Biggish telescope

[Brian O]

Linked telescopes with large separations have been used to look at black holes.

A further step would be to launch three large telescopes into an orbit around the sun at the Earth's Lagrangian points.

This would give three telescopes at 120 degrees from each other.

Two would be in stable positions at 60 degrees from the Earth and one at 180 degrees, directly behind the Sun.

They would be in direct sight of each other and two would be in direct contact with the Earth.

If this were to work, the next step could be to use similar positions around Mars or any other planet.

Any thoughts?

[Astronomist]

You are referring to optical interferometry. As far as I am aware for this technique to work the light paths of the component telescopes must be physically brought together, meaning it simply is not feasible over the very long distances you describe. AFAIK the largest optical interferometer is the VLT at ~140 metres maximum baseline length. For radio telescopes however the data can be brought together via a computer, meaning extremely long baselines of thousands of miles are possible.

[Earl]

1 hour ago, Astronomist said:

You are referring to optical interferometry. As far as I am aware for this technique to work the light paths of the component telescopes must be physically brought together, meaning it simply is not feasible over the very long distances you describe. AFAIK the largest optical interferometer is the VLT at ~140 metres maximum baseline length. For radio telescopes however the data can be brought together via a computer, meaning extremely long baselines of thousands of miles are possible.

with greater bandwidth surly the same proces can be done with digital optical images

[Astronomist]

43 minutes ago, Earl said:

with greater bandwidth surly the same proces can be done with digital optical images

I assume this would have been done already if it was possible. Perhaps the computing power required is unfeasibly large?

[robin_astro]

23 hours ago, Earl said:

with greater bandwidth surly the same proces can be done with digital optical images

It is more a precision issue. The feeds from the multiple telescopes have to be kept in phase to a fraction of a wavelength (of light in the case proposed). Though there have been various proposals, I understand this is beyond our current technological capability

Robin

Edited April 5 by robin_astro
clarity

[robin_astro]

9 minutes ago, robin_astro said:

Though there have been various proposals, I understand this is beyond our current technological capability

This is an example,

https://ui.adsabs.harvard.edu/abs/2023AAS...24146307B/abstract

Though technology is being developed which might one day make it possible or perhaps achieve the even higher precision needed for space based gravitational wave measurements

https://lisa.nasa.gov/

a mission scheduled for launch mid 30's

[Brian O]

So the principle might be feasible but not within current technological limits.

There must be a point of diminishing returns in spreading out telescopes over vast distances.

How about using three Lagrange points around our Moon?

They could be in contact with each other as well as direct contact with the Earth.

 

[TiffsAndAstro]

Sounds awfully risky putting more  transmitters/relays in space.

Best we stay quiet/passive sensors only. Dark forest game theory and all that

[Astronomist]

9 minutes ago, TiffsAndAstro said:

Sounds awfully risky putting more  transmitters/relays in space.

We have been beaming radio waves across space for nearly a century, I think if anyone was interested in us we would have found out about it by now.

[woldsman]

9 minutes ago, Astronomist said:

We have been beaming radio waves across space for nearly a century, I think if anyone was interested in us we would have found out about it by now.

Relatively few exoplanets have been discovered within 100 light years and most of these do not favour the development of life. It would also take another 100 years for the most distant of any exoplanet with technology capable of receiving and broadcasting radio signals to send a reply.  However, the strongest argument that a very advanced civilisation does not lie within range rests on the separate fact that we have not detected any evidence for its existence (eg no sign of any probes roaming the vicinity of our place in the Milky Way).  Hence, you may well be right. 

Edited May 16 by woldsman

[TiffsAndAstro]

27 minutes ago, Astronomist said:

We have been beaming radio waves across space for nearly a century, I think if anyone was interested in us we would have found out about it by now.

Couldn't (politely) disagree more. 

Even though the risk is low, the stakes are incredibly high.

[TiffsAndAstro]

28 minutes ago, woldsman said:

Relatively few exoplanets have been discovered within 100 light years and most of these do not favour the development of life. It would also take another 100 years for the most distant of any exoplanet with technology capable of receiving and broadcasting radio signals to send a reply.  However, the strongest argument that a very advanced civilisation does not lie within range rests on the separate fact that we have not detected any evidence for its existence (eg no sign of any probes roaming the vicinity of our place in the Milky Way).  Hence, you may well be right. 

That's some really huge anthropomorphic assumptions to base our potential extinction on though.

Best to stay as quiet as possible just in case, surely?

I remember the hilarity at a uni lecture when I answered that the biggest problem in physics was the Fermi paradox and it's possible solutions. The solutions we can come up with are not very reassuring.

I think it even more an interesting and disturbing subject than it was way back then.

Edited May 16 by TiffsAndAstro

[woldsman]

2 hours ago, TiffsAndAstro said:

That's some really huge anthropomorphic assumptions to base our potential extinction on though.

Best to stay as quiet as possible just in case, surely?

I remember the hilarity at a uni lecture when I answered that the biggest problem in physics was the Fermi paradox and it's possible solutions. The solutions we can come up with are not very reassuring.

I think it even more an interesting and disturbing subject than it was way back then.

Extinction of the human race at some point is (very probably) inevitable but the question could be recast in terms of the costs/benefits to whatever life form exists on Earth. Actually, costs/benefits seems to be what determines the level of risk.

The costs of physically mounting an invasion of Earth (if that is your fear) from distances of tens or hundreds of light years appear immense. This is distinct from merely replying to a radio message with a radio message. It is very hard to see the potential benefits of conquest outweighing these costs. The anthropomorphic assumption is that the aliens would be like humans in terms of aggression - for which we simply have no evidence. If benign, the costs of contact would be less but still so high as to be a deterrent. Exchanging messages over vast timescales could be as good as it gets. 

However, the question seems academic for the reasons given. 

Tracking back to the original post, I'm not sure how relevant this discussion is. Apologies to the mods if this is too off-topic. 

 

Edited May 16 by woldsman

[TiffsAndAstro]

1 minute ago, woldsman said:

Extinction of the human race at some point is (very probably) inevitable but the question could be recast in terms of the costs/benefits to whatever lifeform exists on Earth. Actually, costs/benefits seems to be what determines the level of risk.

The costs of physically mounting an invasion of Earth (if that is your fear) from distances of tens or hundreds of light years appear immense. This is distinct from merely replying to a radio message with a radio message. It is very hard to see the potential benefits of conquest outweighing these costs. The anthropomorphic assumption is that the aliens would be like humans in terms of aggression - for which we simply have no evidence. If benign, the costs of contact would be less but still so high as to be a deterrent. Exchanging messages over vast timescales could be as good as it gets. 

However, the question seems academic for the reasons given. 

I think a fleet of sublight ships arriving wouldn't be the most likely. 

I agree it's a game of risk/reward, and while the potential rewards are likely very high the risk is everything.

It's a terribly interesting and terribly moot point, however, as I don't see my new political movement gaming much traction worldwide and so there's not a lot the planet is likely to do to address it.

Maybe mitigating the risk is the best we might manage. Like not having all our eggs in one basket. 

[Ags]

20 minutes ago, woldsman said:

The costs of physically mounting an invasion of Earth (if that is your fear) from distances of tens or hundreds of light years appear immense.

But what if they really, really don't like us? So it's not a matter of cost-benefit, but a point of principle for them?

[Ags]

On 04/04/2024 at 15:43, Astronomist said:

You are referring to optical interferometry. As far as I am aware for this technique to work the light paths of the component telescopes must be physically brought together, meaning it simply is not feasible over the very long distances you describe. AFAIK the largest optical interferometer is the VLT at ~140 metres maximum baseline length. For radio telescopes however the data can be brought together via a computer, meaning extremely long baselines of thousands of miles are possible.

Our present computers can only handle the data produced for radio interferometry, but computers advance inexorably. We will reach a point where this will be possible for visual wavelengths too.

[John_D]

16 hours ago, woldsman said:

Relatively few exoplanets have been discovered within 100 light years and most of these do not favour the development of life. It would also take another 100 years for the most distant of any exoplanet with technology capable of receiving and broadcasting radio signals to send a reply.  However, the strongest argument that a very advanced civilisation does not lie within range rests on the separate fact that we have not detected any evidence for its existence (eg no sign of any probes roaming the vicinity of our place in the Milky Way).  Hence, you may well be right. 

I read somewhere that radio/TV transmissions from earth decay to below the cosmic background level within a few light years. I could probably do the maths but I haven't had any coffee yet 😁

[woldsman]

7 hours ago, John_D said:

I read somewhere that radio/TV transmissions from earth decay to below the cosmic background level within a few light years. I could probably do the maths but I haven't had any coffee yet 😁

Not sure about this and don’t ask for the maths but… a telescope can capture light photons and radio telescopes other parts of the spectrum so transmission over long distances is clearly possible. Helps if the signal repeats and it would have to be stronger than background radiation(?). The last bit of the journey through an atmosphere probably the most critical. Can radio signals be lensed (no idea!)?!

[Astronomist]

Just now, woldsman said:

Can radio signals be lensed

yes, they can.

[John_D]

1 hour ago, woldsman said:

Not sure about this and don’t ask for the maths but… a telescope can capture light photons and radio telescopes other parts of the spectrum so transmission over long distances is clearly possible. Helps if the signal repeats and it would have to be stronger than background radiation(?). The last bit of the journey through an atmosphere probably the most critical. Can radio signals be lensed (no idea!)?!

Hmm, having waded into Google I'm none the wiser really but this SETI FAQ is interesting:

If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth?

In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments.