What would happen to an object falling towards a black hole?

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Discussion Overview

The discussion revolves around the behavior of an object falling towards a black hole, particularly focusing on the concept of free fall, geodesics, and the implications of rotational dynamics. Participants explore theoretical scenarios and the limits of speed in the context of general relativity.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that a geodesic path would be followed by a free-falling object, questioning whether rotational dynamics would affect this scenario.
  • Another participant clarifies that in special relativity, an inertial frame of reference is preferred, and discusses the implications of constant acceleration and relativistic effects on mass and speed.
  • A third participant questions the exclusion of free fall for a non-rotating body due to rotational dynamics, asserting that there is a speed limit as observed from a distance.
  • Further, a participant emphasizes that free fall implies no proper forces acting on the object, and discusses the concept of a test particle released from rest far from a black hole as a thought experiment.
  • Participants reference a technical paper on free fall in Schwarzschild spacetime, indicating a need for understanding general relativity to access the material.

Areas of Agreement / Disagreement

Participants express differing views on the role of rotational dynamics in free fall and the nature of reference frames. There is no consensus on the implications of these factors, and the discussion remains unresolved regarding the visualization of free-falling objects in various scenarios.

Contextual Notes

Some assumptions about the nature of reference frames and the conditions of free fall are not fully explored. The discussion also touches on the complexities of general relativity and the limitations of understanding without a solid grasp of the underlying mathematics.

Pierre007080
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Hi Guys,
I have a problem visualising a free falling object to use as a use as a theoretical reference body. I assume that a geodesic path would be the path that such a body would follow, but surely rotational dynamics would preclude such a situation. If there were theoretically such a body, would it just carry on accelerating forever toward some theoretical gravitational centre or is there some speed limit (light?)
 
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hi pierre

you don´t normally choose an accelerating thing to be a frame of reference. in special relativity you choose an inertial frame of reference, which would be a frame of reference with uniform motion, not undergoing any kind of acceleration.

one could imagine a body which is being accelerated by some (magical) constant force forever. let's say we take a spot in space to be our inertial frame of reference. this body would start up with no velocity relative to the reference frame, then the acceleration would kick in and last forever. this body would gain speed forever, although it could never reach the speed of light. if this body was at almost the speed of light it would seem to us that the acceleration results in ever smaller increases of speed, but(and that might seem strange) the mass of the object would increase, which is accounting for the ever greater kinetic energy.
 
Pierre007080 said:
Hi Guys,
I have a problem visualising a free falling object to use as a use as a theoretical reference body. I assume that a geodesic path would be the path that such a body would follow, but surely rotational dynamics would preclude such a situation. If there were theoretically such a body, would it just carry on accelerating forever toward some theoretical gravitational centre or is there some speed limit (light?)
I don't understand your problem. Why would rotational dynamics exclude free-fall of a non-rotating body ?

There is a limit to the speed that can be attained, as measured by a distant stationary observer. This paper discusses free fall in the Schwarzschild spacetime.

arXiv:gr-qc/0411060v2 (31 Aug 2006)
 
Hi Mentz,
Thanks for the response. Perhaps the qestion should be: is it possible to imagine an object in space that is not an integral part of some or other rotating system? Would the rotational speed not then prevent this object from being "free falling"?

Mentz, please excuse my ignorance of the system, but how do I access this paper you ave referenced fo me above?
 
Hi Pierre,
falling freely means that the object in question has no proper forces ( like rocket engines or solar sails) pushing it. This includes the great majority of astronomical objects, which are either orbiting something ( which is free fall) or being attracted by something else and falling towards them.

However we can 'imagine' what happens if a test particle is released from rest a very long way from a black hole and allowed to accelerate undisturbed towards it. It's called a 'thought-experiment'.

The paper is technical and you need to understand some GR. It can be got here

http://arxiv.org/abs/gr-qc/0411060
 

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