On Saturday, May 23, 2015 at 8:36:40 PM UTC+10, Liz R wrote:
>
> I'm not sure why comp would predict that physical laws are invariant for 
> all observers. I can see that it would lead to a sort of 
> super-anthropic-selection effect, but surely all possible observers should 
> exist somewhere in arithmetic, including ones who observe different physics 
> (that is compatible with their existence) ?
>

I really must dig up the old thread! But I'm not saying comp does entail 
invariant physics for all observers, just that if there are different 
physics, the substitution level must be very low indeed. Think of the 
original scenario in the UDA: a person in Washington is suddenly 
annihilated, and then duplicated in Helsinki and Moscow (or whatever). That 
operation creates a 50% probability of finding oneself in Helsinki or 
Moscow. But the ultimate point of the UDA is that one's actual probability 
of finding oneself in Helsinki or Washington depends on the total measure 
of *all* virtual environments within which that observer is instantiated in 
an environment that looks like one of those cities. One can't isolate a 
particular virtual system from the trace of the UD. So you can't create an 
arbitrary physics in an environment that looks like either city (or 
anywhere). Well you can, but any observer will always find their own 
physics to be the measure of *all* their continuations in arithmetic. So 
there can't be an environment that is like Helsinki or Moscow at some point 
but that has different physical laws. Carry this logic over to the scenario 
of a person standing in an empty room - the physics the person experiences 
will be the measure of all such identical persons standing in empty rooms. 
The question here is what constitutes the observer? How detailed would a 
simulation of me have to be before it became a subjective *duplicate* of 
me, its continuations my continuations? If there is a person A somewhere in 
the UD who is experiencing an empty room with physics A, and another 
identically configured person B somewhere else experiencing physics B, what 
is stopping the continuations of A mixing with the continuations of B, so 
that the measures combine into a merged physics? There has to be something 
in both observers' computational states that distinguishes them 
sufficiently that their experiences cannot interfere with one another - the 
comp equivalent of decoherence. (In fact if QM effects are the 
manifestation of UD observer measures, the threshold at which these effects 
start to kick in should probably give us a strong clue about how low the 
substitution level is!)

Observers and their experiences, including physical laws, can't be kept 
apart by physical or temporal space, but only by differences in the 
computational states that define them. Physics is emergent from the 
computational properties of observers, and therefore any difference in 
physics experienced by different observers is a function of their 
mathematical configuration. If we find that there are observers in other 
universes who experience different physics, then it must be the case that 
the substitution level for those observers includes their entire universe.

That said, if I recall our previous discussion correctly, Bruno disfavoured 
the idea of different physics for different observers. He seems to believe 
it should indeed be invariant. That position appears to me to be at odds 
with the direction of modern cosmology.



On 23 May 2015 at 21:23, Pierz <pie...@gmail.com <javascript:>> wrote:
>
>> Some time ago on this list I had a fascinating exchange with Bruno that 
>> has stayed with me, fuelling some attacks of 4am philosophical insomnia - 
>> an affliction I imagine I'm not the only person on this list to suffer 
>> from! If you try to nail Bruno down on some aspects of his theory, he has a 
>> tendency to get all Sg Grz* and p[]<>p on you at a certain point, making it 
>> difficult to progress without a PhD in modal logic - despite the fact that 
>> I suspect that the ideas are fundamentally simple. Nevertheless in the 
>> course of the discussion, Bruno *did* acknowledge that his theory 
>> predicts that the laws of physics are invariant across space and time, 
>> because they are supposed to arise out of pure arithmetic (being the 
>> hypostases of the FPI bla blas).  Indeed, for the dissolution of the 
>> material within the arithmetical to go through (logically), then the 
>> regularities that we call physical law cannot depend on geography, since *ex 
>> hypothesi* they arise from number relations which are prior to time and 
>> space. Yet physics - or cosmology - seems to be headed full-steam in a 
>> different direction, towards the conclusion that physical law is indeed 
>> dependent on geography, the laws we observe being dependent upon an 
>> observer selection process. That is, we see physical laws finely honed for 
>> life, because life can only exist in those regions where the laws are 
>> conducive to life. I'm less sure about this, but I think it might still be 
>> OK for physical law to geographically determined in this sense, so long as 
>> there are no other observers in different parts of the multiverse who see 
>> different laws, but to assume such a thing seems foolish. Why should we 
>> believe that of all the possible permutations of the parameters which 
>> determined physical, there is only a single solution which permits life? 
>> There might be many different 
>>
>> So on the face of it, the recent measurements of the mass of the Higgs 
>> boson, which are strongly suggestive of a multiverse might be seen as 
>> empirical evidence against 'comp'. Yet there is a way - namely an 
>> *extremely* low substitution level. You'll recall that the substitution 
>> level is the level at which a digital substitute can be made for a brain 
>> such that the self (whatever that is) survives the substitution. This might 
>> be quite high - perhaps its sufficient to mimic neuronal interconnections 
>> in software? Or it might be very low - maybe we need to go down to the 
>> molecular level and simulate chemistry. However, it would be a big surprise 
>> I imagine for the digital survival enthusiasts if the required level was 
>> the entire multiverse! Yet that conclusion seems inescapable if the 
>> emerging multiverse cosmology (and comp) is correct.
>>
>> Why would a low substitution level save the day for comp? Because, as 
>> stated before, if the physics observed by some conscious being is dependent 
>> solely on number relations (as UDA purports to prove),  and number 
>> relations are pure abstractions prior to matter, space and time, then 
>> physics cannot be contingent on geography, because *it* is contingent on 
>> matter, space and time. So if comp is correct, and it is also correct that 
>> we live in a multiverse such that observers see different apparent laws in 
>> different parts of that structure, then the only solution (ISTM) is to make 
>> the observer large enough to encompass the geographical variation.  
>>
>> But such a low substitution level seems counter to most of the common 
>> sense assumptions about consciousness that are the basis for the logic of 
>> UDA seeming plausible at all. It would commit us to the idea that 
>> teleportation of the 'same' consciousness from Washington to Helsinki is 
>> impossible, because we couldn't isolate the person's consciousness within 
>> any reasonable physical limits, such as their brain or body. We'd need to 
>> substitute the entirety of everything, including Helsinki and Washington 
>> themselves! But what then is the status of a teleported person, if such a 
>> thing could be achieved? If we reassemble the exact same organization of 
>> molecules such that nobody, not even the person, could tell the difference, 
>> then how has the substitution level *not* been achieved?
>>
>> Perhaps the answer to the conundrum lies in the definition of physical 
>> law? Perhaps things like the cosmological constant, the masses and charges 
>> of particles and so on, which I would normally regard as aspects of the 
>> laws of physics (and which recent results suggest may not be the same in 
>> all parts of the multiverse) are not the *real* laws of physics. Rather 
>> it is the deeper laws which underly those geographically contingent 
>> apparent laws which are the true laws of physics, and which derive from 
>> number relations. However, that manoeuvre won't save us, because then in 
>> order for an observer to experience a certain set of apparent physical 
>> laws, I need to specify within which branch of computations (multiverse 
>> region) I am instantiating that observer. That is the same as saying that 
>> the substitution level is very, very low, because in order to duplicate an 
>> observer, I need to duplicate the entire universe-generating computational 
>> branch that they are in, not just their personal memories and so on. 
>>
>> Then again, maybe I should not be surprised by this substitution level, 
>> because if the wave function is the manifestation of my computational 
>> duplicates and their relative measure, then any genuine duplicate of me 
>> would be part of that quantum wave function measure, and making a copy of 
>> me *in the same universe* would not have that effect. Only if I could 
>> make a fungible duplicate of the universe and insert it into the deck would 
>> I be able to influence physics and make a real substitution rather than a 
>> poor copy. 
>>
>> This suggests to me that either comp has overlooked something about the 
>> nature of consciousness and is wrong, or that cosmology is wrong and there 
>> is only one physics everywhere, or that, even though comp is right, the 
>> artificial duplication of consciousness is impossible because consciousness 
>> is determined by its relationship with the entirety of existence, perhaps 
>> in much the same way that the wave function of an electron has to "know 
>> about" all the other electrons in existence in order to obey the exclusion 
>> principle. The whole within the part and all that jazz.
>>
>> Or I missed something, not that that has ever happened before... ;)
>>
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