This seems significantly shakier than even the idea of quantum immortality.

Lets call your idea "Boltzmann Brain Immortality". That is, the idea that "because a Boltzmann Brain version of me might possibly pop into existence somewhere in the multiverse at some point in time, ever, I am immortal".

I have two main objections to this: 1) Boltzmann Brains are generally considered a problem in theories of physics which allow them. That is, if a model of physics allows Boltzmann Brains to be possible, with non vanishing probability in comparison to 'real' intelligent life, this is considered generally considered a flaw in the theory.

2) I wouldn't consider a Boltzmann Brain version of me to qualify as 'life' or 'immortality', since there si no continuity of experience - the Boltzmann Brain just vanishes again an instant later.

Regarding 51% attacks, proof of work algorithm and alternatives: https://download.wpsoftware.net/bitcoin/new-pos.pdf

This is a good technical article that describes the mining/consensus algorithm of bitcoin, (but maybe not very readable to non-technical people). It also discusses the main current alternative, proof of stake, and shows that an issue with proof of stake which is not present in proof of work is that anyone who is new to the network or goes offline and then is reconnected is required to trust some entity / community / etc, that the blockchain they are using is the 'correct' one, and not one which was reforged over a period of time using old private keys purchased from former holders, etc.

"This is not a distributed consensus! It is a different sort of consensus, which may be formed amongst always-online peers in a decentralized way, but depends on trust for new users and temporarily offline ones. It is correspondingly vulnurable to legal pressure, attacks on “trusted” entities, and network".

On the other hand, Bitcoin's proof of work algorithm is expensive and energy consuming, while Proof of stake is low cost.

Depending upon the purpose you are using the blockchain for, this is a tradeoff that might be acceptable. If the goal of the blockchain is to be the ultimate store of ALL value, then I think Bitcoin's Proof of Work algorithm is probably required. If the goal is to utilize blockchain technology for various other applications, where you might not need to pay for absolute security and merely being 'very difficult' to attack might be sufficient, the lower cost alternative might be superior, imo. There is more of an element of human consensus and trust in PoS than in PoW, for example, you might have to trust a developer team, the reputation of a company, or the collective community of users.

However, large mining pools also are a threat to decentralization, as you noted. If a few or even a couple mining pools control enough hash power to launch an attack, then you have to trust the mining pool operators in PoW just like you have to trust a developer / community / company / whatever who you are downloading a blockchain snapshot from in PoS.

I don't think there are yet any definitive answers on these issues yet, which is why I favor diversifying among different experiments. Of course, many others believe they have the answer, so they either only want Bitcoin, or only want <whatever else>. If the Bitcoin maximalists are correct, they save themselves the ~10% cost of diversifying among the different experiments right now. I'll pay the uncertainty tax and diversify in order to not be wrong.

It looks like other blockchain technologies (altcoins) have been the victim of 51% attacks, so I'm going to read up on their repercussions. I wonder if they were carried out by bitcoiners who don't like competition?

It occurs to me that little can probably be done to stop attacks on distributed systems by large actors with non-monetary goals. If people are willing to throw a lot of resources into destroying a fledgling technology, they will probably succeed.

I do have an idea for a distributed public ledger in which attacks are possible but always negative-sum. I have little experience with cryptography so its probably rubbish. If it looks to not be terrible I will probably post it here for comment.

The necessity for each wallet to contain the entire block chain.

This isn't actually an issue. Lite wallets exist.

Governments have never seemed keen to give up their monopoly on the money supply.

Indeed, they would prefer not to give up this monopoly. Earlier attempts at creating things similar to Bitcoin such as e-gold failed because they lacked the decentralization component, and could be attacked by governments. However, it is extremely difficult for Governments to kill bitcoin. They can make it dangerous to use in their localities, but thats about it. At the present time it seems that most governments are not even attempting to take this action. Bitcoin has been legitimized sufficiently in the US, and has hundreds of millions of dollars of VC funding poured into its infrastructure now, so it would be difficult for the government to now do a 180 and try to ban its use.

The computing power wasted by mining.

Or as you noted, 'used inefficiently'. I agree this is a problem. The question is: is there actually a better answer out there which does not require this. If a solution existed which was equal in ability to secure the network but required less computaiton power (energy), then it would clearly be superior. There are a number of other methods being experimented with in altcoins. I don't think there is a clear answer right now. (But there are definitely lots of people who believe strongly that proof of work is the only way, and some people who believe strongly that it is nothing but a waste of energy).

After reading about BC and 51% attacks, I am beginning to think "the network effect is the mind killer" might be a more general expression of "politics is the mind killer".

If you mean that lots of people tend to become devoted to one blockchain, and start treating it like a religion where it is the only true blockchain and all others must die, then yes there are people who do that. (Both for bitcoin and for others). It can be mind killing for many. Tribalism is the mind killer!

That said the size of the network of adopters of a blockchain ledge is probably the most critical measure of its success. Bitcoin has grown significantly over the years in this regard which is why it is valuable. So when people quote network effect as being a big deal, they are correct.

far exceeds the value of Gold

To you, maybe, to an Indian family, not likely.

Also, if by "Bitcoin", we mean "Bitcoin and/or any future blockchain technology that replaces it"

No, we do not, because at issue is the future value of the current investment in Bitcoin.

which indicates that Gold has a strong network effect

Not just that. Being only a store-of-value is a poor functionality set. The Indian gold jewelry doesn't just sit in a vault -- it is worn on big occasions and serves a major status display.

The odds for that scenario are approximately equal to the odds that quantum computers are impossible.

Right, I agree, my 5% * $34000 is only slightly Pascalian. I'm only using the Pascal reference because it is the best representative example I know of the general class of such scenarios (note that other "Pascalian" scenarios of this type are fairly common in the investment world; every startup crank loves throwing out the whole "if you think there's only a 0.1% chance I'm right, you'll get an EV of $100b * 0.001 = $100m" line). If you know of a better name for the category, please share. I also used the Drake Equation as an analogy elsewhere in that r/buttcoin thread; perhaps that might be a better fit.

Some random comments:

So Bitcoin's lack of a "fundamental use value" floor is not a serious disadvantage of Bitcoin against gold.

Theoretically, no, practically, it still is. Humans are humans and the whole history and, um, aura of gold makes a "simple equilibrium flip" not very likely in the near future.

Measuring Bitcoin against "gold market cap" is dangerous because gold has uses which Bitcoin cannot replace. For example, traditionally most of the wealth of Indian families (those who have wealth, of course) have been kept as gold, specifically golden jewelry. Bitcoin will not replace that use. Another big advantage of gold is anonymity which Bitcoin will not be able to replicate either.

The probabilities of the various events required for BTC to receive this status are roughly within an order of magnitude of the 5% mark.

Why do you think so?

And what exactly is the reference class that you put Bitcoin into?

my expected-value estimation (10% of gold market cap = $700b = $34000 per BTC * 0.05 chance = $1700 per BTC EV

Don't think in terms of point estimates, think it terms of full distributions (which here will not be symmetric).

in those worlds where someone actually can torture 3^^^3 people for fun they will likely be able and willing to do it again, so my cooperation may end up leading to the torture of more than 3^^^3 people

We are entering nonsense territory here, as the set up implies that someone who can torture ^^^3^^^ people for fun still need something from you and, moreover, needs your free and willing consent. Recall that the original Pascal Mugger is Omega and I doubt that you can incentivize Omega by cooperating or not.

Some random comments:

So Bitcoin's lack of a "fundamental use value" floor is not a serious disadvantage of Bitcoin against gold.

Theoretically, no, practically, it still is. Humans are humans and the whole history and, um, aura of gold makes a "simple equilibrium flip" not very likely in the near future.

Measuring Bitcoin against "gold market cap" is dangerous because gold has uses which Bitcoin cannot replace. For example, traditionally most of the wealth of Indian families (those who have wealth, of course) have been kept as gold, specifically golden jewelry. Bitcoin will not replace that use. Another big advantage of gold is anonymity which Bitcoin will not be able to replicate either.

The probabilities of the various events required for BTC to receive this status are roughly within an order of magnitude of the 5% mark.

Why do you think so?

And what exactly is the reference class that you put Bitcoin into?

my expected-value estimation (10% of gold market cap = $700b = $34000 per BTC * 0.05 chance = $1700 per BTC EV

Don't think in terms of point estimates, think it terms of full distributions (which here will not be symmetric).

in those worlds where someone actually can torture 3^^^3 people for fun they will likely be able and willing to do it again, so my cooperation may end up leading to the torture of more than 3^^^3 people

We are entering nonsense territory here, as the set up implies that someone who can torture ^^^3^^^ people for fun still need something from you and, moreover, needs your free and willing consent. Recall that the original Pascal Mugger is Omega and I doubt that you can incentivize Omega by cooperating or not.