Reflection and the measurement, and time irreversibility

[Dmitry67]

Reflection is not considered to be a measurement. Reflection, like using lenses is considered to be a time-reversible process. It is not a measurement and it does not erase the coherence (interference pattern)

Here is what I don't understand

What happens to the momentum of the photon? The light pressure? If I put a mirror (flying in a zero gravity and vacuum) right behind 2 slits, mirror will start rotating very slowly in a different directions depending on the path of the photon

Where is a flaw?

 

[Avodyne]

If you can measure the mirror's momentum well enough to detect which slit the photon went through, the posistion will be uncertain enough to destroy the interference pattern.

 

[Dmitry67]

My mirror is flying in the empty space. If it is hit by 1 photon, it begins to rotate making 1 full rotation per 1 year. So I make an experiment and decide to check the position of a mirror 3 month later. What is going to happen to the interference pattern?