Hi, thanks for your question. I have a big piece covering all of this in more detail which I plan to post in a couple of days once I’ve finished writing it. In the meantime, please accept this ‘teaser’ of a few problems in the prevailing conception (PC):
Dealing with hybrid systems. If we are operating in a regime where there are two contradictory sets of dynamical laws, we do not know what kind of evolution the system will follow. An example of such a system is one where both gravity (as governed by general relativity) and quantum mechanics are relevant. In such a cases, under the PC, it is difficult to make any predictions of what kind of behaviour systems will exhibit, since we lack the dynamical laws governing the system. However, by appealing to general counterfactual principles (the interoperability principle and the principle of locality), which cannot be stated in the PC, we can make predictions about such systems, even if we don’t know the form of the dynamical laws.
The 2nd Law of Thermodynamics. Under the PC, the 2nd is difficult to express precisely, since all dynamical laws are reversible in time, but the 2nd law implies irreversible dynamics. This is normally dealt with by introducing some degree of imprecision or anthropocentrism (eg. through averaging or coarse graining, or describing the 2nd law in terms of our state of knowledge of the system). However, the 2nd law can be stated precisely as a counterfactual statement along the lines of ‘it is impossible to engineer a cyclic process which converts heat entirely into work’.
The initial state problem. Under the PC, the state of a system can be explained in terms of its evolution, according to dynamical laws, from a previous state at an earlier time. This makes it difficult to explain early states of the universe: if a state can only be explained in terms of earlier states, then either the universe has an initial state, which we cannot explain (since there are no earlier state), or the universe does not have an initial state we have an infinite regress, explaining each state in terms of earlier states, going on forever. Neither of these options seem satisfactory.
Hi, thanks for your question. I have a big piece covering all of this in more detail which I plan to post in a couple of days once I’ve finished writing it. In the meantime, please accept this ‘teaser’ of a few problems in the prevailing conception (PC):
Dealing with hybrid systems. If we are operating in a regime where there are two contradictory sets of dynamical laws, we do not know what kind of evolution the system will follow. An example of such a system is one where both gravity (as governed by general relativity) and quantum mechanics are relevant. In such a cases, under the PC, it is difficult to make any predictions of what kind of behaviour systems will exhibit, since we lack the dynamical laws governing the system. However, by appealing to general counterfactual principles (the interoperability principle and the principle of locality), which cannot be stated in the PC, we can make predictions about such systems, even if we don’t know the form of the dynamical laws.
The 2nd Law of Thermodynamics. Under the PC, the 2nd is difficult to express precisely, since all dynamical laws are reversible in time, but the 2nd law implies irreversible dynamics. This is normally dealt with by introducing some degree of imprecision or anthropocentrism (eg. through averaging or coarse graining, or describing the 2nd law in terms of our state of knowledge of the system). However, the 2nd law can be stated precisely as a counterfactual statement along the lines of ‘it is impossible to engineer a cyclic process which converts heat entirely into work’.
The initial state problem. Under the PC, the state of a system can be explained in terms of its evolution, according to dynamical laws, from a previous state at an earlier time. This makes it difficult to explain early states of the universe: if a state can only be explained in terms of earlier states, then either the universe has an initial state, which we cannot explain (since there are no earlier state), or the universe does not have an initial state we have an infinite regress, explaining each state in terms of earlier states, going on forever. Neither of these options seem satisfactory.
It’s important to note that the reversability of microphysical laws, is
not apriori or necessary. It something that was discovered.
it only applies to microphysical laws. So 2LT, being macroscopic, is still physics, as everyone except Deutsch thinks.
the problem is not so much stating it as justifying it microphysically.