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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Tests and extrapolation.
We didn’t do tests in outer space, but we did tests in all sorts of environments, with all kinds of variables, on earth. If there is no difference in the laws of physics within a thousand situations on earth, there is no reason to suggest it would be different in outer space.
It becomes even more logical when you think of the variables that are different in outer space. There’s less (or at least different) gravitational influence, and there’s no atmospheric pressure. But there’s a lot of variation in atmospheric pressure on earth, and that doesn’t influence physics laws.
All this was enough to be pretty damn sure, but we weren’t a 100% (relatively speaking, scientists always doubt) until we sent shit into space.
So it depends on the specific “Physics law” you are talking about. Because we have actually done a number of space launches specifically to figure out how stuff worked up there, especially in the early days.
But a lot of our understanding of physics already came from looking at stuff in outer space *long* before we ever *went* to space.
For example, it was from our understanding of gravity that people calculated that there must be a planet out past Uranus, and they even calculated exactly where it *should* be. So astronomers pointed their telescopes where the physicists told them to. That unknown planet?
Neptune.
So had every reason to expect we understood how gravity in space worked.
The same goes for electromagnetism, we discovered the Earth’s magnetic field and understood its interaction with the Sun and other sources of carges particles. Long before we went to space.
That means we already understood how two of the fundamental forces of the universe worked in space (the other two have to do with tiny atomic scales stuff, which we had no reason to expect to change, either)
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.
We don’t.
Physics doesn’t allow us to “know” things. Physics allows us to make educated guesses. Someone really clever suggests a theory that *seems* to work. The more it seems to work, the harder we try to disprove it by finding a situation where it fails. The further we go without being able to disprove the theorem, the more confident we become of its validity.
Now, two things:
First, just because a certain law of physics is shown to *not* hold universally doesn’t make it useless. Newtonian mechanics doesn’t work in situations with really fast velocities, or really large masses. Still, it’s the framework NASA uses to land spacecraft on the moon, so in most situations it’s super good enough.
Second, *Science in general* isn’t in the business of pricing things. If I claim that gravity is *actually* caused by invisible magical pixies, there’s not a thing you can do rigorously disprove that. Science operates based on *reasonable doubt*
Lets say I’m on trial for murder. There’s ironclad camera evidence and a signed confession. Does that prove I did it? No, of course not. I can claim that the murder was committed by a robot replica of me from the planet Zorg, and no one can disprove it. Is it reasonable to believe that? Nope, of course not.
In the same way, we assume (some of) the laws of physics behave the same way everywhere in the universe, because that’s the reasonable assumption given our experience.
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