Something still isn’t clear to me. As far as I understand, even before Einstein they assumed that the laws of physics are identical in all frames of reference. So what is the innovation here “from the standpoint of the solution”? (I’m not asking about the second principle, the constancy of the speed of light.)

Correct, but they didn’t understand that for this to hold, you have to change the space-time transformations between different frames of reference.

The question is what the laws of physics are.
Something that depends on the observer’s point of view is not a physical law, and one cannot say of it that it exists. For example, the electric field (which becomes magnetic depending on the velocity) does not exist. And that is an innovation.

I still haven’t managed to fully grasp what you mean. This isn’t criticism; it’s really just something I still don’t get.
As far as I understand, Newtonian physics also has transformation laws between different frames of reference. If I’m right, and if, as you explained here, the principle is that the laws of physics are identical in all frames of reference, then there’s nothing new here in any fundamental methodological sense.
Where am I going wrong?

This principle is Galileo’s, not Einstein’s.
What Einstein innovated was regarding the speed of light, that it is constant in all inertial frames, and from this it follows that time and space are relative. And that is new and hard to grasp.

To Doron

Indeed, from the perspective of what you call the first principle, there was no innovation here. The innovation is that in order for it to fit with the second principle, one has to give up Galilean transformations (which are intuitive according to how things appear to our eyes) and adopt Lorentz transformations, which are a major innovation (that is, in systems that have relative velocity between them, time does not pass at the same rate—in one it passes more slowly than in the other—and likewise the lengths of the same objects get a different value in each of these systems; the same table can have a length of 2 meters in one and 3 meters in the other).

In fact, even Lorentz transformations are not Einstein’s innovation. They are Lorentz’s, who conceived them in order that Maxwell’s equations (the electromagnetic equations) would have the same form in systems moving at a relative velocity to one another. But he assumed the existence of the ether for this purpose (the existence of a medium in which these waves move forward and which fills all of space, so that the transformations would fit the Newtonian mechanical worldview that existed until then). Einstein succeeded in deriving them from the two principles you mentioned, without any connection to Maxwell’s equations and without assuming the existence of the ether (for whose existence there was no evidence, and whose existence also created several problems). He showed that this is a property of mechanics and not only of electricity and magnetism. That is, that it is something more general and universal. And therefore that the Newtonian mechanical picture of the world is not correct. That was the great innovation.

Many thanks for the answer. I’m thinking it over.

Immanuel (and others),
Can one then summarize and say something like this: Einstein’s fundamental methodological innovation, from the standpoint of the constancy of the laws of physics, is basically their extension to mechanics as well. Whereas before Einstein people believed in fixed lawfulness regarding certain fields (electromagnetism, etc.), once Einstein entered the picture a way was discovered to generalize across different fields.
Right?
If so, that fits very well for me with the philosophical principle that Einstein planted in the background of his physics (the centrality of postulation).

The great innovations do not concern methodology, but rather the destruction of ancient beliefs—basic human worldviews that do not accord with reality.

The fact that the speed of light does not change (and therefore from this assumption it follows that time and space are connected and dependent on one another, and can also change) runs contrary to the way we experience the world.

And as proof: his great mistake was that he did not destroy the ancient belief that the stars are not moving.

Ancient beliefs are a slippery matter.