The Laws of Physics Must be Comprehensible

Brett Hall
Conjecture Magazine
4 min readDec 5, 2020


The idea that there could be physical laws or other concepts that only alien life (or machine superintelligence) and not humans can understand has a long tradition which is gaining ever more traction. One proponent of this idea is Neil Tyson. Another is Martin Rees, who said that our brains evolved for the African Savanna, which echoes Richard Dawkins’s assertion that we only evolved to appreciate his so-called “middle world.”

The argument from these thinkers — almost universally accepted by public intellectuals — is that the laws of physics may be so subtle, or difficult, or alien, that the feeble mind of the human will be unable to comprehend it.

But there cannot be things we will forever be unable to comprehend.

Understanding something means creating an explanatory theory about that thing. When someone else has already created an explanation, it’s only an explanation for you once you have re-created it in your own mind. In doing this, you might even improve it. Sometimes we don’t understand things. But eventually we are able to, if we try hard enough. So far that has always worked — and there is no reason whatsoever to believe it will fail. But this is not an argument of the form “it’s always happened in the past, therefore it will happen in the future.” No. The argument that the universe is comprehensible to people — like us — is much deeper than that. It rests upon a truth about the laws of physics discovered (mathematically proved actually!) by quantum physicist David Deutsch about what computation is — and how people, with their brains, perform computations. And the brain is a universal explainer.

At the frontier of science, there are always open questions, but they are solved only to reveal more, and more interesting problems. There can be no wall to progress. Here is why, and here is why aliens cannot be different in quality to us (though they may be different in quantity, which is to say they may have faster brains or the capacity to hold more in short term memory):

An explanation is just a sequence of statements that are connected and follow one from another to account for an aspect of reality. The sequence is finite.

In order to construct an explanation you will need some memory (to store your explanation on) and a processor (in order to run the explanation so that it’s understood). Now should you need more memory: you can write it down. Should you need more than that: a computer is good. The full explanation of, say, Einstein’s theory of general relativity, takes some pages. Anyone who chooses to pay attention for long enough can grasp it.

Say there is a more complete explanation that united general relativity and quantum theory (and there must be), and say the aliens possess it. The logic of Tyson and Martin would lead to a contradiction, as follows:

1. Assume no human can understand it.
2. The explanation must consist of a sequence of statements.
3. One or more of the statements is incomprehensible.
4. This can only mean that it is too long to hold in memory or that it takes too long to process.
5. But increases in memory using technology like paper or computers are possible. Increases in processing speed are also possible using calculators (although even now we make strides towards brain augmentation).
6. So, the only physically relevant aspects of the computer that come to bear on “comprehensibility” are improvable. Therefore, we can always understand some explanation that we need to. In other words, we can understand anything an alien can.
7. Our assumption was false.

Memory and processing speed aside: what other capacity of a computer could be required for us to “understand” an explanation? Our ability to construct explanations consists of cycles of creatively varying existing explanations and then criticizing them.

So assume no human can understand your explanation because their brain is not fast enough. Increase their ability to process those hard steps either with a computer that can execute the numerical steps. Or assume the human cannot understand because they cannot hold all of the explanation in working memory for long enough. Then increase the working memory, perhaps with paper, shortcuts, computers, or other technology. Problems are soluble.

An alien life is just another physical system made out of stuff that we find in the universe and so obeys the laws of the universe. If you don’t believe in magic, then you must understand that whatever the aliens can do, so can humans, given the requisite knowledge.

There must always be a finite list of steps between explanations of reality we have and that which an alien (or machine superintelligence) has likewise constructed. No matter how sophisticated the science, epistemology, or thinking preferences of other minds might be, they cannot escape the laws of physics. These laws mandate that energy needs cannot be infinite or that an infinite sequence of instructions need to be carried out to compute the solution to a problem whose solution is already known. So it is with aliens and with us.

The argument that, nevertheless, aliens might possess cognitive capacities that exceed our own in some poorly defined domain that does not include memory and clock speed is, therefore, an appeal to the supernatural. If you ascribe to aliens the same capacities that have been traditionally deemed to be the properties of a god, you can say “there are some things we fallible humans will never achieve.” Indeed. But that is no longer science, or rationality. That is magical thinking.

Brett Hall is the host of ToKCast, a podcast about the work of David Deutsch. His website is



Brett Hall
Conjecture Magazine

Host of “ToKCast” a video and audio series about the work of David Deutsch and related issues. See