6 ms·

Always blows my mind that because light travels through space, you can literally see into the past. Imagine, way way down the line, eventually meeting a civiliz

by asxd 5y ago

Always blows my mind that because light travels through space, you can literally see into the past. Imagine, way way down the line, eventually meeting a civilization from a far away planet, and they could potentially show you actual photographs of Pangaea.

xwdv 5y ago
More than Pangea… if they mastered the ability to resolve vast distances they could show us the herds of dinosaurs roaming the world, and then their total extinction, a Timelapse of the rise of human civilization, ancient Egypt and the Roman Empire, if only we could truly meet a civilization way down the line, or perhaps they would come to meet us, given their obsession.
- JoeAltmaier 5y ago
  Perhaps if there is a large reflector in space somewhere, that light could be passing back by us today! If we had a large enough collector, we could create an image.
  - spaetzleesser 5y ago
    In theory black holes could do that. Some photons will slingshot around it and go straight back.
    - wumpus 5y ago
      We haven't seen a photon ring yet, and when we do, there won't be that much information in them. Perhaps after technology has advanced another 1000X...
- asxd 5y ago
  It's cool to think that first contact between two space-faring civilizations could potentially involve a mutual exchange of detailed historical imagery that neither civilization could have captured on their own.
  - xwdv 5y ago
    Indeed, though it’s probably likely in the history of the universe this has never happened, as what are the odds of two distant civilizations separated by many light years meeting and both offering historial imagery to each other? The chance to capture relevant images will have passed if they do not specifically plan for it.
    - asxd 5y ago
      Probably unlikely, yeah. It would have to be the result of several lucky and serendipitous events, I'm sure. The idea of seeing into the past seems so other-worldly though, it's hard not to dream :-)
tegeek 5y ago
Unfortunately, that is not possible. Earth isn't a star and not big enough to provide this much data even outside of our Solar System, let alone millions of light years away.
- ceh123 5y ago
  To add some back of the napkin calculations to this: Angular resolution of the earth at 66 million light years away would be approximately 2e-17 radians. Using the Raleigh Criterion [0] for lens size for the visible light spectrum (700nm for the best case scenario), you would need a lens with a diameter of about 4e10 meters. That's about the radius of Mercury's orbit around the sun. If you want to see dinosaurs, say 1m resolution, that's about 1.5e-24 radians at 66M light years, needing a lens of diameter 5E17. The entire solar system has a diameter of ~3e14. So even if your lens was the size of the solar system you'd still be off by a factor of 1000 trying to resolve the dinosaurs. At these scales you start running into some pretty fundamental engineering and physics problems with building a telescope this big. Warning: this math may not be totally right, I'm just procrastinating some PDE homework right now, but the scales should be roughly correct. [0] https://en.wikipedia.org/wiki/Angular_resolution#The_Rayleigh_criterion https://en.wikipedia.org/wiki/Angular_resolution#The_Rayleig...
  - devoutsalsa 5y ago
    I’m imagining an advanced civilization with a telescope capable of doing observing dinosaurs, but only ones being thinks that it an interesting use of the telescope. So they work super hard and get exactly one Earth day’s worth of observing time to look at dinosaurs w/ no possible rescheduling. When the day finally comes… clouds.
  - asxd 5y ago
    This is admittedly a bit over my head, but does that mean it is technically possible that an image of earth could be captured from the distance needed to see Pangaea? Thinking about this has sparked a bunch of questions I hadn't thought of before. For instance, does information encoded with light degrade over long distances in a vacuum? If not, it does seem like a mega-lens could potentially capture such an image right?
awb 5y ago
How big would the telescope need to be to be able to produce high-res images of Earth from a distance of 200M+ light years away? I realize that a civilization could be 50M light years away and witness Pangea, but the idea of a civilization 50M light years away observing Pangea and then persisting data for 150M years presents it’s own challenges.
- ceh123 5y ago
  Check out my reply to a sibling comment. TLDR: huge
- deleted 5y ago
  [deleted]

by asxd 5y ago

xwdv 5y ago

More than Pangea… if they mastered the ability to resolve vast distances they could show us the herds of dinosaurs roaming the world, and then their total extinction, a Timelapse of the rise of human civilization, ancient Egypt and the Roman Empire, if only we could truly meet a civilization way down the line, or perhaps they would come to meet us, given their obsession.

JoeAltmaier 5y ago
Perhaps if there is a large reflector in space somewhere, that light could be passing back by us today! If we had a large enough collector, we could create an image.
- spaetzleesser 5y ago
  In theory black holes could do that. Some photons will slingshot around it and go straight back.
  - wumpus 5y ago
    We haven't seen a photon ring yet, and when we do, there won't be that much information in them. Perhaps after technology has advanced another 1000X...
asxd 5y ago
It's cool to think that first contact between two space-faring civilizations could potentially involve a mutual exchange of detailed historical imagery that neither civilization could have captured on their own.
- xwdv 5y ago
  Indeed, though it’s probably likely in the history of the universe this has never happened, as what are the odds of two distant civilizations separated by many light years meeting and both offering historial imagery to each other? The chance to capture relevant images will have passed if they do not specifically plan for it.
  - asxd 5y ago
    Probably unlikely, yeah. It would have to be the result of several lucky and serendipitous events, I'm sure. The idea of seeing into the past seems so other-worldly though, it's hard not to dream :-)

tegeek 5y ago

Unfortunately, that is not possible. Earth isn't a star and not big enough to provide this much data even outside of our Solar System, let alone millions of light years away.

ceh123 5y ago
To add some back of the napkin calculations to this: Angular resolution of the earth at 66 million light years away would be approximately 2e-17 radians. Using the Raleigh Criterion [0] for lens size for the visible light spectrum (700nm for the best case scenario), you would need a lens with a diameter of about 4e10 meters. That's about the radius of Mercury's orbit around the sun. If you want to see dinosaurs, say 1m resolution, that's about 1.5e-24 radians at 66M light years, needing a lens of diameter 5E17. The entire solar system has a diameter of ~3e14. So even if your lens was the size of the solar system you'd still be off by a factor of 1000 trying to resolve the dinosaurs. At these scales you start running into some pretty fundamental engineering and physics problems with building a telescope this big. Warning: this math may not be totally right, I'm just procrastinating some PDE homework right now, but the scales should be roughly correct. [0] https://en.wikipedia.org/wiki/Angular_resolution#The_Rayleigh_criterion https://en.wikipedia.org/wiki/Angular_resolution#The_Rayleig...
- devoutsalsa 5y ago
  I’m imagining an advanced civilization with a telescope capable of doing observing dinosaurs, but only ones being thinks that it an interesting use of the telescope. So they work super hard and get exactly one Earth day’s worth of observing time to look at dinosaurs w/ no possible rescheduling. When the day finally comes… clouds.
- asxd 5y ago
  This is admittedly a bit over my head, but does that mean it is technically possible that an image of earth could be captured from the distance needed to see Pangaea? Thinking about this has sparked a bunch of questions I hadn't thought of before. For instance, does information encoded with light degrade over long distances in a vacuum? If not, it does seem like a mega-lens could potentially capture such an image right?

awb 5y ago

How big would the telescope need to be to be able to produce high-res images of Earth from a distance of 200M+ light years away? I realize that a civilization could be 50M light years away and witness Pangea, but the idea of a civilization 50M light years away observing Pangea and then persisting data for 150M years presents it’s own challenges.

ceh123 5y ago
Check out my reply to a sibling comment. TLDR: huge
deleted 5y ago
[deleted]