Relative Motion (A Thought Experiment)

Yes, I've considered this too. But again, I'm curious about the question of relativity.I know that they orbit around their centre of mass but do they actually move relative to their centre of mass? The way I visualize it (and I may be completely wrong about this), the two gravitating bodies and their centre of mass, relative to each other, stay exactly where they are. From all three points of reference wouldn't you see the other two as stationary (in a tidally locked system)?It seems to me that it would be necessary to have a point of reference outside the system. Anything that is a part of the system (planet, moon, and centre of mass) will see it as motionless. If we allow that they do orbit each other, we still won't see that from within because there is no relative motion within the system. The system "moves" as a whole, but only relative to an external point of reference.The point is that, in this scenario, there is no external point of reference. I think what I'm having trouble with is whether or not there is a difference between a system (any system) that has an "overall" motion with no external, relative point of reference and a system that has no "overall" motion at all.Just to be clear about this, I'm not arguing against the idea of motion. I for one believe that these hypothetical bodies could orbit each other, just as they do in this universe, and I have no doubt that you could detect the effects of their orbits.What I'm really trying to wrap my head around is how this can be when there is nothing relative to their orbit. My mind has trouble dealing with this one because "motion" would seem to lose all meaning if it's not relative to something. As far as I can tell, motion is defined as changes in relative proximity and orientation. If there is nothing to relate to, how can these changes occur?The same thing with the original question. Could a sole planet, alone in an otherwise barren universe, rotate for example? My mind seems to experience a jarring contradiction here. Almost simultaneously, I don't see why not...and...I don't see how it possibly could.Am I making any sense? Because I certainly don't feel like I am.

Seriously? You mean it's still considered a legitimate theory (or at least hypothesis)? I always thought it was one of those long dead ideas like the steady state theory. Well I must admit I'm surprised. I honestly had no idea that the concept was still given serious consideration. I always thought that the particle/wave duality of light showed how the ether was not necessary. As I understood it, light being able to travel as particles and waves, is capable of travelling through empty space, whereas a mere wave requires a medium through which to propagate.It seems that I misunderstood. That's what I get for being an "amateur scientist".Please feel free to set me straight on this.

It's not. It is. It's not.The problem with the ether hypothesis was that it wasn't proposed because of some kind of direct evidence. It was proposed because it was thought to be necessary. Unfortunately, even the hypothesis itself makes it hard to find any evidence to support its existence. How can you even detect something that's supposed to be able to go through everything without a problem? Yes, you are correct. However, do you really know what the duality of particle/wave nature of light is? It's an interesting concept, but it can only be shown mathematically and no more, just like the dimensions beyond our space-time. No, you have not misunderstood. You mean you're gay?

---

The Laminator
For goodness's sake, please vote Democrat this November!

I know you didn't, and forgive me if you feel accused. To inhabitants on the earth, it would have no meaning. To them, it wouldn't appear that there is any orbiting at all, and more or less all motion *IS* is a matter of appearances. I think it's best regarded as an abstraction. It's the continuum of associations that we make in our minds between our memories of the past and our observations and the present. If we didn't know that they were orbiting (which, since you stated the they were, is what made your question tricky ) there would be no way to discern that they were moving absent some additional point of reference moving non-uniformly to the earth-moon system. I'd say no.

That only addressed the psycholgical aspect. People go on rollar coasters at Darien Lake becuase they FEeL viscerally the same you abstracted. I think we moderns speak too much of space and time as if they were the same things as the black and white stripes that if rotated around your head would cause involutary motions physiologically much like Pavlof once thought.This message has been edited by Brad McFall, 07-24-2004 02:58 PM

Have a look at this site:
Page Not Found | Science Mission Directorate
Go half a page down and watch the "full-length movie".This shows a spinning merry-go-round. On it there is no relative motion between the participants. But the ball they throw behaves very different than if the platform is stationary. I think, maybe, the same effect would be detectable in the case of the lone earth-moon system.However, there is also the idea of Mach's principle. You might want to google that.

I disagree. The dual nature of light (and all matter) is demonstrated experimentally by the two slit experiment.

T650 If we are on the surface of earth aboard a train travelling at 60 mph we can use the train as a fixed reference point and state that the earth is moving relative to our reference point on board. It is not indecisive but relative to the reference frame. Well the problem here is that you will not have a reference frame to establish that you are moving however if in doing experiments aboard the spacecraft you had determined that in all your trials that an object moves in reaction to an opposite force then you could tentitively consider motion on your part also due to the thrust of the engine.You could not verify that though.It would go a long way to explaining also why you experience the need to react to the acceleration by bracing your legs against it. They would each orbit about the barycenter of their gravitaional system. One would orbit the other in reference to the other one.This message has been edited by sidelined, 07-24-2004 03:46 PM

for thinking that your point of reference would have to be outside of the universe ???as in a higher medium to move into for motion to be evaluated as actually happening...

RingoKidA point of reference must be seen to be evaluated as relative to your motion.

no i don't actually because I can't see the inflation horizon of the universe nor the pre bang singularity so what reference is there for any motion at all ???apart from the obvious fact that things moveOk I've gone a done it again haven't I ???...shown an absolute ignorance of relative motion and logicDr could we have the white jacket over here please ???

Ohhh Now I get your question!Why don't the two fall into each other?!? Are the two orbiting each other about their barycenter or is the universe orbiting the two about their barycenter.The only difference between the two orbiting each other and the universe spinning around them is that in the former they stay apart, and in the latter they fall together.So motion MUST be in relation to space itself or else the two WOULD fall into each other.

Not necessarily. Young's experiment only confirmed the wave-like nature of light. However, it gave rise to the concept of field.

---

The Laminator
For goodness's sake, please vote Democrat this November!

The 'field' concept predates Young's 1805 experiments by 300 years.

Sorry about that, then.Do you happen to know who first proposed it? Or did it just come out of the blue?

---

The Laminator
For goodness's sake, please vote Democrat this November!