The laws of physics may not be what they seem Yuichiro Chino/Getty Images
I was recently reading an old article by string theorist Robbert Dijkgraaf in Quanta Magazine titled “There are no laws of physics”. You might find it a little strange for a physicist to claim that there are no laws of physics, but I agree with him. In fact, not only do I agree with him, but I think my field is better off for it. And I hope to convince you of that too.
First of all. What we often call the laws of physics are really just coherent mathematical theories that seem to correspond to certain parts of nature. This is as true for Newton’s laws of motion as it is for Einstein’s theories of relativity, Schrödinger’s and Dirac’s equations in quantum physics or even string theory. They are therefore not really laws as such, but rather precise and coherent ways of describing the reality that we see. This should be obvious from the fact that these laws are not static; they evolve as our empirical knowledge of the universe improves.
Here’s the thing. Although many scientists see it as their role to discover these ultimate laws, I simply do not believe they exist.
A hundred years ago, such an opinion would not have been controversial. Previously, most of the so-called laws of physics were all directly related to concrete aspects of the natural world, such as Hooke’s law which describes the force required to stretch a spring or Boyle’s law of the relationship between pressure, the temperature and volume of a gas. But that started to change in the early 20th century when people like Albert Einstein set out to find the ultimate theory of everything. He spent the last 30 years of his life looking for one to no avail. Dirac also believed in this view, having apparently said that all chemistry could be derived simply from his equation – although I think that particular remark is probably apocryphal.
There are approximately 86 billion neurons in the human brain. This is less than the number of stars in the Milky Way which is only a tiny part of the known universe. The universe seems almost infinite compared to the finite capacity of the human brain, leaving us perhaps little chance of understanding the ultimate laws. What’s amazing is that we can make sense of certain aspects of the universe through the laws of physics. It was perhaps Richard Feynman who first said that the question is not how smart we humans are at understanding how nature works, but how smart nature is at following our laws!
As we learn about nature, we can refine our descriptions of it, but it’s endless – like peeling an endless onion, the more we peel, the more there is to peel.
Take the example of string theory. It’s a mathematically very strict and rather magical theory in the way it treats gravity and quantum mechanics equally, which matches many of our observations of the universe. It shows great promise, but so far has struggled to provide concrete testable predictions beyond our current understanding.
It also has a rather thorny stumbling block known as the landscape problem, where literally zillions of universes (about 10500, the number is so large that it seems obscene) are acceptable solutions of the theory. If string theory is correct, we can declare victory because one of those zillions of universes must be our universe, and all we have to do is somehow find that solution particular to understand what the laws of physics are for us. Of course, this is an impossible task due to the exceptionally large number of possible universes existing in the landscape, and all with their own distinct laws.
This scenario is often called the multiverse. All possible laws, conceivable and inconceivable, are allowed in a possible universe, and the laws of physics are no longer significant or unique in any fundamental sense, because they depend entirely on where one looks in the landscape. multiverse. It’s ironic that the theory of everything turned out to involve a whole that is exponentially larger than anything anyone could have imagined before.
One possible conclusion from this is that the conventional reductionist approach to particle physics, where natural laws are increasingly focused on smaller and smaller building blocks (like molecules, atoms, and particles) and the fundamental forces (like gravity and electromagnetism) acting between them, is not more a fruitful way to look at the physical world. 10500 universe, with only one of them possibly obeying the laws necessary to adapt A wise man.
We are left with only the landscape, where the “laws” depend on the specific universe with which we are dealing. It’s so complex that the whole idea of natural laws has to be changed. It’s a seemingly odd end to a laudable journey that began with atoms as the hypothetical indivisible constituents of matter 2,500 years ago and witnessed a great recent triumph in the experimental discovery of the particle. from Higgs in 2012. Ultimately, our physical laws aren’t intrinsic at all entirely dependent on where we are in the landscape.
As a theoretical condensed matter physicist, I do not find this scenario daunting at all, quite the contrary. The fact that there is an essentially infinite number of possible laws only makes science more exhilarating, as exploring the landscape will forever remain an active and creative activity. Theoretical physics can never end because the landscape is simply too vast.
I know from my 40 years of experience working with real physical phenomena that the whole idea of an ultimate law based on an equation using only the building blocks and fundamental forces is unrealizable and essentially a fantasy. We never know precisely which equation describes a particular laboratory situation. Instead, we still have to build models and approximations to describe each phenomenon even though we know that the equation controlling it is ultimately some form of Schrödinger’s equation!
“And quantum mechanics?” you might ask. For nearly 100 years, it has been tremendously successful in matching all of our experiences to the quantum scale. But quantum mechanics is actually more like a set of rules that we use to express our laws rather than an ultimate law itself. For example, the Standard Model of particle physics, the theory of superconductivity, and the theory of atomic spectra are all constructed using the rules of quantum mechanics, but they have little to do with each other. Moreover, space and time are variables that must be put by hand in theory, whereas space and time should come naturally from any ultimate law of physics. It has remained perhaps the greatest mystery in fundamental physics with no solution in sight.
It is hard to imagine that a thousand years from now physicists will still be using quantum mechanics as a fundamental description of nature. Something else should replace quantum mechanics by then, just as quantum mechanics itself replaced Newtonian mechanics. I have no idea what that something else could be, but I see no particular reason why our description of how the physical universe seems to work should suddenly peak at the start of the 21st century and stay stuck forever in quantum mechanics. That would be a really depressing thought!
Newton’s laws have been extraordinarily successful for 300 years, but we had to overcome them as we learned more about the universe, and the same should happen with quantum laws someday in the future.
Any new unknown theory of the future must build on and incorporate the physics of quantum mechanics, just as quantum mechanics builds on and incorporates classical mechanics. Our understanding of the physical world must continue indefinitely, unhindered by the search for ultimate laws. The laws of physics are continually evolving – they will never be ultimate.
Sankar Das Sarma is a theoretical physicist based at the University of Maryland, College Park. His interests are varied, ranging from the strange properties of matter to how information should be understood in the quantum realm.
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