1. A method for determining physical properties and/or quantities relevant to combustion of a gas and/or a gas mixture, the method comprising: flowing the gas and/or gas mixture from a gas reservoir through a critical nozzle and past a microthermal sensor, wherein the same mass flow is applied to the critical nozzle and the microthermal sensor; measuring a pressure drop in the gas reservoir as a function of time; determining a first gas property factor (Γ*), which is dependent on a first group of physical properties of the gas and/or gas mixture, wherein the first gas property is derived based on a time constant of the pressure drop; determining a second gas property factor (Γ), which is dependent on a second group of physical properties of the gas and/or gas mixture, from a flow signal generated by the microthermal sensor, wherein the second gas property factor contains or is dependent on a heat capacity (c p ) of the gas and/or gas mixture; determining a thermal conductivity (λ) of the gas and/or gas mixture using the microthermal sensor; and determining a physical property and/or a quantity relevant to combustion through a correlation between the physical property and/or the quantity relevant to combustion, and the first and second gas property factors (Γ*, Γ) and the thermal conductivity (λ).