Thread: May 2008 (LHC) Particle Accelerator - Miracle or Catastrophe?

He also said they would be tiny.

It's easy to fall into the trap of treating a black hole like some kind of object with incredibly high mass packed into a tiny space, but that's only a requirement for their natural formation, which only happens when a star's mass causes the inward force upon its matter to exceed the electrostatic repulsions between the matter, which can only happen when the star has a huge mass; hence natural black holes have huge masses.

If a black hole was formed at the LHC it would have the mass of a few nucleons; if you think about it, its gravitational effects would be no different than if a gas molecule were floating around your head.

Originally Posted by Xei

He also said they would be tiny.

I meant that there gravitational force would be tiny.

I really didn't even think about what the size would be, although I assumed it would be small...

Earlier on someone said "oh noes were all gonna get sucked into a black hole" and then someone else said "the force would be tiny and the hole would collapse quickly."

Originally Posted by Xei

He also said they would be tiny.

It's easy to fall into the trap of treating a black hole like some kind of object with incredibly high mass packed into a tiny space, but that's only a requirement for their natural formation, which only happens when a star's mass causes the inward force upon its matter to exceed the electrostatic repulsions between the matter, which can only happen when the star has a huge mass; hence natural black holes have huge masses.

If a black hole was formed at the LHC it would have the mass of a few nucleons; if you think about it, its gravitational effects would be no different than if a gas molecule were floating around your head.

Then why are we even talking about this? Obviously I know how this shit works. A black hole of even several hundred pounds wouldn't have any effect even millimeters away.

I'm just answering/correcting your points. I assumed you didn't know that much because your string example was so inappropriate, but if you do then hey.

I'm just chatting, it's an interesting subject.

Originally Posted by drewmandan

A black hole of even several hundred pounds wouldn't have any effect even millimeters away.

Could you have a black hole of several hundred pounds? I always thought they needed enough mass to create a gravitational field strong enough to 'suck in' light. Unless with a several hundred pound black hole, it just had a really small event horizon.

Does anyone know what causes a tiny black hole to collapse? The whole idea of black holes I find very interesting, despite my lack of knowledge about them.

Originally Posted by Schmaven

Could you have a black hole of several hundred pounds? I always thought they needed enough mass to create a gravitational field strong enough to 'suck in' light. Unless with a several hundred pound black hole, it just had a really small event horizon.

Does anyone know what causes a tiny black hole to collapse? The whole idea of black holes I find very interesting, despite my lack of knowledge about them.

I don't really know, but I'd say they suck in enough stuff to implode on itself, sorta?

As I said, black holes only have large masses in nature because that is required to make a star shrink to zero size.

As soon as you get mass with zero size you will have a black hole. This is because gravitational force increases as you approach the mass. If the mass has zero size you can get infinitely close and hence there must be some point around the mass where the gravitational force is strong enough to pull light in.

All black holes decrease their mass. I don't know very much about this but basically it's because of Hawking radiation. As I understand it, in space, particles and antiparticles are constantly being created, they diverge, then come back together, and anihilate. On the event boundary though, when this happens, one of the particles will go outside of the black hole, and its antiparticle will fall back in, and this causes the black hole to gradually loose mass. This would happen very quickly if the black hole had very small mass.

Originally Posted by Schmaven

Could you have a black hole of several hundred pounds? I always thought they needed enough mass to create a gravitational field strong enough to 'suck in' light. Unless with a several hundred pound black hole, it just had a really small event horizon.

That's exactly right. The radius of the event horizon is a function of mass. And if you plug in the numbers, you will see that it's very small indeed. Actually, let me do that.

For 100 kg I'm getting a radius of about 1.5e-25 m, or well under the radius of an atom.

Originally Posted by Schmaven

Does anyone know what causes a tiny black hole to collapse? The whole idea of black holes I find very interesting, despite my lack of knowledge about them.

All black holes have this process called Hawking radiation, by which they lose mass in the form of radiation as predicted by quantum mechanics and information theory. For the details you would have to ask Hawking. But the idea is, the actual rate of mass loss increases as the size of the black hole gets smaller. The consequence of this is that not only do smaller black holes take less time to evaporate because they have less mass, but they take even less time because they lose mass quicker. So black holes the size of subatomic particles basically evaporate in a Planck time, and black holes of a few hundred pounds may take a few picoseconds. On the other end of the scale, regular size, stellar black holes take trillions of years to evaporate.

CORRECTION: Stellar mass black holes take 10^67 years to evaporate (Wiki)

Snap.

If a black hole of low mass (a few thousand kg or something) was close enough to a planet, would it just suck in mass from the planet and become even more massive, and thus increase it's event horizon radius and increase it's range of devouring more mass and growing even more? That sounds too badass.

Originally Posted by Schmaven

If a black hole of low mass (a few thousand kg or something) was close enough to a planet, would it just suck in mass from the planet and become even more massive, and thus increase it's event horizon radius and increase it's range of devouring more mass and growing even more? That sounds too badass.

A few thousand kg black hole wouldn't be able to encounter matter in such high density that it would be able to stave off its own evaporation. Even if it was encased in solid critical mass uranium it probably wouldn't stand a chance of expanding. It might survive in the core of a star or large planet like Jupiter, maybe.

To really have a chance of a black hole expanding it needs to be several times the mass of our sun.