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.
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
In order to use them as a signaling platform (how?) the signal would have needed to have been sent several billion years ago.
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.
I’m sure there are plenty of civilizations that have done this, but on the time scale of the universe no one happens to look at just the right moment.
But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
Don’t radio waves weaken proportionally to the square of the distance? No one would be able to detect them past a (relatively) small distance.
Is it only one direction or does it work the same from the other side?
Should work the other way too. Physics and symmetry:)
Thats probably not happening at that scale. I know this is the premise of interstellar communication in the three body problem. It's not real.
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.
Using things at that scale to talk? It's not a thing in either case.
This is seriously cool. One lens galaxy is amazing, but two! (Too bad that this is not steerable.)
Underlying paper: https://arxiv.org/abs/2411.04177
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?
Surely any such eclipse lasts a long time. From the perspective of our lifetimes it is static.
Cool! Was hoping to see a magnification amount like 100x etc
If the lens curved light back toward us, could we see earth several million years ago?
@Dang is there a version of /best but for comments? The thought experiment in this comment broke my mind.
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.
To zoom into a reflection on a lens or a water droplet?
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:
Earth formation: 4.54b years ago
2.3b * 2 = 4.6b years ago
10.2b * 2 = 20.4b years ago
"The helical model - our solar system is a vortex" https://youtube.com/watch?v=0jHsq36_NTU
So they were looking in the neighborhood, basically found light sources that looked like they might be duplicates and they were, therefore lensing.
Can we then find more lensing with even more compounding on purpose instead of accidentally if we sift existing data for such dupes?
Fund the SGL Telescope!
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
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.
Does this find make it any more justifiable to build and would it now be the highest single priority target for a SGL telescope?
Yeah, you basically need to launch a new one for every target you want to image.
I'd think to make it practical you'd have to have kind of (semi-) automatic space based assembly infrastructure that builds them and launches them. Launching these probes individually seems like it would be impractical. Building that infrastructure wouldn't be easy at all and I don't see that happening in the next 50 years.
Probably even many, because it‘s energetically impractical to stop at the focal point.
"way harder than it sounds" is how we move forward
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
This is true, but also, keep in mind that the JWST was insanely hard and almost cancelled a few times :)
The SGL would be much, much harder than the JWST would be, and the JWST was already stretching our capabilities.
The SGL needs to be 650AU away from us. Voyager 1 and 2 are currently 165AU and 120AU away.
The JWST is 0.01 AU from us.
And you can only look in one direction after the probe finally gets into position. Once you're 650AU away, it's not really feasible to move "sideways" far enough to look at something else.
>we move forward
Do you work in something related to Astro?
> the finding will allow other researchers to more precisely calculate the Hubble constant
How would a compound lens lead to a better estimate of the expansion rate of the universe?
Disclaimer: I am a layman, not trained at all. But I am interested in this stuff.
Our most powerful telescopes can see "back in time", by looking at stuff far enough away that it took nearly the entire age of the universe for the light to reach us.
I would guess that we can use this natural compound lens to "see farther" with our current telescopes than we might otherwise be able to see.
Our current best telescope, the JWST, can almost see to the very beginning of when it was possible to see, somewhere between 300k and 200M years after the big bang [0].
Somewhere in this time period, the universe cooled enough for normal matter to form.
The JWST still cannot see the actual 'edge' of when this occurred.
Maybe with this natural compound lens, we can see all the way to the edge.
And if we could see where the edge actually is, then maybe we can refine the estimate to a tighter range than [300k,200M], which would give us a better estimate of the expansion rate of the earlier universe.
[0] https://www.universetoday.com/168872/webb-observations-shed-...
From the abstract:
> This unique configuration offers the opportunity to combine two major lensing cosmological probes: time-delay cosmography and dual source-plane lensing since J1721+8842 features multiple lensed sources forming two distinct Einstein radii of different sizes, one of which being a variable quasar. We expect tight constraints on the Hubble constant and the equation of state of dark energy by combining these two probes on the same system. The z2=1.885 deflector, a quiescent galaxy, is also the highest-redshift strong galaxy-scale lens with a spectroscopic redshift measurement.
Not an expert, just trying to add some more context.
With time-delay cosmography[1] one exploits that unless the source is perfectly in the center of the line of sight, then the photons that make up one lensed copy have traveled a different distance from the source than photons that make up a different lensed copy. This effect can be used to measure absolute distance and give an accurate measure of the Hubble constant.
With dual source-plane lensing[2] one exploits that if two different sources lensed by the same lens, one can take the ratio of the measurements between the two sources and get results that are significantly less affected by the lens itself and is completely independent of the Hubble constant.