via Scientific American on 11/25/09
You have probably seen the TV commercial in which a cell phone technician travels to remote places and asks on his phone, “Can you hear me now?” Imagine this technician traveling to the center of our Milky Way galaxy, wherein lurks a massive black hole, Sagittarius A* (Sgr A*), weighing as much as 4.5 million suns. As the technician approached within 10 million kilometers of the black hole, we would hear his cadence slow down and his voice deepen and fade, eventually turning to a monotone whisper with diminishing reception. If we were to look, we would see his image turn increasingly red and dim as he became frozen in time near the black hole’s boundary, known as the event horizon.
The technician himself, however, would experience no slowing of time and would see nothing strange at the location of the event horizon. He would know he had crossed the horizon only when he heard us say, “No, we cannot hear you very well!” He would have no way of sharing his last impressions with us--nothing, not even light, can escape from gravity’s extreme pull inside the event horizon. A minute after he crossed the horizon, the gravitational forces deep inside the hole would tear him apart.
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The technician himself, however, would experience no slowing of time and would see nothing strange at the location of the event horizon. He would know he had crossed the horizon only when he heard us say, “No, we cannot hear you very well!” He would have no way of sharing his last impressions with us--nothing, not even light, can escape from gravity’s extreme pull inside the event horizon. A minute after he crossed the horizon, the gravitational forces deep inside the hole would tear him apart.
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