Antimatter Singularity

[Kojiami]

Just a thought i've had, what if you had enough antimatter mass for it to collapse in itself like a black hole? I mean, i know you'd get a black hole made of antimatter, but what if you threw matter at it then? Would it anihilate, breaking down the event horizon, or would the matter get completly ripped apart and not do anything?

[insane_alien]

well, assuming information is somehow preserved when it enters a black hole... the matter would annihilate with the antimatter when it got to the singularity. BUT the only way the black hole would lose mass would be to emit the gamma photons released in the interaction. since black holes don't emit light. this isn't going to happen. it would just get more massive.

[Kojiami]

So instead of a singularity made of antimatter, you'd get a singularity made of gamma photons?

[Klaynos]

It's a singularity, surely what it's made of doesn't really matter? And can infact never be found out as no EM radiation can escape it?

[insane_alien]

well, we don't even know if anything remotely like matter/antimatter/photons can even exit inside the event horizon. we'll probably never know(well, at least in the next few tens of millenia anyway)

[Kojiami]

It takes matter to make gravity. It takes gravity to make a singularity. It takes a singularity to create an event horizon.

 

Common logic, so it's assumable there would be matter in there.

[insane_alien]

matter is not the source of gravity. MASS is. photons have mass(relativistic mass) therefore they have a gravitational field albeit tiny.

[Kojiami]

Yes, but energy (Usually) doesn't have mass. So matter generally makes gravity, since all matter has mass.

[insane_alien]

energy usually(always) does have mass. you do know the consequences of E²= (mc²)² + (pc)² don't you?

[timo]

energy usually(always) does have mass. you do know the consequences of E²= (mc²)² + (pc)² don't you?

What if [math] m=0, \, p \neq 0 [/math] ? Anyways, you´re better off stating that energy (rather than mass) was the source of gravity - you run into trouble justifying photon contributions, otherwise. @Kojiami: What is matter?

[abskebabs]

What if [math] m=0, \, p \neq 0 [/math] ? Anyways, you´re better off stating that energy (rather than mass) was the source of gravity - you run into trouble justifying photon contributions, otherwise. @Kojiami: What is matter?

Is this true? Energy is a source of gravity? So when Light is bent round, or cannot escape a black hole it experiences a mutual attraction with te black hole because it has energy? I thought this was rather due to the effects of the black hole curving spacetime.

 

You are most certainly right about relativistic mass, lphotons have no rest mass, so they cannot have a relativistic mass.

[timo]

Is this true? Energy is a source of gravity?

Let´s say it is a better lie than saying mass was the source of gravity. The source of gravity (in the sense that it takes the position mass had in Newtonian Gravity) is the energy-stress tensor (http://en.wikipedia.org/wiki/Stress-energy_tensor).

 

For your confusion about energy being the source of gravity, it is probably important to clearify what the "source" means. In the equation telling you how a particle moves (the equation of movement, the geodesic equation ), there is no term that is dependent on the particle´s mass or energy; it is solely dependent on the geometry (~= curvature) of space.

But a theory of an interaction consists of more than the question how a particular field (the gravitational field, i.e. the geometry of spacetime) affects the particles in it. The theory must also contain a part telling you what the field looks like and how it behaves. This part is the field equation (in the case of GR the Einstein equation). It´s the field equation where energy comes in as the source that shapes the geometry.

 

I think the reason why the "only dependent on the geometry and not on mass/energy"-part is sometimes stressed is that it is in contrast to eletromagnetism. There, electric charge not only creates the electromagnetic field, but the movement of particles within an electromagnetic field is also dependent on their charge while in GR no such charge term comes in.

[abskebabs]

Thx, this is starting to make sense, especially the comment on electromagnetism...tho an understanding of GR is still years beyond me I feel. I will get there tho. Actually, I dont even fully understand SR yet.