Gravity Accelerating Objects To The Speed Of Light

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Discussion Overview

The discussion revolves around the hypothetical scenario of a penny dropped in an infinitely deep elevator shaft and its acceleration under gravity, particularly in relation to the speed of light and black holes. Participants explore the implications of such a scenario, including concepts of escape velocity, event horizons, and the effects of space-time curvature.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question the feasibility of an infinite downward direction while maintaining substantial gravitational pull.
  • There is a discussion about the energy required to accelerate an object as it approaches the speed of light, with references to mass increase and special relativity.
  • One participant introduces the concept of a black hole and its event horizon, suggesting that an object falling into a black hole approaches the speed of light as it nears the event horizon.
  • Another participant challenges the relevance of air resistance in the context of space, arguing that it does not apply to the scenario being discussed.
  • Some participants propose that once an object crosses the event horizon, it cannot be observed crossing it due to time dilation effects, while others suggest quantum mechanical interpretations involving tunneling.
  • A later post rephrases the scenario to focus on the geometry of space-time near a black hole and questions whether the penny would stop accelerating at extremely high speeds.
  • There is mention of the singularity and its implications for density and energy, with some suggesting that mass inside the singularity has infinite density.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the acceleration of objects under gravity, the relevance of black holes, and the implications of approaching the speed of light. The discussion remains unresolved with no consensus on the interpretations or implications of the scenarios presented.

Contextual Notes

Limitations include assumptions about the nature of gravity in an infinite shaft, the effects of air resistance in a vacuum, and the interpretations of quantum mechanics versus classical physics regarding objects near black holes.

ScienceNerd36
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If you were to drop a penny down an elevator shaft that was infinite in the downward direction, what would begin to happen when the penny is accelerated by gravity to the speed of light or at least very close?
 
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How can the elevator shaft have an infinite downward direction and still have substantial gravitational pull in that direction?

I'm guessing the spirit of your question is what keeps the velocity of a constantly accelerating object below the speed of light?

The simple answer that I usually hear is that it requires energy to accelerate an object and the faster you go the more energy is needed to continue to accelerate because your mass increases as you speed up. The special-relativity answer I don't understand but has something to do with it violating the geometry of space-time.
 
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How about an object when it crosses the event horizon into a black hole before it impacts with the core?
 
What is, "escape velocity at the event horizon of a black hole", Alex...?
 
Which question are you answering?

Elevator shaft and "downward direction" aren't exactly metaphors that would make me think he was implying the sort of scenario that involves black holes.
 
Sorry, that was a Jepoardy reference. Jeff was proposing the only scenario where the question has any connection to reality - an object falling into a black hole approaches C as it approaches the event horizon.
 
ScienceNerd36 said:
If you were to drop a penny down an elevator shaft that was infinite in the downward direction, what would begin to happen when the penny is accelerated by gravity to the speed of light or at least very close?

To accelerate to infinite speed, the field must be so strong.. which happens only in case of black holes and you won't get your penny back
 
Wouldn't you want to take air resistance into account? Correct me if I'm wrong, but if there was air, the object would stop accelerating after a while.
 
I'm sorry, but neither of those two posts are relevant/useful here: You can't accelerate something to infinite speed and air resistance isn't relevant if you accelerate something in space.
 
  • #10
You can't accelerate something to infinite speed

Yes it can, if it crosses the event horizon.The escape velocity of a body becomes c at the mass-equivalent radius which implies infinite proper velocity
 
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  • #11
OK, let me rephrase the question.

(1) Imagine that space-time is warped as it would be in the presence of a black hole. And I'm speaking only of the geometry.
(2) Now let's imagine dropping a penny down this infinite bit of space-time curvature.
(3) As it falls and falls it accelerates until it is at a speed of 99.999999999% the speed of light. Will the penny then stop accelerating?

And if there are any mistakes in this form of the question please point them out, but don't start a conversation over what I might have meant.
 
  • #12
Will the penny then stop accelerating?
Yes, once it is inside the singularity
(3) As it falls and falls it accelerates until it is at a speed of 99.999999999% the speed of light.
You could say c, because mass inside the singularity is said to have infinite density and energy
 
  • #13
Current theory is...

Classically speaking, the penny's time rate approaches zero as it approaches the event horizon, and we never see it cross the event horizon. Quantum mechanically speaking, the particles of the penny tunnel across the event horizon to the singularity.

But then "current theory" might change in a few decades.
 

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