
Fast Radio Bursts from Extragalactic Light Sails - DeusExMachina
https://arxiv.org/abs/1701.01109
======
kangnkodos
If we are receiving the FRBs, the focused beam must be pointed towards earth.
So the spaceships with light sails must be headed in the direction of earth.
Get ready for the invasion!

~~~
colanderman
Well that's silly. How do they plan to decelerate?

~~~
evgen
You have two sails in concentric rings that are connected, with your craft
attached to the outer ring. When you want to decelerate you disconnect the two
rings and and tweak the reflection of the inner ring to be somewhat outward
focused and give the inner ring a little push. As it moves forward the energy
bouncing off the inner ring is directed backwards to the outer ring, which
slows. As long as the inner ring reflect more energy backwards (and to the
outer ring) than the outer ring is getting from your source the outer ring
slows down. Really hard to describe, but easy to draw. First proposed by
Robert L. Forward.

~~~
Darthy
Images here:
[http://www.lunarsail.com/LightSail/rit-1.pdf](http://www.lunarsail.com/LightSail/rit-1.pdf)
(pages 5, 7 and 8).

------
kator
Maybe I'm just crazy but there are a list of things I hope we figure out in my
lifetime, and extraterrestrial intelligence is right up there in the top ten.

~~~
M_Grey
I think that's one of those things that's better to have been born well after
(assuming a good outcome) or born well before (assuming a bad outcome). It's
really hard imaging the transition as anything other than misery and chaos.

~~~
fsloth
Uh, why would proof of extra terrestrial intelligence induce misery and chaos?

~~~
M_Grey
You're right, I'm sure the billions of deeply religious people would cope with
literal proof that we're not a privileged and special "creation". Even worse,
they might _not_ accept that.

Plus new tech, new perspectives, old power structures being overthrown, etc...
etc...

Things would change, and change is good for the _future_ , but dangerous to
those living through it.

~~~
vivekd
What is it with tech/science forums and the belief that religious people are
crazy, backwards, zealots who would go crazy causing enormous destruction when
faced with compelling new scientific revelation. . . this despite the fact
that theologians from nearly every religion, including Christianity, Islam,
Hinduism have considered extraterrestrial life and claim it does not
contradict with their religious beliefs.

~~~
M_Grey
_What is it with tech /science forums and the belief that religious people are
crazy, backwards, zealots who would go crazy causing enormous destruction when
faced with compelling new scientific revelation. . ._

[http://www.philipstallings.com/2015/06/the-biblical-flat-
ear...](http://www.philipstallings.com/2015/06/the-biblical-flat-earth-
teaching-from.html) Leaps readily to mind, along with the current state of
Israeli politics, and you know... just a lot of politics.

You're right that lots of theologians are frankly much more impressive than
the average adherent. What a pity that we're not surrounded by billions of
theologians.

~~~
vivekd
When you talk about biblical flat Earthers you are talking about a very small
subset of Christians, to claim that all Christians are like them is akin to
claiming that all Muslims are like ISIS.

Similarly Zionism is not really a religious view as much as it is a political
one. This can most clearly be seen in the fact that orthodox Jews oppose the
state of Israel. They correctly interpret the Torah as saying that Jews have
had the holy land taken away from them by God and it can only be re-
established by God, not by the the act of men. Similarly the Koran says
outright that Allah had given the holy land to the Jews, and groups like the
Muslim brotherhood and Hamas that seek take Israel are motivated by political,
not religious goals.

If anyone is going to create violence and chaos at first contact, it's not
religious people but rather politicians that have a stake in a system that
exposure to other, more equal or efficient systems may upend and
industrialists that have a stake in the technologies that first contact will
replace. There are so many other, historically consistent places to look for
potential sources of revolt than mere ordinary people (in fact the majority of
the human population) who are merely in search of the divine and greater
meaning.

~~~
M_Grey
It's always a "small subset". A "small subset" is rabidly anti-abortion. A
"small subset" thinks women should be subservient to men, wear burkas, or stay
at home and have lots of kids. A "small subset" thinks the Earth is 6000 years
old. A "small subset" thinks that it's just a matter of time before the End
Times. A "small subset" thinks that Shia/Sunni is apostasy. A "small subset"
thinks gay people are evil, thinks that people shouldn't use contraception,
etc... etc...

It's always these little small subsets hiding the allegedly "vast silent
majority", but unfortunately they add up, they fight, and they ruin it all for
the rest of us. I don't worry about the physicists with faith, I worry about
the other 99.9999%.

------
openasocket
extragalactic travel seems to be a really dangerous and difficult prospect.
The journey will take millions of years (assuming no FTL travel), and there's
basically nothing in between. Even if your species is immortal or something,
there's serious risks. You need to bring everything to need for the journey,
including energy, because there aren't any stars you can stop at along the way
to gather solar energy. You'd have to be very careful planning things so you
don't wind up stranded partway.

~~~
riskable
If you're effectively immortal why would you want to hang around the same
place forever? You wouldn't. In fact, you might _hope_ for "something to
happen" along a 100,000-year trip just to shake things up a bit!

Also, don't assume that alien life is like ours. It could be many orders of
magnitude more efficient and in all likelihood isn't even biological in nature
if they've reached the point where a million-year journey is feasible. It
could just be a bunch of AIs constantly re-making themselves from resources
they pass by as they coast through the universe.

They might not even have a destination! They could literally just be a bunch
of machines that "live" in space. Floating around from place to place,
grabbing resources from asteroids as they go by.

Lastly, in regards to energy: Why assume solar? Once you've reached speed
you're not going to slow down much. Just leave the sails open to protect your
craft from debris. I'd also expect a _nuclear_ battery in such a craft to
power on-board components. There's plenty of radioactive material in space to
draw from for renewal as well. You also don't have to worry about disposal!
Just toss it towards the nearest star system or asteroid belt and get a bit of
thrust out of the action :)

~~~
openasocket
I was talking about traveling between galaxies, my understanding is there's
essentially nothing between them: no asteroids to mine. So you'd need to bring
everything you might need in advance. But maybe I'm wrong, maybe there is a
decent amount of debris floating between galaxies?

> They could literally just be a bunch of machines that "live" in space.
> Floating around from place to place, grabbing resources from asteroids as
> they go by.

Whenever I think of what an advanced civilization would look like, I picture
something like this (though not necessarily just machines). Something semi-
nomadic, an entire civilization of ships in a big fleet, wandering together
through the galaxy, stopping at various systems to gather some resources or
explore the planets. Maybe the fleet breaks up and goes in different
directions for a time, and rendezvous later.

~~~
Arizhel
>I was talking about traveling between galaxies, my understanding is there's
essentially nothing between them: no asteroids to mine. So you'd need to bring
everything you might need in advance. But maybe I'm wrong, maybe there is a
decent amount of debris floating between galaxies?

The current thought now is that there's likely quite a few "rogue planets" out
there, and other asteroids that haven't gotten captured by a star. However,
the density of such things is likely to be so low, and you won't know until
you get there what they're composed of, so it seems like a bad idea to plan a
trip assuming you're going to stop at a bunch of asteroids and rogue planets
to pick up supplies; you'll easily make your trip far, far longer. Don't
forget also the big problem in long-distance space travel is speed. If you
want to get to a particular star system, you need to get up to speed and stay
there until you're ready to decelerate. You can't afford to slow down and stop
at a bunch of rocks along the way, and you'll be going far too fast to capture
the small ones. Most of your fuel will be used in acceleration and
deceleration, so you can really only do that once most likely.

>Whenever I think of what an advanced civilization would look like, I picture
something like this (though not necessarily just machines). Something semi-
nomadic, an entire civilization of ships in a big fleet, wandering together
through the galaxy, stopping at various systems to gather some resources or
explore the planets. Maybe the fleet breaks up and goes in different
directions for a time, and rendezvous later.

That doesn't sound like an "advanced civilization" at all, that sounds like a
nomadic gang. An advanced civilization will value stability, and stay on their
home planet(s) where all their infrastructure is located. They may very well
send out exploratory missions, but those nomadic wanderers will not be the
civilization itself, just one small part of it.

~~~
openasocket
> An advanced civilization will value stability, and stay on their home
> planet(s) where all their infrastructure is located

My thoughts were that a sufficiently advanced civilization would desire
exploration, both for resources and scientific advancement. And you don't want
your people spread out too far (for some definition of far), for a variety of
reasons, the biggest being the consequences of the delay in communication and
travel. For instance, scientists in different solar systems would find in next
to impossible to collaborate: it could take years for news of one group's
findings to reach the other, at which point they may very well have
independently discovered the same thing, which is inefficient. Also, if one of
the systems is attacked, or has some sort of crisis that requires assistance
(plague, natural disaster, etc), the rest of the civilization would be unable
to react in a timely manner. In short, it's safer to stick together.

Therefore, it would make a lot of sense to put your whole civilization into a
fleet of ships with all your infrastructure (or maybe a single giant ship,
Death Star sized), and move around. You could stay in a single solar system
for a few millennia mining resources, or hop around looking for life.

Sticking to one place or a few nearby places is also an option, but I think it
lacks certain advantages a fleet civilization would have.

~~~
Arizhel
>Also, if one of the systems is attacked, or has some sort of crisis that
requires assistance (plague, natural disaster, etc), the rest of the
civilization would be unable to react in a timely manner. In short, it's safer
to stick together.

This is incorrect. This is the "all your eggs in one basket" problem: if you
have a big crisis in your civilization, you _don 't_ want everyone in one
place, because your whole civilization could get wiped out. A civilization
this advanced is likely also a very large civilization, so it makes more sense
for it to have different parts in different places, just in case.

As for communications, as the other responder pointed out, a continuous
transmission, assuming the data rate is high enough, will help keep the
different locations in sync. Who cares if scientists independently discover
things? Hopefully a civilization that advanced won't be so worried about
patent rights.

As for "hopping around" looking for life, you'll do a whole lot better keeping
your civilization in one place (or a few permanent locations better yet) and
sending probes or exploration teams to a bunch of different places at once.
Moving your entire civilization to only one star system at a time would be
horribly slow, and sticking everyone in a giant death star means your energy
requirements for transporting your civilization between stars would be
ridiculous.

A fleet civilization wouldn't have any advantages besides mobility. You only
need that if you have something you're trying to get away from, or have a
well-founded concern that staying in one particular place could be dangerous.
For Battlestar Galactica, it made sense because they were constantly being
chased by the Cylons, and even then, the show did a pretty good job, at least
at first, of showing what a PITA it is constantly being on the move. For a
large, highly advanced civilization that doesn't have a bunch of genocidal
robots chasing it, I just don't see how there's any advantage to remaining
highly mobile. Mobility requires a lot of energy and greatly limits you in
other ways. For a modern analogy, look at people today who live in RVs. Sure,
they can drive their whole home away quickly and don't have to worry much
about packing up to move, but they don't have much space, their home is easily
damaged compared to normal dwellings, and it costs a lot to move it (because
of the poor fuel economy). The only way living in starships makes any sense is
if energy is basically free for you, which includes having a way to store
immense quantities of it, because you'll need a lot when you're between stars.

~~~
openasocket
Hmm your arguments make sense. I think I was overvaluing mobility, because I
figured once reaching a post-scarcity society exploration would become the top
priority.

My only other point is that the continuous transmission idea only works up to
a point. Two populations that sufficiently far (I'd say hundreds of light
years, but it could be thousands or millions of light years) apart are
essentially different civilizations, because their societies would drift out
of sync. Think about how much our culture, our language have changed in the
past few centuries, and the rate of change in our society in only increasing.
Extreme longevity or immortality might slow down the rate of change, but I'd
argue that it wouldn't stop completely.

I guess my point is that civilizations have a maximum radius over which they
can function, otherwise societies will drift apart until they are essentially
distinct.

~~~
Arizhel
>Hmm your arguments make sense.

That's something I don't see much on these forums! Thanks!

>I think I was overvaluing mobility, because I figured once reaching a post-
scarcity society exploration would become the top priority.

I know Star Trek isn't the most realistic TV show in the world, but I do think
it (esp. TNG, esp. seasons 3+ because 1-2 sucked!) did a pretty fair job of
showing what a post-scarcity society would look like, though to be fair energy
was somewhat limited, but not that much.

In the show, most people/beings in the Federation lived on their home planets,
or on colonies. There were a LOT of colonies; it seemed they were shown or
mentioned every other episode. Most biological beings, assuming they evolve on
a planet, and don't upload their minds into androids or something, are
probably going to want to continue something like the lifestyle their
ancestors had. In addition, there's huge logistical advantages to having
stable facilities on planets. Where does the Federation build its starships?
On planets, or in orbital construction yards (most likely, the components are
largely made planetside, especially small but valuable ones like their
computer equipment, and the ships are assembled in orbital shipyards). Where
does the Federation mine the resources needed for ships and other stuff?
Probably largely on planets and moons, though not necessarily the ones they
live on, but the mines are probably very long-term and stable. And where does
the Federation get the antimatter it needs to power its ships? According to
the technical manual IIRC, they synthesize it from solar energy somehow, since
antimatter is not naturally occurring in this universe. So all the
infrastructure their society depends on for exploration (which is what many of
those starships spend their time doing) is located in relatively fixed
locations. Plus, the number of citizens in the Federation is surely enormous
(they have thousands of members IIRC, and Earth alone probably has at least 5
or 10B by that time, depending on how many perished in WWIII and how many left
the planet for colonization and of course the birthrate). The number of
Federation citizens living full-time on starships is surely a tiny, tiny
fraction of the total number.

>Two populations that sufficiently far (I'd say hundreds of light years, but
it could be thousands or millions of light years) apart are essentially
different civilizations, because their societies would drift out of sync.

That's true, but it really depends on the size of the civilization. If our
civilization grew to span the nearest 50 star systems, for instance, they'd
still all be within 16 light-years [1]. That's a pretty good-sized
civilization IMO, and 16 years isn't _that_ long to wait for a news about
what's going on the homeworld (though it also means it's about 32ly between
the farthest two colonies). A civilization spanning thousands or millions of
ly would either be an incomprehensibly enormous civilization, or one which is
really picky about which star systems it bothers with.

[1]
[https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brow...](https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs)

If you expand that radius to 30ly, now you're looking at probably hundreds of
stars. Couple that with the immortality you mention, and assume very stable
governments (since a civilization with governments like ours is not going to
be spanning multiple star systems, and wouldn't even get far off the planet)
and I do believe the rate of change will be much slower so that it's not that
big a deal if you don't learn about some interesting news or new music or
something from one of the other colonies until it's 50 years old. And don't
forget, we consider ourselves (humanity) as having a singular civilization,
but how in-sync are we between different nations? Not that much; we don't even
speak the same languages much of the time. Most likely, in such a
civilization, the different worlds would have different cultures, and there's
only be so much interconnection between them, mostly for trade but also
probably tourism and such. But I guess now we're getting into an argument over
the exact definition of "civilization"; do we have a singular one now, or are
the US and China two separate civilizations with trade and cultural exchange?
What about centuries ago when communication was all by hand-carried letter or
word-of-mouth?

------
jlebrech
I've often thought to ask whether we'd even come up with technology to pick up
fast moving objects in space heading towards us even before we have the
capacity to travel at those speeds ourselves.

we've always observe things in nature and then replicated them, if we saw
something move faster than light that would advance our technology even if
it's just by knowing it exists elsewhere.

~~~
kator
More than once I've been in a meeting where someone said "But competitor A
spent 1 Billion dollars building that". And I would quip back "And now we know
it can be built and it won't take a billion dollars to do it".

I agree, the real value is know something is possible from there all things
related make more sense and many decisions can be made based on that one fact.

------
throwaway7645
Didn't read the article, but it's always fun following these lines of thought.
We have no evidence of life outside earth, but darn it...we can't be the only
ones here...I mean we can, but that just doesn't sit well with me. I wonder if
almost any civilization would end up using lightsails powered by beams or if
many skip it in favor of some other technology.

~~~
felipemnoa
It will probably be something similar to this [1] that allows humans/aliens to
travel to distant worlds. As per my limited understanding, nothing can move
faster than light in space-time, but it seems that it may be possible for a
space-time wave to move faster than light. We would just ride that wave.

[1]
[https://en.wikipedia.org/wiki/Alcubierre_drive](https://en.wikipedia.org/wiki/Alcubierre_drive)

~~~
M_Grey
Remember that any such device allows you to travel backwards in time. Does it
still seem so plausible to you when you realize that 'c' isn't some kind of
cosmic speed limit, but _the speed of causality in the universe_?

~~~
pavel_lishin
Other than the fact that it seems mind-boggling, is there any reason to
believe that time travel is forbidden by the laws of physics, or that
causality is an absolute?

~~~
openasocket
Time travel isn't forbidden. At least, there are solutions to the Einstein
field equations that allow for the existence of wormholes between two points
in space-time. But that doesn't mean there are wormholes in our universe, or
that wormholes could be created (that last part is a little tricky, it's not
easy to talk about causality when dealing with time travel). There could well
be other laws of physics that prevent time travel, but general relativity
seems to allow it.

~~~
M_Grey
It's a solution that assumes things like a perfectly uniform sphere of gas
collapsing from infinity (Schwarzschild geometry), without any angular
momentum. Even then, the ERB isn't traversable. A lot of the talk around
wormholes and time travel suffers from map-territory issues.

For example, if you look at the maximally extended Schwarzschild geometry (the
Kruskal-Szekeres extension) you see two asymptotically flat regions of
spacetime connected by a "wormhole". It's _probably_ just an artifact of the
model though, and not anything physical.

A lot of the, "Math allows" stuff probably falls into that category, which is
why when it comes to relativistic masses and velocities, you can't ignore
quantum effects either.

------
jbmorgado
I'm as Astronomer. I think it's very interesting to read about these kind of
scenarios in novels, but I don't think they have a place in a scientific
publication.

We are researchers, we try to explain the universe by improving our
understanding of the physical processes that lie behind what we observe. The
moment we bring aliens or gods into the picture to explain something for which
we don't have an answer, we are doing a disservice to science.

~~~
pavel_lishin
It doesn't sound very scientific to automatically discount an act of an
intelligent being as the source of some phenomenon.

~~~
fusiongyro
What sounds more scientific to you: "we don't know what causes effect A" or
"we postulate elves are causing effect A"?

~~~
pavel_lishin
"We don't know what causes effect A" isn't science, it's just a statement that
we don't know something.

If the elvish hypothesis proposes some experiments for testing and disproving
it, then yes - it sounds more scientific.

~~~
fusiongyro
Yeah, but you don't have experimental design for the alien intelligence
"hypothesis." This is just emotionally satisfying drivel. There's nothing
unscientific about not having a hypothesis when more information is being
gathered. The paucity of data on FRBs makes any hypothesis right now almost
worthless.

We don't even know for sure that the majority of FRB data we have are from
non-terrestrial phenomena. FRB occurrences at Parkes correlate strongly with
lightning storms near the observatory.

But sure, it's probably angels or little green men. Why not. That's a
hypothesis, you're doing science Jimmy!

