Practical Metaphysics

Introduction

Metaphysics asks questions no experiment can settle: what is real, what is fundamental, whether anything can come from nothing. Most people dismiss them as impractical. This essay explains why they are worth taking seriously, offers a starting point for asking them, and then gives my own answers.

1. Is Metaphysics Practical?

For many, metaphysics is souls, odd conversations about consciousness, and crazy people. They see no practical value in metaphysics, because what cannot be falsified by testing shouldn’t be trusted. Our best guard is falsifiability. Science is built on this rule, and it protects us from staking important decisions on bad ideas. Since metaphysics cannot be empirically tested, many believe the subject can be safely ignored.

But ignorance has consequences. Consider:

When Georges Lemaître, a physicist who was also a priest, proposed in 1931 that the universe began from a “primeval atom,” Fred Hoyle resisted in part because a beginning seemed to invite a creator. He backed a steady-state universe with no beginning, and on BBC radio he mockingly named his rival’s idea the “Big Bang.” In 1965 the discovery of the Big Bang’s leftover heat settled which of them was right, but not why there was anything to begin. But Hoyle never accepted the Big Bang, and he defended versions of the steady state until his death in 2001. His belief that there could be no beginning had decided the question for him before the evidence arrived.

Many people are functional physicalists: they act as if only the physical exists, even if they would never say so. They wave off metaphysical conversations and are quick to dismiss the people who start them. Physicalism itself is a metaphysical position, and it can’t be falsified. Every experiment measures something physical, so no experiment could reveal something that isn’t. A physicalist might shrug: so what? I live in a physical universe. But as Hoyle’s case shows, metaphysics steers the search whether we notice it or not.

The physical world demands metaphysical assumptions. Why does anything exist at all? What caused the Big Bang? Was there a first cause? These questions don’t come only from religion and superstition. They come directly from experience.

So metaphysics can’t be avoided, and the practical objection is only half right. Untested ideas shouldn’t be trusted. But trusting isn’t the only thing we do with ideas. We also search with them.

2. Steered Search

In the 1970s the computer scientist Edward Fredkin became convinced that the universe is a computer: space as a grid of cells, updated step by step by simple rules. No one could test that. But he followed it. The basic laws of physics can run backward without losing information. If the universe is a computer, Fredkin reasoned, then computation must be able to do the same. Ordinary logic can’t: an AND gate that outputs 0 doesn’t tell you what went in. So with Tommaso Toffoli he worked out reversible logic, including the gate now named after him. In 1981 Fredkin helped organize the conference at MIT where Richard Feynman argued that simulating nature would take a computer built on quantum mechanics. Reversible gates became basic building blocks of the quantum computers that followed. The universe may not be a computer. The belief still led somewhere real.

Science could not have told Fredkin what to look for. It can test a hypothesis, but it is silent on which hypothesis to make. That choice comes from somewhere else: hunches, analogies, beauty, and beliefs about ultimate questions. Those beliefs are metaphysics, whether or not we call them that.

Discovery is a search through possibilities, and there are two ways to search: near and far.

Searching near means exploring what is already at hand. Engineers live here. Thomas Edison tested thousands of materials for a light bulb filament before settling on carbonized bamboo. The Wright brothers built a wind tunnel in 1901 and tested some two hundred wing shapes. Near search is systematic, and it works.

Searching far means imagining what might be, with no guarantee it connects to anything. Theorists live here. In 1854 Bernhard Riemann described geometries of curved space, which no one had a use for. Sixty years later they were exactly what Einstein needed for general relativity. G. H. Hardy wrote in 1940 that “no one has yet discovered any warlike purpose to be served by the theory of numbers.” Today it secures nearly every purchase made on the internet.

No one could have predicted which far ideas would pay off, least of all the people who had them. We don’t know where the next breakthrough will come from, and near search alone only finds what is close to what we already know. Demanding that every question be testable before we explore it rules out much of the exploration space.

So dismissing metaphysics is an incorrect application of the rule of falsification. Falsifiability is a rule for judging claims: deciding what to trust and act on. It is not a rule for searching: deciding what to wonder about and where to look. Applied to judgment, it guards against dogma. Applied to search, it rules out questions before anyone knows where they lead.

Asking a question is not the same as making a claim. Karl Popper, who made falsifiability famous, used it to separate science from everything else, not to separate the worthwhile from the worthless. He held that ideas outside science can still be criticized. Falsifiability belongs at the gate where an idea becomes something we trust and act on. It doesn’t belong at the edge of where we are willing to look.

3. Starting Point

Reality is infinite. By reality I don’t mean the observable universe, which has an age and a horizon. I mean everything that exists, including whatever, if anything, lies beyond or hosts our world.

The oldest argument I know comes from Archytas, a Greek mathematician and a friend of Plato, around 400 BC. Imagine standing at the edge of the universe and throwing a spear. Either it flies on, and there was more beyond the edge, or something stops it, and that something is beyond the edge. Either way, the edge wasn’t the end.

History has played that thought experiment out many times. The Earth was the center of everything, then the Sun was. In 1920 astronomers still seriously debated whether our galaxy was the whole universe. In 1924 Edwin Hubble measured the distance to the Andromeda nebula and showed it was another galaxy far outside our own. There are now thought to be hundreds of billions. Every edge we have found so far has moved.

The physicist David Deutsch moves the edge further with an argument from computing. A quantum computer factoring a 250-digit number, he calculates, would draw on something like 10⁵⁰⁰ computations at once. The visible universe contains only about 10⁸⁰ atoms. If the visible universe were all of reality, it wouldn’t hold the resources to do the calculation. “Who did factorize it, then?” he asks. “How, and where, was the computation performed?” His answer is a multiverse far larger than anything we can see. Many physicists doubt that answer, but the question stands.

Computers point beyond our world in another way too. Players have built working computers inside Minecraft, a computer running inside a program running on a computer. In The Computation Conjecture I argue that if worlds can host worlds, we have no principled reason to think the nesting stops, and no way to confirm from inside that we are at the bottom.

The usual objection is that something finite doesn’t need to have an edge. The surface of a sphere is finite and has none, and space itself might close up the same way. But even a closed universe begs for a cause. For me that is the most convincing argument for infinity: the problem of the first cause. Everything we have explained so far has a cause, and the Big Bang raises the same question: what caused it? A first cause would have to be the one thing with nothing behind it. Every argument I’ve seen just moves the question out a step. So I hold that the chain of causes has no first link, and that reality has no end.

Minds are finite. Every mind has limited memory, limited time, and a limited vantage point. It sees the world through models, and as I argue in More Better, every model leaves something out.

The confident ones are often the most instructive. In 1894 the physicist Albert Michelson declared that “the more important fundamental laws and facts of physical science have all been discovered,” and that future discoveries “must be looked for in the sixth place of decimals.” The next year Wilhelm Röntgen discovered X-rays. Radioactivity followed in 1896, the electron in 1897, quantum theory in 1900, and relativity in 1905. Michelson was one of the best experimenters alive, and his own work helped lead to relativity. He wasn’t foolish. He was finite, and he couldn’t see what he couldn’t see.

Worse, a mind inside a world only has access to that world’s rules. A character in Minecraft would find redstone just as fundamental as we find electricity. In What Is a Computer? I call this observer locality: a closed world looks fundamental from inside, whether or not it is.

Put them together. A finite mind cannot hold an infinite reality. Whatever it knows, there is more it doesn’t, and it can’t tell from inside how much more. So any final answer about the whole of reality claims more than a finite mind can support.

That is why I think this starting point is rational rather than just humble. It doesn’t even depend on reality being infinite. A finite reality vast enough to exceed every mind leads to the same conclusion. Infinity only makes it permanent: no amount of learning closes the gap.

4. My Views

Here’s what I currently find attractive.

1. Reality is infinite, and minds are finite. See section 3.
2. Information is more fundamental than matter. The same computation runs on transistors, brass gears, water in pipes, or redstone. Everything physical about it changes, and the computation survives. What survives every change of substrate looks more fundamental than the substrate. It’s a strong claim, and I hold it open to refutation. Every computer I know of runs on something, and I haven’t seen an account of information running on nothing. If the two turn out to depend on each other, or something deeper underlies both, I’m wrong.
3. Everything that can exist does exist. This is the principle of plenitude, and it goes further than infinity. An infinite reality need not contain everything: there are infinitely many even numbers, and none of them is odd. I find plenitude compelling, but I can’t establish it.
4. Everything is discovered, not created or invented. I’m drawn to the view that creativity is a search over information space. I take inspiration from computation since it’s easy to see infinite combinations in computer science. Look closely at an invention and you find a new arrangement of old things. Gutenberg’s press combined the screw press used for wine and olives, a goldsmith’s skill at casting metal, and oil-based ink. And inventions keep turning up in more than one place at once. Newton and Leibniz each developed calculus. Darwin and Wallace each arrived at natural selection. Alexander Graham Bell and Elisha Gray filed papers for the telephone on the same day in 1876. That is what you would expect if the ideas were already there to be found, and the people nearest to them found them.

Conclusion

Metaphysics has practical value. It steered Fredkin toward reversible logic, and it steers anyone who assumes only the physical exists, whether they notice or not. It has dangers too. Hoyle’s belief that there could be no beginning decided the question for him before the evidence arrived. The difference isn’t whether we hold metaphysical views, since we all do. It is whether we use them to search or trust them as answers, and whether we let the world correct us.

That is how I try to think about my ideas. None of this is final, and that is the point: in an infinite reality, the search can go on.

Further Reading

• What Is a Computer? and The Computation Conjecture, for the argument from computation and observer locality.
• More Better: Modeling and the Frame Problem, on what every model leaves out.
• Thinking About Thinking, on fallibilism as a habit of mind.
• David Deutsch, The Fabric of Reality (1997), especially chapter 9, for the argument from quantum computation.
• Karl Popper, Conjectures and Refutations (1963), especially “On the Status of Science and of Metaphysics,” on how untestable ideas can still be criticized.
• Arthur Lovejoy, The Great Chain of Being (1936), which named and traced the principle of plenitude.
• Jürgen Schmidhuber, “A Computer Scientist’s View of Life, the Universe, and Everything” (1997), which argues that all computable universes exist.
• Robert K. Merton, “Singletons and Multiples in Scientific Discovery” (1961), on why the same discovery keeps turning up in more than one place.