A couple of SciAm articles that may be worth discussing

[Martin]

personally I think what they say in the first article (Carr and Giddings) is highly speculative and likely to be wrong----it depends on there really being extra dimensions as imagined by string thinkers. don't hold your breath

but maybe someone wants to discuss the possibility that Carr and Giddings raise anyway

the first one is:

 

http://www.sciam.com/print_version.cfm?articleID=000CCC72-2AED-1264-980683414B7F0000

 

April 25, 2005

 

Quantum Black Holes

Physicists could soon be creating black holes in the laboratory

 

By Bernard J. Carr and Steven B. Giddings

 

"Ever since physicists invented particle accelerators, nearly 80 years ago, they have used them for such exotic tasks as splitting atoms, transmuting elements, producing antimatter and creating particles not previously observed in nature. With luck, though, they could soon undertake a challenge that will make those achievements seem almost pedestrian. Accelerators may produce the most profoundly mysterious objects in the universe: black holes.

When one thinks of black holes, one usually envisions massive monsters that can swallow spaceships, or even stars, whole. But the holes that might be produced at the highest-energy accelerators--perhaps as early as 2007, when the Large Hadron Collider (LHC) at CERN near Geneva starts up--are distant cousins of such astrophysical behemoths. They would be microscopic, comparable in size to elementary particles. They would not rip apart stars, reign over galaxies or pose a threat to our planet, but in some respects their properties should be even more dramatic. Because of quantum effects, they would evaporate shortly after they formed, lighting up the particle detectors like Christmas trees. In so doing, they could give clues about how space-time is woven together and whether it has unseen higher dimensions.

 

 

A Tight Squeeze

In its modern form, the concept of black holes emerges from Einstein's general theory of relativity, which predicts that if matter is sufficiently compressed, its gravity becomes so strong that it carves out a region of space from which nothing can escape. The boundary of the region is the black hole's event horizon: objects can fall in, but none can come out. In the simplest case, where space has no hidden dimensions or those dimensions are smaller than the hole, its size is directly proportional to its mass. If you compressed the sun to a radius of three kilometers, about four-millionths of its present size, it would become a black hole. For Earth to meet the same fate, you would need to squeeze it into a radius of nine millimeters, about a billionth its present size.

 

Thus, the smaller the hole, the higher the degree of compression that is required to create it. The density to which matter must be squeezed scales as the inverse square of the mass. For a hole with the mass of the sun, the density is about 1019 kilograms per cubic meter, higher than that of an atomic nucleus. Such a density is about the highest that can be created through gravitational collapse in the present universe. A body lighter than the sun resists collapse because it gets stabilized by repulsive quantum forces between subatomic particles. Observationally, the lightest black hole candidates are about six solar masses.

 

Stellar collapse is not the only way that holes might form, however. In the early 1970s Stephen W. Hawking of the University of Cambridge and one of us (Carr) investigated a mechanism for generating holes in the early universe. These are termed "primordial" black holes. As space expands, the average density of matter decreases; therefore, the density was much higher in the past, in particular exceeding nuclear levels within the first microsecond of the big bang. The known laws of physics allow for a matter density up to the so-called Planck value of 1097 kilograms per cubic meter--the density at which the strength of gravity becomes so strong that quantum-mechanical fluctuations should break down the fabric of spacetime. Such a density would have been enough to create black holes a mere 10–35 meter across (a dimension known as the Planck length) with a mass of 10–8 kilogram (the Planck mass)...."

(continued at the SciAm site)

 

=========

the other one is

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009A312-037F-1448-837F83414B7F014D

 

FEATURE ARTICLES

May 2006 issue

 

 

The First Few Microseconds

In recent experiments, physicists have replicated conditions of the infant universe--with startling results

By Michael Riordan and William A. Zajc

 

 

"For the past five years, hundreds of scientists have been using a powerful new atom smasher at Brookhaven National Laboratory on Long Island to mimic conditions that existed at the birth of the universe. Called the Relativistic Heavy Ion Collider (RHIC, pronounced "rick"), it clashes two opposing beams of gold nuclei traveling at nearly the speed of light. The resulting collisions between pairs of these atomic nuclei generate exceedingly hot, dense bursts of matter and energy to simulate what happened during the first few microseconds of the big bang. These brief "mini bangs" give physicists a ringside seat on some of the earliest moments of creation.

During those early moments, matter was an ultrahot, superdense brew of particles called quarks and gluons rushing hither and thither and crashing willy-nilly into one another. A sprinkling of electrons, photons and other light elementary particles seasoned the soup. This mixture had a temperature in the trillions of degrees, more than 100,000 times hotter than the sun's core..."

 

(continued at SciAm)

[5614]

Regarding the first article on artificial black holes:

 

I think that black holes could be made and probably will be, but whether or not they prove higher dimensions is, as you said, highly speculative.

 

I think they will be able to give a greater insight into some of Hawkings work and will act as experimental proof that black holes decay, if they're gonna make black holes then lets hope that Hawking is right that they decay! I think he's right, but there's always those who don't.

 

It will also being interesting experimental view on the whole relativity vs. quantum theories on what happens to the information in a black hole.

 

I think the results could be interesting, not for a specific answer, but just in general.

[Bettina]

I have a question.

 

Why are they bothering with the RHIC accelerator with its 100 GeV when the LHC will be one million GeV when completed in 2008. (Was supposed to be 2007 )

 

Isn't this a lot of money for something thats going to be obsolete? Or is there more to this.

 

Bee

[5614]

LHC has been postponed till 2008? Aww, that's a shame...

 

RHIC might not be the most powerful in the world but it will still be powerful enough to make discoveries and run new experiments. The RHIC complex runs many experiments and employs hundreds or probably thousands of scientists, are you saying they should stop it all just because there is a bigger and better one round the corner?

 

RHIC will still be useful because it is still capable of doing high power experiments, not as high as LHC, but high enough for it to yield useful results. Sure LHC could do these experiments too, but LHC has its own experiments it wants to do. The two accelerators serve different purposes and both are valid purposes.

 

Also LHC is run by CERN, RHIC was sponsored by the US. They're different companies doing different things with their own money.

 

Also I couldn't find anywhere saying that LHC has been postponed till 2008. Also not sure where you got the 1 million GeV from either, according to the official site it will have 7 TeV or 7000 GeV.

[Bettina]

Also I couldn't find anywhere saying that LHC has been postponed till 2008. Also not sure where you got the 1 million GeV from either' date=' according to the official site it will have 7 TeV or 7000 GeV.[/quote']

 

I got it on page 6 of Martins link. I think I misunderstood the GEV but here is the quote.

 

 

"Many physicists are now preparing for the next energy frontier at the Large Hadron Collider (LHC) at CERN. Starting in 2008, experiments there will observe collisions of lead nuclei at combined energies exceeding one million GeV."

 

Bee

[timo]

LHC has two operational modes: The proton-proton mode which is the 14 TeV, and a less famous heavy ion mode (the lead) which is at higher center-of-mass energies. Dunno the value there but the 10^6 GeV will probably correct.

 

Edit: It is: http://public.web.cern.ch/Public/Content/Chapters/AboutCERN/CERNFuture/WhatLHC/WhatLHC-en.html

[5614]

Oh yeah, because 1150 TeV = 1,150,000,000 MeV which is just over 1 million MeV.

conversion here: http://www.google.co.uk/search?hl=en&q=1150+TeV+to+MeV&meta=

 

I think where it says starting in 2008 doesn't mean that is when the whole collider will be ready, it means that is when that part (or that indivdual experiment) will begin.

[Martin]

Oh yeah' date=' because 1150 TeV = 1,150,000,000 MeV which is just over 1 million MeV.

...[/quote']

I think you are right in your conversion except that just made a typo and wrote M where you meant to type G

but it looks confusing. so if you can still edit you might correct it to say

"just over 1 million GeV"

[Martin]

One of the main people responsible for proposing to look for micro black holes at LHC, as a test of extra dimensions, is JoAnne Hewett

 

here is a press release with picture and some quotes

 

http://www.physorg.com/news10682.html

 

Here is her technical journal article with the calculations and precise statements and all:

http://arxiv.org/abs/hep-ph/0503178

 

the original press release claimed too much and there was some objection

and the journalist corrected it and added an asterisk to the title saying that

what was being proposed was a test of string theory*

 

(*under certain conditions)

 

the publicity departments at a place like Stanford SLAC have a difficult balancing job and

a bit of hype may get into how they TALK about a paper

but that does not affect that Hewett's paper is solid interesting work IMO

 

she is one of the people that run a group blog called Cosmic Variance

[insane_alien]

the density is about 1019 kilograms per cubic meter, higher than that of an atomic nucleus.

 

so just denser than water then? did you mean tonnes or something? or am i completely missing the point entirely?

[timo]

One of the main people responsible for proposing to look for micro black holes at LHC' date=' as a test of extra dimensions, is JoAnne Hewett

 

here is a press release with picture and some quote

 

[goes to hunt the press release']

I cannot recommend looking into her stuff, anyways. I remember blocking the printer room of a neighbouring institute for several hours by printing out a rather long paper of hers (our printer here refused printing it at all). This illegal use of institute-printers for the purposes of non-members (=me) would have gone unnoticed if not for those sexually understimulated physicists who had to find out what this "joanne.pdf"-job is .

[Martin]

... if not for those sexually understimulated physicists who had to find out what this "joanne.pdf"-job is .

 

what were they thinking! she just has a nice smile

 

 

but, in fact, it might not be a very good test of string actually

(some comments at woit's blog about that)

 

which a trouble with string, not JoAnne.

 

maybe her analysis shows a way to falsify LOOP gravity instead!

 

type of QG called spinfoam models has been worked out in 3D and 4D and depends somewhat on dimension

One would probably want to discard it is extra dimensions were found to be real. So finding micro BH at LHC would, one can argue, falsify the spinfoam models!

 

But not finding BH at LHC would probably NOT make string theorists give up. It probably is too much to say it would falsify string.

 

I tend to think that JoAnne has given an honor point (of being falsifiable or testable) to the Loop people's models.

 

Perhaps you see it differently?

 

============

 

Insane, if I remember right, the usual Planck density (of one planck mass per cubic planck length volume------i.e. unit mass per unit vol) is about 10^19 times water

[timo]

what were they thinking! she just has a nice smile

I doubt that the solid-state guys had exactly her in mind when they read the name of the file on the print-queue. We had to find excuses for using their printer, so I didn´t explicitely ask why the filename raised the attention.

 

 

but, in fact, it might not be a very good test of string actually

(some comments at woit's blog about that)

[...]

But not finding BH at LHC would probably NOT make string theorists give up. It probably is too much to say it would falsify string.

 

I tend to think that JoAnne has given an honor point (of being falsifiable or testable) to the Loop people's models.

 

Perhaps you see it differently?

Naturally, I honor all collider-predictions which proof or rule out certain models - even if they are made with the wrong event generator . Even if they just narrow the available parameter-space of proposed models, that´s already fine.

 

In the case of strings, however, my impression (which is totally taken out of thin air and certainly influenced by the bad reputation string theory has here) was that the parameter space of possible string models seems rather unlimited. This of course reduces the value of an exclusion-statement to ... well, in first approx to "parameter space excluded over parameter space avaliable equals zero".

 

I defenitely can´t judge about the relevance of the paper for string theory and less for lqg. But I could at least read and try to understand the paper.

EDIT: At least this one was printable on the theory-printers

[Royston]

With creating black holes...how exactly are they creating such high compression, and how is this acheived in a particle accelerator ?

[5614]

Black holes come along when there is very dense matter.

 

In a particle accelerator particles are moving very quickly with a lot of energy.

 

Now if I fire two particles with high energy towards each other they're going to collide, at the point when they do they will be very close (the high energy they have will overcome some of the repulsive forces they feel) and you could call the two particles quite dense.

 

Now obviously 2 particles don't make up a black hole, but if you were to fire many particles all together at high energy then, because of the high energy, they will all be able to overcome some of the repulsive forces between the particles and so will be able to get very close to each other, aka become very dense.

[Royston]

Thanks 5614, so are all the particles colliding at the same point to create the required density. If the fundamental forces are being broken, so the particles can be packed closer together...is it the energy, rate and direction at which the particles are being fired, that creates a small blackhole at a specific point ?

[Royston]

Sorry I was being lazy...didn't read till the end of the article. It's a lot clearer now. Dammit, I wish I'd stop asking questions on topics I won't be able to get my head round until I've finished my degree I come across as a right doofus.

[5614]

So does that mean I don't need to answer?!

 

It's just that the particles have enough energy to overcome the force which normally makes them repel.

 

Just like if I shot you at a concrete wall at say 0.5c you would have enough energy to get nice and close to it !

[Royston]

So does that mean I don't need to answer?!

 

It's just that the particles have enough energy to overcome the force which normally makes them repel.

 

Sorry 5614' date=' I missed this...but yeah (despite my confusing response) you did answer my question.

 

Just like if I shot you at a concrete wall at say 0.5c you would have enough energy to get nice and close to it !

 

Remind me to steer clear of your research, when you become a top physicist.