Infinitie tidal forces at event horizon?

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Discussion Overview

The discussion revolves around the effects of tidal forces on an observer falling into a black hole, particularly as they cross the event horizon. It explores the conditions under which these forces become significant and the implications of black hole size on the experience of the falling observer.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants claim that an observer falling into a black hole experiences tidal forces that could rip them apart as they cross the event horizon, while others argue that these forces are negligible for large black holes until the observer approaches the singularity.
  • It is suggested that the impact of tidal forces depends on the size of the black hole, with smaller black holes presenting more significant tidal forces compared to larger ones.
  • A participant provides a mathematical calculation of tidal forces using the Schwarzschild metric, indicating that for a solar mass black hole, the tidal force could be extremely high, while for a million solar mass black hole, it would be much lower.
  • There is a mention of the need for a double-check on the calculations presented, indicating some uncertainty about the figures provided.

Areas of Agreement / Disagreement

Participants express differing views on the effects of tidal forces at the event horizon, with no consensus reached on which viewpoint is correct. The discussion remains unresolved regarding the conditions under which tidal forces become significant.

Contextual Notes

The discussion includes assumptions about the size of black holes and the conditions under which tidal forces are evaluated. There are also unresolved mathematical steps in the calculations presented.

Ray Eston Smith Jr
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Many websites claim that someone falling into a black hole would be ripped apart by tidal forces as he crosses the event horizon. Others say that the falling observer feels nothing special as he crosses the event horizon - he doesn't get torn apart by tidal forces until he gets close to the singularity (assuming the black hole is big enough so that the tidal forces don't tear him apart way before he reaches the event horizon).

Which viewpoint is correct? Or does it depend on the frame of reference of the observer?
 
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It dpeends on the size of the black hole, for a large black hole the tidal forces will be unoticeable, for a very small black hole they beocme much more important. It alos dpeneds on the size of the frame of refernce, as obviously the larger the object, being drawn in the larger the tidal forces.

The tidal forces would not be infinite, except at the singularity I imagine.
 
Ray Eston Smith Jr said:
Many websites claim that someone falling into a black hole would be ripped apart by tidal forces as he crosses the event horizon. Others say that the falling observer feels nothing special as he crosses the event horizon - he doesn't get torn apart by tidal forces until he gets close to the singularity (assuming the black hole is big enough so that the tidal forces don't tear him apart way before he reaches the event horizon).

Which viewpoint is correct? Or does it depend on the frame of reference of the observer?

It depends mainly on the size of the black hole. I'd recommend Kip Thorne's book "Black Holes & Time Warps" for a good popular treatment of the topic.

For the detailed calculation

Warning: geometric units

The tidal force in the Schwarzschild basis metric works out to be 2m/r^3, and the event horizon is at r=2m, so the tidal force is 1/(4m^2).

Converting this to standard units, the tidal gradient in (meters/sec^2)/meter = 1/sec^2 will be

[tex] \frac {c^6} {(2 G m)^2}[/tex]

where c is the speed of light, and G is the Gravitatioanl constant

if m = 1 solar mass, I get 1e10 sec^-2, which is a billion gravities per meter.

If m = 1,000,000 solar mass, one has a comfortable .001 gravities/meter

where 1 gravity = 9.8 m/s^2 (approx 10 m/s^2).

This is a static calculation, but velocity towards the bh won't affect the tidal force.

I could use a double-check of the figures, but I think the answer is right...
 
Pervect is correct. I spent all night on that and you were really starting to make me mad.
 

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