I was wondering about gravitational lensing as an alternative to inflation to account for the smooth nature of the CMB,

 

If our observable segment of the universe was surrounded by a vast dense patch of matter, couldn't light travelling towards us be lensed by this and spread evenly so that we observed a homogenous background.

 

To clarify, our CMB would in this case be a magnified section of a smaller area, the lensing effect spreading this local point evenly across our view of the universe as we look back in time. IE the CMB is just a small area smudged out across the sky.

 

So rather than inflation spreading the radiation out rapidly, gravitational lensing spread a small section over a wider area.

 

Possible?

Don't see how this would work in ALL directions.

Don't see how this would work in ALL directions.

 

The area we were in was quite dense with matter, the region the became our galaxy and local clusters was surrounded by a shroud of matter in all directions, only select portions of the CMB were projected by lensing around us. There wouldn't need to be all directions, in fact two hemispheres would provide the best chance of a matching smoothness.

 

It does seem a bit contrived, but is actually quite simple when compared to inflation.

No for one thing we would be able to measure those gravitational anomolies via the integrated Sache-Wolfe effect. Secondly lensing could never be in every direction without distortion. Thirdly this wouldn't explain how the BB theory managed to predict the correct element ratios via BB nucleosynthesis. Nucleosynthesis needed the supercooling and reheating phases to get those mixtures.

Also lensing wouldn't explain the temperature variations. The average blackbody temperature is also homogeneous and isotropic. Though the further back in time you look the hotter it gets.

Secondly lensing could never be in every direction without distortion.

 

Just to expand on this, gravitational lensing is caused by a local concentration of mass in the same way that optical lensing can be caused by a local thickening of glass. You can't have a lens that surrounds you and provides the same magnified image no matter where you look.