Tag Archives: BBC

BBC botches physics in series on free will

The BBC recently came out with a three-part series on free will. Part 2 is about physics. If you’re going to infer lessons from physics, it helps to get the physics right. They don’t. Part 2 of the BBC series can be found here: https://www.bbc.com/reel/playlist/free-will?vpid=p086tg3m

The picture above analogizes a series of physical events to a chain of dominoes, in order to talk about cause and effect. But there’s something odd about this metaphor, if the dominoes are supposed to represent the physical universe: look at that first domino, in black. What makes it tip over? Something from outside the universe, a “god” so to speak, intervenes to set the whole thing in motion. We seem to have jumped from physics to theology.

This would just be a nit-pick, if the negligent treatment of the “start” in the model did not affect the conclusions drawn. But it does, as we will see.

But first let’s look at some additional physics mistakes in the video. Jim Al-Khalili says “When we think we’re making free choices, it’s just the laws of physics playing themselves out.” Well no, the laws of physics alone don’t cause anything. The laws of physics are rather abstract. If you want to understand how a concrete action came about, you need not just laws of physics but also what physicists call “boundary conditions”, AKA concrete reality. Especially bits of concrete reality that heavily interact with the action in question. For example, you. Of course, perhaps Al-Khalili didn’t mean “just the laws of physics” quite so literally. But it matters how you phrase things, especially when you accuse people of only thinking they’re making free choices. Your grounds for calling them mistaken had better not be based on distorted depictions of the physics.

From the “libertarian” side of the philosophical debate, Peter Tse makes a different mistake – or maybe just poorly worded statement: “Patterns of energy don’t obey the traditional laws of physics.” Unless he means “classical physics” (in which case: say “classical”), that’s not true. The Wikipedia article on Lagrangian mechanics is a good resource for seeing just how deeply physics treats patterns of energy. “The kinetic and potential energies still change as the system evolves, but the motion of the system will be such that their sum, the total energy, is constant.”

Block universe as a loaf of bread, from BBC video

Since Einstein, physicists have known that space and time are not independent, but aspects of a single four-dimensional manifold, spacetime. For observers in different inertial reference frames, which direction counts as “time” will differ. A metaphor called the “block universe” is sometimes used to describe this, where we only depict two spatial dimensions and then repurpose the third to represent time. Jim Al-Khalili uses a loaf of bread, with different times being different slices.

The block universe is like a loaf. OK, let’s go with this metaphor: one end of the loaf is very hot (we call it the Big Bang) and the other is cold. There are certain patterns that stretch from one end of the loaf to the other. If we know the pattern (laws of physics) and we know the boundary conditions (full state of any slice) we can derive the state of any other slice. Why say that the hot end caused the cold end to be the way it is? Why not say that the cold end caused the state of the hot end? After all, the mathematical derivation works equally well in that direction. Better yet, why not admit that “causality” is a useless concept at the level of a complete description of the universe, and just look at the bidirectional laws of nature instead? Why not start your analysis in the middle (but nearer to the hot side), and work your way toward both ends? The last option is a lot more practical, since that middling point is where you are.

The idea that the Big Bang is the Big Boss and we are just its slaves has no basis in science. Remember that “god” that tipped over the first domino? He’s creeping back in through the back door of Al-Khalili’s thinking. He thinks the Block Universe is dominated by its early times. You can only get such domination by swapping out a scientific view of time and causality, and sneaking in an intuitive picture of time and causality in its place.

Al-Khalili does that when he says “The past hasn’t gone … the future isn’t yet to be decided.” The narrator does that when she says “every single frame of that animation already exists and will exist forever.” Argh, no! Time is within the loaf! If you’re going to use a metaphor, stick with the structure you used to create it – don’t sneak your intuitive conception of time into the background while leaving scientific time in the foreground, now portrayed spatially.

Al-Khalili says “the future … is fixed, even though we don’t know it yet.” This conclusion would repeal the very laws of physics Al-Khalili was claiming to honor. The future is dependent on us because, to repeat myself, laws of physics must be applied to boundary conditions to derive a prediction about the future, and those boundary conditions include us.

Modern physics does destroy the traditional “solution” to the “problem of free will”. What these commentators don’t seem to notice is that it also destroys the traditional “problem” of free will. When you notice that your intuitive ideas of time and causality conflict with science, you need to figure out the full consequences of the science, not take one point from science and then re-apply your intuitive ideas. The future isn’t set in stone. It’s set in spacetime. And spacetime is lighter than air.