[quote][quote="Gerbil94"]
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Originally Posted by lyndonashmore
Hi gerbil 94,
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They look at ‘two images’ of a distant quasar lensed by some mass in front. Then, by looking at the relative apparent intensities of the two ‘images’ they can tell how much further light from one image has travelled than the other.
Measure the difference in redshifts between the two images and whallah, H can be found. Sounds simple.
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No, the time delay between the images is what is measured (H0 is inversely proportional to the time delay). The equivalent redshift difference is tiny. Also, the magnification ratio between the images does not directly determine H0. |
True, teach me not to remind myself first before posting!
Try
This
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Apart from their intrinsic interest, gravitational lenses have exciting cosmological applications. If the background quasar is variable, the time delay between variations of two different components in the image allows us to calculate the difference in the paths of the corresponding rays from the distant quasar. Given the distances (i.e. redshifts) of the galaxy and quasar, the absolute scale of the system -- and hence the Hubble expansion constant Ho - can be calculated. A preliminary result from a lens being studied at Jodrell is around 65 km/s/Mpc, although there are still some uncertainties in models of the system. Other science, such as modelling of mass distributions of the intervening galaxies, is also possible. This allows estimates of the masses of these galaxies and hence a clue to the amount of "missing", non-luminous mass in the universe.
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You haven't actually answered my question, I think. I asked why you used numbers derived from what you state to be an invalid theory to support yours. You quote estimates for H0 from lensing; surely these are at best right by coincidence?
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No I use numbers from observations - the defunct theory is someone's interpretation of these results,
Cheers,
Lyndon