Is our universe stationary ?

That was in my thread.If you're interested, you mentioned it here.As for the question of the universe moving, I don't think there's any reason, in principle, that it couldn't be, but I think we would ultimately run up against the same wall as in my previous thread. Namely, how do we test this? Since all motion is relative, the only way to detect "universal motion" would be to have a frame of reference outside the universe.

Paul, did you ever read my thread regarding relative motion? I never did feel that I came to any satisfactory conclusions regarding those scenarios (although I'm clearer now on some of the specifics). If you have anything you can add there, I'd love to hear from you. The nature of movement (or motion) is one of the things I was trying to pin down in the aforementioned thread, and although I would have previously agreed with your definition, these days I'm not so sure it's that simple.If we say that motion is a change in spatial location then we are making space an absolute frame of reference so, by definition, it cannot move. It would be like asking if the surface of the Earth can move along the surface of the Earth. Now that's not a problem, in itself. The problem is how do we then define "spatial location"?One of the (tentative) conclusions I came to in the other thread was that, for motion to be defined in terms of space, there must be "absolute" locations in space. Otherwise how can anything change its location in space?Personally, I think a better (or at least, more "universal") definition of motion is; a change, over time, in the relative orientation and/or distance of systems/reference frames.The universe, as a whole, could be considered a "system" so if space does possess some kind of "absolute" quality, and if there is another frame of reference to relate it to, then it could be said to be moving.I have no idea how we could test this, though. Even if we could show absolute points of reference in space, we couldn't relate them to anything but the systems within space, since we have no way of detecting any "external" reference frames.Of course, these points are entirely moot if it turns out that there aren't any absolute locations in space. We are then left with the conclusion that no system truly changes its spatial location, it merely changes its location relative to other systems.By the way, this is just my take on it. Personally, I'm neither arguing for nor against the idea. I don't know if space (or the universe) moves or can move. To be honest, I think the nature of the question makes it very hard to ever find out. It's interesting to think about, though. Indeed, those thought experiments have been frustrating me for years.

Hi Paul.Firstly, I must apologize. I don't think I was clear about my intention. I am not arguing that space actually does have absolute locations; I'm just entertaining the possibility based on my, admittedly limited, understanding of relativity. I'm sorry I wasn't more clear about that. Hmm...well I know I discussed the concept of motion relative to space somewhere in the thread but I don't recall exactly where.Very briefly, the relevance to my original question (which I think also applies to this topic) was that if space were to have "absolute" locations, it would essentially solve my dilemma regarding the lone system scenario.I don't remember precisely where that came up, though. I apologize. Yeah, I don't think my choice of words was very helpful. I'm not sure that "absolute" is really what I'm trying to convey. All I really mean is that, I don't think "a change in spatial location" is really a "complete" (if you wish) definition, in the sense that it can't be applied to space itself.Obviously, it is complete enough for our everyday purposes, but I don't think it would suffice for the purpose of the topic in question. If we define motion as a change in spatial location, we've effectively rendered the concept of spatial motion meaningless by definition. Yes, I know. I didn't mean to suggest that I think there are absolute locations in space. All I meant was that I'm not sure how something can change spatial location if there is nothing inherent in that location to distinguish it from any other. At the risk of drifting back to my old topic, if you were to remove all but one system from the universe, how could you determine whether or not it is moving relative to any arbitrary point in space?Again, let me emphasize, I'm not arguing that there are absolute locations, I'm just trying to understand. I know that motion is relative and that's what leads to my confusion when referring to motion "through space".I can't see how a point of reference in space can have any meaning unless there is something about that point that is identifiable. On the Earth, for example, you can determine your motion, relative to the landscape, by selecting a landmark which is fixed relative to the landscape. We can both agree on a location. We can objectively determine that a tree, for instance, is fixed relative to the surrounding landscape. We can perform tests to see if we have a relative motion to it. For the life of me, though, I can't see how to do the equivalent with empty space. Yes, that was my point; I don't think there would be any way to test the idea since we can't detect any "external" frames of reference. Heh, as I said, I think we got our wires crossed. I was agreeing that we can't do that.My only real concern was that, for the purpose of this discussion, defining motion in terms of space itself may be somewhat limiting. If we want to ask whether or not the universe, as a whole, is moving then we would have to measure it against something, as you said, independent of it. And I completely agree that we have no way to do this.I'm only saying that, in principle I don't see any reason that it could not be true. But in practice, I don't think we can ever know, even if it is true. Hmm...Technically, would this be a violation of Occam's razor? There's nothing to discount the possibility, but there is no way we can ever actually know. I know that's not quite the definition of Occam's razor but perhaps it applies, none the less?Incidentally, I apologize if I've come across the wrong way, Paul. It isn't my intention to argue; I'm only here to learn. I know that you're more knowledgeable of this subject than I am so please forgive any misunderstandings I may have. Some of these concepts have been plaguing my thoughts for years and I'm sure that what you're telling me is correct, it's just that I still have trouble wrapping my mind around some of it.In any case, I just want to be clear that I'm not being confrontational; my questions are always sincere. Sometimes I feel kind of guilty "arguing" these points with people that do it for a living so I hope you'll forgive (and correct) my ignorance. I want to understand.

Oh man...I'm sorry, Brad. I tried to understand, I really did. Well, thanks anyway for the reply.

Thanks Paul. I often worry that I may come across the wrong way. I try to look at an idea from all possible angles, and in doing so, I may come over as arguing for a point that I'm not. I'm glad you understand this. Myself, I don't have any formal education in either; all I know is what I've read. That's why I appreciate the help of those, here, more educated on the subjects than myself. Aside from that, I just try to understand things within the (limited) framework I already have. Like the man said, "Just doin' what I can with what I got."

Well lookie there...Brad, I think I understood something you wrote! Was this a reply to my question in this post? If so, thank you.Personally, I think you just need to slow down a bit and perhaps proofread what you've written before you post it. Or even break it down and deal with one point at a time. I understand that you're short on time but you seem fairly intelligent and it's a shame that much of what you say probably gets passed over because, by and large, people just can't understand it.Anyway, I'm off topic so I won't continue this here. My apologies to Admin.

Hi Brad. Rather than continue off topic in this thread, I've made my reply to you here.

Hi jar. I'm not Paul (duh!) so I hope you don't mind me sticking my head in. If there is no way to detect anything outside the car then I would say no. Because the pocket of air inside the car is moving with the car. Relative to the car, the air inside is stationary (well, it does still move around, of course, but stationary within reason).EDIT: Damn, he beat me.This message has been edited by Tony650, 08-30-2004 05:40 PM

I, for one, don't think we can, which was my original point; the universe may exist within some "greater" realm (higher dimension, hyperspace, etc), relative to which, it is moving.However, I think it's like any number of things that could be true, but by their very nature, we can never know. Personally, I can't think of any way we could test such a hypothesis.I don't know if this is Paul's take on it, of course; this is just my opinion.