I really shouldn't be nervous about this...right? [img]/phpBB/images/smiles/icon_wink.gif[/img]

An article from 2001 about proposed creation of miniature black holes here:
http://www.sciencedaily.com/releases...1101060839.htm

Find the paper by physicists Steven Giddings and Scott Thomas here:
http://www.arxiv.org/abs/hep-ph/0106219

This esoteric research may offer direct proof of unified field theories that predict the existence of extra dimensions beyond the three we live in. It is apparently from minute protrusions of these extra dimensions on the Quantum level, that these tiny black holes might exist.

Theoretically, tiny black holes should evaporate in extremely short time spans.

(Rather than drop to the center of the Earth and eventually absorb our entire planet, or open portals to dimensions that can't be closed.) (I'm just being entertaining with these classic Sci-Fi thoughts...right?)

[img]/phpBB/images/smiles/icon_eek.gif[/img]

Well, an isolated miniature black hole will evaporate very quickly - disastrously so, if it's fairly massive (like, say, the mass of a mountain released as energy all at once).

But I'm not so sure about what happens if the microhole is in an environment where it can draw in new material. My guess would be, if it's able to pull in mass faster than it's evaporating, it could remain stable... and if its infall rate is greater than the evaporation rate, it would grow.

But is the Earth's atmosphere dense enough to meet this criterion for a "stable" microhole? Is even solid rock dense enough? Is neutronium? I doubt it, but I don't know how to calculate it. After all, the event horizon of such a hole is teensy... much smaller than the radius of a proton... so it would always be "a long way" from any matter, even if it was located inside an atomic nucleus.

Except... it would have halacious tides, and might be able to draw in nuclei from much, much farther away than its event horizon.

Gulp!

I actually used this idea in a science fiction novel I wrote (sorry, it's unpublished). My microhole started out as 400 tons of lead. Things went downhill from there...

But I made some assumptions about the hole's infall radius that I can't really justify.

Hmm... I don't wanna figure out the exact numbers, but I don't think a mountain-mass black hole would have a whole lot of gravity. So it wouldn't actually do much in the way of pulling other objects towards it, and as for air molecules, a breeze would be strong enough to carry anything away from it...

I'm not saying that it wouldn't eat matter, I'm just saying that it would probably happen pretty slowly. An atom would have to get really close to be affected.

<font size=-1>[ This Message was edited by: Simon on 2002-02-25 15:16 ]</font>

The following assumes I've done my math correctly - a tenuous assumption at best.

A black hole that would evaporate in 1 second due to Hawking radiation would have a mass of about 2.3e5 kg. This gives a Schwarzchild radius of 1.8 x 10^(-22) meters. This is about 4 orders of magnitude smaller than an electron.

Eek!
<font size=-1>[Edited to correct math error not so Eek! after correction]</font>

A black hole with the same radius as an electron has life span greater than the universe.

Eek! Eek!




<font size=-1>[ This Message was edited by: Wiley on 2002-02-25 17:57 ]</font>

Those numbers look pretty close to what I got for my 400-ton microhole. Same order of magnitude, I think.

The point isn't that it has relatively small gravity of its own, though; what brings in the goodies is the gravitational gradient, and that's immense, locally. The microhole would be a true "spacetime warp", producing incredible effects... but on a very small scale.

In my story, I started by figuring the thing would leave a one-atom-wide hole through a planet as if fell through. Unfortunately, that turned out to be negligible; the Earth would still outlive the 5 billion years (or so) the sun has left. So I worked backward from how long I wanted it to take to eat a planet, waved my hands a little, and argued that it drew in atoms from a 10-atom radius or so, and grew exponentially; I got the number down to a few thousand years -- and considerably less before the effects began to be serious (earthquakes etc.)

Whew! The Earth will succumb to our madness long after I'm dead. I can live with that. [img]/phpBB/images/smiles/icon_smile.gif[/img]

I suppose the size any black hole created in a lab will be constrained by the amount of matter/energy used to create it. My guess is they would be hard pressed -sorry, couldn't resist- to create own bigger than few grams. I shan't worry.

The article of the original post says these mini-black holes evaporate in 1e-17 seconds which corresponds to a mass of 0.5 kg.


<font size=-1>[ This Message was edited by: Wiley on 2002-02-25 17:51 ]</font>

If it isn't too difficult to type out in this venue, would you please post the math for that? I suspect it would be very interesting. Thanks.

If it's math you seek, also check out the original paper I linked above. (It's almost as dense as the objects themselves.) [img]/phpBB/images/smiles/icon_wink.gif[/img]

The comments on this thread are quite interesting. Thanks all.

Also, as was pointed out earlier in this thread, the other link (to the news item) states:

"Giddings answered that one of British physicist Stephen Hawking's greatest discoveries is that black holes evaporate. Small ones evaporate exceedingly quickly, in around 10 to the minus 17 seconds. "They simply don't have time to absorb an appreciable amount of matter before they explode," he said. When they explode they are expected to send out a tiny amount of radiation, which scientists will be able to detect."

Radiation detected after the event is right in line with the kind of physics being done with slamming particles together in colliders. I don't come close to understanding it, but these tiny black holes are perhaps not unlike cosmic rays colliding -- except the extra dimensions (if they exist,) increase the effect of gravity on a particle into the black hole range by amplifying (my misguided word) its attraction through the extra protruding dimensions.

Strange stuff.





<font size=-1>[ This Message was edited by: Chip on 2002-02-25 21:51 ]</font>

The math is a little more than I would want to type out, but I did a search this morning and found the following web page: Black Hole Evaporation. Basically you assume the black hole is a ...ahem... a black body radiator at the Hawking temperature. This gives the rate that energy/mass is radiated. Solve for the time differential and integrate to get total time.

If you want more math, the try here. This is a graduate level introduction, i.e., a good working knowledge of general relativity and quantum mechanics is assumed.

Thanks for the links everyone! I'll have to go through them slowly, but I think I should be able to figure them out. The one on black hole evaporation is particularly interesting. I was aware of the radiation issue, but I had just never thought about a black hole actually evaporating. Wacky.

Lol! I wouldn't worry too much, as any holes made in an accelerator would have a mass that could be easily stated in GeV or TeV, rather than kg, g, or mg [img]/phpBB/images/smiles/icon_smile.gif[/img]

Sounds very cool... hope they succeed... and I hope we don't find out the hard way that BHs don't evaporate! But if that's the case, it will certainly be a boost to NASA's budget, as suddenly getting off of this rock becomes a high priority! [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

__________________
If E = MC², why do I have less energy the more mass my body acquires?
That is all.

--Azpod... Formerly known as James Justin

Wouldn't the evaporation of small black holes contradict the notion that "there are no real black holes in the universe"?
How could they evaporate, if they had never been black holes in the first place?
Would a micro-neutron star evaporate too?...

Since Hawking, black holes aren't really black. They do emit energy. Their effective temperature is inversely proportional to mass so that black holes of a few solar masses have temperatures on the order of micro Kelvins. Black holes of this size have a lifespan longer many times the age of the universe, consequently Hawking radiation does not have any astrophysical significance.

The black holes to be created in the laboratory are hot and decay rapidly. (We hope. [img]/phpBB/images/smiles/icon_smile.gif[/img]) Black holes are one of the few places where quantum mechanics and general relativity meet, so being able to test "quantum gravity" in the lab should open up new doors.

Neutron stars don't evaporate like black holes do. Hawking radiation, the cause of the evaporation, requires an event horizon, which Neutron stars do not have.

There was an article in Scientific American some years ago, entitled "The Breakdown of Empty Space." Apparently, in the vicinity of a heavy atomic nucleus, you can get "Hawking Radiation," i.e., the "realization" of one of a virtual pair of particles. The other particle is caught by the nucleus. So, if the surface of a neutron star is sharp or sheer enough (and it seems as if it ought to be) then it probably would emit tiny amounts of Hawking Radiation...

Silas

It seems like this would not conserve energy. If a particle/anti-particle pair are spontaneously created in normal space, they are attracted to each other and destroy each other. The combined process conserves energy although the separate processes of creation and destruction do not. So if in normal space, the virtual pair do not recombine, the process will violate the conservation of energy.

The black hole gets around this by the event horizon. Below the event horizon, spacelike becomes timelike and timelike becomes spacelike, everything becomes reversed. So the anti-particle caught by the black hole removes energy from it.

This is how I understand the process, and I am neither a black hole nor a particle physics expert. So take everything above with a big Everest size grain of salt.


<font size=-1>[ This Message was edited by: Wiley on 2002-03-01 15:50 ]</font>

There is still something that I don't understand.
Some people claim that there cannot be "real" black holes in the universe because it would take an infinite amount of time - in the outside, normal space - for the singularity to form. Since the age of the universe is generally assumed to be finite, no such infinite amount of time has ever gone by. Therefore there are no real black holes in the universe.
(I hope I got this right...)
My question is: if there can't be any real black holes in the universe - only objects *on the verge of becoming* black holes, after an infinite amount of time -, then a micro-black hole would never actually form, and thus it would never actually evaporate.
Am I right, or am I way off track?...

I think the main thing is the event horizon, not the singularity. If the singularity take an infinite amount of time to form, the event horizon still exists. If the event horizon still exists, then the black hole can evaporate. I expect that the experiment, should they succeed in creating a black hole, will explain some of the structure of a black hole, possibly including the question about the formation of the singularity.

__________________
If E = MC², why do I have less energy the more mass my body acquires?
That is all.

--Azpod... Formerly known as James Justin

I'm not sure but your question may really be about the different observers.

Consider an observer far away from a black hole. The observer sees the matter falling into the black hole slow down and eventually stop at the event horizon. Time dilation between the event horizon and the far away observer becomes infinite. In other words, to the far away observer time appears to stop at the event horizon. This effect, where all incoming matter appears to stop and collect at the event horizon, has let some scientist to call black holes as "cosmic junkyards".

Now consider an observer falling into the black hole. This observer would not notice anything special as he or she passed the event horizon. The observer just keeps falling and falling.

Now I think I see what informant was asking.

Yes, the singularity would never truly form. If we could directly measure the radius of a black hole, we would get infinity. When we talk about the radius of a black hole, we are actually refering to the reduced circumference, the circumference divided by 2 pi. This is an observer independent quantity.

While the singularity has not formed, there can still be an event horizon. Thus if enough mass to create a black hole of radius 1 km were compacted into a sphere of radius 1mm, there would be an event horizon at 1 km. You don't need a singularity to have an event horizon because when we determine the field outside of a body, we can treat that body as point source.

Mostly, I think this shows we still have a long way to go before we truly understand what happens inside a black hole.

I most certainly HOPE they would evaporate quickly!!! [img]/phpBB/images/smiles/icon_eek.gif[/img]

I think small mass black holes require quantum gravity(which we don't have yet) to predict what would happen if they were as small as a particle or two.