Constantly, people are in contact with light. Thus the opinion prevails that the nature of light is known. However, light has many secrets: for example time stands still when "sitting" on a beam of light. In a way it is possible to travel into the future. By focusing the light of a laser with a microscope objective, it is possible to pack more light quanta into that pinhead than the universe has stars. There, the temperature becomes as hot as inside the sun. The pressure of the light allows handling microscopic particles as if using a pair of (optical) tweezers. This is even possible in the interior of living cells without opening them. Such effects of light are routinely used at the Leibniz Institute for Age Research in Jena to study life processes. Using sharply focused light the DNA in the interior of a living cell can be damaged with high accuracy. Subsequently fluorescent light can be used to study how the cell repairs the damaged DNA. This reveals how errors during DNA repair contribute to aging and how such problems can be avoided.
Compared to the electron microscopy, the advantage of visible light is that processes in the interior of living cells can be observed. Until recently it was not possible to separately observe two objects which are closer to each other than half the wavelength of light (approximately a quarter of a micrometer) using visible light. This dogma - named after the cofounder of the Carl Zeiss Company Ernst Abbe - appeared to be equally carved in stone as it is on his memorial stone at the "Fürstengraben" in Jena. The experimental circumvention of this dogmatic Abbe criterion was honored 2014 with the Nobelprice for Stefan Hell, a good colleague of the microscopy researchers at the Leibniz Institute for Age Research in Jena.