Whatever Happened to Ning Li?

[sol invictus]

Read Villata's journal entry. Matter and anti-matter both have positive mass, but they don't necessarily attract each other gravitationally.

Out of curiosity I read that paper. It's total nonsense. In fact it proves the opposite of what he claims it does - it proves that matter and anti-matter attract (as is obvious for all sorts of other reasons anyway).

I can tell you precisely where the first mistake is, if you like.

I have no idea how that got through peer review, but then, I've never heard of that journal and the papers in the latest issue look dubious at best.

 

[Farsight]

Intuition says that two apparently distinct concepts that are always mutually inclusive, i.e., there is always gravity where there is electromagnetism and vice versa, are inherently unified.

Agreed.

Whenever two fields can be unified, one field can be explained in terms of the other. If a vector has two components and the dot and cross products are known as well as one of its component, one can mathematically determine the value of the other component. Note: I don't even think you need all of the information I gave to do that, but I'm listing superfluous information just to be certain and I don't feel like checking right now.

Sounds reasonable.

Because magnetic effects can be diminished by electricity and vice versa.

Agreed. Sadly even though electricity and magnetism were unified a hundred a fifty years ago, since when we've known that it's the electromagnetic field, a lot of people still talk about electric fields and magnetic fields as if they're two totally different things.

There is no charge without mass.

Absolutely.

Gravitational repulsion between matter and antimatter has been suggested by Massimo Villata in his peer-reviewed paper "CPT symmetry and antimatter gravity in general relativity" published in Europhysics Letters and submitted on March 25, 2011.

He's wrong I'm afraid. He doesn't understand gravity, and other things too. Have a look at arXiv and see http://arxiv.org/abs/1109.1201 for this little snippet:

"This is done in agreement with the Feynman-Stueckelberg interpretation for antimatter as matter that travels backwards in time".

Feyman is one of my heroes, but that's not what antimatter is like. And matter doesn't travel forward in time either. They just have different chiralities.

It's also possible that matter-antimatter pairs have repulsive gravity upon "annihilation."

They don't. Really. They both have positive mass, there's no such thing as negative mass. And gravity is proportional to mass, not charge.

I suspect that Einstein's idea of unifying gravity and electromagnetism with a symmetric and anti-symmetric tensor for both gravity and electromagnetism respectively was the right idea and one of the quaternion factorizations to do this is correct.

Not sure.

Circumstances exist where a gravitational field from our frames of reference right now would be viewed as an electromagnetic field.

I think that's the wrong way round actually. Try this out: draw a grid with a bulge at the bottom to represent a photon, the horizontals getting flatter higher up. A_μ is the pressure in the bulge, E is the curvature, B is the is the rate of change of curvature. Take a derivative for D and the sinusoidal electromagnetic waveform, and think of electromagnetism as "curved space".

Now draw another grid, but imagine a zillion overlapping photons spread out along the bottom of it. You end up drawing all-flat horizontals which are further apart at the bottom and closer at the top. You've still got pressure at the bottom, but now you call it g_μν. If a photon moves horizontally across the middle of this grid it veers downwards, and you can plot its path with a curved line and think of gravity as "curved spacetime".

 

[Dancing David]

Read Villata's journal entry. Matter and anti-matter both have positive mass, but they don't necessarily attract each other gravitationally.

What?

Yes they do.

 

[Ziggurat]

Intuition says that two apparently distinct concepts that are always mutually inclusive, i.e., there is always gravity where there is electromagnetism and vice versa, are inherently unified.

But they are not always mutually inclusive. You can't have electromagnetism without gravity, but you CAN have gravity without electromagnetism.

Because magnetic effects can be diminished by electricity and vice versa. There is no charge without mass.

But there is mass without charge. Neutrinos, for example.

Circumstances exist where a gravitational field from our frames of reference right now would be viewed as an electromagnetic field.

Uh, no. No such circumstances exist.

 

[Astrodude]

Out of curiosity I read that paper. It's total nonsense. In fact it proves the opposite of what he claims it does - it proves that matter and anti-matter attract (as is obvious for all sorts of other reasons anyway).

I can tell you precisely where the first mistake is, if you like.

Yeah, absolutely.

I have no idea how that got through peer review, but then, I've never heard of that journal and the papers in the latest issue look dubious at best.

I assumed the European Physical Society was a well established group. That assumption may have been false. It's not a European equivalent of the American Physical Society. Nevertheless, EPS seems credible, just small. Their EPL journal is found in the libraries of MIT.

Villata is an astronomer at the Turin Observatory so he must know the peer-review process.

 

[sol invictus]

Yeah, absolutely.

OK. In this version, the error is in eq. (9). CPT is a transformation that acts on the coordinates, not on the trajectory of one particle or the other, so you cannot "transform one of the two components". That's simply gibberish.

Indeed, he has already found that the geodesic equation is unaffected by CPT, as is Einstein's equation. But that automatically means that matter and anti-matter must attract, because you can solve Einstein's equations for (say) an anti-earth, get exactly the same geometry you'd get for the earth (since Einstein's equations are unaffected), and then find the geodesics for an ordinary particle in the spacetime of the anti-earth, and - since the spacetime is the same as the earth's - get exactly the same attractive trajectories.

I assumed the European Physical Society was a well established group. That assumption may have been false. It's not a European equivalent of the American Physical Society. Nevertheless, EPS seems credible, just small. Their EPL journal is found in the libraries of MIT.

Villata is an astronomer at the Turin Observatory so he must know the peer-review process.

Well, I don't think I've ever read a paper published in that journal before, and I'm very familiar with this field.

 

[Astrodude]

But they are not always mutually inclusive. You can't have electromagnetism without gravity, but you CAN have gravity without electromagnetism.
...
But there is mass without charge. Neutrinos, for example.

The extent to which modern science has determined that neutrinos don't have any electromagnetic charge is limited by the measuring capabilities available. I'm not able to distinguish between experiments conclusively proving the neutrinos must be perfectly neutral and experiments that are hampered by measurement capacity. Has anyone ever attempted to induce an electric charge onto a neutrino?

 

[Ziggurat]

The extent to which modern science has determined that neutrinos don't have any electromagnetic charge is limited by the measuring capabilities available. I'm not able to distinguish between experiments conclusively proving the neutrinos must be perfectly neutral and experiments that are hampered by measurement capacity. Has anyone ever attempted to induce an electric charge onto a neutrino?

There is no need to. If neutrinos have a charge, even a small charge, they would interact with light. If they have a magnetic moment, even a small magnetic moment, they would interact with light. Which would mean that as we look out into the universe, a universe filled with neutrinos, we would see them. They might be very faint individually, but there are a hell of a lot of them. Yet we see nothing. Why? Because they have no charge, and they have no magnetic moment.

Plus, of course, any net charge on the neutrino would violate charge conservation, which is a VERY big no-no which would break all of electrodynamics.

 

[theprestige]

There is no need to. If neutrinos have a charge, even a small charge, they would interact with light. If they have a magnetic moment, even a small magnetic moment, they would interact with light. Which would mean that as we look out into the universe, a universe filled with neutrinos, we would see them. They might be very faint individually, but there are a hell of a lot of them. Yet we see nothing. Why? Because they have no charge, and they have no magnetic moment.

Plus, of course, any net charge on the neutrino would violate charge conservation, which is a VERY big no-no which would break all of electrodynamics.

Why do I have a mental image of Chow Yun Fat flying sideways across the room, Theory in one hand, Observation in the other, shooting down lesser ideas in a hail of slow-motion gunfire, while doves scatter artistically in the background?

 

[Astrodude]

Plus, of course, any net charge on the neutrino would violate charge conservation, which is a VERY big no-no which would break all of electrodynamics.

This, I know is not accurate. Different neutrinos could have different charges or the charge could be made up from somewhere else.

 

[Dancing David]

This, I know is not accurate. Different neutrinos could have different charges or the charge could be made up from somewhere else.

Um, no, what Zig is saying (don't blame him if I mess it up), is that in the interactions that produce neutrinos can not carry any charge it is all accounted for in the other particles. So if the neutrino had any charge it would violate charge conservation.

There is no somewhere else it could come from.

http://en.wikipedia.org/wiki/File:Beta_Negative_Decay.svg

http://en.wikipedia.org/wiki/Beta_decay

The charges are conserved there is a proton, the emitted electron and the neutrino.

Where is the other charge?

 

[Astrodude]

Um, no, what Zig is saying (don't blame him if I mess it up), is that in the interactions that produce neutrinos can not carry any charge it is all accounted for in the other particles. So if the neutrino had any charge it would violate charge conservation.

There is no somewhere else it could come from.

The charges are conserved there is a proton, the emitted electron and the neutrino.

Where is the other charge?

The assumption that an atom is a closed system is false. The charge conservation could be from charge somewhere else in the universe or from charge in an antineutrino.

 

[Ziggurat]

This, I know is not accurate. Different neutrinos could have different charges or the charge could be made up from somewhere else.

So you're positing the existence of another almost massless particle with charge, but which is also mysteriously invisible despite having a charge, AND which has no spin? Because in addition to charge conservation, we've also got to conserve angular momentum.

If you keep having to patch a theory which doesn't even have any experimental support, chances are you're wasting your time.

The assumption that an atom is a closed system is false. The charge conservation could be from charge somewhere else in the universe or from charge in an antineutrino.

No. Charge must be locally conserved. You can't just wave your hand and make charge appear somewhere else, it has to happen in the same location as you create your neutrino. And you can't produce neutrino-antineutrino pairs from nuclear reactions, because the whole point is that you need ONE neutrino to account for angular momentum conservation. Add in a second neutrino (which, BTW, is observed to not happen), and you're violating angular momentum conservation again.

 

[ctamblyn]

@Astrodude:

Ziggurat's point about the scattering of light is good evidence that the neutrino has zero charge (or, if you prefer, a charge so small that we cannot detect it).

David mentioned beta decay. If we're allowed to assume that local charge conservation holds (and there have been no observed violations), then the total charges on each side of the decay process

neutron --> proton + electron + electron-antineutrino

must be equal. If the sum of the electron and proton charges were not zero, then hydrogen gas would carry a net charge. Given that hydrogen is the most abundant element in the universe, the upper bound on that net charge must be truly tiny (I'm afraid I do not have the details, though).

So we're left with the charge on the neutron being equal to the charge on the antineutrino, to within very tight limits. But if the neutron carried a charge then atoms with neutrons (i.e. virtually all atoms other than hydrogen) would carry a small net charge. Consider the number of atoms in the earth alone - it should be possible to obtain an extremely low upper bound quite easily, but physical intuition already tells you it must be something incredibly tiny.

Furthermore, the particles we know to be charged (quarks, electrons, muons, ...) all carry an amount of charge equal to an integer multiple of (e/3), -e being the electron charge. For theoretical reasons, it is reasonable to disbelieve that the neutrinos' charges would be exceptional, and to believe that they are exactly zero.

In the end, the assumption of exactly neutral neutrinos is just the simplest model which is consistent with the observed facts.

Edit during preview: I just came across this paper, which you might find interesting:

http://iopscience.iop.org/1742-6596/203/1/012100/pdf/1742-6596_203_1_012100.pdf

According to that, the experimental upper bound on the neutrino charge is 10^-21 of the electron charge. The bound was obtained through reasoning similar to that which I outlined above (the observed neutrality of matter, charge conservation in beta decay, etc.).

 

[Farsight]

This, I know is not accurate. Different neutrinos could have different charges or the charge could be made up from somewhere else.

Neutrinos travel at the speed of light, so think of them as being more like photons than electrons. A photon doesn't have any charge. But you can put a photon through pair production to create an electron and a positron, which do have charge. Think of that as chopping a sinusoidal electromagnetic wave in half and "trapping and wrapping" the negative and positive field-variations as standing fields with different chiralities.

Now go back to the neutrino: when a field variation is propagating at c there's no sense in which it's a standing field, so it can't have any charge.

 

[Ziggurat]

Neutrinos travel at the speed of light

No they don't.

 

[Astrodude]

@Astrodude:

Ziggurat's point about the scattering of light is good evidence that the neutrino has zero charge (or, if you prefer, a charge so small that we cannot detect it).

I expect the latter because the mass is so small. Since experiments for a long time as well as theory predicted that neutrinos were massless, only to be likely shown wrong in the 1990s, it's reasonable to suspect that the electric charge will be detected eventually. Charge conservation is not violated because different neutrinos could have different charges.

 

[ctamblyn]

I expect the latter because the mass is so small. Since experiments for a long time as well as theory predicted that neutrinos were massless, only to be likely shown wrong in the 1990s, it's reasonable to suspect that the electric charge will be detected eventually.

Well, it would be very surprising given what we know at the moment but not technically impossible. It would, however, mean a much greater overturning of what we believe than the discovery of the neutrinos' non-zero masses.

Charge conservation is not violated because different neutrinos could have different charges.

Could you explain in more detail how this would work? In particular, how does this account for charge conservation in the beta decay process discussed above?

 

[Farsight]

No they don't.

Yes they do. Neutrinos from Supernova 1987A arrive along with the photons, they don't lead them or lag them. And the recent OPERA results didn't show the neutrinos to be lagging c, which they'd need to do if the neutrinos had mass.

 

[sol invictus]

Yes they do. Neutrinos from Supernova 1987A arrive along with the photons, they don't lead them or lag them. And the recent OPERA results didn't show the neutrinos to be lagging c, which they'd need to do if the neutrinos had mass.

At least two of the three neutrino species have mass, that's known for certain. Their mass is perfectly consistent with the experimental bounds you mention.

In other words, you're wrong.