List of Special Relativity Paradoxes.

  • Thread starter greswd
  • Start date
703
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Here's a catalogue of paradoxes in Special Relativity, for convenience sake.

If I've missed out any, do notify me.


Ladder Paradox:
A ladder enters a barn. In the barn's frame the ladder is length contracted and fits nicely, but in the ladder's frame the barn is length contracted and it won't fit. If doors at both ends of the barn shut, what will happen.

Easily dealt with using the relativity of simultaneity. Both doors do not simultaneously shut in the ladder's frame.


Bug-Rivet Paradox:
Similar to the Ladder Paradox, with a bug hiding in a hole. A Length COntracted rivet can't squash the bug in the bug's frame, but it is the other way round for the rivet.

This paradox is tricky as there is no way out for the rivet.


Cooling Paradox:
If a metal rod is heated till it glows, both ends cannot cool at the same rate in all frames.


Twin Paradox:
The mother of all paradoxes.


Trouton-Noble Paradox:
If there is no net torque in one frame, will length contraction produce one in another frame?


Ehrenfest Paradox:
A rotating cylinder and Length Contraction implies a different value of pi.


Detonator Paradox:
A variant of the Bug-rivet paradox. A bomb is activated by completing the circuit. Will it explode if a wire is passed through both terminals? Again, length contraction causes confusion.


Falling Rod Paradox.
A length contracted rod falls into a grate, but otherwise in the rod's frame. Also solved with relativity of simultaneity, this time involving a physical bending of the rod.


Bar/Ring Paradox:
A variant of the falling rod paradox, with the grate replaced by a ring, and no acceleration involved.

The solution is that due to length contraction of the bar in the ring's frame, in the bar's frame it is not directly aligned with the ring.
 
Last edited:
3,871
88
Here's a catalogue of paradoxes in Special Relativity, for convenience sake.

If I've missed out any, do notify me.

Ladder Paradox
[..]
Bug-Rivet Paradox:
[..]
This paradox is tricky as there is no way out for the rivet.
Tricky? Recently explained here in detail (search the forum).
Cooling Paradox
[..]
Twin Paradox:
[..]
Trouton-Noble Paradox:
[..]
Ehrenfest Paradox:
A rotating cylinder and Length Contraction implies a different value of pi.
:rofl: (sorry, could not help it!) - search the forum for explanations that leave π intact. :smile:
Detonator Paradox:
A variant of the Bug-rivet paradox. A bomb is activated by completing the circuit. Will it explode if a wire is passed through both terminals? Again, length contraction causes confusion.
[..]
Falling Rod Paradox.
[..]
Bar/Ring Paradox:
One more:
http://en.wikipedia.org/wiki/Bell's_spaceship_paradox
 
831
5
Another one: An experiment for an entangled electron-positron pair as intrepreted from two different inertial frames moving at relativistic speed with respect to each other.
 
703
16
Another one: An experiment for an entangled electron-positron pair as intrepreted from two different inertial frames moving at relativistic speed with respect to each other.
whats the name of that?
 

jtbell

Mentor
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Ladder Paradox:
Also commonly known as the "barn and pole" paradox, with a pole-vaulter carrying a pole, instead of a ladder.
 
703
16
i didnt include bell's spaceship paradox because this involves acceleration.
 
3,871
88
i didnt include bell's spaceship paradox because this involves acceleration.
So what? So do the twin paradox and the Ehrenfast paradox. SR handles acceleration fine. :smile:
 
Feenburg's Twin Paradox is another good one.
 
Ehrenfest Paradox is one I wasn't familiar with, fascinating!!
 

Fredrik

Staff Emeritus
Science Advisor
Gold Member
10,730
404
Ehrenfest Paradox is one I wasn't familiar with, fascinating!!
It's a good one. It really confused me when I first encountered it. The key to understanding it is to realize that it's impossible to bring a disc to rotation without forcefully stretching the material.
 

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