Does Light Take Longer to Reach Us Through a Gravitational Lens?

[scupydog]

Hi. Does the light from a lensed object take longer to reach us, than the light from an unlensed object at the same distance.

I mean because the light from a lensed object has a curved path.

Thx. Dave...

 

[Chronos]

Correct. For discussion see:
http://arxiv.org/abs/astro-ph/9606001
Lectures on Gravitational Lensing
authors: Narayan, Bartelmann

 

[Jonathan Scott]

Hi. Does the light from a lensed object take longer to reach us, than the light from an unlensed object at the same distance.

I mean because the light from a lensed object has a curved path.

Thx. Dave...

Yes, it takes longer to reach us but this is normally mainly because of the Shapiro delay effect rather than simply the curved path. Basically, light slows down slightly in a lower gravitational potential, closer to a massive object or system, as if it were in a medium with a refractive index slightly greater than 1. The amount of deflection relates to the gravitational field (how rapidly that potential changes with sideways displacement along the light path) but the amount of time delay mainly relates to the potential along the path.

 

[scupydog]

Hi.

Correct. For discussion see
http://arxiv.org/abs/astro-ph/9606001
Lectures on Gravitational Lensing
authors: Narayan, Bartelmann

Thx so much for this info, i will read now.

 

[scupydog]

Hi

Yes, it takes longer to reach us but this is normally mainly because of the Shapiro delay effect rather than simply the curved path. Basically, light slows down slightly in a lower gravitational potential, closer to a massive object or system, as if it were in a medium with a refractive index slightly greater than 1. The amount of deflection relates to the gravitational field (how rapidly that potential changes with sideways displacement along the light path) but the amount of time delay mainly relates to the potential along the path.

The shapiro effect... i'll look into that. Thx.