Fusion of hydrogen or helium normally requires at least the conditions found in the the cores of stars . High temperatures and densities
allow hydrogen and helium nuclei to get close enough to fuse together into bigger nuclei
and release a TON of energy, powering even more fusion while releasing enough extra to
power the star, or if you set this situation up on earth, you might have a hydrogen bomb. But it’s actually possible for fusion to
occur at temperatures much, much lower than the core of the sun - like, room temperature,
for example. Now, I’m not talking about the infamous
“cold fusion” of the 1980s that hasn’t been shown to work or involve any, well, fusion
- no, I’m talking about the room-temperature fusion of the 1950s that actually does work:
fusion with the help of muons! Nuclear fusion, of course, happens when atomic
nuclei, like hydrogen nuclei , come close enough together that their strong nuclear
attraction can overcome their electric repulsion, and they fuse together into a single,
bigger nucleus - like helium . This typically happens in a plasma, that is,
a super hot soup of electrons and atomic nuclei, where if it’s hot enough every once in a
while two nuclei bump hard enough into each other to fuse . But fusion can in principle
happen in regular, non-plasma molecules, too - like the hydrogen molecule, in which two
hydrogen nuclei are kept relatively near to each other by sharing electrons . The nuclei
don’t stay separated a rigid distance apart, though - they vibrate and wiggle and every
so often, they can, in principle, get close enough to fuse together. But with hydrogen - or nitrogen, or oxygen,
or pretty much all other molecules - this happens exceedingly rarely (which is why our
atmosphere, which has a fair amount of molecules, isn’t a giant fusion bomb). However, things are different if you replace
the electrons with particles called muons, which are basically exactly the same as electrons
except 200 times heavier . Muons, being essentially heavy electrons, form atoms and
molecules in almost the exact same way as electrons, but since they’re heavier, their
orbits are much closer to the nucleus than an electron with the same energy and angular
momentum would be . And this means that atoms and molecules held together with muons instead
of electrons are about 200 times smaller, and their nuclei are correspondingly about
200 times closer together. And being closer together makes nuclei many
many many times more likely to fuse together, so much so that hydrogen molecules made with
muons can fuse together at temperatures much lower than the core of the sun - even room
temperature!! Which was predicted in 1947 and experimentally
achieved in 1956 . Physicists have even managed to achieve muon-aided nuclear fusion at temperatures
close to absolute zero. So at this point, you’re probably asking
yourself: if room-temperature nuclear fusion exists, why aren’t we using it to power
modern civilization? Well, while muon-facilitated fusion is indeed
fully legit nuclear fusion at non-crazy temperatures, there are some major problems which prevent
it from being used as a power source. First, muons don’t live very long . Unlike electrons which have an in principle infinite lifespan, after
about 2 microseconds muons spontaneously decay into an electron and some neutrinos, so if
you’re going to do anything with muons, you have to do it real quick! This turns out not to matter much for the
purposes of facilitating fusion, but because of their short lifespan, there aren’t a
ton of muons around - so if you want a reliable supply of muons, you pretty much have to make
them with a high energy particle accelerator , which takes a lot of energy per muon - at
best about 5 giga electron volts , or about 50 times the E=mc^2 mass-energy of a muon itself. Now, luckily you don’t need a muon for every
single pair of hydrogen nuclei you want to fuse, because after a pair of nuclei fuses
into helium the muon can go off and help more nuclei fuse …and then help more… and more…
and more…. EXCEPT, every so often , the muon doesn’t
- it’ll get stuck as part of the newly fused helium atom , and can’t facilitate any additional
fusing. This means that each muon only helps an average
of 150- fusions of nuclei before it gets stuck . And since each fusion of nuclei releases
about 18 mega electron volts of energy , this means that, after 150 fusions, each muon facilitates
an average of 2700 mega electron volts, or 2.7 giga electron volts, of energy generation. Which means that, unfortunately, the numbers
don’t add up - Remember it currently takes around 5 GeV of energy to produce a muon, but each
muon only generates about two and a half GeV of energy before getting stuck to a nucleus. That is, muon-facilitated fusion is a net
consumer of energy (rather than being a source of energy). This is the best case possible with current
technology, and the numbers are still off by a factor of 2 before even reaching any
sort of break-even where muon-facilitated fusion could generate as much energy as it
consumes. And we’d need to be much better than just
breaking even, energy-wise, to make a viable commercial power plant. Pretty much the only hope for muon-facilitated-fusion
is to figure out how to make muons for less energy, or figure out how to have less of
them stick to the helium nuclei, or how to unstick them once they’re stuck - which
are all hard problems limited by the unchangeable physical properties of muons and nuclei, and
so we’ve made quite slow progress in over 70 years of research. The summary is that muon-induced fusion exists,
it’s fascinating science, but it’s not going to be powering the world any time soon. To dive deeper into the energy sources that
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Cold fusion is a glorious part of the scientific field. Some guy says that he has created cold fusions in his garage and invites over scientists and journalists to film it. He never shows them how it works or let them see the inner working. But he says that "scientists have now seen that it works". Suddenly a huge part of laymen say that cold fusion is now real and that we can make extremely cheap and safe energy. Then... nothing. Then wait 10 years and some new random guy does the same trick and again goes to the media with it.
Then the guy also goes on CNN and is just interviewed by the news anchor only. Just journalist questions. No critical scientific questions at all. Boom, views and more laymen say that cold fusion is a real thing. The journalist believed him = ergo it is real.
So isn’t this exclusively muon-catalyzed fusion? Forgive me if it went over my head but I don’t see where the cold fusion comes into this process.