time travel applications


by epkid08
Tags: applications, time, travel
isly ilwott
isly ilwott is offline
#37
Aug20-08, 12:42 PM
P: 72
Quote Quote by MeJennifer View Post
Ok so we do not seem to disagree on that one.
Being so simple, it would be difficult to disagree on that one.


You are ignoring the principles of relativity again. Remember motion is always relative in relativity!
I've not ignored it...and motion is always relative (period).

It seems that you understand that motion is relative as you write now: "motion relative to a fixed point outside of the sphere"! However you are mistaken about the first part, all the points except for the center are in motion with respect to each other. You might want to consult the literature about relativity and rotating disks or balls.
Simplify this to a disc. Consider two fixed horses on a spinning Merry-Go-Round. They are not in motion relative to each other. They are both in motion relative to an observer standing in the ticket line.


By the way, I presume you mean a ball instead of a sphere as a sphere does not even have a center.
There are hollow spheres and solid spheres. Both have centers. By your way of thinking, a perfect circle drawn on a sheet of paper has no center.

The center of a sphere is simply that one and only one point that is equally distant from every point on the surface of the sphere, whether the sphere is hollow or not.

I seems that the problem you are having is that you think in terms of absolute positions and locations. There are no such things in relativity as 'positions' and 'locations' are only relative concepts.
Of course there are. The very idea of relativity depends on positions and locations.

It will be scary to ever see MENTOR under your name.
MeJennifer
MeJennifer is offline
#38
Aug20-08, 12:50 PM
P: 2,043
Quote Quote by isly ilwott View Post
There are hollow spheres and solid spheres. Both have centers. By your way of thinking, a perfect circle drawn on a sheet of paper has no center.
Do you understand the difference between a ball and a sphere or a disk and a circle?
isly ilwott
isly ilwott is offline
#39
Aug20-08, 12:56 PM
P: 72
Quote Quote by MeJennifer View Post
Do you understand the difference between a ball and a sphere or a disk and a circle?
Is that ever a rhetorical question?

I realize that mathematicians consider only the surface, but they still call the centerpoint the center. It is not part of the sphere but is its center. The samer holds for the circle drawn on paper. It still has a center...that is not part of the circle.

The word "sphere" has Greek origins "sphaira, ball".
MeJennifer
MeJennifer is offline
#40
Aug20-08, 02:54 PM
P: 2,043
Quote Quote by isly ilwott View Post
I realize that mathematicians consider only the surface, but they still call the centerpoint the center.
A sphere has no center.

At any rate it seems I cannot be helpful to you, so I leave it at that.
matheinste
matheinste is offline
#41
Aug20-08, 06:30 PM
P: 1,060
Hello isly ilwott.

I suppose the surface of a sphere is a two dimensional manifold and has no centre. But it is normal and common usage to refer to the centre of the volume it encloses when thought of as being embedded in three dimensional space ( a ball ), as the centre of the sphere. We all know what it means.

Matheinste.


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