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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 t

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.

kcmastrpc 2y ago
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.
- Voultapher 2y ago
  But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
  - drexlspivey 2y ago
    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.
    - shagie 2y ago
      Omnidirectional source, yes. However, beamed sources don't fall off that way. A search for optical laser emission from Alpha Centauri AB - https://academic.oup.com/mnras/article/516/2/2938/6668809 https://academic.oup.com/mnras/article/516/2/2938/6668809 > ... This search would have revealed optical laser light from the directions of Alpha Cen B if the laser had a power of at least 1.4–5.4 MW (depending on wavelength) and was positioned within the 1 arcsec field of view (projecting to 1.3 au), for a benchmark 10-m laser launcher For comparison, with our measly human technology... https://www.ukri.org/news/uk-science-facility-receives-85m-for-worlds-most-powerful-laser/ https://www.ukri.org/news/uk-science-facility-receives-85m-f... > The Vulcan 20-20 laser is so named because it will generate a main laser beam with an energy output of 20 Petawatts (PW) alongside eight high energy beams with an output of up to 20 Kilojoules (KJ). This is a 20-fold increase in power which is expected to make it the most powerful laser in the world. Or even five decades ago (TODAY!) ... https://en.wikipedia.org/wiki/Arecibo_message https://en.wikipedia.org/wiki/Arecibo_message > The entire message consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW. https://www.seti.org/seti-institute/project/details/arecibo-message https://www.seti.org/seti-institute/project/details/arecibo-... > The broadcast was particularly powerful because it used Arecibo's megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo's.
      - WJW 2y ago
        Anywhere in the galaxy within the super narrow beam that the Arecibo antenna happened to cover at the time, at least.
      - ben_w 2y ago
        A perfectly parallel source wouldn't fall off with inverse square, but all real sources are not — and cannot be — perfectly parallel. What you get from lasers is very high gain in the direction it is pointed in, but it's still subject to the inverse square law. It's capable of being enough gain to be interesting, to be seen from a great distance. If you engineer it so the gain is enough to outshine the rest of the parent galaxy in the direction it is pointed, then that's effectively good enough because the galaxy is also following inverse-square and you'll continue to outshine the parent galaxy even as you and it both get weaker, but it's still falling off inverse-square.
        shagie 2y ago
        I stand corrected on the inverse square. I still hold that it would be possible to send and detect signals set with intention with not too much more advanced technology than what we have.
    - quantadev 2y ago
      The energy density drops off as inverse square law, but the photons go forever. Radio is just photons (light) so it goes forever until it interacts with something it hits. The expanding universe will stretch it's wavelength slightly however.
      - WJW 2y ago
        Sure, but the amount of photons as a percentage of the background radiation drops as a function of the distance. It's not all that far away in cosmic distances when any signal from Earth is millions of times less powerful than the noise level.
        quantadev 2y ago
        > amount of photons as a percentage of the background That's what "density" means. (i.e. the amount of something per unit volume) > noise level A photon will travel thru space forever without losing energy, unless it hits something. What noise are you talking about?
        WJW 2y ago
        > A photon will travel thru space forever without losing energy, unless it hits something. What noise are you talking about? I'm talking about the https://en.wikipedia.org/wiki/Noise_floor https://en.wikipedia.org/wiki/Noise_floor, in particular the unavoidable receiver noise caused by the cosmic background radiation. A single photon is not a viable communication signal, certainly not at interstellar distances. In practice you need to send out some sort of modulated beam. Even very narrow beams have nonzero dispersion, so the further you get the lower the signal energy will be at an antenna of a given size. So to get more energy you'd need a bigger antenna, but that in turn means receiving more of the background noise as well. In practice there is a minimal signal strength level at which it is still practical to receive the signal. Long story short: A photon will go on forever (unless it hits something), but a radio signal rapidly spreads out so much that no realistic receiver will be able to recover it from out of the cosmic background noise.
snakeyjake 2y ago
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.
- buran77 2y ago
  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.
  - montagg 2y ago
    But if you can do that, you know you have plenty of time for a civilization to develop on the other end to listen. Might just not be us.
    - buran77 2y ago
      That's assuming the development of the two civilizations starts simultaneously and is predictable to the point the signal reaches the other side. That side of the lenses may never see a civilization developing at all, or at least not one surviving long enough to receive that obscure signal. These distances and time periods are unfathomably long. I can see predicting the alignment of galaxies but predicting a civilization with an adequate evolution stage will exist at the right spot, at the right time is very different. Any civilization with this power of prediction probably has a level of advancement that makes the difference between humans and amoeba look positively non-existent, and probably wouldn't bother with broadcasting lowly radio waves into the universe. I can't imagine the universe and evolution of life being so deterministic and predictable especially over this time scale, no matter what tech you have.
augusto-moura 2y ago
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
yreg 2y ago
Is it only one direction or does it work the same from the other side?
- M_bara 2y ago
  Should work the other way too. Physics and symmetry:)
  - ted_dunning 2y ago
    Yes in a vague sense. And No in a strong practical sense. Lensing works in reverse except for time delays which make the idea much more complex. The object's past is projected to us now, but our past would be projected to somewhere that the far object no longer occupies. Double lensing makes this even less reversible. When the light we are now seeing was emitted, the lensing wasn't in place. In fact, the galaxies doing the lensing hadn't even evolved to the state that we see them in. So if we sent a response to what we see now, it wouldn't make it back to the lensed objects. That's just for single lensing. Double lenses are a massive coincidence of events at 4 points in time and space (emission, first deflection, second deflection and observation). That means that light going the other way wouldn't have the two intermediate points in the right place at the right times so it all breaks down for us and the object we see. There are some points that would be double lensed in the reverse direction but the locations and times for the source and observer have only very vague correlation to our location and the location of the object we see.
    - quantadev 2y ago
      A simpler answer is just what happens if you look thru a telescope or binoculars "the wrong way" (backwards). The correct way shows a "zoomed in" view of that you're viewing, but looking the wrong way shows a "zoomed out" view. So lifeforms on the other end of this cosmic "lens[es]" cannot use it to see us better, because in fact it makes us look further away from them than we are, from their perspective.
      - ben_w 2y ago
dmead 2y ago
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.
- jajko 2y ago
  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.
  - dmead 2y ago
    Using things at that scale to talk? It's not a thing in either case.
    - syndicatedjelly 2y ago
      This Wikipedia page suggests otherwise - https://en.wikipedia.org/wiki/Gravitational_lens https://en.wikipedia.org/wiki/Gravitational_lens
- deleted 2y ago
  [deleted]
0xDEADFED5 2y ago
sheesh, everyone knows we'd just use the sun as an RF amplifier first
JoeAltmaier 2y ago
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'.
- z3phyr 2y ago
  When we do start getting anywhere else in the solar system in reasonable time, then and only then will eclipses be "not special events". Until then..
0xDEAFBEAD 2y ago
What's the advantage of sending a signal through the lens relative to sending it in some other arbitrary direction?
waltbosz 2y ago
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.
vlovich123 2y ago
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.
veunes 2y ago
That’s some sci-fi gold

kcmastrpc 2y ago

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.

Voultapher 2y ago
But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
- drexlspivey 2y ago
  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.
  - shagie 2y ago
    Omnidirectional source, yes. However, beamed sources don't fall off that way. A search for optical laser emission from Alpha Centauri AB - https://academic.oup.com/mnras/article/516/2/2938/6668809 https://academic.oup.com/mnras/article/516/2/2938/6668809 > ... This search would have revealed optical laser light from the directions of Alpha Cen B if the laser had a power of at least 1.4–5.4 MW (depending on wavelength) and was positioned within the 1 arcsec field of view (projecting to 1.3 au), for a benchmark 10-m laser launcher For comparison, with our measly human technology... https://www.ukri.org/news/uk-science-facility-receives-85m-for-worlds-most-powerful-laser/ https://www.ukri.org/news/uk-science-facility-receives-85m-f... > The Vulcan 20-20 laser is so named because it will generate a main laser beam with an energy output of 20 Petawatts (PW) alongside eight high energy beams with an output of up to 20 Kilojoules (KJ). This is a 20-fold increase in power which is expected to make it the most powerful laser in the world. Or even five decades ago (TODAY!) ... https://en.wikipedia.org/wiki/Arecibo_message https://en.wikipedia.org/wiki/Arecibo_message > The entire message consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW. https://www.seti.org/seti-institute/project/details/arecibo-message https://www.seti.org/seti-institute/project/details/arecibo-... > The broadcast was particularly powerful because it used Arecibo's megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo's.
    - WJW 2y ago
      Anywhere in the galaxy within the super narrow beam that the Arecibo antenna happened to cover at the time, at least.
    - ben_w 2y ago
      A perfectly parallel source wouldn't fall off with inverse square, but all real sources are not — and cannot be — perfectly parallel. What you get from lasers is very high gain in the direction it is pointed in, but it's still subject to the inverse square law. It's capable of being enough gain to be interesting, to be seen from a great distance. If you engineer it so the gain is enough to outshine the rest of the parent galaxy in the direction it is pointed, then that's effectively good enough because the galaxy is also following inverse-square and you'll continue to outshine the parent galaxy even as you and it both get weaker, but it's still falling off inverse-square.
      - shagie 2y ago
        I stand corrected on the inverse square. I still hold that it would be possible to send and detect signals set with intention with not too much more advanced technology than what we have.
  - quantadev 2y ago
    The energy density drops off as inverse square law, but the photons go forever. Radio is just photons (light) so it goes forever until it interacts with something it hits. The expanding universe will stretch it's wavelength slightly however.
    - WJW 2y ago
      Sure, but the amount of photons as a percentage of the background radiation drops as a function of the distance. It's not all that far away in cosmic distances when any signal from Earth is millions of times less powerful than the noise level.
      - quantadev 2y ago
        > amount of photons as a percentage of the background That's what "density" means. (i.e. the amount of something per unit volume) > noise level A photon will travel thru space forever without losing energy, unless it hits something. What noise are you talking about?
        WJW 2y ago
        > A photon will travel thru space forever without losing energy, unless it hits something. What noise are you talking about? I'm talking about the https://en.wikipedia.org/wiki/Noise_floor https://en.wikipedia.org/wiki/Noise_floor, in particular the unavoidable receiver noise caused by the cosmic background radiation. A single photon is not a viable communication signal, certainly not at interstellar distances. In practice you need to send out some sort of modulated beam. Even very narrow beams have nonzero dispersion, so the further you get the lower the signal energy will be at an antenna of a given size. So to get more energy you'd need a bigger antenna, but that in turn means receiving more of the background noise as well. In practice there is a minimal signal strength level at which it is still practical to receive the signal. Long story short: A photon will go on forever (unless it hits something), but a radio signal rapidly spreads out so much that no realistic receiver will be able to recover it from out of the cosmic background noise.

snakeyjake 2y ago

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.

buran77 2y ago
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.
- montagg 2y ago
  But if you can do that, you know you have plenty of time for a civilization to develop on the other end to listen. Might just not be us.
  - buran77 2y ago
    That's assuming the development of the two civilizations starts simultaneously and is predictable to the point the signal reaches the other side. That side of the lenses may never see a civilization developing at all, or at least not one surviving long enough to receive that obscure signal. These distances and time periods are unfathomably long. I can see predicting the alignment of galaxies but predicting a civilization with an adequate evolution stage will exist at the right spot, at the right time is very different. Any civilization with this power of prediction probably has a level of advancement that makes the difference between humans and amoeba look positively non-existent, and probably wouldn't bother with broadcasting lowly radio waves into the universe. I can't imagine the universe and evolution of life being so deterministic and predictable especially over this time scale, no matter what tech you have.

augusto-moura 2y ago

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

yreg 2y ago

Is it only one direction or does it work the same from the other side?

M_bara 2y ago
Should work the other way too. Physics and symmetry:)
- ted_dunning 2y ago
  Yes in a vague sense. And No in a strong practical sense. Lensing works in reverse except for time delays which make the idea much more complex. The object's past is projected to us now, but our past would be projected to somewhere that the far object no longer occupies. Double lensing makes this even less reversible. When the light we are now seeing was emitted, the lensing wasn't in place. In fact, the galaxies doing the lensing hadn't even evolved to the state that we see them in. So if we sent a response to what we see now, it wouldn't make it back to the lensed objects. That's just for single lensing. Double lenses are a massive coincidence of events at 4 points in time and space (emission, first deflection, second deflection and observation). That means that light going the other way wouldn't have the two intermediate points in the right place at the right times so it all breaks down for us and the object we see. There are some points that would be double lensed in the reverse direction but the locations and times for the source and observer have only very vague correlation to our location and the location of the object we see.
  - quantadev 2y ago
    A simpler answer is just what happens if you look thru a telescope or binoculars "the wrong way" (backwards). The correct way shows a "zoomed in" view of that you're viewing, but looking the wrong way shows a "zoomed out" view. So lifeforms on the other end of this cosmic "lens[es]" cannot use it to see us better, because in fact it makes us look further away from them than we are, from their perspective.
    - ben_w 2y ago

dmead 2y ago

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.

jajko 2y ago
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.
- dmead 2y ago
  Using things at that scale to talk? It's not a thing in either case.
  - syndicatedjelly 2y ago
    This Wikipedia page suggests otherwise - https://en.wikipedia.org/wiki/Gravitational_lens https://en.wikipedia.org/wiki/Gravitational_lens
deleted 2y ago
[deleted]

0xDEADFED5 2y ago

sheesh, everyone knows we'd just use the sun as an RF amplifier first

JoeAltmaier 2y ago

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'.

z3phyr 2y ago
When we do start getting anywhere else in the solar system in reasonable time, then and only then will eclipses be "not special events". Until then..

0xDEAFBEAD 2y ago

What's the advantage of sending a signal through the lens relative to sending it in some other arbitrary direction?

waltbosz 2y ago

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.

vlovich123 2y ago

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.

veunes 2y ago

That’s some sci-fi gold