[jeffreyH (OP)]

No you certainly do get the point and bring up some very interesting counter points. Keep it up. We learn more when debating.

[Bill S]

In fact we cannot tell if v is in reality greater than zero. Because it could be everything else that is moving, including our base frame. Again none of this actually affects the value of v. It's just we don't know what v actually is.

In fact, apart from values for v, which we can measure, relatively, we don’t know if v actually exists in relation to space.

[jeffreyH (OP)]

Thy

In fact we cannot tell if v is in reality greater than zero. Because it could be everything else that is moving, including our base frame. Again none of this actually affects the value of v. It's just we don't know what v actually is.

In fact, apart from values for v, which we can measure, relatively, we don’t know if v actually exists in relation to space.

With empty space you have no reference which is why I proposed the photon lattice.

[Bill S]

With empty space you have no reference

Precisely.

which is why I proposed the photon lattice.

An excellent idea for working with the concept of space, but does not alter the impossibility of making measurements of motion relative to actual space.

[jeffreyH (OP)]

I think space may have been a bad choice as a reference. However, using it brought out some useful points. When we think of space-time we think of a coordinate system composed of t,x,y,z. The time component then becomes ct. Therefore Minkowski space-time recognises this problem with empty space.

Also we have an extension of coordinate systems called Hilbert spaces which can have more than 4 dimensions up to an infinite number of dimensions. There is that infinity again!

[puppypower]

Take two observers a distance s apart. An object moves between them exactly halfway and with local velocity v. The potential at the position of observer a gives a time dilation of d1. Observer b has a time dilation of d2. Neither observer a or b affect the velocity v and yet they both calculate it differently. Does this show that the absolute velocity of an object is not determined by time dilation?

Note here that absolute velocity is determined by comparison with the speed of light in vacuum as determined in a preselected inertial 'base' frame.

If you consider the twin paradox, upon return, one twin aged slower due to time dilation. On the other hand, although the  slower aging twin also showed distance contraction, while in motion, there is no permanent change in his size when he returns. The twin that ages slower, does not also stay smaller, even though the change in time is permanent.

The same is true of clocks that slow down in orbit. They may lose time, but they do not permanently stay smaller even though we may see both time dilation and distance contraction while in motion. The reason for this difference is what we see and measure is the reflected and/or emitted light. Our eyes do not measure atoms. The light that we see and use to  infer shows both time and distance changes; wavelength and frequency, but the clock's matter only changes in time in the final analysis. The half life of radioactive isotopes may get longer and show difference in concentrations, but atomic distances stay the same, even if we saw change is distance and time based on the light.

What this tells me is that time dilation is the dynamic variable since it leads to a permanent change. Time leads and impacts both the matter and the light that we see. In terms of the energy we use for inference, frequency and wavelength always need to multiply to the speed of light. The time dilation of the matter, leads to a permanent change in frequency of associated light, that alters the wavelength of the energy. However, the change in time does not lead to a permanent change in the distances of the matter; sizes, since these two things do not have to multiply to a constant, as does light. Distance contraction of the light, does not mean it occurs in the matter.

Every experiment where we can measure and direct compare the matter and the light emissions  show this correlation; only the light shows permanent changes in distance. What that tells me is much of what we see in the universe, in terms of light, may not be 100% due to relative motion of the matter. The same affects can occur due any source of local time dilation in the matter.  For example, a super nova will cause it mass density to decrease. This actually changes the  material distances which will cause local time to speed up. This will look like a Doppler shift even if center of gravity is fixed, since the permeant change in time will cause wavelength to follow. 

[jeffreyH (OP)]

@puppypower Nothing gets smaller. If you don't understand Lorentz transformations just say so.

[jeffreyH (OP)]

@puppypower Try starting with this.
https://en.m.wikipedia.org/wiki/Bondi_k-calculus

[Bill S]

I like the look of the Bondi k-calculus.  At first glance, even I can understand the maths.  All I need now is time to read it. 

Michael Huemer takes an interesting look at the twin paradox at:

http://home.earthlink.net/~owl232/twinparadox.pdf

[jeffreyH (OP)]

It allows for easy understanding of the principles of special relativity.
https://en.m.wikipedia.org/wiki/Hermann_Bondi

[jeffreyH (OP)]

I like the look of the Bondi k-calculus.  At first glance, even I can understand the maths.  All I need now is time to read it. 

Michael Huemer takes an interesting look at the twin paradox at:

http://home.earthlink.net/~owl232/twinparadox.pdf

Lot's of people should read this. Especially the part about acceleration playing no part in the solution.

[guest4091]

jeffreyH;

Does this show that the absolute velocity of an object is not determined by time dilation?

Time dilation is a motion induced phenomenon, an effect, not a cause.
The measured velocity of an object by an observer is independent of the observer's time dilation
A measures M velocity twice with light signals, or once if they have a common origin..
v=Δx/Δt.
Δx and Δt both contain t', the dilated A time, so it's removed from the calculation, leaving
V=(m-a)/(1-am). (lower case is speed for upper case)

Note here that absolute velocity is determined by comparison with the speed of light in vacuum

A spacetime diagram, with x, ct axes, shows speed plots or history of positions, v/c, within the context of SR, i.e. relative speeds, since it rejects absolute rest frames.

If you assign a velocity to all n-1 objects in the universe relative to object n, it has no object to serve as a reference and has no velocity, since the universe has no reference.
Note that any other choice of object yields the same result.
.

[jeffreyH (OP)]

I shall refer back to Special Relativity by N.M.J Woodhouse. On page 114 we find the following.

Two points should be noted.  First the fact that the spaceship can complete a round trip of 44,000 light-years in 40 years does not involve a violation of the prohibition on faster-than-light travel since the distance and the time are measured in different frames; the distance is measured on earth and the time is measured on the spaceship. The calculation illustrates an important fact; it is consistent with special relativity to travel as far as you like in as short a time as you like, provided that the distance is measured before you set out and the time is measured along your worldline.