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There has been some speculation on this subject by Church theologians and philosophers.
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Bottom line, there is a lot of mystery involved so some words might seem contradictory or inconsistent, but at least some of the confusion comes from the doctrine that in the next world time A) will be no more, or B) will be very different from the time we now know.
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A and B are not mutually exclusive and can be seen as two different ways of looking at the same thing.
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A reason the rules on indulgences were changed is because saying there is no time as we know it in the next world makes it hard to explain what a 7 days' indulgence means, compared to 40 days or a quarantine, if there is no time, as such, in Purgatory. If it's not "time as we know it," then why say "days" or "quarantines" (which refers to a length of time on the calendar, similar to the duration of Lent).
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One of the attributes that angels enjoy is agility, which means the ability to move through the universe at the speed of thought. Well, to our way of thinking, speed implies the passing of time. The saints in heaven will share this angelic faculty of agility so that they will be able to move with the speed of thought, but what does that have to do with there being no time as we know it?
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As St. Paul says, we see now imperfectly, as through a glass darkly, but then we shall see with vision clear.
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A lot of the Protestant and other non-Catholic errors come from their expectation that the next world will be just like this one, so they imagine what their best day has been in their life and project that onto what they would expect every day to be like in heaven. Or take Moslems for example, with their 72 virgins being the be-all-and-end-all of paradise. Did they ever wonder how enjoyable that would be for the virgins? Or Hindus or Buddhists with their so-called meditation consisting of achieving the ultimate goal by emptying the mind of all thought. Nothingness is bliss, then? Not according to Catholic doctrine.