Monday, December 8, 2008

Black Holes

Dr. Syphers,

I have heard a lot of concern about black holes resulting from an atom smasher. I understand that these black holes would be of little consequence due to size and stability, but you mentioned to another student that they would quickly "evaporate." How can a black hole evaporate... actually, what exactly IS ia black hole?


P.S. Thanks so much for your time, which this project must have taken a lot of. Your answers were very complete and I feel like I have a greater knowledge about supercolliders and such. I really enjoyed getting to ask you questions, so thank you!

Thank you Lindsay,

About 100 years ago, Albert Einstein developed a new theory called the General Theory of Relativity. The theory describes how particles and light behave in reference frames that are accelerating. In particular, the theory shows that gravity can actually be thought of as space and time being "curved" by the presence of mass and energy. Thus a large star curves space around it and planets and spacehips traveling nearby will follow trajectories in space and time due to this curvature. For most "ordinary" cases, it gives the same results as Newton's old theory of gravity -- elliptical orbits, and so forth. However, Einstien's new theory was even more successful, as it explained why the planet Mercury's orbit seemed to "precess" in a way that Newton's theory of gravity couldn't explain. The theory also predicted that light rays will actually be "bent" in a strong gravitational field. This was soon observed to be true through measurements made during a total solar eclipse, and Einstein became world famous overnight!

Anyway, this same theory predicts that if there is enough mass and energy in one place in space, the gravity can be so strong -- space-time can be so curved -- that nothing can get away from the object, not even light. Since light cannot escape this region, it is called a "Black Hole." It requires a great deal of mass in a very small region of space. To date, there has not been any definitive evidence of a Black Hole, though there are some fairly good candidate regions of space that seem to imply a Black Hole might be there (like at the very center of the galaxy).

It wasn't until the 1970's that another famous scientist, Stephen Hawking, developed a theory that showed that a Black Hole (should one exist) should actually evaporate. His theory brings "quantum mechanics" into the Black Hole picture, and involves what are called "virtual particles" being created and instantly annihilated near the "edge" of the Black Hole. Anyway, he shows that this quantum mechanical process can lead to the evaporation of the Black Hole; the larger the Black Hole the longer it would take to evaporate. So, IF little Black Holes "could" be produced in our accelerators, they'd be very very tiny and would last only a very very short time.

I've only given the flavor of the issue; maybe we can talk more details in a future posting. Maybe you'll get to study it in more detail in college(!). It's very fascinating stuff!!

Thanks, and have a great school year,

-Mike Syphers

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