# List of Special Relativity Paradoxes.

#### greswd

Here's a catalogue of paradoxes in Special Relativity, for convenience sake.

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

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.

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.

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

If there is no net torque in one frame, will length contraction produce one in another frame?

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

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.

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.

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.

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#### harrylin

Here's a catalogue of paradoxes in Special Relativity, for convenience sake.

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

[..]
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This paradox is tricky as there is no way out for the rivet.
Tricky? Recently explained here in detail (search the forum).
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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.
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.
[..]
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One more:

#### bobc2

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.

#### greswd

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
Also commonly known as the "barn and pole" paradox, with a pole-vaulter carrying a pole, instead of a ladder.

#### greswd

i didnt include bell's spaceship paradox because this involves acceleration.

#### harrylin

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.

#### Erich Schoedl

Feenburg's Twin Paradox is another good one.

#### FeynmanIsCool

Ehrenfest Paradox is one I wasn't familiar with, fascinating!!

#### Fredrik

Staff Emeritus
Gold Member
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.
This.

#### Fredrik

Staff Emeritus
Gold Member
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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