On the most usual assumption, ...

On the most usual assumption, the universe is homogeneous on the large scale, i.e. down to regions containing each an appreciable number of nebulae. The homogeneity assumption may then be put in the form: An observer situated in a nebula and moving with the nebula will observe the same properties of the universe as any other similarly situated observer at any time.
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 Hermann Bondi

Quotes from the same author

The scientist … must always be prepared to deal with the unknown. It is an essential part of science that you should be able to describe matters in a way where you can say something without knowing everything.
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 Hermann Bondi
If you walk along the street you will encounter a number of scientific problems. Of these, about 80 per cent are insoluble, while 19½ per cent are trivial. There is then perhaps half a per cent where skill, persistence, courage, creativity and originality can make a difference. It is always the task of the academic to swim in that half a per cent, asking the questions through which some progress can be made.
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 Hermann Bondi
All science is full of statements where you put your best face on your ignorance, where you say: ... we know awfully little about this, but more or less irrespective of the stuff we don't know about, we can make certain useful deductions.
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 Hermann Bondi
[Science doesn't deal with facts; indeed] fact is an emotion-loaded word for which there is little place in scientific debate.
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 Hermann Bondi
An observer situated in a nebula and moving with the nebula will observe the same properties of the universe as any other similarly situated observer at any time.
 See image
 Hermann Bondi