On 08-04-2022 19:04, Brent Meeker wrote:

On 4/7/2022 8:00 PM, smitra wrote:On 07-04-2022 18:25, Brent Meeker wrote:On 4/7/2022 8:25 AM, smitra wrote:On 07-04-2022 03:05, Bruce Kellett wrote:On Thu, Apr 7, 2022 at 10:52 AM smitra <smi...@zonnet.nl> wrote:On 07-04-2022 02:30, Bruce Kellett wrote:The preferred basis is not determined by algorithms -- it is determined by robustness under decoherence. You can redefine everything so that your theory is no longer quantum mechanics --butthat is a fairly pointless exercise.That's the preferred basis as used in practice. But that's useless in this context and it would amount to doing things things backward. Observers cannot be defined using decoherence. That you do robustness under decoherence allows for us as stable observers to exist. So decoherence explains our existence.It also explains our ability to make measurements and recordresults.To claim that this is not a fundamental account of measurement isjustsilly. Nothing is more fundamental than quantum entanglementevidencedin decoherence.While entanglement is a phenomenon that exists at the fundamentallevel, effective macroscopic concepts can never be fundamental, theyhave to be explained using the fundamental microscopic theory inwhich many macroscopic concepts do not even exist.You need to keep in mind that there are different meanings of "fundamental". Those "macroscopic concepts" like measurements andrecords and facts are epistemically fundamental; and remain sohowevertheories change. The reductionist base of the current theory isontologically fundamental, but it may be replaced by a new theorywitha different ontology, as QM replaced Newtonian mechanics and statistical mechanics replaced thermodynamics. Being ontologically fundamental is a precarious position.Yes, and that means that the new theory must reduce effectively to theold theory in the macroscopic regime where the old theory makes(almost) correct predictions.That incorrectly insinuates that the old theory only makes accurate predictions in the macroscopic domain. For example, I suspect that the solution to the problem of quantum gravity will imply natural cutoffs at the Planck scale which we now often invoke heuristically. Just because an ontology is microscopic doesn't make it immune to replacement. Strings or loop quantum gravity are microscopic too.

`Yes, I agree here. Another example is statistical physics. We teach`

`students about the equal prior probability postulate, but it's not`

`actually true. However we do know that the predictions made by assuming`

`this are correct. The question why statistical mechanics works, is then`

`an interesting problem. See e.g. here:`

https://en.wikipedia.org/wiki/Eigenstate_thermalization_hypothesis

If we then ask fundamental questions about e.g. the existence of amultiverse that can only be addressed by getting the details about thedynamics at the microscopic level correct, then it's not appropriateto fix up the theory by introducing notions from the macroscopicdomain that should in principle follow from the fundamental dynamicsat the micro-level.The notion of "result" and "measurement" are not introduced, they are fundamental to knowledge. They are exactly where MWI gets into trouble. By saying there is no result of an experiment it muddles the concept of probability.

`In a Bruno-type copying experiment one can get multiple outcomes with`

`various distributions too. If 100 Brents are created with one of them`

`going to get $1 millions what is the probability that you'll win $1`

`million? If instead of identical Brents we create 100 random persons`

`such that one of them is guaranteed to be Brent and one of them is`

`randomly chosen to receive $ 1 million, then the probability would be`

`1/100. If we then tweak the random person generator so that the random`

`persons that are not Brent start to look more like Brent, then that`

`would not matter for the 1/100 probability. So, we can take the limit`

`where the other persons become exact copies of Brent.`

`So, we can deal with probabilities in cases where all outcomes for an`

`observer are realized.`

BrentThe appearance of permanent records should follow from decoherence.But it makes sense to consider states of algorithms that processinformation as a more general notion of observation.SaibalBrent

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