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How do astronomers know that distant galaxies are accelerating?
I saw a program that mentioned Dark Energy, went and looked it up but I still don't get it. Wikipedia says 74% of the Universe is Dark Energy, which we know nothing about. We apparently think this because distant galaxies are moving away from us(their light is red shifted) at a greater rate than galaxies that are closer. So what is the basis for believing that the red-shift is caused by acceleration rather than by some other factor that effects light (e.g., space dust over billions of light-years, or interaction with the background radiation) or acceleration of Earth itself?
1 Answer
- ronwizfrLv 71 decade agoFavorite Answer
The basis for believing that the red shift is caused by the expansion, is that nothing else would work of such large distances. Dust obscures as well as reddens, in a way that is correlated. But for objects far away the distance can be determined using standard candles, like Supernova that have the same luminosity everywhere (give or take a factor of two or three)
The calibration with Supernova has shown that the relation between speed and distance is not constant, but has increased after about 1 billion years. This implies that there is another force at work, besides gravity, one which we don't know anything about yet.
