Farsight

RELATIVITY+ I’ve always held Albert Einstein in the highest regard. I admire his ability to think outside the box, and empathise with his curiosity and desire to understand the world in terms we can grasp and understand. Interestingly, when you read about Einstein, you realise that some things are incorrectly attributed to him, and there have been some subtle but crucial shifts in interpretation that he wouldn’t agree with. If Einstein was still alive today, I think we would have a different interpretation of Relativity. I think he would have explained the postulates he used in Special Relativity and General Relativity, and would have united both theories into something new. I’d like to introduce you to my vision of where Einstein would have gone. I’ve given it a name that is easy to remember and hopefully conveys the right message: RELATIVITY+. There’s already a General Relativity+, but I want something even more general, and relativity++ isn’t so easy on the tongue. We start with time. Albert said “time is suspect”, but we’ve rather forgotten that. We’ve also rather forgotten his Princeton years with Godel. We misinterpreted Godel’s rotating universe as something that permits time travel instead of rendering it impossible, and we brushed aside Einstein’s conclusion. That time is a relative measure of change, and whilst it's a dimension in the measure sense, it really isn't a dimension like the dimensions of space where we have freedom of movement. It exists like heat exists, but like heat, it is a “derived effect of motion” rather than something fundamental. For details read TIME EXPLAINED. Time is the guilty party. Because once you understand time, you hold Einstein's key to all the doors in Physics: Spacetime is a Space. It’s rather difficult to accept this, because it’s difficult to analyse your own long-held concepts. There are psychological factors at work, associated with the phrase “Catch ‘em young”. Since ”Time is Money” and as an illustration why you should persevere, I offer an essay MONEY EXPLAINED. No, time is not money. But it isn’t quite what you thought it was, and if you can accept this you’re starting to understand ontological thinking. It’s a matter of looking at what’s really there, and asking yourself soul searching questions about the concept you hold dear. In the picture below, squares A and B are the same colour. Sounds amazing, but it's true. Follow this echalk optical illusions link to check it out. One such question is: ”If I understand it, can I explain it?” If you think you understand something but you can’t explain it, then you don’t understand it. You perhaps already understood money, and you may already be aware of some parallels between money and energy. But do you understand energy? See ENERGY EXPLAINED. Energy is in essence stress, quantified by volume. It’s that simple. In empty space with nothing to hold it in place, a stress travels, like a ripple in a rubber sheet. We call it a photon. It has momentum. But it’s all relative. If it’s the photon moving, you feel its momentum when it hits you. If it’s you moving, you feel its inertia when you hit it. When you really understand this relativity, you understand just how simple mass is. See MASS EXPLAINED In its barest essence, mass is energy going round in circles. When you push an object you deform these circles in the direction of motion, creating a partial spiral. The energy now moves in a helical fashion, rather like a spring. To stop the object you have to push the “springs” back into circles. It’s wonderfully elegant, and what’s more it tells you that everything is basically made of light. We live in a “hard light” world. Everything is drawn in light, and when we measure the speed of it, it’s like we’re measuring the length of our shadow with the shadow of our ruler. We can now understand what Einstein meant in chapter 22 of General Relativity about the non-constancy of the velocity of light. And we can now understand Gravity: GRAVITY EXPLAINED Gravity is not really a force. That’s why unification was so difficult. It’s like an extended tension gradient opposing matter/energy stress. The speed of light is always 300,000km/s but light defines our time. The speed of light isn’t constant, and that’s what the gravity is. There’s no magical mysterious spacetime curvature. Not when spacetime is a space. Not in a world drawn in light. It’s just the permittivity of space that changes. The capacitance. The thing we call c changes, it is not flat. And it all comes down to charge, which is a story of something and nothing. Understanding this is the next challenge. And once we understand it all, we can set to work. And if we can make it work, we’re on the road to the stars. And I like to think that the name of the road is: RELATIVITY+. © “Farsight” 2007

This essay is part of a set, and is intended to illustrate that something very common is perhaps not what you thought it was.

I know this might not sound like physics, but bear with me, because Time is Money, isn't it? Show me some money, I say. So you pull out a £10 note. We both know that’s money right? Wrong. Check the small print: “I promise to pay the bearer on demand the sum of ten pounds”. Your tenner isn’t really money. It’s what’s known in the trade as a promissary note. A mere promise to pay money. Basically it’s an IOU, but from the Bank of England. OK if you’re in the States or Oz maybe you don’t get the small print, but your buck or buckaroo is still a promissary note, a mere IOU, it’s not really money. OK you say. How about this here penny? You hand it to me. I turn it over in my hand. It’s coppery and shiny. New. Freshly minted. But what is it? It’s a piece of stamped metal. Nowadays it's copper plated steel, but there’s been all sort of variations involving copper tin and zinc, usually alloyed as a bronze. I could make them in my garage. But it isn’t worth it, especially “Since May 2006, all circulation Canadian pennies from 1942 to 1996 have an intrinsic value of over $0.02 USD based on the increasing spot price of copper in the commodity markets...” Anyhow, a penny is similar to the milk tokens I remember from when I was a kid. And those useless slot-machine tokens I brought home from Blackpool. That shiny new penny is just a glorified milk token, acceptable to more than just the milkman. And what notes and coins are is cash. Money tokens. They aren’t really money. We have to forget about cash. Where do you keep your money? I ask you. In the Bank you reply. Where in the Bank? I say. In the vault, you say. To which I say: But that’s not money, that's just cash. You change tack and tell me your money isn’t in the vault. It’s in your account. You’ve got your salary going into your bank account every month. Whoa. Where is this account? I say. In the bank, you say. Where in the bank? I say. On the computer, you say. I could say "Where on the computer?" but I won't. Because now we’re getting somewhere. Your money is just intangible information, maybe on a computer somewhere. Before they had computers your money was in a ledger. It was just a bit of inky writing in a big black book. With as much real existence as a bit and a byte and a bar tab. And every month your employer tells your bank to reduce his glorified bar tab and increase yours. Did you get that? Money is just a glorified bar tab. An agreement about IOUs. Nothing is moving into anywhere, or out of anywhere else. Ah, I can hear you saying, what about the gold standard? Shrug. Gold was only “money” because everybody agreed that this nice and shiny metal was worth having. So were pretty little sea shells once upon a time. Imagine a pirate landing on a deserted island, the native people wiped out by some pestilence. The pirate kicks amongs the ruins, hawking and spitting at finding only sea shells and no gold. Because there isn’t any money if people don’t agree that its money. Because money doesn’t exist. Not really. That’s why when you spend money it doesn’t disappear. It isn’t destroyed. You’ve got less of it, and the shop’s got more, but nobody’s really got more or less of anything. It’s just a bar tab. Do you know how money is created? Governments allow banks to lend money to people who build houses and cars and flatscreen TVs that everybody agrees are valuable. Then the money that was magicked out of nowhere really does exist. But it doesn’t really exist because it was never really created in the first place. But it does. And it doesn't. But it gets things done, and it makes the world go round, and everybody wants it. Doesn’t really exist. Doesn’t get created or destroyed. Makes the world go round. Everybody wants it. Does that remind you of anything? Does that remind you of Energy?

I haven't violated the laws of physics. It's a very simple, very basic scanario. You just don't know what I've been doing or where I've been. But you do know that I was away for a year of my time while you waited for seven years of your time. And light defines time. What does that tell you about our respective cs?

Let's say that I have a videotape that lasts a year, where you can see the running time along with me holding up my transverse metre rule and counting traverses. I appear normal, you have no evidence of any acceleration, and no information about whether I've taken a long journey into space or stepped into some "gravity machine".

Yes, it is possible to travel to other planets and star systems in a convenient time span. But it would take a whole pile of resources to do this. You would need very large ships accelerating to huge speeds requiring enormous energy. Then time dilation reduces the elapsed journey time as experienced by the voyagers. The thing is, it would be a whole lot easier to get our own house in order down here on Earth. All people have to do is have fewer children. It's that simple. Oh and cut out all those foreign holidays. And live closer to work. And share a car. And eat local food. All the easy things. Sadly if people don't pay attention to all this, nature will. With increasing population and increased travel, the likelihood of some sweeping pandemic increases every year. But hey, look on the bright side. You won't be saying Eek Eek Eek, because you'll be coughing your lungs up.

Foodchain: No, time isn't an entity. You cannot "move" through time, time has no length, it doesn't flow, you cannot see it, and you cannot hold it in your hand. There is no real geometry to it - Minkowski's fourth dimension is a mathematical artifice. Time is a measure of change compared to other change. Since it's a measure it's a dimension, but it really isn't like the Dimensions of space. It's rather like heat, a derived effect of motion. As such it exists, but it isn't fundamental. Amazingly this rational view, which is the one Einstein held from circa 1949, is deemed speculative by crackpots who entertain notions of time machines. So please search the internet for "TIME EXPLAINED v2.1"

Swansont, I know all that, and it's not me mixing frames, it's you. Let me see if I can explain it another way: Imagine you and I are standing in a lab, each with a transverse metre rule and a light clock. I go out of the door and you stand there for seven years counting traverses. You count seven trillion traverses. Then I walk back in. You know something is up because my hair is still brown whilst yours is speckled with white. I don't have the extra wrinkles, and my beard is only down to my chest. You wonder if I've been somehow frozen, but then I show you my results, vindicated by recordings and other evidence that satisfies you that I am sincere. Now to ensure that there is no confusion regarding frames: you do not know what I have done and you do not know whether I have travelled. I counted only one trillion traverses, far less than your seven trilion traverses. I also demonstrate to your satisfaction that whilst I was away I measured the speed of light to be 300,000km/s. You similarly measured the speed of light to be 300,000km/s, and you show me your evidence to my satisfaction. But I counted only one trillion traverses whilst you counted seven trillion traverses. Ergo despite the fact that we measured c to be tha same, it was not. It was different.

This is an improved version of the original version, thanks for the feedback, and if you can give any more I'll be only pleased to receive it.

Energy is generally misunderstood. Our schoolroom textbooks tell us that energy is the capacity to do work, and work is the transfer of energy. The words go round in circles without getting to the heart of it, and children grow into adults with no clear concept of what energy is. Let’s start by saying that energy is the property of a thing. It is not a thing in its own right. To illustrate this, I can talk about a red balloon, a red bus, or a red red ruby. All these things have the property that we call red. A thing can be red, but you cannot remove this red and hold it in your hand. You can remove the paint or the dye and hold that in the palm of your hand, but you’re still holding a thing that is red. You cannot remove the red from the dye to hold the red in the palm of your hand. Even when you imagine red, the image in your mind’s eye is a thing. You always need a thing to be red. There is no such thing as “raw red”. In similar vein there is no such thing as “raw energy”. Another illustration is money. You can spend money like you can expend energy. But the money doesn’t disappear, just as the energy doesn’t disappear. Somebody else now has your money, just as some other thing now has your energy. Think about an old house, nestled in the countryside. It’s picturesque, worth a lot of money, and it’s built out of cob. Way back when, some guy put some energy into shifting earth and straw to make the walls of this house. He did the same with the wood, which grew out of the earth because the trees put energy into shifting water and CO2. The guy made money out of that house. They paid for the energy he put into it, through the work he did moving stuff. That’s why money and energy are similar. They get things moving, they get work done. One makes the world go round, and the other one makes the world go round too. But money isn’t what energy is, and nor is motion. You need mass and motion before you can talk about energy. Consider a 10 kilogram cannonball, in space, travelling at 1000 metres per second. We talk about how much kinetic energy this cannonball has. We talk about KE=½mv² and we do the maths and get five million Joules. But what has the cannonball really got? Its mass seems real enough, I hefted it into my spaceship this morning before I took off. And its motion seems real enough too, because one false move and it’ll be smashing through my viewscreen taking my head off. To find out more, I take a spacewalk to place a thousand sheets of cardboard in the path of my cannonball. Each sheet of cardboard exerts a small braking force, slowing the cannonball to a halt. This takes two seconds. We know that the cannonball will punch through more cardboard in the first second than in the second second, because it’s slowing down. So we deduce that a cannonball travelling at 1000m/s has more than twice the kinetic energy of one travelling at 500m/s. We can do the arithmetic for each second, then slice the seconds up finer and finer, and we end up realising that the ½v² is the integral of all the velocities between v and 0. But what we don’t realise is that kinetic energy is a way of describing the stopping distance for a given force applied to a given mass moving at a given velocity. You can flip it around to think about force times distance to get something moving. Or you can think in terms of damage. But basically that cannonball has “got” kinetic energy like it has “got” stopping distance. It’s similar with momentum. That’s a different way of looking at the mass and the motion, based on force and time instead of distance or damage. We look back to our cannonball and cardboard, and we know by definition that in the first second the same amount of time passed as in the second second. So we realise that a cannonball travelling at 1000m/s has twice the momentum of one travelling at 500m/s. But what we don’t realise is that momentum is a way of describing the stopping time for a given force applied to a given mass moving at a given velocity. A cannonball has “got” momentum like it has “got” stopping time. But wait a minute. I didn’t fire the cannonball at 1000 metres a second. I dropped it off at a handy spot out near a GPS satellite, then zipped off in my spaceship in a big fat loop. It’s me doing 1000m/s, not the cannonball. The cannonball is just sitting there in space. It hasn’t got any kinetic energy at all. I’ve got it. But I don’t feel supercharged with five million Joules of energy coursing though my veins. So where is it? Where’s the kinetic energy gone? It isn’t anywhere really, because all that cannonball has got, is its mass, and its motion. And that motion is relative to me. Kinetic energy is not a thing. It’s just a relative property. So, let’s examine this property. How do you make something move? Easy. Hit it with something else that moves. And how did you make that something else move? Where did it all start? I pitch you a cannonball, you whack it with a baseball bat, and it tumbles away at one metre per second. You made that cannonball move. Now, where did the energy come from to make it move? From your muscles: “The release of ADP and inorganic phosphate causes the myosin head to turn, causing a ratchet movement. Myosin is now bound to actin in the strong binding state. This will pull the Z-bands towards each other. It also shortens the sarcomere...” It all gets a little complicated, but it’s all down to bond angles. Bonds within molecules change, and the change releases energy. Sometimes it’s a simple single change of bond angle, something like a leaf spring flattening out with a push. Sometimes there’s more than one, and the molecule resembles an elasticated deck-chair that surges from one configuration to another giving up some of the bond energy. And sometimes the molecule takes a rather different shape. A familiar shape: They look like springs because they are springs. That’s the size of it. The energy to move your muscles is stored in tiny compressed springs. Yes, they’re electromagnetic springs rather than solid rigid springs, but that’s what all solid rigid springs are. That’s how the muscular energy is stored. It’s the same for other chemical energy, and I quote: “In the early 1980's it was pointed out that cubane's very high density and high heat of formation would make it an especially good explosive, especially if each carbon could have a nitro group attached. The resulting molecule would decompose to eight molecules of carbon dioxide, and four molecules of nitrogen, and release a lot of heat in the process. A cubane with a nitro group on each carbon is called octanitrocubane. Several factors are important in making a good explosive. The decomposition must be energetic. In cubane derivitives, the strain energy ensures a very energetic decomposition.” It’s the strain energy. There’s compressed springs in there. It’s the same with nuclear energy, only the springs are stronger. The sun gets its energy from nuclear fusion. Squeeze a couple of hydrogen atoms together and you make helium. But when you do, ping, something breaks, and things spring out between your fingers, things like photons. 4 1H + 2 e --> 4He + 2 neutrinos + 6 photons It’s the same too for matter/antimatter annihilation. Somehow somewhere some kind of spring is letting go, and photons come bounding out at gamma-wave energies. A photon is an interesting thing. Particle physics comes with mental baggage that says it’s a speck, a point, a particle. But we have long wave radio which reminds us that photons can be 1500m long. A photon isn’t a speck. It’s more like the slink in a slinky spring. Only the slinky spring here is space, that vacuum void with its permittivity and permeability. A photon is a like a ripple on an electromagnetic ocean between the stars. A boat on this ocean can ride the ripple and the ripple passes on by. But tie that boat to the sea bed with a rubber rope, and you can capture the energy of the ripple, and save it in starch, or coal, or oil. You can use it to make your leaves or build your house, and whack that cannonball. It all comes down to springs. Compressed springs. The energy is in the compression. The stress. It all started at the beginning of the universe. Visualize a dark cylindrical room. You’re in the middle of it, the walls are banded and helical, you feel a tremble, and you realise with horror that the room is the biggest baddest spring you’ve ever seen. It is exerting an incredible pressure, but is bound by thick steel cables called “symmetry”. The cables are under impossible tension, and you can hear ping ping ping as individual cable wires snap. Symmetry is about to break, and you know your “prime mover” will disintegrate into a fireball of nuclear and electromagnetic springs that will go bouncing out to fill the night and make the world what it is. The dark cylindrical room is analogy of course. Analogies are based on the things we experience with our senses, and these are not the things of the subatomic world. So analogies can be dangerous, like too much butter. But the Universe will wind down. Because the springs are not so much analogy, nor is the stress that compresses them. And that’s what your energy is. Stress is the same as pressure, which is the same as negative tension. And to quantify it we have to know that in physics stress is force per unit area, and energy is force times distance, so energy is stress times volume. So here’s the new definition: Energy is the capacity to do work, and is in essence a volume of stress. You know you can’t hold stress in the palm of your hand, and a volume of it doesn’t make it something you can get hold of. That’s why you can’t hold pure energy in the palm of your hand. There is no such thing as “pure energy”, just as there is no such thing as “pure pressure”. Because it’s the property of a thing, even when it’s the very last property that makes a thing the thing that it is. But you can hold energy in your hand. It’s a subtle difference, but it’s very simple. Just squeeze a fist. Use your right hand. Squeeze it tight. Now touch your left thumb to your right thumb. Feel that blood pressure. Now look at the volume of your fist. Stress is pressure, and there’s a volume of it in that fist. Your fist has energy. And if you swing that fist, it has even more. As to how, it’s all to do with pushing little circles into little spirals and so making little springs. But to explain that, I’ll have to explain mass...

I don't give maths because I'm trying to offer grasp, insight. I can't use mathematics to do this because the axioms used as the foundation stones for mathematics cannot be explained by mathematics. Try explaining t via maths, and you'll understand where I'm coming from. So, it hasn't been shot down. Thank you. All this mud I'm seeing won't bring it down either. I thought I had addressed the transverse c contention. Nevertheless let me reiterate: my tranverse c measurement in my frame will always be 300,000km/s. But if I undergo time dilation, my 300,000km/s is not the same as yours. We know this because on my return we counted and compared traverses. You try to explain the difference by saying my light in my frame travelled a longer path in your "preferred" frame. But you're missing the obvious - my time dilation occured because my c was less than yours, in my frame, and it defines my time so I can't measure a lesser value. Think ontologically. Ask yourself what you'd see if you could view the time-dilated me via some magical instant TV camera.

I'm sorry spunnery, you're wrong. Special Relativity is right. The speed of light is the same for all observers. However the reason for the postulate is rather difficult to grasp. It's because, as Einstein said, "time is suspect". Once you understand it, it takes you into new areas based upon a new interpetation of Special Relativity, but you don't end up saying it's wrong.

No, when you scale up the analogy you have three dimensions. See TIME EXPLAINED for why that +1 isn't a dimension. Instead it's a measure of motion through the three dimensions that are actually there. LOL, no chance. Edtharan's logic is circular, and uses the axioms to defend the inferences drawn from them. Yes, a change in vacuum permittivity. And you obviously haven't even read GRAVITY EXPLAINED. Very logical. Very rational. Very scientific. Wrong. It's space, not spacetime. That's the key. And gravity probe B hasn't "proved" it. Are you sure about that? Because you aren't interested in it enough to actually read GRAVITY EXPLAINED. You're siding with Edtharan without due cause, and he holds dogmatic axiomatic concepts that are taking him nowhere, but he just won't examine them. Instead he exhibits hostility towards this attempt to move forward. There's a psychology at work here, and people just can't see it, like the A and B squares that are the same colour. Realise this: if anybody is going to get us to be the stars, it won't be the likes of Edtharan. It'll be the likes of me. PS: I'm developing a model here. It's something of a toy, but it flies, and nobody can shoot it down. I'm calling it RELATIVITY++. Make a note of that.

That's the flat rubber sheet plus an extra dimension. Three. That's three Dimensions. Note that permittivity can be measured and so considered a "dimension". Just like temperature and other things. But these should not be confused with Dimensions. Mathematical space is not space. It is artificial, imaginary, an artifice for calculation. See above. You're too busy playing debating societies to actually read what I'm saying. Any normal person would ask a simple brief question to clarify a point, but you build a whole sandcastle on your error. Not true. All you've ever said is Farsight you're wrong because time is a dimension, a circular argument that uses the axiom itself to defend what you infer from it. Ah, see previous posts. In discussions, but not in essays. So I was right. You were wrong. And yet here you are clutching at "didn't state explicitly" straws. Here we go again. You're just making it up as you go along. Stop kidding yourself. You're the one here with the straw man arguments. And if you want to see ad hominem read what some of the other posters have said. About me. Take a toy motor boat. Put it in the boating lake ready to go. Then get a tanker full of molasses and tip them all down one side of the boating lake. Wait a while. Now start your motor boat. What path does it take? No. Gravity changes its velocity. Not so, I've had useful input from other sources where I've thanked people for their feedback and resolved to make some change. And come off it, Edtharan, you have not made an ounce of effort to examine both sides here. No. You play your mind games. I'll do the physics.

I haven't introduced any new dimensions. Is that Catch 22 or Chicken and Egg? I have to start somewhere, and I'm starting here. So you say, incorrectly, and you're really clutching at straws. Whatever happened to the open mind? It's an essay. On a second rate chitchat forum. In Speculations. Jesus H Christ! LOL, not so. I've just searched my previous essay. You're making this up as you go along. You're being dishonest. They're just new interpretations. The working name is Relativity++. And my explanations do not violate one another. Really Edtharan this is getting ridiculous. Oh FFS this is absurd. It uses gravity to explain gravity. Of course it travels in a curve. Apply a constant sideways force to a boat and you'll get a curve. I'm sorry Edtharan, but that's quite enough. You don't understand, you don't want to understand, and you never ever will. I'll make sure I give you a mention at some future date.

Sometimes I wonder if that polarizability of the vacuum is what space is, Albers. The vacuum would truly be nothing without it.

It's inside the moving body, spunnery. If you let the handbrake off a car and push it, you're exerting force on it to get it going. If you push it for say five seconds you're giving it some amount of "momentum". Then you stop pushing, and the force has gone into the car. There's no force acting on it any more, but it keeps on going because it's got that momentum. If you run round and get in front of it, the force it hits you with depends on how fast you stop it. Ummm. Don't try this at home. The easiest way to think about what's going on here is to imagine that every atom of the car is tracing a circular path. When you pushed the car you bent these little circles into spirals, and every atom of the car moves forward, and keeps on moving forward. You have to push the spirals back into circles to stop the car moving. Like the other guys said, do pay attention to the terminology.

I'm listening, Albers.

Thanks Swansont. That's perfectly fine. I hang my head in shame. Apologies. All: I was wrong in post 9. Sorry. I mixed up my Ggs and my relativity.

I didn't mean to suggest that. I was thinking of gravity actually.

Swanson: tell me about the 1x mass and 100x mass attracting. Then tell me about the 10x mass and the 100x mass attracting. If you apply the physics correctly I'll be interested to see how you use the G. And if you manage to demonstrate that spunnery was correct, please accept my apologies in advance.

fredrik: I've intended to give a verbal and pictorial explanation that delivers grasp, so that the reader can actually understand gravity. I want the reader to know what it really is, in terms of mass and energy, and how it is not in truth a force. The deeper abstractions hopefully are in other essays, namely TIME EXPLAINED, ENERGY EXPLAINED, and MASS EXPLAINED. I haven't attempted to include any mathematical formulism because I am in essence explaining axiomatic terms used within mathematics. Terms like t c E m and G. As to whether my aims are correct and whether I succeed in them, that remains to be seen. If I do succeed, mathematical formulism will follow. Mathematical formulism is not my end goal. And nor is mere understanding. But first things first. First I need feedback, and some serious considered challenge to the picture I present.

spunnery: That's what you call an axiomatic explanation. If you start with the G you will end up with acceleration that is independent of mass. Interestingly, it isn't quite correct. We can see this we conduct an experiment with masses of 1x, 10x, and 100x in free space. The 100x mass stands in for the earth. If we "drop" the 1x and 10x masses together they will "fall" towards the 100x "earth" mass at the same rate, and will "hit the ground" at exactly the same time. Note that the 100x mass is alse attracted towards the smaller masses which act like a single smaller mass of 11x. If however you repeat the experiment with the 1x mass, then later with the 10x mass, they will collide with the 100x mass after different elapsed times in accordance with the attraction of the larger mass to the smaller. Obviously with the earth and normal masses this effect is miniscule, but it does demonstrate that G isn't a perfect constant. Severian: My "gravity is not a force" answer is not a casual answer. However you might view my explanation as speculative, and this thread is perhaps not the best place for me to give it.

Dstebbins: No, gravity is not a force. But I'm afraid your logic is incorrect.

Yes, this rubber analogy is the reverse of electrodynamics in this respect. I struggled with that for a while, wondering whether to move to another analogy, but thought I'd cover the "reverse image" in a later essay covering space and charge. Maybe I need to clarify this or even change tack. Hmmn. Thanks for the input. Swansont: give it a chance, c depends on impedance √(μ0/ε0) and IMHO it's unreasonable to insist that impedance can never change. Whilst we always measure c to be the same it's like trying to measure your shadow, but the only thing you can measure it with is the shadow of your ruler.