system
Given the following post, respond as if you're commenting on Reddit:
human
How does period life expectancy adjust when cohort life expectancy goes down?

My understanding is that when cohort life expectancy grows, period life expectancy lags because period life expectancy is measuring life expectancy of all existing cohorts, whereas life expectancy for the new, youngest cohorts would be expected to be higher.

We've just gone through a pandemic where period life expectancy declined in the US two years in a row. Presuming SARS-Cov-2 doesn't go away, and we have a new added cause of death at 2021/2022 rates, would we expect a similar downwards lag? 

I'm wondering if we would expect period life expectancy to stay the same as it was in 2021, other things equal? Or would it continue to decline further?
gpt
Period life expectancy is a snapshot of today. Cohort is a prediction of the future. Period life expectancy would only go down further if more people died. If COVID and everything else stays constant, period life expectancy will stay constant, and cohort life expectancy will come down to match.