Like was there some concrete validation which proved that the laws work same outside the atmosphere of the Earth in space too? Since space was an unknown factor in early days
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Because of something called the Cosmological Principle, which states that–over large spaces–the universe is homogenous (more or less the same stuff/distribution of stuff everywhere) and isotropic (uniform in every direction). This was first put forward by Newton in the *Principia Mathematica*, and we’ve been building from it ever since. What made the *Principia* so foundational (among many other things) was that Newton was able to lay down the convincing (and ultimately correct) theory that the motion of celestial bodies was described by gravity everywhere. We of course already knew how gravity worked *on* a planet, and the inverse square law accurately describes gravity in both situations (bodies on a planet, motion between planets and other bodies). So that’s a very big clue that physical forces behave everywhere in the same way.
So far, all of our observations seem consistent with the Cosmological Principle. It is perhaps impossible to say *for certain* that there isn’t some supremely distant region of the universe (beyond our cosmological event horizon) in which physical laws are different, but so far we’ve never observed anything like that in the 90-ish billion lightyear swath of universe that we *can* observe.
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