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 Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...The Space and Astronomy Agora Re: Hypothetical Gravity Questions Forum List | Follow Ups | Post Message | Back to Thread TopicsPosted by Dvaid Haller on May 18, 1997 23:21:42 UTC

: : : : : Hello! I was wondering how much gravity our bodies can withstand before the effects of gravity become intolerable. The reason I ask is that it's obvious to me that the state of your body would start to deteriorate long before you even reached the event horizon of a black hole. Given that the farther you are from an object, the less the attraction there is between you and the object, what would be the safest minimum distance you could be to a black hole's event horizon without endangering your health? : : : : : Well, the question you've posted is a little ambiguous. I assume by distance you mean standing distance(not flying away or racing toward).: : Any fighter pilot will tell you that nine G's and you lose conciousness(blackout) negative 3 G's and the same thing happens(red out): : On the other hand you might be fine with one Gee of acceleration jumping off of a twenty story building...until you hit the ground.: : Now, in terms of the sheering force of gravity as you approach the event horizon of a black hole, its reasonable to say that I have no earthly clue at what distance the effects would be detrimental, but I'm anxious to find out.: : Here's an idea. You build a scenario of some detail and I'll see if I can pick a few brains with nothing better to do. : : : : Here's some more ideas. Consider a person in orbit around the earth; they are essentially weightless, because the centripetal: : acceleration away from earth as they orbit is exactly balanced by the gravitational force toward the planet. Now, picture the: : same thing around a black hole. If you can accelerate yourself (slowly!) to a high enough speed to remain in a stable orbit around a black hole,: : you would experience zero gravity and therefore no physical or mental distortion. depending on your distance from the singularity;: : however, your speed might be so high that you would experience relativistic effects (although you might not notice them), and if you get too close to the: : event horizon, you might not be able to correct for small changes and get sucked in! : : : Hi, Bruce! I've read your comments in this forum and really like what you have to say. I'm curious: How do you know so much about black holes and physics in general? Now to my serious question: What is this centripetal acceleration AWAY from the Earth you're referring to? Isn't centripetal acceleration the acceleration TOWARD the center of a circle, not AWAY from it? Also, I thought that astronauts in orbit did in fact experience the Earth's gravity (Isn't it called microgravity?); it's just that gravitational attraction decreases with distance. The key to orbitting is having a velocity fast enough not to fall to the Earth and sufficiently slow so as not to escape the gravitational field. Your ideas about orbitting a black hole otherwise seem sound, although we'd want enough gravity (9.8 m/s2 optimally) to retain the structure of our bodies. And we can easily correct our calculations for relativistic effects using Einstein's transformations. * The problem with the orbital solution for getting close to a black hole is that the gravitational field of a black hole is so great that it varies appreciably over short distances at any meaningful range from the event horizon...these so called "tidal forces" will, for example, exert a greater pull on the surface of our spacecraft closer to the event horizon and a lesser pull on the surface facing away. In the case of a black hole, the difference can be so great that our spacecraft is literally torn apart, even in an otherwise "stable" orbit. A stable orbit (and no orbit is truly stable, except in an ideal two-body system...) requires a comparatively weak gravitational field. In general, one must be careful applying the physics of the prosaic "regular" universe to extreme cases such as black holes. -D.H.

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