# Where does other energy go when matter and antimatter annihilate?

1. Aug 13, 2011

### cyborg6060

If a particle has a certain potential energy then collides with its antiparticle, releasing energy according to $E=2mc^2$, what happens to the PE of the two particles?

Let's say that a particle has a gravitational potential energy of X, wouldn't the antiparticle need to have a GPE of -X in order to preserve the conservation of energy? Wouldn't that imply that antimatter is repelled by gravity?

Thanks for the help.

2. Aug 13, 2011

### cmb

Mesons and gammas.

Electrons and positrons produce [only] two directionally-opposite 511 keV gammas (their rest-mass energy).

I expect gravitational energy is all wrapped up in the rest-mass energy equation, somehow. There again, you can expect a symmetrical expulsion of mesons also from more massive reactions, so I guess the answer is that a half of the energy heads down the gravitational field and a half up it, so no net change to any gravity considerations, perhaps?

3. Aug 13, 2011

### Staff: Mentor

The resulting photons have a gravitational PE also. (In spacetimes where energy is conserved)

4. Aug 13, 2011

### cyborg6060

So what would happen to other energies, such as kinetic energy? Let's say two antiparticles collide with certain velocities, v; where would their KE manifest itself after annihilation?

5. Aug 13, 2011

### Staff: Mentor

In greater energy of the products. In fact, that is essentially the whole point of building high energy colliders.

6. Aug 13, 2011

### Superstring

The photons would have greater energy.

7. Aug 13, 2011

### CDCraig123

I was under the impression when matter and anti matter meet it is simply a conversion of matter to energy 100% much like a nuclear bomb while a atomic bombs conversion rate of like 0.02 % matter to energy not really sure on the numbers. A matter anti matter explosion would leave nothing but energy. And if you are wondering what happens to any gravitational potential energy if there is no matter there is no gravity and i think you have to have at least 2 bodies to have gravitational potential energy so it would just be returned to the other body. If two rocks made of matter are orbiting one an other, and one is stuck by a anti matter rock all the stored gravitational potential energy would be given to the reaming rock. Or if you had a lb 10 ball of matter and a 10lb ball of anti matter moving at 50 km/s when they meet and exploded the explosion would take into account that gravitational potential energy and the explosion would have a velocity of 25 km/s in the direction that the anti matter ball had been moving at 50km/s before they collided relative to space around it. We would have a hard time seeing this as it would be in the middle of a explosion. At the end of the day no energy/matter has been gained or lost everyone is happy unless i am totally crazy and wrong and i could be.

P.S. there is anti matter on planet earth and i have not heard of any anti gravity properties as that would be amazing, awesome and would make some sense of the universe.

8. Aug 13, 2011

### Superstring

This is true for particles that annihilate at rest. Conservation of energy demands that any kinetic energy that the particles had before they annihilated must remain, i.e. if a positron and an electron came together with 1 unit of kinetic energy each, then the two resultant photons after annihilation will each have energy of mc²+1 units where m is the mass of either the positron or electron.

This is not true. Photons (which have zero mass) are effected by gravity.

Yes, this is true.

This makes absolutely no sense. What actually happens is that the products of the annihilation still have potential energy (with respect to the other rock, in your example).

I really have no idea what this example has to do with gravitational potential energy. What you described is an example of conservation of momentum (at non-relativistic speeds).

Not long-term. Once it appears it is annihilated almost immediately, though there is some small amount on (or in) Earth at any given time.

I'm not really sure what that has to do with anything, but antimatter does not have negative mass so it wouldn't result in "anti-gravity." What it has is the opposite charge to its matter counterpart.

Last edited: Aug 13, 2011
9. Aug 13, 2011

### diazona

I was actually just reading something today that says that's not necessarily true. According to the article, although antimatter does have positive (inertial) mass, we've never created enough to actually check that it responds to gravity in the same way as normal matter.

10. Aug 13, 2011

### Staff: Mentor

I have never understood this phrase. What is this unembodied energy that matter is supposed to be transformed into? Generally matter is converted into photons or other bosons.

11. Aug 13, 2011

### Superstring

Thank you for the read. An edited version of my earlier statement should be: "There is no evidence at this time to suggest that antimatter responds to gravity any differently than matter."

12. Aug 13, 2011

### CDCraig123

i said
And if you are wondering what happens to any gravitational potential energy if there is no matter there is no gravity

and you said
This is not true. Photons (which have zero mass) are effected by gravity..... really..

I said no mass no gravity are you going to tell me that Photons have gravity?
If photons have gravity they has mass.
If photons do not have mass they do not have gravity.

witch of these answers is true?

Everything else i said are simple examples of how i could answer the guys question perhaps you could build on something i said or something else said i like building because it takes people places. Telling use your opinion not if you think we or i am right or wrong not trying to be rude :)

13. Aug 13, 2011

### diazona

Well, I'm not Superstring, but...
Yes.
Neither of those statements is true. Photons have zero mass, but they are affected by gravity, and general relativity predicts that they do attract other bodies gravitationally.

14. Aug 13, 2011

### Staff: Mentor

Really, really. Even in Newtonian physics massless particles will be accelerated by gravity.

Yes. Not only are they affected by gravity they can produce a gravitational field. Google pp-wave spacetime.

This is not correct. The source of gravity is not mass. It is the stress energy tensor, which is non zero for light.

15. Aug 13, 2011

### CDCraig123

Photons are effected by Gravity but only indirectly. Any mass creates a gravitational field which warps space-time around it. Photons travel through space-time as light in a straight line (as a energy carrier). If space time warps to the left so do the photons passing though it. So gravity warps space-time and space-time effects lights passing through it. This is how photons can be effected by gravity indirectly and still have zero mass.

16. Aug 13, 2011

### D H

Staff Emeritus
CDGraig123: Read the last line of DaleSpam's last post very carefully. Dale is correct, you are not. The source of gravity is the stress energy tensor, not mass. A bucketful of photons (a mirrored bucket full of photons) can act as a gravitational source.

17. Aug 13, 2011

### CDCraig123

The stress-energy tensor is the source of the gravitational field in the Einstein field equations of general relativity, just as mass is the source of such a field in Newtonian gravity. Now I wonder where gravity comes from in string theory so now that I have researched more theory I will do what so many fail to do. I do not know for sure where gravity comes from.

Oh I forgot Quantum gravity theory in my list of ideas of where gravity comes from.

Last edited: Aug 14, 2011
18. Aug 14, 2011

### CDCraig123

Its interesting you ask that I really love questions like this (the kind with no real answer). I would guess anything that was not matter but was energy or that could carry energy like a photon. I am sure there would be some form of radiation and lots of heat. The only real world thing I can draw on is a PET scan. A PET scan an injection of Positrons or (anti-electrons) into your blood stream. When positrons meet with electrons in your brain they annihilate one an other, turning into energy and a Gamma ray witch the scanners pick up. This makes a image of your brain. I am really digging deep on this one, as I have no idea if Positrons would react like anti matter will when it is introduced with it's opposite charged counter part. In other words if i had to guess a matter anti matter explosion would be a big gamma ray heat bomb you wouldn't wanna be in the same room. :) :) :)

19. Aug 14, 2011

### A.T.

Photons are affected by Gravity in the same way as all objects. The acceleration of an object due to gravity is independent of object's mass, in both: Newtonian Physics and General Relativity.

All free falling objects travel through space-time in a straight line, or geodesic.

20. Aug 14, 2011

### CDCraig123

21. Aug 14, 2011

### WannabeNewton

As DaleSpam already clarified, it is not just mass but the Stress - Energy tensor which is coupled to the gravitational field. This means that energy density, energy/momentum flux, and pressure all contribute to non - zero curvature. I should point out that objects only travel in straight lines locally in an arbitrarily curved space - time while in free fall. A geodesic is the straightest possible path in curved space - time as two geodesics can still converge/diverge globally even if they start out parallel.

22. Aug 14, 2011

### Staff: Mentor

The same is true of massive particles. In your description Newton's apple falling from the tree is affected by gravity only indirectly. The falling apple travels through spacetime in a straight line. If spacetime warps to the left so does the apple passing through it.

23. Aug 14, 2011

### Staff: Mentor

Exactly, so the products of the anhilation reaction are a pair of gamma rays i.e. a pair of photons. If the original positron and electron have a high KE then the resulting photons will have a higher energy also. Since they originate at the same location as the positron and electron they will also have the same gravitational PE as the original positron and electron. Energy is conserved across a particle creation/anhilation reaction.

24. Aug 14, 2011

### Dotini

Apparently some quantity of antimatter is permanently trapped in a magnetic belt around Earth. Some folks may already be scheming to harvest its energy!

http://www.bbc.co.uk/news/science-environment-14405122
http://www.niac.usra.edu/files/studies/final_report/1071Bickford.pdf

A thin band of antimatter particles called antiprotons enveloping the Earth has been spotted for the first time.

The find, described in Astrophysical Journal Letters, confirms theoretical work that predicted the Earth's magnetic field could trap antimatter.

The team says a small number of antiprotons lie between the Van Allen belts of trapped "normal" matter.

The antiprotons were spotted by the Pamela satellite (an acronym for Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) - launched in 2006 to study the nature of high-energy particles from the Sun and from beyond our Solar System - so-called cosmic rays.

The new analysis, described in an online preprint, shows that when Pamela passes through a region called the South Atlantic Anomaly, it sees thousands of times more antiprotons than are expected to come from normal particle decays, or from elsewhere in the cosmos.

Dr Bruno said that, aside from confirming theoretical work that had long predicted the existence of these antimatter bands, the particles could also prove to be a novel fuel source for future spacecraft - an idea explored in a report for Nasa's Institute for Advanced Concepts.

Respectfully submitted,
Steve

Last edited: Aug 14, 2011
25. Aug 14, 2011

### cmb

Fascinating!! Thanks for those links! I'd not have expected that.