We find no sense in talking about something unless we specify how we measure it; a definition by the method of measuring a quantity is the one sure way of avoiding talking nonsense.
Hermann BondiThe scientist โฆ 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.
Hermann BondiThe test of science is not whether you are reasonableโthere would not be much of physics if that was the caseโthe test is whether it works. And the great point about Newtonโs theory of gravitation was that it worked, that you could actually say something about the motion of the moon without knowing very much about the constitution of the Earth.
Hermann BondiAn 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.
Hermann Bondi