One man's opinion.
For me, I am grateful I live in a time when I can use a human invention to view images, taken by another human invention, of galaxies 13.5 billion light years away that probably no longer exist and be educated enough to sit down and calculate in terms of miles just how far those specks of light have traveled.
Aristotle, Caesar, DaVinci, Newton, Kepler, Napoleon, Faraday and Einstein never saw what I have seen from my desktop.
Sad? No. Privileged.
And, really, this picture is just a fraction of a fraction of the down payment on the concept of big: This is merely an illustration of how big one galaxy is. There are eighty billion galaxies. 
 Tune in tomorrow for a new estimate, of course.
The galaxy sounds big at first, but only because our lives are so short. If we built Von Neumann probes we could take over the galaxy in a mere million years. That's nothing on a geologic time scale. The fact that the solar system has sat around for 4 billion years without being eaten by Von Neumann machines makes me pretty certain that we're alone.
The paper provides an explanation for us not having seen those probes that still allows other civilizations to exist. From the abstract:
"Attempts to model interstellar colonization may seem hopelessly compromised by uncertainties regarding the technologies and preferences of advanced civilizations. If light speed limits travel speeds, however, then a selection effect may eventually determine frontier behavior. Making weak assumptions about colonization technology, we use this selection effect to predict colonists' behavior, including which oases they colonize, how long they stay there, how many seeds they then launch, how fast and far those seeds fly, and how behavior changes with increasing congestion. This colonization model explains several astrophysical puzzles, predicting lone oases like ours, amid large quiet regions with vast unused resources."
Even our civilisation, any number of things could still go wrong before we are able to explore the universe.
I wouldn't be surprised if we find a decent amount of life of the single cell variety. There is also the possibility of a civilisation far older than ours that never really got going on the intelligence path, or are lacking a good supply or certain base materials to really get going.
That's quite a leap you're making. One very strong counterargument boils down to simple economics: where's the profit motive in building a fleet of von Neumann probes to 'eat' every solar system in the galaxy? Who is going to pay for this effort, and what returns do they expect?
If it takes a million years to colonize a galaxy, then unless you plan to live for two million years you aren't going to see the full fruits of your effort.
As a race our attention span seems to be narrowing. As far as I can tell, despite or perhaps because of recent advances in applied science, we're actually losing our propensity to engage in multidecade R&D projects. The next LHC-scale project is going to be an almost impossible thing to sell to the governments that will have to agree to finance it, and it would take years for us to return to the Moon if our survival depended on it. We are most definitely not moving in a direction that will lead to the sort of expansionism you're talking about.
Edit: here's another thing, with regard to the absence of 'radio bubbles' from other civilizations. It's really, really dumb, from a technical perspective, to transmit RF signals that are distinguishable from background noise. It means you're wasting power and throwing away channel capacity.
Look at an HDTV transmitter on a classical spectrum analyzer sometime, and you won't see much in the way of coherent structure -- you'll just see a pedestal where the noise floor seems a bit higher than usual. This means that the 'radio bubble' is not a bubble, but two nested spheres with only about 100 light years of space between them. To observe emissions from an advanced civilization, we need to look at just the right time, between the development of RF technology and information theory. Otherwise we won't hear a thing.
where's the profit motive in building a fleet of von Neumann probes to 'eat' every solar system in the galaxy? Who is going to pay for this effort, and what returns do they expect?
You only have to build one Von Neumann probe, and there's a massive benefit to taking over your light cone: You make sure nobody else does.
Even if million-year life spans are out of our reach, why does one have to live to see the full fruits of one's effort? The world doesn't cease to exist when you die.
So this hypothetical civilization has conquered aging, death, and the drive for rapid gratification, but fails at elementary game theory?
Even if there were multiple civilizations in a galaxy, a single "defector" civilization would have vastly more matter under its control than civilizations that did not use Von Neumann probes to expand. With such a huge advantage, they would quickly destroy all competitors.
Sorry, but I'm still not getting the 'advantage'. This strikes me as one of those games where the only winning move is not to play.
Fortunately, the loss of its empire is a process that always seems to leave the nation in question better off, at least in modern times. As I see it the only possible justification for total galactic conquest is self-defense: do unto others before they can do unto you, more or less as you put it. Any advanced civilization that doesn't see that as a self-defeating justification is so different from my way of thinking that I couldn't possibly deal with them on any terms, offensive or otherwise.
Basically, what you're saying is that the only way to survive and prosper in the Universe is to be a murderous, psychopathic douchebag on a galactic scale. Not down with that, sorry.
Were these your words, or not?
You're projecting human flaws and attributes on an advanced race that would, by necessity, be almost nothing like humans. It simply does not follow that because the solar system has not (yet) been turned into grey goo, we must be alone in the galaxy.
The push for the moon was extraordinarily costly - but an entire nation, the richest on earth at the time, was behind it. It was a national effort, a calling together of an entire people, a lining up of all effort and a relative lack of detractors.
There are plenty of prior examples of this type of cohesive effort - Britain in World War 2 springs to mind. But many others in prior history as well.
Therefore I would say the lack of decade-spanning effort is not because people now are different, there just is a paucity of generational ideas that get everyone excited. If something falls down on a partisan basis, then it's just not good enough as an idea to unite an entire people. History, after all, is really a long string of dull years punctuated by exciting events.
The LHC may be the last of it's type, but then how many people are really excited about particle physics, no matter how good the possible benefits might be? I would not say our attention span is narrowing, merely reverting to the mean.
[NB That nice round figure has stuck in my memory since I first saw Cosmos in the early 80s]
"And so he built the Total Perspective Vortex--just to show her.
And into one end, he plugged the whole of reality as extrapolated from a piece of fairy cake, and into the other, he plugged his wife: so that when he turned it on she saw in one instant the whole infinity of creation and herself in relation to it.
To Trin Tragula's horror, the shock completely annihilated her brain, but to his satisfaction he realized that he had proved conclusively that if life is going to exist in a Universe of this size, then one thing it cannot afford to have is a sense of proportion."
WARNING: You may become nauseous, dizzy and afraid if you sit playing with this for too long.
Fundamental particles are true point particles and no spatial extent has ever been found for them.
So it's not just a lot of empty space - it's nothing except empty space.
That said, 200 light years is an enormous size. Everything that is large enough to take up more than one pixel on the map of our galaxy if freaking huge! People may disagree about the factual relevance of the radio bubble, but it's still immensely cool that we managed to project something this big out there into the world. Looking at this beautiful image of the Milky Way and seeing the unstable little flicker centered on our humble home, I can't help but wonder how many other radiospheres are out there and when they might finally overlap with ours (if they haven't already).
How insignificant we all are, in the grand scheme of things.
(Then my mind overflows when I ask myself the question of "what the hell is the universe?")
The sheer magnitude of order on our planet since the dawn of life - uncanny biodiversity, the rapturous elegance of cellular systems and organisms - and more recently, of our species - the culture, the technology, the spectacularity of both our achievements and failures - is anything but insignificant.
Maybe this happens all the time elsewhere outside our 200-light-year dot. But even if it's common, I propose that it is significant wherever it happens. The universe is significant. And we're a part of it.
Try and put religious arguments aside (while this will have some overtones) for a moment and work with me here and not throw the notion of time having no beginning or end which is equally frustrating to comprehend.
Reverse the creation story and you wind up at the beginning with light and darkness. Before light there was darkness or nothing.
But what was before the "darkness" or nothingness? The religious will say God whom has no beginning or no end, but how did God or energy pop into to existence if there was nothing?
Then, put yourself in God or energy's place... You are in a "space" with nothing around you... everything is void... Then where did "you" come from?
I know this is linear thought and time and the universe should not be considered in this way many in the field of science and mathematics explain... I understand the many dimensions that are possible and how time should be viewed, but it still doesn't answer the question of how something, anything came of nothing...
One idea is that time and space started with the big bang. So asking what happened before the big bang is somewhat pointless because causality did not exist. Things could happen without cause or consequence.
PS: Our preconception of how reality operates break down on the vary large, the vary fast, and the vary small. Trying think how things operate without matter, energy, space, or time is something of a fool's errand IMO.
The probable reality is not that the universe came from nothing, but that the universe is nothing. In a flat universe (which is what we believe we are) the symmetries of the universe cancel each other out such that, accounting for the mass and energy, the universe is a state where 0 = 0.
Essentially, as particles expand and spread out, the universe will reach a point where there is not enough energy localized in one area to support anything.
Of course this is just one theory. etc etc
Basically, I was waxing on the idea of existence, and what it meant. Might be another angle for you to consider.
Sure thing. Thanks. :)
There was no "space" with 'nothing around you'. Space is relative. Without time it isn't just a void... it doesn't exist.
A mathematical structure? Perhaps a perspective/viewport/subset of the entirety of mathematical possibility? What's between nothing and 'something' (0 and 1)?
Seems to me that's only a valid question if asked by a consciousness experiencing it (tree/woods/sound yada yada).
If you don't know yet, that's what earth looks like from just beyond Pluto's orbit.
Also interesting to note in these discussions is the Hubble deep field image. These 3000-ish galaxies are covered by a quarter at arm's length when you look into the sky --> http://en.wikipedia.org/wiki/File:HubbleDeepField.800px.jpg
We are indeed small and insignificant, but alone? Doubtful at best.
If we're the only (or even just one of few) intelligent beings (!) in the Universe then our significance is huge.
Sagan is absolutely amazing. It really does put things in perspective.
I often read this, but I have no idea why this should be the case. Since we only have a single data point, we can only really infer that the probability of life naturally occurring on a random planet is greater than zero.
We do know however that there are a finite number of stars in the universe, let's say 10^24. If turned out to be the case that the actual probability of life occurring on a planet was say, 10^-40, then we could very well be alone in the universe.
This 200ly sphere does not equal detectable radio signals from Earth. SETI is looking for radio signals from the stars, yes, but they are looking for a focused and high-energy attempt from ETs to contact someone by beaming at specific stars. Radio "leaked" from regular transmissions typically does not carry a signal over interstellar distances.
Now, the Arecibo message should carry over a couple of hundred light years easily, but it was transmitted for three minutes only, and if you miss it, you miss it.
If they don't, it would seem pointless to contact aliens, by the time they send their ambassador on a multi-generational ship to Earth we humans may have already been extinct.
People thought humans wouldn't break the sound barrier for engineering reasons, not because the laws of physics prevented it. And just because people in the past thought something was impossible doesn't mean it will one day be possible. 100 years ago, physicists thought perpetual motion machines were impossible.
Bad example, man, the "anything is possible" crowd hasn't necessarily conceded that point either....
I'm not actually 100% sure my interpretation of GR is correct, if anyone of the people who know more about it could elaborate, I'd greatly appreciated it (for example, I think acceleration has effects on time, too, which could crush my "long distance travel in no time"-theory).
The main uncertainty is at estimating the level of radio technology that can be available to alien civilizations.
I wonder if wolfram alpha could rise to the challenge.
Stars by Distance:
"....the thickness of the Milky Way is 50/100000 or 5/10000 of its maximum size making it flatter than a sheet of writing paper."
You can not calculate how flat something is by estimating from such a photo!
2. A typical sheet of writing paper is 10um or so in thickness and 20cm or so in extent. The ratio is 1/20000, which is 10x smaller number than even his (wrong) 50/100000.
3. His figure of 150ly is based on the distribution of molecular clouds. This seems an absolutely ridiculous way of measuring the thickness of the galaxy, about as sensible as measuring the dimensions of a human being by the distribution of their stem cells or something. It seems that the choice was motivated by wanting the smallest possible thickness figure.
4. The figure of 150ly for molecular cloud heights is too small. See figure 3 of http://iopscience.iop.org/1538-4357/619/2/L159/pdf/18343.web...; the right-hand portion of the figure shows average heights, which indeed are in that range, but as you can see from the left-hand portion there's a lot of variation and there are plenty of molecular clouds well above 150ly. (Note that the vertical scale in that figure is in parsecs; a parsec is about 3.26ly.)
So. The author of that page (1) selected the "thinnest" measure he could find, (2) used too low a value for it, (3) dropped a factor of 3, and (4) still got a result 10x thicker than a typical piece of paper.
(That's assuming that "flat" means "thin". The Milky Way is not particularly close to being planar, either.)
The milky way does not have a clear cut end, so you need some kind of definition on where to stop, and there are many ways to do so.
And you should stop estimating thickness by looking at photos. Brightness often masquerades as thickness in photos.
I don't understand your graph. What is the RA axis?
Galileo was born only about 164000 days ( ~ 4 million hours ) ago.
And that's already over twice as long as 200 years.
It makes me sad when I think about how a life time is a mere thousand months.
Sort of how an archaeologist can look at the surface of earth in a sat. photo and determine there was once human activity in a location based on ground disturbances, etc.
Also, as communication capacities increase, more and more of that is moving into cables and not radio transmitters. High-power Earth-Satellite and Earth-Earth transmitters are being replaced with low-power point-to-point wireless links. The power of radio traffic leaking off the Earth is not growing very much, if at all.
I look at that and think 'Wow, our presence is already felt that far/wide and we've barely started to walk'. Incredible.
It's a graphic of course but still you forget what you're looking at and how far away and how big it is.
Seriously, the page was completely empty until I unblocked that scripts on that and his main site.
Relax, it's PhysEx.
I haven't expanded much on the thinking behind these, because I mean them merely as examples of my main point and if I go on too long about them it becomes very tempting to miss it in a flurry of nitpicking about the details of various scenarios. My actual point is that we don't really know what happens, because we don't know what those engineering limits will be. There are some scenarios where the universe naturally favors species getting along, and there are scenarios in which the universe naturally favors species attempting to extinguish each other with all possible speed.
Assuming no ETs exist within our 200ly bubble, if ETs somehow discovered our signal and made contact, our level of knowledge would jump a few centuries at least.