AI can tackle mathematical problems that have stumped scientists, but physicist Jim Al-Khalili says understanding time may require something that today’s machines lack: imagination.
In his new book, On Time: The Physics That Makes the Universe Tick, Al-Khalili examines why scientists still cannot agree on what time is or explain why it moves in only one direction. He argues that answering those questions may require a new understanding of physics, the kind of conceptual breakthrough he believes remains beyond today’s AI systems, despite their growing mathematical prowess.
“These different descriptions of time are so different that we don’t know how to reconcile them,” Al-Khalili, Distinguished Professor Emeritus in Physics at the University of Surrey in the UK, told IBM Think in an interview.
Al-Khalili, a nuclear physicist and BBC science broadcaster, believes AI could eventually help resolve those contradictions. However, he says answering fundamental questions about the universe still requires human intuition, not just computational power.
Al-Khalili will explore some of these questions at a November 18 event in London, where he will join Juan Bernabé-Moreno, Director of IBM Research Europe for the UK and Ireland, to discuss whether quantum computing could overtake AI as the next major technological breakthrough. The discussion, “The Age of Becoming,” is hosted by Intelligence Squared in partnership with IBM.
According to Al-Khalili, one of the biggest obstacles to understanding time is that physicists still lack a single explanation of what it actually is.
“It’s a real thing. It’s a tangible part of our physical reality,” Al-Khalili said. “It’s not our invention; it’s not just in our minds; it’s not just that thing that clocks measure.”
Al-Khalili’s book explores three descriptions of time that physicists have yet to reconcile. In many equations, time is little more than a number that tracks how things change. Einstein’s theory of relativity tells a different story, treating time as a fourth dimension woven into the fabric of space. Thermodynamics, the study of heat and energy, adds another complication: time has a direction, an arrow pointing from the past toward the future.
Einstein also showed that time doesn’t pass at the same rate everywhere. A clock’s rate relative to another depends on motion and gravity. According to the National Institute of Standards and Technology, GPS satellites need relativity corrections because their clocks run at different rates than those on Earth.
Quantum mechanics, Einstein’s theory of relativity and thermodynamics help scientists make accurate predictions about the physical world. But as Al-Khalili points out, they have yet to produce a single explanation of time that works across all of physics.
Consider what happens when a glass falls onto a kitchen floor. It shatters into pieces, yet those fragments never spontaneously reassemble. The puzzle, Al-Khalili explained, is that many fundamental equations of physics work whether time runs forward or backward.
Physicists generally explain the difference in terms of entropy, a quantity related to the number of microscopic arrangements available to a system. According to the second law of thermodynamics, entropy in an isolated system tends not to decrease.
Al-Khalili thinks physicists have the question backward. Rather than trying to explain why time moves forward when the equations suggest it could run either way, he argues that time may have a built-in direction and that the equations describe unusual exceptions.
“The universe has an arrow; it has a direction to time,” he said.
He illustrated the argument with a pendulum. Place a pendulum inside a vacuum chamber to remove air resistance and minimize friction. A video of it swinging would look much the same whether played forward or backward.
Expose the pendulum to air, however, and its swings gradually diminish. Run the recording backward and the pendulum appears to gain energy without an apparent source.
Al-Khalili argues that the equations describing reversible time rely on idealized systems that are isolated from their surroundings. “The true nature of reality in our universe is that everything’s interacting with everything else, and there is a direction to time,” he said.
In his view, the direction of time may be fundamental. The mathematical equations that appear to work equally well backward and forward would then describe special cases rather than the underlying nature of reality.
Al-Khalili acknowledges that this is a minority position. Physicists have not established whether time’s direction is fundamental or emerges from other physical processes.
One possible route to an answer lies in quantum gravity. The attempt to reconcile quantum mechanics, which describes matter and energy at very small scales, with Einstein’s theory of gravity, which explains how mass and energy curve spacetime, produces the effects we experience as gravity.
Such a theory would need to account for time’s different roles in both frameworks.
“The correct theory of quantum gravity may tell us something about how to reconcile those aspects of the nature of time,” Al-Khalili said.
He also pointed to research into the Big Bang anddark energy, the mysterious phenomenon associated with the universe’s accelerating expansion. Those investigations could help physicists understand whether time had a beginning and what might happen to it in the distant future.
Al-Khalili thinks a successful theory of quantum gravity might finally explain how the different descriptions of time fit together. But physicists have been trying to reconcile quantum mechanics and relativity for decades without finding an accepted answer.
Al-Khalili said AI’s ability to tackle complex mathematical problems could make it a valuable tool for physicists, but he doubts today’s systems can provide the intuition needed to rethink fundamental theories.
“I don’t think AI has that intuition, that imagination to really solve some of these big questions,” he said.
He distinguishes between solving a mathematical problem and recognizing that the problem itself may have been framed incorrectly. His own argument about the direction of time depends on questioning an assumption that has guided physics for more than a century.
Still, Al-Khalili knows physicists who are eager to work with increasingly powerful AI systems.
“We look to AI to give us a helping hand, rather than begrudge AI taking our jobs from us,” he said.
Al-Khalili began examining these questions through a research project funded by the John Templeton Foundation, which brought together physicists, philosophers and mathematicians. Writing the book later made the investigation personal.
Now in his seventh decade, he said thinking about time has sharpened his awareness of mortality. One question particularly interests him: Why do people dread the eternity after death but rarely worry about the eternity before birth?
He suggested the difference partly reflects the human desire to leave something behind, some evidence of a life lived.
“Think about our place in time: we exist for such a tiny interval compared with the age of the universe itself,” he said. “You have a small amount of time; make the most of that time, because it’s a real thing.”
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