Any civilization that would need to communicate even across a few 100 light years would be capable of doing so.

How large an area would you need to cover to accuratly dim a star's output to an array at another star, say 100 light years away, if you positioned yourself towards the edge of the solar system? Is this cost effective, or any faster than using targeted EM?

1: https://en.wikipedia.org/wiki/The_Dark_Forest

Jupiter-sized is good enough for some 3700 light-years with 2016-era technology [1]. We know because that's one of the current methods of detecting exoplanets [2].

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[1] http://www.sci-news.com/astronomy/kepler-1647b-circumbinary-...

[2] https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...

Planetary transistion detection isn’t just a question of size (of both the star and the planet) and it’s orbit but also of alignment of the orbit of the planet, the orbit of earth and the two systems.

Now with a predetermined communication array the alignment isn’t a problem more so you can use a light shield at the receptor similar to StarShade which will be used to block the light from the star allowing Kepler to image the planets directly to block the majority of the light from the star which would reduce the required size of your transmitter further.

It’s quite likely that over a distance of even a few 100 light years with a modulator as small as a few 100 km across might be sufficient.

You'd need a spectacularly static civilisation to engage in any meaningful communication over the timespans involved.

Besides, if you’re an AI or an uploaded brain, you can send yourself over a communications link. That’s pretty valuable, regardless of whether you ever intend to return!

The news in my town is of interest to me, nobody else would care about the latest live music at the local stage.

Science might be of interest, but the problem is both cultures will work in parallel, so we can assume that majority of advances one planet discovers are discovered by the other planet in the mean time.

The nearest star (which might not even have a habitable planet) to earth is too far away for science collaboration other than the "here is new type of signal we are sending your way, see if you get it", and even then you take the risk that the other planet chooses to not listen for whatever reason (it wouldn't surprise me if some theory require this level of cooperation). It is close enough that some "we are studying this lead, so you probably want to look at something different to avoid duplicate work".

As we get farther and farther from the other planet collaboration is less and less useful. You quickly reach a point where the planets can advance faster by duplicating effort than talking to each other (other than as a much latter verification of current theories)

Of course if we colonize a planet 100 light years away you can assume a few hundred years of the colonists working hard to establish the colony and so getting science and technology feeds from Earth will be useful since then they can make a copy of widgets without having to design it from scratch. Eventually they will get established and start producing their own science locally, and soon the feed will be useless and not of interest.

After going back to India, merely showing things to people on Google Maps was an experience of its own.

People went like: Do people in other countries, live that well?

I'd fathom when we see some advanced civilization we would probably react the same way.

Also keep in mind than until recently on earth we used transmission mechanisms for long-on-earth distances that were closer to the order of magnitude of 100-year transmission time (a few months) than to present transmission time (a few milliseconds).

I don't know if it is possible for a civilization to connect the past to the present over such long periods of time. The individuals in each generation would have to pick up, use and pass on all the information that came before.

Our capacity to take past information into account, individually and collectively, is very limited, even if it gets stored somewhere. We can see that in many debates on here where arguments of the past are repeated many times over without younger participants having any awareness of what's been said before.

We can compensate for that to some degree by continuously retelling old stories. But relearning old stuff necessarily competes with new information for our limited mental capacity and so old information inevitable degrades over time.

Even religions, where there is a strong emotional incentive to retell old stories, are struggling mightily with even understanding what the original authors meant by the words they used and how to apply any of it to the current situation.

I think for a civilization to retain its collective memory over much longer periods of time requires completely different individuals. It requires individuals that are able to grow their mental capacity at the same pace as the amount of accumulated information grows.

If you consider the combinatoric explosion, this is unimaginable in a biological organism based on evolution and ultimately even in an AI.

Definitely in civilization time that leaves a lot of room for a few milion years here and there, but still, we could be the oldest and most advanced (at the same time I do hope there is a civilization out there less eccentric and egocentric as ours...)

If it's communication, that implies a two-way exchange of ideas. The galactic equivalent of blogging would be like all such communications: typically of more interest to the sender than the receiver.

If we assume a long-lived species that can receive a response within its lifetime, we must also assume that during the intervening time little enough of the context has changed that the answer is still relevant. That means a species and a civilisation that has extremely little change over hundreds of years.

This is what I mean by an extraordinarily static civilisation.

(But if it's so static, what could possibly be said that has material bearing on anything? :-)

Radio is much better bet.

Latency hardly matters when the majority of the lag is the 100 light year leg: you first spread out your whole message to the surface of the filter with a high bandwidth distribution medium. Then each section of the filter switches in sync, encoding the message without relying on a real-time input from a central location light seconds away

Why not use an array of smaller polarizers that can be modulated when they block the path of a bright but less adjacent star’s light to the recipient?

You can phase the switches and "aim" the star's signal at a point in the sky. Lower-frequency modulation can get signals to observers not on the direct line, at a lower bandwidth, and you can probably sweep these. Worst case you can blink the whole affair slowly; a star with a five second light curve is going to be pretty interesting.

Like the way the earth is large enough to block the sun on the entire moon during a lunar eclipse.

Building a static support for your polariser might also prove challenging.

Your noise floor is now vastly greater.

I've also been thinking of whether or not some sort of stellar laser or maser might be possible. Modulating a narrow, tightly focused beam.

By polarizing light, do you mean that a device would intercept the photons escaping from the sun and then changing their wavelength to encode a message similar to Morse code?

Or do you mean something else entirely?

Edit: a word

https://en.wikipedia.org/wiki/Polarization_(waves)

But it doesn't have to be polarization just any easy modulation of the light, polarization is just easy to do since all you need is a huge polarizer and a few reaction wheels.

Think about planetary transitions; we can detect those quite easily this is how we find exoplanets these days, in fact we can fairly accurately identify the composition of the planet's atmosphere and the atmosphere is a fairly thin slice of the entire planet's silhouette.

So the only thing you need to do is to position a sufficiently big object it doesn't have to be even that big (still huge in our scale but something in the range of 100's or even 1000's of kilometers across would likely be sufficient the radius of the earth is only 6300KM~ and we can detect planets smaller than the earth AFAIK, and it can be as thin as a solar sail and considering we already build satellites with antenna that unfold to the size of a few football fields it might be possible even with our current level of technology or something not that far off) because you take advantage of the distance between planetary systems that object needs to be able to modulate the light it can be polarization, abstraction, color filtering.

To put it simply make a huge ass thin TFT LCD let the sun act as a backlight and put it in a stelar synchronous orbit from the vantage point of the star system you want to communicate with so it would always appear in line between it and your local star and blink your messages away.

If you want to go for the golden star then build a huge ring which also is capable of acting like lense this can allow you to have a communication array which can also direct the signal in a relative narrow beam.

Minor typo: you mean "photons".

Like modern 3D glasses.

"...mit $700 trillion to renew your subscription to PubStar. Sol System, please remit $700 trillion to renew your subscription to PubStar. Sol System, please remit $700 trillion to renew your subscription to PubStar. Sol Sys..."

While we can expect a sufficiently advanced civilization to be in control of vast sources of energy, we need to consider losses, because nothing can be 100% energy-efficient. If sending data to the next node of your intergalacticnet requires you to deal with a Hiroshima per second of waste heat, yours is not a particularly attractive communication channel.

And, unless you have a very large heat exchanger, you are vulnerable to side-channel attacks where a third party can detect the heat you need to dissipate.