A...question.

[avevale_intelligencer]

I'm wondering if it's possible to explain this to me without beginning with "It's not quite as simple as that..." Because I think it kind of is.

As I understand it, it's a basic principle of physics that all motion is relative, that there is nothing in the universe that is at absolute rest. The moon moves relative to the earth, the earth to the sun, the sun to the galaxy, the galaxy relative to the Local Group, and so on outward. I get all that; the first part I understand. It's the second part that gets me.

Because if A is in motion relative to B, then B must in respect of that particular motion be at rest relative to A. For every motion, every expenditure of kinetic energy, there must be a thing which is at rest relative to the moving thing. So surely, eventually, when you get to the end of that long string of movement and sum all the velocities and directions, logically there must be a thing, or a point in space, or a field or something, which is at rest relative to everything. If everything in the universe is moving outwards, there must be an in to be moving outwards from.

There is in the Sagittarian 'verse. Towards the end of the Sagittarian Age, scientists traced back the paths of all known metastellar bodies, based on data collected over the preceding several thousand years, and located a point in space which, according to their findings, approximated to the point of origin of the universe, and a team of specialists used one of the three remaining Gilchrist machines capable of large scale transmissions to travel there. They found, precisely at the indicated point, a roughly spheroidal black rock about eight miles in diameter, and for some years thereafter speculation raged across the nets about whether any of its surface features could be interpreted as deliberate markings, whether its age corresponded to that of the rest of the matter in the universe, and so on; in short, whether it had been put there or just got left behind. No conclusive answers were ever forthcoming; the only solid fact about the rock that could be ascertained was that, as far as could be told, relative to every galaxy, nebula, star, planet and asteroid in the universe, it was at rest. Everything was moving away from it, and had been for billions of years; it wasn't moving at all. And so, as ever, people made up their own minds according to their preferences. But that's fiction, and this is real life, probably.

I realise that this is a variation on the old Unmoved Mover argument which was one of Aquinas's proofs of deity, but that's not where I'm going with this. I would honestly like to know in what way my logic is faulty, if it is. If it can be done in a way that I can see makes sense, that would be good.

And if the Higgs field turns out to be the thing relative to whch everything else is moving, that would be rather neat.

Comments

[pickledginger.livejournal.com]

The thing relative to which everything is moving is everything (well, almost everything) else.

If A is moving with respect to B, then B is moving with respect to A.

Imagine two skaters on the ice, spinning madly, but their hands clasped between them. The world whirls by, but for each, the other is the one still point. Relative motion: None.

Now, imagine each lets go of the other. They spiral apart across the ice. Relative motion: Lots.

Hold close to your one still point.

[howeird]

I don't think your logic is faulty. I think, with our current technology, there is not enough data to find that point.

[the-magician.livejournal.com]

imagine a crowd of people, all going in different directions ... some of them getting closer to you, some getting further away ... they are all in motion with respect to you, and to each other ... you are the one point "at rest".

Imagine a raisin in the dough of a raisin loaf ... as the loaf rises, each raisin gets further away from every other raisin ... if you are that raisin then every raisin moves away from you ...

where are all the raisins moving away from? From each other ... and that's the current (groan) thinking of how the universe is expanding, it's just getting bigger ... so there's more distance between every galaxy, every star etc. except for where they are close enough for gravity to overcome that expansion (so orbits, and collisions) and occasionally where something blows up in an unbalanced way and so accelerates in a different direction (or gets hit by something else)

so any point you want to pick, is at rest and everything else is moving away. So, yes, *you* are the centre of the universe!

[zanda-myrande.livejournal.com]

And then there is the floor. Or the ice rink. Or the cake tin. *Something* which does not move relative to everything else.

And to say "it's just getting bigger"...how does that mean it doesn't have a point of origin? Isn't it true that in any expanding object there are parts of it that are actually moving in the same direction, albeit at different speeds, and that there is a centre, or central area, corresponding to the original lump of dough, which moves hardly at all?

[zanda-myrande.livejournal.com]

The still point is the point between them, isn't it?

[peteralway.livejournal.com]

Trace back everything to its original point,, and it's *here.* Residents of another galaxy do the same, and they will tell you it's *there*. How can they be both right? Because we were at the same place at the start.

The lack of a floor, or an ice rink, or a cake tin, or a reference graph paper, was the great head-'splodey discovery of a hundred years ago. The term for it at the time was "ether." The lack of that thing that is at rest for real, for sure, and not merely seemingly at rest compared to us, is the heart of relativity.

[mdlbear]

That would be true if the universe was a sphere, expanding into a 3-dimensional Euclidean space. But it's not -- there's *nothing* outside of the universe, which is apparently shaped like the surface of a hypersphere. Or something like that. So, if there's a point it's all expanding away from, it's somewhere outside the actual universe, in hyperspace. Think the surface of a balloon, only 4-dimensional. As seen _from the surface_, everything is expanding away from everything else, and there's no center point on the surface.

Since the fourth dimension is time, the "center" is the point in 4-space where/when the big bang happened.

[thnidu.livejournal.com]

The only plausible privileged candidate for the still point, or the point relative to which everything else is measured, is the center of mass of all the matter in the universe.

[filkerdave.livejournal.com]

It's obvious that New York City is the Center Of All Things

[filkerdave.livejournal.com]

An object is guaranteed to be at rest only relative to itself. But "at rest" is a relative term.

[janewilliams20.livejournal.com]

I'd agree, with one proviso. Yes, you take the average of all masses and their positions (in as many dimensions as required, not just 3D), and you've found the centre. But all of those masses are moving, changing. Relative to an absolute frame of reference (which we assume has only a theoretical existence), that centre of mass is moving, isn't it?

[aunty_marion]

Heisenberg Rules Possibly OK.

[the-magician.livejournal.com]

what others have said ... remember that there could be many universes, each with different rules of physics, we just happen to be in this one.

There is no flour, cake tin or ice rink.

Everything moves, and where there is no thing, then still nothing is at rest ...

every individual thing is at "rest" and everything else is moving relative to it ...

... to make it more complex, when you talk about movement, you are really talking at a change of position in a time (for example 5 miles per hour in a particular direction) but if you are floating in free space and accelerate towards a space ship at 100mph, but that space station is moving away from you at 200mph ... then it will just appear you are stationary and the space ship is moving away. And if you are at a steady 100mph, then there is no acceleration, so you won't feel that movement (like being in a very gentle elevator where you can't tell if you're moving) or being on the surface of the earth travelling at hundreds of miles an hour as you sit in your living room chair.

All motion is relative to something else, and all distant galaxies are moving away from us, therefore we could say we're at the centre.

[the-magician.livejournal.com]

The point between them is moving at 700mph as the earth rotates, and as the earth moves around the orbit that "still point" is moving in a giant circle/spiral around the sun, and as the solar system rotates around the galactic core, and as the galactic core moves away from the other galaxies ... there is no still point, it's turtles all the way down.

[zanda-myrande.livejournal.com]

Yes, but relative to the two of them the point is at rest. Bringing in all the other motions just underlines my point, that each one is defined by the point relative to which it's at rest (centre of the earth, the sun, the galactic core) and therefore (or so it seems to me) so must the sum of all motions be defined by something that is still. Otherwise it can't be defined at all, and the arrow can never hit the tortoise.

Saying "it's turtles all the way down" is just something to say. Language can encompass it, so can imagination up to a point, but logic falls over. And given the vast amount we still don't know about the universe, I don't see how such a definite negative statement can be defensible. And that's what I was hoping someone could explain to me: the how.

[zanda-myrande.livejournal.com]

And the fact that the heart of it is a void, a lack, an empty space, may be one of the reasons why I can't get on with it. It's the difference between saying "we haven't found/discovered/identified x yet" and "there is definitely no x." I'll always go for the first, every time.

[peteralway.livejournal.com]

Aww, special relativity isn't that bleak! Slippery and sneaky, sure, but not so bleak and empty!

[the-magician.livejournal.com]

yes, relative to those two it is at rest, but relative to other things it isn't, *everything* is relative, which may or not be why it is called "relativity"

You can only come up with a "sum of all motions" by picking a group of things and ignoring other stuff.

No-one knows how much stuff is out there in the universe, but between dark matter and dark energy, I believe that we can only "see" about 5% of the universe, so really hard to do a "sum of everything".

The only thing "at rest" is the observer. Read up on inertial frames of reference.
http://en.wikipedia.org/wiki/Inertial_frame_of_reference

[batyatoon]

I see no reason to assume there couldn't be a point that is at rest with respect to everything.

But neither do I see any reason to assume that there must be such a point. It feels like an aesthetic argument rather than a logical one to me.

[pbristow.livejournal.com]

"Because if A is in motion relative to B, then B must in respect of that particular motion be at rest relative to A."

Er... not unless you've changed the meaning of the word "relative"! =:o}

If A is in motion with respect to B, then B is in *equal and opposite* motion with respect to A.
Now, in some cases, it's convenient to think of one of those things as "the one that's really at rest" and the other as "the one that's really moving". (When you're on a train trip to London, it's generally more convenient to assume that it's the train that might eventually start moving, if the driver ever turns up, rather than speculate about how long it's going to take for London to get off it's arse and start coming down the track towards you.) But the whole point that Einstein uncovered was that once you take all the elements of the situation into account, it turns out not to matter one jot whether you chose thing A as the reference frame, or thing B, or some other thing C... Whichever frame of reference you assume to be the "real" one, you end up deducing exactly the same set of movements anyway. The maths may be *easier* of you start with a certain frame - usually the one that goes along with whatever's the biggest and most inflential part of the system you're looking at; it may also be easier to visualise the problem from one particular refernce frame - usually the one that makes the situation look most like an everyday human situation.. but at the end of the day whether the maths is easy or hard, as long as you get it *right*, then you end up describing the same situation anyway.

Thus in Special Relativity - which deals strictly with constant motion is a straight line) - we find that there is no good reason to *assume* that any frame of reference is more valid than any other.

Well, OK so far, but that's just a tiny set of artifically constrained cases... So then we step back a bit and look at the bigger picture: General Relativity. Does this "nowhere is more special than anywhere else" observation still apply when we start looking at accelerations, and curved motions, and gravity? Well the maths gets a lot more complicated, but ultimately, yes, that's still what we observe: Both the theoretical mathematics *and* the objective observations give us the same results, provided we pick a reference frame that is in constant motion, i.e. is not accelerating or decelerating or changing direction.

Much later, along comes the Big Bang theory, telling us why it is that everything we see in our long-range telescopes seems to be running away from us, and the answer is of course that it's no more running away from *us* than we are, say, running away from the Andromeda galaxy. Everything is simply getting further apart from everything else. There is no arrow, of any kind, pointing in any particular direction to say "this is where it all started".

If it helps, try thinking of it this way: The "place" where it all started isn't a oint in space, it's a point in spacetime. The "place" where it all strated is the big bang. If you go looking for that place today, you'll never find it, because it isn't today, it's back thataway... [POINTS THUMB IN THE GENERAL DIERCTION OF PRE-HISTORY]

[pbristow.livejournal.com]

" For every motion, every expenditure of kinetic energy, there must be a thing which is at rest relative to the moving thing."

First, there's a misconception here about energy: *motion* doesn't require expenditure (or transfer) of energy; *acceleration* does. But I don't think that affects your main point.
2nd: Well no, there doesn't *have* to be. There *might* be, in any particular case, of course: If two cars join the M4 heading west, and sit neck and neck in adjacent lanes doing exactly the same speed, then yes, relative to each other, they're both at rest, and it's PC plod at the side of the road with the speed gun who's doing 90mph... and in the wrong direction, too boot!

"If everything in the universe is moving outwards, there must be an in to be moving outwards from."
"Outwards" isn't meaningful here, it's just an idea we tend to automatically lapse into when we try to compare the big bang to everyday explosions. What we observe is that everything is moving *apart*. Everything is getting further away from everything else (well, barring a few bits and pieces that have got swung around onto weird trajectories).

Suppose I take a piece of elastic, and draw a line of dots on it, very close together. Now I stretch the piece of elstic: The dots get further apart. Where is the "starting point" of their motion?

Well, if I had first pinned one end of the elastic to my bedpost, and then pulled on the other, you might say, "ahah! The dots are all getting further away from the pin in the bedpost"... But only if you can see there is a bedpost, and a pin. And even then, you might have been tricked: What you didn't know is that I was standing still, and my beefy mates Jeff and Pete were carefully dragging the bed across the room to make the elastic stretch. Armed with this new information, you decide that the pin is the moving end and my fingers are gripping the still end...

But what if instead, you look at the elastic... and theres no pin. Theres no fingers gripping it, anywhere. You keep looking further along the elastic, trying to find the fixed point, or at least some evidence of stress lines radiating from what must be a place where things are being held still... But there's nothing. The elastic goes on forever, and it keeps on stretching, and the dots keeping getting further apart from each other, and no one can say which ones are moving left or moving right, *except* in reference to each other.

That's the kind of universe we appear, as far as any can so far tell, to be living in.

[pbristow.livejournal.com]

As far as I'm aware, there is nothing in any of our current obersvations of the universe to suggest that such a point exists, let alone give us a clue as to where to find it. Now, that doesn't *prove* there isn't such a point... But couple it with (a) a very effective and well-supported explanation of the origin of the universe and the nature of spacetime that renders the existence of such a point both unnecessary and unlikely, and (b) the fact we can side-step an awful lot of needless mental gymnastics, and still get all our sums right, by not worrying about whether we're measuring with respect to the "right" reference frame or not - and you can see why physicists generally find it sensible to assume it doesn't exist, until further notice.

[pbristow.livejournal.com]

...But if the universe is a closed hypersphere, then such a point is impossible to determine. It's actual a meaningless idea in that context. You can *conceptualise* a centre, but that centre is not a part of the thing you're trying to find the centre of.

[pbristow.livejournal.com]

" It feels like an aesthetic argument rather than a logical one to me. "

Indeed.

[pbristow.livejournal.com]

"No conclusive answers were ever forthcoming; the only solid fact about the rock that could be ascertained was that, as far as could be told, relative to every galaxy, nebula, star, planet and asteroid in the universe, it was at rest. Everything was moving away from it, and had been for billions of years; it wasn't moving at all. "

I'm afraid that's just a completely self-contradictory notion. If A is not at rest with respect to B, then B cannot be at rest with respect to A. Either of them may be at rest with respect to *something else*, however. But either they're *both* at rest relative to each other, or they're *both* moving - equally and oppositely - relative to each other. There are no other options, because that's what the phrase "relative to" *means*.