Today, I want to riff on Sean Carroll's stimulating contribution to 13.7 this past weekend by bringing up a few open scientific questions that are particularly baffling.
These are the kinds of questions that may not be answerable, which brings us to the complementary side of the fear of knowing — the fear of not knowing. How do we deal with questions that have no answers? They also play an essential part in our search for meaning, be it through the sciences, the arts and, of course, different modes of spiritual devotion.
Let me first write down the challenges (possible unknowables) and then list what it would take to overcome them from a scientific perspective:
- We can't know what's beyond our cosmic horizon, the bubble of information defined by the distance light has traveled since the Big Bang, around 46 billion light-years.
- We can't explain in deterministic fashion the essential randomness that takes over at the quantum level, having to accept that the possible outcomes of a measure are probabilistic.
- We can't construct a self-referential logical system that is closed, in the sense that every statement within that system can be proved, as the Austrian mathematician Kurt Gödel showed with his incompleteness theorems.
- A computer cannot include itself in a simulation; it is thus impossible in principle to simulate the universe as a whole, since the simulation would by necessity include itself.
- Humans may be cognitively impaired in understanding their own consciousness, a problem known in the cognitive neurosciences and related philosophical discussions as the "hard problem of consciousness."
This is just a sampler, as I covered some of these in my last book and revisit them in my upcoming book, The Simple Beauty of the Unexpected. Of course, the notion of an unknowable must be considered with care, given that what may seem unknowable today may become knowable tomorrow. However, at least for the examples above, this unknowable-to-knowable transition would require very fundamental revolutions in our understanding of physical reality, such as the following:
- Faster-than-light travel needs to be possible, or inter-universe-connecting traversable wormholes need to exist and be stable. (Wormholes are somewhat like tunnels in spacetime that are mathematically possible in Albert Einstein's Theory of Relativity. The reader may think of them as an imaginary network of subway tunnels across space, an image Arthur C. Clarke explored beautifully in 2001: A Space Odyssey. Unfortunately, current models of wormholes call for very exotic physics, bordering on the implausible.)
- A whole new way of thinking about quantum physics needs to be developed, one that explains the apparent randomness of results from measurements. Previous efforts based on local "hidden variables" theories don't work.
- A new, self-contained logical structure for mathematics would have to be created, an apparent impossibility.
- New concepts in computing, where a machine can simulate itself, would need to emerge, an apparent impossibility.
- The human subjective sense of self that baffles the cognitive neurosciences would have to be explained as an emergent property of complex neuronal activity.
In one way or another, all these unknowables share one common characteristic, in that they require achieving some sort of total knowledge, an all-encompassing explanation of a given physical and/or biological system from within:
- To know the universe as a whole, without being able to step outside of it.
- To explain all possible results in a quantum system, including the relative probabilistic weight for each of them.
- To have a complete mathematics.
- To have a complete simulation, one that includes itself.
- To have the brain explain itself in its entirety.
It is the fish-in-a-bowl dilemma. How can we acquire an outsider's view of a system that we belong to without compromising what we see? As we confront such questions, we are like the fish in a bowl. We can and should use our creativity and ingenuity to come up with possible scenarios that can give us at least a partial view of what lies "outside" the bowl, a scaffolding that allows us to step out and look back in. But we should also realize that unanswerable questions are part of how we make sense of the world and learn from our limitations, without fear of not knowing all answers.
Marcelo Gleiser is a theoretical physicist and cosmologist — and professor of natural philosophy, physics and astronomy at Dartmouth College. He is the co-founder of 13.7, a prolific author of papers and essays, and active promoter of science to the general public. His latest book is The Island of Knowledge: The Limits of Science and the Search for Meaning. You can keep up with Marcelo on Facebook and Twitter: @mgleiser