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Gravitational Lensing to Observe Ancient Earth

rein.pk

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Re: Gravitational Lensing to Observe Ancient Earth

#11

Post by pkrein »

aphyr wrote: post #10

The practical limitation isn't just magnitude, but resolving power. Atmospheric disturbance makes it difficult to resolve anything smaller than a meter from orbit, and the diffraction limit means the further are away from the thing you want to observe, the wider your telescope needs to be. Since the distortion effects near a black hole are near-asymptotic, the features we want to see have very small subtended angles,…

Aperture synthesis (several widely-separated telescopes looking at one object) is often used to increase the resolving power. http://en.wikipedia.org/wiki/Aperture_synthesis

Re: Gravitational Lensing to Observe Ancient Earth

#13

Post by shill »

fsiefken wrote: post #7

You need to read 'The Light of Other Days', detailing the use of microscopic wormhole lenses to observe ancient earth: http://en.wikipedia.org/wiki/The_Light_of_Other_Days

I had an idea to write a story about this when I was a kid. In my version, planets made of pure mercury were sought by detectives for their potential crime-solving reflections of Earth at various points in history.

Re: Gravitational Lensing to Observe Ancient Earth

#14

Post by mikemoka »

pkrein wrote: post #11
aphyr wrote: post #10

The practical limitation isn't just magnitude, but resolving power. Atmospheric disturbance makes it difficult to resolve anything smaller than a meter from orbit, and the diffraction limit means the further are away from the thing you want to observe, the wider your telescope needs to be. Since the distortion effects near a black hole are near-asymptotic, the features we want to see have very small subtended angles,…

Aperture synthesis (several widely-separated telescopes looking at one object) is often used to increase the resolving power. http://en.wikipedia.org/wiki/Aperture_synthesis

yes but if we manage to do everything (including unwarping the earth's reflection in the image) we would only see how our planet looked like 6 light years ago (3 for the light to arrive to the black hole and 3 to go back) and we won't be able to discern anything but the earth's surface, is that right?

Re: Gravitational Lensing to Observe Ancient Earth

#15

Post by pkrein »

mikemoka wrote: post #14
pkrein wrote: post #11

Earlier quoted context omitted.

Aperture synthesis (several widely-separated telescopes looking at one object) is often used to increase the resolving power. http://en.wikipedia.org/wiki/Aperture_synthesis

yes but if we manage to do everything (including unwarping the earth's reflection in the image) we would only see how our planet looked like 6 light years ago (3 for the light to arrive to the black hole and 3 to go back) and we won't be able to discern anything but the earth's surface, is that right?

oh -- yeah seeing what people are doing on Earth via a black hole is totally out of the question technologically. that's pretty much the conclusion of the article.

Re: Gravitational Lensing to Observe Ancient Earth

#17

Post by pkrein »

DeepDuh wrote: post #16

I've never seen that image of our galaxy's central region, it's fascinating! Is "Sgr A" the black hole, Sagittarius A*? If yes, why would it be bright? I thought it's inactive.

Sgr A is the black hole Sagittarius A* as far as I know. The black hole itself isn't bright. As far as I understand, the swirling gas around it (outside the event horizon) is what's sending out all the light.

What do you mean by inactive?

Re: Gravitational Lensing to Observe Ancient Earth

#18

Post by ISL »

You don't want the light reflected by 180 degrees - it needs to be reflected where Earth is going to be; a much harder problem. For the easy case quoted in the article of 6 light years, any collimated light would need to be properly directed at the sub-nanoradian (milliarcsecond) level (which is possible -- see sig and [0]).

Interesting to think about, even if it is an incredible observational challenge.

Fun application for the Arecibo radar, if it's still running. Locking into a modulated signal might yield the necessary SNR?

[0] http://en.wikipedia.org/wiki/File:Diffraction_limit_diameter...

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