Mordred

Perhaps you can specify which calculation and at which size scale ? Is this specific to how time dilation works under the metric ? If so I can show you a "standard" means of determining the speed limit. That's all relativity truly states about the speed of light, it cannot exceed the value c. That and the invariance to all observers. At no point did relativity state that light cannot move less than c.

Yeah I recall that paper as well... I agree with your last post about it

again looking at pop media style articles rather than the actual science sigh... Here is a food for thought. We don't require light to prove the accuracy of relativity.

We don't try to account for every miniscule influence. Many are neglibible, those are averaged out over large scales. We do strive to improve that averaging which is why research is still ongoing. The averaging method always includes an error bar, to account for localized anistropy, greater detail simply reduces and improves the error bar or sigma level. Might help if you study how LCDM works in cosmology. http://arxiv.org/pdf/hep-ph/0004188v1.pdf :"ASTROPHYSICS AND COSMOLOGY"- A compilation of cosmology by Juan Garcıa-Bellido http://arxiv.org/abs/astro-ph/0409426 An overview of Cosmology Julien Lesgourgues http://arxiv.org/pdf/hep-th/0503203.pdf "Particle Physics and Inflationary Cosmology" by Andrei Linde http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

What part of we already account for this didn't you understand? You keep trying to find pop media articles to support your case. Yet keep posting articles you don't fully comprehend. The last article being unrelated to the topic

no

A true vacuum is an impossibility, there is always some, however miniscule mass- energy even if it is just quantum fluctuations. We detect mass distribution of the interstellar and intergalactic medium by those relations I described above. The universe is modelled by the thermodynamic relations of the mediums described above, this includes the mediums influence over large distances on light paths.

yes we already account for the medium properties of space. This is done via redshift style calculations. More complexely the Sache-Wolfe integrated and non integrated. Scientists have always known c isn't constant in a medium and that space contains particles. This is the basis behind Baryon accoustic oscillations of the CMB.

The thread was created as you responded to another thread incorrectly with a false understanding.

If she is anything like my wife, that will just raise her hackles.

Another common misunderstanding by those not familiar with relativity. I hate pop media articles grr. At least it included the arxiv article. It clearly shows the author isn't claiming relativity wrong. Just that the results may or may not have implications. However he did not correlate those implications outside of his experiment. The pop media coverage implies a conflict with relativity which isn't detailed in the arxiv paper.

Here is another detail. Sagittarius a will make a Kepler curve worse not better. If you use Newtonian dynamics for galaxy rotation curves without DM, you will get a Kepler curve. Adding mass to the disk itself only compounds the problem. DM halo distribution allows mass to remain roughly uniform as a result of radius. Not that Sagittarius makes any difference, the majority of research on rotation curves involved Other galaxies. Not necessarily our own, as you say we can't easily measure our own galaxy, but measuring Andromeda is easy by comparison.

When I get time enough to be properly focussed. I'll look through it. Busy week

What's to figure out. The time dilation is a consequence of spacetime curvature. All physical processes. Including decay rates is equally affected. The atomic decay rate just allows us to measure this change in time. It is no different than the muon whose mean lifetime depends on its decay rate just like the atomic clock. It literally doesn't matter what process you use. The time dilation will be the same. All information exchange is equally affected. In particle physics this is your force interactions and other interactions between particles. However time dilation doesn't restrict itself to information exchange rates, a particle by itself will undergo changes without interactions. These processes are also affected.

There are plenty of examples of time dilation that does not involve a clock or even observers. Muon lifetime decay for example, muons could not reach Earths surface, (their lifetime is too short) without time dilation. Any falling particle that involves gravitational redshift is time dilated. This isn't simply a case of velocity or frequency when a particle exceeds its mean lifetime. Nor does it matter what you use for a mechanical clock. Time dilation affects all physical processes and information exchange between particles etc equally.

I believe he referring to a tendency in numerous posts. Particularly the vast majority of the "Look at my model, its solves everything" style threads. The funny part is those threads are easy to spot how much someone knows just from their posts. At least with physics subjects. I can't speak for others. 1) improper use of terminology 2) claims of grandeur beyond what their model shows 3) Low math or complete lack of. number one I can see on communication problems but 2 is definitely a psychological outlook "grandeur" 3) could be communication (latex etc,) but often not.

Its easier to visualize without being finite or infinite if you treat it as a fluid or gas. We use the ideal gas laws to model expansion. As the volume increases, density decreases. There doesn't need to be any outside for this to work. Nor is there any requirement for a finite universe. This works in both cases. As the temperature reduces roughly the same everywhere expansion maintains a homogeneous and isotropic adiabatic expansion.

the thread where you specifically included block on the OP. http://www.scienceforums.net/topic/98845-models-for-making-sense-of-relativity-physical-space-vs-physical-spacetime/page-1 Though a seperate thread may be better on just block itself. Although Memmammal and I have roughly the same understanding on presentism, eternalism there is little point.

I found using pmatrix a little easier than matrix latex. That might work better for your generator which I don't use.

He certainly isn't aware that increasing pressure increases gravity. Lol can you imagine the affect on weather systems...

no both inflation and expansion are homogeneous and isotropic in terms of expansion. An easy way to understand the difference. Draw a right angle triangle. Now in the homogeneous and isotropic case increase the distance on each leg equally. All angles are preserved. In the isotropic case apply expansion only to 1 leg. All angles are not preserved. this results in angle changes

excellent point. The reason I liked the second analogy over the Rubber sheet is that it immediately introduces freefall due to curvature. Rather than force which the rubber sheet implies. The straight x line showing "no gravity" or rather no potential gradient. This being your Euclidean frame. When you add curvature you have in the freefall case potential gradient. Now both models do show this but in the last case, the freefall motion acceleration is better shown as a consequence of curvature rather than force. All the required details to calculate the spacetime geodesics via parallel transport can be demonstrated using two parallel gridlines and how parallel transport is lost due to curvature. That model tool is far more flexible than described on the video. A side note using mass density is only one part of the stress tensor "which tells space how to curve" there is also vorticity and flux. For the case of freefall we set those two terms at zero. the x line in the video will be your spacetime geodesic, The best part is the spacetime graph method simply shows geodesic motion without implying a materialistic component "rubber" to spacetime but sticks with the geometry. As far as tensor density you can't have less than zero unless zero is assigned at some arbitary higher value. Particularly on the scalar quantities. For that matter you require a multi particle system to have a stress tensor. However its simply your SM particles, not spacetime itself. Which the rubber sheet tends to imply through misconceptions.

No the two cases would not be identical. A universe with a centre and expanding outward is inhomogeneous and anistropic. Has a preferred location and direction. Expansion data shows the expansion as homogeneous and isotropic. Geometrically the two are dinstict in preserving angles. Ordinarily I would refer you to the balloon or raisin bread analogy but your post indicates your already familiar with them

I liked that vid thanks for sharing.

That isn't the intention. The intention is simply making sure we are all on the same page. Particularly on how those two terms are being used. I liked your last post Memmammal. You seem to be far more familiar with block arguments. Is my understanding between presentism and eternalism correct? Block isn't something I've spent a lot of time debating. If I made any errors in my analysis I would definetely welcome corrections. If Tim wishes to keep block out of this thread, throw your assessment of my understanding onto the block thread.(lol even though the OP includes my poor mans attempt at block argument)