# Is antimatter a theory or does it exist?

1. Aug 13, 2008

### azzkika

Is antimatter a theory or does it exist??

Does antimatter really exist?? if so, what is it made of, if not matter?? and is it subject to the same laws as normal matter?? i personally cant see how it is possible. in another thread i read that in a void where there is nothing it is possible for matter to emerge from nothing as long as an equal amount of antimatter emerges.

i know this is a theory, but has it ever been observed??

i personally think the mass and energy of the universe is unchangeable, but as ever there are differing opinions on this. for it to be unchangeable the antimatter theory must be incorrect as antimatter if it did exist could be composed of antimass, as anything that exists requires mass no matter how small. even light has mass, just a very very very small mass per photon.

2. Aug 13, 2008

### ZapperZ

Staff Emeritus
Re: Is antimatter a theory or does it exist??

Er... antimatter a "theory"? What do you think they have been colliding at the Tevatron all these years? Or even at LEP before it went away? And guess what the "P" in PET scan means that is now used in many medical procedure?

Zz.

3. Aug 13, 2008

### Staff: Mentor

Re: Is antimatter a theory or does it exist??

We define anti-matter as particles that have opposite charge to the particles (proton & electron) that constitute the matter (atoms) of which we and our environment is composed.

See - http://hyperphysics.phy-astr.gsu.edu/hbase/particles/antimatter.html

The positron (positively charged electron) is the anti-particle of the electron, and the anti-proton (negatively charged proton) is the anti-particle of the proton.

4. Aug 14, 2008

### Hertyque

Re: Is antimatter a theory or does it exist??

I like your thinking. Matter and antimatter are made of the same stuff. It's just that they are in different configurations. Giving antimatter the opposite charge of what we consider to be matter.

Its this charge difference that allows matter/antimatter collisions to occur with little to no need for force(like trying to fuse protons).

5. Aug 14, 2008

### D H

Staff Emeritus
Re: Is antimatter a theory or does it exist??

Of course it does. You are mistakenly thinking that antimatter means negative mass. An anti-electron (aka a positron, the P in PET) has the same mass but exactly the opposite charge as an electron. The same goes for anti-protons: same mass but opposite charge as a proton.

You are entitled to your own opinions, but not your own facts. The fact is that mass and energy are interchangeable. The US used this fact to its advantage to end World War II against Japan. Were this fact not true, the Sun couldn't shine. The photons in the sunlight are mass converted to energy in the center of the Sun by means of nuclear fusion.

No, it doesn't. Photons are massless.

6. Aug 14, 2008

### mathman

Re: Is antimatter a theory or does it exist??

One point that has not been made. Charge is not the only factor in matter antimatter difference. Neutrons have anti-neutrons, although both are uncharged.

7. Aug 14, 2008

### Staff: Mentor

Re: Is antimatter a theory or does it exist??

I did leave out neutrals, which also have their anti-matter partners.

Perhaps this will help - http://www2.slac.stanford.edu/vvc/theory/hadrons.html

The baryons have (qqq), where q is a quark (u, d, s), while their anti-particles are ($\bar{q}\bar{q}\bar{q}$).

http://www2.slac.stanford.edu/vvc/theory/antiquarks.html

Last edited: Aug 14, 2008
8. Aug 14, 2008

### humanino

Re: Is antimatter a theory or does it exist??

Photons as defined by QED. Otherwise, you can not rule out an unobservably small photon mass. This is actually very convenient, because you can make your calculations with a tiny photon mass, forgetting about gauge invariance, and set the photon mass to zero at the end of the day will not spoil your result.

Exchange all quantum numbers in general should do the trick. Electric charge, color charge, weak charge, helicity...

9. Aug 14, 2008

### Staff: Mentor

Re: Is antimatter a theory or does it exist??

That's not a good example, because neutrons are composed of quarks, which are individually charged, with the total charge being zero. An antineutron is composed of the corresponding antiquarks, which each have the opposite charge to their respective quarks, with the total still being zero.

A better example would be the neutrinos, which are fundamental particles as far as we know, and which have antiparticles.

10. Aug 15, 2008

### azzkika

Re: Is antimatter a theory or does it exist??

i asked the question because i read somewhere that anti matter explodes upon coming into contact with normal matter therefore we dont have any. obviously i am wrong. thanks for informing me. lol

and i cannot believe photons are massless as they exist. i believe they are just so light as to be almost unmeasurable and when coming into contact with other mass an equal weight is dispersed by reflection / refraction etc. hence all things dont lose or gain mass from light.this is only as i cant believe a thing can have zero mass and exist, (apart from a void or a vacuum i suppose).

Last edited: Aug 15, 2008
11. Aug 15, 2008

### Alfi

Re: Is antimatter a theory or does it exist??

If you are wrong then so is the Star Trek propulsion system. hehehe

12. Aug 15, 2008

### ZapperZ

Staff Emeritus
Re: Is antimatter a theory or does it exist??

Luckily, physics is typically verified not simply based on beliefs, but experiment. Till you can show an experimental evidence that photons have a non-zero, detectable mass, then your belief has no foundation.

And a photon isn't a "thing", the same way "kinetic energy" isn't a thing.

Zz.

13. Aug 15, 2008

### Alfi

Re: Is antimatter a theory or does it exist??

When I Google 'is a photon a thing' , I get sent right back to here. https://www.physicsforums.com/showthread.php?p=1749537

Lightarrow says: (post #45)
"The subatomic particle that carries the electromagnetic force and is the quantum of electromagnetic radiation. The photon has a rest mass of zero, but has measurable momentum, exhibits deflection by a gravitational field, and can exert a force. It has no electric charge, has an indefinitely long lifetime, and is its own antiparticle."

Sounds like a 'thing' to me. If not, in gravitational lensing, What is getting lensed?

14. Aug 15, 2008

### D H

Staff Emeritus
Re: Is antimatter a theory or does it exist??

Antimatter and matter do annihilate one another upon coming into contact, and that is exactly why we don't have (much) antimatter around us. That is also exactly how positron emission tomography works. Carbon-11, nitrogen-13, oxygen-15, and fluorine-18 decay via positron emission into other kinds of nuclei. For example, carbon-11 decays into boron-11 with a half-life of about 20 minutes. The positrons emitted from the decay don't live very long. As soon as they meet up with electrons the positrons and electrons annihilate one another. The PET scanner detects the gamma rays that result from this annihilation.

15. Aug 15, 2008

### blechman

Re: Is antimatter a theory or does it exist??

Statements like this give me that same, terrible feeling as you get when you scratch your nails against a chalkboard! It's not azzkika's fault, or anyone's fault I suppose, but it's sad that this kind of logic pushes into the public forum, and leads people to spectacularly false conclusions.

The problem, azzkika, is scale! If you take an electron and a positron (antielectron) and throw them together (slowly so kinetic energy is irrelevant), then out would come two photons, with a total energy of 500 keV (500,000 electron-volts). 1 eV is about $10^{-19}$ Joules, where 1 Joule is (roughly) the energy of a 1kg weight moving at 1 m/s. As you can see, this hardly qualifies as an "explosion!"

However, let's say you're not talking about a SINGLE electron or positron, but let's say you have a CHUNK of matter and antimatter, like a gram or more. There are something like $10^{27}$ electrons in a gram, so when you multiply it out, it suddenly becomes quite a LARGE explosion!

But you see, there are no antimatter chunks around here! So this kinda thing just doesn't happen. And it would be near impossible to make a chunk of antimatter that large, just because it wouldn't be stable in our matter-dominated universe! That is, it would fall apart before it ever got that big.

Antimatter explosions are PURE science fiction!!

This issue of scale is very important in physics! This same kind of logic leads people to protest outside our national labs because we're gonna make "black holes that will swallow up the universe!" Er....

NO!

16. Aug 15, 2008

### Alfi

Re: Is antimatter a theory or does it exist??

Thank you blechman.

I know your reply was to azzkika, but I want to thank you for the answer anyway.
Clear and understandable to people like me with far more curiosity than knowledge.

I grew up on Sci-Fi and have seen so many of the 'impossible' things become reality that it blurs the distinction between what is, and what can or cannot be.

Even during the emergence of the 'big bang' ? I was sort of under the impression that such energy was in part an explanation for the expansion phase ( inflation ? ) and the subsequent universe we have today.
Or is that just more Science fiction?

That statement sounds simple and correct also.

( don't go into detail please. I don't want to hijack the thread topic. ) Just curious.

Last edited: Aug 15, 2008
17. Aug 15, 2008

### blechman

Re: Is antimatter a theory or does it exist??

The issue is what you mean exactly by 'impossible'!! I would claim that creating a macroscopic nugget of antimatter is quite impossible by today's standards, strictly from an engineering standpoint, and that it's certainly not what's happening at particle detectors (which I know is not what you suggest, but I just want to clear that up).

without going into details at all (there are a few issues with this statement you made, but I don't want to get into that here): I should have been more careful and say that such things are impossible TODAY (when the universe has cooled off considerably since the inflation epoch.

Referring to azzkika's statement: I take issue with the colloquial use of the word explosion - one thinks of an atom bomb going off! Not the case in any practical sense. People hear the word "matter" and "antimatter" in the same sentence and they think: "OH G-D, the universe is gonna explode!!" This is the myth I was trying to debunk. Just because one matter particle meets one antimatter particle in a bar, doesn't mean the big bang is going to repeat itself!

details avoided as much as possible.

I'm sorry to sound so jaded (I'm trying very hard not to sound offensive), it's just that it is very important to keep this notion of size and scale in mind when talking about these things - I have had sooo many people come to me asking about super-explosions at Fermilab since there is "matter-antimatter collisions" there, it's just hard not to have my blood pressure go up! It's not that it's anyone's fault, it's just that the general public isn't correctly informed about what's really going on. I hope this little rant, as silly as it might be, helps people to see my point.

ADDED: I also don't mean to "hijack the thread" - I"m sorry if that's what I ended up doing.

18. Aug 15, 2008

### Alfi

Re: Is antimatter a theory or does it exist??

Consider me as one of the 'general public' and again, I thank you for helping us update our views.

I understand your point. Please don't implode our planet. hehehe Arrrrrgggg ! Ya I see the frustration.
Keep the blood pressure in check, and persevere. We need you.

19. Aug 15, 2008

### ZapperZ

Staff Emeritus
Re: Is antimatter a theory or does it exist??

It depends on what you mean by a "thing". Would the OP consider this as a thing as well? After all, he/she found it difficult for a "thing" to have no mass. Do you also consider "kinetic energy" to be a thing? After all, it has "energy", can do work, and in many cases, can be measured. Is this consistent with what you call a "thing" like the pen on your desk?

Zz.

20. Aug 15, 2008

### Alfi

Re: Is antimatter a theory or does it exist??

Do you also consider "kinetic energy" to be a thing?

No, Because the statement is not complete to me. The kinetic energy... of this thing, is the complete statement.

If we can detect a single (thing) proton. It becomes a thing to me with all the attributes of a thing for that reason. One of the attributes to the thing may be Kinetic energy, but the attribute is not the thing in itself.

Does kinetic energy get lensed in a gravity field?