A...question.
Aug. 24th, 2012 11:15 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
avevale_intelligencerI'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.
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.
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no subject
Date: 2012-08-27 01:46 am (UTC)" 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.