The expansion of the Universe as we know it today is one of the most fascination aspects of the physics behind phenomena of our Universe. The metric expansion of the Universe is defined as an intrinsic expansion phenomena where the scale of space itself changes. Only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales. This expansion model is only valid for large scales (roughly the scale of galaxy clusters and above). At smaller scales matter has become bound together under the influence of gravitational attraction and our local galaxy is not expanding at the metric expansion rate as the universe ages.
NOTE: many vCalc equations are embedded throughout vCalc descriptive pages like this page. Even though they may not stand out in the text, if you hover over the name of an equation it will likely be linked to an actual, pop-up executable equation. For example:
Most everyone has heard of the law which governs travel nearing the speed of light. We know the speed of light (2.99792458E8 m/s) is a limit placed on velocity. The speed of light is an absolute limit -- or is it?
"While special relativity prohibits objects from moving faster than light with respect to a local reference frame where spacetime can be treated as flat and unchanging, it does not apply to situations where spacetime curvature or evolution in time become important. These situations are described by general relativity, which allows the separation between two distant objects to increase faster than the speed of light, although the definition of "distance" here is somewhat different to that used in an inertial frame. The definition of distance used here is the summation or integration of local co-moving distances, all done at constant local proper time. For example, galaxies that are more than the Hubble radius, approximately 4.5 gigaparsecs or 14.7 billion light-years, away from us have a recession speed that is faster than the speed of light. Visibility of these objects depends on the exact expansion history of the universe. Light that is emitted today from galaxies beyond the cosmological event horizon, about 5 gigaparsecs or 16 billion light-years, will never reach us, although we can still see the light that these galaxies emitted in the past."1
This is almost unnerving in its implications. Because the expansion of the Universe is increasing more for areas of the Universe further away from us, there are parts of the universe that we can never know. The light from these distant parts of our Universe can never reach us as the distance in between us these distant parts of the galaxy is growing faster than the speed of light. The expansion of the universe, in a more general estimate is 67 km/sfor every million parsecs further away from us.
Our Universe is expanding at a greater and greater rate for distant objects further and further from us. The edge of the Universe is expanding and in a sense it is expanding into nothing, as time and space are essentially created where the Universe expands at its limits.
The time it would take to travel distances in our local Universe are mind boggling: Astro Travel Time
Likewise, the distances are immense: Astro-Distances
It is not the distance or the time or the physics that prevents us from visiting the stars, it is our all-too-limited lifetimes as humans. The extremes of distances and times expressed by these vCalc equations can only be surmounted by science fiction leaps in technology.