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Comment by icapybara | Hacker News Reader

Optical engineer here. For anyone not in the field, “photonics” is a fancy academic term for optical systems that involve waveguide structures. You can do some neat things with waveguides that you can’t do with more traditional optics like lenses, prisms and mirrors.

I think the paper’s title is a bit sensationalist (a callout to extraterrestrial life in an optics paper? Really?) but it’s basically talking about how these devices can help improve spectroscopy and imaging, which are the only two tools astronomers have.

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The other end of the spectrum from detecting bio-signatures of life on individual planets, would be mega structures.

Once a civilization began harvesting the energy of a few star systems, it would have a good chance of colonizing their whole galaxy in a blink of an eye.

(100 thousand years, plus or minus an order of magnitude, as compared to universe time in billions of years.)

So we would be much more likely to see totally colonized galaxies, rather than partially colonized.

I would be curious about which instruments would detect infra-red galaxies, I.e. galaxy sized objects where all starlight was put to use, with only infra-red light as waste.

And would that be an object that would stand out if a major telescope came across it, or require specific initiative to search and find?

And speaking of optics, is there any reason to suspect an efficient civilization would leak lower frequency light than infra-red?

Any advanced civilization will quickly lose interest in space exploration. Just a phase.

> would have a good chance of colonizing their whole galaxy in a blink of an eye

But what's the motivation to do that, so that the collapse is bigger? Beyond just because it could also many good reasons not to do that...

Life. Individuals compete. Resources have limits, and life quickly scales to them.

Life harnessing new resources is the most constructive way to compete.

Creatures that expand, expand exponentially.

Creatures that don’t, collapse exponentially.

It takes a minuscule percentage of a population to be expanders, for the whole population to quickly become expanders.

It would take an exceptional explanation to explain why creatures that could expand, don’t.

An exceptional explanation on par with explaining how a balloon could be popped in a vacuum, but the compressed air inside somehow remained in place instead of dispersing.

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Also - starlight is going unused on a galactic scale. Actively managing energy production will enable a larger, longer, and more efficient future.

But as we've seen with human societies once you reach a certain level of affluence you tend to reproduce less not more. Why would we assume that civilizations that are presumably far more advanced and affluent than ourselves would desire to expand? Expansion is fast on galactic timescales, but it's still very slow in the scale of a human lifetime. We don't tend to undertake projects knowing that we won't finish them within our lifetimes.

Again, only a tiny fraction of a civilization needs to be motivated to expand for a civilization effectively be a fully expanding civilization.

1/1,000, 1/1,000,000 ... it doesn't matter how small the fraction is to start.

Affluence in humans vastly increases consumption. By several orders of magnitude. Billionaires enjoy jets, yachts, and build companies that use vast resources to accomplish new things.

AI isn't going to be concerned about human lifetimes. 20 years to the nearest star for a laser sail ship smaller than a human takes physics we have now. For nano tech that would be a massive ship.

If you want a teleological argument, here is one: Life expands by colonizing and adapting to new environments and inventing new capabilities. Then expanding and adapting over and over again in response to each wave of change. Life expanding across the galaxy will produce beauty and complexity we can't imagine.

I strongly disagree, it's not beyond the dreams of humans to travel a few light years away with generational starships. How are you going to travel all the way across the galaxy without faster than light travel. We could send humans in the journey to the nearest stars within the next thousand years. At least we could start the ships. That's with only a little bit more technology than we have today. But colonizing the galaxy takes imagining things we have no idea if they will ever be possible, like faster than light travel.

Using lasers and light sails small craft can be accelerated to a noticeable fraction of the speed of light.

We will be sending entire civilizations of nanobots, or at least small artificial organisms.

At 5% of the speed of light, including travel, reproduction & relaunches, a civilization like that at the center of the galaxy will reach the rim in 100,000 years.

At the nano level time effective massively expands. Activity at that scale operates with speeds many magnitudes faster than gargantuan Ent-like beings like us, can easily imagine. :)

It isn’t a journey suitable for humans, and our position here is changing rapidly decade to decade. The galaxy was never going to belong to humans, but hopefully our progeny.

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Then there is hope from physicists, that harnessing stellar level energy will allow faster than light warp travel. That would let beings cross the vast spaces between galaxies.

>But colonizing the galaxy takes imagining things we have no idea if they will ever be possible, like faster than light travel.

Not at all depending on the timeframe you want to talk about in.

For example, one way to travel around the galaxy is to find some other object with a very fast orbit and colonize it. Then as it goes along you throw off seed ships. This is the whole idea behind 'von neumann probes'. Massive numbers of things working in parallel can get a lot of work done.

I understood the article above saying we could finishing colonizing most of the galaxy in little time, say 1000 years. But the galaxy is much larger than 1000 light years so without FTL travel (impossible afawk), that's why I said you can't do it.

But were you saying "get started on this in 1000 years" instead of finish in 1000 years?

The mention of extra-terrestrial life is not as much of a red herring as you might imagine.

The National Academies Decadal Survey for Astrophysics ("Astro2020") recommended that NASA study an ~6m aperture telescope that would be capable of direct-imaging of exoplanets, and obtaining spectra of these exoplanets sufficient to detect atmospheric constituents that are associated with life. The nominal name for the telescope is HWO - Habitable Worlds Observatory.

So this is very much an object of legitimate study, tech development, prototyping, etc. NASA's program for doing this is called GOMAP (https://science.nasa.gov/astrophysics/programs/gomap). The motivation being to consider novel approaches now, before the architecture is settled.

Detection and spectral characterization require excellent resolution and suppression of direct light from the host star, while preserving light from the planet.

The people on the author list are working on novel photonics-based approaches to do this.

As one example that I know about, and that your remark hints at, photonics approaches capture and manipulate amplitude and phase. There are photonic components that can achieve (in principle) any transfer function (filter), not just ones that can be implemented in glass. Doing this can help greatly to suppress starlight.

(I work in the area.)

>“photonics” is a fancy academic term for optical systems that involve waveguide structures

And for the laymen like me, "optical systems that involve waveguide structures" is a fancy term for fiber optics (and related systems).

Lots of exciting possibilities in here and good work by the authors previously but this one is a bit of "white paper" paper describing what could be done in the future if the money is there

Where in the scale of spectroscope and imaging would one put LIGO?

And polarimetry!

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