What happens when a particle and an anti particle collide

[robertjford80]

This is from Lisa Randall's Knocking on Heaven's Door:

acceleration is simpler since the same magnetic field can be used to direct protons and antiprotons in opposite directions. But the most important reason has to do with the particles that could be produced.
Particles and antiparticles have equal masses but opposite charges. This means that the incoming particle and antiparticle together carry exactly the same charge as pure energy carries—namely, nothing. According to E = mc^2, this means that a particle and its antiparticle can turn into energy, which can in turn create any other particle and antiparticle together, so long as they are not too heavy and have a strong enough interaction with the initial particle-antiparticle pair.

So when particles and antiparticles collide they get converted into pure energy. I've always thought of energy as what causes particles to move, for example, a billiard ball with X joules can transfer that kinetic energy to another billiard ball on collision causing it to move. Correct me if I'm wrong. What happens then to the surrounding area when particles and antiparticles collide and annihilate? Does it cause the particles around them to move?

 

[Simon Bridge]

Everything is energy - including matter.
Randall means that the particle and anti-particle's mass gets converted into a photon.
That entire passage seems quite confused. eg. particles and antiparticles don't have to be opposite charges - they don't even need to be different particles.
E=mc² means that energy and matter are just different ways of describing the same thing.

 

[Bill_K]

Robert, You're right, there's no such thing as "pure energy", energy must be carried by one or more particles. The point is that after the collision there is plenty of energy available, and what happens is the next step:

which can in turn create any other particle and antiparticle together, so long as they are not too heavy

The energy is distributed to the new particles that have been created.

 

[robertjford80]

The energy is distributed to the new particles that have been created.

Good, that clears up a misunderstanding on my part.

 

[Darwin123]

Everything is energy - including matter.
Randall means that the particle and anti-particle's mass gets converted into a photon.
That entire passage seems quite confused. eg. particles and antiparticles don't have to be opposite charges - they don't even need to be different particles.
E=mc² means that energy and matter are just different ways of describing the same thing.

Correct. For that reason, particles other than photons can be formed when a particle and antiparticle collide.

Particles other than photons can form in a particle-antiparticle annihilation.At high energies, all sorts of particles form in any particle-antiparticle collision.
Low energy collisions between positrons and electrons form photons only. This is because electrons interact only through their electromagnetic field. Therefore, neutrinos are unlikely even though they require low energy. Nucleons are something else.
A nucleon and and antinucleon can form almost any type of particle even at low energies when they annihilate. This is because nucleons interact via several types of field. They interact by the electromagnetic field (photons), the strong field (gluons) and the weak field (W-particles). Hence when two nucleons interact, they can form photons, mesons and paired baryon-antibaryon pairs.
At high kinetic energies, almost any particle can form in particle-antiparticle annihilation.
Here are some links to nucleon-antinucleon reaction.

http://iopscience.iop.org/1402-4896/5/3/003
A Comment on Nucleon-Antinucleon Annihilation and the Possibility to Determine the Spin for Resonances in the Direct Channel of This Process
by Lars Brink, Physica Scripta Number 1, July 2012 (015001-015801)
Abstract
“The process of nucleon-antinucleon annihilation into pions is considered from the point of duality. The possibility of measuring the spin of an intermediate resonance is discussed.”

http://prola.aps.org/abstract/PR/v119/i4/p1390_1
“Pion Multiplicity in Nucleon-Antinucleon Annihilation
Bipin R. Desai
Phys. Rev. 119, 1390–1394 (1960)
Abstract
In the annihilation problem we have considered the influence of the Ball-Chew model, according to which, at low energies, only a few of the eigenstates of the nucleon-antinucleon system need be considered. The effect of the selection rules that forbid certain pion multiplicities is thereby examined. The energies considered are 50 Mev, 140 Mev, and 0 Mev in the case of protonium—the bound system of a proton and an antiproton.”

http://prola.aps.org/abstract/PR/v135/i5B/pB1186_1
SU3 Invariance in Nucleon-Antinucleon Annihilation
by Tanaka, Phys. Rev. 135, B1186–B1190 (1964)
Abstract
“The relations among the amplitudes for nucleon-antinucleon annihilation into two mesons, and also those for annihilation into a baryon-antibaryon pair and a decuplet-antidecuplet pair, are obtained on the basis of SU3 invariance.”

In principle, a positron-electron annihilation may form neutrinos. However, electrons do not interact very strongly via the weak force. They interact through their electromagnetic force. So the formation of neutrinos is predicted to be very rare at low energies. At high energies, mesons form. However, I don't know if you want to call this particle-antiparticle annihilation.

http://en.wikipedia.org/wiki/Electron–positron_annihilation
Electron–positron annihilation
“Since neutrinos also have a smaller mass than electrons, it is also possible—but exceedingly unlikely—for the annihilation to produce one or more neutrino–antineutrino pairs. The same would be true for any other particles, which are as light, as long as they share at least one fundamental interaction with electrons and no conservation laws forbid it.
f either the electron or positron, or both, have appreciable kinetic energies, other heavier particles can also be produced (such as D mesons), since there is enough kinetic energy in the relative velocities to provide the rest energies of those particles. It is still possible to produce photons and other light particles, but they will emerge with higher energies.”

 

[Karimspencer]

Yes this is what e=mc2 is , the matter that is equivalent to energy can be turned into energy only if it's collided with an anti-particle.
However, if the mass of the matter is huge, it can give out lots of energy!

 

[EskWIRED]

Yes this is what e=mc2 is , the matter that is equivalent to energy can be turned into energy only if it's collided with an anti-particle.
However, if the mass of the matter is huge, it can give out lots of energy!

Does that energy warp spacetime to the same extent that the former mass once did?

 

[Cadaei]

A boom.

 

[Simon Bridge]

Yes this is what e=mc2 is , the matter that is equivalent to energy can be turned into energy only if it's collided with an anti-particle.

Not just for annihilation:
http://en.wikipedia.org/wiki/Binding_energy#Mass-energy_relation
... it shows up all the time.

However, if the mass of the matter is huge, it can give out lots of energy!

Considering the scale factor is of order 10¹⁷ this "huge" amount of matter need not be all that huge.
Releasing the energy of one gram of matter is equivalent to about 22 tons of TNT.
Consequences of an open-air blast of 1kg of TNT.

Does that energy warp spacetime to the same extent that the former mass once did?

Depends - if all the energy is still in the same space then of course it does: this situation is what mass is. If the energy is more diffuse then it has less effect - just like if you have a more diffuse distribution of matter.
But what you are trying to ask is answered in this Q&A:
... a box of photons will indeed cause as much gravity as a box of coal with the same total energy.

 

[Karimspencer]

Yes Simon , you are right , however considering that it's kinda of hard to get 1 gram of anti-matter, 1 gram can be considered huge by that logic...

 

[Simon Bridge]

:) I didn't say anything about antimatter - that's one gram of any matter.
But you did say "with an antiparticle" so I'll give you that one.

(That 1g lump annihilated with antimatter would come out as 44T of TNT btw)

 

[Karimspencer]

Oh ok :)
Is it possible for labs to make 1 kg of anti-matter to collide with 1 kg of matter?

 

[Simon Bridge]

I think it's possible in principle - just very very difficult.
I understand that antihydrogen has been made and the difficulty now it to slow it down enough for study.

Large quantities of antimatter do exist in nature though.

 

[Karimspencer]

I know what i am going to say now is irrelevant but my quote button is blocked and i can't quote anybody , how can i use it ...

 

[Simon Bridge]

You can quote by cutting and pasting - and just writing in the quote tags.
You should be able to quote people - if this keeps up, flag a admin.

(but if you mean the radio-button, in "options", below the quick-reply box, that don't work for me neither.)

 

[Karimspencer]

thanks

 

[Karimspencer]

"I think it's possible in principle - just very very difficult."
You make perfect sense, thanks ...

 

[L-x]

"I think it's possible in principle - just very very difficult."

very very difficult is an absurd underestimate. Producing and containing 1kg of antimatter is "possible in principle" in the same way that counting every particle in the observable universe is "possible in principle".

 

[Karimspencer]

"Producing and containing 1kg of antimatter is "possible in principle" in the same way that counting every particle in the observable universe is "possible in principle""

Scientists have found ways to calculate the number of atoms in the universe. I am guessing you can do so by finding the average volume of the atom and the volume of all matter in the observable universe(planets, stars...) and then you can divide the volume of that matter by the average volume of the atom to find the number.
I might be wrong and you must consider a lot of other things.

 

[L-x]

Scientists have indeed, and you're thinking along nearly the right lines: cosmological observations allow scientists to make a reasonable estimate of the energy density of matter in the universe, and calculating the volume of the observable universe is straightforward (though interestingly, due to the expansion of the universe, that volume isn't just 4/3 pi (age of universe times c)^3). In fact it's calculations like this which have lead to conclusions that the universe is full of mysterious "dark matter", because when cosmologists predict how much "stuff" we should be able to see, they get an answer that's about 5 times bigger than what we can actually observe through telescopes.

I didn't say calculate though. I said "count", as in getting the exact number. All I meant (in a slightly silly way, admittedly) is that someone obtaining that much antimatter is not going to happen in the remotely foreseeable future.

 

[Karimspencer]

I know ... it's unpractical and unreasonable how ever it's known that there are 2 * 10to the power 78 atoms in the universe.

 

[Karimspencer]

That's just an estimate

 

[Karimspencer]

And you don't find the volume of the universe , you have to find the volume of the matter in our universe.

And only 0.0000000000000000000042 % of the universe consists of matter.

 

[mfb]

And only 0.0000000000000000000042 % of the universe consists of matter.

This number is wrong by a factor of about 10^21 (source: The Cosmic Energy Inventory). This is approximately the same difference as between the size of a single atom and the orbital radius of earth.

 

[Karimspencer]

oh ok

 

[jnorman]

what about for virtual particle pairs created from the quantum foam? are they made from energy, and if so, where does this energy go? what is the difference between the particles made from virtual pair production and particles made from high-energy photons? thanks

 

[L-x]

And you don't find the volume of the universe , you have to find the volume of the matter in our universe.

And only 0.0000000000000000000042 % of the universe consists of matter.

I'd be fascinated to know how one could estimate the volume of matter in the universe without using the method I outlined above. I'd also be interested to know how you came up with that percentage.

 

[Karimspencer]

i googled it

 

[L-x]

what about for virtual particle pairs created from the quantum foam? are they made from energy, and if so, where does this energy go? what is the difference between the particles made from virtual pair production and particles made from high-energy photons? thanks

The technical difference between virtual and real particles is that virtual particle are "off shell" meaning that their mass energy and momentum does not satisfy the relation E^2 - P^2 = M^2, however virtual particles should be thought of as a sort of mental abacus that help us calculate things about interactions, rather than as real particles that just happen to have strange properties.

 

[mfb]

I'd be fascinated to know how one could estimate the volume of matter in the universe without using the method I outlined above. I'd also be interested to know how you came up with that percentage.

Volume is not a meaningful quantity here - most of the matter is very thin interstellar plasma of variable density, and the remaining part is mainly plasma in stars. Just a small fraction is solid.

How to estimate the matter density? Mainly: observe it. The total amount of matter is then given by a multiplication with the size of the observable universe.

 

[Simon Bridge]

Um - as interesting as working out how many atoms there are in etc etc isn't it a bit off topic? I intended my statement to be an absurd understatement :) Even attempting to manufacture, without bothering to contain, the mere 1g that was my example would be silly.

 

[L-x]

Volume is not a meaningful quantity here - most of the matter is very thin interstellar plasma of variable density, and the remaining part is mainly plasma in stars. Just a small fraction is solid.

How to estimate the matter density? Mainly: observe it. The total amount of matter is then given by a multiplication with the size of the observable universe.

That's precisely the point I was trying to make.