In general relativity, the gravitational field is reflected by the curvature of space. Space is curved in the direction of gravity source, and the effect of gravity on light is the same, that is, light still moves along the curved space. In order to facilitate imagination, one-dimensional space is removed and a time axis is used to study two-dimensional plane motion. The two-dimensional plane is curved in the direction of gravity, just like an elastic membrane, and the position with mass is like pressing a stone to form a pit. In this way, when the object on the plane is close to the stone, it will slide into the into the pit, which is the mechanism of gravity. No matter how far it is, it will slide into the into the pit, but the gravity is small in the distance. But when we describe the motion of these objects, they still move in a plane, that is, the curvature is still zero. At this time, both light and ordinary low-speed objects are moving in this plane. Suppose the curvature of this 4-dimensional space is 0, because their trajectory curvature is 0.
2. What is the concept of star in "1light-year star"?
It should be a concept invented by some popular science books, or an inaccurate translation. It can be understood that the curvature of these celestial bodies is the same on the light-year scale, which can be confirmed by current observations. There is no experimental basis for whether there is a difference on a larger scale. So far, we can't arbitrarily say that it is the same. In other words, the radius of curvature of our space is at least 1 light-year. How big it is, it is impossible to determine according to the current observation facts. That is to say, whether our 4-dimensional space is straight (space curvature is zero), spherical (space curvature is greater than zero) or hyperbolic (space curvature is less than zero) is still inconclusive, but at least it is straight on the scale of 1 light-year.
3. If their radius of curvature is 1 light-year, the curvature should be quite small. Why can such a small curvature of spacetime have such a great effect and firmly "adsorb" us on it?
The so-called firm "adsorption" is a picture based on the gravitational field in our three-dimensional space. In the gravitational field of three-dimensional space, if nothing can attract an object, it will slide in the direction of gravity. In fact, when gravity is described as a space, there is no such sliding, which can be said to be static. Just as an object in weightlessness can stay anywhere in space, it is the same. So it doesn't have much impact. The origin of this problem may be this 6544.
There is also a question about curvature.
When considering the curvature of a point on a curve, we can't simply say that it is a point, but we must also consider the area near it.
This is probably the meaning of curvature, that is, the concept of differential, just like saying that we should consider the nearby point when calculating the derivative. The nearby point is very close and can be regarded as a point. I don't know if the landlord understands advanced mathematics, but I think the author intends to explain a differential concept in popular language here.
I don't know whose article the landlord read and where it came from. As a scientific paper, this is very imprecise, and as a popular science book, we should not create these concepts stiffly. If we translate documents, the translator himself may not understand the original author's thoughts.
The above is purely personal understanding, the landlord can refer to it and adopt it as appropriate. I hope it helps you.