Black Holes

Article: http://www.straightdope.com/classics/a1_200.html

I know something else that would happen were you to be the oh-so unlucky person to meet this fate. Now, imagine that you are floating randomly through space (ignore the problems associated with this) and you happen upon a black hole. You start to get pulled towards it. Now, you know the nature of black holes. Not even light can escape their immense gravity. Stars can be strung out as they get sucked in; entire planets can be ripped apart. So, what’s this say about little old you? It’s quite simple, actually. As you approach the black hole, whichever part of you is nearest to it would be going faster than the part which is farthest. Now, considering the immense gravity of a black hole, this would easily tear you in half. Ok, so now you are in to pieces. The gravity would again go to work on those pieces, and then those would get ripped in half, and so on.

:smack: I knew I should have just gone to that tupperware party.

That’ll depend considerably on the size of the black hole. The radius of a black hole is proportional to its mass, but tidal forces (the difference in force on different parts of an object) are inversely proportional to the cube of the distance from the center. What this means is that the tidal forces at the horizon of a black hole depend on the size of the hole, and they can be very small, for a large enough hole. For a supermassive black hole such as are found in the cores of galaxies, you could cross the horizon completely unscathed. Not that it would make much difference, mind you: After crossing the horizon, you’d have about a minute, tops, before you reached the singularity in the center of the hole, and the tidal forces are guaranteed to get strong enough to shred you sometime before then.

Ah…spaghettification. :wink:

An interesting thought experiment about this involves stripping matter into its ultimate constituents.

At first, tidal forces pull and break off chuncks from the main body, then individual atoms from molecules. Then, electrons are pulled from the nuclei they orbit, followed by the nucleus itself being dissociated into individual protons and neutrons. Finally, these nucleons are torn into quarks, which themselves are torn into…???

Nobody knows. Frankly, I’m not sure anybody knows what’s up at the electron-stripping level, since that’s in an area of such high spacetime curvature that gravity and electromagnetism are approximately equal in magnitude. At quarks it’s the strong nuclear force and gravity. We’d need a TOE to really figure it out.

  1. there is no such thing as john wheeler’s classical “black hole.” at least, not “locally.” 2. on the other hand, what we observe to be our universe may in fact only be what a particle looks like, from the inside, as it is falling into a black hole. 3. the conceptual problem is, people tend to think of black holes as three dimensional objects or places “exisiting” within the normal, day-to-day experience of our perceived three-dimensional universe. but the universe we see is only a three-dimensional projection, or image. it is a product of our imagination, and not “real.” 4. when a massive star collapses “locally,” we see some of the local effects of locally extremely compact gravitational fields, but not the effects of “real” black holes. in other words, we can learn something about “black holes” from these local objects by extrapolation, but we are not experiencing local interaction with actual, bottomless"black holes." only what might be called cosmic potholes. 5. these cosmic potholes are described in detail by hawking’s work, but they are not really black holes. 6. interestingly, a true black hole interacting on the local level would be completely and entirely invisible to our local measurements. one reason for this is that a true black hole would not be in a specific place, like at the center of the milky way. like merlin’s dragon, it would be everywhere. it would be everything. 7. in other words, the “real” “black hole” we appear (indirectly, of course) to be falling into now is not only “outside” the visible universe as we imagine our universe to be in three dimensions, it is, in fact, here, there, and everywhere. 8. again, as hawking has demostrated in theory, that’s why the locally massive objects we see aren’t really black and aren’t really holes. but they do help us understand the effect, in three and more dimensions, the “real” black hole we’re falling into right now on our visible universe of radiation pressure. for example, it helps us understand how every point in our universe can appear to be the centerpoint when every other point also appears to be the center point, from that point. 9. hawking also demonstrated that there is not only no “Big Bang” in time, there is also no Big Bang in space. this is one distinction between superheavy local objects and "real’ black holes: the locally determined moment, not to mention location, of gravitational collapse as seen from the outside of a local “black hole” is the opposite of what we are experiencing on the large scale: that is, a universe which, in locally measurable terms, has ALWAYS been falling into a black hole, and always will be. no “beginning,” no “end,” no “center,” and no “outside.” 10. again, local “black holes,” like the one at the center of our galaxy, do give us some hints about “real” black holes. but if you want to know what it’s like to fall into a real black hole, look around, smell the roses, and feel yourself breathing. and be sure to enjoy the ride. there is no getting off.

Speaking of Black Holes, when I was married my wife had this credit card account I didn’t know about…

I am curious - how did you figure the “about a minute”?

The Schwarzschild radius of the biggest known black hole (18B solar masses) is about 6*10^10 km, I think. That means that at c, to an outside observer (not that there can be one) it will take about 2 days to traverse that. Of course, you’d be traveling almost at c, so due to time dilation, it would take you only a tiny amount of time, probably, to reach singularity, even if you somehow manage to start from standstill (the GM/r^2 at that radius should be around 100g). But I am wondering how you calculated the 1 minute thing.

Re-Spaghettification, how do reletavistic effects affect this from an outside perspective. Dont’s distances compress at high fractions of “c”?