Whatever do you mean by that?
There are proponents of us being holograms. I don't believe in that theory but that theory is even gaining traction with respected physicists.
If we, by chance, are a hologram then nothing in our perception is physically real, only virtually real. That would include encounters with other civilizations.
I guarantee you ... they know about hydrogen, and helium, and lithium and all the rest
As for the elements being universal, yes to the extent we know them and their light emissions from other celestial measurements.
That doesn't guarantee that other life forms would perceive them as we do. What if their world is made of antimatter? What if they have no interest in atomic theory as we use it?
“If we, by chance, are a hologram then nothing in our perception is physically real, only virtually real.”
The hologram theory is a simplification of what is being proposed—because we don’t have very good language to describe it.
One of the best analogies I have read is this:
Imagine that what we call “reality” is a computer screen with icons on it.
We can accomplish all the tasks we need by clicking on the appropriate icons and using whatever software is there.
However, no matter what wonderful “things” we can accomplish with that method we are not discovering “the nature of the universe” because we have no access to the actual 0s and 1s that make up the software—we do not even know they exist.
There could be alien civilizations that “discovered” the 0s and 1s and learned how to “hack” the software so the screen could be made to do “impossible” things.
Our “laws of physics” would just be the “laws” governing the computer screen and the icons, and would have nothing to do with the underlying structure supporting them.
Then they're not getting here, and we're not getting there. They're not just far away, they're in a completely different and incompatible reality from us.
What if they have no interest in atomic theory as we use it?
Then they fall into the category of slightly smarter than a dog. Seriously ... it's not a matter of "atomic theory as we use it". It's a matter of atomic theory full stop. There are universals. Atomic structure is one of them.
If we, by chance, are a hologram then nothing in our perception is physically real, only virtually real.
Now you're getting into some weird realms of philosophy and theology (yes, I read your PM) ... But almost every theistic religion, including my Christianity, basically holds that we exist because God said so, and the universe is the way it is because God wants it that way. As scientists, we're working out exactly what God said ... as engineers we're finding ways to manipulate what God said to our purposes. And any "aliens" we might meet which come from our physical reality are working with the same things God said that we are ...
And then there's the belief that "aliens" are really beings from a non-physical part of what God said; that they're really demons posing as flying-saucer pilots ... And if that's the case, I actually agree that we have no hope of really understanding them and that they're not bound by the laws of physical reality.
On the subject of universals, pure mathematics is another, as is basic physics. Pi only equals 3.14159265etc in base-10. But pi equals the circumference of a circle divided its radius. The gravitational, electrical, and magnetic forces are all inverse radius squared phenomena. Everywhere. There are others ... break these, and the universe just doesn't work any more.