Does antimatter fall up or down?

Labarbapostiza

The age old question.

If you were able to press a magic button and instantly become an antimatter you. Would gravity repel you into outer space?

There are arguments that you would not and you would still feel the force of gravity pulling you down.
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatter_fall.html

But, I don't know if I'm all that convinced. The CERN antihydrogen project say they've trapped something like four hundred odd antiprotons, and they think they're falling down. I don't know how conclusive they are.

There are good reasons to believe the protons might fall up. (Or at least I feel there are).

I believe Dirac first got the notion for antiparticles by looking at Einsteins relativity equation [LATEX]E = mc^{2}[/LATEX] had negative solutions.

You can pop a negative number into E....and that will give you an antiparticle. But, for the equation to solve correctly, m, the mass must also be negative.

By simply plugging a negative mass into Newton's equation, the Force turns negative (in relation to how the force is normally positive). Negative masses would flee from positive masses.

Thoughts?

mcmoustache

Unless I'm missing something, anti-particles have negative charge, not negative mass. For example, positrons are anti-electrons. They have a positive charge and the same mass as an electron. They don't have a negative mass.

In other words, they would fall down.

Labarbapostiza

mcmoustache wrote: »

Unless I'm missing something, anti-particles have negative charge, not negative mass. For example, positrons are anti-electrons. They have a positive charge and the same mass as an electron. They don't have a negative mass.

In other words, they would fall down.

Yes, the absolute mass of an antiproton is the same as the absolute mass or modulus of the mass of a proton.

But, is positive and negative mass possible, or is it even absolutely necessary.

Look at Einstein's equation [LATEX] E = mc^{2} [/LATEX]

For the sake of clarity, I'm going to calculations where the units are in absolute protons. E will equal the energy of proton. m will be the mass of a proton. I'll leave out units I just want to illustrate the concept.

First, with a positive proton.
[LATEX] 1 = c^{2} [/LATEX]

Now, with the antiproton, which has negative energy.
[LATEX] -1 = c^{2} [/LATEX]

It simply does not work out, 1 does not equal -1.

It has to be
[LATEX] -1 = -c^{2} [/LATEX]

An antiparticle for the sake of this equation must have negative mass.

I believe the AEgIS experiment at CERN was working on it but I can't remember if anything has been published yet. It is an interesting theory but I personally know no physicists who believe it as it has several large caveats. For example, photons are particles that are their own antiparticles and yet they definitely fall down. How can you explain this?

Labarbapostiza

Deleted User wrote: »

I believe the AEgIS experiment at CERN was working on it but I can't remember if anything has been published yet.

Yeah, I checked up on their page just a few days ago. So far they've been able to capture a little over 400 (something like 468) antiprotons, in their trap.

It is an interesting theory but I personally know no physicists who believe it as it has several large caveats.


For example, photons are particles that are their own antiparticles and yet they definitely fall down. How can you explain this?

It's worth thinking about. What I did there with Newton's equation, turning the force negative just by the sign of one of the masses. If gravity was mediated by some kind of force carrier like charge, the smaller mass would take off like a rocket.

If however, if gravity is more like Einstein's General Relativity, then a smaller antimatter mass would fall, but larger masses would push away from each other.

So, if we could say Einstein's matter tensors for positive matter, suck in relation to other positive matter, and the same for negative matter in relation to negative matter. The tensors would push, in relation to masses of opposite time evolutions of their respective wave functions. Antimatter and matter would repel.

Photons being their own antiparticle....Correct me if I'm wrong, but doesn't that idea come from probability theory, that a photon sucking from one direction, is indistinguishable statistically from a photon pushing from the opposite direction. I'm not saying this is wrong. But it does stump me thinking how I would set about measuring whether antiphotons were rising in gravity rather than falling. And, the tensors for individual photons, or even a lot of them, is so small, the lensing effects so far observed have been due to large astronomical masses.

The antiparticle/particle vacuum pair creation is another argument against Newtonian gravity. Under Newtonian gravity in gravitational wells, photons would be released .....actually it would get very ugly very quickly...

Morbert

Quantum field theory tells us antiparticles have positive inertial mass. Quantum field theory doesn't describe gravity, and so it might be the case that they have negative gravitational mass.

Labarbapostiza wrote: »

Now, with the antiproton, which has negative energy.

Dirac was motivated by E < 0 solutions to Einstein's energy-momentum equation, but this doesn't mean antiprotons have negative energy. Instead, he argued that all these negative energy states are normally occupied, and an antiproton is an unoccupied negative energy states, and therefore has positive energy.

Labarbapostiza

Morbert wrote: »

Quantum field theory tells us antiparticles have positive inertial mass. Quantum field theory doesn't describe gravity, and so it might be the case that they have negative gravitational mass.

There would be an absolute need for a negative gravitational mass. It would be a very ugly universe if the vacuum didn't cancel its' own gravity.

The theory for the cosmological constant is that it is the residual mass/gravity after the vacuum cancellations. It slightly pushes.

Dirac was motivated by E < 0 solutions to Einstein's energy-momentum equation, but this doesn't mean antiprotons have negative energy.

Negative in the sense of the E = mc^2 equation. Grasping around for why this must be so, (alighting on the Maths Stack Exchange). The numeric sequence has symmetry on zero, with equal infinities of cancelling out + and - values on either side.

It would appear that this is not just an abstract mathematical concept, but an underlying necessity of physical reality. Plus and minus are indistinguishable from each other in the sense of their symmetry relationship with zero. They could be called Red and Blue, or Blue and Red.

Instead, he argued that all these negative energy states are normally occupied, and an antiproton is an unoccupied negative energy states, and therefore has positive energy.

People get confused by theoretical physics. I was looking at Jim Al-Khalili science blog (which he no longer maintains), and he asked the question at one point, whether Dirac was just playing around with maths. I don't think Dirac was playing around with maths. I think he fully realised particles have the same symmetry on zero as the numeric sequence.

Let's look at the numeric sequence. The integer sequence for example.

1,2,3,4.....inf = 1+1-1, 2+1-1, 3+1-1,.....you got the picture.

Is this meaningful for physical reality?

[LATEX] \Psi = \Psi[/LATEX]
[LATEX]\Psi = \Psi + 0 [/LATEX]
[LATEX]\Psi^{\dagger } = \Psi^{\dagger }[/LATEX] The dagger is backward in time evolution.
[LATEX]0 =\Psi + \Psi^{\dagger }[/LATEX]
[LATEX]\Psi = \Psi + \Psi + \Psi^{\dagger }[/LATEX]
[LATEX]\Psi = \Psi + \Psi + \Psi^{\dagger }+ \Psi + \Psi^{\dagger }[/LATEX] Goes on forever.

Morbert

There would be an absolute need for a negative gravitational mass.

Most physicists think the gravitational mass of antimatter will be the same as the gravitational mass of matter. There are reasons to believe this is the case.

Negative in the sense of the E = mc^2 equation.

Yes. in the sense of the E = mc^2 equations, antiparticles do not have negative energy or negative mass.

Mass is not a Noether charge. It does not need to be conserved. If you have a particle with mass m and an antiparticle with mass m, the end result of their annihilation can be particles with zero mass, because mass is not conserved.

Unlike mass, energy/relativistic mass is conserved, but particle-antiparticle annihilation does not result in a system with zero energy/relativistic mass. An antimatter explosion will have lots of energy.

A vacuum state can produce matter-antimatter virtual pairs. This is because even though the vacuum state is an eigenstate of the Hamiltonian (reporting zero energy), it is not an eigenstate of local energy measurements. I.e. What permits particle and antiparticles to briefly emerge from the vacuum is not negative energy of antiparticles, but rather the uncertainty principle.

Bit cynical

I would go with antimatter falls down for the reasons Morbert outlines. Matter and anti-matter can annhilate to form photons. If these photons are trapped in a box then they will, due to their relativistic mass, contribute to the overall mass of the box. The amount they contribute is equal to the combined mass of matter and antimatter.

If matter and anti-matter had opposite values of mass, then there would be no net mass contribution. But suddenly upon annihilation the box would increase in apparent mass.

Having said that, it would be interesting if this experiment at CERN finds otherwise.

Labarbapostiza

Morbert wrote: »

Most physicists think the gravitational mass of antimatter will be the same as the gravitational mass of matter. There are reasons to believe this is the case.

Can I currently beat the CPT (Charge, Polarity, Time) theorem; no. But I have some strong intuitions.

I've just started reading some books by Julian Schwinger. In the preface of one there's a few paragraphs were he does talk about those intuitions, and there are a number of open questions, where all anyone has at present is intuitions.

An antimatter explosion will have lots of energy.

I don't know, I would like to see that experimentally confirmed. I'd like to see if the antiprotons do other things, or not. At the minute they're still trying to build up the number of antiprotons they can hold in the trap. We'll see.

A vacuum state can produce matter-antimatter virtual pairs. This is because even though the vacuum state is an eigenstate of the Hamiltonian (reporting zero energy), it is not an eigenstate of local energy measurements. I.e. What permits particle and antiparticles to briefly emerge from the vacuum is not negative energy of antiparticles, but rather the uncertainty principle.

Okay, put aside the QED vacuum state, for a moment. The principle of a geometric space emerging from the vacuum, does not require the uncertainty principle. It depends on a possibly untestable hypothesis based on more rudimentary geometric principles.

[LATEX]x^{3} = x^{3}[/LATEX]
[LATEX]x^{3} - x^{3} = 0[/LATEX]

The exponent can go to infinite dimensions, x can be a point that is in fact a line of infinitesimal length, the smallness of which is irrelevant as smallness or bigness is relative to something else. If nothing else exists, or exists in the sense of being accessible, then the actual length of the line is of absolute irrelevance.

Are these volumes physical realities or just maths. And this is where time like dimensions come in. Without a time like dimension, existence or non existence is irrelevant. But if you ad a time like dimension, from an exterior perspective, the volumes do not exist, but internally there is existence. And within there is the possibility of time evolving matter to exist.

The only astronomical observation that would indicate accessibility and interaction with these volumes is the cosmological constant. There is no observation of a bubbly foam.

In current theory there isn't a particle that binds the time-like dimensions with geometrical space dimensions. Though there is a theory the that some kind of force carrier, or multiple force carriers exist.

I do not have a good answer.

Okay, antimatter having a repulse gravity may have no physical reality, but I think it's worth thinking about for entertainment purposes if nothing else.

If we had lots of antimatter in our universe and it did result in high energy releases on contact with matter, it's something we'd see astronomical evidence of, we don't. Imagine if it's there, but doesn't have high energy release when annihilating with matter.

Imagine if it had repulsive gravity, and obeyed General Relativity. Smaller mass would fall to earth but bigger and more distant masses would be pushed away, coralling in similar formations to positive masses. Imagine if this stuff did something weird with photons, and we can't see the stars, because instead of their light pushing the cells in our retina, it's pulling them (okay, I instantly recognise what's wrong with that idea. But it would work in a science fiction world where you can be highly cavalier with physics in general).

Spandex John

particle + particle = attraction
antiparticle + antiparticle = attraction
particle + antiparticle = repulsion

That's the idea, yes?

Labarbapostiza

Spandex John wrote: »

particle + particle = attraction
antiparticle + antiparticle = attraction
particle + antiparticle = repulsion

That's the idea, yes?

Yes..that's the idea......when we're talking about gravity. (If we were talking about charges, electrons would normally repel each other, but with gravity they'd attract each other.)

Labarbapostiza

Morbert wrote: »

Yes. in the sense of the E = mc^2 equations, antiparticles do not have negative energy or negative mass.

In Quantum Chromo Dynamics, most of the mass of the proton is attributed to gluons. It's an application of General Relativity. Combining the gluons with antigluons, most of your proton mass vanishes. And I believe the theory also holds that the quarks plus their corresponding anti quarks, vanish.

There's a controversy over Dirac's masses, to a point Dirac didn't know what it meant in the end.

And there are other confusions. I was watching a short lecture by professor Peacock of Edinburgh, which must have been made relatively recently, where he says something like the cosmological constant should be infinity, but nobody knows why it's not, and the explanation will need new physics. No. There is a good answer, which I'm not going to explain, but the wrong answer comes from a misunderstanding of fluctuations.

To explain, with the least pain, the terms quantum fluctuation and vacuum fluctuation, are often used interchangeably. And their relationship to the Heisenberg uncertainty principle, can add to the confusion.


[LATEX]\Delta x^{3}.\Delta t=\Delta x^{3}.\Delta t[/LATEX]

This is a geometrically true statement.

[LATEX](\Delta x^{3}.\Delta t)-(\Delta x^{3}.\Delta t)=0[/LATEX]

This is also geometrically true. And there you have your vacuum fluctuation. And it makes no reference to quantum phenomena. Descriptions of quantum phenomena require a space-time substrate. Ignoring the basic geometry, in the hope space-time will be explained within the framework of quantum theory, is going to lead nowhere.

Another thing you can see from the equation, is in a volume of 0, time runs in both directions.


Okay, and here is another interesting thing. Getting back to particles in boxes...Take first an empty box. It would be wonderful if you could magically spin the empty volume in the box, but you can't, but what the observer can do is circle the box at a velocity, and relative to the observer the empty volume will have angular momentum. Will the observer see anything, like photons. No. But if there was a photon in the box, and let's just say the box has perspects walls, or no walls at all, it's just a volume, the circling observer will see photons of a higher energy than if they were stationary relative to the box.

Now, something impossible, if the observer could reverse their direction in time. The faster they circled the box, the lower the energy of observed photons. Until poof, it's gone. But what happens if they go a little faster, does it reappear?

And back to when the observer is circling and empty box. Are there in fact photons there, increasing in energy with the velocity of the observers circling, but there is some reason the observer cannot see them.

Some of what I've described is readily observable. So, you could ask, is a photon a thing in itself, or is it a volume of space-time with an angular momentum relative to other parts of space-time.