# The World Doesn't Revolve Around You

1. May 14, 2010

### BL4CKCR4Y0NS

You know that saying?
"The world doesn't revolve around you"

If by "world" we'll use Earth ... how much mass would one need for the Earth to literally revolve around the subject?

2. May 14, 2010

### Staff: Mentor

I think you may have to more precisely define "revolve around".

3. May 14, 2010

### BL4CKCR4Y0NS

Orbit?
Just like the Earth revolved around the sun.
Just like the Earth orbits the sun.

4. May 14, 2010

### Staff: Mentor

Imagine you have two objects mass of the Earth revolving around their center of mass. That means they both revolve around a point lying exactly in the middle between both of them. (For simplicity let's assume they are point masses and they are not destroyed by tidal forces blah blah blah).

Which one revolves around which?

5. May 14, 2010

### BL4CKCR4Y0NS

Well what if I was stationary. I'm not orbiting around anything.
So if I am not moving, how much mass then?

6. May 14, 2010

### Staff: Mentor

There is no such thing as "stationary". Or, if you want to assume you are stationary and everything happens in a coordinates centered around you, world always revolves around you, no matter what your mass is.

I am afraid you are trying to ignore physical reality and find an answer to ill posed question. There is no answer.

7. May 14, 2010

### dulrich

The Sun itself is not stationary -- it is being pulled around by the motion of the planets. So even the mass of the Sun is insufficient.

8. May 15, 2010

### Staff: Mentor

I was thinking about something like "center of the mass is inside of the body". But it has to be clearly stated.

Last edited by a moderator: Aug 13, 2013