# The Naked Scientists Forum

### Author Topic: Relativity bending of light wrong example?  (Read 1642 times)

• Jr. Member
• Posts: 11
##### Relativity bending of light wrong example?
« on: 27/01/2010 10:34:39 »

I've read in some "Relativity Simplified" article that example of  accelarating lift which creates "gravity"  which has a light source on one wall which will hit the other wall slightly lower position and the same should happen due to the natural gravity. The article says it's due to the accelaration of the lift. However my understanding is that is due to the velocity of the lift that the light beam will hit the other wall on a slightly lower position?

Am I misunderstanding something?

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Relativity bending of light wrong example?
« Reply #1 on: 27/01/2010 11:19:37 »
You're absolutely right that if you're in an elevator moving with a constant speed relative to some light source shining through the wall, that the light entering one side will hit the other side at some point further down the wall than if you were in an elevator that wasn't moving at all.  I think the point you're missing is that even though it hits the opposite wall further down, the light has taken a straight line path to get there.  In special relativity, where the elevator isn't accelerating, light moves in a straight line.

If instead, your elevator is accelerating upwards, the light from outside will take a curved path on its way to the far wall.  The argument usually goes from there to say that you can't tell acceleration of the elevator from a stationary elevator being pulled on by gravity, and so under gravity light must also take a curved path.

• Jr. Member
• Posts: 11
##### Relativity bending of light wrong example?
« Reply #2 on: 28/01/2010 05:13:00 »
Thank you very much Jpetruccelli, I undestood the phenomenon.

#### The Naked Scientists Forum

##### Relativity bending of light wrong example?
« Reply #2 on: 28/01/2010 05:13:00 »