Self-rotating body with speed of light

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Discussion Overview

The discussion centers around the hypothetical scenario of a self-rotating solid cone accelerating to the speed of light in space. Participants explore the implications of such a scenario, including the effects on the cone's structure and the behavior of its apex, which consists of a single atom. The conversation touches on concepts from relativity, including time dilation and the nature of rigid bodies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the fate of a self-rotating cone as it approaches the speed of light, specifically whether it would disintegrate and which part would be affected first.
  • Another participant suggests that a bystander moving close to the speed of light would perceive the rotating cone as rotating slower due to time dilation.
  • A participant emphasizes that there are no truly rigid objects in relativity, noting that any rapidly rotating object would distort into a different shape, with effects worsening further from the apex.
  • It is proposed that even if the cone were made of a sufficiently flexible material, the energy required to spin it to the speed of light is not available in the universe.
  • One participant reiterates the point about the infinite mechanical work needed to achieve such a speed, reinforcing the impracticality of the scenario.

Areas of Agreement / Disagreement

Participants generally agree on the impossibility of reaching the speed of light and the non-existence of truly rigid objects in relativity. However, there are differing views on the specific effects on the cone's structure and the implications of time dilation as perceived by a bystander.

Contextual Notes

The discussion includes assumptions about the nature of rigid bodies in relativity and the energy requirements for achieving light speed, which remain unresolved. The scenario is highly theoretical and speculative.

rsuryatheja
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Hello,

I am not a physics guy but I got this idea, sorry if this is a dumb question.

What happens if a self-rotating solid cone that accelerates to speed of light in space. Imagine that it has a circular base and at the apex there is only one atom.

What happens to it, it it going to get disintegrated when it reaches the speed of light? Is conical base is going to be effected first or the apex of one atom?
 
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Do you mean that you have a body that rotates and then you take a bystander who moves really close to C compared to this rotating body and imagines how he would see it?
What would happen is that according to a bystander it would now rotate slower due to time dilation.
 
First of all there are no truly rigid objects in relativity. If you rotate anything very fast it has no choice but to distort into a different shape. The apex wouldn't be affected, but the stretching or squashing would get worse further away.

Secondly, even if you had a sufficiently flexible elastic cone that wouldn't shatter into pieces, there isn't enough energy in the Universe to spin the cone fast enough to reach the speed of light.

EDIT: I assumed above that you were referring to the rotational speed reaching the speed of light, not that the cone was rotating slower but moving sideways as well. But there's still not enough energy for anything to reach the speed of light.
 
Last edited:
DrGreg said:
First of all there are no truly rigid objects in relativity. If you rotate anything very fast it has no choice but to distort into a different shape. The apex wouldn't be affected, but the stretching or squashing would get worse further away.

Secondly, even if you had a sufficiently flexible elastic cone that wouldn't shatter into pieces, there isn't enough energy in the Universe to spin the cone fast enough to reach the speed of light.

Very true, the mechanical work to accomplish such a feat is infinite.
 

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