[GourmetDan]

"Well, then buy yourself a pendulum. If your [sic] not so good at math go to the North or South Pole and watch what happens. In about 24 hours the pendulums swings will have rotated a full circle. How can you explain that? Some angles or the earth is rotating?"

"Well, you'll get an "error". A small one, less than 1/365. Is the "error" due angles or because our earth is orbiting around the sun?"

Your logic is in error.

Basically, your position is that in a heliocentric model, the universe applies a force to the pendulum that holds it steady while the earth rotates underneath it.

However, when you switch to a geocentric model, you assume that the universe no longer influences the pendulum.

I do not make that error, but recognize that the universe exerts the same force on the pendulum whether the model is heliocentric or geocentric.

Make sense to you?

"You still have problems with Einstein's point of view? Every coordinate system (CS) is valid. But not every CS makes sense. This is one difference between math and physics."

The problem is that your own thought process is not consistent. Not that my choice of CS is flawed.

[MHalblaub]

"However, when you switch to a geocentric model, you assume that the universe no longer influences the pendulum."

My assumption is, you need so called fictitious or pseudo force to explain with a geocentric model what you see or you do what Einstein and Infield explained: "Can we formulate physical laws so that they are valid for all CS [coordinate systems]". You have to alter the physical laws if you use a non-inertial reference frame.

An egocentric model is also valid in your sense. It works well for me playing tennis or hockey. But I won't use it to describe the motion of my car. There I prefer a flat earth model. For airplane navigation I hope the pilots use a geocentric model. They use indeed a heliocentric model with their gyroscopes. Your model depends on the error you can allow. For the lowest error you need the Mach's Model.

You can stay with your geocentric model but I won't believe you'll be satisfied to calculate a flight to the moon properly with your physical laws.

Einstein and Infield were talking about a mathematical trick.

KISS