Saturday, January 10, 2009

Beyond this horizon, everything sets

kw: book reviews, nonfiction, cosmology, black holes

The book took me a long time to finish, and left me puzzled. What, and how, am I to think about these things? Beneath the notice of most of us, an intellectual war has been raging among a small number of physicists, a generally respectful war, carried out with great civility, but concerning the fundamentals of physics and the reality of our Universe.

Of course, scientists cannot be silent about things that deeply move them, so many publications have ensued, but mostly in journals read only by other physicists. A rare popular press article has appeared, say in Scientific American or Popular Science, about universal holograms, or information loss, or variously named "strings", or accelerating cosmological expansion.

As it turns out, the four items mentioned just above are all related, at least to Leonard Susskind and a number of contemporary physicists. In his new book, The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics, Dr. Susskind explains the central role of black holes in the controversy, and how they tie together all the important physics concepts of the late 20th and early 21st Centuries.

I won't go into any detail here, because I can't. Not only is the book large, more than 400 pages, but the author has already simplified his arguments a great deal in order to reach a nonmathematical public.

I do just have to express my puzzlement over his discussion that, to an outside observer, an object gets heated as it falls to the event horizon of a black hole, even if it is the only thing in the vicinity. Of course, the now-familiar accretion disk heats incoming stuff by friction. But the observed heating is based on the observation itself:
  • The gravitational redshift approaches infinity for "light" that reaches us from an object that is approaching the event horizon.
  • Let us remember, the event horizon is the point at which gravity stops light entirely. Any electromagnetic energy that originates or reflects from something at or below the event horizon can only proceed inward.
  • Time dilation also approaches infinity in the same manner.
  • For us to see it, the falling object we are watching must be emitting or reflecting radiation that began as much shorter wavelengths than what we detect. Eventually, our "camera" might record an image using visible photons that began their journey to us as gamma rays.
  • These very high-energy photons (gamma rays) imply very high temperature. So the object we are observing must be very hot.
I looked and looked, but never found out what exactly is heating up the object in question, just this circular argument about high-energy photons. Thus, at the moment I counter-contend that for a freely falling object, the only source of heating is tidal friction. Start with a big enough black hole (galactic mass or so), and the tides and heating are minimal. However, suppose the object is not freely falling. Suppose it is a thermometer on a long (and very strong) rope!

Such a thermometer would be heated all right, by the photons hitting it as they freely fall into the black hole. Depending on how close to the event horizon you can get it, the thermometer could be flooded by gamma ray photons that began life as infrared or visible photons, or even the microwave background radiation. But to a freely falling object, the photons seem to have the same energy they had when both they and the object were far from the black hole.

Although I am a science junkie, there is a limit to my understanding. The point of the book is, to me, that science is a very human endeavor. It would be no fun at all were it carried out only by emotionless robots. I am not sure such robots could do science, however, because they'd at least need motivation, and the motivation, "My programmer built in a requirement to 'do science'," is cold comfort indeed.

No, scientists are human, albeit in a few cases, humans who have learned to disagree without being too disagreeable. They hold their views with the same passion that St. Francis and Billy Sunday held theirs, and evangelize with identical fervor.

As a result of the black hole war, new mathematical tools were developed to help "rewire" the brains of a few physicists so they can understand a new paradigm. Boy, I thought particle physics was confusing. Now these guys are operating in realms where the a proton is as big and empty as a galaxy (which is 99.9999% space between stars), compared to a thing called the Planck Mass.

By the way, there is a lot of hope for the LHC (Large Hadron Collider), which will get working again once it is repaired after last year's broken magnet. People fear it will produce tiny black holes that might grow larger and swallow stuff up. Those black holes are the point, and they won't grow. Any black hole that weighs less than a kilogram will evaporate, due to Hawking radiation, in less than 10-22 seconds. It'll make bang somewhat smaller than the bang that created it, but in that slice of a second it ought to produce a ton of data for the scientists to mull over. It just might provide experimental confirmation of some of the things Dr. Susskind has written about.

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