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Artificial black holes: on the threshold of new physics

By by Michelle / May 23, 2003


For several decades now, there has been a fundamental problem with modern physics. The problem is actually an embarrassment of riches: we have not one, but two systems that describe the universe remarkably well. One is quantum mechanics, which describes the rich and subtle behavior of waves and particles. The other system, general relativity combines space and time into one continuum, providing us with the best description of the movement of the planets and the expansion of the universe.

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Scientists have realized that to truly understand the universe, we've got to make these two systems work together, even merge into a single, more accurate depiction of reality. But the two systems have not given up their independent identities easily. The challenge has been to find conditions in the universe where both the effects of quantum mechanics and general relativity are significant and measurable.

For this to be the case, you've got to pack a whole lot of mass (as general relativity mainly relates to gravity), into an extremely tiny volume (where quantum effects become important). Where do you think those conditions might exist? Fortunately, the universe has provided us with such a natural laboratory for fundamental physics: black holes.

Black holes are gravitational relics of dead stars. They are, quite literally, bottomless pits in space and time that are capable of swallowing any amount of material. Everything a black hole swallows gets compressed into an unimaginably tiny central region called a singularity. According to our current knowledge, this singularity is infinitely dense, and infinitely small. And if you think that doesn't make any sense, you're not alone.

Scientists have long viewed the central region of a black hole with the same kind of suspicion that early mariners held for regions of the map that read "there be monsters." It just can't be right. If the only thing we can say about the singularity is that it doesn't make any sense, then there must be a problem with the way we're trying to understand it. So there, deep in the hearts of black holes, may lie the clues to how quantum mechanics and general relativity dovetail together under extreme conditions.

Unfortunately, there's an intrinsic problem with actually observing what conditions near the center of a black hole are like. Black holes, most famously, have the ability to suck light itself into their maws, effectively cutting themselves off from the rest of our universe. The "point of no return" for light as it nears a black hole is called the event horizon, as no event can ever be observed taking place beyond it. There seems to be no way to get any information about what is happening inside a black hole, as no kind of signal can ever come out.

Or can it? In the 1970's, the well-known physicist Stephen Hawking proposed a way in which black holes radiate energy away, eventually "evaporating" completely. Over time, the black hole gradually leaks away all its energy and disappears in a final burst of radiation.

The final death throes of a black hole, scientists suspect, might be very illuminating indeed. Exactly how a black hole dies and what sort of information is carried in the Hawking radiation could tell us quite a bit about what the center of a black hole is really like.

But there are two major problems with observing the last gasp of a black hole. For one thing, the nearest black holes we know of are light-years away, making accurate measurements of Hawking Radiation nearly impossible. Secondly, black holes take a huge amount of time to evaporate, the time being proportional to their mass. Even relatively small stellar black holes would take longer than the current age of the universe to dissipate, and the monster black holes in the middle of galaxies may be the last things to exist in our universe, taking ten thousand trillion trillion trillion trillion trillion trillion trillion trillion years to die away (sorry, I just have to do that sometimes. That is the actual estimate of how long a massive black hole will last).