Acceleration: Blind in a Car & a Pendulum

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Discussion Overview

The discussion revolves around the scenario of being in a car with a pendulum while blind to the surroundings, exploring whether the observed behavior of the pendulum can conclusively indicate the car's acceleration. The scope includes conceptual reasoning about acceleration, gravity, and the implications of the Unruh effect.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that the pendulum bending towards the observer could indicate acceleration, but others argue that it could also be due to the car traveling up an incline at constant velocity.
  • One participant notes that while the car may be accelerating, it could also be stationary on a slope, highlighting the ambiguity in the scenario.
  • A participant introduces the idea that there is no scientific experiment that could definitively distinguish between the effects of gravity and acceleration in a closed environment.
  • Another participant mentions the Unruh effect, proposing that an accelerating observer would detect black-body radiation, which could serve as a subtle indicator of acceleration compared to an inertial observer.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views remain regarding the interpretation of the pendulum's behavior and the implications of acceleration versus gravitational effects.

Contextual Notes

The discussion includes assumptions about the observer's inability to perceive external conditions and the limitations of experiments in distinguishing between acceleration and gravitational effects.

sr_philosophy
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You are in a car and there is a pendulum suspended in front of you. You have no idea of what is going outside, i.e., you are completely blind from the surroundings. You can see only the pendulum and the interior of the car which has nothing else. You find that the pendulum is at the beginning straight down and later you find that it is bending towards you. (I hope you understand) Can you conclude that the car is accelerating?
 
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sr_philosophy said:
You are in a car and there is a pendulum suspended in front of you. You have no idea of what is going outside, i.e., you are completely blind from the surroundings. You can see only the pendulum and the interior of the car which has nothing else. You find that the pendulum is at the beginning straight down and later you find that it is bending towards you. (I hope you understand) Can you conclude that the car is accelerating?
No, the car could be traveling up an incline at constant velocity for example.
 
Last edited:
sr_philosophy said:
Can you conclude that the car is accelerating?

No, the car may be accelerating, but it is also possible it is stationary on a slope.

If you are in a windowless room, and the room tilts backwards, there is no possible scientific experiment you could do to discover weather it is gravity pushing you to the side of the room, or if you are simply accelerating.

There is symmetry between acceleration and gravity.
 
there is no possible scientific experiment you could do to discover weather it is gravity pushing you to the side of the room, or if you are simply accelerating

Actually there might be!...an effect discovered by Bill Unruh! Measurements of environmental temperature would reveal a gas of "hot" photons not present in a gravitational field. But this is very,very subtle.

The Unruh effect, which Unruh discovered in 1976, is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none. In other words, the accelerating observer will find himself or herself in a warm background.
http://en.wikipedia.org/wiki/Bill_Unruh
 

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