Black Holes and wavelength

[Paul Murphy]

I'm reading Leornard Susskind's book, The Black Hole War, and I came across something that contradicts everything I've heard about black holes. Can someone explain what Susskind means by the paragraph on page 151-152 of his book? In general, this section of the book is about how Beckenstein calculated the entropy of a black hole.

 

"Recall from chapter 4 that the resolving power of a light beam is no better than its wavelength. Now in this particular case, Beckenstein did not want to resolve a spot on the horizon; he wanted to be as fuzzy as possible. The trick was to use a photon of such long wavelength that it would be spread out over the entire horizon. In other words, if the horizon has the Schwarzchild radius R, the photon should have about the same wavelength. Even longer wavelengths might seem like an option, but they would just bounce off the black hole without getting trapped."

 

Is he saying that photons with a wavelength longer than the radius of the event horizon are not trapped by black holes? I've never heard of that being the case.

[Mr Skeptic]

That's an interesting question. Normally, an object smaller than a wave will not obstruct the wave's passage, as the wavefunction of the wave will mostly just go around it. But a black hole... hm. A black hole doesn't really have a size -- the event horizon is just the part of the black hole we will never see without going into it. I'm not really sure how to answer your question. Perhaps ajb, Martin, or Bob_for_short will have a better idea.

[Paul Murphy]

That's an interesting question. Normally, an object smaller than a wave will not obstruct the wave's passage, as the wavefunction of the wave will mostly just go around it. But a black hole... hm. A black hole doesn't really have a size -- the event horizon is just the part of the black hole we will never see without going into it. I'm not really sure how to answer your question. Perhaps ajb, Martin, or Bob_for_short will have a better idea.

 

I thought this was a simple yes or no type of question, but no takers. I did some searching of the web and there is no mention of this that I can find, other than Susskind's book. Are there any forum members who know if all radiation of a wavelength greater than the diameter of the event horizon will "bounce off" a black hole?