5 ms·

Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light, capturing the light simultaneously, and then resolvi

Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light, capturing the light simultaneously, and then resolving the image via async computation later? I think this is called interferometry and I know it's hard because you need _very_ precise timing, but I'm curious if that would be possible or not. (Maybe you can get the timing in sync with atomic clocks, or by sending a laser to both from a central point that lets them keep time with some very tight tolerance?) Weird idea but I wonder if there are ways to take this from "crazy tech" to "hard tech".

colechristensen 2y ago
The precision you need for interferometry depends on the wavelength, and being able to do this over astronomical distances at visible wavelengths would indeed be a challenge. I think the scale is timing more accurate than 0.1 nanoseconds and distance accuracy on the order of 100 nanometers. Near those orders of magnitude at least and over astronomical distances that might be measured in AU. Then again the precision of the gravitational wave instruments measure distance on the order of the width of a proton, so who knows. Terrestrial infrared and optical interferometry telescopes are on the bleeding edge right now.
- vlovich123 2y ago
  "Boring" cesium atomic clocks can do 50 ps per day with the best cutting edge optical clocks coming in at ~739 fs per day. Optical clocks would only need to resynchronize once every ~ 135 days while cesium clocks would need to do it every 2 days to get 0.1ns of accuracy. I think the bigger challenge may be how you would transport the clocks after synchronization to maintain it across astronomical distances since they're very sensitive to any kind of acceleration. Since you have to regularly re-synchronize them in space anyway, that feels like the engineering problem you'd have to solve - how do you synchronize two atomic; the current record is synchronizing to within 0.32fs at a distance of 300km [1]. [1] https://spectrum.ieee.org/atomic-clock-femtosecond-accuracy https://spectrum.ieee.org/atomic-clock-femtosecond-accuracy
chgs 2y ago
On a cosmic scale what does simultaneously mean? Two object in a distinct orbit will be in different planes of reference
- hatthew 2y ago
  Presumably it means that two light rays that leave the same point on the planet simultaneously (but going in slightly different directions) arrive at the two telescope satellites simultaneously
cyberax 2y ago
> Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light The Sun. Literally. Satellites have to be that far for the Einstein ring to be bigger than the apparent size of the solar disk. Edit: to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. So if you're too close to the lensing object so that the Einstein ring is not larger than it, you'll just see a part of the object to be a bit more bright. Also, the gravitational lens does not actually _focus_ the image, it distorts it into a band around the lensing object.
- Dalewyn 2y ago
  >to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. Or to put it another way: A gravity lens bends space so that the light from behind an object curves around it while travelling straight.
  - tbrownaw 2y ago
    "Normal" lenses bend light more strongly farther out towards the edges. Gravitational lensing is shaped differently.
    - Dalewyn 2y ago
      The point is you aren't bending the light, no the light is travelling straight. You are bending the dimension, the light travels straight through a bent dimension thus coming out curved. I think that's mindblowing.
      - oneshtein 2y ago
        No, light doesn't travel in straight lines. Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part. This difference in speed, caused by _interaction_ between the photon and gravitational field of the body, results in the bending of the light's trajectory. Bending of spacetime is just a simplification of this process to model that easier.

colechristensen 2y ago

The precision you need for interferometry depends on the wavelength, and being able to do this over astronomical distances at visible wavelengths would indeed be a challenge. I think the scale is timing more accurate than 0.1 nanoseconds and distance accuracy on the order of 100 nanometers. Near those orders of magnitude at least and over astronomical distances that might be measured in AU. Then again the precision of the gravitational wave instruments measure distance on the order of the width of a proton, so who knows. Terrestrial infrared and optical interferometry telescopes are on the bleeding edge right now.

vlovich123 2y ago
"Boring" cesium atomic clocks can do 50 ps per day with the best cutting edge optical clocks coming in at ~739 fs per day. Optical clocks would only need to resynchronize once every ~ 135 days while cesium clocks would need to do it every 2 days to get 0.1ns of accuracy. I think the bigger challenge may be how you would transport the clocks after synchronization to maintain it across astronomical distances since they're very sensitive to any kind of acceleration. Since you have to regularly re-synchronize them in space anyway, that feels like the engineering problem you'd have to solve - how do you synchronize two atomic; the current record is synchronizing to within 0.32fs at a distance of 300km [1]. [1] https://spectrum.ieee.org/atomic-clock-femtosecond-accuracy https://spectrum.ieee.org/atomic-clock-femtosecond-accuracy

chgs 2y ago

On a cosmic scale what does simultaneously mean? Two object in a distinct orbit will be in different planes of reference

hatthew 2y ago
Presumably it means that two light rays that leave the same point on the planet simultaneously (but going in slightly different directions) arrive at the two telescope satellites simultaneously

cyberax 2y ago

> Is there anything stopping you from putting 2+ satellites out "closer" but in the path of the lensed light The Sun. Literally. Satellites have to be that far for the Einstein ring to be bigger than the apparent size of the solar disk. Edit: to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. So if you're too close to the lensing object so that the Einstein ring is not larger than it, you'll just see a part of the object to be a bit more bright. Also, the gravitational lens does not actually _focus_ the image, it distorts it into a band around the lensing object.

Dalewyn 2y ago
>to make it a bit more clear, the gravitational lens does not quite behave like a normal lens. Instead, you see the light from _behind_ the object. Or to put it another way: A gravity lens bends space so that the light from behind an object curves around it while travelling straight.
- tbrownaw 2y ago
  "Normal" lenses bend light more strongly farther out towards the edges. Gravitational lensing is shaped differently.
  - Dalewyn 2y ago
    The point is you aren't bending the light, no the light is travelling straight. You are bending the dimension, the light travels straight through a bent dimension thus coming out curved. I think that's mindblowing.
    - oneshtein 2y ago
      No, light doesn't travel in straight lines. Stronger gravity around massive objects causes slow down of the part of a light wave closer to object, compared to outer part. This difference in speed, caused by _interaction_ between the photon and gravitational field of the body, results in the bending of the light's trajectory. Bending of spacetime is just a simplification of this process to model that easier.