Expressing opinions does not create new, reliable scientific knowledge. Instead scientists observe, make claims, deduce the effects of their claims, and then conduct experiments suited to possibly observe these effects. So it's not just claiming. And the laws of physics exist by themselves, even when there is no human society to discover and know them.
It's a different story how knowledge is passed on or accepted by society.
We know that the proof of authority is the weakest and most unreliable type of evidence. But still the proof of authority dominates in practical everyday life. We believe things because our parents or teachers tell us, even if we had the possibility to check them ourselves from a scientific point of view. But parents and teachers are not the source of knowledge, they are only transmitters.
In the humanities ("Geisteswissenschaften", and similar disciplines) the situation is different. Knowledge is rather believable and not falsifiable, but only accepted on the authority of the person who uttered the sentence.