Quote:
Originally Posted by Robh
Very interesting research.
Abell 1689 (+ dark matter) causes the gravitational lensing. The greater the mass, the more the light path is curved. The deviation of light from this expected path is a measure of the expansion of space. If space is expanding, the light path needs to bend more to still reach Earth. This effectively requires an increase in the mass of Abell 1689 as compared to a static space.
Correct or not?
Regards, Rob.
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Well, dangerous as it might be Rob, I'll have a go at this one.
Lensing is predicted by Einstein's GR. The light is bent when it passes close to a large mass. The effects of Grav Lensing are due to the curvature of spacetime. It is not a change in the material that the light passes thru that causes the bending, but a change in the strength of the grav field. Light does slow down in the presence of gravity but this effect is completely independent of the colour of the light. All colours are bent by exactly the same angle. This angle depends on how much spacetime has been warped and the incident path of the light - the closer it comes to the centre of the dimple in spacetime, the larger the deflection.
From this deflection they can determine the mass that should be contained within the 'lens'. And in most cases, this calculated mass far exceeds the mass measured by other means (of intervening galaxy causing the lens). So the mass must be coming from 'dark matter' stuff that doesn't appear in the visible spectrum but which effects gravity.
I reckon I'll be shot down for that explanation ... (I think its pretty OK, though).
Cheers