Antimatter & Gravity: Is it Repulsed by Matter?

[Robert Noel]

I'm watching a video on Youtube entitled "Angels and Demons - The Science Revealed" in which the topic of discussion is antimatter. During this video, the lecturer (from Berkeley) mentions that there are some who believe that antimatter would be repelled by the gravity produced by matter (in the video, he uses an "anti-apple" possibly falling up and away from our Earth as an example).

Is the idea of antimatter being repelled by the gravity of matter actually entertained by reputable physicists or is it considered nonsense? I think of gravity and acceleration being indistinguishable and wonder how an antiparticle could possibly care whether it is in the gravitational field of matter or antimatter. If antimatter is contained and put in a centrifuge made of matter and set to spinning, would it actually react differently than matter? Could it actually care if the centrifuge is made of matter or antimatter? And by the same token could it possibly care if it falls into the gravitational field of a planet or antiplanet (assuming gravity and acceleration are indistinguishable)?

 

[javierR]

Anti-gravitating matter (and anti-gravitation in general) is not a known part of our universe, though science fiction writers and cranks love talking about it. Antimatter, on the other hand, is a bit of a misnomer, because it is matter all the same, and so as you suspected the rules of gravitational interaction for antimatter are the usual ones. Every elementary particle of nature has an anti-particle (it can be itself, like the photon). The positron, e.g., is the anti-electron. In our universe, though, it turns out that anti-particles are vastly outnumbered by the "familiar" particles; and when anti-particles meet their particle partners, they annihilate. When electrons and positrons interact they result in photons. Anti-matter can also refer to the building of atoms made out of anti-particles: A positron and anti-proton form an anti-hydrogen atom. So while anti-particles/anti-matter are not really exotic in the theoretical structure of quantum field theories (they are a fundamental part of them afterall), they end up being exotic in the universe, and they result in annihilation when they meet up with our familiar particles, so imaginations can tend to take off.

 

[Robert Noel]

That's what I thought. That's why I was surprised to hear a lecturer from a university mentioning that while most believe that antimatter reacts to gravity generated by matter just as any matter does, there are those to think otherwise. He even mentions a possible experiment to test the idea, and I thought "is this guy nuts?" The video was allegedly produced by Berkeley University! Perhaps I was taking him in the wrong context (or he wasn't being very clear).

 

[strangerep]

[...] That's why I was surprised to hear a lecturer from a university mentioning that while most believe that antimatter reacts to gravity generated by matter just as any matter does, there are those to think otherwise. He even mentions a possible experiment to test the idea, and I thought "is this guy nuts?" The video was allegedly produced by Berkeley University! Perhaps I was taking him in the wrong context (or he wasn't being very clear).

One should perhaps keep in mind that it has not yet actually been verified
that antimatter gravitates the same way as matter. Last time I checked
(which is admittedly some years ago) people were hoping that if enough
antihydrogen could be produced under sufficiently controlled conditions
one might be able to do the experiment and answer the question properly...

But I'm not sure what the current status is.

 

[Bob S]

Anti-hydrogen is routinely being made at CERN:
http://alpha.web.cern.ch/alpha/
Scientists would like to measure the (anti) gravitational force of antihydrogen, but it will require (among other things) cooling to temperatures of a few millikelvins. At least, they have made the first entry on the table of anti-elements.

 

[Robert Noel]

But as I said, I can't help but think even proposing such an experiment would be ludicrous. Gravity is gravity no matter what the charges of particles (or the constituent particles of atoms) happen to be. Again, if matter of any kind is put into a centrifuge and is made to experience acceleration/false gravity (I believe it was Einstein who proved that gravity and acceleration are indistinguishable), you can't expect antimatter to react differently than matter. Antimatter must experience the same gravitational forces in a centrifuge as matter, regardless of the material the centrifuge is made of (if antimatter is contained in magnetic/electric fields, then the antimatter can not possibly care what kind of material the centrifuge holding the container is made of...it can only experience the spinning effect of the centrifuge) . Whether we put the antimatter container in a centrifuge or on a quickly accelerating train or rocket is irrelevant -acceleration is acceleration is gravity.To suggest that antimatter would react differently in a centrifuge than it would in the gravitational field of matter is to suggest that gravity and acceleration are NOT indistinguishable. I see that as a major flaw in any idea regarding "anti-gravitation" of antimatter, unless of course, Einstein had it all wrong...somehow, I doubt it.

Edit: The only zany sci-fi thing I could of that would suggest that antimatter would behave differently than matter in the gravity created by matter, and thus in a centrifuge, would be that antimatter experiences time in a different direction than matter, which is also ludicrous because it would mean that antimatter actually originated in the antimatter container and traveled toward the particle collision. 10lbs of matter, 10lbs of antimatter, doesn't matter (no pun intended)...it must surely all fall into any gravity well the same way...no?

 

[strangerep]

But as I said, I can't help but think even proposing such an experiment would be ludicrous. Gravity is gravity [...] you can't expect antimatter to react differently than matter. Antimatter must experience the same gravitational forces in a centrifuge
as matter [...]

Unfortunately, there is currently no experimental evidence in support of your assertions.
We simply don't yet know the answer.

 

[Robert Noel]

Well, I just can't logically accept that if we put antimatter on a train and quickly accelerate the train, the antimatter is going to want to shoot forward in the direction of travel and compress against the front side of the container, exhibiting anti-gravity...or would it be anti-inertia?

If there were a galaxy of stars made of antimatter, and antimatter did exhibit such a strange phenomenon, would the spinning of the galaxy not make it want to compress inward rather than spiral outward? You can't have it both ways...if antimatter only gravitates toward antimatter, then centrifugal forces would also, by axiom, have on antimatter an opposite of the effect we observe with matter since it exists in our spacetime, and not some antispacetime .

Fun to think about though eh?

 

[aggy]

There is no anti gravity, there is also no anti gluons or anti photons, end of story.

 

[Dmitry67]

there ARE anti protons!
http://en.wikipedia.org/wiki/Antiproton

There is an antimatter:
http://en.wikipedia.org/wiki/Antimatter

Quite expensive:
Antimatter is said to be the most costly substance in existence, with an estimated cost of $62.5 trillion per gram

 

[aggy]

learn to read and where can i buy a gram of antimatter?

 

[Dmitry67]

learn to read?
Did you check the "artificial production" chapter?
Antimatter is produced routinely, but in small quantities.

 

[aggy]

Yes learn to read, I put there are no anti photons NOT anti protons, What makes you think you know more about anti matter than me? Did you know that it is used everyday in hospital P.E.T scanners? Do you know anything about the "theoretical" mirror anti world? Do you know how many experiments can be carried out to prove or disprove its existence? Do you know how many of those experiments have been carried out and the results of those experiments? Do you know you should do a lot more research before bothering other people with your thoughts?

 

[aggy]

I think that the lecturer (from Berkeley) was meaning that if so much antimatter mass could be created that it formed an anti gravitational field then it could repel against gravity. That sounds feasible but would require a large amount of antimatter.
Your comments made about the formation of galaxy's are irrelevant in this universe, and your comment that antimatter only exists in our spacetime and not an "antispacetime" are only your opinion. There are 6 experiments that can be carried out to prove or disprove the existence of a mirror antiverse. All experiments involve analysing light from distant stars. So far 3 of these experiments have been carried out and all 3 experiments prove positive to the theory of a mirror antiverse. We don't yet have the capability of conducting the other 3 experiments. Therefore there is no reason to disgard the possibility of there being an "antispacetime" as you put it.

 

[aggy]

... would be that antimatter experiences time in a different direction than matter, which is also ludicrous because...

Co ordinate time is an easy thing to understand, you experience it everyday. Proper time isn't like that at all. http://en.wikipedia.org/wiki/Proper_time

Antimatter might experience time in a "different direction" than matter, who knows? but there is nothing ludicrous about the idea when time itself is quite ludicrous, just ask my friends.

 

[hamster143]

Without a doubt, there are good theoretical reasons to expect that antimatter gravitates in the same manner as normal matter ... however, one of the ways to move physics forward is to take untested assumptions / theoretical predictions and test them. There are equally good theoretical reasons to expect that all "regular" matter responds to gravity in the same way (a neutron, a proton, and an electron in a vertical vacuum tube would fall at exactly the same speed - the "weak equivalence principle"), and that did not stop physicists from expending effort to design more and more precise experiments to test these predictions, ultimately confirming them to within 1 part in 10¹².

 

[aggy]

I'm sure that antimatter reacts to gravity exactly the same as matter, but if a large enough antimatter mass was created so that it had its own gravitational field then that gravitational field might repel normal gravity. Being that the field was created by antimatter then it could have an opposing and repelling effect on gravity, but that is pure speculation... it is equally true that the gravitational field will react to gravity as normal gravity and both fields will attract, nobody would know until it is done. I'm pretty sure there's an antimatter experiment similar to this being done on the space station when it's operating.

 

[Vanadium 50]

You might want to take a look at the guidelines on overly speculative posts.

 

[aggy]

I agree that 2+2=4 .
If everything is known about a subject then the answer is obvious, maths is obvious, if not everything is known about a subject then how can you give a precise answer, a lot in particle physics is speculation so what makes you so sure the answer is 4?
I said it is equally likely that an anti gravity mass will repel gravity as it will attract, so there are 2 equal possibilities or are you saying there is only 1 possibility, now THAT's speculation!

I wonder if its possible to discuss anything in physics forums without somebody throwing in this antagonising cut'n'paste:

Two plus two continue to make four, in spite of the whine of the amateur for three and the cry of the critic for five.