3 ms·

> 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

> 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.

cvoss 2y ago
> 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.
- dhosek 2y ago
  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?
  - dhosek 2y ago
    Of course, just by virtue of context in this discussion, the answer is kind of given away.
- Starlevel004 2y ago
  > 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.
ChrisMarshallNY 2y ago
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.

cvoss 2y ago

> 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.

dhosek 2y ago
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?
- dhosek 2y ago
  Of course, just by virtue of context in this discussion, the answer is kind of given away.
Starlevel004 2y ago
> 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.

ChrisMarshallNY 2y ago

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.