Monday, August 15, 2011

How Soon is Oh Fuck It, I Hate The Smiths

Via Sully I see THIS re: the paradox of the present being the past whenever we look up at the sky:
As almost everyone knows, when you stare into the depths of space you are also looking back in time. Catch a glimpse of a relatively nearby star and you see it as it existed when, perhaps, Lincoln was president (if it's 150 light-years away). Stars near the edge of our own galaxy are only seen as they appeared when the last ice age was in full bloom (30,000 light-years away). And those giant pinwheel assemblies of stars called galaxies are glimpsed, as they existed millions, hundreds of millions or even billions of years in the past.
We never see the sky as it is, but only as it was.
Stranger still, the sky we see at any moment defines not a single past but multiple overlapping pasts of different depths. The star's image from 100 years ago and the galaxy image from 100 million years ago reach us at the same time. All of those "thens" define the same "now" for us.
I guess it's comforting to know that in no recent past was the universe destroyed, but this one struck a personal note for me:
Let's take a few examples. Light travels faster than any other entity in the physical universe, propagating with the tremendous velocity of c = 300,000,000 m/s. From high school physics you know that the time it takes a light signal moving at c to cross some distance D is simply t = D/c.
Since, as we know, all I learned in physics was how to play kickball.

No comments: