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RE: Special Relativity Question / Barn Paradox

Just one added point to the other responses. The fact that this problem
is often called the BARN PARADOX is because IF the runner sees the pole
fit in the barn (or between the markers) she will know that it is she
moving and not the barn--a violation of one of the postulates of special
relativity. The whole exercise is to show that she DOES NOT see the pole
fit, and in fact sees just what she should to interpret the sequence as
though the barn was moving towards her. I've worked this out once in gory
detail--involves both time dilations and length contractions.

From: (ken fox)
Subject: Special Relativity Question / Barn Paradox
Date: Thursday, April 25, 1996 4:32 PM

I need your help again. Here is a paraphrase of a problem from the 1993
IB(higher level exam) that I am struggling with.

A super fast runner has a 4m pole ( her frame) and is moving at 0.866c
relative to me. I have set out two poles in my frame that are 2m apart
and I
notice that her pole fits neatly between the two as she passes. Now,
sees the two markers to be 1m apart.
"Does she say that the pole will fit between the markers? Is there a
contradiction here? Explain."

I have run the RelLab simulation of the Barn where the doors close and
so that in my frame they are closed simultaneously ( a key concept here
think) when she is in the barn. In her frame the doors do not close at
same time but the front and back doors close and shut to allow the pole
through. Does the runner say the pole fits? The runner sees the front of
pole at the front door long before she sees the back of the pole at the

We had a great debate in class and most of us decided she ,too, thought
pole did fit but we are not all (including me) convinced. Can anyone
help me


ken fox

Richard W. Tarara
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556

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