[yor_on]

Rereading you Sim. Are you using Newtons definitions? Quantity of matter as mass, and Quantity of motion as the product of velocity and mass?

Then quantity of matter as mass makes sense to me, but I'm not sure how you think of quantity of motion as the product of velocity and mass? Do you include for example momentum and/or relative mass in that? Because that's the mechanical laws we use since Newton? Well, momentum may be new but 'relative mass' is a concept that have followed us a long time, in one shape or another.

So how do I look at 'gravity'? Simple, to me it's what's not explained. How did Einstein reach the rest of his conclusions?

"Einstein bases SRT on two fundamental principles: the principle of relativity and the principle of the constancy of the velocity of light. The principle of relativity originated in Galilean-Newtonian mechanics: Any frame of reference in which Newton's law of inertia holds (for some period of time) is now called an inertial frame of reference. From the laws of mechanics it follows that, if one such inertial frame exists, then an infinity of them must: All frames of reference (and only such frames) moving with constant velocity with respect to a given inertial frame are also inertial frames. All mechanical experiments and observations proved to be in accord with the (mechanical) principle of relativity: the laws of mechanics take the same form in any of these inertial frames.

The principle of relativity, as Einstein stated it in 1905, asserts that all the laws of physics take the same form in any inertial frame-in particular, the laws of electricity, magnetism, and optics in addition to those of mechanics."

So we seem to agree there? We both define your own 'room time geometry' as uniquely 'the same'. The funny thing about that is that the revelation of all frames outside your own being 'different' blinds people. The only way we use it is in defining it as 'entropy' or 'the arrow of time', but to my eyes it's a 'constant' of sorts.

Gravity then?

"he assumed that a person cannot distinguish whether he is in a gravitational field or under constant acceleration, i.e. these two things are equivalent. This assumption provided a link between gravity and mass, or gravity and energy. He concluded then that mass and energy must affect the gravitational field. Secondly, he stated that the gravitational field is not actually a force as Newton has described, but instead a curvature in space. To put it in simple words, the bodies are affected by gravity not because of a force directly exerted on them but because space is curved and therefore they have to follow space's grid. The presence of mass or energy does not affect the bodies directly; it affects the space first, and then the bodies move in this curved space. Earth always moves in a straight line (not in the Euclidian sense though). The presence of sun curves space, and therefore curves this straight line and forces earth to appear to be moving in an ellipse... Imagine being in a sea (or pool) using your finger to create ripples on the water. The presence of your finger in the water creates these waves and alters the geometry of water, it's not flat anymore. If you look through the rippled water you'll see the bottom distorted. Well, the same things happens to 3D space if you try to move your finger like that on the air! Your finger has mass and it actually can create ripples in space... The only reason you cannot see them as in the water is that the mass of your finger is so small that the ripples it creates are of the tiniest magnitude; there are so small that do not affect anything considerably."

Now, this analogue made by the author is rather cool. The problem with it is that it gives SpaceTime a 'density'. Do we accept that? I'm not sure I do. What we can say is that any description we use built on previous experiences probably are wrong when describing 'SpaceTime. It's a very large step between looking at SpaceTime from the viewpoint of celestial mechanics versus as compared to relativity, and to drag over concepts that works so well on our earthly scale to explain the universe?

[yor_on]

This is some questions I have. First, why do I keep on about 'relations'? Look at the universe, you have space, all empty. No matter what we expect on the quantum level there isn't a 'thing' in empty space macroscopically. It's a dark lonely emptiness with some small islands of matter. Do particles exist on their own in space? Not readily, and not alone, as I know it? And I'm not talking bosons here, but particles of restmass. Now look at it from the viewpoint of 'relations'. Then those islands sparkle with relations, they are the most concentrated places of relations existing. How do matter 'grow', and, why can it 'grow'? How can we consist of a 'insurmountable' amount of energy, each one of us, and still be able to function, transform other types of matter into ourselves and use it?

It has to be another way of looking at it. And doing it as relations seems to work for me. Think of the question we had recently here, what will happen if we could 'time travel' to the 'past'. Would we land where we started, or in space as the earth and the universe are moving in time. I said that it all should adapt, all dimensions together, as it should be one undivided 'SpaceTime'. The implications of that are staggering to me suddenly. Because I also think of the universe as a place that have this rule of 'least energy expended'.

Can you see what that way of looking at it implies? That the whole universe would adapt to your 'time travel'. Now, if that way of looking is right then a Lorentz contraction suddenly have a much larger possibility of being 'real', instead of just some geometric illusion. Because when we see it we are in fact 'time traveling', even if in the other direction temporary, in time that is.

So can we test that idea? I think Einsteins ideas already have done that. And he seems to be right too. You have a unique arrow of time, in that arrow, no matter what you do, times arrow will be the same. But the 'universe at large' will adapt to certain properties, invariant mass and motion. And that is not really what I expected if it is correct? What happened with the idea of 'least energy expended' here, if so? Well, when you 'time travel' do you really influence all other objects around you. Not if you stand where they are, so the rule may still work?

So what is wrong here? There is a dichotomy in that I might assume that when you use motion or invariant mass for your time travel you do change the universe at large and the fact that when meeting up with your twin you will find that he felt no such 'influences' acting upon him just because you traveled near light. So if I'm correct in my thinking and also assume that you really change the universe, aka, 'Lorentz contraction' and 'time dilation' both are 'real. Where does it place the 'interactions'?

[Bill S]

Axioms do not need proofs

Surely, axioms become axioms only because their proof has already been established, at least to the satisfaction of those who accept their axiomatic status.

[yor_on]

Yeah, a axiom is like one and one makes two.

Weird stuff like that But it is also a axiom that all uniform motion shows an absence of gravity, and inertia of course. Assigning a gravity to uniform motion would need a new definition, of either uniform motion, or gravity and inertia. That it follows a 'geodesic' induced by gravity, does not state that you can feel that gravity working on you in a 'black box' scenario. And that's also what make all uniform motion 'equivalent' to my eyes, and so all 'uniform motions/speeds' following that geodesic.

But yes, gravity must be there, even though unmeasurable in that uniform motion as we can observe light 'bending' around invariant mass, like the sun. But then we're discussing 'frames of reference' again. In the black box there is no way I know of proving it, ignoring tidal forces now, like frame dragging.
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Reasoning along those lines you will find it natural to define it as being 'at rest' relative gravity. And if you find that natural you will need to look at where our definitions of gravity 'breaks down'. That should be a Black Hole as I see it, all light/time cones pointing one way. and if that is the 'state' where you will find matter disappear then, maybe, you might want to define that as the ultimate state of rest . Quite questionable as you as easily then can assume all 'speeds' following a geodesic as being 'at rest', but it's still the state in where we expect matter to ??

[simplified]

Axioms do not need proofs

Surely, axioms become axioms only because their proof has already been established, at least to the satisfaction of those who accept their axiomatic status.

My definition of gravity is imperfect. But you have no definition of this at all. And at all you can only jump over sequence. []

[hakaya]

Time is in three parts in the future that never arrived and are available only in my dreams, man, 'which currently exists only to separate the small second and the last to go on forever in the memory man', but not always. return unless an error and we do tend to repeat.

[Paul25]

Time is more related to movement

[talanum1]

Time is as defined in the attachment.

No, time would not cease to be if there was no light. The definition is clear about this. All that is required are particles with no charges on a circle in a Riemann Sphere.

[yor_on]

I am trying to understand exactly what time is. When I think about time I immediately link it to light. Astronomers often tell us that they are able to take pictures of the universe billions of years in the past and that this is due to the amount of time it takes for light to travel. As I understand it, if I am looking up into the night sky what I am seeing is actually the past, in the case of the sun light I am seeing approximately 8 minutes into the past where as looking at the stars I could be looking many millions of years into the past. This is where I start to get boxed in with my own limited knowledge and perhaps some of you more knowledgeable people could enlighten me. If there was no light would time cease to exist altogether? I appreciate anyone taking the time to help me try and understand this.

Graham

You can connect the passing of time to 'c', lights speed in a vacuum. Both are local 'constants'. That doesn't tell you what time is though, just that there is a equivalence between those two. We have no explanation for why 'c' is 'c' either, just experimental proofs. A vacuum is devoid of light, unless you have matter inside it, although that may be arguable. You need to place that sun and that matter inside this vacuum to get it to interact, creating heat. So no, I think time is more than just a interaction, it's a local constant, experienced through your wristwatch.
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syntax

I shouldn't split it into a sun and matter, the first sentence is correct, the second is wrong. A sun doesn't differ from f.ex earth. Both are matter in different states.
=

And damn, do I hate those yellow suns appearing in my old posts. Due to a failed update.

[Bill S]

Possibly, what we need is a definition of time, in the absence of anything/everything else.

[talanum1]

Possibly, what we need is a definition of time, in the absence of anything/everything else.

Look at my definition at post #247.

[Bill S]

Time is as defined in the attachment.

Presumably you refer to the definition in the attachment.  Valid as this might be as a mathematical definition, it does not provide a physical example of time, "in the absence of anything/everything else", that I could see.  Of course, the cursory way in which I am obliged to look at these things, these days, could mean I missed it. 

[alancalverd]

How about going back to the obvious?

Time is what separates sequential events. If you can discern a "before" (a piece of paper) and an "after" (a pile of ash) then these observations were separated by an amount of time.

And whilst we are defining the deeper mysteries of the universe, gravity is the force between massive objects that depends only on their mass and separation.

[Bill S]

Time is what separates sequential events. If you can discern a "before" (a piece of paper) and an "after" (a pile of ash) then these observations were separated by an amount of time.

Good definition of time in the presence of other things, but still no definition of time in the absence of everything else.  I certainly can't find such a definition, but hope springs eternal, and all that.

[PmbPhy]

Apples in Geezer's garden  are their quantity, but motion is not quantity of motion. Because the quantity of apples can decrease or increase.  Quantity of motion only increases.
 Here I am wrong,because quantity of  created apples only increase.

Quantity of motion is defined to be momentum in physics. In physics time]/i] is undefined as being intuitively known to all to all observers.

[Bill S]

time]/i]

For the benefit of the maladroit; is that time/distance?

[alancalverd]

Time is what separates sequential events. If you can discern a "before" (a piece of paper) and an "after" (a pile of ash) then these observations were separated by an amount of time.

Good definition of time in the presence of other things, but still no definition of time in the absence of everything else.  I certainly can't find such a definition, but hope springs eternal, and all that.

In the absence of anything else there can be no change, so time is meaningless. To use the philosopher's default object, if there were no ruminant quadrupeds, "cow" would be meaningless. If nobody spoke English, so would this entire post!

My neolithic ancestor Ug showed Og the spanner he had invented "For tightening bolts". "Cool too, bro! What's a bolt?"

[Bill S]

That’s fine. Would a fair paraphrase be: “In the absence of anything other than time, the concept of time would be meaningless”?

[talanum1]

“In the absence of anything other than time, the concept of time would be meaningless”?

This translate as:  "The concept of time would be meaningless, in the presence of only time." or: "The concept of time would be meaningless, in the presence of only meaningless time."

[Bill S]

That sounds like a very convoluted "yes".