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Reply	Jon-Richfield says: They use whatever they can get. That is what scientists do in general. There is a whole range of classes of evidence for distance and time, ranging from parallax, classes of stars and their inferred luminosities, red shift, you name it, they use it if they can. Would you like to elaborate on your question? I am unsure what you have in mind.  (no votes) Tags: physics, cosmology.
	posted on 2011-01-05 14:02:45 | Report abuse

Reply	Georg says: In general, they make use of so called "clocks". Georg    (no votes) Tags: physics, cosmology.
	posted on 2011-01-09 14:56:04 | Report abuse