Adam Elga

If the universe is really long lasting as it is, according to some theories, um,

It's enough time for various fluctuations to happen, including fluctuations who are conscious.

And so many fluctuations that due to just enough independent variation being instantiated for a long enough time than enough times, it'll turn out that of the observers that for all you know, or for all your evidence goes, are you, the vast majority of them are

Boltzmann brains, meaning piles of gook that just formed out of nothing, out of pure random chance.

If that's true, and if it's true that when you're looking at a possibility in which there are lots of observers who, for all your evidence goes, might be you, you should be somewhat even-handed about

Thinking about which one of those you are, think back to the alarm clock case.

This is like, I invite you to think of this case on the model of an alarm clock case where there are just lots of wakenings and some of them are just fluctuation wakings.

You should think my probabilities about which ones I am should be roughly equally apportioned, in which case the vast majority, since the vast majority

of those wakenings are Boltzmann brain wakenings, I should think I'm really confident that I'm a Boltzmann brain.

That's the initial, that's the first pass of how we seem to get into trouble.

Well, there is a very...

serious tradition in contemporary epistemology.

Indeed, I would say maybe the dominant tradition that a certain amount of what's called externalism is true about the relationship between evidence and experience and what your evidence is.

And an instance of a distinctive externalist view would be that two creatures could be physical duplicates, for example, at a particular time,

and so have brain firings that are exactly matching and so on, maybe light going into their optic nerves in exactly the same way.

And yet, one of them has much, much stronger evidence than the other.

This is often associated with the work of Tim Williamson in contemporary work and

If you have that kind of picture, then our evidence is much stronger than just the proposition, I seem to be having a particular sort of experience and I have certain apparent memories.

Maybe your evidence is, no, there's an apple in front of me.

There's a desk in front of me.