DO BLACK HOLES HAVE NO HAIR? Stephen Hawking Lectures (Part-2)

When John Wheeler introduce the term 'black hole' in 1969, it replaced the earlier name 'frozen star'. Wheeler's coinage emphasized that the remnants of collapsed stars are of interest in their own right, independently of how they were formed. The new name caught on quickly. It suggested something dark and mysterious. But the French, being French, saw a more risque meaning. For years, they resisted the name trous noir, claiming it was obscene. But that was a bit like trying to stand against le weekend, and other Franglais. In the end, they had to give in. Who can resist a name that is such a winner?

                                                                                                                                       From the outside, you can't tell what is inside a black hole. You can throw television sets, diamond rings, or even your enemies into a black hole, and all the black hole will remember is the total mass, the state of rotation and the electric charge. John Wheeler is known for expressing this principle as 'a black hole has no hair'. To the French, this just confirmed their suspicions. A black hole has a boundary, called the event horizon. This is where gravity is just strong enough to drag light back and prevent it escaping. Because nothing can travel faster than light, everything else will get dragged back also. Falling through the event horizon is a bit like going over Niagara Falls in a canoe. If you are above the falls, you can get away if you paddle fast enough, but once you are over the edge, you are lost. There's no way back. As you get nearer the falls, the current gets faster. This means it pulls harder on the front of the canoe than the back. There's a danger that the canoe will be pulled apart. It is the same with black holes. If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole. The result is you will be stretched out longway and squashed in sideways. If the black hole has a mass of a few times our sun's you will be torn apart and made into spaghetti before you reach the horizon. However, if you fall towards a much larger black hole, with a mass of million times the sun's, you'll reach the horizon without difficulty. So, if you want to explore the inside of a black hole, make sure you choose a big one. There is a black hole with a mass of about four million times that of sun at the center of our Milky Way galaxy.