Unclear expression

[vanveen]

Hello, could anybody help me please?
I've recently read the following poem:
Louis Macneice
Star-gazer.

Forty-two years ago (to me if to no one else
The number is of some interest) it was a brilliant starry night
And the westward train was empty and had no corridors
So darting from side to side I could catch the unwonted sight
Of those almost intolerably bright
Holes, punched in the sky, which excited me partly because
Of their Latin names and partly because I had read in the textbooks
How very far off they were, it seemed their light
Had left them (some at least) long years before I was.

And this remembering now I mark that what
Light was leaving some of them at least then,
Forty-two years ago, will never arrive
In time for me to catch it, which light when
It does get here may find that there is not
Anyone left alive
To run from side to side in a late night train
Admiring it and adding noughts in vain.

What exactly does its final line mean? I know what its literal translation is, but perhaps there is some kind of wordplay used there, or something. So I'd be very grateful if someone could interpret it for me.

[Tdol]

He'll be dead before the light that was leaving the stars at the time of the first verse arrives here . The adding noughts probably has something to do with the arithmetic in calculating these distances- if there's no one to see the light, then all those zeros involved in travelling light years are meaningless- that's how I interpret it, though it's not very clear to me.