5 ms·

Depends on your frame of reference. No, really: http://en.wikipedia.org/wiki/Relativity_of_simultaneity http://en.wikipedia.org/wiki/Relativity_of_simultaneity

by Cushman 16y ago

Depends on your frame of reference. No, really: http://en.wikipedia.org/wiki/Relativity_of_simultaneity http://en.wikipedia.org/wiki/Relativity_of_simultaneity There's not really such a thing as "right now, over there". To use the obvious example, from the perspective of the light, no time has passed since it was emitted at the object and our observing it.

pyre 16y ago
I think the point is that if we were able to instantaneously transport ourselves there we would be observing a 50 million + 30 year old black hole. Nobody talks about things from the the perspective of a photon (in casual conversation, at least).
- eru 16y ago
  If you could transfer yourself in an instant, you can even go back in time---with some relativistic trickery.
- baddox 16y ago
  That's false, or rather, undefined. To "instantaneously transport ourselves" implies that there is an absolute time frame shared by us and the black hole, i.e. if it's 3:00 PM our time when we transport ourselves, we'll appear at 3:00 PM "black hole time." There simply is no such concept in relativity. For two events A and B separated in space, some observers will see them happening simultaneously, some will see A occur before B, and still other will see B occur before A.
  - JoeAltmaier 16y ago
    Yeah, we hear that a lot. But we also know to the millisecond "how long" it took the light to get here etc. Yes, they are different frames of reference. But if we crawled over there we know exactly how much time had passed there, and how old the black hole would be when we got there.
    - jerf 16y ago
      You said "instantaneously". That usually would imply traveling outside of your lightcone. That really is undefined; an "instantaneous" transport from here can end up anywhere outside of your lightcone, which are all equally well(/poorly) defined in relativity. You can't distinguish those points in either time or space without creating a preferred reference frame. This is the same reason FTL drives are also, fundamentally, time machines. It's really a very profound thing; there's no "yeah, but really we know there's an absolute time frame underneath it all"... there really, really isn't an absolute time frame, and you really, really can't say how old the black hole would be if you "instantaneously" transported there; it is just as valid to instantaneously appear when it is 31 years old as it would be to appear when it is 100,000,029 years old (taking of course the estimated age as its true age). Or, IMHO, just as invalid because FTL and instantaneous truly don't exist. Yes, if you change your claim to be sublight and non-instantaneous we can compute how old it would be, but that's a profound goal post shift. The Minkowski metric is a mindbender, the moreso once you realize that it is not some weird mathematical abstraction with no connection to reality, it is reality, or at least a much better approximation than the one we instinctively use. The "weird mathematical abstraction with no connection to reality" is the implicitly Euclidean/Galilean metric that exists in our heads. (Which can actually be demonstrated to contain fundamental contradictions if you poke them hard enough.)
      - baddox 16y ago
        Which fundamental contradictions of the Euclidean/Galilean metric are you referencing?
        jerf 16y ago
        http://www.mathpages.com/rr/s3-07/3-07.htm http://www.mathpages.com/rr/s3-07/3-07.htm It may help to read the preceding bit of the work. It is probably also not necessarily clear which part of that page is talking about the fundamental contradictions of the metric if you haven't read the preceding chapters. The key sentence that makes the point I am referring to is "Before blithely dismissing this concern as non-sensical, it's worth noting that modern physics has concluded (along with Zeno) that the classical image of space and time was fundamentally wrong, and in fact motion would not be possible in a universe constructed according to the classical model.", where the "classical model" is one based on a Euclidean metric in which time is simply another spatial dimension that acts weird for no apparent-within-the-model reason, rather than being an actually special dimension as it is in the Minkowski metric. Also, "In all four of Zeno's arguments on motion, the implicit point is that if space and time are independent, then logical inconsistencies arise regardless of whether the physical world is continuous or discrete." where again, space and time being independent is a characteristic of the Euclidean/Galilean metric. (A little rough to be pointing you to the middle of that very-fine work, but it makes the point far better than I can.)
  - Dylan16807 16y ago
    No, it doesn't have to be absolute at all. It just has to be shared. And the frame of reference is roughly shared, just not closely enough for 30 years to matter. If I'm doing my math right, the redshift of M100 works out to less than 700 years variation over a 50 million year timespan.
- run4yourlives 16y ago
  You are assuming time is constant. It is not.
- augustl 16y ago
  > if we were able to instantaneously transport ourselves That is simply not interesting. We aren't able to instantaneously transport ourselves. So what we think might happen when we do that, is pure fantasy.
steve19 16y ago
Did the object exist 31 years ago? Sure it did.
- zohebv 16y ago
  Not in all frames of reference. There is a frame of reference in which the object appeared just 30.5 years ago. This would be a frame of reference which would be moving from the star towards the earth at 0.9999999999999999*c
  - steve19 16y ago
    Don't we generally report the age of objects relative to themselves (generally not in astronomy or physics)? You are not -1 or +5 in age (relative to myself).
    - zohebv 16y ago
      Generally yes (but not at astronomical scales), when everyone shares the same frame of reference. Moreover the star and earth in all likelihood don't share the same frame of reference. The distance between the two of us is very tiny. The error in simultaneity between the two of us would be the time it takes a light ray to travel between the two of us. 84 milliseconds in the worst case. So I cannot have a -1 or +5 in age difference with you. The wiggle room is around 84 ms. If you are 1 light year away, the wiggle room now expands to 1 year! Depending on the observer I am 0 or +1 years older than you. On astronomical scales the wiggle room is quite huge. For example there is a frame of reference in which the blackhole celebrates its 30th birthday AFTER the year 2009. When such a frame exists it does not make sense to say that the star is now 50M years old. There is no notion of simultaneity. The word "now" is profoundly misleading. There is no absolute time. Lets say you are a soldier that drops a bomb that kills 30 people. However from your POV you see only 3 dead people. You cannot claim that in your frame of reference only 3 people died. You can only say "I saw 3 dead people". In reality 30 people died. Similarly, there are innumerable frames of reference in which the 30th birthday of the blackhole occured after the year 2009 on earth. So it is misleading to say that the star is now 50M years old.
zohebv 16y ago
This is correct. Relativity destroys all notions of simultaneity between 2 distant objects. We only have causally and non-causally related events. In this case, the black hole at age 35 can only causally affect us in the year 2015. To put it simply, there exists a frame of reference in which the year 2010 on earth occurs before the 35th birthday of the black hole. So to say that the black hole is 50,000,030 years old in the year 2010 on earth is misleading. It is only true for one very particular frame of reference i.e. the earth.

by Cushman 16y ago

pyre 16y ago

I think the point is that if we were able to instantaneously transport ourselves there we would be observing a 50 million + 30 year old black hole. Nobody talks about things from the the perspective of a photon (in casual conversation, at least).

eru 16y ago
If you could transfer yourself in an instant, you can even go back in time---with some relativistic trickery.
baddox 16y ago
That's false, or rather, undefined. To "instantaneously transport ourselves" implies that there is an absolute time frame shared by us and the black hole, i.e. if it's 3:00 PM our time when we transport ourselves, we'll appear at 3:00 PM "black hole time." There simply is no such concept in relativity. For two events A and B separated in space, some observers will see them happening simultaneously, some will see A occur before B, and still other will see B occur before A.
- JoeAltmaier 16y ago
  Yeah, we hear that a lot. But we also know to the millisecond "how long" it took the light to get here etc. Yes, they are different frames of reference. But if we crawled over there we know exactly how much time had passed there, and how old the black hole would be when we got there.
  - jerf 16y ago
    You said "instantaneously". That usually would imply traveling outside of your lightcone. That really is undefined; an "instantaneous" transport from here can end up anywhere outside of your lightcone, which are all equally well(/poorly) defined in relativity. You can't distinguish those points in either time or space without creating a preferred reference frame. This is the same reason FTL drives are also, fundamentally, time machines. It's really a very profound thing; there's no "yeah, but really we know there's an absolute time frame underneath it all"... there really, really isn't an absolute time frame, and you really, really can't say how old the black hole would be if you "instantaneously" transported there; it is just as valid to instantaneously appear when it is 31 years old as it would be to appear when it is 100,000,029 years old (taking of course the estimated age as its true age). Or, IMHO, just as invalid because FTL and instantaneous truly don't exist. Yes, if you change your claim to be sublight and non-instantaneous we can compute how old it would be, but that's a profound goal post shift. The Minkowski metric is a mindbender, the moreso once you realize that it is not some weird mathematical abstraction with no connection to reality, it is reality, or at least a much better approximation than the one we instinctively use. The "weird mathematical abstraction with no connection to reality" is the implicitly Euclidean/Galilean metric that exists in our heads. (Which can actually be demonstrated to contain fundamental contradictions if you poke them hard enough.)
    - baddox 16y ago
      Which fundamental contradictions of the Euclidean/Galilean metric are you referencing?
      - jerf 16y ago
        http://www.mathpages.com/rr/s3-07/3-07.htm http://www.mathpages.com/rr/s3-07/3-07.htm It may help to read the preceding bit of the work. It is probably also not necessarily clear which part of that page is talking about the fundamental contradictions of the metric if you haven't read the preceding chapters. The key sentence that makes the point I am referring to is "Before blithely dismissing this concern as non-sensical, it's worth noting that modern physics has concluded (along with Zeno) that the classical image of space and time was fundamentally wrong, and in fact motion would not be possible in a universe constructed according to the classical model.", where the "classical model" is one based on a Euclidean metric in which time is simply another spatial dimension that acts weird for no apparent-within-the-model reason, rather than being an actually special dimension as it is in the Minkowski metric. Also, "In all four of Zeno's arguments on motion, the implicit point is that if space and time are independent, then logical inconsistencies arise regardless of whether the physical world is continuous or discrete." where again, space and time being independent is a characteristic of the Euclidean/Galilean metric. (A little rough to be pointing you to the middle of that very-fine work, but it makes the point far better than I can.)
- Dylan16807 16y ago
  No, it doesn't have to be absolute at all. It just has to be shared. And the frame of reference is roughly shared, just not closely enough for 30 years to matter. If I'm doing my math right, the redshift of M100 works out to less than 700 years variation over a 50 million year timespan.
run4yourlives 16y ago
You are assuming time is constant. It is not.
augustl 16y ago
> if we were able to instantaneously transport ourselves That is simply not interesting. We aren't able to instantaneously transport ourselves. So what we think might happen when we do that, is pure fantasy.

steve19 16y ago

Did the object exist 31 years ago? Sure it did.

zohebv 16y ago
Not in all frames of reference. There is a frame of reference in which the object appeared just 30.5 years ago. This would be a frame of reference which would be moving from the star towards the earth at 0.9999999999999999*c
- steve19 16y ago
  Don't we generally report the age of objects relative to themselves (generally not in astronomy or physics)? You are not -1 or +5 in age (relative to myself).
  - zohebv 16y ago
    Generally yes (but not at astronomical scales), when everyone shares the same frame of reference. Moreover the star and earth in all likelihood don't share the same frame of reference. The distance between the two of us is very tiny. The error in simultaneity between the two of us would be the time it takes a light ray to travel between the two of us. 84 milliseconds in the worst case. So I cannot have a -1 or +5 in age difference with you. The wiggle room is around 84 ms. If you are 1 light year away, the wiggle room now expands to 1 year! Depending on the observer I am 0 or +1 years older than you. On astronomical scales the wiggle room is quite huge. For example there is a frame of reference in which the blackhole celebrates its 30th birthday AFTER the year 2009. When such a frame exists it does not make sense to say that the star is now 50M years old. There is no notion of simultaneity. The word "now" is profoundly misleading. There is no absolute time. Lets say you are a soldier that drops a bomb that kills 30 people. However from your POV you see only 3 dead people. You cannot claim that in your frame of reference only 3 people died. You can only say "I saw 3 dead people". In reality 30 people died. Similarly, there are innumerable frames of reference in which the 30th birthday of the blackhole occured after the year 2009 on earth. So it is misleading to say that the star is now 50M years old.

zohebv 16y ago

This is correct. Relativity destroys all notions of simultaneity between 2 distant objects. We only have causally and non-causally related events. In this case, the black hole at age 35 can only causally affect us in the year 2015. To put it simply, there exists a frame of reference in which the year 2010 on earth occurs before the 35th birthday of the black hole. So to say that the black hole is 50,000,030 years old in the year 2010 on earth is misleading. It is only true for one very particular frame of reference i.e. the earth.