Dragan Glas
Well-Known Member
Greetings,
But I was really trying to get down to the simplest way to point out to Creationists that their use of "immaterial" = "supernatural" is not valid.
Kindest regards,
James
Which is essentially what I said/meant - the "how" explanation depends on whichever theory one picks.Aelyn said:I'm not sure what you mean by that, and re-reading your previous reply I'm not sure I'd completely understood that one either; I'd assumed you were using "gravity" as an empty label when you said gravity warps spacetime but now I wonder whether you were misunderstanding the theory of relativity. To cover the bases I'll explain the theories of gravity as I understand them, and at the same time try that explanation of why one hypothesis is more substantive than another that I wasn't sure how to do earlier.Dragan Glas said:Hmm, well I'd have said that massive bodies cause gravity - but I see what you're saying about it depending on which physics one is using - Newtonian, Einsteinian, etc.
To get back to basics, the phenomenon we have is that certain objects move in certain ways - planets orbit in ellipses around the Sun, apples fall onto the Earth, etc. Newton found that if we assumed all massive objects exerted a force on each other proportional to their mass and inversely proportional to the square of the distance between them, such a force would account for all those different movements - that force was called "gravity".
All we know in this context is that massive objects exert this force on each other - we don't know why, or how (in fact IIRC it was a complete coincidence in Newtonian terms that gravitational mass was the same as inertial mass, i.e. that the "m" in F=Gmm'/R2 was the same "m" as in F=ma). If we try to "explain" this by saying that massive objects induce an immaterial gravitational field that causes the movement of far-away objects to be affected, for this explanation to be in any way distinguishable from just "massive objects affect the movement of other massive objects" (or "massive object spookily act on other massive objects at a distance") you'd need some indication this gravitational field exists independently from the movements it induces (otherwise you might as well just have the movements). In other words, does the gravitational field of the Sun exist in places where there is no massive object to be affected by it ? Presumably otherwise what's the point, but if the gravitational field is defined only and exclusively by how it affects massive objects, then there is literally no way to find out. Gravitational fields can be a useful mathematical or conceptual tool, but as long as they're mathematically equivalent to there not being a gravitational field that's all they can be : a mathematical tool.
Now in the Theory of Relativity gravity doesn't exist as a force. Massive objects cause spacetime to curve, not because of the force of gravity attracting spacetime or something like that. The often-used analogy of bowling balls on a rubber surface also has the often-used caveat that bowling balls actually curve rubber surfaces (and little balls roll around that curve) because they're attracted by the Earth's gravity, whereas what makes spacetime curve around massive objects is not the same thing at all. AFAIK we don't know what it is, unless the Higgs condensate has something to do with it.
According to the Theory of Relativity, gravity is actually a pseudo-force, like the "force" that pushes you back on an accelerating car or train or the centrifugal "force" that pushes spinning things outward. Those aren't actually forces, the movements involved are just objects moving inertially in a non-inertial frame of reference, so that within that frame of reference it looks like a force is acting on them, when actually it's the frame of reference that's accelerating and either pulling them along or leaving them standing so that they look like they're accelerating backwards. Same thing with orbiting planets or falling apples : they're inertially taking the shortest route from point A to point B through curved space, which if you assume space is flat makes it look like a force is causing their trajectory to curve.
So now we've got "massive objects cause warped space which affects the movements of other massive objects"; is "warped space" an empty hypothesis like I say "gravitational field" is ? Well, if we ask the same questions of it that I asked for the gravitational field the answers are more clear - is space near the Sun warped even in points where there isn't a massive object there to be affected by it ? - Yes, the statement "massive objects warp spacetime" clearly doesn't depend on their being another massive object at that point in space. Would this have other effects beyond F=Gmm'/R2 ? Yes - warps in spacetime won't just affect massive objects, we'd expect to see effects on light or on passing time and other elements of the Universe beyond just mass. Even if there weren't any effects we could check in practice, the equations involved in the Theory of Relativity are different from those involved in Newtonian gravity so mathematically speaking there is a difference between a world where curved space causes apples to fall and one where immaterial fields, or spooky action at a distance, or anything else causes it.
To get back to your answer, massive bodies "cause gravity" whichever theory you pick; the question is how they "cause gravity", and which ways of conceptualizing this process are actual hypotheses about the world and which are conceptual tools.
But I was really trying to get down to the simplest way to point out to Creationists that their use of "immaterial" = "supernatural" is not valid.
I think also that my initial memory of the experiment ,with the filings forming more distinct "lines", may have been due to slight variations in the filings - some bigger, some smaller - creating more contrast than would otherwise have occurred between the "lines" and blank areas.Aelyn said:That's interesting. I did study physics beyond the iron fillings bit (I probably have something not too far from a bachelor's), and it was clear the separate lines were conceptual; the equation defining what the magnetic force was at any point worked for any non-zero point, i.e. the force existed everywhere outside of the magnet. We even had to draw those lines sometimes; IIRC (and I very well might not) they're the equivalent of the lines on a topographical map : they indicate all the points that are at the same level, but they're not the only such lines that exist, only those you chose to draw. (the reason I have a problem with the topographical map analogy is that there is a directionality involved in magnetic fields and that's actually what the lines show; hence why iron fillings illustrate them nicely, because they tilt themselves to align with what that direction is wherever they happen to be. The equivalent drawing for an electric field or a (Newtonian) gravitational field would be lines radiating straight outwards)I have to concede that my conception of magnetic lines/shells were from a remembered physics class many, many years ago, where the physics teacher used a bar magnet with iron filings to demonstrate the magnetic field.
As I recall, the filings formed distinct lines - with very few filings in-between.
However, having found an article with a picture of a similar experiment, it's clear that the above impression was caused by too few filings.
Kindest regards,
James