geordief

But you would from the space station,would you? So the measurable difference would extend a small distance from the body? Is there a general boundary for any body beyond which the internal redistribution of mass becomes completely unmeasurable and within which it is measurable?

Yes I see that.

More or less ,but I was also wondering whether there could be a (privileged) frame of reference based at the that origin (the origin of spacetime itself) that would get around the "problem" of all the discordant "nows" https://www.scienceforums.net/topic/120718-how-does-gravitational-mass-work/?do=findComment&comment=1125449 "..... wonder whether it is possible to talk of the whole system evolving from its earlier origin until "now" ( No one "now" but all the "nows" perhaps meeting at this origin when spacetime came into existence) No ,but thanks for the pointer.(I am just starting Einstein's Popular Exposition /GR section anyway and that will probably take me a good few weeks, if I am lucky to get through)

Edit from It seems that MigL did talk about a distinction between asymmetric and symmetric changes https://www.scienceforums.net/topic/120718-how-does-gravitational-mass-work/?do=findComment&comment=1125407 That is the same thing?

If the Earth (or any body or collection of bodies) undergoes changes such as loss -ie redistribution of all the ice in the world , would that cause any change to its the gravitational field? (say measured from the Moon) I confess to being a slow (and obtuse) learner .If I am repeating my original positions (actually I would say most of my "points" are framed as , and in actuality are questions), then thank you for telling me that as I do not want to waste your or others' time. If I do this ,I will try to "cut it out". Ophiolite ,who some will remember as a respected poster here and elsewhere once criticised me for "cherry picking" arguments and that too can be a habit which is hard to disengage from.

So it is possible to talk of a global geometry....Could that geometry in principle describe the process from the origin of spacetime until "now" in one sweep ? Aside from the practicalities ,would that be a thought experiment? Or maybe by global you just meant non local? (the aggregation of local measurements?)

Sorry I misunderstood you to be implying the Earth could be stationary in my previous reply to your post. It was the system you were describing as stationary. (still not sure What that means) Still ,it was the Earth's place in this dynamic system that made me think of describing Earth's contribution (which I accept cannot be considered in isolation) evolving in a similar way to the way I wonder whether it is possible to talk of the whole system evolving from its earlier origin until "now" ( No one "now" but all the "nows" perhaps meeting at this origin when spacetime came into existence)

But the Earth is not stationary .It evolves as a system and it's contribution to the overall gravitational field **must evolve too,I'd have thought. And I was using the Earth as an example so as to extrapolate to the Solar system,our Galaxy,our group of Galaxies and so on to imagine an interconnected global (and dynamic-so not synchronous) gravitational field. If there was a point in time that could be identified as that time when gravity first came into play (apparently not as a result of a Higg's interaction) could that point in time be considered as some kind of an origin of the field? ** ie to the field of the Solar system

So we can't talk about an overall gravity field ,say for the Earth? And we can't talk about it evolving?

I have been chewing on this cud for some time now. If the field was/is already there does that mean that there, was a gravity field formed sometime after BB that has evolved to the configuration we now see and that evolution was accompanied by gravitational waves at every step of its progress? Any gravity field we see is a part of the universal gravity field and that universal gravity field is the "descendant" of the first gravity field that was formed after BB..... And that first gravity field was caused when the Higgs field caused mass to exist? That might explain why you can't have mass without a gravity field or vice versa,I suppose.

Yes I understand that ,but what about Einstein's passage? Are those "equations" rigororous or are they really just "illustrative"? ( this is a book for the layperson)

From Einstein's Popular Exposition https://www.bartleby.com/173/19.html "According to Newton’s law of motion, we have (Force) = (inertial mass) × (acceleration), where the “inertial mass” is a characteristic constant of the accelerated body. If now gravitation is the cause of the acceleration, we then have (Force) = (gravitational mass) × (intensity of the gravitational field), where the “gravitational mass” is likewise a characteristic constant for the body. From these two relations follows: (acceleration)=[(gravitational mass)/(inertial mass)] x(intensity of the gravitational field) If now, as we find from experience, the acceleration is to be independent of the nature and the condition of the body and always the same for a given gravitational field, then the ratio of the gravitational to the inertial mass must likewise be the same for all bodies. By a suitable choice of units we can thus make this ratio equal to unity. We then have the following law: The gravitational mass of a body is equal to its inertial mass." Can I take it from what you said that Einstein was not really being mathematically rigorous? Is he perhaps "jumping ahead" and just presenting a plausible mathematical argument for the lay public ? I found it hard to follow his equation and if you say that this relationship is more experimental than logical ,I will be relieved.....unless this is indeed rigorous I will have to re examine it.

Does being indistinguishable mean uncountable? Would there be less than at other times or just the same number in a smaller confine? I don't think I was trying to describe any "instant" ,just the period immediately following after that estimated "instant"**.Does your description apply to that "epoch"? *Do you mean "can only"? **ie T+10^-43 seconds and after.

As we run the clock backwards does that rigorously show that the configurations get simpler? (and so the value for system mass based on that parameter must get less) . Studiot quote: "As you know I am not a cosmologist and I cna't answer this question, even if they think they can, though in my lifetime I have seen their answer change many times" (If ,as you seem to say the consensus for the value of system mass around the BB has changed over the last few decades that seems to indicate it is not a simple question.)

(if I am allowed to "snipe"), would such a reconfiguration of a system change the overall value for the system's mass and does it follow that ,for the largest system of which we have knowledge, that its mass changes all the time ? Would that mean that ,around the time of BB that value was smaller,even vanishingly small? (or larger even?)

Which are those fields? How many of them are there?

I hope I wasn't doing that. If we take a small body with mass in a pre-existing * gravitational field, this body will (I am supposing) contribute its own field in its infinitesimal degree to it. Does this infinitesimally small contribution continue without drawing on some energy reserves inside the body itself (ie does the body use up its sources of mass or does it replenish them from the prexisting "external" (?) gravitational field? Do different sources of gravitational fields "top up" or "drain" each other in this way? *Ideally I would have this pre-existing field to be as small as possible for purposes of clarity.

Oops ,missed the first replies So gravitational mass is a property of the entire system? Is it not possible to consider a massive body so far removed from other bodies that it is only its own field that is in play*? And can we stipulate that this body is homogenous and non rotating? Does that change anything? (Do I have to consider the forces inside the atom as sources for the field?) *Maybe isolated fields are also physically meaningless?

I have just come across this terminology and wonder how it works (also eager to "blood" my use of the term ) So,if we have a massive body far removed from other such bodies,I understand that it will curve the surrounding spacetime(or create a gravitational field) So my question is "Does this gravitational mass dissipate as a result of having caused this effect"? And ,perhaps relatedly does the Gravitational field created by this massive body expand at the speed of c from the massive body in a similar way to how an em wave does (as an expanding sphere)? If it does ,does it carry away the mass of the body so that it dissipates eventually?

These invariant intervals ,can it be usefully said that they are not subject to any uncertainty in their measurements? If we picture them as"sticks" ,do they follow spacetime curvature? And they never "touch"? Would there be such a thing as relations between individual "sticks" (only "degrees of separation",perhaps ?)

very interesting.Does that viewpoint apply to both SR and GR? Looked at differently*, is it possible (in the model) to abstract space from spacetime by using regions of spacetime where t equals a constant.? When we look out at the night sky is the picture we see such a slice of spacetime ? ( a frozen point in spacetime) * a different point ,actually(I think Markus touched on it it in his earlier post when he said "Space on its own would then be just the spatial part of that network" ) https://www.scienceforums.net/topic/89395-what-is-space-made-of/?do=findComment&comment=1124830

Well I suppose part of my brain might have just tacitly accepted that (but it is not a question that keeps me awake at night or hopefully a preconception I would revisit on anyone else)

I took the article to be aimed at the layperson and that it benefited from keeping it simple. I am half way through the book you recommended. (Einstein's Popular Exposition 1952 edition) It does not disappoint and I was pleased to find that I could follow the SR section although I had to go over it around 3 times . The GR half is shaping up to be quite a bit harder.

If maths was * up to the task that would be a nice question . Is the Universe made from ideas or from things,?(an ancient discussion I think .. Plato?) *seems it is not,it just tags along behind.

So ,instead of trying to model the Universe as we find it you suggest we try to model it as it should be? Sounds like a step back unless it is one step back and two steps forward We should be asking DTrump for advice as he is the chaos man. You might be right about B Russel-maybe that was what turned me off him (or maybe it was his bad rep at the time)