On Fri, Oct 16, 2020 at 5:49 PM Jason Resch <[email protected]> wrote:
> On Thu, Oct 15, 2020 at 6:07 PM Bruce Kellett <[email protected]> > wrote: > >> On Fri, Oct 16, 2020 at 9:51 AM Jason Resch <[email protected]> wrote: >> >>> I noticed that Victor Stenger's position on entropy, as described here: >>> https://arxiv.org/pdf/1202.4359.pdf on page 7, appears to be the same >>> as described by the cosmologist David Layzer in a 1975 issue of Scientific >>> American: >>> https://static.scientificamerican.com/sciam/assets/media/pdf/2008-05-21_1975-carroll-story.pdf >>> >>> The basic idea, which is described graphically here: >>> https://www.informationphilosopher.com/solutions/scientists/layzer/arrow_of_time.html >>> >>> It is a counter-argument to the commonly expressed idea that the >>> universe began in a low entropy state. Rather, it explains how the >>> expansion of the universe increases the state of maximum possible entropy. >>> If the universe expands more quickly than an equilibrium can be reached, >>> then there is room for complexity (information / negative entropy) to >>> increase. >>> >>> Why is it that the "low entropy" myth is so persistent, and this >>> alternate explanation is so little known? Some physicists, such as Penrose >>> are still looking for alternate explanations for the special low entropy >>> state. What fraction of physicists are aware of Stenger's/Layzer's view? >>> Does it appear in any physics textbooks? Has it been refuted? >>> >> >> It is refuted by the idea of unitary evolution in QM. Unitary evolution >> means that everything is reversible, If new microstates are created as the >> universe expands, then this expansion cannot be reversed: the creation of >> such microstates gives an absolute arrow of time. This is generally >> rejected, because physicists tend to believe in unitary dynamics. If >> dynamics are not unitary, then the universe is not governed by the >> Schrodinger equation, and arguments for the multiverse collapse. >> > > I understand unitarity for a fixed physical system with certain finite > boundaries. But how does that work for the case of an expanding universe? > If you define the wave function for the observable universe at time 1, what > is the wave function for time 2? Doesn't the number of possible states in > time 2 not increase beyond what it was in time 1, given new information has > entered the system from the cosmological horizon? > If there is a unitary operator that takes the wave function at time 1 to time 2, the the evolution is unitary and reversible. Horizons play no part in this. > Also, I think we can borrow a lesson from quantum computing to shed some > light on the problem of irreversibility and entropy. Quantum computers need > to use reversible logic gates to prevent premature decoherence. Reversible > circuits generate garbage (ancilla) bits as a result of the continued > operation of the computation. (see > https://en.wikipedia.org/wiki/Ancilla_bit and > https://quantumcomputing.stackexchange.com/questions/1185/why-is-it-important-to-eliminate-the-garbage-qubits > ). > > If we extend this analogy to the universe, can we envision the rise of > complexity/macroscopic order in a similar way to the locally growing order > of a reversible computation, which must generate waste heat > ("garbage/ancilla bits") leading to global rise in entropy? So long as > there are enough places to dump these ancilla bits (such as into the low > temperature, non-equalized environment), then there is space for growth of > local order through the process of reversible computations. > The quantum process of generating the ancilla bits is unitary, hence reversible. If these bits are treated as garbage and thrown away, then the result is irreversibility. No new space for bits is created. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLQiA8uSHXjUZdatUfbVMRZn7gLzfd%3DAE5pZKdFpJC%2ByoA%40mail.gmail.com.
