the universe is a sphere whose edge is nowhere and whose center is everywhere. You are stationary, relativistically speaking, even when you are walking or driving a car or flying near the speed of light. You are the reference point that perceives the rest of the universe. You are at the center of the universe. The galaxies are flying away from you. Night and day only have meaning because you perceive the light and the dark. I hope that helps.
What is it about threads like this that induce so many tangents without ever answering the question? 
The answer to the OP question is basically, yes, things can be stationary. However, you need a reference against which to say that. For example, I am stationary with respect to my desk and computer. However, relative to the center of the Earth we are moving at roughly 700 kilometers per hour to the east due to the Earth’s rotation. We are moving 30 kilometers per second relative to the Sun, and some 200 kilometers per second relative to the center of the Galaxy.
Can one thing be said to be stationary relative to the rest of the Universe? No. There is no absolute frame of reference in the Universe, any one is just as good as another. Some are more useful that others (like, assuming the surface of the Earth is stationary) but all are equal in the eyes of Einstein.
All motion is relative motion. There is no such thing as absolute motion. This is basic in special relativity.
In an otherwise “empty universe” there can be no motion whatsoever.
Special relativity is symmetric therefore any frame of reference can consider itself to be at rest, and both observers would see the other’s clock running slow. So moving at near light-speed by itself has no meaning with respect to a true age difference. One of the frames has to undergo an acceleration in order to create a true time difference.
I thought everyone should be “polite” BA. Wasn’t it the lack of politeness that caused you close your site for awhile?
Shame on you!!! 
Uh, yeah, what you said. That was an attempt to simplify gone a bit far…
Ok sorry. BTW, if your interested, do a search on Mach’s Principle it covers this concept pretty well. Mach was one of the guys who had a considerable impact on Einstein.
BA, I thought everybody was trying to answer the OP.
Ring, Interestingly, it was reading Mach that got me started thinking about this. It took another thread to finally prompt me to post.
LWF, this doesn’t apply to rocketship moving in a linear fashion. As such, I don’t feel this:
Originally posted by warmgun
Say you are riding on a bus going 50 mph and you throw a ball out of the back window at what would have been 40mph had you been standing on the surface of the earth. The ball thrown from the bus would be moving at -10 mph in relation to the thrower (as seen from the earth, the place the earth twin would be), even though it was accelerating. We know that the ball is accelerating because were a twin to be in the ball at the time of throwing, he would feel the G force.The twin riding in the ball, even though it is accelerating, is traveling at a lesser velocity the earth twin. This should cause the earth twin to age more slowly - not the ball (accelerating) twin.
So, since the earth is already moving at a constant velocity (like the bus) and you launch a rocket (like the ball) in the opposite direction, wouldn’t this be the same thing?
has been adequately addressed. It seems to meet the criteria given by most posters here.
Regardless, I do appreciate the help.
BA, I thought everybody was trying to answer the OP.
Ring, Interestingly, it was reading Mach that got me started thinking about this. It took another thread to finally prompt me to post.
LWF, this doesn’t apply to rocketship moving in a linear fashion. As such, I don’t feel this:
Originally posted by warmgun
Say you are riding on a bus going 50 mph and you throw a ball out of the back window at what would have been 40mph had you been standing on the surface of the earth. The ball thrown from the bus would be moving at -10 mph in relation to the thrower (as seen from the earth, the place the earth twin would be), even though it was accelerating. We know that the ball is accelerating because were a twin to be in the ball at the time of throwing, he would feel the G force.The twin riding in the ball, even though it is accelerating, is traveling at a lesser velocity the earth twin. This should cause the earth twin to age more slowly - not the ball (accelerating) twin.
So, since the earth is already moving at a constant velocity (like the bus) and you launch a rocket (like the ball) in the opposite direction, wouldn’t this be the same thing?
has been adequately addressed. It seems to meet the criteria given by most posters here.
Regardless, I do appreciate the help.
warmgun -
the issue with your specific example is that you imply the twin-in-the-ball is “travelling at the lesser velocity”, and thus “this should cause the earth twin to age more slowly.” Remember that there is no “lesser” velocity. Any two non-accelerating objects in different frames perceive themselves as still and the other as moving. Put another way, ALL non-accelerating motion is relative, per BA, Ring, and SPOOFE. In the case of the twin “paradox,” in which one twin remains unaccelerated, the one who accelerated ends up with the clock running behind. In your example, it would be the twin in the ball.
I think this addresses the OP (all unaccelerating objects have equal claim to stillness) and your specific later question (the twin in the ball isn’t in fact going “slower,” but he is accelerating, and his clock will hence be behind upon rejoining his brother). Without getting too far into general-relativity considerations of gravity and centripedal acceleration, does that cover it Ring, BA, and U-Filter?
–the stretch
Logicaly speaking, only an object with infinite mass can truly and absolutely be stationary in an inertial reference frame.
Since even a black hole has finite mass, true absolute stillness is impossible.
- Bozo bit: on (Macintosh)
- Normal.dot (Windows)
[sub][sup] “…and it’s spelled with an ‘e’…” [/sub][/sup]
I think so, but I’m not particularly comfortable with the specifics of general relativity. Let’s see what anyone else has to say.
Just to point out, that in the case of supersonic jets flying around the earth, they are accelerating, even at cruise speeds. They are flying ‘around’ the earth after all, which means they are constantly changing their heading (slightly). Otherwise they’d leave the earth at a tangent and we’d never get to compare clocks.
The planes flying around the world are a bad example, because that’s a GR effect. They’re accelerating, but they’re actually accelerating less than a person on the ground, due to the gravity equivalence. The difference in clocks is opposite what SR would predict alone.
The key to the twin paradox is that there’s three reference frames, not two. You’ve got the frame of the Earthbound twin, the frame of the astronaut going out from Earth, and the frame of the astronaut returning. You can say that any single one of those frames is stationary (or even some other frame entirely, but let’s not go there), but you can’t say that two of them are. If you take the Earth to be stationary, then it looks like the Earth clocks are running normally, and the ship clocks are running slow for both legs. If you take one leg of the rocket trip as stationary, then it looks like the clocks on the rocket are normal on that leg, the clocks on the Earth are slow, and the clocks on the other leg are even slower. Any way you do it, the end result is the same.
If you believe in the Big Bang, there is only one spot in the universe that is not moving in relation to other parts of it: the center of the primordial bang.
Nope…common misconception. If you accept Big Bang Theory, then there is no center or edge in 3D space. The Big Bang was not an explosion of stuff into empty space. It was the creation of space and the beginning of time. In effect, the Big Bang happened at every point in the visible universe simultaneously.
So it turns out that Spoofe is in fact the center of the universe.
Who knew?