Ivanov2000

Yes, just trying to make the 'can time actually slow down' thing more palatable to everyday experience. This: Something to do with an expanding universe, I suspect. Belongs to: What I want to know is why only forward in time, and why the speed limit is c. ...not the rest. It was actually a separate post, but the software joined them together.

Imagine moving at a constant speed, say 100mps, in a fixed direction. You start at the origin on a 3d graph, and take a picture of that graph once per second. Each shows you 100m further from the origin. Your possible position would be somewhere on a 100m radius, 200m, etc... Ok, now flatten your 3d space onto the x/y plane, and use the z-axis for time, and your 'speed' is c. So now if at rest in space, you will be moving at full 'speed' through time. If you move though space, you will not move as fast through time, as some of your motion is through space. If you move full speed though space, your motion through time is 0. Ok, so we talking a hemisphere now as only forward motion through time is allowed, and I don't think it would actually be spherical neither, but you get the idea. In space time, nothing is actually at rest, everything moves at c, sorta. What I want to know is why only forward in time, and why the speed limit is c. Something to do with an expanding universe, I suspect.

I don't think about what is beyond the known universe much, doesn't seem to be much point to that. At the other extreme standard model seems to work, but it is just a model. What is actually there, no idea. I doubt human mind can really comprehend, it's too far beyond what it evolved to understand. Hadron, heavier particles. Maybe some clue to dark matter. Not really been any major breakthrough during my lifetime, so maybe something is due.

...

I'm a mathematician, I don't measure things. I read section 2.2.

1. "physical conditions that manifest the effects de- scribed as the expansion of space are not met" manifest: readily perceived by the eye or the understanding; evident; obvious; apparent; plain ie-> the conditions that make the effects obvious do not exist, not-> the effects do not exist. 2. "Are you saying gravity actually prevents space expanding, or gravity merely prevents matter moving apart as space expands?" In the former, space does not expand, in the latter, it does.

That does not say that space does not expand in your bedroom, it merely says that the effect is not obvious under those conditions. The implication is that space does, indeed, expand in your bedroom. In fact, as far as I can see, the 'homogeneous' and 'isotropic' conditions are only there to simplify the calculation. Are you saying gravity actually prevents space expanding, or gravity merely prevents matter moving apart as space expands? If the latter, I would agree, but that does not appear to be what Strange is saying: "Space expands when there is a uniform (homogeneous) distribution of matter." "Where the distribution of matter is not homogeneous, then you don't get expansion."

This does not agree with what I have read elsewhere.

Not sure I ever mentioned acceleration expansion. The point is, why would space time expand away from matter? Doesn't make any sense. So it does expand near matter but gravity holds matter close.Ok, but Newton's inverse square is based on fixed background. In expanding background gravity would have to be greater than that to hold everything in place, or... there is something else going on, which, if weak, but linear, will show up when gravity is weaker - which is where the reference to MOND and dark energy come in, and those stars doing odd things at the outer edge of some galaxies... where the acceleration due to gravity is less than a certain amount that has a curious relationship to c and H. And the point of the point is that the other thing going on that mass just don't like moving.

H is a mystery... I'm thinking Hubble constant in 1st link. in 2nd link, I spent about half hour wondering what H was, then realised it should be sinh. Correct?

Yes, moving the same as it already is, is one of the 'good reasons' for moving. "Problem is this would mean the effect is greater with larger values of x" In fact, probably a constant acc, determined by rate of space time expansion somehow, but that still doesn't work. I got here via mond. From what I understand, gravity no longer follows the inverse square below a certain acc, which does not make a lot of sense (since the inverse square comes from the surface area of expanding sphere - seems to me that a straight inverse relation would require 2d space). So I'm thinking leave gravity alone, there's something there in addition to gravity, something small that doesn't show up until the force of gravity is tiny. But not dark matter, that doesn't really work neither.

Why is that? Matter does not like to move, without good reason, not though space anyway. It happily moves through time. Anyway, if you have two bits of matter x distance apart in expanding space, two things can happen 1. they move towards each other, to maintain distance x or 2. space distorts locally to maintain distance x. Maybe a bit of both, anyway, you can call either gravity. So is gravity just matter's reluctance to play ball with the expansion of space time? Problem is this would mean the effect is greater with larger values of x, which don't seem to be the way things work.

Yes, changes in gravity. If the mass/energy content of the universe is constant, I can see that the overall curvature is not going to change much, and that curvature will expand with space time, beyond the horizon. This would suggest that it was fixed at birth of universe. Any changes would be local, within the horizon(s) - but would there in fact be any changes at all?

"gravitational waves can not be used to pull a mass towards you anymore than shining a flashlight at a piece of iron will draw it towards you" Thanks, I think this line made it clear. However, I have read that if the sun were to vanish, the change in gravity would not affect earth for 8 minutes. If this is correct, then a cosmic horizon does exist for gravity? If this horizon is expanding, would that not result in more distant space expanding at a greater rate? It also explains how gravity can 'leave' a black hole (I assume gravitation waves cannot).

Gravity has one 'charge', mass EM has two, + and - Strong has 3 colors I'm not sure if this pattern means something.

Ok, so if gravity propagates in waves at c, I have few questions. 1. Does the cosmic horizon also apply to gravity? 2. Is gravity 'red shifted' by expansion of space? 3. Is this taken into account in current models of expanding universe? 4. Would this explain dark matter/energy to some degree?