A way around this would be if you’re not completely updateless, but if you instead have already updated on the fact that you do exist.
It's not a given that you can easily observe your existence. From updateless point of view, all possible worlds, or theories of worlds, or maybe finite fragments of reasoning about them, in principle "exist" to some degree, in the sense of being data potentially relevant for estimating the value of everything, which is something to be done for the strategies under agent's consideration. So in case of worlds, or instances of the agent in worlds, the useful sense of "existence" is relevance for estimating the value of everything (or of change in value depending on agent's strategy, which is the sense in which worlds that couldn't contain or think about the agent, don't exist). Since in this case we are talking about possible worlds, they do or don't exist in the sense of having no measure (probability) in the updateless prior (to the extent that it makes sense to talk about the decision algorithm using a prior). In this sense, observing one's existence means observing an argument about the a priori probability of the world you inhabit. In a world that has relatively tiny a priori probability, you should be able to observe your own (or rather the world's) non-existence, in the same sense.
This also follows the principle of reducing concepts like existence or probability (where they make sense) to components of the decision algorithm, and abandoning them in sufficiently unusual thought experiments (where they may fail to make sense, but where it's still possible to talk about decisions). See also this post of Vadim's and the idea of cognitive reductions (looking for the role a concept plays in your thinking, not just for what it could match in the world).
Thanks for the reply and all the useful links!
It's not a given that you can easily observe your existence.
It took me a while to understand this. Would you say that for example in the Evidential Blackmail, you can never tell whether your decision algorithm is just being simulated or whether you're actually in the world where you received the letter, because both times, the decision algorithms receive exactly the same evidence? So in this sense, after updating on receiving the letter, both worlds are still equally likely, and only via your decision do yo...
I recently had a conversation with a staunch defender of EDT who maintained that EDT gives the right answer in the Smoker’s Lesion and even Evidential Blackmail. I came up with the following, even more counterintuitive, thought experiment:
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By doing research, you've found out that there is either
(A) only one universe or
(B) a multiverse.
You also found out that the cosmological theory has a slight influence (via different physics) on how your brain works. If (A) holds, you will likely decide to give away all your money to random strangers on the street; if there is a multiverse, you will most likely not do that. Of course, causality flows in one direction only, i.e. your decision does not determine how many universes there are.
Suppose you have a very strong preference for (A) (e.g. because a multiverse would contain infinite suffering) so that it is more important to you than your money.
Do you give away all your money or not?
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This is structurally equivalent to the Smoker's lesion, but what's causing your action is the cosmological theory, not a lesion or a gene. CDT, TDT, and UDT would not give away the money because there is no causal (or acausal) influence on the number of universes. EDT would reason that giving the money away is evidence for (A) and therefore choose to do so.
Apart from the usual “managing the news” point, this highlights another flaw in EDT: its presumptuousness. The EDT agent thinks that her decision spawns or destroys the entire multiverse, or at least reasons as if. In other words, EDT acts as if it affects astronomical stakes with a single thought.
I find this highly counterintuitive.
What makes it even worse is that this is not even a contrived thought experiment. Our brains are in fact shaped by physics, and it is plausible that different physical theories or constants both make an agent decide differently and make the world better or worse according to one’s values. So, EDT agents might actually reason in this way in the real world.