

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