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Gravitational Lensing to Observe Ancient Earth

rein.pk

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Re: Gravitational Lensing to Observe Ancient Earth

#31

Post by teamonkey »

potatolicious wrote: post #30
andr3w321 wrote: post #27

I find it sort of ironic that everyone here thinks this would be awesome, but are completely opposed to hovering predator drones observing our every action 24/7. Obviously it's all a matter of who has access to the data, but essentially the data would be the same.

Even disregarding the resolution problems as brought up by ebilsten, and assuming we have some magical tech that would allow us spy-satellite-like capabilities with this... we'd still be looking at Earth decades in the past. I for one could not care less if historians centuries in the future want to observe me through a black hole. Its effects on freedom and civil rights is basically nil, unlike predator drones.

Azimov explored this idea in his short story The Dead Past

http://en.wikipedia.org/wiki/The_Dead_Past

Re: Gravitational Lensing to Observe Ancient Earth

#32

Post by salgernon »

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

This book has come up several times in several recent (unrelated) hacker news threads. I find the prescience of the privacy concerns (and how people react to never ever having privacy again) relevant to today's world of drones and oversharing via social media. And of course it's just got that good Clark science tone.

Re: Gravitational Lensing to Observe Ancient Earth

#33

Post by wasnotwas »

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.

As I have understood, "Black Hole" is something of a misnomer, as the singularity is in fact an intensely compact ball of matter/energy radiating x rays, etc. Matter releases energy as light in various wavelengths, including x, gamma, etc, but once inside the heart of the "hole" it is unable to emit ANYTHING. The net effect, however, is a surrounding veil of electromagnetic spectral emissions. Matter/energy can't escape once inside, but on the way in it puts on a hell of a show.

Re: Gravitational Lensing to Observe Ancient Earth

#34

Post by yakiv »

Does anyone here know why the Einstein cross has 4 of the repeated image instead of being a continuous repetition around the lens object? It seems to me like you should see the magnified image as a sort of circle instead of having a finite number of repetitions.

Is this related to the lines forming a cross you see in pictures of stars?

Re: Gravitational Lensing to Observe Ancient Earth

#35

Post by ComputerGuru »

potatolicious wrote: post #30
andr3w321 wrote: post #27

I find it sort of ironic that everyone here thinks this would be awesome, but are completely opposed to hovering predator drones observing our every action 24/7. Obviously it's all a matter of who has access to the data, but essentially the data would be the same.

Even disregarding the resolution problems as brought up by ebilsten, and assuming we have some magical tech that would allow us spy-satellite-like capabilities with this... we'd still be looking at Earth decades in the past. I for one could not care less if historians centuries in the future want to observe me through a black hole. Its effects on freedom and civil rights is basically nil, unlike predator drones.

In Orson Scott Card's "Pastwatch: The Redemption of Christopher Columbus" (awesome book, btw! I don't think he's planning on writing the remaining 2 in the trilogy, though :() they have machines that do exactly this, letting them monitor ancient history up to a decade ago: anyone, anywhere on the planet. The catch is that the builders of the machine actually have access to real-time monitoring, but pretend this isn't the case to avoid public outrage.

Re: Gravitational Lensing to Observe Ancient Earth

#36

Post by comex »

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

This is really off topic, but once - I think I was 13 or 14 - I found a book just lying around somewhere at what passed for my summer camp. I read the whole thing; I guess I must have tried to return it, but I don't remember that part. The book was interesting enough that I wanted to read it again at some point, but I had long since forgotten its name.

This is that book.

I guess I could have found the name of the book by actively asking around, but still - I love the coincidence. Thank you.

Re: Gravitational Lensing to Observe Ancient Earth

#37

Post by andrewflnr »

ISL wrote: post #18

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 applica…

I don't know if it's harder to get the light to where earth is going to be. There's still exactly one angle that will work, and we would have to trust to luck either way to send us the right photons. It's not like anyone is aiming.

Re: Gravitational Lensing to Observe Ancient Earth

#39

Post by privong »

yakiv wrote: post #34

Does anyone here know why the Einstein cross has 4 of the repeated image instead of being a continuous repetition around the lens object? It seems to me like you should see the magnified image as a sort of circle instead of having a finite number of repetitions. Is this related to the lines forming a cross you see in pictures of stars?

The lines forming a cross in pictures of stars is a separate phenomenon. That is due to diffraction from the support structures of the secondary mirror.

For a detailed answer to why the Einstein cross has 4 images, see: http://physics.stackexchange.com/questions/14056/how-does-gr...

Re: Gravitational Lensing to Observe Ancient Earth

#40

Post by privong »

DeepDuh wrote: post #26
pkrein wrote: post #17

Earlier quoted context omitted.

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?

By inactive I meant that it's not swallowing anything currently, but I guess if it has attracted a gas cloud this is simply not true. Must be quite a sight. Imagine there's a civilization on one of the central stars (if that's even possible considering the bursts of radiation they must get there) - I wonder what the night sky would look like.

The activity level (in terms of how much material is falling into it) is fairly low, such that it doesn't qualify as being an "active galactic nucleus". However, a gas cloud (called "G2") will be passing close enough to the supermassive black hole that it will be tidally disrupted and part of the cloud will fall into the black hole. This will give us a chance to see enhanced accretion, though still not of the level for it to be considered "active".
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