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there is actually a science change that happened, and it's not (entirely) just politicians changing their mind. The big thing going from X-ray (2d) to CT (spin an X-ray machine around and take a ton of pictures to recreate a 3d image) did a lot to let security people see inside of a bag, but the hitch is that if you see a blob of gray is that water, shampoo or something else? The recent advance that is letting this happen is machines who will send multiple wavelengths of X-ray through the material: since different materials absorb light differently, your machine can distinguish between materials, which lets you be more sure that that 2litre is (mostly) water, and then they can discriminate |