Intresting blackhole fact I jsut found.

[DemoCoder]

Blackholes show that an object's "size" is pretty much an illusion. Matter can be compressed much smaller than its "natural" size, just look at the compression ratio between a neutron star and its uncompressed state.

At some point, the gravitational force becomes so large that not even the degeneracy pressure between electrons or between neutrons, et al, can resist, and eventually there is nothing to stop the collapse.

In highly compressed states, matter behaves more like waves, and the idea that matter acts like little marble spheres you learned in high school chemistry or physics, where they have a defined volume/radius, and cannot occupy the same place at the same time, goes out the window.

Bose-Einstein condensate also shows how you can coax atoms to lose their identity and huddle closer together.

By definition, any object whose radius is smaller than its Schwartzchild radius is a blackhole.

 

[BlackAngus]

Hey all!
Ive read b3d fourms for quite a while now , and usually have nothing to say. (still dont really). But I have to say you are all FREAKS!!!!!!!
With that said this thread made me join up.
I just wanted to say some of you guys are brains, and thanks for some of the links here to good articles and lectures.
Hopefully Ill have something more constructive to add in the future. =)

BA

 

[Fred]

Semi classically, you can have Microscopic black holes. In fact the Large Hadron Collider in Cern (due in 2006) that accelerates particles to the TeV scale might indeed form tiny black holes. If you pack enough energy in a small enough space (past the schwarschild radius) you'll get a black hole.

These will evaporate and leave a spectrum that should in principle be detectable.

The thing is, its a little bit hazy in the case of a microscopic bh because quantum field theory is not really sufficiently advanced to fully understand the properties.

String theory is an attempt at Quantum gravity, but it still has a ways to go. There are other alternatives, like loop quantum gravity, Non commutative geometries, etc etc

Personally I don't like String theory, it irratates me at this stage frankly, its still extremely raw. Ill give a link to a summary of that in a few

As for singularities in general relativity and black holes. One has to understand that its a little bit complicated. One can in general, rewrite the metric so that certain traits of the singularity are removed. In the case of a schwarschild bh, these are called UV coordinates or Kruscal Schecheres coordinates

 

[Bigus Dickus]

Out of curiosity, does someone know the equation describing how Hawking radiation relates to the mass of a black hole? All this talk about a tennis ball mass black hole has me wondering how long such a microscopic black hole could survive before vaporizing itself. I'm guessing a very, very short time.

As interesting as miniature black holes are, I find the concept of extremely large and relatively low density black holes to be equally fascinating. It is possible for a black hole to be "black" without the gravity inside causing matter to collapse to a point (or whatever the "correct" theory of quantum gravity will ultimately reveal that it collapses to)... at least not for a relatively long time. If our universe is closed (which, at the moment, it doesn't appear to be), then it could be considered a black hole, and would appear as such to an outside observer (or so I'm thinking... I could be missing a crucial distinction there).

 

[arjan de lumens]

Using a few formulas I found here and here the amount of Hawking radiation and the lifetime of a black hole can be computed rather straightforwardly. For a black hole with the mass of a tennis ball, I get a lifetime of about 10^-19 seconds, give or take an order of magnitude or so. Which indicates that even if you managed to create such a beast, it would immediately explode with the power of a medium-size nuclear weapon.

 

[Heathen]

Which indicates that even if you managed to create such a beast, it would immediately explode with the power of a medium-size nuclear weapon.

So how big are the jobbies Cern will create?

 

[arjan de lumens]

The collision energy of the CERN LHC is stated to be 7 TeV (see under 'Design Performance'), which would be about 1.2* 10^-23 kilograms, or 1.1*10^-6 joule, or, in case of a black hole, a radius of about 1.8*10^-50 meters. Which, AFAIK, wouldn't be noticeable to a human. Given that this is still much weaker than what cosmic rays can do, I wouldn't worry too much.

 

[Bigus Dickus]

Thanks arjan... that's what I was thinking.

 

[Neeyik]

Arjan - it would also evaporate in about 10^-85 seconds too. I think one could argue that black holes simply could not be created on this basis.

 

[arjan de lumens]

One issue with black holes is that they are believed to possess only mass, charge and angular momentum and no other defining characteristics. So if a black hole appeared during the tests at CERN, it could, at least in principle, no matter how small and short-lived it is, break a bunch of the symmetries and invariants that otherwise hold true for particle-particle interactions.