Is there any such thing as an absolute?

Well, there's the speed of light...
By adding the terminal 9, by the way, you make that first bit untrue.Nevertheless, we can choose to dismiss whatever we like, it doesn't make them go away, though. We can say God created the Earth and the universe etc in 6 days and that I know this absolutely, and then simply dismiss things which have non-zero chances of being true that challenge my 'knowledge'. If we want we could do that kind of thing. Then you're wrong.Look - forget the extreme philosophical examples for a moment.You have a head injury. You wake up and next to you see someone who looks like your mother/wife/sister/brother/father whatever, but it isn't them. They do sound like them. And they've studied them well based on the content of their speech. But it isn't them. They assure you they are who they appear to be. They have your loved one's passport, the imposters! Then more imposters from your friends and family turn up.This is your perception of reality. Its how things are from your perspective.They tell you about the head injury and Capgras Delusion, but they're clearly just trying to trick you for some reason. Are they CIA? CSIS? Aliens?

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As a starting point I would like to dispute the idea that imagining a reality that is in opposition to what we observe is a valid objection to the idea that we can be sure of what we observe.

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You observe imposters - can you be sure of that or do you have Capgras syndrome? I'm saying reality is in opposition to what you observe. I think this is a valid objection to the idea that we can be sure of what we observe.If you want to get picky about 'observation' you are free to replace my example with some kind of hallucinatory condition instead.

Know absolutely? No amount of times will be sufficient. It's unlikely, but a freak Quantum Tunnelling event does have a certain probability of occurring, I suppose. Probably. No. Otherwise you could dismiss the probability of winning the lottery as zero. After all, you could play all your life without winning. Indeed, that's what'll probably happen.The real probability is very nearly zero.
The practical, every day probability is zero. We've only observed the tiniest fraction of such interactions. No. They can be good enough for practical purposes, but never absolutely zero. After all, you may be being deluded about the consensus. There's about a 5% chance you will suffer a psychotic episode once in your life. So there should always be some doubt.

The reason I used it was because of that. You can play the lottery each week for the rest of your life without winning and probably will if you tried. This is analogous to you bumping into a wall over and over again.That doesn't make the probability 0. With the lottery example, we can observe others winning, and we can calculate the exact probabilities which explain why winning is rare. It needs to be 0.0.9999.... IS 1. It's not a tiny infinite bit smaller than one and we just call it 1. It IS 1. Exactly and precisely 1. On the other hand the chances of walking through a wall are not exactly 0. It is > 0. So 9/9 ≠ 1? The laws of physics actually allow a solid object to pass through another solid object. To know what is going on or to have absolute knowledge of what is going on? The two are different. I think therefore I am?

1/9 = 0.111111...
3/9 = 0.33333.....
7/9 = .7777....
9/9 = 0.9999......Its a quirk of our numbering system that there are multiple ways of representing numbers. 0.99999~ = 1 ? is still open if you want to get to grips with the hows and whys! I'm a militant agnostic!