搜了下，，
http://casa.colorado.edu/~ajsh/collapse.html
看了下，我顶楼的分析是有问题的，，在外面的观测者看来黑洞确实不可能在有限的时间里形成，外面的观察者看到的永远是一个正在形成中的黑洞，不管是光波还是引力场，所有的证据都显示现实的黑洞是一个外带一层永远不会消失的球壳的天体，，，
一个物体落入黑洞，那么黑洞外的观测者所感受到的引力等于原来的黑洞和一个永远停留在视界上的物体共同产生的引力场，，外面的观测者永远也不会感受到这物体坠入奇点产生的新的引力场，，，，，，，对外面的观测者说，黑洞视界附近聚集的物质会越来越多，他们永远不会穿过视界撞到奇点，，，黑洞永远是动态的，，，
9. From the point of view of an outside observer, a star collapsing to a black hole never appears to collapse, but rather freezes at the horizon. How then can it be said that the star collapses to a singularity, if it never appears to collapse even till the end of the Universe?
10. If nothing can escape from a black hole, how can you feel the gravity from it?
Answer to the quiz question 9: The star does in fact collapse inside the horizon, even though an outside observer sees the star freeze at the horizon. The freezing can be regarded as a light travel time effect. As described here, space can be regarded as falling into the black hole, reaching the speed of light at the horizon, and exceeding the speed of light inside the horizon. Thus photons that are exactly at the horizon and pointed vertically upwards hang there for ever, their outward motion through space at the speed of light being cancelled by the inward flow of space at the speed of light. It follows that it takes an infinite time for light to travel from the horizon to the outside world. The star does actually collapse: it just takes an infinite time for the information that it has collapsed to get to the outside world.
Answer to the quiz question 10: Gravity does not escape from a black hole. Gravity moves at the speed of light, and cannot get from inside the horizon to the outside world. The gravity felt by a person outside a black hole is the gravity of the stuff that fell long ago into the black hole. |
显身卡
