Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

While standing on a planet its gravitation force is noticeable and manifests only through the normal force, e.g. if jupiter had rocky surface, standing on the surface will apply about 2.5 times more force than when standing on earth. However sky diving on earth and on jupiter (without atmosphere) would apply the same amount of "destructive" force, that is 0. Thus gravitation force cannot really destruct matter without something for the matter to interact with.
If a black hole with no matter falling into it exists, will a person with space suite die if he would "jump" into it? he will have nothing applying "destructive" force on it, just kinetic energy that cannot manifest without something to hit.

share|improve this question

2 Answers 2

I may be thinking a bit too simple here, but doesn't gravity imply collision/contact at some point in time? In other words, what would cause your black hole (which is simply a point with density such that nothing can escape)?

share|improve this answer
    
The single point that is causing the black hole can never be reached because of time dilation. people say that a person that will fall into a black hole will die. my question is why will he die if nothing applies force on him –  Dani Dec 23 '11 at 15:04

We can be sure you will die because of tidal forces. Assume you are falling towards the black hole feet first, then your feet are closer to the singularity so accelerate faster than your head. As you approach the singularity the difference gets so great it will tear you apart.

Also your left and right sides are accelerating towards a single point (the singularity) so they are accelerating along paths that converge. That means your left and right sides are being pushed together, so as you get near to the singularity you'll be squashed sideways as well as being stretched out.

This will always kill you because for any black hole the tidal forces become infinitely strong as you reach the singularity (though quantum gravity probably intervenes before the forces actually become infinite). If it's any comfort, for small black holes the tidal forces only get lethal in the last few milliseconds so you probably wouldn't feel much.

It's relatively easy to calculate what happens to an observer falling into a black hole, and the observer reaches the singularity (and their death) in a finite time. You'll find the calculation in most books on General Relativity. If you're interested I can suggest a couple of fairly accessible books. In General Relativity it isn't possible to say what happens at the singularity because the curvature becomes infinite. Since physicists are reluctant to believe infinities occur in nature, most people believe that General Relativity is only an approximate theory and near the singularity you need to do your calculations with a quantum gravity theory instead. Unfortunately no-one knows what this other theory is.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.