Antimatter And Gravity

[Buffy]

The trouble I have with this is that there is no unique way to determine which particles are particles and which are antiparticles. The choice is arbitrary. When you choose one particle to be "particle" then its antimatter particle or "antiparticle" is determined. Of course there is always the situation where testing its antigravity properties tells you which is "really"  the antiparticle, i.e. the choice is no longer arbitrary.

 

The thing is that "particles" are what make up virtually all matter, and "anti-particles" are really, really hard to find. So while "arbitrary" it's still a consistent and easy to explain distinction with easily testable definition.

 

 

For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled, :phones:

Buffy

[sanctus]

Buffy, your assertion hold only as long as we live in a matter dominated universe.

 

Pmb, I liked in the article the bounds they have, anti-matter does surely not give 65 Gs :-)

[Buffy]

Buffy, your assertion hold only as long as we live in a matter dominated universe.

 

Right but we do, and at that point it becomes the simple semantic argument that when we talk about "the dominant kind of matter" we mean matter, and when we talk about "the kind of matter that's hard to find" we call it anti-matter, and all observers in *that* universe can agree on that definition.

 

 

By a tranquil mind I mean nothing else than a mind well ordered, :phones:

Buffy

[Moontanman]

I am always considered the possibility that at the moment of the big bang the expansion went in two time directions, one negative time and positive time. From the stand point of an observer in either universe both directions are forward in time and space. The negative time direction contains primarily anti matter and our positive time direction contains primarily matter. 

 

I tried to post a picture of the big bang but for some reason it wouldn't let me, it is on google images and it is the one i know we all have seen many times anyway. http://t3.gstatic.com/images?q=tbn:ANd9GcRc_xPABspR1lfgRMh9Ay1-2YjENBbpsi1RC2oeMq-1Sc5QGa1q3g

 

Just imagine another expansion in the opposite direction, if this could be true then the universe is both infinite in time and space even though it had a beginning... 

[CraigD]

This sounds like the subject at http://newscenter.berkeley.edu/2013/04/30/is-antimatter-anti-gravity/

This Berkeley news story is about the experiment described in “Description and first application of a new technique to measure the gravitational mass of antihydrogen”, Nature Communications (Apr 2013) by CERN’s ALPHA collaboration and others.

 

It takes a different approach than the one the AEGIS collaboration’s been working on for 5+ years that I mentioned in post #12. The AEGIS experiment seeks to shoot a horizontal stream of cold neutral antimatter and see how it falls (or “arcs”). The “new technique” experiment takes the simpler approach of just releasing some neutral antimatter and seeing how it falls.

 

The difficulty is that the neutral antimatter involved isn’t a nice solid ball of anti-iron that’ll drop (or something else) in a simple way, but a cloud of cool (0.1 to 0.003 K) anti-hydrogen that disperses in all directions. Analyzing how such a cloud is affected by gravity takes complicated statistical analysis of the data shown in this graph:

The green dots and the lower, more arcing line are for a computer model-generated simulation of 10000 antiatoms, the red circles and the nearly straight line for 434 actual antiatoms. The clumping of point at the top and bottom of the graph is an artifact of it displaying annihilation positions by their vertical (y) positions rather than their angle relative to the center of the trap.

 

Clever as the experiment is, at a glance, its results aren’t very good, because the actual measurements don’t correlate much with the simulation. The anti-atoms appear to be weightless!

 

Maybe more experiments with the new approach will work better, but I suspect we’ll have to wait for the AEGIS experiment to get precise, conclusive results.

 

I am always considered the possibility that at the moment of the big bang the expansion went in two time directions, one negative time and positive time.

This reminds me of a famous conversation between Richard Feynman and John Wheeler, were Wheeler suggested that, if an electron could somehow change into its antiparticle (a positron) – which is equivalent to it reversing its direction in time – then there might be only one electron/positron in the universe, looping forward and backwards in time – an idea known as the one-electron universe.

 

The problem with this and other “antiparticles are particles traveling backward in time” is that the best cosmological models have nearly equal numbers or particles and antiparticles which annihilate in about the first 10 sec after the Big Bang producing most of the photons in the universe, the remains of which are the cosmic microwave background. Models like the one-electron universe (which can be extended to other elementary particles, so that there’s only one of each of them) is that they seem to require that the universe at all times have equal amounts of matter and antimatter, which strongly contradicts observed reality.

[Moontanman]

My idea is that in the reverse time expansion anti matter dominates and in the forward time direction matter dominates not that matter and anti matter were formed and rushed in opposite directions, still just bald speculation... 

[HydrogenBond]

Beta decay has matter giving off anti-matter; positron. This means the anti-matter positron was originally peacefully coexisting in the matter nucleus. The reverse of this has matter absorbing the anti-matter positron without going boom. It is not always mutually destructive. This is why I look at these differently, than the traditions  that assume both can't coexist when old observations have shown this for years. 

[CraigD]

Beta decay has matter giving off anti-matter; positron. This means the anti-matter positron was originally peacefully coexisting in the matter nucleus.

That’s not the meaning that people conversant with quantum particle physics take from B⁺ decay, in which a proton (p⁺) ceases to exist, and a positron and electron neutrino (e⁺ + v_e) are created. We would say not that the positron was in the proton (which was in the nucleus), but that its positive charge was. Another way of saying this is that charge is conserved in B⁺ decay, but number of protons or positrons is not.

The reverse of this has matter absorbing the anti-matter positron without going boom. It is not always mutually destructive. This is why I look at these differently, than the traditions that assume both can't coexist when old observations have shown this for years.

This reminds me of more from the famous Wheeler-Feynman conversation I mentioned in post #22.

Feynman: "But, Professor, there aren't as many positrons as electrons."

Wheeler: "Well, maybe they are hidden in the protons or something."

For more, see the full text of Feynman’s 1965 Nobel lecture.

 

The idea of positive charge being "hidden" antimatter, is an old one.

 

The idea doesn’t fare well in light of QCD, because it explains the positive charge in protons as being due to it containing 2 up quarks with charge +2/3, and 1 down quark with charge -1/3. It remains a fun idea to think about, though, and one I think every science enthusiast should have fun with.

[Pmb]

I have no problem with this assertion being testable. I'm merely saying that there is absolutely no reason to suspect antimatter to exhibit anti-gravity affects.

[OldBill]

Gentlemen, I don't think we'd really need CERN or AEGIS to resolve this.  I propose we take a ball of matter plus a ball of anti-matter up to the top of the Tower of Pisa, drop them simultaneously, and see which one doesn't hit the ground first.  Or tie them together, and see if they only go halfway down, and stop there.

 

Old one: 

Neutron walks into a bar and asks the bartender (a proton), "How much for a beer?" Bartender replies: "For you, no charge."  Neutron says "Are you sure?"   bartender replies "I'm positive." 

 

Da-dump

[CraigD]

I have no problem with this assertion being testable. I'm merely saying that there is absolutely no reason to suspect antimatter to exhibit anti-gravity affects.

From a standard quantum mechanical viewpoint, I agree.

 

However, from this viewpoint, we have no reason to suspect that anything exhibits any gravitational effects of any kind. Quantum mechanical theories have yet to successfully explain gravity. This hasn’t caused much practical trouble, because gravity is much weaker (about 10²⁵ to 10³⁸ times) than the other fundamental forces.

 

I expect that AEGIS and similar experiments will find no difference between inertial and gravitational mass of ordinary matter and anti-matter. Give that the search for a successful theory of quantum gravity has been such a long, hard scientific travail, I sorta wish for a surprise, as it might shake up everyone’s assumptions and lead the search in a new and better direction.

 

Gentlemen, I don't think we'd really need CERN or AEGIS to resolve this. I propose we take a ball of matter plus a ball of anti-matter up to the top of the Tower of Pisa, drop them simultaneously, and see which one doesn't hit the ground first. Or tie them together, and see if they only go halfway down, and stop there.

LOL, OldBill!

 

Seriously, the problem with your proposal is that nobody has a ball of antimatter, just some tiny, short-lived wisps of anti-hydrogen gas. Those wisps were fantastically expensive to make – when I researched this 2005 post, I found calculations putting the cost at about $US 62,500,000,000,000 (65 trillion) per gram, and the total amount produced to date at less than 2 billionths of a gram.

 

Also, even if you could make or find one, a good-size (let’s say a bit more than 0.5 kg) ball of antimatter is not something you’d want to be playing with. It’s E=mc² energy would be about 10¹⁷ J, or in more familiar big-explosions units, 20 mega-tons, or 1000 Hiroshimas.

 

“Just dropping” balls of matter and antimatter (or, more precisely, tossing them horizontally) is essentially what AEGIS plans to do. They just have to figure out a way to do it with very small amounts of gas, rather than nice big iron balls like Galileo’s legendary ones.

[pgrmdave]

 I propose we take a ball of matter plus a ball of anti-matter up to the top of the Tower of Pisa, drop them simultaneously, and see which one doesn't hit the ground first.  Or tie them together, and see if they only go halfway down, and stop there.

I love the idea of this, but I suspect that it'd be tough to find survivors who could reliably determine which hit the ground first.  Or just survivors in general.

[Moontanman]

Evidently great minds think alike!!! see post #21

 

Edited December 12, 2014 by Moontanman

[Moontanman]

Hey come one guys, I might have got this correct! At least comment on it... 

[Rade]

Hey come one guys, I might have got this correct! At least comment on it... 

Question ?   It is not clear to me that your comment that the mirror universe could be antimatter is presented in the video ?   Does the mirror universe hypothesis claim that both universes should be matter, or does it allow that one could be matter and the other antimatter..this is what is not clear to me.   Feynman has shown that one correct mathematical interpretation of antimatter is that it moves backward in time, but it is not clear to me that this is the position taken in the video.

[CraigD]

Evidently great minds think alike!!! see post #21

I can see how you’d get that impression from that YouTube video, but I think its author is misinterpreting – or at least interpret very imaginatively - the paper it briefly shows as its source.

 

Here’s the arXiv preprint of the paper: “Identification of a gravitational arrow of time”, 2 Sep 2014 Julian Barbour, Tim Koslowski, and Flavio Mercati.

 

The paper is short and technically simple, involving a metric the authors believe has never before been proposed, which they call “shape complexity”, with which they show that a simulation of 1000 bodies using simple, classical Newtonian time and gravity, decreases up to a “central turning point” time, then increases. They then propose that, using this metric as an alternative to more conventional entropy measurements to define the direction of “the arrow of time”, it shows a universe in which time “runs backwards”, then “runs forward”. They call this alternative “a gravitational arrow of time”.

 

It’s a fun paper for the hobbyist, however, because most of us could reproduce the work, a rarity for physics. All you need is a computer – no giant particle accelerator or other high tech goodies required! :)

 

Their model doesn’t involve antimatter or the big bang. It’s strongly reminiscent of Mach’s conjecture, not surprisingly, as Barbour and Koslowski are known for work on the subject. Barour is famous – or, according to some, infamous – for playing around with alternative to conventional definitions of time.

[Moontanman]

I can see how you’d get that impression from that YouTube video, but I think its author is misinterpreting – or at least interpret very imaginatively - the paper it briefly shows as its source.

 

Here’s the arXiv preprint of the paper: “Identification of a gravitational arrow of time”, 2 Sep 2014 Julian Barbour, Tim Koslowski, and Flavio Mercati.

 

The paper is short and technically simple, involving a metric the authors believe has never before been proposed, which they call “shape complexity”, with which they show that a simulation of 1000 bodies using simple, classical Newtonian time and gravity, decreases up to a “central turning point” time, then increases. They then propose that, using this metric as an alternative to more conventional entropy measurements to define the direction of “the arrow of time”, it shows a universe in which time “runs backwards”, then “runs forward”. They call this alternative “a gravitational arrow of time”.

 

It’s a fun paper for the hobbyist, however, because most of us could reproduce the work, a rarity for physics. All you need is a computer – no giant particle accelerator or other high tech goodies required! :)

 

Their model doesn’t involve antimatter or the big bang. It’s strongly reminiscent of Mach’s conjecture, not surprisingly, as Barbour and Koslowski are known for work on the subject. Barour is famous – or, according to some, infamous – for playing around with alternative to conventional definitions of time.

 

 

 

 

 

I kind of combined the video with the anti matter going back in time idea, seemed reasonable on the hobby level...  :vava:

Edited December 18, 2014 by Moontanman