Reality → Scale → Macro world → Universe
| Some rounded numbers to remember | |||
|---|---|---|---|
| speed of light | 300,000 km/s | ||
| distance to moon | 300,000 km | or | 1 lightsecond |
| distance to sun | 150 million km | or | 8 lightminutes |
| distance to nearest star | 4 lightyears | ||
| diameter of our galaxy | 100,000 lightyears | ||
| distance to nearest galaxy | 2.5 million lightyears | ||
| oldest detectable signal | 14 billion years | ||
At a distance of 2.5 million lightyears, the Andromeda galaxy is the nearest large spiral galaxy outside the Milky Way. Andromeda and Milky Way are the most massive of a few tens of galaxies belonging to the Local Group, which measures about 10 million lightyears. Many of the smaller and irregular-shaped galaxies of the Local Group are satellite galaxies of the massive galaxies. Our local group together with about 100 other 'local' groups form the Local Supercluster, whose size is about 100 million lightyears. There are believed to be millions of superclusters. Apparently, these clusters are part of a still larger structure that looks like an irregular three-dimensional net of filaments (also described as ‘walls’ or ‘sheets’) with huge voids between them. Light from these largest observed structures has travelled billions of years to us, so what we observe is a long gone structure, not the present structure [1] .
The cosmic microwave background radiation and the related big bang theory suggest an age of the universe of 13.8 billion years. During this time, light might have traveled a distance of tens of billion lightyears; we don't know the true extension. Some cosmologists and astrophysicists suggest fantastic, but unprovable, multi-dimensional branes and multiverses as answer to questions like "what existed before the big bang?" or "what does the universe expand into?".