One fun thing think about is that these two galaxies are only aligned from our perspective in the universe. Viewed from a different location, and they're just two normal galaxies.
Also, imagine having the technology to send signals through the lens and get the attention of intelligent life on the other side.
>In order to use them as a signaling platform (how?) the signal would have needed to have been sent several billion years ago.
Conceivably, a civilization could predict in advance that two galaxies would form a lens configuration, and send a signal that arrived just as the lens formed, correct?
Even assuming a civilization can predict the alignment of the lenses (galaxies), they'd still need quite a powerful signal just to reach the first lens, let alone the second, and then a potential civilization who may be listening at just the right time on the other side. Hard to beat background noise even at distances of a few light years.
So conceiably someone could have sent a signal from the other part of the lense some billion years ago and we "just" need to figure out what to listen for.
It's kind of interesting in terms of analytics... can we predict when lenses will appear and disappear, from our perspective? What might we do with that information once we are more advanced?
And technically they are only temporarily so, given enough millions of years they will drift apart and lose the alignment.
Also, other stars can come to align in the future. Makes me wonder if we can antecipate other cases like this and create a future schedule of "To Observe" so future generations can look at them. Although, these generations might be so distant from ours that might not even be considered of the same species
Similarly, eclipses are pretty much arbitrary. You stand somewhere else in the solar system, nada. Or go fly over into the shadow of whatever, eclipse any time you like!
And why do we ignore the most common eclipse, the 'terrestrial eclipse'? Happens literally all the time. Also called 'night'.
I love that my pondering comment generated so much discussion. Much more technical than I can fathom.
Another thought that occurred to me, we humans are short lived and trying to think about the length of time such a message would take to travel far exceeds out lifetime. Even the thought of humanity lasting that long is difficult. But imagine if there were intelligent life forms that lived a single life on galactic timescales. To them, this discussion of sending a message that reached someone wouldn't be so pessimistic.
But elsewhere in the universe it would just be two other galaxies forming the lens. The Copernican principle would suggest that any phenomena we observe are likely to be common in the universe.
Not really, its premise is using our Sun, not some lens composed of 2 galaxies (that would probably misalign well before our signal would reach them), not sure how you came up with such an idea.
It would be cool if we some day had special days of astronomy where every telescope is turned to galactic eclipses the way they once did for solar eclipses.
The sky is huge and we are moving, so surely some would happen in our lifetimes?
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is.
It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way.
The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years.
So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
I made this comment before but someone on HN made a good argument is way harder than it sounds and given it's size/cost/function it'd basically have to point in one direction, it's not like an easily moveable telescope you can scan around with.
No, because the light requires twice the time to travel there then back. If Earth did not move relative to the lens, it would work. Sadly we move, a lot, so what was here 2x ago was something not-earth.
To see earth, the lensing would been to be focused on where Earth was 2x ago. Still possible in theory, and you might even argue just as likely as a fully reflecting curve. But you'd not call it "back towards us". It would need to be "curved to where earth was".
Seems like if you could retrodict the position of past lenses, and predict their effects, perhaps it would somehow be possible to send a spacecraft to a specific location in order to observe Earth's past.
The idea being that a spacecraft traveling at 99% of light speed can't ordinarily catch up with light reflected by Earth. But if the light curves, and the spacecraft can travel directly towards where the light will end up (spacecraft traveling "as the crow flies"), it might be possible to catch up.
Same way I might be able to catch up with Usain Bolt at a track event if he's forced to run on the track, and I'm allowed to run across the turf in the middle.
Would this be the case even if you were moving toward or along-side the 'reflector' (black hole/other body)? For the sake of discussion assume we are at or beyond the focal point.
Technically? But the image would be very very very small, so we'd need a detector bigger than the solar system (guesstimate) to see it. That's to see it: I can't imagine what it would take to resolve the image. The tricks in this paper are a start.
> The first lens is relatively close to the source, with a distance estimated at 10.2 billion light-years. What happens is that the quasar’s light is magnified and multiplied by this massive galaxy. Two of the images are deflected in the opposite direction as they reach the second lens, another massive galaxy. The path of the light is a zig-zag between the quasar, the first lens, and then the second one, which is just 2.3 billion light-years away
So, given a simplistic model with no relative motion between earth and the presumed constant location lens:
Earth formation: 4.54b years ago
2.3b * 2 = 4.6b years ago
10.2b * 2 = 20.4b years ago
Does it matter that our models of the solar systems typically omit that the sun is traveling through the universe (with the planets swirling now coplanarly and trailing behind), and would the relative motion of a black hole at the edge of our solar system change the paths between here and a distant reflector over time?
I believe this could only happen around a black hole. In that case, yes: light that we emitted umpty-million years ago could be shot back at us. The problem is that there would be no focussing. At best it would be like looking at an Earth 2 x umpty-million light years away. I'm guessing that it would actually be worse, with the black hole dispersing light.
(IANAastronomer, but I have opinions on any given topic...)
In case anyone was wondering, like me, what the MJy unit in the lower diagram is: It's Mega-Jansky. Just funny that it's then being rescaled by 10^-9. Why didn't they use Milli-Jansky in the first place?
> It's Mega-Jansky... Why didn't they use Milli-Jansky
*megajansky, millijansky
"All prefix names are printed in lowercase letters, except at the beginning of a sentence.
Unit names are normally printed in upright type and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title...
When the name of a unit is combined with the name of a multiple or sub-multiple prefix, no space or hyphen is used between the prefix name and the unit name...
However yes, you raise a good question. I was surprised to learn that astronomy and astrophysics prefer CGS, so by convention the diameter of the Sun is given in centimeters, and the mass of the Sun in grams! For janskys there's no excuse though.
Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images.
Complete newbie on the topic of GL but I find it very interesting.
Q: We seem to want to use our sun for GL experiments. And that requires sending something out 500 AU out for focal length purposes. My question is somewhat theoretical so assume there are no alignment issues for the following thought. Are we not already at the "focal point/line" of some other 'entities' (sun/heavy body/galaxy/etc) gravitational lens?
Hmm... is that what this paper is talking about - the fact that the GL observation was made from Earth on some infinite focal length. Listening to other YT videos on the topic seemed to imply the resolution would be much higher. Or is the resolution location/technology related?
Readit News
Also, imagine having the technology to send signals through the lens and get the attention of intelligent life on the other side.
At 10 billion light years away from the most distant lens it is 100% certain that they are no longer in a gravitational lensing configuration.
For a frame of reference, the Milky Way will be in the middle of its epic merger with Andromeda in about 5 billion years.
Conceivably, a civilization could predict in advance that two galaxies would form a lens configuration, and send a signal that arrived just as the lens formed, correct?
Also, other stars can come to align in the future. Makes me wonder if we can antecipate other cases like this and create a future schedule of "To Observe" so future generations can look at them. Although, these generations might be so distant from ours that might not even be considered of the same species
And why do we ignore the most common eclipse, the 'terrestrial eclipse'? Happens literally all the time. Also called 'night'.
Another thought that occurred to me, we humans are short lived and trying to think about the length of time such a message would take to travel far exceeds out lifetime. Even the thought of humanity lasting that long is difficult. But imagine if there were intelligent life forms that lived a single life on galactic timescales. To them, this discussion of sending a message that reached someone wouldn't be so pessimistic.
Deleted Comment
The relationship is (must be) symmetrical. Were this not so, it would violate a principle called "Maxwell's Daemon" (https://en.wikipedia.org/wiki/Maxwell%27s_demon).
Underlying paper: https://arxiv.org/abs/2411.04177
The sky is huge and we are moving, so surely some would happen in our lifetimes?
It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way.
The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years.
So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
https://www.universetoday.com/149214/if-we-used-the-sun-as-a...
Seriously, we could build that, it's at the limit of our tech but if it was either we walk on the moon again or build SGL, I'd pick SGL
walking on the moon was beyond our limits when it was announced
JWST was insanely hard and almost cancelled a few times, look at it now
Deleted Comment
To see earth, the lensing would been to be focused on where Earth was 2x ago. Still possible in theory, and you might even argue just as likely as a fully reflecting curve. But you'd not call it "back towards us". It would need to be "curved to where earth was".
The idea being that a spacecraft traveling at 99% of light speed can't ordinarily catch up with light reflected by Earth. But if the light curves, and the spacecraft can travel directly towards where the light will end up (spacecraft traveling "as the crow flies"), it might be possible to catch up.
Same way I might be able to catch up with Usain Bolt at a track event if he's forced to run on the track, and I'm allowed to run across the turf in the middle.
From "Hear the sounds of Earth's magnetic field from 41,000 years ago" (2024) https://news.ycombinator.com/item?id=42010159 :
> [ Redshift, Doppler effect, ]
> to recall Earth's magnetic field from 41,000 years ago with such a method would presumably require a reflection (41,000/2 = 20,500) light years away
To see Earth in a reflection, though
Age of the Earth: https://en.wikipedia.org/wiki/Age_of_Earth :
> 4.54 × 10^9 years ± 1%
"J1721+8842: The first Einstein zig-zag lens" (2024) https://arxiv.org/abs/2411.04177v1
What is the distance to the centroid of the (possibly vortical ?) lens effect from Earth in light years?
/? J1721+8842 distance from Earth in light years
- https://www.iflscience.com/first-known-double-gravitational-... :
> The first lens is relatively close to the source, with a distance estimated at 10.2 billion light-years. What happens is that the quasar’s light is magnified and multiplied by this massive galaxy. Two of the images are deflected in the opposite direction as they reach the second lens, another massive galaxy. The path of the light is a zig-zag between the quasar, the first lens, and then the second one, which is just 2.3 billion light-years away
So, given a simplistic model with no relative motion between earth and the presumed constant location lens:
Does it matter that our models of the solar systems typically omit that the sun is traveling through the universe (with the planets swirling now coplanarly and trailing behind), and would the relative motion of a black hole at the edge of our solar system change the paths between here and a distant reflector over time?"The helical model - our solar system is a vortex" https://youtube.com/watch?v=0jHsq36_NTU
(IANAastronomer, but I have opinions on any given topic...)
https://en.wikipedia.org/wiki/Jansky
"All prefix names are printed in lowercase letters, except at the beginning of a sentence.
Unit names are normally printed in upright type and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title...
When the name of a unit is combined with the name of a multiple or sub-multiple prefix, no space or hyphen is used between the prefix name and the unit name...
Examples: pm (picometre), mmol (millimole), GΩ (gigaohm), THz (terahertz)"
Source: https://www.bipm.org/en/publications/si-brochure
However yes, you raise a good question. I was surprised to learn that astronomy and astrophysics prefer CGS, so by convention the diameter of the Sun is given in centimeters, and the mass of the Sun in grams! For janskys there's no excuse though.
Can we then find more lensing with even more compounding on purpose instead of accidentally if we sift existing data for such dupes?
> ... "acts as a compound lens" ...
Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images.
I often see remarks like this one -- "Acts as a compound lens!" -- but that's not correct. It's more like this: https://arachnoid.com/relativity/graphics/curvature_diagram....
Such alignments are more likely to produce what's called an "Einstein ring" (https://en.wikipedia.org/wiki/Einstein_ring). Very useful, but not remotely a "compound lens".
See Figure 7 in (https://arachnoid.com/relativity/index.html#General_Relativi...) for an interactive gravitational lens simulator.
Q: We seem to want to use our sun for GL experiments. And that requires sending something out 500 AU out for focal length purposes. My question is somewhat theoretical so assume there are no alignment issues for the following thought. Are we not already at the "focal point/line" of some other 'entities' (sun/heavy body/galaxy/etc) gravitational lens?
Hmm... is that what this paper is talking about - the fact that the GL observation was made from Earth on some infinite focal length. Listening to other YT videos on the topic seemed to imply the resolution would be much higher. Or is the resolution location/technology related?