What is the world made of?

Admonit asked us to think about: What is this world made of, ultimately or fundamentally?
(I posted my reply in the wrong place... apologies for the duplication)

I am also interested in the evolution of people's ideas about what the world is made of. I'd love to know more.

Since I rambled, here's my short answer on what, as i understand it, physics says about the question:

Long ago, Democritus said: the world is made of Atoms & the Void.

This was an incredibly fruitful proposition, but now, in its pursuit, atoms & the void have lost their independent existence.

These days, quantum physics suggests answers like:
The world is made of energy.
OR
The world is made of information.
OR
The world is made of correlations.

here's my long answer:
For millennia, physicists have been calling the smallest piece of any given element an “atom,” meaning INDIVISIBLE. But in the late nineteenth century it began to appear that all atoms themselves were made of a few common materials. You can build a Lego house with only one kind of building block, you can write a message in Morse code with only two kinds of symbols, and you can construct the hundred-odd elements of which the world (and we) consist from architectural arrangements of only three kinds of particles. Gold and oxygen, lead and helium, arsenic and calcium--they are all made of the same three things: electrons, protons, and neutrons. In itself, an amazing discovery.

The protons & neutrons together make up the nucleus, which is a hundred thousand times smaller than the atom as a whole. The electron is even tinier. The atom--and thus you and everything that is built from atoms--is mostly as empty as the skies.

Meanwhile Einstein showed that space and time are not independent & eternal but are all part of one thing, which we now call spacetime (special relativity, 1905). Then in General Relativity (1916), he showed that space--emptiness--is affected by what is in it. Spacetime is bent by matter.

But it gets weirder and more amazing. In 1928, Dirac discovered that light could spontaneously become a particle of matter and a particle of antimatter--for example, an electron and a positron. Matter is spontaneously created out of light. It happens all the time and it can go the other way too: if a electron finds a positron, they will annihilate each other in a burst of light--matter becomes light.

This all goes to verify Einstein's famous statement of 1905 that matter and energy are different forms of the same thing
(E = mc^2).

Similarly, when the huge accelerators send sub-atomic particles crashing at each other, where you might expect fragments of broken particles, instead you find a host of NEW particles, far more and bigger than could fit inside the supposedly smashed particle. Matter is created out of the energy of the collision.

So... what is the world made of? "atoms" are not the final answer, and neither, really, are "elementary particles," which can endlessly be turned into each other or created out of energy. (So we don't even need to go into quarks, which are the constituents of neutrons and protons!)
Maybe "energy" is an answer.

But it can't be the whole answer, because one of the facts of quantum mechanics is that things seem to be changed by, or to depend on, observation. As to what that means, or if it means anything, there almost as many perspectives as there are quantum physicists. But the fact is that our most fundamental theory of "what the world is made of" has this feature, that it seems to say that matter on the atomic scale instantly reacts to being observed.

Many of the new wave of physicists who are interested in information theory would say that INFORMATION is what the world is created out of. Their motto is "IT FROM BIT" ("it," as in "i saw it. it was right there" and "bit" being the smallest piece of information, 1 or 0). I wish i could explain this whole point of view, but i don't come close to understanding it, so i can only mention it for the interested mind.

Finally, other physicists have, in wrestling with quantum mechanics, come to the conclusion that the most fundamental thing about the world is CORRELATION--that correlations between objects are more fundamental than the "objects" themselves, which change when they are observed, etc. The most dramatic correlation of quantum physics is the phenomenon of entanglement, where a particle that has once interacted with another particle, no matter how far they ultimately separate, acts as if it is responding to measurements done on its faraway friend.

You can see why people begin to think religion and quantum physics have something to say to each other, and i definitely caught echos of quantum physics in the two beautiful posts on "the epistemological role of love" and "we are what we behold." Not to mention the world beginning with "LET THERE BE LIGHT," or "IN THE BEGINNING WAS THE WORD."
A disclaimer, though: it always seems to be a mistake to tie religion down to science, because science will always change.