This site is about gravity on the scale of galaxys. I will demonstrate that Newtonian physics does not have to be modified to explain the rotation curve of our galaxy, nor do we have add anything like 'dark matter' to save Newtons law of gravitation. This site is meant to be an invitation to everyone in theoretical physics to refute my line of reasoning.


Received wisdom has it, that Newtonian gravity does not give a correct description of the observed gravitational acceleration of the stars of our galaxy. It is widely held that, according to Newtonian physics, the acceleration should be: a ~ 1/r2. Instead, we observe: a ~ 1/r.
The last relation has an important and very observable consequence: the rotational (tangential) velocity of every star in the outer region of a galaxy becomes the same at all distances from the centre.
The difference between the (supposed) Newtonian gravity and the observed gravity therefore is often illustrated by a graph of this velocity, the so called 'rotation curve':

To explain this discrepancy between theory and observation, two theories are proposed:
1: There be a lot of 'dark matter' surrounding the galaxy, that provides for the extra gravity, or
2: Newtononian gravity had to be modified (MOND: MOdified Newtonian Gravity)
Both of them have their qualities and their problems, but that is not the issue here.
I will argue that neither one is a correct description of observed reality. Instead I will show that Newtonian gravity has been misinterpreted. When applied correctly there is no discrepancy between theory and observation. For our galaxy Newton predicts exactly what has been observed: an acceleration of a ~ 1/a, and a rotational speed of 230 km/sec.