**Super collider sparks super conversation**

MY BROTHER JAE ASKED

> So can this (www.cnn.com) really work?

> What would the black holes be like?

I RESPONDED

> Black holes may exist where a highly dense organization of mass is

> ample to cave in on itself. But for a black hole to continue to grow

> it must acquire mass … else, it collapses …

>

> So, if a black hole is so small that during its brief existence it

> cannot actually obtain any matter around it, then it burns out. The

> black holes this machine could create cannot gobble galaxies, let

> alone an arm chair in the office of the observer, for they are only a

> millionth of an inch across with about as much gravitational pull as a

> baseball on a moth. Nothing.

JAE INQUIRED

> even at that, where does the matter go that gets sucked in? let’s

> say an arm chair was sucked in, where would it go?

I RESPONDED

> So that is the interesting part. Some theories show a wormhole to

> another part of our universe (which would be a white hole, a place where

> matter just appears for no apparent reason) or into a parallel universe,

> the strength of the field energy enough to collapse the space-time

> continuum and bring two universes in contact.

>

> Let me get an expert … hold on :)

>

> kai

Hi Guys

Nice to “meet” you, Jae.

What Kai has described so far is pretty accurate. As far as the question of where the matter that a hole swallows goes, it is not completely understood because the interior of a black hole itself is not completely understood. This opens the doors for a lot of speculative ideas, including what what Kai mentioned. However, if you want to stick to what is generally accepted by physicists, here goes —

The problem with the black hole interior, is that it contains a mathematical singularity or an infinity. The reason for this infinity is that once matter has collapsed enough (i.e. become dense enough) that an event horizon has formed around it (i.e. a black hole has formed) it can be proved that the matter has to keep getting compressed indefinitely. In simpler words, because gravity is so strong for a such a compact object, it has to keep collapsing under its own weight — indefinitely. Nothing can stop this gravitational collapse. So, what is the end result of such a process? It would have to be a mathematical infinity — because it would eventually end up as a point (zero-size) with all that mass — the physical density (mass per unit volume) would literally be infinite! And we don’t think that Nature has real infinities floating around, so we know that is a serious problem in our understanding.

This infinity is also the reason that we can’t tell what happens next. Imagine you had a computer simulation crunching the numbers that follow the process of gravitational collapse. When the simulation would reach that infinitely dense state, the numerics would simply fail because they wouldn’t be able to handle a genuine, physical, infinity. This is the root cause of why our understanding of the interior structure of black holes is stuck. In addition, if you added more matter into the hole, it would also eventually settle in with the interior singularity!

There is hope though. We actually know why we encounter this problem — we even expected it! The reason is that in this picture we’re ignoring the Physics of the small i.e. quantum physics. The hope is that if we correctly incorporate both gravitational and quantum physics concepts — we wouldn’t have this problem.

Now, the problem of “quantum gravity” as needed here, is a big open problem in theoretical physics. Its over 60 years old and even individuals like Einstein and Feynman have tried their luck at it — with no success. The only thing that has come close, is String Theory, but that too has major issues of its own. I actually work on an approach to quantum gravity myself (with collaborators, of course) — one that is less ambitious and less radical when compared with String Theory. And we are trying to answer these types of questions in the context of that theory. This theory is called “loop quantum gravity” or “quantum geometry” and it is showing lots of promise. One of the cool results (results, not assumptions) of this theory is that space-time is fundamentally discrete (at a very small scale)! This is a radical shift from how we normally think of space and time, and is likely to help us address a host of current problems in theoretical physics. Stay tuned ;-)

Sorry this became somewhat long. But, I hope this helped a bit ..

Regards,

Gaurav

———————————————–

GAURAV KHANNA

UMass Dartmouth, Physics

http://gravity.phy.umassd.edu/

“Black holes are where God divided by zero.” – Steven Wright