# (TFT) hollow Cidri

```From: Joe Hartley <jh@brainiac.com>

```
. . . I think that the assumption of an equal mass is incorrect, and that you could use a value for mass easily
```enough to make Cidri's gravity similar to Earth's without it
being unrealistic.

This may or may not require hollowness in the center
of the planet, though I tend to think it does.
```
```
```
Yes I can do this. I can find a way to make it work. And specifically with an anti-grav object in the middle as was originally suggested. The total mass will be substantially greater, but the way it behaves is different.
```
```
The program I'm tinkering with now uses gravity to run a stable solar system. In the process I have learned quite a bit about the nature and math of Newtonian physics. First off I have solved the "two body" problem so I can run the 88 largest bodies simultaneously. Secondly as Newton invented Calculus to prove, no matter the shape of the body gravity may be assumed to originate from the center of mass.
```
```
Without going into it, and just leaping to terminology I'm currently steeped in, the proposal would change the planet from having a "center of mass" to having a "gravity corona." And then, yes, it becomes entirely possible. But to illustrate the elegance that I saw in Scot's suggestion I wanted to first summon the problems that it eventually solves.
```
```
doubling the radius = 1/40 grav if you are still using center of mass. (already posted)
```
the second post I had written....

```
```But if we make all life 1/40th the size of earth normal....

we would have 160 x the surface area of earth

and...

everyone could walk on water.

David Michael Grouchy II
```
```
```
To show that certain key behaviors of physics would give away any changes in scale.
```
```
And the planed third post would introduce the concept of a "gravity corona" with appropriated descriptions and supporting arguments. Instead I just submit the pure math here in the form of an algorithm. In my gravity lab program the following works. And elegantly at that.
```
d := DistanceSqr(p1,p2);
```