Popper on scientific objectivity

…science and scientific objectivity do not (and cannot) result from the attempts of an individual scientist to be ‘objective’, but from the friendly-hostile co-operation of many scientists.  Scientific objectivity can be described as the inter-subjectivity of scientific method…

Two aspects of the method of the natural sciences are of importance in this connection.  Together they constitute what I may term the ‘public character of scientific method’.  First, there is something approaching free criticism.  A scientist may offer his theory with the full conviction that it is unassailable.  But this will not impress his fellow-scientists and competitors; rather it challenges them : they know that the scientific attitude means criticizing everything, and they are little deterred even by authorities.  Secondly, scientists try to avoid talking at cross-purposes…In the natural sciences this is achieved by recognizing experience as the impartial arbiter of their controversies.  When speaking of ‘experience’ I have in mind experience of a ‘public’ character, like observations, and experiments, as opposed to experience in the sense of more ‘private’ aesthetic or religious experience; and an experience is ‘public’ if everybody who takes the trouble can repeat it…

This is what constitutes scientific objectivity.  Everyone who has learned the technique of understanding and testing scientific theories can repeat the experiment and judge for himself. 

Karl Popper, The Open Science and Its Enemies, Chapter 23 (p217-218, Vol.  II)