1) if gravity is only a map, why it exists outside of our brain? Anyone can have their opinion about gravity, but that doesn't mean that a different map it's going to let you fly or have a different acceleration from the correct map;

Gravity is within arational reality, it's our label whether it is classical or modern physics. Gravity is a human projection. Your brain is a human projection. These things are easy logical conclusions, so should they be easily seen as such?

2) why the brain, who is many, many orders of magnitude above the smallest constituents of reality, should be able to perceive the underlying territory with a simple and undefined things like "silent of all thoughts"?

I don't really understand what your question is about. Is it about who is capable of understanding the insights provided?

Regardless if I misunderstand, what I said is probably one of the most difficult things to achieve but "silent of all thoughts" was simply an argument, a map, if you do become silent of all thoughts, reality does not disappear. All those thoughts were maps, the present moment is the way it is.

Then some thoughts will sneak in obviously because you can't really silence all thoughts with thoughts. You just get more thoughts, because you believe you are in control. That is creating maps. You don't flow with the stream of life, you are resisting.

The brain is a remarkable thing, you should be able to perceive underlying territory at any moment, since that is the way it is. That you understand that "YOU" is a logical conclusion, the same with gravity, anything :)