Every time you 'observe' a reaction you interfere with it. It is simply the need to send a photon to interact with the reaction in order for us to see what is happening.

If the photons (or other particles you use) interfere with the reaction, they might slow it down or even stop it.

This is obviously an oversimplified explanation but it works. There is a lot of other ‘nonsense’ about what quantum stage the system is in, and if you can bounce it around between the stages so it would not change.

What are photons? How can they affect reactions?

Has anyone seen photons? (I mean: Is there a sufficient proof of their existence?)

Is there a correlation between the amount of observers and the impact of the observation on the reaction that is being observed?

Please answer my questions in a simple way like you did in your first reply. Remember, I'm used to think that when you 'observe' anything, you can see only the light rays which have "bounced" back from it. I also don't accept the quantum theories, firstly because they don't seem to explain anything in the "real" world.

"Has anyone seen photons?"