Frank Wilczek, winner of the Nobel Prize for Physics in 2004, has written a compelling book about the universe: Fundamentals: Ten Keys to Reality.
Here's a passage from his Afterword chapter that I like a lot. It is indeed strange that we make such a division between internal and external worlds, when in truth there is only one thing going on.
The child of our introduction, now an adult, may come to understand the fundamental conclusions that science, following its radically conservative method, reaches about the physical world.
Then she is prepared to revisit the starting point of her adventure with reality, and to view it afresh, in the light of her knowledge.
She can choose, in this sense, to be born again.
It is not a trouble-free choice. It is disruptive. But the choice is unavoidable, as a matter of integrity. You've seen in this book a small sampling of the evidence for the scientific fundamentals. That evidence is overwhelming and indisputable.
To deny it is dishonest. To ignore it is foolish.
And so our heroine comes to reconsider the division of experience into internal and external worlds. The fundamentals of science have taught her a lot about what matter is. She knows that matter is built up from a few kinds of building blocks, whose properties and behavior we understand in detail.
And she knows, from direct experience, that scientists and engineers can use such knowledge to make impressive creations.
Her iPhone allows her to communicate instantly with friends around the globe, to tap into humanity's accumulated knowledge at will, and, though pictures and recordings, to snatch her sensory world from time's devouring flow.
She has learned, too, that the special objects she recognizes as other people, and herself, are made from the same sort of matter as the rest of the world
Many once-mysterious aspects of living things such as how they derive their energy (metabolism), how they reproduce (heredity), and how they sense their environment (perception), she can now understand from the bottom up.
For we now understand, in considerable detail, how molecules -- and ultimately, quarks, gluons, electrons, and photons -- manage to accomplish those feats. They are complicated things that matter can do, by following the laws of physics. No more, and no less.
These understandings do not subtract from the glory of life. Rather, they magnify the glory of matter.
In light of all this, it is radically conservative to adopt what the great biologist Francis Crick has called "the astonishing hypothesis": that mind in all its aspects, is "no more than the behavior of a vast assembly of nerve cells and their associated molecules."
Indeed, this amounts to extending Newton's method of analysis and synthesis to brains. Experiments in neurobiology have been following that strategy aggressively.
And although our understanding of how minds work is still incomplete, so far, in thousands of sensitive experiments, the strategy has never failed. No one has ever stumbled upon a power of mind in biological organisms that is separate from conventional physical events in their bodies and brains.
Even in their most delicate experiments, physicists and biologists never had to make allowances fo what people nearby were thinking. By now, any failure of Crick's "astonishing hypothesis" would be astonishing.
Upon that realization, the division of experience into internal and external worlds comes to seem superficial. For babies, that division is a useful discovery, and for adults, it is a convenient rule of thumb. But our best understanding suggests that there is just one world, after all.
Matter, deeply understood, has ample room for minds. And so, also, it can be home to the internal worlds that minds house.
There is both majestic simplicity and strange beauty in this unified view of the world. Within it, we must consider ourselves not as unique objects ("souls"), outside of the physical world, but rather as coherent, dynamic patterns in matter. It is an unfamiliar perspective.
Were it not so strongly supported by the fundamentals of science, it would seem far-fetched. But it has the virtue of truth. And once embraced, it can come to seem liberating. Albert Einstein spoke to this, in a kind of credo:
A human being is a part of a whole, called the Universe, a part limited in time and space. He experiences himself, his thoughts and feelings, as something separated from the rest, a kind of optical delusion of his consciousness. This delusion is a kind of prison for us.