I mean, we can only study things on Earth… But everything that has crashed here has been what we expect, and everything we can see looks like what we expect, so probiably.
The entire point of science is to extrapolate conclusions about things you can study to the things you cant, and worry about being wrong only when someone discoverers something inconsistent.
Astronomers send the light from distant stars through a device called a spectroscope. It is like a prism, and breaks the light into individual frequencies. There are peaks in the spectrum that are specific to the atoms that emit the light. This is how astronomers determine what a distant star is made of. This is also how helium was identified in the spectrum of the sun before it was identified on Earth.
As I said, the spectrum from an atom is tightly coupled to physical constants that control quantum behavior. So if the arrangement of spectral lines from a distant star are the same as the spectral lines we see on earth, we can infer that those physical constants are the same across the universe.
There is a principle in science called the [cosmological principle](https://en.wikipedia.org/wiki/Cosmological_principle) which basically (ELI5 version) says the universe is the same everywhere when viewed on large scales. Matter distribution, matter composition and so on.
Of course, we have not been everywhere in the universe but I doubt there are many scientists who would disagree with that. The periodic table which describes the elements would be the same everywhere in this universe.
So far no one has made any observations to suggest otherwise. Everything at the edge of our vision (so billions of lightyears away) seems to be working according to the same principles we formed observing our immediate neighbourhood (the earth and solar system).
One of the main guiding ideas in physics is indeed that the laws of physics work the same everywhere, and it seems to hold.
There are some hints that maybe, just maybe, some things change in time, bit nothing concrete. If anyone actually gets proof of that, it’s an easy Nobel.
Mostly yes. But there are some atoms in the universe at temperatures that do not naturally occur on Earth. So those are going to behave differently (but if you somehow took an atom from Hearth to those temperatures, it would be the same).
Then you also have difference in just how common some atom is. For example, Helium is one of the most common atoms in the universe, but it’s comparatively pretty rare on Earth.
“Atom” is the name we give to an, in some ways arbitrary, level of magnification under which we describe how ‘energy’ behaves. An atom is not a ‘thing’ in the way we imagine, it is much rather a system of predictable and universal behavior.
The reason we’ve picked these kinds of behaviors and their interactions as fundamental is because they appear to be just that.
So, atoms must be the same across the universe, because that’s one of the reasons we use this kind of model in the first place.
Other ideas and systems could be devised (and have been devised) to talk about the rules of reality on that level, but if they were only applicable, say, on earth, they would be much less useful.
Who is to say atoms on earth are the same? Just all the ones we have measured have been the same, and so we draw a natural conclusion that they all must be the same.
We don’t hold it true to be an undeniable fact. We will question anytime something would change if it does, but it hasn’t yet. That is science. We change our understanding due to observations.
Most objects we have tested have been the same. We have tested hige pressures, zero pressures, high and low temperatures. All of these are typical variables in space. Radiation levels, etc. What we do not account for is things like dark matter as this is still an uncertain topic, and other things closer to quantum physics. I am severely uninformed about this myself, but I hope to spend some weeks or months to get as up to date with developments as I can grasp myself.
But we can only test what condotions we can create. And even creating them through artificial means may not create natural universe conditions precisely. But what we have tested all come out to be the same. And we see no signs of an altering of morphology of atoms through these conditions outside of the realm of possibility of what we currently understand.
So yes, for now, we understand it to be a nucleus of an atom, and electrons of an atom, all adhere to specific conditions no matter where in the universe you are. A hydrogen atom will always absorb energy similarly and emit energy similarly throughout the universe, and we can detect it and understand it to have hydrogen properties no matter where in the universe the hydrogen atom is.
That we know of, of course. Who knows, maybe there has been a recent paper which observes some changes, or may be one in the future with better instruments to observe atoms closer and closer to a black hole, or what happens to atoms during a nova. Who knows.
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