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This is a stupid question but I don't know anything about fusion: How is it possible for X energy to create X+Y energy in output? Doesn't that violate some fun
by bmmayer1 4y ago
This is a stupid question but I don't know anything about fusion:
How is it possible for X energy to create X+Y energy in output? Doesn't that violate some fundamental law of physics?
- ceejayoz 4y agoYou're using X energy to release Y energy from the fuel (the pellet, containing deuterium and tritium). It was there already, just not in a usable form.
- simiones 4y agoThe energy is "released" from the binding energy of the nuclei. It's similar to how throwing a bottle of nitroglycerine can generate a huge explosion, even though you use a tiny amount of energy to throw it.
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- jperras 4y agoEnergy is released when two atomic nuclei combine to form a larger atomic nuclei. There's a threshold of energy required to attain this fusion reaction (otherwise there would be no light nuclei in the universe), and once the nuclei combine there's energy that is released, similar to how some chemical reactions can be exothermic in nature.
- tekla 4y agoYou have a piece of wood. You ignite it with a match. This causes a self sustaining reaction in the form of fire that releases far more energy than the match could ever create. This is effectively what is happening with any energy generator.
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- karpierz 4y agoYou take a lighter and light gasoline on fire, using X energy. Then once the gasoline catches on fire, it'll burn on its own, releasing Y energy. Same principle, different means.
- dsfyu404ed 4y agoYou know how when you burn something you release the energy in the chemical bonds? Fusion and fission are like that but for atoms instead of molecules.
- jameshart 4y agoExcept… chemical bonds don’t ‘store’ energy. Molecules are a low energy configuration. It takes energy to rip them apart! But, O2 molecules, with their double bond, don’t take much energy to break apart. If they do, and then pair up with say a bunch of Hydrogen and Carbon atoms that were nearby in some long chain or something, they form bonds that are stronger - that take more energy to break - and you end up with some leftover energy. Water and CO2 molecules are an even lower energy configuration. but the extra energy you get wasn’t exactly ‘in’ the oxygen bond though - any more than when you have a ball at the top of a hill it has potential energy ‘in’ it.
- dsfyu404ed 4y agoThere's a fundamental tradeoff between technical precision and explaining things in a way that's relatable to simpler stuff. Deal. With. It.
- davrosthedalek 4y agoNot if the original description is exactly the opposite of what happens. You get energy out by making stronger bonds.
- m55au 4y agoStronger bonds by definition are lower energy bonds. So you get energy out by making the total bond energy go lower or "releasing it".
- a-priori 4y agoIt's not "creating" energy, it's releasing energy. The original atoms (exactly which atoms depends on the reactor, but let's assume it's deuterium and tritium) have a certain starting energy. When you fuse them together the resulting atom (helium-4, if you start with deuterium and tritium) moves it into a lower energy state. Since the fused atom has lower energy than the input atoms, the fusion reaction releases the difference in energy, which you can then capture.
- paxys 4y agoThe input energy X is used to create the conditions of high temperature and pressure that are needed for fusion to take place. When fusion happens, two hydrogen atoms fuse together into one, losing a bit of mass in the process. The mass difference is converted into energy Y (using E=mc2). In this case, Y was greater than X, so there was a net gain in useful energy.
- spullara 4y agoIf you look at the mass before of their fuel, 1 deuterium atom + 1 tritium atom: 2.01410177811 u + 3.01604928 u = 5.03015105811 u vs the mass of the fusion products of 1 helium atom and 1 neutron: 4.002602 u + 1.008 u = 5.010602 u You'll notice that even though we started with 5 neutrons and 2 protons and ended up with the same number there was some additional binding energy that is unaccounted for in the new configuration. This is the energy released by the fusion reaction via E = mc^2. Here we see the mass difference is: 5.03015105811 u - 5.010602 u = 0.01954905811 u Converting that to energy you find that is 17.6 MeV. As you go up the periodic table fusing nuclei you will get less and less marginal energy until you get to iron where at that point fusion become net negative and fission is then takes over where breaking nuclei apart gains energy, marginally more as you go up the periodic table. That's why you want to fuse light particles and fission very heavy particles. It is also why there is so much iron as it is kind of the base state of both of these reactions.
- aaroninsf 4y agoThis is an A+ comment—helpful, well-formatted, concise, with bonus interesting additional detail. Thank you.
- eklitzke 4y agoTangentially related, but I think this is an interesting fact, all the atoms in our universe/galaxy/solar system with a mass up to that of iron are formed in the core of stars in stellar fusion. Hydrogen fuses into helium, and as a star nears the end of its lifetime you get heavier elements like lithium, carbon, and so on. Under normal stellar fusion no elements heavier than iron will be produced, and iron is only element number 25. If you just looked at nucleosynthesis through the lens of stellar fusion, it isn't obvious that there should be any heaver-than-iron atoms at all in the universe. These heaver-than-iron elements are created in a very interesting and exotic process. When a large enough star dies it explodes in a supernova, and a huge amount of energy and neutrons are released in a very short period of time. This supernova generates enough energy and neutron material that small amounts of heavier elements like gold, platinum, etc. are created through exotic nuclear fusion reactions, even though these heavy fusion reactions are energy-absorbing. It's interesting to think when you're wearing jewelry made from gold or platinum, all of those atoms in your jewelry were created during the death of a star.
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- Sporktacular 4y agoThe Y comes from the mass of matter converted in to energy. The mass of the material before the reaction is greater than the mass of its products. The law you're referring to might be the conservation of energy, but that applies to non-nuclear reactions and is more accurately called the law of conservation of mass-energy. In this case the energy in times the mass at the start is still equal to the energy out times the mass at the end. For the energy to increase, the mass must decrease to produce the Y in your equation.
- wodenokoto 4y agoI think you should think of it as “this lumber only needs 1 match to light it on fire while that lumber requires 10 matches to get started.”
- xdavidliu 4y agosometimes, when two small particles fuse, they become a single larger particle, but the larger particle's mass is slightly less than the sum of the masses of the two smaller particles. The slight difference becomes energy released, and the amount of energy released, roughly speaking, is E = mc^2.
- delaaxe 4y agoLatest xkcd: https://xkcd.com/2710/ https://xkcd.com/2710/
- nkrisc 4y agoMass and energy are equivalent. You're using X energy to reduce the mass of your fuel and converting that mass into Y energy. When X < Y you have useful energy production at the cost of the mass of your fuel. Energy is conserved. The reason nuclear fusion is such a desirable goal is because it only takes a relatively small amount of mass to convert into a relatively large amount of useful energy, and the mass (the fuel) is relatively easy to obtain. Like all energy generation, it's converting one type of energy into another, more convenient type, to do useful work. Like a hydroelectric dam converting the potential energy of water into more useful electrical energy. Energy is conserved when water spins a turbine, it's just that electrical energy is more useful for work than the potential energy of the water. Of course you can still use the potential (or kinetic) energy of the water directly, such as with a water mill. But the energy to work ratio is worse in that form (especially if the work to be done is far away from the watermill). Whenever you build a fire you need to input some amount of energy to begin the chemical reaction that releases energy. In this instance we get not electrical energy, but energy in the form of infrared and visible light, to heat our home and light our way. Yet the total energy released by the fire far surpasses the energy you used to start the reaction, but because the wood's mass is consumed, energy is ultimately conserved. You have converted wood (not useful for heating your home) into infrared light (useful for heating your home).
- lr1970 4y ago> Mass and energy are equivalent. Mass is energy at rest, hence equivalence with exception of massless particles like photons that have zero mass and non-zero energy. Also, photons travel with the speed of light in vacuum and cannot be found at rest in any frame of reference. Modern physics is fun, isn't it? P.S. Neutrinos were thought to have zero mass as well, but according to the Standard model they have mass.
- nkrisc 4y agoYeah, my explanation is very much simplified.
- 867-5309 4y agoequally confusing is the BBC article which mentions the energy used for the reaction does not include the energy needed to power the lasers, which renders it a net loss
- dpacmittal 4y agoSame way you use spark plug to get the engine going in an ICE car
- garfieldnate 4y agoI think it's more like a release of potential energy; kind of like how you can lightly nudge a large object teetering on the edge of a cliff and it'll make a huge splash at the bottom. It took a lot of energy to create the big splash, but you didn't need much to trigger it.
- rmbyrro 4y agoNothing is being actually "created", just converted.
- ihaveajob 4y agoA daily life parallel: You can use a lighter to put a small amount of energy into a bunch of wood to extract more energy than you put it. In the case of fusion, this energy is coming from fusing hydrogen atoms, rather than a chemical reaction.
- benevol 4y ago
- emmelaich 4y agoThe answers you got are excellent but a short response might just say you don't start with just X energy. In a sense it's no more mysterious (conservation of energy-wise) than adding the energy of a spark results in the energy of the wood fire. i.e. energy is transformed, not created as you quite accurately write.
- jackmott 4y ago
- steve76 4y ago
- syngrog66 4y agoE = mc^2 the "extra" comes from the mass
- anigbrowl 4y agoY is the energy that was holding some hydrogen atoms together which you have liberated (while destroying the atoms in question but that's OK cause it's abundant).
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- elif 4y agoto answer essentially, because matter is energy, you can use conversion energy to turn matter into its stored energy.
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- eru 4y agoThe analogy is that settings a pile of wood on fire requires a small amount of fire to start a big fire. Energy in total is still conserved, but it makes engineering sense to compare the size of the starting fire to the total inferno created.