The stranger asked me to find the first page.

I laid my left hand on the cover and, trying to put my thumb on the flyleaf, I opened the book. It was useless. Every time I tried, a number of pages came between the cover and my thumb. It was as if they kept growing from the book.

‘Now find the last page.’

Again I failed. In a voice that was not mine, I barely managed to stammer, ‘This can’t be.’
Still speaking in a low voice, the stranger said, ‘It can’t be, but it is. The number of pages in this book is no more or less than infinite. None is the first page, none the last. I don’t know why they’re numbered in this arbitrary way. Perhaps to suggest that the terms of an infinite series admit any number.’ ”

Borges touches upon space and time when he says…

“If space is infinite, we may be at any point in space. If time is infinite, we may be at any point in time.”

The author’s dilemma of analyzing this Book of Sand leads him to insomnia and he keeps looking for patterns until he realizes that there is no end to infinite possibilities. He then just ‘loses’ the book in a library.