I would say that it might not logically presuppose the existence of a world, but that it does pragmatically presuppose it — Janus
No one really believes they are the only person or that there is no external (to the body) world — Janus
If I also believe that I am here discussing for a purpose, it could very well be that I believe that I am interacting with the very contents of my mind — Lionino
Well yes, there are good reasons to doubt that the cup will remain in the cupboard. The point here is simply that your "when I am not perceiving the world, there is no reason that I can believe in the existence of the world" is not a good reason to think that the cup has disappeared from the cupboard.There might had been a situation... — Corvus
This had me puzzling. How do you go about buying coffee? There's the package on the shelf at the store, brightly labeled "Dark Roast". But when one is not perceiving the coffee, there is no reason that one can believe in the existence of the coffee. Hence there is no reason to believe the label on the package. Does one tear the pack open to confirm the contents? But when you drop it into your shopping bag, you again cease to have reason to believe in the existence of the coffee! LIfe becomes difficult, for both you and store security.If you were buying some coffee... — Corvus
I can’t speak on the more scientific aspects of that paper, but on that final section, although it’s the case that any randomly selected brain is most likely a batty brain, it’s also the case that any randomly selected non-batty brain is most likely a Boltzmann brain. — Michael
Yep, I think that's right.
But there is a further step. There are far more batty brains than Boltzmann brain. But there is a further step. Supose you are a quantum fluctuation, having just popped into existence last Tuesday. The chances of you persisting into the next few seconds are vanishingly small. Chances are the world around you is ephemeral, and will disappear, or at the least not continue in a coherent fashion.
And yet for us, the world continues on in a regular and predictable fashion. Well, at least outside of dormitory kitchens.
And that is the argument from Batty Brains - that the world persists shows that it is very unlikely that you are a Boltzmann brain.
That seems to be how the argument goes. — Banno
In Boltzmann brain scenarios, the ratio of Boltzmann brains to "normal observers" is astronomically large. Almost any relevant subset of Boltzmann brains, such as "brains embedded within functioning bodies", "observers who believe they are perceiving 3 K microwave background radiation through telescopes", "observers who have a memory of coherent experiences", or "observers who have the same series of experiences as me", also vastly outnumber "normal observers". Therefore, under most models of consciousness, it is unclear that one can reliably conclude that oneself is not such a "Boltzmann observer", in a case where Boltzmann brains dominate the universe. Even under "content externalism" models of consciousness, Boltzmann observers living in a consistent Earth-sized fluctuation over the course of the past several years outnumber the "normal observers" spawned before a universe's "heat death".
As stated earlier, most Boltzmann brains have "abnormal" experiences; Feynman has pointed out that, if one knows oneself to be a typical Boltzmann brain, one does not expect "normal" observations to continue in the future. In other words, in a Boltzmann-dominated universe, most Boltzmann brains have "abnormal" experiences, but most observers with only "normal" experiences are Boltzmann brains, due to the overwhelming vastness of the population of Boltzmann brains in such a universe.
Most Boltzmann brains are short-lived, but most long-lived brains are Boltzmann brains. — Michael
Your argument is that because most red balls have no green stripe then if my ball has a green stripe then it is most likely not a red ball. That is wrong. If my ball has a green stripe then it is most likely a red ball. — Michael
Well, the thread is about the world, not about solipsism — Banno
probably for another thread — Banno
But it hasn't disappeared yet, and the longer it doesn't disappear the less likely that it is a quantum fluctuation. — Banno
t only follows that the probability that I am a Boltzmann brain gets smaller as the time increases. — Michael
it is always the case that the probability that I am a Boltzmann brain is greater than the probability that I am not a Boltzmann brain. — Michael
In an infinite space of infinite possibilities, there are presumably an infinity of non-Boltzmann brains, so I dont; see that you have grounds for asserting that they are less common than ordinary brains... — Banno
In a single de Sitter universe with a cosmological constant, and starting from any finite spatial slice, the number of "normal" observers is finite and bounded by the heat death of the universe. If the universe lasts forever, the number of nucleated Boltzmann brains is, in most models, infinite; cosmologists such as Alan Guth worry that this would make it seem "infinitely unlikely for us to be normal brains". One caveat is that if the universe is a false vacuum that locally decays into a Minkowski or a Big Crunch-bound anti-de Sitter space in less than 20 billion years, then infinite Boltzmann nucleation is avoided. (If the average local false vacuum decay rate is over 20 billion years, Boltzmann brain nucleation is still infinite, as the universe increases in size faster than local vacuum collapses destroy the portions of the universe within the collapses' future light cones). Proposed hypothetical mechanisms to destroy the universe within that timeframe range from superheavy gravitinos to a heavier-than-observed top quark triggering "death by Higgs".
If no cosmological constant exists, and if the presently observed vacuum energy is from quintessence that will eventually completely dissipate, then infinite Boltzmann nucleation is also avoided.
Or maybe we will reach agreement that there is something quite specious about this argument. — Banno
It doesn't follow that I am most likely not a Boltzmann brain. It only follows that the probability that I am a Boltzmann brain gets smaller as the time increases. But due to the sheer number of Boltzmann brains, it is always the case that the probability that I am a Boltzmann brain is greater than the probability that I am not a Boltzmann brain. — Michael
It wasn't about the existence of a cup, or any particular physical objects as such. It was rather about the the nature of our belief in the existence of the unperceived objects or world. — Corvus
That the discussion in this thread pressuposes a belief in a real world outside our minds, my comment is a rebuttal exactly to that claim.
— Lionino
I would say that it might not logically presuppose the existence of a world... — Janus
1. There are far more long-lived Boltzmann brains than long-lived humans — Michael
But we are not talking about whether there are any Boltzmann brains, so much as whether you are a Boltzmann brain.
And the chances of that continue to shrink. — Banno
And it's always the case that the probability that I am a Boltzmann brain is greater than the probability that I am not a Boltzmann brain. — Michael
There's plenty of insuperable philosophical issues, and it's easy to make up even more. — Banno
If. — Banno
And each time you reply, that chance shrinks, and not just a little bit, but by a truely extraordinary quantity. — Banno
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