In general relativity, the laws of physics can be expressed in a generally covariant form. In other words, the real world does not care about our coordinate systems. However, it is often useful to fix upon a particular coordinate system, in order to solve actual problems or make actual predictions. A coordinate condition selects such coordinate system(s).
Famous quotes containing the word conditions:
“What is Americanism? Every one has a different answer. Some people say it is never to submit to the dictation of a King. Others say Americanism is the pride of liberty and the defence of an insult to the flag with their gore. When some half-developed person tramples on that flag, we should be ready to pour out the blood of the nation, they say. But do we not sit in silence when that flag waves over living conditions which should be an insult to all patriotism?”
—Anna Howard Shaw (18471919)