Relativity - The Train Paradox (Time Dilation and Length Contraction)

The train paradox is a famous example of the strangeness of relativity. Demonstrates just how non-intuitive reality can be.

Described here by Professor Richard Muller of the University California, Berkeley. Taken from Lecture 22 of the spring 2006 webcasts of Physics For Future Presidents. Also known as Descriptive Introduction to Physics. Empahsis is on conceptual understanding, rather than mathematics.

Full lecture:
http://www.youtube.com/watch?v=nNgzqpKZwhE

All Lectures:
http://www.youtube.com/view_play_list?p=095393D5B42B2266

Category:

Education

Tags:

• Relativity
• Einstein
• physics
• science
• paradox
• lightspeed
• Lorentz
• spacetime
• university
• Richard
• Muller

[sug15]

What is the name of this class?

[theinquisitor]

@sug15, Physics For Future Presidents, see the description box for more detail and links to the full lectures.

[kourosh89]

I didn't know Ron Jeremy was a professor.

[artiriti]

@ Plpoo

Shut upp you MORON!!!!!

[SuperMagnetizer]

"I'm actually 7 times thinner! I look like a pancake!" But if you actually were a pancake, then you would be dead, so it's a good thing that all of this is baloney. Optical illusion. Think about it.

[sackman11]

Too bad that he's a climate change denialist.

[gr8vibes2]

theory theory theory

[thremtopod315]

he sounds a lot like Neil Degrasse Tyson

[atmtensorsredsplanb]

This is awsome

[ricomajestic]

@SuperMagnetizer "appears" is actually a bad word here. It implies that there is one frame where the tunnel has the "correct" length which would be inconsistent with relativity. There is no "correct" length

[gokuhawks14]

@theinquisitor I gave you a thumbs up! I love time dilation. It is not junk science.

[CACBCCCU]

I'm stuck on the 5:09 idea of the back gate being blown backward. Seems reasonable that one can assume, without avoiding most of the relativistic gist of the situation, that the train is largely inelastic, it has only one car, and that either the front or the back wheels can stop it instantaneously. One upshot of a simultaneity shift seems to be the back of the car is at a delayed time - the back gate is supposed to drop down after the front gate although it appears simultaneous when stationary.

[CACBCCCU]

At 5:12 both tunnel doors get "smashed out" if the train stops itself in the tunnel. It's difficult to accept that the rear door is smashed "out" in the opposite direction as the train was moving, the back of the train supposedly appears to move backward relative to the tunnel doors. I've seen it described as time-reversal, and that relativity alows for the ordering of events to be reversed as seen by two different frames, whereupon the concept of causality gets tossed out. Skeptical is not bad.