4 ms·

No, it happened 26,000 years ago in our time frame as well

candiodari 7y ago
I don't get how that works. 26,000 years ago it would have been FAR outside of our "light cone". In other words it was completely beyond anything that affected our world. Only recently that changed. So doesn't it make sense that it only became part of reality yesterday ? And therefore to say that it happened yesterday. The famous supernova of 1572 AD also very much didn't happen anywhere close to 1572 AD.
- Legogris 7y ago
  So let's say you travel at the speed of light towards that event. When you arrive, 26,000 years later, would you then say the event happened 26,000 or 52,000 years ago? If the former, have you just travelled 26,000 years into the past, or did time stand still for 26,000 years from your perspective? I'd argue your clock has still moved forward 26,000 years. If we would take a snapshot of the Universe VM spacetime at the current moment at the start of the event, the "now" in time would have to correspond to the current state for every other location if you want it to be useful and not only intuitive.
  - mg631 7y ago
    From my understanding, if you travel at light speed, space is compacted to very tiny distances and time stops. If you take the math of relativity to its extreme, time for you has stopped and your trip took no time. It actually takes no time because there is actually no distance between you and the black hole. But this is where paradoxes come in because the black hole, stationary from in its frame of reference, would still experience 26,000 years and not see you arrive until then. From my understanding, general relativity solves this paradox with de-acceleration causing the one who was traveling at the speed of light seeing the rest of the universe's clocks' speed up. So technically, your clock would have not moved 26,000 years forward, but other's would have.
    - wruza 7y ago
      Not a physicist, but afaik you are right. If you go with the speed of light (or close enough), your travel time goes to zero. It is common misconception that to “reach the stars” you have to spend a couple of lives. In fact, you can get there before you finish your sandwich. This makes me think of lone sad CMB photons, who accidentally stop by hitting an atom and cannot even recognize a tiny bit of the universe they remembered since. A spark moment, and they lost everything to billions of years.
      - candiodari 7y ago
        Does that also mean they would get hit by all the light energy that hit them on the way on the moment of "arriving" in that collision ? Or is it just the first collision ever that stops them and they just happen to miss every last particle in outer space for 13 billion years perhaps.
    - krastanov 7y ago
      > But this is where paradoxes come in because the black hole, stationary from in its frame of reference, would still experience 26,000 years and not see you arrive until then. Special relativity solves this fine (there is no paradox in it for that particular thought experiment), no need to involve general relativity. There is nothing paradoxical about the observer near the center of the galaxy not seeing you until you are near, because you are traveling at speed almost as great as the speed of the information carrier (the light you emit if we are talking about space, or the sound you make if we are talking about something on Earth). So you actually do not even need relativity to explain the "they do not see us coming". You do need relativity to explain the fact that to you all of this took only a blink of an eye.
      - mg631 7y ago
        My bad I meant to talk about the fact that there is no universal reference frame, so in your frame you would believe you aren't moving, but the black hole is moving towards you. In in a scenario where you are traveling at .99c, from your frame of reference you are not traveling at all and the black hole is traveling to you, so you see the black hole experiencing incredibly slow time passage. However, that is not what the black hole sees. Hence a paradox.
crooked-v 7y ago
The problem is that "26,000 years ago" depends on perspective. For example, if space aliens were on a rocket that took off thousands of years ago but traveled at nearly the speed of light, they might say now (where "now" is approximately equal to our "now") that this actually happened 21,000 years ago. In other words, you can say "26,000 years ago from Earth's perspective", but it isn't the definitive answer for everything in this galaxy, and it definitely isn't the same answer for the rest of the universe.
- xadhominemx 7y ago
  I mean you’re kind of mixing up two concepts. Distances and the passage of time do depend on frame of reference. But that’s not the same thing as saying something we observe today happened today in our “time frame”. In our frame of reference, this event happened 26,000 light years away 26,000 years ago.
- flavor8 7y ago
  Carlos Rovelli has an excellent book called The Order of Time which helps a lot with grokking this. There is no universal clock. Time is relative.
- krastanov 7y ago
  To add to the other comments that are attempting to correct you (although the downvotes seem unwarranted): the misconception you are presenting is one of the most common ones I see in students when teaching relativity. The event did happen long time ago and the fact that time and space are relative have nothing to do with the fact that it takes us some time to see/hear that an event has happened.
  - raattgift 7y ago
    > that time and space are relative have nothing to do with the fact that it takes us some time to see/hear that an event has happened I am struggling to guess exactly what you mean by that. Could you clarify? Is the first part of the quote (up to "have") just a statement about coordinate charts? If not, and it helps with the clarification, I know how SO+(1,3) (and more particularly the one-parameter SO(1,1) boost subalgebra of O(1,3)) relates to the gauge symmetry of massless |helicity| >= 1 particles and flat spacetime, and I'm pretty sure you do too.

I don't get how that works. 26,000 years ago it would have been FAR outside of our "light cone". In other words it was completely beyond anything that affected our world. Only recently that changed. So doesn't it make sense that it only became part of reality yesterday ? And therefore to say that it happened yesterday. The famous supernova of 1572 AD also very much didn't happen anywhere close to 1572 AD.

Legogris 7y ago
So let's say you travel at the speed of light towards that event. When you arrive, 26,000 years later, would you then say the event happened 26,000 or 52,000 years ago? If the former, have you just travelled 26,000 years into the past, or did time stand still for 26,000 years from your perspective? I'd argue your clock has still moved forward 26,000 years. If we would take a snapshot of the Universe VM spacetime at the current moment at the start of the event, the "now" in time would have to correspond to the current state for every other location if you want it to be useful and not only intuitive.
- mg631 7y ago
  From my understanding, if you travel at light speed, space is compacted to very tiny distances and time stops. If you take the math of relativity to its extreme, time for you has stopped and your trip took no time. It actually takes no time because there is actually no distance between you and the black hole. But this is where paradoxes come in because the black hole, stationary from in its frame of reference, would still experience 26,000 years and not see you arrive until then. From my understanding, general relativity solves this paradox with de-acceleration causing the one who was traveling at the speed of light seeing the rest of the universe's clocks' speed up. So technically, your clock would have not moved 26,000 years forward, but other's would have.
  - wruza 7y ago
    Not a physicist, but afaik you are right. If you go with the speed of light (or close enough), your travel time goes to zero. It is common misconception that to “reach the stars” you have to spend a couple of lives. In fact, you can get there before you finish your sandwich. This makes me think of lone sad CMB photons, who accidentally stop by hitting an atom and cannot even recognize a tiny bit of the universe they remembered since. A spark moment, and they lost everything to billions of years.
    - candiodari 7y ago
      Does that also mean they would get hit by all the light energy that hit them on the way on the moment of "arriving" in that collision ? Or is it just the first collision ever that stops them and they just happen to miss every last particle in outer space for 13 billion years perhaps.
  - krastanov 7y ago
    > But this is where paradoxes come in because the black hole, stationary from in its frame of reference, would still experience 26,000 years and not see you arrive until then. Special relativity solves this fine (there is no paradox in it for that particular thought experiment), no need to involve general relativity. There is nothing paradoxical about the observer near the center of the galaxy not seeing you until you are near, because you are traveling at speed almost as great as the speed of the information carrier (the light you emit if we are talking about space, or the sound you make if we are talking about something on Earth). So you actually do not even need relativity to explain the "they do not see us coming". You do need relativity to explain the fact that to you all of this took only a blink of an eye.
    - mg631 7y ago
      My bad I meant to talk about the fact that there is no universal reference frame, so in your frame you would believe you aren't moving, but the black hole is moving towards you. In in a scenario where you are traveling at .99c, from your frame of reference you are not traveling at all and the black hole is traveling to you, so you see the black hole experiencing incredibly slow time passage. However, that is not what the black hole sees. Hence a paradox.

crooked-v 7y ago

The problem is that "26,000 years ago" depends on perspective. For example, if space aliens were on a rocket that took off thousands of years ago but traveled at nearly the speed of light, they might say now (where "now" is approximately equal to our "now") that this actually happened 21,000 years ago. In other words, you can say "26,000 years ago from Earth's perspective", but it isn't the definitive answer for everything in this galaxy, and it definitely isn't the same answer for the rest of the universe.

xadhominemx 7y ago
I mean you’re kind of mixing up two concepts. Distances and the passage of time do depend on frame of reference. But that’s not the same thing as saying something we observe today happened today in our “time frame”. In our frame of reference, this event happened 26,000 light years away 26,000 years ago.
flavor8 7y ago
Carlos Rovelli has an excellent book called The Order of Time which helps a lot with grokking this. There is no universal clock. Time is relative.
krastanov 7y ago
To add to the other comments that are attempting to correct you (although the downvotes seem unwarranted): the misconception you are presenting is one of the most common ones I see in students when teaching relativity. The event did happen long time ago and the fact that time and space are relative have nothing to do with the fact that it takes us some time to see/hear that an event has happened.
- raattgift 7y ago
  > that time and space are relative have nothing to do with the fact that it takes us some time to see/hear that an event has happened I am struggling to guess exactly what you mean by that. Could you clarify? Is the first part of the quote (up to "have") just a statement about coordinate charts? If not, and it helps with the clarification, I know how SO+(1,3) (and more particularly the one-parameter SO(1,1) boost subalgebra of O(1,3)) relates to the gauge symmetry of massless |helicity| >= 1 particles and flat spacetime, and I'm pretty sure you do too.