I would say that it might not logically presuppose the existence of a world, but that it does pragmatically presuppose it — Janus

:up: That is the topic, my faulty use of "logical possibility" was a display of a language addiction of mine.

No one really believes they are the only person or that there is no external (to the body) world — Janus

I would guess so, but my illustration is to show that, if such a person were to exist, there would be no pragmatic contradiction:

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

A solipsist may also be pragmatically justified in being cautious and not endangering others because, he may believe that, if he interacts (jumps) in such a way (off the) with the contents of his mind (bridge), his existence might cease. That surely raises the problem of how he came up with the conclusion that his existence might cease, as our belief in death likely comes from our intuition that there are other minds, and the association between consciousness and behaviour (unmoving dead body = no consciousness), and believing in other minds is contradictory (logically this time) with solipsism. But I would say that believing something without a reason is not a contradiction but rather a display of irrationality.

And I will quote myself: And it is fantasy, because I just made it up, but I am just defending that solipsism does not entail [this performative] contradiction.

There might had been a situation... — Corvus

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.

If you were buying some coffee... — 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.

Object permanence develops in a wee babe, and for some disappears during undergrad philosophy courses.

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.

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

That would be an invalid argument.

Assume that there are 1,000 short-lived Boltzmann brains, 100 long-lived Boltzmann brains, and 10 long-lived human brains. Most Boltzmann brains are short-lived, but most long-lived brains are Boltzmann brains.

From the Wikipedia article:

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

Most long-lived brains are batty brains. That yours is not a batty brain shows that on the balance of probability it is not a Boltzmann brain.

That the world persists shows that it is very unlikely to be a mere statistical aberration.

Well, the thread is about the world, not about solipsism, so the argument used did nto directly address sophisms. probably for another thread.

Yep.

Solipsism requires a particular picture of how things are, in particular of a "self" very different to the self that I have. It's a self that hides things from itself... somewhat mad.

It's just simpler to supose things to be pretty much as they appear, with other people and objects that persist over time when unobserved and surprises and occasional true statements and hopefully rarer errors.

Perhaps I can put it like this: I don't really need to write a reply to your post, because if you are a Boltzmann brain, then the overwhelming probability is that you will phizzle out in a puff of probability before you read it.

So if you are reading this, you are probably not a Boltzmann brain.

Yeah, I know. there will be one Boltzmann brain somewhere that persists until it reads this sentence. But what were the chances of it being you?

You still there?

The more your read this, the less likely it is your are a Boltzmann brain...

Still there?

Best stop while you are ahead...

Hey, don't get upset with me - I'm just a statistical aberration....

Or the world is as it seems, and you needn't worry about it ceasing in the near future, and I really am being a bit of a dick.

Now what do you think? :wink:

There are 1,000 red balls with no green stripe.
There are 100 red balls with a green stripe.
There are 10 blue balls with a green stripe.

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.

So:

There are 1,000 short-lived Boltzmann brains.
There are 100 long-lived Boltzmann brains.
There are 10 long-lived human brains.

Most Boltzmann brains are short-lived brains, but most long-lived brains are Boltzmann brains. Therefore if I am a long-lived brain then I am most likely a Boltzmann brain.

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

No, it isn't.

And your reply renders it even less likely that you are a quantum fluctuation.

Yes, it is. You claimed that:

1. Because most Boltzmann brains are short-lived then if I am long-lived then I am probably not a Boltzmann brain.

This can be generalised as:

2. Because most X are Y then if not Y then probably not X

Substituting in something else for X and Y:

3. Because most red balls have no stripe then if the ball has a stripe then it is probably not a red ball

My example above shows why (3) is false, and so why (2) is false, and so why (1) is false.

Well, the thread is about the world, not about solipsism — Banno

Solipsism is the denial that the human mind has any ground for believing in the existence of anything but itself, anything but itself is the (outside) world.

probably for another thread — Banno

That sounds good to me. Time for lasagna and shake!

Nuh. I'm arguing that since you picked out a ball with a green stripe, chances are it was red, and will disappear momentarily. But it hasn't disappeared yet, and the longer it doesn't disappear the less likely that it is a quantum fluctuation.

This is fun, since the longer this discussion continues, the less likely it is that you are a quantum fluctuation...

Solipsism is the denial that the human mind has any valid ground for believing in the existence of anything but itself, anything but itself is the (outside) world. — Lionino

Sure. It's based in a very odd notion of "valid". And, for that matter, of "human mind".

But it hasn't disappeared yet, and the longer it doesn't disappear the less likely that it is a quantum fluctuation. — 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.

Sure. It's based in a very odd notion of "valid". And, for that matter, of "human mind". — Banno

:up:

probably for another thread.

t only follows that the probability that I am a Boltzmann brain gets smaller as the time increases. — Michael

Yep.

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 don't see that you have grounds for asserting that they are less common than Boltzmann brains...

But keep going. Again, the longer you persist, the more likely that you are an ordinary brain.

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

From the Wikipedia article:

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.

In no case is there an infinity of non-Boltzmann brains. In some cases there are an infinity of Boltzmann brains.

To avoid the Boltzmann brain hypothesis you need to hope that either there is no cosmological constant or that the universe is a false vacuum.

Again, the longer you persist, the more likely that you are an ordinary brain. — Banno

But never as likely that I am a Boltzmann brain.

Keep it up.

Maybe some time you will get lucky, and dissipate before the next reply...

Or maybe we will reach agreement that there is something quite specious about this argument...

Or maybe we will reach agreement that there is something quite specious about this argument. — Banno

The argument is valid:

1. There are far more long-lived Boltzmann brains than long-lived humans
2. I am long-lived
3. Therefore, I am more likely to be a Boltzmann brain than a human

Our current scientific theories suggest that (1) is true.

It would be strange to suggest that our current scientific theories are probably wrong simply because you don't like the conclusion.

Unless you have some actual evidence against either (1) or (3), your rejection of the argument is simply a matter of faith (as I said before).

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 seems to me there is a problem with you being a Boltzmann brain and yet so predictable. Should we expect that if you are a BB? Where's the batty?

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

But it's not a belief. The world really exists. And it really exists precisely because there is nothing outside of ideas or perceptions. Since there is nothing outside those, there is no "outside" at all, and since there is no outside, the so-called "inside" is actually the world itself. So the world does exist. It lies within the idea itself. Idealism leads to realism and realism leads to idealism. It's a "loop".

It seems to me there is a problem with you being a Boltzmann brain and yet so predictable. Should we expect that if you are a BB? Where's the batty? — wonderer1

See here.

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

All discussion is existentially dependent upon language use. Language use requires shared meaning. Shared meaning is existentially dependent upon a plurality of creatures drawing the same correlations between the same things(or close enough). Solipsism, and discussions about it, both depend upon a plurality of language users.

Where there has never been language use, there could have never been any discussion such as this one. It does not matter if one believes that or not.

1. There are far more long-lived Boltzmann brains than long-lived humans — Michael

There are an awful lot of "if"'s in the argument.

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.

So please, continue.

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. Even if we were to continue this discussion for 1,000 years.

That seems to beg the question and blend epistemological with ontological idealism.

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

If.

And each time you reply, that chance shrinks, and not just a little bit, but by a truely extraordinary quantity.

All is grist to my previous contention:

There's plenty of insuperable philosophical issues, and it's easy to make up even more. — Banno

I will continue to take the world as being pretty much as it appears.

If. — Banno

Yes, and our current scientific theories suggest that the "if" is true.

And each time you reply, that chance shrinks, and not just a little bit, but by a truely extraordinary quantity. — Banno

And it's still always the case that the probability that I am a Boltzmann brain is greater than the probability that I am not a Boltzmann brain.

I will continue to take the world as being pretty much as it appears. — Banno

And you're welcome to do so. But it's a faith, not something supported by empirical evidence.