I am talking about a horizontal line that is straight and goes on forever.
I dont think you understand my point. Lets say you are in
Collinsville, Oklahoma, USA and have 4000 mile long level.
One end in NJ and one in Ca
The people at the extreme ( CA, NJ) will laugh if you tell them the level is horizontal.
Now one guy from Ca walking along the way towards oklahoma will find this line to be more and more level but wont be perfect till he reaches Collinsville
or more precisely your home.
Theoretically the level is not leveled anywhere passed the bubble. It is an infinity of points which describes a circle
No, it does not describe a circle. A circle is a set of points in a plane that are equidistant from a central point.
Using the X-Y plane, lines have equations of the form Y = mX + b with a traditional horizontal line in that plane m = 0
circles have an equation of the form Y^2 + X^2 = R^2 (for circles centered at the origin)
If my memory is correct circles are of the form (Y-a)^2 + (X-b)^2 = R^2 when the origin of the circle is at (b,a)
You need to consider the reference point. When you start talking about things that go on to infinity, using the gravitational field of the earth as a reference point just doesn't make sense.