I know next to nothing about astronomy and physics and such, but, having read several recent stories about that new particle accelerator, I have to ask:

What would prevent a manmade black hole from consuming everything around it, growing in size and eventually consuming the entire planet? Is it that the blackhole wouldn't have enough mass to be stable or prevent almost instataneous evaporation?

Black holes evaporate by Hawking radiation. The rate of evaporation is a function of mass. A stellar mass black hole will outlast the universe. A planetary mass black hole will last a few million to a few billion years. A black hole with the mass of an atomic nucleus will last less than a nanosecond, barely enough time to fall (under gravity) the width of a proton.

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That depends on what you mean by outlasting the universe. Certainly they wouldn't evaporate before the universe became very, very cold and dark.

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This was the big scare at the building of one of the particle accelerators in the US. However, indeed particles are accelerated close to the speed of light and hence their mass increase with the well known gamma. However, a "particle" can only collapse to a BH in its own frame, and there it just has its normal rest mass and cannot collapse into a BH.

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善數, 不用籌策 (shàn shù, bù yòng chóu cè)
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“A good scientist has freed himself of concepts and keeps his mind open to what is”
道德經, 二十七 (dào dé jīng, 27)

OK, what I meant was the universe as fit for "life as we know it", not until the universe dies of heat death (since heat death won't occur until the last SMBH evaporates).

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I was under the impression that Earth mass black holes (if any) evaporate in much less than millions of years. Their event horizon is submicroscopic, so infalling matter usually does a sling shot maneuver and/or collides at very high speed just outside the event horizon. This produces intense radiation that insures that very little mass gets inside the event horizon. Earth may have several mini black holes with a small fraction of Earth's mass orbiting each other inside the core of Earth. The only evidence (I know of) is Earth possibly has more internal heat than we can account for by more probable heat sources. Earth and Mercury also have the highest average density in our Solar system.
The laboratory micro black holes have less than 1 kilogram of mass, and are thus so tiny, they would need to dismantal a quark to get it inside the event horizon. Does anyone think a quark can be dismantled?
As tusefen suggested the laboratory BH may exist in the black hole's frame of reference, but not in our frame of reference.
On the other hand, some parts of the theories are likely wrong, so my opinion is: we should not risk Earth by making black holes until we can make them outside our solar system. The knowledge we can gain is likely not worth even an infinitesimal risk. Neil

Uhhh, NO, I did not suggest it in that way. I suggested that a particle in an accelerator gains mass, as it is accelerated, so in our frame it is suddenly super heavy and should go to the weight watchers, but in its own frame it just has its original rest mass, and hence, the particle accelerator cannot create a BH in the laboratory.

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善數, 不用籌策 (shàn shù, bù yòng chóu cè)
He who is good at counting, uses no counting tools
“A good scientist has freed himself of concepts and keeps his mind open to what is”
道德經, 二十七 (dào dé jīng, 27)

And I would add to these theoretical arguments the very simple observational argument-- if people could make black holes in a the laboratory using high energy particles, note that nature already makes these particles in deep space and bombards the Earth with them all the time. We could never do something nature isn't already doing, and no black holes are causing any problems now.

Actually, a black hole the mass of the earth would have a radius of about 8.9mm

Furthermore, the slingshot does not work with a black hole. You can't use Newton's laws of motion in such conditions. Matter does actually spiral into the hole. You would get some spectacular collisions of infalling material; the result of such collisions will send some material into the hole and others fired away. A black hole that size would suck up plenty of mass. In the absence of new material, however; it would evaporate in about 5.66 * 10⁵⁰ years. That is much much longer than the age of the universe.

The life time of a black hole is proportional to the cube of its mass. A black hole weighing about 230 tonnes would evaporate in about a second.

Details for calculations at this thinkquest page.

Cheers -- Sylas

Ah, the voice of reason.

Besides, speed and or collisions DO NOT create black holes!

The only black holes we know about are caused by gravitational collapse!

After all, it takes a star at least 3-8 times as massive a our sun to make a black hole, any less than that at a stars end and it becomes a neutron star.

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Someone feel free to correct me, I'm sure I'm wrong with my reasoning here, but my intuition tells me that speed/collisions create black holes because the collision of these tiny particles causes a state of extremely dense matter, dense enough to form a tiny artificial black hole (a few atomic nuclei in mass, right?)

Nielzero, the primary reason for the amount of heat under the Earth's crust isn't pressure, it is radioactivity. Potatoes are more radioactive than apples for that reason. The difference is slight topside where we are, but in the core the radioactivity is so strong it melts solid rock. I'll try to dig up some corraborating links.

I stand corrected. Pulled from Wikipedia's entry on the Earth's Core:
"While the scientifically mainstream explanation for these temperatures gradients is that the heat is simply left over from the planet's initial formation, a theory espoused by J. Marvin Herndon states that fast breeder nuclear reactor type reactions occur in the core of Earth."

Well, I was wrong Live and learn!

Why wouldn't the slingshot work so long as you avoid the event horizon?

Can a falling object actually enter a black hole?

Yes, see the discussion here.

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