Light has been seen leaving an atom cloud before it entered

In the quantum realm, seemingly impossible things are happening every day. Thanks to quantum effects, a particle of light can exit a cloud of extremely cold atoms before it even enters.

When light goes into a material, its speed changes as its particles, or photons, interact with the atoms around them. Atoms inside a material absorb and then release any photons that enter, causing a delay in their travel time. But…