I think I heard someone explain this before. It's something like that they move the object forward while they zoom out. Also the object moving forward has to be moving faster than the camera zooms out.
If I'm not mistaken, the effect isn't just a zoom in/out, it is a combination of zoom and dolly. When a camera is dollyed out/zoomed in (or the reverse) and timed right, the subject stays centered and focused while radically charging the perspective of the background.
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I don't know the optical physics behind it, but when done well, the effect is dramatic.
It's called a push/pull. pushing the camera/dolly in, while pulling out (zooming) the lens. making the world smaller, crushing subject and surrounding. The reverse or pull/push expands the world making you feel lost in wide open world. But to answer Iccarus question changing lens from wide angle to close up shifts the same info do a different perspective. it can be very disorienting which is why its used to great effect or you look like a idiot trying to pull off a bad zoom.
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I don't know the optical physics behind it, but when done well, the effect is dramatic.
http://en.m.wikipedia.org/wiki/Dolly_zoom
http://m.funsubstance.com/fun/171492/focal-length-kitty/
But you've probably seen it already by now.