Dude, where's my anti-graviton?

[LouisWu]

I had read a response in a pretty old post in the cosmology forum stating that anti-gravitron's can't exist. I was hoping to follow up on that here in this new thread.

Can someone explain that in more detail?

It's always struck me as odd that the other 3 fundamental forces, Electromagnetic, Strong Nuclear and Weak Nuclear, come in positive and negative pairings and it seems like the statement "and Gravity is always attractive" is simply tacked on for convience.

So my personal, amateur theory goes:

Half of the universe is composed in Repulsive Material

By that I mean, what if:

As the universe cooled, gravity decoupled from the the other 3 forces types in attractive and repulsive forms. The half that causes "attractive gravity" binds with the materials of the universe forming attractive matter that naturally collects together. The fundamental repulsive "matter", "energy", "quanta", whatever, naturally separates from itself and all other matter in the universe. Slowly, areas of high matter density collect to form stars, solar systems, galaxys, etc. The repulsive matter spreads out amongst the least dense areas of the universe.

In my view, this:

1) Would cause the accelerating universe, as all that distributed repulsive material pushes against everything else in the universe.

2) Would explain the change in acceleration of the universe. At first, the attractive and replusive material would be highly disordered. As the attractive matter and repulsive got organized over time, the forces would align better increasing the acceleration of the universe.

3) Would create 50% more matter in the universe, helping to explain much of the missing matter in current observations.

 

[mgb_phys]

There is no reason to think that an anti-graviton would have negative gravity.
Anti-particles have exactly the same mass as 'normal' particles and so have 'attractive' gravity.

 

[LouisWu]

OK, seems I'm using the wrong terminology, thanks for the clarification. Is there a standard physics term for a theoretical particle, quanta, or unit of energy that universally repells?

 

[mgb_phys]

Not really, an anti-particle has the opposite charge of the norrmal particle but doesn't need to be charged.
So a positron (+ve anti-electron) will attract to an electron but will repel a (+ve) proton.
An anti-neutrino has zero charge just like a regualr neutrino.

One of the problems with gravity is that there is no model that predicts a repulsive gravity which makes it difficult to fit into the same theories as electricly charged particles.

 

[Mentz114]

OK, seems I'm using the wrong terminology, thanks for the clarification. Is there a standard physics term for a theoretical particle, quanta, or unit of energy that universally repells?

Gravitons are spin-2 bosons, and bosons are their own anti-particles. If you want to set up a system of repulsive 'stuff', write the Lagrangian for an attractive system and change the sign of the potential energy.
Also, one can include the repulsive stuff in GR cosmology by adding a (negative ?) constant to the field equations.

 

[AlphaNumeric2]

Gravitons are spin-2 bosons, and bosons are their own anti-particles.

The W+ and W- are each others antiparticles since they have a U(1) charge. Particles must have no charge under any of the Standard Model forces if they are to be their own antiparticle, since C flips all charge signs. The photon and Z are their own antiparticles. Gluons are charged under themselves so there is a difference between a gluon and it's antiparticle. On purely theoretical grounds, the graviton would be it's own antiparticle though.

 

[Mentz114]

Thank you, AlphaNumeric2.

 

[LouisWu]

Thank you Mentz and Alpha for the information and the way forward. Went over to Wiki and the Lagrange/Euler equations look vaguely familiar from undergrad physics. I have a lot of reading to do ;)