Interesting question

I've recently seen a question asked dealing with relativity, which got me
thinking, and I would appreciate any clarification.

If a craft leaves earth at near the speed of light and travels for a while,
the local time of the craft is thought to progress slower than on earth,
causing the perceived time of the occupant to be, say, a few days, while
years have passed on earth.
The question is this:
Since movement itself is only meaningful in relation to an object that is
regarded as a fixed point in space, how is it determined what actually
moves? According to this, it might as well be the craft that stands still,
and the earth that moves away.
So, which will age slower - the earth, or the craft, or neither, and why?

What's wrong with this? I figure there must be something wrong with it, but
I guess I don't understand general relativity as well as I ought to.

Thanks in advance :-)

Dear Laura:

"Laura" wrote in message
...
I've recently seen a question asked dealing with relativity, which got me
thinking, and I would appreciate any clarification.

If a craft leaves earth at near the speed of light and travels for a
while,
the local time of the craft is thought to progress slower than on earth,
causing the perceived time of the occupant to be, say, a few days, while
years have passed on earth.
The question is this:
Since movement itself is only meaningful in relation to an object that is
regarded as a fixed point in space, how is it determined what actually
moves?

The object that accelerates is what is moving.

According to this, it might as well be the craft that stands still,
and the earth that moves away.
So, which will age slower - the earth, or the craft, or neither, and why?

The craft and its occupants will experience less proper time than an
unaccelerated frame.

What's wrong with this? I figure there must be something wrong with it,
but
I guess I don't understand general relativity as well as I ought to.

Actually, special relativity. You don't have to consider the acceleration,
except as a differentiator between frames. It is displacement and velocity
that provides the difference in age.

Thanks in advance :-)

Be sure and check out the FAQ:
URL:http://www.math.ucr.edu/home/baez/physics/
scroll down to Special Relativity

David A. Smith

"Dr. Min" wrote in message
...
On Sat, 6 Dec 2003, "Laura" wrote:
I've recently seen a question asked dealing with relativity, which got me
thinking, and I would appreciate any clarification.
If a craft leaves earth at near the speed of light and travels for a
while,
the local time of the craft is thought to progress slower than on earth,
causing the perceived time of the occupant to be, say, a few days, while
years have passed on earth.
The question is this:
Since movement itself is only meaningful in relation to an object that is
regarded as a fixed point in space, how is it determined what actually
moves? According to this, it might as well be the craft that stands
still,
and the earth that moves away.
So, which will age slower - the earth, or the craft, or neither, and why?

-----BEGIN PGP SIGNED MESSAGE-----

It's the relative mass. A relatively tiny object moving
relative to a massive object satisfies such equation of
mass, i.e. the equation of mass in motion. The strictly
actual relationship between actual objects is effective
in the equation of their relationship. Think about this.
You are postulating the relative motion of two specific
objects of specific mass. Your hypothetical craft isn't
likely one trillionth the mass of Earth. This tiny mass
moving at near c is plainly the subject of differential
motion relative to the massive & therefore stable Earth.
The Earth is moving along just fine. It's the craft and
its "timewarp" occupants who are experiencing the brunt
of space-time differentiation. The mass is equally--and
this is precisely equal--"c" squared in proportion, rel-
ative to these two objects in question. External forces
enter into the equation obviously, but in simple theory
we can be reasonably certain that the tiny craft is the
object of drastic physical change relative to the Earth.
And here "physical" implies that it includes everything,
be it understood by modern science, occult, or whatever.
Perhaps its the intrusion of the cosmic infinity forces
upon the equation which over-complicates the whole idea?

That's my opinion,
Daniel Joseph Min

Unfortunately, it is both wrong
and useless.