On Thu, Jan 28, 2021 at 11:20 AM Pierz Newton-John <[email protected]> wrote:
> On 28 Jan 2021, at 11:03 am, Bruce Kellett <[email protected]> wrote: > > On Thu, Jan 28, 2021 at 10:44 AM smitra <[email protected]> wrote: > >> >> FAPP, therefore not well defined at all. Sticking to FAPP you could >> never have discovered Special Relativity, General Relativity, found the >> correct way to resolve Maxwell's Demon paradox, etc. etc. >> > > FAPP is well-defined for all practical purposes. That is all that you > require for special and general relativity, statistical mechanics, and the > rest of physics. You cannot point me to any physical result that is not > FAPP -- we have only limited measurement precision, after all. And that is > good enough for real-world physics. > > Bruno’s point IIUC is that FAPP is OK for the physics you have now, but > possibly not for the next physics. "Irreversible FAPP” means irreversible > today. It’s true that there does come a point with decoherence where the > state is irreversible, but that point is arbitrary and depends on the > technology you have available. > That is not true. Decoherence ultimately involves the emission of IR photons into outerspace -- through heat dissipated in the atmosphere if no other way. Such effects are truely irreversible, not just FAPP, because once you have lost photons to space there is no way to get them back -- you can't chase after them and turn them around..... The point about decoherence is that the irreversibility is ultimately a matter of the laws of physics. FAPP is just for laboratory purposes, but in the wider context, the irreversibility is absolute, not just FAPP. Proposals for testing MWI involve extending that point further and further. > If you can reverse a quantum state that has evolved to macroscopic > complexity, you can get interference and you’re on your way to showing that > QM is indeed universal, and that MWI may be the best theory. FAPP is just > giving up on testing, say, the Frauchiger-Renner experiment, which may > prove to be tomorrow's equivalent of testing Bell’s theorem - not possible > when the theorem was created, but possible later on. > I think you have failed to understand the physics underlying FAPP. It is not just a matter of technology. FAPP is for laboratory convenience, but ultimately, the irreversibility is built into the laws of physics. 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/CAFxXSLQ2puatoEnK7AXL3MTyBDCuBdPg92%3D3SQuT%2Bc3szNgBdA%40mail.gmail.com.
