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As we are putting the finishing touches on our Large Aperture Telescope 🔭, now might be a good time to explain what science goals it serves. The problem is that there are many to choose from! (Image credit: Mark Devlin) 1/8

In our 2018 science goals paper (arxiv.org/pdf/1808.07445) there are six sections dedicated to the science SO can do. Of those, five are primarily involving the LAT. Only looking for degree-scale B-modes (the SAT's speciality) eludes it. 2/8

Because the LAT has a much larger mirror, it can resolve finer details on the sky. The resolution is roughly 1/40th of a degree, about the same as someone with a 6/10-7/10 vision. This makes us able to see the small deflection of CMB light by matter's gravity. (Image credit: ESA/Planck) 3/8

Side note: Gravitational lensing can also transform E-mode polarization into B-modes. Those were only first detected by the South Pole Telescope in 2013. 3b/8

Because it is a purely gravitational effect, lensing is sensitive to dark matter, so we can see its effect over the whole history of the universe by observing CMB lensing. 4/8

We expect some of it will be missing, because some matter will be defying gravity. It turns out if you are going at relativistic speeds, you're not very sensitive to the pull of your typical dark matter blob. 6/8

This is a scale-dependent effect, so we know how to identify it. It is also sensitive to the mass of the relativistic particles zipping through. That includes neutrinos! (Image from the CMB-S4 science book arxiv.org/abs/1610.02743) 7/8

So you can use the largest objects in the Universe (the CMB and large scale structure) to weigh the lightest elementary particles (neutrinos) which is the coolest thing ever. There's a lot more we can do with the LAT but this thread is already fairly long, so let's save it for next time. 8/8