Is movement in space relative or absolute?

poita · Apr 26, 2005

Is there such a thing as an absolute standard to which anything moving can be related to? Or is all movement just a change in position relative to something else? I know that movement at different speeds can affect time (or is it acceleration and deceleration that affects time?) but how is movement defined in an absolute sense? This is why i'm unsure about this. If i fly in a counter direction to the earths rotation at the same speed as the earth then in effect i'm staying still. But then i'm circling the sun with the earth so i need to circle the sun counter to the earths orbit. But then i'm circling the Galaxy so i need to (theoretically of course) counter orbit the Galaxy. But the the Galaxy might be orbiting a cluster (not sure if that's so) so i need to fly counter to that. Then the cluster is expanding outward so i need to fly toward the dead center of the universe at the same speed the universe is expanding. I would need to travel at incredible speeds to do this of course but as it's a hyperthetical question please indulge me. So my question is . . . . am i moving if i do this or have i actually achieved ultimate stillness? That's why i ask the question. Is movement entirely relative or absolute?

tony873004 · Apr 26, 2005

Circular movement is not completely relative. Imagine if I have a fly in a jar, and I attach it to a string and swing it in a circle over my head. The fly feels an artifical gravity caused by the circular motion. A spider sitting on the wall, outside the jar watches this, but feels no artificial gravity since she is outside the jar. But all of a sudden, I declare the jar to be the reference to which the rest of the universe is compared. In that instant, the fly in the jar ceases to feel the artificial gravity, and the spider on the wall experiences the artificial gravity from being in a universe that is wobbling around the stationary jar. NOT!! So rotational motion is not relative. But linear motion is. There are a few ways to try to define a stationary coordinate system for the universe. You could average the velocities, masses and positions of everything in the universe. Or you could reference it off the cosmic microwave background radiation left over from the big bang (but it moves too at the speed of light, and in all different directions).

Saiph · Apr 26, 2005

actually, you can use GR to do that...but it's a very complicated and brain hurting matter. It also doesn't make as much sense. but you're right, you can distinguish between accelerating reference frames. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nexium · Apr 26, 2005

Speed is relative to something. Imho it is reasonable to say there is no such thing as absolute speed nor is there an absolute standard. We can not say how fast we need to travel on a convoluted path to say we are absolutely stationary. Neil

poita · Apr 26, 2005

So the consensus here then is that movement is a relative state? Then what is it that affects time or the way time affects those moving differently to those moving less or more. Is it acceleration and deceleration that speeds and slows times effect up and down or simply velocity? But if velocity is only defined relativly how is it that time can have predictable effects. The occupants of two space ships leaving a stationary space station at near the speed of light in opposite directions at identical speeds would feel the same passage of time. But in fact you could say one of them is headed towards the center of the universe and the other away. So isn't one basically staying still and the other moving. So how does time decide which one to affect and by how much. Time may be relative but it's principles are not arbitrary.

Saiph · Apr 26, 2005

it affects both. Both frames of reference see the other one correctly, even if both predict the other to be time dilated. It's screwy yes, but correct. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

poita · Apr 27, 2005

So of the three: 1. Space ship heading at near the speed of light towards the center of the univers. 2. The space station that is not moving except that in holding it's place it is actually expanding out ward at the speed of the universes expansion. And 3. The space ship that is moving away from the center of the universe at near the speed of light . . . . . . is any of them more still or more moving than the other? Of course this whole questions of mine assumes that the whole universe as a mass is still. If in fact the univers is like a hand grenade that expplodes in mid arch through the air then the whole expanding explosion it's self could be moving. In that case, aplied to the universe you could suggest that the ship moving away from the center of the universe at near the speed of light is in face achieving stillness (if it's on the trailing end of the assumed moving universe) as relative the to space the hurtling univers is moving it is pulling away from the universe but standing still. yes the mind boggles and though i don't know the answer i have a sense of nature and my guess is that one reason it's so hard to grasp answers sometimes is because we look for yes or no and i suspect that one of the deeper truths to science and the univers is that sometimes things are able to be 'yes and no' at the same time. i think Chaos theory himts at this with ordered chaos and chaotic order.

Saiph · Apr 27, 2005

they can all be considered moving, or still with equal validity....even if the universe as a whole is moving. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

poita · Apr 27, 2005

So then there truly is no such thing as absolute when it comes tomovement. It's always realative?

Saiph · Apr 27, 2005

yep. Any acceleration makes it...well, less relative, but using GR even that can be surmounted. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

poita · Apr 28, 2005

Then what exact property about high speed movement is it that affects time? It it simply speed (though if all movement is relative then there is no such thing as speed, only, how quickly you close or open a distance between you and a point in space). Or is it as i think i once read, acceleration and deceleration that affects time?

Saiph · Apr 28, 2005

well, for you, the moving person, you won't notice a thing. Time is perfectly unaltered for you, you will never notice a change. It's only when you try to compare your clocks to everyone else that they disagree, same goes for how far you've traveled (or they've traveled). But, everyone is right. More on that later (but it's synonomous to how a right triangle can have many different leg lengths, but will always have the same hypoteneus! go pythagorean theorem!) <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

poita · Apr 29, 2005

I understand that there is no right and wrong clock. I like the triangle metaphor, it helps very much to visualise it. My question though is, what 'exactly' is it that causes the difference in time? Is it that the two clocks are moving at different speeds? Is it the acceleration and deceleration ( then would a short journey with a lot of acceleration and deceleration to near the speed of light affect time more than a longer journey that only accelerated a certain amount)? Or is it something to do with the fact that the faster we go the more mass we have and it could infact be gravity that is slowing time and not speed at all, just happens that where there is speed there is more mass? I'm aware of the general area that affects time but not really the specifics.

Saiph · Apr 29, 2005

both speed and acceleration have an effect. Gravity does slow time down, because it is indistinguishable from acceleration. Only your inertia increases with speed, not your actual mass (or rest mass). The term relativistic mass is a poor one, a misnomer. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

rlb2 · Apr 29, 2005

So then there truly is no such thing as absolute when it comes to movement. It's always realative? The word Einstein wanted to use to help explain it all was equivalence ...... Relativity was used by the media because theory of equivalence didn't sound as good as theory of relativity..... <div class="Discussion_UserSignature"> Ron Bennett </div>

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