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Comment by ChrisMarshallNY | Hacker News Reader

> are still intact today

I would suggest, instead, that we can still see their light.

They may have popped their clogs, long ago, and we would not have known, as we're seeing their old videotapes.

There's something called the "Cosmic Event Horizon," or somesuch. It's the distance from us, that we'll never be able to see, because it is more than 13.8 billion light-years away, and we'll never see anything beyond.

Every time I think about the distances and scales of the universe, I get a headache.

[EDITED TO ADD] I wasn't talking about the nearby stars, and neither were they. That quote was talking about distant, red-shifted galaxies.

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> They may have popped their clogs, long ago,

Nearly every single star we can see in the entire Laniakea supercluster is still shining today.

The universe is big, but stars live for a really long time.

> still shining today

It's an interesting quirk of these discussions of events at relativistic scales that it's very hard to precisely speak about what we mean whenever we reference time.

For all of us "here", who are within non-relativistic distance of each other, "today" is a meaningful point in time. But what does our "today" mean for that far-away star? I think you are trying to articulate that, if the star is X light years away from us, after X years from "today" we will still be receiving light that has traveled from the star to "here". But you might instead mean that if a traveller were to depart from "here" "today" at near relativistic speed, when he arrives at the star he will find it still shining "there" at "that time".

But notice those are definitely not the same data point about the star. The first data point will arrive here in X years to show us the star was still shining X years previously. But the traveler will collect the second data point (almost immediately for himself, by the way) and may find the star dead. This can happen if he and the star's last light cross paths in flight.

My favorite thing along these lines is a question from my undergrad special relativity textbook:

A pole vaulter carrying a 40m pole is running at a speed such that to an observer, he appears contracted by ½. He runs through a barn of length 20m and the doors at each end of the barn are closed simultaneously.

But to the pole vaulter, the barn appears contracted by ½ and thus appears to be 10m long to him. What does he see when the doors are closed?

Of course, just by virtue of context in this discussion, the answer is kind of given away.

> It's an interesting quirk of these discussions of events at relativistic scales that it's very hard to precisely speak about what we mean whenever we reference time.

No it isn't. This is a stupid psued talking point.

Depends on what type of star.

The only stars that have never been observed to die, are red dwarfs.

I think blue giants are the shortest-lived ones.

Ours is in the middle. I think they give the Sun about four billion more years.

BTW: That was a rhetorical statement. The issue is, we don't actually know what's going on, today.

If they're circling the Milky Way, they are close, in a cosmic sense.

The milky way is only 100,000 light years across.

Stars of a certain small size will also continue shining for a trillion years.

Yeah, it's interesting that folks seemed to take offense at what I said. It's really pretty much exactly what you'd hear, from any astronomer (which I'm not, but one of my favorite shows is How the Universe Works).

Not all stars are created equal. Blue giants may only live a few billion years, while red dwarfs will last practically forever.

These are 13 billion year old stars that are only 30,000 light years away, that’s like one part in 40,000 of how long they’ve lived. They are most certainly still there shining. Is just incorrect to be pedantic about there light being there but maybe not them.

That was a rhetorical statement. It's a "Here, there be dragonnes" type of thing. We say stuff like that, hereabouts, all the time. My statement was incredibly mild, compared to some of the crazy stuff people say, here.

Shrug, unnecessary pedantry is indeed a theme around here, I try to resist the urge but am guilty of it myself from time to time.

I suspect that a number of folks didn’t realize where the quote came from.

They were talking about distant galaxies, not the relatively nearby stars.

Blue giants live only a few million years to a few tens of millions of years.

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