Monkey Hunter demonstration in GR

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Discussion Overview

The discussion revolves around the Monkey Hunter demonstration, particularly how it would be interpreted within the framework of General Relativity (GR). Participants explore the implications of a uniform gravitational field and the conditions under which the thought experiment could be realized in a GR context.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how the concept of "directly" hitting the target should be defined in the context of the demonstration.
  • Another participant suggests that using a laser sight to define "directly" could clarify the scenario, proposing that the gun could be positioned outside a black hole's event horizon while aiming at a monkey behind it.
  • There is a discussion about the implications of simultaneity in GR, particularly regarding the simultaneous dropping of the monkey and firing of the gun, which could be defined for closely positioned objects.
  • A later reply humorously emphasizes the fate of the monkey and bullet, suggesting they would both end up at the singularity if fired from near a black hole.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of the thought experiment, particularly regarding simultaneity and the conditions under which the demonstration could occur in GR. No consensus is reached on these points.

Contextual Notes

Participants have not fully resolved the implications of defining "directly" or the conditions for a uniform gravitational field in a GR context. The discussion remains open to interpretation and further exploration.

Who May Find This Useful

This discussion may be of interest to those exploring the intersections of classical mechanics and General Relativity, as well as those interested in thought experiments in physics.

flatmaster
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I'm not sure if this has been discussed before.

We all know about the Monkey Hunter Demonstration. Assuming a uniform gravitational field, a projectile shot directly at a target will strike the target as long as the target has zero velocity at t=0 and both the projectile and target begin to accelerate under gravity at t=0. Of course, the physical demonstration is a hunter shooting a monkey with the monkey dropping from the branch the instant the gun is fired. I think we worked through the math in undergrad.

My question is how would this thought experiment change within GR?

Also, Would this experiment be possible? Is there any place close enough to the GR - classical barrier that has a huge, but classically uniform value for g over the three spatial coordinates? Is there a place where you can say F = mg*yhat with a large value for g?
 
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How do you propose to define "directly"?

(And will you be symmetric in applying the "uniform" requirement?)
 
Last edited:
Totally cool question!

cesiumfrog said:
How do you propose to define "directly"?
Seems to me that the only sensible way to define "directly" is that the gun has a laser sight, and the laser sight is making a red dot on the monkey's chest.

Suppose the gun is located outside the event horizon of a black hole, at a radius the permits circular orbits for rays of light. Then the monkey could actually be right *behind* the gun, but the laser sight would be hitting the monkey in the chest.

Now you run into a problem with defining the notion of dropping the monkey simultaneously with the firing of the gun. But GR does allow simultaneity to be well defined for spatial positions that are close to one another, and the monkey is close to the gun -- it's right behind the gun.

So you fire the gun and drop the monkey behind it simultaneously. Clearly the monkey will disappear below the event horizon very quickly, and so will the bullet.

Well, the bullet is certainly going to hit the monkey, because they will both impact on the singularity.
 
Save the monkeys! :-p
 

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