<p>For the sake of this question, let's assume intelligent life exists elsewhere in the Universe, and let's also assume it has a similar level of science and technology to humanity at present. How far would that alien world have to be from Earth in order to detect anything about life or technology on our planet?</p>
<p>Furthermore, how does the answer change as we vary the distance? E.g. with current methods, how much about Earth would be detectable from 10ly vs 100ly, 1000ly etc?</p>
<p><strong>EDIT</strong>: I realize similar questions have been asked before, but they are close to a decade old, and the answers point to research on detection capabilities that's sometimes even older. In the past few years, I've come across several news articles discussing research on bio- and technosignatures, so I was wondering if the answer to my question has now changed.</p>

CC BY-SA 4.0
2024-04-22T02:31:12.790Z
Does this answer your question? https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life
Allure
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2024-04-22T03:18:59.443Z
@Allure somewhat - the question is mostly about detecting life, although the answers do go a bit into one possible technosignature - radio emissions. I wonder if in the 9 years since the question was asked we've gotten further ahead in what we could detect, and at what distances.
RuslanD
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2024-04-22T05:41:47.973Z
See also https://astronomy.stackexchange.com/questions/8605/if-alpha-centauri-as-solar-system-exactly-mirrored-our-own-what-would-we-be-ab and https://astronomy.stackexchange.com/questions/18059/can-seti-certify-whether-or-not-proxima-b-is-inhabited-by-beings-using-electroma
ProfRob
CC BY-SA 4.0
2024-04-22T05:50:38.030Z
and https://astronomy.stackexchange.com/questions/1037/how-would-we-detect-an-earth-doppelganger-planet
ProfRob
CC BY-SA 4.0
2024-04-22T10:43:35.383Z
@ProfRob thanks - I did go over some of the linked questions and saw your answers there. Has anything changed about our detection capabilities since them? Some of the literature you've cited - e.g. Cullers and Tarter - is from 20+ years ago, and I'm aware more research has been done recently on techno- and biosignatures.
RuslanD
CC BY-SA 4.0
2024-04-22T10:54:05.957Z
Maybe you could modify your question to say/ask precisely that, so that it is not closed as a duplicate.
ProfRob
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2024-04-22T13:29:45.880Z
The distance to *reliably* detect life-bearing planets is much less than the distance to *fortuitously* detect such planets.  The closest Sun-like stars, such as Alpha Centauri, could host Earth-like planets teeming with life and with an oxygen-rich atmosphere, and we would have no clue.  The Fermi paradox is a paradox not because technological civilizations are (easily) detectable at a distance, but that they should already be right here in this solar system: the rate of civilizational expansion-- even without magic FTL-- should be so large compared to the time available.
antlersoft
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2024-04-22T17:03:21.133Z
Does this answer your question? [How far away could we detect that Earth has life?](https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life)
ProfRob
CC BY-SA 4.0
2024-04-22T23:56:49.440Z
@ProfRob I've updated the question as you suggested, to reflect that I'm interested in the current state of the art. Thanks!
RuslanD
CC BY-SA 4.0
2024-04-23T00:07:42.093Z
@antlersoft thanks for that perspective. There are still a lot of assumption in there - that civilizational expansion is desirable/sought, that it's able or intended to cover the entire galaxy, etc. etc. In many ways, the Fermi paradox strikes me as asking: "if they were like us in essential respects, then where are they?" Of course, the if-part of this question is highly conjectural.
RuslanD
<habitable-zone><seti><fermi-paradox>
How detectable would Earth life or technology be with current methods, depending on cosmic distance?
RuslanD
# How detectable would Earth life or technology be with current methods, depending on cosmic distance?

(Asked by: username_0 on 2024-04-21)

For the sake of this question, let's assume intelligent life exists elsewhere in the Universe, and let's also assume it has a similar level of science and technology to humanity at present. How far would that alien world have to be from Earth in order to detect anything about life or technology on our planet?

Furthermore, how does the answer change as we vary the distance? E.g. with current methods, how much about Earth would be detectable from 10ly vs 100ly, 1000ly etc?

**EDIT**: I realize similar questions have been asked before, but they are close to a decade old, and the answers point to research on detection capabilities that's sometimes even older. In the past few years, I've come across several news articles discussing research on bio- and technosignatures, so I was wondering if the answer to my question has now changed.

**Tags:** habitable-zone, seti, fermi-paradox

> **Comments:**
> **username_1**: Does this answer your question? https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life  
> **username_0**: @username_1 somewhat - the question is mostly about detecting life, although the answers do go a bit into one possible technosignature - radio emissions. I wonder if in the 9 years since the question was asked we've gotten further ahead in what we could detect, and at what distances.  
> **username_2**: See also https://astronomy.stackexchange.com/questions/8605/if-alpha-centauri-as-solar-system-exactly-mirrored-our-own-what-would-we-be-ab and https://astronomy.stackexchange.com/questions/18059/can-seti-certify-whether-or-not-proxima-b-is-inhabited-by-beings-using-electroma  
> **username_2**: and https://astronomy.stackexchange.com/questions/1037/how-would-we-detect-an-earth-doppelganger-planet  
> **username_0**: @username_2 thanks - I did go over some of the linked questions and saw your answers there. Has anything changed about our detection capabilities since them? Some of the literature you've cited - e.g. Cullers and Tarter - is from 20+ years ago, and I'm aware more research has been done recently on techno- and biosignatures.  
> **username_2**: Maybe you could modify your question to say/ask precisely that, so that it is not closed as a duplicate.  
> **username_3**: The distance to *reliably* detect life-bearing planets is much less than the distance to *fortuitously* detect such planets.  The closest Sun-like stars, such as Alpha Centauri, could host Earth-like planets teeming with life and with an oxygen-rich atmosphere, and we would have no clue.  The Fermi paradox is a paradox not because technological civilizations are (easily) detectable at a distance, but that they should already be right here in this solar system: the rate of civilizational expansion-- even without magic FTL-- should be so large compared to the time available.  
> **username_2**: Does this answer your question? [How far away could we detect that Earth has life?](https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life)  
> **username_0**: @username_2 I've updated the question as you suggested, to reflect that I'm interested in the current state of the art. Thanks!  
> **username_0**: @username_3 thanks for that perspective. There are still a lot of assumption in there - that civilizational expansion is desirable/sought, that it's able or intended to cover the entire galaxy, etc. etc. In many ways, the Fermi paradox strikes me as asking: "if they were like us in essential respects, then where are they?" Of course, the if-part of this question is highly conjectural.  

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