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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 can also compare the measured lensing to predictions of the statistical properties it should have if the large-scale structure of the universe only consisted of normal matter and dark matter that gradually assembled into the "cosmic web" of the previous picture. 5/8

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