The c=ℏ=G=1—question

• The notion of physical quantity is defined including multidimensional quantities.
• The notion of dimensional fundamental constant is defined.
• Geometric structure of space–time is constructed from time measurements only.
• Quantum mechanics is formulated without quantization and without ℏℏ.

The question whether the invariant speed c  , Planck constant ℏℏ, and gravitational constant G can be put equal to 1 is analyzed. The discussion is based on fundamental considerations concerning the notion of physical quantity. It is found that the issue is not a matter of appropriate unit selection. Further it is shown that classical space–time geometry and quantum mechanics can be formulated in such a way that the invariant speed and the action quantum are truly one and do not have to be set equal to one.