Zero kelvin is the lowest possible temperature. At absolute zero, all motion comes to a standstill. It is obvious that a lower temperature is not feasible because there is no velocity smaller than zero and no energy content less than nothing.

As a scientist, I play in the top league - the Olympics, the World Championships - and I want to be in the lead. As a runner, I set personal goals, and I want to push beyond my own personal limits. I was very happy when I practiced for several months and then reached my goal to run a marathon in 2:50.

After earning my Ph.D., I stayed at the Max-Planck Institute as a postdoc, working on laser excitation of Rydberg states of triatomic hydrogen and helium hydride. I also succeeded in analyzing all the emission spectra of helium hydride, which I had discovered during my Ph.D.

Amplifying atoms is more subtle than amplifying electromagnetic waves because atoms can only change their quantum state and cannot be created. Therefore, even if one could amplify gold atoms, one would not realize the dreams of medieval alchemy.

Laser cooling opened a new route to ultralow temperature physics. Laser cooling experiments, with room temperature vacuum chambers and easy optical access, look very different from cryogenic cells with multi-layer thermal shielding around them.