Gravitational force of antimatter

[murongqingcao]

Hi,

I have been confused about whether there is any gravitational force between antimatter as what have between matter...and also whether there is gravitational force between antimatter and matter?

Thanks
Ron

 

[Mark M]

Hi,

I have been confused about whether there is any gravitational force between antimatter as what have between matter...and also whether there is gravitational force between antimatter and matter?

Thanks
Ron

Hi Ron,

Remember, anti-matter is the same thing as matter, except with opposite characteristic (e.g. charge) , so that when they collide, they annihilate into a photon. So yes, they do have a gravitational pull.

 

[murongqingcao]

Hi Mark:

Thanks for the help...then how about between matter and antimatter...is there any gravitational interaction between them which follows the 1/r^3 law before they collide with each other?

Thanks
Ron

 

[Vanadium 50]

There is no 1/r^3 law. It follows the same 1/r^2 as matter does.

 

[DaveC426913]

Yes, as far as we know, gravitationally, matter and antimatter are interchangeable.

 

[K^2]

Yes, as far as we know, gravitationally, matter and antimatter are interchangeable.

Has anybody actually tried to verify this experimentally?

 

[alexg]

Has anybody actually tried to verify this experimentally?

Antimatter has been created and stored for as long as 16 minutes. If it did not react normally in a gravitational field, it would have showed up in the containment unit.

 

[K^2]

Antimatter has been created and stored for as long as 16 minutes. If it did not react normally in a gravitational field, it would have showed up in the containment unit.

That's a few ions in a magnetic trap. I'm not sure the magnetic trap is designed to measure weight of the ions at all, and if it is, how precise can it be? Got any refs that actually cite measured gravitational mass?

 

[alexg]

That's a few ions in a magnetic trap. I'm not sure the magnetic trap is designed to measure weight of the ions at all, and if it is, how precise can it be? Got any refs that actually cite measured gravitational mass?

I'm trying to find something on Cern's website, but so far all I've got is the press piece.

http://www.livescience.com/15270-physicists-weigh-antimatter-amazing-accuracy.html

Ah, here's the Cern piece.

http://press.web.cern.ch/press/PressReleases/Releases2011/PR10.11E.html

 

[K^2]

That's inertial mass, not gravitational.

P.S. I don't want to sound like a crazy person who thinks they are not equivalent. But it would be really neat to see an experiment showing that anyhow.

 

[DaveC426913]

Has anybody actually tried to verify this experimentally?

That's why I said 'as far as we know'. We haven't really made enough to easily do the experiment.

 

[murongqingcao]

Hi Guys:

Thanks for all the kind response...sorry for that r^3 mistake...it has been long since I touched the formula in school...

I am not a physics professional...my interest on the issue is from philosophical perspective...now based upon your responses I could assume that when a huge mass of matter and a huge mass of antimatter are near by, they would be pulled towards each other by the gravitational force like the one to pull matter into the black hole...and the force would follow the relation GmM/r^2...so an antimatter black hole could indeed merge with a matter black hole (that would be brilliant, right), since they don't push each other away but instead pull each other closer...that solves my confusion.


Thanks

 

[DaveC426913]

...when a huge mass of matter and a huge mass of antimatter are near by, they would be pulled towards each other by the gravitational force like the one to pull matter into the black hole...and the force would follow the relation GmM/r^2...so an antimatter black hole could indeed merge with a matter black hole (that would be brilliant, right), since they don't push each other away but instead pull each other closer...that solves my confusion.
Thanks

No. The moment any matter came into contact with antimatter they would annihilate in a burst of gamma rays. Depending on what masses we're talking about (maybe asteroids, maybe stars) the bodies might not even be solid, they might be gaseous. Which means they have an envelope of matter around them. The annihilation and gamma ray bursting might begin while the bodies are still some distance apart.

You would not get a black hole; they would not co-exist in the same place.

 

[murongqingcao]

Dave:

Thanks for the clarification about "The annihilation and gamma ray bursting might begin while the bodies are still some distance apart."...

By the way, I was not meaning that the matter and antimatter form a black hole together...I was saying that if there is an ANTIMATTER BLACK HOLE, and there is another MATTER BLACK HOLE...they might not be very close to each other...however, since black holes are of huge mass, so that there might be great pulling force between them because of the gravitation...based on your response, I guess we should say that when two such black holes are moving towards each other because of gravitational pull, the annihilation might happen before they are even physically close to each other (say, a few hundred lightyears away), right?

Thanks again

 

[mfb]

Black holes are easy to describe, you just need their mass (or energy), their charge and their angular momentum. There are no "matter black holes" or "antimatter black holes". Both are identical.
What they carry around outside their Schwarzschild radius may be different and depends on their origin, but that is a different story.

 

[K^2]

Well, the matter and anti-matter black hole would carry a whole bunch of opposite quantum numbers, but yes, they don't make any difference to the outside, and once the black holes merge, it's not like radiation has any better chance of escaping than matter. You really shouldn't see a difference.

 

[murongqingcao]

mfb/K^2:

Thanks for the response...as I understand that both of you are saying that no matter what are within the black hole, there is no longer any difference between antimatter or matter...anything pulled into a black hole become part of the mass and contribute to the charge and angular momentum...thanks for the clarification...

but this causes me another confusion...I have heard people questioning why our universe only has matter and no antimatter is observed...but based uopn your response, it seems that the answer could be as simple as that the missing antimatter are all in some black holes, right?

Thanks

 

[niklaus]

There is an experiment in the works at CERN that attempts to measure the effect of Earth's gravity on a antihydrogen beam. I don't think there are any results yet, but here is the website: http://aegis.web.cern.ch/aegis/home.html

 

[murongqingcao]

niklaus:

Thanks for the link...it seems that they are trying to confirm that the gravity between matter and antimatter would be the same as the gravity between matter and matter...let's wait and see what they would tell us...

however, based upon the response in this thread I feel that theoretically people believe that the gravity between matter and antimatter should be the same as what is between matter and matter, right?

Thanks

 

[niklaus]

Yes, it would be a big surprise if it wasn't the same, but we don't know for sure until we measured it.

 

[murongqingcao]

thanks...I guess if it is the same as expected then we might explain the disappear of the antimatter with the same amount of the mass as this current universe by assuming that they might be in some black holes since within the black holes there is no difference between antimatter and matter, right?

Thanks

 

[K^2]

but this causes me another confusion...I have heard people questioning why our universe only has matter and no antimatter is observed...but based uopn your response, it seems that the answer could be as simple as that the missing antimatter are all in some black holes, right?

Yes, it's a possibility. If there are a lot of primordial black holes out there, they can account for both fraction of dark-matter and matter-anti-matter imbalance. But it seems like we'd find some other evidence of this by now.

There are other mechanisms that are more likely. Super symmetry makes predictions about transition between matter and anti-matter. It's considered a standard mechanism, but so far, it's poorly supported by experiment.

Another possibility is purely geometrical. Antimatter propagates backwards in time. Now, it doesn't matter to the propagation of actual physical observable objects, but depending on what space-time was like at the big bang, it's entirely possible that excess anti-matter is "before" the big bang. Or in other words, effectively a twin universe expanding on the other side of it. It could also be more symmetric, with time layered like spherical shells. In either case, you'd end up with almost exclusively "matter" wherever you are, and all the "anti-matter" would be on the opposite side of the time-line.

There is an experiment in the works at CERN that attempts to measure the effect of Earth's gravity on a antihydrogen beam. I don't think there are any results yet, but here is the website: http://aegis.web.cern.ch/aegis/home.html

Thanks. That's exactly the sort of thing I've been looking for.

 

[murongqingcao]

K^2:

Thanks! Now I feel much clear about the issue!

 

[JamesOrland]

Another possibility is purely geometrical. Antimatter propagates backwards in time. Now, it doesn't matter to the propagation of actual physical observable objects, but depending on what space-time was like at the big bang, it's entirely possible that excess anti-matter is "before" the big bang. Or in other words, effectively a twin universe expanding on the other side of it. It could also be more symmetric, with time layered like spherical shells. In either case, you'd end up with almost exclusively "matter" wherever you are, and all the "anti-matter" would be on the opposite side of the time-line.

Now hold on a second. What do you mean antimatter propagates backwards in time? If that were the case, wouldn't CPT symmetry make antimatter exactly like matter? That is, wouldn't antimatter propagating backwards in time be... well, matter?

 

[DaveC426913]

thanks...I guess if it is the same as expected then we might explain the disappear of the antimatter with the same amount of the mass as this current universe by assuming that they might be in some black holes since within the black holes there is no difference between antimatter and matter, right?

Thanks

Well, simply proposing where it's hiding doesn't get us far. We need a plausible explanation of how it got there.

Antimatter propagates backwards in time.

This claim has come up on PF before. IIRC, anti-matter being time-reversed was a speculation put forth by Feynman, but it never went anywhere and sort of languished.

 

[JamesOrland]

This claim has come up on PF before. IIRC, anti-matter being time-reversed was a speculation put forth by Feynman, but it never went anywhere and sort of languished.

From what I understand, Feynman just proposed that maybe all electrons were a single electron that went all around through time and worked out mathematically what that would mean, and found out all the properties of a positron by accident.

 

[K^2]

This claim has come up on PF before. IIRC, anti-matter being time-reversed was a speculation put forth by Feynman, but it never went anywhere and sort of languished.

In QED and QCD, an anti-particle is represented by a time-reversed current. Furthermore, they carry negative 4-momentum. Now, whether this has any physical significance or not is an open question, but a backwards-propagation does properly describe the physics. That's what all our standard model particle physics is based on. This could be just a convenient description, of course. To any observable, it doesn't make a difference. Until you start dealing with stat-mech, time is just a parameter, and whether it's increasing or decreasing along the path of particular particle doesn't make any difference.

However, depending on geometry, that can make a difference at Big Bang. Consider a simple EP annihilation event at 0th order. You have electron coming in, emitting two photons at two vertices, and recoiling "back in time". Or, you can view this as a positron coming in and annihilating with electron. (But which vertex did annihilation take place at, hm?) Anyways, the reason for two photons emitted is conservation of angular and 4-momenta. Another way to conserve that momentum is to have electron leave in the same time direction. So electron comes in, electron comes out. We can simplify it to a single "vertex", which is now a 2-point function, lacking the photon, also known as the propagator. So it looks like an electron that simply buzzed through. Nothing interesting.

Now place that "vertex" at t=0 of Big Bang. Suppose, geometry is such that universe expands on both sides. So on both sides, you'd conclude that you are on t>0 side of the Big Bang. Entropy is increasing, so you must be moving forward in time, and the Big Bang is in the "past". However, the electron we threaded through to both sides is going with the time flow on one side, and against it on the other. (Again, actual direction is by convention, so the guys on the other side would say that we got it wrong, but whatever.) So you end up with matter and anti-matter split between two time lines.

Naturally, just speculation. I'm only mentioning it as a possibility. But it is a possibility that is entirely consistent with the standard model and General Relativity, and it does not require any bells and whistles from Symmetry or Strings.

 

[JamesOrland]

That looks beautiful, but if you take any inflationary universe scenario into account (esp. one that suggests eternal inflation), what would that make of t < 0? I mean, it looks like any t < 0 just means a time before our bubble became a true vacuum from a false vacuum state.

Unless, of course, you also propose a beginning to eternal inflation (as has been suggested) and claim that on one side we have eternal matterial inflation and on the other, eternal anti-matterial inflation. But... that sounds wrong :P

 

[murongqingcao]

how about a classic interpretation simply based upon the fluctuation theory of statistical physics as follows:

1) since it is said that the total mass of our current universe might be only one out of several billion of the total mass of the original matter and antimatter, it was indeed within the range of statistical fluctuation...which means that while most matter and antimatter were annihilated due to recollision after they were created, some small amount that were within the amount of the statistical fluctuation range were left before the universe started to inflated rapidly;

2) after the inflation, since the space started to expand due to dark energy, a few clusters from the initial statistical fluctuation started to depart from each other at great speed. One of the cluster formed the universe we are in today

3) as the expansion going on, the initial matter and antimatter clusters are so far away from each other that they would never meet each other again...

If this classic interrestation makes a bit sense...then it means that somewhere far away from us, there might be a antimatter universe in the same 4-dimensional space-time as ours, but we would never meet with them due to the space expansion.

how does this sound?

Thanks

 

[K^2]

Problem is that on largest scale, matter seems to be distributed in "strands" rather than isolated clusters. There is no clear separation that would allow for some areas to have just matter and others just anti-matter.

That looks beautiful, but if you take any inflationary universe scenario into account (esp. one that suggests eternal inflation), what would that make of t < 0? I mean, it looks like any t < 0 just means a time before our bubble became a true vacuum from a false vacuum state.

Unless, of course, you also propose a beginning to eternal inflation (as has been suggested) and claim that on one side we have eternal matterial inflation and on the other, eternal anti-matterial inflation. But... that sounds wrong :P

Not sure what you mean. I'm suggesting that its symmetric around t=0. If it's expanding ad-infinitum on one side, it does the same on the other. If it eventually collapses here, it does the same on the other side. If it pulses, then what I'm calling t=0, is just one of the nodes.

 

[JamesOrland]

According to the eternal inflation models, there is no t = 0. There was no big bang, no initial singularity. Instead we have an eternal inflationary universe, which may or may not possesses an initial singularity (t = 0) itself, and our universe (and I don't mean O.U., I do mean our whole Universe) is just a bubble within it, a true vacuum state in a huge false vacuum universe. Of course, our bubble is not unique in any way, just one in many. But under that logic, t < 0 means the time in the inflationary universe when our bubble still hadn't been made. So, there is no "node", no "vertex".

 

[murongqingcao]

Problem is that on largest scale, matter seems to be distributed in "strands" rather than isolated clusters. There is no clear separation that would allow for some areas to have just matter and others just anti-matter.

Thanks for the explanation...however, when you said that 'on largest scale, matter seems to be distributed in "strands" rather than isolated clusters' you were based upon the observation of matters...when there were some strands of matters and some strands of anitmatters (both of which was of course much bigger than our current universe) nearby, the very neighborhood would annihilated with each other and left some wide space between them so that the initial "strands" ended up as isolated clusters...and the radiation as the result of this kind of anihilation would be hidden among the initial cosmic background radiation so that we would not see any extra gamma rays...is that possible?

Thanks

 

[JamesOrland]

Thanks for the explanation...however, when you said that 'on largest scale, matter seems to be distributed in "strands" rather than isolated clusters' you were based upon the observation of matters...when there were some strands of matters and some strands of anitmatters (both of which was of course much bigger than our current universe) nearby, the very neighborhood would annihilated with each other and left some wide space between them so that the initial "strands" ended up as isolated clusters...and the radiation as the result of this kind of anihilation would be hidden among the initial cosmic background radiation so that we would not see any extra gamma rays...is that possible?

Thanks

No, it's not really possible. The models we currently have of the universe suggest that it is ergodic (homogenous), there are no huge gaps like the one you mentioned. On a very very large scale, if you looked at the Universe (and could see it, of course, we are ignoring the whole lightspeed limit) you would see a pretty smooth sea of stars, with no separation whatsoever between them, and with patterns repeating every 10^10^115 metres.

 

[murongqingcao]

No, it's not really possible. The models we currently have of the universe suggest that it is ergodic (homogenous), there are no huge gaps like the one you mentioned. On a very very large scale, if you looked at the Universe (and could see it, of course, we are ignoring the whole lightspeed limit) you would see a pretty smooth sea of stars, with no separation whatsoever between them, and with patterns repeating every 10^10^115 metres.

thanks for the response...

I don't know why it is said that the matter in our whole universe is only 1 out of several billions of the matter and anitimatter at the beginning the big bang...

However, if that is true, then our current whole universe is the small cluster in the sense of statistical physics fluctuation...and thus what we can see as the strands in this universe might not be used as the absolute base for reasonning out of the whole if there are some other clusters like our universe left from the big bang time...

we cannot use what we see within the cluster to reason for what is outside the cluster, right?

 

[JamesOrland]

I don't know why it is said that the matter in our whole universe is only 1 out of several billions of the matter and anitimatter at the beginning the big bang...

Um... I'm pretty sure that is not said. Maybe the matter in our Observable Universe is but a fraction of the matter present at the time inflation ended, but the whole universe is infinite (as far as most recent evidence points, mind you).

However, if that is true, then our current whole universe is the small cluster in the sense of statistical physics fluctuation...and thus what we can see as the strands in this universe might not be used as the absolute base for reasonning out of the whole if there are some other clusters like our universe left from the big bang time...

we cannot use what we see within the cluster to reason for what is outside the cluster, right?

Well, for the answer to the last question, not so. We can use what we see within our cluster as a model of what other clusters might look like (here I'm using cluster to mean Observable Universe).

On the other hand, the evidence I'm talking about isn't only what's currently in our causally connected world, but also what once was under that category. I am going to thread again in dangerous territories here by talking about things of whose details I am not wholly sure. The λCDM model, which is the currently accepted model of the universe, states that the universe is mostly homogenous all around, and I do mean outside of our cluster. How they know that? I haven't a clue, but I think it has something to do with Cosmic Microwave Background Radiation. Of course, I might be just blabbering like a lunatic here, so I'm hoping that someone with a better understanding of such topics might help you here.

Or maybe you could ask about this at the Cosmology forum. They certainly know better than I do!