I’m trying to figure out how antimatter is actually created, and the net is being obtuse about it. As I understand it, in the lab they bombard a material with either a laser or high energy particles of some sort, and the result is short-lived antimatter. What I’m specifically trying to figure out is what the antimatter is actually created from. Is the energy that’s released somehow converted to antimatter, or are particles in the original material switched over to their anti equivalents?
And also, when antimatter comes into contact with plain old matter, they annihilate each other and turn back into energy, right? Why does that happen? And do they release the same sort of energy that went into making them?
Thanks in advance.
There’s a saying in particle physics that “anything not forbidden is mandated”
So basically, if enough energy is available, and no conservation laws would be broken, the possibility exists that antimatter would appear. You are converting some form of energy (e.g. photon energy or kinetic energy) into mass energy in the form of rest mass of the created particles.
The “Enough energy” threshold is 1.02 MeV, since that is the combined rest mass energy of an electron/positron pair. You need the pair for a number of reasons - first and foremost that lepton number (electrons are in a family of particles called leptons) is conserved. An electron has a lepton number of +1, the positron, -1. So lepton number doesn’t change with the creation of the pair. Baryon number (baryons include protons and neutrons) is also a conserved quantity, so if you want to create a proton/antiproton pair you can do so, but that will cost you almost 2 GeV of energy.
That conservation law precludes a particle from changing into its antiparticle, for particles in those families.
During the annihilation, a particle and it’s antiparticle will convert into two (or more) photons. You need two in order to conserve momentum.
Well, you start with nothing and then take away the matter…
If you’re willing to read what my layman’s memory remembers: antimatter is created together with matter out of energy. You can see it clearly in Feynman diagrams, where one energy wiggly line splits into two ‘matter’ lines, one for matter, another for antimatter.
By the same token, when antimatter comes into contact with matter, it does indeed turn back into energy. It probably is so by definition: antimatter is the stuff that transforms to energy when meeting matter.
I don’t understand that ‘sort of energy’ stuff. Is there more than one kind on quantum-level?
This of course is only a layman’s memory. I’m sure an expert will be along shortly to give a full and precise explanation.l
From Physics Central:
So basically you send a high-energy photon (I think it has to be an X-ray to be high-energy enough, but I can’t be bothered to dig up the equations to say for sure) near, say, a plutonium atom, and you get a positron/electron pair for your trouble.
Firstly antimatter is created in a variety of different ways: collisons, decay products, etc., but I don’t think that’s what your asking.
In 1928 Paul Dirac formulated the Dirac equation which combined quantum mechanics with special relativity, like it’s classical counterpart it contained solutions where the energy of a particle is less than -mc[sup]2[/sup], howevr in classical physics these are rejected as unrealistic as there is no mechanism to go from a postive to negative energy state, but in QM there was no way to rule out a sponteous transition from a postive to negative state. To avoid such transitons Dirac suggested that these negative states were already filled (the “Dirac sea”) and thus transiton is prevented by the Pauli exclusion principle. Dirac then considered what would happen if a photon of twice the energy of the modulus of one of these negative states excited an electron in one of these filled negative states into the postive state of the same energy, the net result being that there was now a vacant energy state. This vacant energy state would then have the same momentum (but with a reverse sign) momentum as an excited electron and would behave exactly like a postively charged electron. This particle was christianed the positron and is the antiparticle of the electron, experimental evidence 5 years later showed it’s existance (though the idea of the dirac sea of filled negative states was later modifed into the idea of the Dirac field). This idea can be applied in a simlair way to other particles.
The three total Lepton numbers (l[sub]e[/sub][sup]TOT[/sup], l[sub]μ[/sub][sup]TOT[/sup], l[sub]τ[/sub][sup]TOT[/sup]) are not thought to be universally conserved properties (as this lead to problems with gauge symmetry in for example Hawking radiation), neither is Baryon number, though they are usually conserved.
As shown above phton must have at least 2m[sub]e[/sub]c[sup]2[/sup] in order to create an electron-positron pair.
- a phton must have an enrgy of at least 2m[sub]e[/sub]c[sup]2[/sup] in order to create an electron-positron pair.
*photon
Antimatter is created when her sister mommymatter has a baby.
To reduce it to its simplest form: Energy --> matter + antimatter. Matter + antimatter --> energy. The reaction can go either way, and the energy involved can be of any form. Yes, there are different forms of energy at the quantum level, just like there are different forms of energy at the classical level.
Whenever you make antimatter particles, you also make matter particles, but we’ve already got plenty of them lying around, so they’re not remarkable. So we describe the process as “making antimatter”.
Just wondering, the energy needed to create a particle-antiparticle pair is the same as the result of their mutual annihilation?
me thinks it should be… just checking
Indeed. Such are the joys of symmetry!
Somewhat related question - how do we know most of the universe is matter rather than antimatter?
So the release of energy is the splitting of matter and antimatter?
We have chosen to call the material of the known universe “matter”. They are just convenient labels–if the dominant atomic orbital particle had a positive charge we’d be calling that= the electron instead. We know the universe is mostly one type because that is the only sort we have observed to interact with us.
It is almost certain that most of the mass in the universe is not antimatter; several galaxies are in the process of colliding;
if one galaxy of a colliding pair were antimatter (as would be expected to happen many times by chance) the resulting explosion would be the brightest thing in the universe.
This has not been observed; the conclusion is that antimatter is very rare.
Antimatter is manufactured on Earth in high energy collision experiments at places like Fermilab, and this process is very inefficient and expensive; Antimatter is the most expensive substance obtainable. Once an anti proton (for instance) has been created in a collision it then can be separated from all the other millions of particles produced in such collisions using magnetic fields.
To imagine an antimatter economy, one has to imagine a more efficient process for the creation of antimatter (fuction) and much more abundant energy;
luckily the Sun creates as much energy as two million tonnes of antimatter per second deep inside itself, as part of the fusion process. Much of this energy actually comes from the creation of positrons, which are annihilated.
This energy eventually finds its way to the surface of the Sun and becomes sunlight. The Earth as a whole intercepts (the energy equivalent of) two kilograms of antimatter produced energy per second…
if we covered the sun in solar collectors at (say) half the distance of Mercury, we could intercept a thousanth of this energy without hardly affecting the temperature of the Earth. ( it would cut down on global warming, anyway…)
Given a somewhat more efficient antimatter production method that we currently use today, we would pretty soon have tonnes of the stuff.
Enough to fuel the ships to the stars that many dream of.
SF worldbuilding at
http://www.orionsarm.com/main.html
fuction?
I mean science fiction…
heh heh…
There are cosmological models where there are equal amounts of matter and antimatter divided into regions of galaxies and antigalaxies, however there is no known mechanism that could keep these regions apart and if this model was correct we expect to see copious amounts of gamma rays from the places where these regions meet, but we don’t.
Is antimatter actually a thing then or is it nothing? Would nothing be antimatter or the complete absence of both matter and antimatter?
Antimatter is pretty mcuh like normal matter, as QED siad above the only reasonb why we christian on sort matter and the other sort antimatter is due to their relative abundances.
The obvious proponent of such theories was Hannes Alfven. In his version, even adjacent stars within a galaxy were supposed to be of opposite type. His explanation for why we don’t see the annihilation at the boundaries between stellar systems was some handwavy plasma physics interaction which was meant to set up some equilibrium between the matter and antimatter at the join. (Granted, Alfven won his Nobel for his work in plasma physics, so his intuition about such things was unparalled, but it still reads like handwaving to me.)
All ancient history and an idea that never convinced anyone. Except to note that humanity currently happens to be carrying out the ultimate direct test of whether adjacent stars are matter or antimatter. Even if Alfven-style boundaries exist, the two Voyager spacecraft are approaching the points where they’ll run into stuff from our neighbouring stars. If that’s (predominately) antimatter, it’ll be bloody obvious very soon.