One of my friends at university is currently very concerned about the possibility that the LHC, when turned on, might create a black hole and suck the earth into oblivion. He is not particularly reassured by Hawkins radiation nor the fact that, if black holes were formed in this manner, they would be formed all the time by cosmic rays and this the earth would have been swallowed long ago as the black holes generated by cosmic rays are traveling at light speed.

So what evidence, theory or anything else can you give that would reassure my friend?

How does he think this Black Hole will form?

I don't have a battery of formulas that my astronomy prof used, but basically you would need to generate a black hole about the mass of Mount Everest in order for it to remain stable and cause damage -- far more than the matter streams used in LHC.

As I don't have proof, take with grains of salt.

I think you would need a lot more mass than what is colliding inside the LHC to create a black hole.

Review of Speculative "Disaster Scenarios" at RHIC:

http://www.bnl.gov/rhic/docs/rhicreport.pdf#

Refer your friend to page 7, Appendix A: Strength of Gravitational Effects.

Particle accelerators are a long ways from creating destructive black holes.

So what evidence, theory or anything else can you give that would reassure my friend?
If the ENTIRE Earth were compacted into a black hole, the event horizon would be about the size of a quarter. Point out to your paranoid friend that the total mass of particles that will be collided in the LHC will be EXTREMELY small compared to the Earth; point out that the mass of the resulting black hole will be accordingly small; and finally, point out that the gravity of this extremely tiny black hole will be as close to zero as the gravity being exerted on him by a single molecule in the chair he's sitting on.

Such a tiny black hole will have none of the turbo-powered vacuum suction black holes are so commonly credited with. Its gravity will be insignificant, and it will only absorb anything that actually happens to collide with it. Which on the scale of particles is extremely rare.

The Sun will explode and the Earth will cease to exist long before such a black hole can consume the planet.

It is theorized(according to multiple accounts) that the LHC may form micro black holes. However, such black holes would be extremely hot, and would collapse rapidly.

EDIT: a quick google search yield an explanation (http://backreaction.blogspot.com/2006/09/micro-black-holes.html#4)

Microscopic black holes aren't stable.

It will likely be to small and not have enough pull to do any damage, but who knows. And remember that is only 1 theory.

Only one way to find out :mischief:

Anyway, I doubt the LHC would be powerful enough to generate a black hole.

Run a plastic comb through your hair, use it to cause static electricity to make your hair stand on end.

Let him know that you just overpowered the gravity of the entire Earth with a comb and passive electrical energy.

Since the Black Hole will have even LESS energy than the Earth, that means it cannot possibly affect the trajectory of any nearby object gravitationally.

Now set a grain of sand in a football field.

Let him know that on the scale that the Black Hole is being created, the nearest other bit of mass will on average be out in the stadiums, and the size of a golfball. Tell him to go into the stadiums and attempt to hit the grain of sand WITH a golfball, and that is about how likely you are to see anything get added to these black holes.

Only one way to find out :mischief:

Anyway, I doubt the LHC would be powerful enough to generate a black hole.

It has a resonable chance of creating a micro black hole, but one which will do anything to anything will need much more energy.

The inverse square law and the low mass of the black hole would ensure that it's gravity is negligible and that the black hole would collapse in a near instant. Even huge black holes can be safely orbited from a distance, they don't suck everything in their path

Actually, the OP pointed out that his paranoid friend wasn't convinced by the idea of a black hole evaporating (that was the "Hawking radiation" part--if I remember correctly, Stephen Hawking was the inventor of the idea that black holes emit radiation and thereby gradually disappear).

The problem is not that the black hole initially has a large gravitational pull, but that it will fall through the earth, sucking up material it passes through, gradually becoming larger and larger (as described at http://www.livescience.com/technology/destroy_earth_mp-1.html , for example).

So the question is, how long would this actually take?

My understanding is that the probability of this happening in the first place is very small. The problem is that journalists and lay people don't understand probability - the scientists being interviewed refuse to say the probability is zero, because it isn't exactly zero, even though from a practical point of view it is no more likely than many other things we would write off as impossible. So the lay person hears this, and thinks there's a realistic possibility, no matter how small, of the end of the world.

So the question is, how long would this actually take?
See my previous comment about the Sun going nova before the Earth is consumed. :)

On its way to the center of the Earth, the black hole will only consume anything that actually collides with it on the way down. And since its event horizon will be about the size of a single atom, and since matter is almost entirely empty space to begin with, it will collide with very little.

See my previous post. The Mini-black hole can easily be kept from falling into the earth by a simple EM force to hold it up if there is ANY EM aspect to it at all. Even without it, the total gravitational attraction between the mini-hole and the earth is quite negligible, so it is unlikely to move that way anyhow.

And should it pass through solid matter, see the second half about tossing golf balls from the seats around a football field and trying to hit a grain of sand in the middle of it. You are more likely to hit that grain of sand than the mini-hole is to intersect any mass and absorb it.

See my previous post. The Mini-black hole can easily be kept from falling into the earth by a simple EM force to hold it up if there is ANY EM aspect to it at all. Even without it, the total gravitational attraction between the mini-hole and the earth is quite negligible, so it is unlikely to move that way anyhow.

And should it pass through solid matter, see the second half about tossing golf balls from the seats around a football field and trying to hit a grain of sand in the middle of it. You are more likely to hit that grain of sand than the mini-hole is to intersect any mass and absorb it.

It's hard enough to get a hole-in-one to 10 cm hole, not to mention 1 mm...

I'd be more worried about killer strangelets

But even they aren't a real threat comparable to a car accident etc.

Even without it, the total gravitational attraction between the mini-hole and the earth is quite negligible, so it is unlikely to move that way anyhow.
Gravitation has the same attraction for everything that has mass--at the Earth's surface, a mini-black hole would still accelerate downwards at 32 feet per second per second.

Though we're in agreement that its odds of actually hitting anything on the way down are extremely low.

The thing that has me wondering is: once the mini-black hole reaches the center of the Earth, there would no longer be any gravitational pull on it--since the source of said gravity is now all around it--but there is a great deal of pressure down there, so the Earth's mass would still be pushing inwards towards the hole.

Then I think about how long it takes the bathroom sink to empty through a hole many billions of times larger than a single-particle black hole, and I stop worrying. :)

The thing that has me wondering is: once the mini-black hole reaches the center of the Earth, there would no longer be any gravitational pull on it--since the source of said gravity is now all around it--but there is a great deal of pressure down there, so the Earth's mass would still be pushing inwards towards the hole.
If the black hole were to fall to the center of the earth, it would not stop at the center. The momentum would keep it going such that it comes out the other side. It would oscillate harmonically, except that it would slow down as it bumps into stuff, and gains mass. If the black hole had non-vertical velocity, that would be preserved, and the path would instead be an ellipse.

But that's assuming that it doesn't decay, and that it doesn't interact electromagnetically, two not quite valid assumptions.

The pressure inside the earth would not affect a neutrally charged subatomic object. If the black hole had a charge then it wouldn't fall the same way; it would be pulled by local charges much more than by gravity.

See, this question is freaky enough that we're all forgetting stuff. :)

I'm solidly in the "the hole would evaporate" camp because Stephen Hawking said it and I pretty much take him at his word--but assuming it didn't: yes, the "hole" would fall back and forth through the Earth, but its event horizon would be so small that I don't think it would hit anything for a LONG time.

Gravitation has the same attraction for everything that has mass--at the Earth's surface, a mini-black hole would still accelerate downwards at 32 feet per second per second.

That is the acceleration that WOULD occur in the absence fo any other forces. My point was that due to that acceleration and the extremely small mass of the mini-Hole, it is quite simple for any other force to counteract the attraction. Of course, the "other forces" is limited to fields since any mass or energy making direct contact is very unlikely and will result in absorption, not interaction. But there are PLENTY of casual fields in the air (listen to the raido if you don't believe me. Or talk on your Cell Phone, or use a Bluetooth handset, or Microwave a burrito, or use Wi-Fi....).

The thing that has me wondering is: once the mini-black hole reaches the center of the Earth, there would no longer be any gravitational pull on it--since the source of said gravity is now all around it--but there is a great deal of pressure down there, so the Earth's mass would still be pushing inwards towards the hole.

The attraction of the earth is only uniform on the surface because the surface is so darn huge compared to the scale we are talking about. As you get closer to the earth (within it) the gravitational pull will decrease. Because now there is less mass beneath you pulling you down, and there is now some mass above you pulling you up.

Yes, the particle will still wind up oscilating were it to get to the center, but it would be a VERY minor oscilation. But again, that assumes there is NO force exerted except for gravity. The electrical field of a single ion would be far more than enough to overcome the rather minute forces of gravity once it gets even halfway through the earth.

Ah. In that case, the black hole would probably stay inside the accelerator. :D

Just make sure nobody shuts the damn thing off...... :eek:

Just launch it into the sun in that case =p