The significant implication of Einstein's special principle of relativity is that
Explanation:
In the last paragraph, the author states: “its significance laid in its assertion that absolute Galilean motion or absolute velocity must ever escape all experimental detection.” That means that Galilean motion or absolute velocity (some physical phenomena) cannot be experimentally ascertained (option 3). Option 1 is true according to the passage but gives partial information (meaningless in the entire realm of physical phenomena not only mechanics). It also uses the past tense whereas the author speaks of it as a scientific fact. Option 2 can be deduced if modification is understood as an extension or addition here but the statement is not a significant implication of Einstein’s special principle of relatively. Option 4 is not supported by the passage.
Hence, the correct answer is option 3.