When Planck demolished classical mechanics by postulating the discretization of energy levels, he kept the second law of thermodynamics, as the one carryover from the old world, guiding him in the new. Later in the 20th century, starting with the work of Claude Shannon, we’ve come to understand a deep link between the concepts of information and entropy.
A paper published last year looked at the properties of potential generalised physical theories, and found that with a minimal set of constraints,the ‘information becoming useless’ sense of the second law of thermodynamic would have to necessarily hold for all these theories. A simplified description of the paper by one of the authors is here. It is, I think, hugely significant that the second law and entropy have survived from classical to quantum theories, and has now been shown to be true in possible future theories of nature, if there is one.
I’ve always been fascinated by the link between information and entropy, and have written about it earlier in this blog. I think that the indications from modern physics are that the concept of information is a fundamental part of what makes up the universe. And it is as fundamental a part as of the physical world as energy, quarks, leptons and bosons. And that is a crucial element of how we think about the universe around us. As John Wheeler had said (and Taimur repeated) many years ago, “It from Bit“. That may well be the question to which the answer is 42!