Answering this question is a part of reality, as are tortoises, turnips and torrential rains. The question might be urging us to say that ultimately reality is “nothing but” swirling electrons, waves, particles and strings, that only physicists have the faintest idea of what they are talking about.
I reject such “nothing buttery” – for in reality there also exists promises and injustice, mathematical truths and logical reasoning, remorse and guilt; and these cannot be understood as “nothing but” the movement of particles. Indeed, there is no convincing understanding in terms of neurological changes of how we experience the world. After all, bats, cats and rats experience the world, but however much we learn about the physical changes in their neurological systems, we shall not know what it is like to have such creaturely experiences.
"Bats, cats and rats experience the world, but however much we learn about the physical changes in their neurological systems, we shall not know what it is like to have such creaturely experiences."
We can look back and see how past philosophers have dealt with this question. All these comments, though, need caveats and nuances: philosophers are not easily shoe-horned into little boxes; their thoughts need deep discussion to establish quite what the arguments are, how the conclusions should be understood and so forth. There’s a theory called Idealism; it is most often associated with a philosopher of the 17th Century, namely Bishop George Berkeley (1685-1753). He argued that all that exists regarding reality are sets of ideas and the spirits or souls or minds that have those ideas: “to be is to be perceived, or to perceive”.
When we talk about material objects such as tables and chairs what we’re really talking about are collections of ideas. Does the tree exist when unperceived by us, when we have no ideas? There’s no need to worry; God is always having such ideas, though there is an obvious question about how our ideas and God’ s relate. That may misleadingly remind us of Plato (c424-347BC), who thought that reality consisted of the eternal forms or ideas, but those forms or ideas are very differently understood from Berkeley’ s ideas. For both philosophers, though, our commonsense view of the material world around us as reality is mistaken.
"Monads are true unities, akin to what we may think of as the “ego”. Each one of us is a ‘rational monad."
Another philosopher of Berkeley’s time was Gottfried Wilhelm Leibniz (1646-1716), who understood the material world, the tables, trees and turnips, as well-founded phenomena grounded in the reality of monads. Monads are true unities, akin to what we may think of as the “ego”. Each one of us is a ‘rational monad’; the material world is grounded in bare monads; in some way, all monads represent the whole universe, “burdened with the past, pregnant with the future” . Further, this world is but one of an infinite number of possible worlds; this one is the best possible, having been chosen by God — an idea that was much mocked by Voltaire in Candide (1759).
https://www.youtube.com/embed/JF61lhEeGng?wmode=opaque
In the 20th century, an American philosopher, D K Lewis (1941-2001), tended to see these other possible worlds as just as real as this world in which we exist. There are other worlds in which exist “counterparts” of us, remarkably similar to this one. There are yet other worlds which are radically different from this; there are worlds with no life at all, maybe worlds such that the only life forms are amoeba.
"Many qualities of the tables and chairs, the trees and fleas, which we take to be real, are in fact the result of the interaction between us and the external items in question."
Other philosophers were more commensensical: Rene Descartes (1596-1650) and John Locke (1632-1704), for example, accepted the existence of material objects, though we make a mistake if we think that “out there” there are colours and smells that exist as we experience them, even if no one is present to experience them.
Many qualities of the tables and chairs, the trees and fleas, which we take to be real, are in fact the result of the interaction between us and the external items in question. A well-known commonsense philosopher, though, is G.E. Moore (1873-1958). Moore insisted that he knew that he had two hands, that he knew that there were tables and chairs that existed independently of him, that the Earth existed millions of years before his existence. That Moorean (Mooronic?) stance is obviously extremely different from, say, Bishop Berkeley’s.