Darkness & Antigravity

[CraigS]

So, it appears that one Dark Energy candidate may be a repulsive type of gravity. The repulsive force between matter and antimatter is predicted by General Relativity and symmetry …

Antimatter gravity could explain Universe's expansion

Ever since antimatter was discovered in 1932, scientists have been investigating whether its gravitational behavior is attractive – like normal matter – or repulsive. Although antimatter particles have the opposite electric charge as their associated matter particles, the masses of antimatter and matter particles are exactly equal. Most importantly, the masses are always positive. For this reason, most physicists think that the gravitational behavior of antimatter should always be attractive, as it is for matter. However, the question of whether the gravitational interaction between matter and antimatter is attractive or repulsive so far has no clear answer.
…
In the new study, … has shown that an answer can be found in the theory of general relativity.
Unlike previous antigravity proposals – such as the idea that antimatter is gravitationally self-repulsive – Villata’s proposal does not require changes to well-established theories.
…
On the other side, the cosmological implications of this finding have shown antigravity as an alternative to (or explanation of) the wooly concept of dark energy for the accelerated expansion of the Universe.”

Entirely theoretical, but under formalised transformation rules, he's saying that mass effectively becomes negative, which reverses the gravitational atraction between matter and anti-matter.

Nice clean logic … but where's all the anti-matter to generate the expansion of the universe ? He says ''possibly in voids" .. the largest structures in the universe.

Anyway, at least he's developed a test to establish or refute the idea … at CERN.

Cheers

[renormalised (Carl)]

There's one way of finding it in the voids, if there's that much around....look for the 511KeV signal of electron-positron annihilation. Even with the sparsity of the hydrogen in the voids, you'd be bound to get some scintillation occurring.

Wouldn't be too dark if you had enough of the stuff mix with ordinary matter, at the time!!!!!

[bojan]

Hm...
So, according to this article, anti-matter and matter are gravitationally repulsive to each other.. ...
I wonder what is happening between antimatter and photons? Mind you, photons are antiparticles to themselves.. So from this stand point, this proposition doesn't make sense.

[renormalised (Carl)]

Originally Posted by bojan

Hm...
So, according to this article, anti-matter and matter are gravitationally repulsive to each other.. ...
I wonder what is happening between antimatter and photons? Mind you, photons are antiparticles to themselves.. So from this stand point, this proposition doesn't make sense.

I've been waiting for someone to mention that....that's the big problem for the whole theory (how would you detect -e/+e annihilation if they repulsed one another??!!!). Little difficult having a photon repel itself

[xelasnave]

Neat stuff Craig.

Thanks for posting.

I dont understand how we could have "negative time" so I feel lost somewhat as I cannot conceptualize a reality such as it suggests.

Also if the voids contain so much anti matter (and antimatter enjoys a property described as attraction) would it not be reasonable to expect that the anti matter in the voids will "glob up" to form stars? (except they are made of anti matter not the matter we know and love?)

Still like my Universes explanation of reality however

alex

[xelasnave]

I just purchased my first math book and my first phsics book out of respect for all of you here.

alex

[renormalised (Carl)]

Originally Posted by xelasnave

I just purchased my first math book and my first phsics book out of respect for all of you here.

alex

Good...start reading

[bojan]

Originally Posted by renormalised

I've been waiting for someone to mention that....that's the big problem for the whole theory (how would you detect -e/+e annihilation if they repulsed one another??!!!). Little difficult having a photon repel itself

The problem I initially had in mind was gravitational lensing... the anomaly should have been detected already

[renormalised (Carl)]

Originally Posted by bojan

The problem I initially had in mind was gravitational lensing... the anomaly should have been detected already

Yes, a massive concentration of antimatter would create a divergent lens, unlike normal matter and the associated lenses. If it even created a lens at all. It would've been very easily detected.

[Robh (Rob)]

Originally Posted by bojan

The problem I initially had in mind was gravitational lensing... the anomaly should have been detected already

Not necessarily. Gravitational lensing occurs when light from a distant object is "bent" by a foreground object of significant mass and focussed in the line of sight of the observer. Einstein published an article on it in 1936 but a visual confirmation did not occur until 1979. It is a fairly flukey occurrence this line of sight and relatively quite rare. In the case of anti-matter, as Carl alluded to, the light would diverge away from this line of sight. No lensing would be observed and nothing out of the ordinary would be perceived. There would be nothing to conclude.

Regards, Rob

[bojan]

Originally Posted by Robh

Not necessarily. Gravitational lensing occurs when light from a distant object is "bent" by a foreground object of significant mass and focussed in the line of sight of the observer. Einstein published an article on it in 1936 but a visual confirmation did not occur until 1979. It is a fairly flukey occurrence this line of sight and relatively quite rare. In the case of anti-matter, as Carl alluded to, the light would diverge away from this line of sight. No lensing would be observed and nothing out of the ordinary would be perceived. There would be nothing to conclude.

Regards, Rob

Rob, not necessarily ( sorry... I could not resist )
If there is enough antimatter to affect the expansion of the universe, surely there must be enough of it to affect the lensing (here and there.. if antimatter has negative gravitation). Instead, only positive lensing was observed, and the observed amount of effect even suggest more mass (dark matter?) than is (currently) visible..

[CraigS]

Folks;

Lensing results in path, and hence image, distortion of the background object. There is no single focussing point. There is a line along which light is bent towards, but this only indicates the centre of mass of the 'lens'. There is no 'convergence' and thus, no 'divergence'.

As such, 'divergence' of the light paths, if the 'lens' is composed of anti-matter would be pure conjecture, which I'm happy to challenge.

Photons from the background source, can act as matter or anti-matter.

Photons have no mass, (whether they appear as matter or anti-matter), so lensing is not caused because of attraction between masses. It is caused by distortion of spacetime around massive objects, and as light follows geodesic paths, it follows the curvature of this spacetime.

If there was a 'blob' of antimatter, it would probably be enormous in size and any field it may create, would be widely dispersed and there would be insufficient anti-matter density to result in some kind of observable 'anti-lens' effect (such as the conjectured 'divergence').

Also, who knows whether anti-matter possess some other property when it interacts with spacetime (or not) ? (Answer: know-one knows).

Cheers

[bojan]

Craig,
That holds if antimatter has negative gravity on itself...
But article suggest that antimatter attracts antimatter, but repulses "normal" matter and that is the situation that should be detectable and I am talking about.
Now, because photons are both "anti" AND "normal", and clearly they are "attracted" to matter, they also had to be attracted to antimatter.

This is the logical problem I have here with this article (and with whole this antimatter proposal )

BTW, anyone knows what is the total mass of the photons in the Universe?

[CraigS]

So,

A second post to delineate the second issue …

The metric expansion of space is on a vastly different scale to lensing effects.

Anti-matter may produce no observable, (conjectured), 'anti matter lensing' properties and yet, may still cause the expansion of the universe.

(Don't ask me how, though. )

Cheers

[CraigS]

Originally Posted by bojan

Craig,
That holds if antimatter has negative gravity on itself...
But article suggest that antimatter attracts antimatter, but repulses "normal" matter and that is the situation that should be detectable and I am talking about.

Where there is matter present, anti-matter would be repelled. There is always matter present in space .. even in voids.

Originally Posted by bojan

Now, because photons are both "anti" AND "normal", and clearly they are "attracted" to matter, they also had to be attracted to antimatter.

Photons aren't attracted to anything !
A photon's path is bent due to curvature of spacetime.

Originally Posted by bojan

BTW, anyone knows what is the total mass of the photons in the Universe?

Zero.

[bojan]

Originally Posted by CraigS

Zero.

By "total" I meant total, together with energy they are carrying.

[sjastro]

Because of CPT symmetry, an observer would see the same lensing effect irrespective if the lens is made from matter or antimatter.
The null geodesic of the photon (or antiphoton) must remain the same for the laws of physics to remain invariant otherwise the symmetry is violated.

The problem I see with this model is that there is no explanation as to why "dark energy" is increasing.
Due to the metric expansion of the Universe one would expect the effects of anti-gravity, like gravity, to decrease as the density of the Universe decreases with time.

Regards

Steven

[CraigS]

Hmmm …

Symmetry may have already been violated, resulting in insufficient anti-matter ?

(Just playin' around here … lets not get too serious ..)

Gotta go … back soon.

Cheers

[sjastro]

Originally Posted by CraigS

Hmmm …

Symmetry may have already been violated, resulting in insufficient anti-matter ?

(Just playin' around here … lets not get too serious ..)

Gotta go … back soon.

Cheers

There are two types of symmetry Craig, continuous and discrete.
Continuous symmetries determine the type of interaction between particles hence the type of particles that exist. Continuous symmetries should tell us there should be an equal ratio of matter to anti matter which clearly is not the case.

Discrete symmetries relate to particular properties of the wavefunction of a particle under certain transformations.

CPT is an example of a discrete symmetry.

Regards

Steven

[CraigS]

Originally Posted by sjastro

There are two types of symmetry Craig, continuous and discrete.
Continuous symmetries determine the type of interaction between particles hence the type of particles that exist. Continuous symmetries should tell us there should be an equal ratio of matter to anti matter which clearly is not the case.

Discrete symmetries relate to particular properties of the wavefunction of a particle under certain transformations.

CPT is an example of a discrete symmetry.

Regards

Steven

Well that's cool.

I didn't know this.

Its interesting though … a pure theory should be assessed within the bounds it sets for itself.
If this one is based purely on CPT transformations, then it should be assessed on the basis of CPT (discrete) symmetry principles.

I yield in my criticisms of it, for this reason.

I did imply in another post, that that this theory might have been a bit 'dodgy'. It clearly has a long way to go, empirically and theoretically.

Thank you, Steven.

Cheers