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The Size of the Human Radio-Broadcast Bubble in the Milky Way Galaxy (jackadam.net)
240 points by thegrossman on Feb 6, 2011 | hide | past | web | favorite | 109 comments

This makes me feel small, sad, and alone.

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.

I agree... but it also makes me yearn for what will be seen after I am gone. I constantly wish I could be frozen and woken up every 1000 years to see what else we have learned about the universe. The fact my glimpse into the cosmos is so fleeting does disappoint me.

That's true but out of all times in history for advancement this may be one of the most interesting to live in. We have developed a global communications and information distribution network, this hasn't been there in the past and you would expect something similar to be present for the rest of all time.

Perhaps it's not necessary to freeze yourself - if Moore's law just ignores physical limitations and keeps going, we could have the technological singularity within our livetimes. It will get quite boring for people working in the computer science field after that ;-)

I've often thought the same. I've no yearning for an afterlife - I am more than willing to accept that once I'm dead, I'm gone. I also have no problem facing my own death - it'll happen when it happens. I certainly don't want to be immortal - that would be one of the most boring things ever, and would completely devalue my relationship with everyone I've met (especially loved ones). I can't however shake this desire to see where we are as a race in 200/2000/20,000 years. I guess all I can do is aim to at least contribute something towards the positive advancement of our race.

Think of it a little differently. Live in the now. You are currently witnessing a time that some of those before you wished they could live to see. How exciting! :)

when we look at the improvements that we've made in the last 100 years it makes me very excited for even the foreseeable future, not even what might happen after that. We live in very interesting times indeed

The magnitude of your "Aristotle, Caesar, ..." hit me hard, smack dab in the face just now. The magnitude of how accessible knowledge is today is amazing, if not the most amazing thing computing has ever done for humanity.

"Space... is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is."


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. [1]



[1] Tune in tomorrow for a new estimate, of course.

I find that reading huge numbers doesn't get the true scale across. It helps to bring the relative scale down to human terms. There are 63,360 inches in a mile. There are about 63,240 AUs in a light-year. So if the Earth was one inch from the Sun, Alpha Centauri would be 4 miles away. In this miniature model, the speed of light is around 7 inches per hour, or 1 mile per year, and our fastest probes take 100 days to move an inch.

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.

Please read `Burning the Cosmic Commons: Evolutionary Strategies for Interstellar Colonization' (http://hanson.gmu.edu/filluniv.pdf) from the wonderful collection `The Economics of Science Fiction' (http://hanson.gmu.edu/econofsf.html).

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."

What if most civilisations either destroy themselves or are wiped out by a comet or changing star conditions or an irregular orbit, or any number of things. If life truly does take as much time to become intelligent enough to actually tackle space travel there is a lot that can go wrong in the 4 billion year interim. Plus that requirement rules out a great number of stars which don't live long enough.

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.

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.

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.

I guess the inferential distance between us is too great. A world in which we colonize the stars is a world where we've fixed some of the problems today (aging, death, existential risks from various technologies). I assume humanity will change substrates to something that lasts a little longer than our current bodies.

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.

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.

So this hypothetical civilization has conquered aging, death, and the drive for rapid gratification, but fails at elementary game theory?

There's no game theory involved. A million years is a blink of an eye on an evolutionary timescale. When the first civilization has Von Neumann machines, their closest competitor is most likely primordial goo. See http://andabien.com/html/evolution-timeline.htm to get an idea of how long it takes for life to evolve.

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.

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.

You don't understand how controlling a significant fraction of a galaxy's matter is advantageous?

No, but then I don't understand the imperial incentive, even here on Earth. I'm a fairly self-centered individual, and a lazy one at that... and as far as I can see, running an empire always seems to be more trouble than it's worth. The whole history of the twentieth century can be written in terms of the world's great powers discovering this little tidbit of truth. I believe the first few decades of the twenty-first will see the US experiencing the same global comedown that Russia, Germany, and Britain have already undergone.

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.

Either you don't understand what I'm saying or you are purposely misconstruing my words so you can have a convenient strawman to take apart.

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

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.

I'm not going to disagree with your general points, but I will say one thing. The reason no large governmental projects have taken place is because the idea is not compelling.

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.

Sagan was quoting 100 billion galaxies each of a 100 billion stars quite a while ago:


[NB That nice round figure has stuck in my memory since I first saw Cosmos in the early 80s]

I love Carl Sagan's "Pale Blue Dot" speech[1] as it not only places us in the universe but puts our silly futile arguments, battles and wars on the tiny stage they are actually fought. As an atheist I like to point to this video as one place I find moral context.


If you're going to quote Douglas Adams, then the Total Perspective Vortex seems even more apt:

"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."

I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

"Two things fill the mind with ever new and increasing admiration and awe, the more often and more steadily we reflect on them; the starry heavens above and moral law within. . . The former view of a countless multitude of worlds annihilates, as it were, my importance as an animal creature, which must give back to the planet (a mere speck in the universe) the matter from which it came, the matter which is for a little time provided with vital force, we know not how. The latter on the contrary, infinitely raises my worth as that of an intelligence by my personality, in which the moral law reveals a life independent of all animality and even of the whole world of sense--at least so far as it may be inferred from the purposive destination assigned to my existence by this law, a destination which is not restricted to the conditions and limits of this life but reaches into the infinite." (Kant, Critique of Practical Reason, 1788)

Try this if you want to feel really small AND really big at the same time: http://htwins.net/scale/

WARNING: You may become nauseous, dizzy and afraid if you sit playing with this for too long.

The "Wrong Version" is hilarious: http://htwins.net/scale/wrong.html

Pretty neat. But no blue whale? That's a strange omission, since it's considered to be the largest animal ever to have existed on earth. Comparisons to our surroundings are interesting, but comparisons to our competitors are just as meaningful.

The really amazing thing about that link is how much empty space we're made up of on an atomic and subatomic level.

On a subatomic (and subnucleonic) scale it's 100% empty space.

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.

And at the intergalactic level. The universe really is extraordinarily vacant for such an interesting place to live.

Very nice! Inclusion of preons is a bit questionable though.

Am I the only one that sits and thinks "wait, I can barely get my local AM station to come in clear enough to be understood - how could any signal possibly be distinguishable beyond 1 lightyear?"

No, and you're absolutely right, too. The human radiosphere might technically be 200 light years across, but that doesn't mean a meaningful amount of data could be extracted from it. Yes, we are putting out a steady hum of energy, but it's hardly announcing our presence. Were it not for high energy radar systems deployed on Earth, we could not even detect a civilization down here from any point in our own solar system, much less decipher any of the data being transferred. And as our civilization matures, the amount of energy radiated into space is actually shrinking.

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).

An intelligent race which knows anything about stars would note that Sol has a disproportionately large output in the radio spectrum. This would likely attract considerable attention and debate as to the cause. Careful analysis would reveal a very precise and regular Doppler shift lasting approximately 365.25 days...

That was my thought too. Given the size of the galaxy, the fact that we registered at all a view of the entire thing is, to my mind, astonishing. Go humans.

In addition to line-of-sight, your AM station is transmitting more or less omnidirectionally. Significant gains (pun intended) can be had by narrowing your beam. Check out the Link Budget Equation: http://en.wikipedia.org/wiki/Link_budget

This kind of stuff always blows my mind away.

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?")

Earth is a big fish in a small interstellar pond. But what a big fish it is!

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.

I can practically give myself an aneurism thinking the following when contemplating how it all began:

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...

That's a limited viewpoint.

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 odd thing, the hardest thing to comprehend, is how our reality continues to exist. The ground state of the universe is a vacuum. Void of matter and shielded from radiation is the quantum foam of field fluctuations and virtual particles that exist on the scale of Planck lengths.

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.

Could you expand upon how causality can cease to exist or what would cause (heh heh) such a thing?

There is the concept of the heat death of the universe. http://en.wikipedia.org/wiki/Heat_death_of_the_universe

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

A few years ago, I wrote a blog post about my thoughts on this, -two posts actually: http://corpusdord.blogspot.com/2006/02/existence-and-non-exi...

Basically, I was waxing on the idea of existence, and what it meant. Might be another angle for you to consider.

Impressive and I have contemplated such along similar lines before. Well done. Of course it doesn't bring an answer closer, but it is a very rational ideal based on everything we know to be true already. We'll have to have coffee and talk about this sometime if I'm ever in MI.

>We'll have to have coffee and talk about this sometime if I'm ever in MI.

Sure thing. Thanks. :)

"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?"

There was no "space" with 'nothing around you'. Space is relative. Without time it isn't just a void... it doesn't exist.

"what the hell is the universe?"

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).

Pale blue dot feels like an apt comparison --> http://en.wikipedia.org/wiki/File:Pale_Blue_Dot.png

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.

>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.

If we're the only intelligent beings in the Universe, then I argue that intelligence is overrated, thus our significance (except to ourselves) is negligible. Unless you go the route of arguing that without intelligence, there is no significance, and thus our self-significance is all the significance there is, in which case you're right - it's huge.

Here's a YouTube link to the entire Pale Blue Dot bit by Sagan: http://www.youtube.com/watch?v=wupToqz1e2g

Sagan is absolutely amazing. It really does put things in perspective.

> We are indeed small and insignificant, but alone? Doubtful at best.

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.

When looking at the radio bubble image, I immediately wondered if the blue color was chosen intentionally as a reference to the Pale Blue Dot. Great coincident association, at least. Similar sense of the infinitesimal scale we live our lives at. Now, let's see some Electron Microscopy.

Yeah, I chose the color for that reason. Also, it's hard to find a color that stands out on a the extreme light / dark background of a galaxy. It just so happens that pale blue is better than most.

"...there is an ever-expanding bubble announcing Humanity’s presence to anyone listening in the Milky Way."

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.

That's something I want to know. With the amount of energy given to our broadcasts, they surely would decay long before traveling any noteworthy distance. I'm curious as to what our most powerful broadcasts have been, and how far they'd travel before becoming unnoticeable. Especially, when compared to the amount of EMR released by neutron stars, pulsars, background noise, etcetera.

From the SETI FAQ: "Detection of broadband signals from Earth such as AM radio, FM radio, and television picture and sound would be extremely difficult even at a fraction of a light-year distant from the Sun. For example, a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope."

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.

Not if you have faster-than-light travel!

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.

FTL is probably not ever possible no matter how technologically advanced a society may be as it would allow for the violation of causality.

You're assuming we already know everything there is to know about causality. It wasn't long ago that some people thought the sound barrier was insurmountable, or that trains would kill their occupants by going too fast.

FTL is equivalent to time travel into the past. If you have one you have the other.

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.

Thanks for saying what I wanted to. Everybody who knows nothing about physics always brings up the "humans can't possibly travel faster than 25mph" thing when someone who does know talks about violating causality, but as far as I've seen it was only printed in a newspaper or two, not espoused by physicists. The speed of light limitation is a necessary part of one of the most precise and thoroughly tested theories of all time.

"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....

What about the bending of space for an instant travel time? That's more of an unknown in terms of possibility from what I have read.

If I understand GR correctly, FTL travel is (in principle) not necessary to reach an alien race in reasonable time, no matter the distance - from the point of view of an astronaut. Due to length dilation, from the point of view of an astronaut, the whole universe gets pretty small when he travels with almost-lightspeed, so that he can travel, say, one lightyear in five minutes (assuming he can survive the acceleration). The problem is that the wait on earth would be pretty long...

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).

There is an analysis of the detectability of human radio signals at:


The main uncertainty is at estimating the level of radio technology that can be available to alien civilizations.

Not to mention whether they'd even bother with radio, if better technologies become available.

I'd like to see this plotted on two dimensions, where the horizontal axis is the year, starting when radio emissions began, and the vertical axis is the number of non-sol star systems that are within the bubble at that time. Binary or trinary systems would count as 1 system, not 2 or 3. This function would obviously be monotonically nondereasing.

I wonder if wolfram alpha could rise to the challenge.

Using the NStED database of stars I find that there are 11,384 cataloged stars within a 200 light year bubble. I thought that it would probably follow an r^3 function but it appears that it follows something closer to an r^2 function - perhaps that is explained by the flatness of the galaxy or just noise? For example, within 20 light years there are only 77.

Stars by Distance: http://dl.dropbox.com/u/3924269/plot_10956.jpg

NStED: http://nsted.ipac.caltech.edu/

Yah, the galaxy is very flat. Depending on how you define the thickness (do you go by majority of stars, or include all outliers) proportionally the galaxy is flatter than a sheet of paper.

I don't think that's true. Other galaxies don't appear as thin or as flat as paper. (Examples: http://apod.nasa.gov/apod/ap031008.html http://apod.nasa.gov/apod/ap020703.html http://apod.nasa.gov/apod/ap060612.html) Typically they're about 100x wider than they are thick.


"....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!

1. He says 150 light years out of 100,000 light years. Then he writes 50/100000, just losing a factor of 3 for no reason at all.

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.)

Wikipedia says the stellar disc of the Milky Way is 1,000 light-years thick and cites http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980317b.... . The core is thicker. Even the image on the page you linked to shows an object that is much thicker than a piece of paper.

Did you miss the part where I said: "Depending on how you define the thickness" ?

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.

Yes, there are many definitions. None of them, however, gives the result that the Milky Way is flatter than a piece of paper. Not even the (rather silly) one used by the author of the web page you quoted; his numbers are wrong.

Thank you. 11k is higher than I would have guessed.

I don't understand your graph. What is the RA axis?

Is the milky way really large or is 200 years a really short time?

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.

Even more discouraging than the size of the bubble is what the bubble's cross-section looks like:


But maybe, just maybe, our industrial and scientific development is producing an occasional side-effect of some kind of as yet-unknown faster-than-light wave which has made it much further out, and significantly more advanced civilizations have the ability to detect it.

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.

Of course, such a wave would be pretty bad news for a certain theory proposed by a certain Albert.

It would be interesting to know how much of the Milky Way SETI has scanned so far. In other words, if someone else out there was running their own version of SETI, how long before they would be likely to find our little radio broadcast bubble?

This reminds me of the opening scene of “Contact” (1997), the movie adaptation of Carl Sagan’s novel by Robert Zemeckis:


To put the blue dot in perspective, its unimaginably beyond the scope of our current technology to travel that far. Pluto by comparison is 13 light-HOURS away and it takes about 10 years to get there. At that rate, it would take approximately 150000 YEARS to reach the same distance to reach the perimeter of that blue bubble. And blue bubble is almost insignificant in relation to our galaxy, which is one of about 100 billion galaxies!

Sadly, it would not be possible to discern manmade radio transmissions from further than a few light-days/weeks.

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.

To me this is really inspiring.

I look at that and think 'Wow, our presence is already felt that far/wide and we've barely started to walk'. Incredible.

Oh, it's a blog entry! There really should be a noscript warning, I thought it was something like http://www.phrenopolis.com/perspective/atom/ at first.

Cool! .. and all this discussion reminds of a line from Calvin and Hobbes - "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."

It's odd how you look at that and go "hunh" but then realize, wait a minute who took the picture of the Milky Way Galaxy?

It's a graphic of course but still you forget what you're looking at and how far away and how big it is.

You should cheer up that we are living in the Slow Zone. That should make us unaffected by the "Straumli Perversion" and other Powers from the Transcend and messing with the Beyond for quite some time.

Sure-fire way to feel small, sad, and alone: typekit.com

Seriously, the page was completely empty until I unblocked that scripts on that and his main site.

Ugh, what is that horrible font? Whatever typekit.com is trying to do (in Firefox 3.6 on Windows 7) isn't very working...

This makes me more hopeful of getting a response from other beings. Perhaps we're not so alone after all.

Relax, it's PhysEx.

Some alien might think - hmmm.... Human Spam again :)

Spiced human ham would likely be incompatible with any alien metabolism.

Curiosity apart what good could it do us to discover or be discovered by aliens?

After substantial thought on the topic by various smart people, the answer seems to depend on the ultimate nature of physics and ultimately the ultimate end point of engineering. If leaving planets is engineering-impossible and we can't fling even small projectiles out of the Solar System at any reasonable fraction of lightspeed, then it's of primarily intellectual interest. If the Singularity is impossible and humans will remain recognizably human for the indefinite future but it's possible to travel between the stars enough to actually colonize things, eventual war of some sort seems pretty likely in most situations, though not necessarily to extinction (though not necessarily not!). If a Singularity is possible and looks something like Accelerando, the future of humanity may be an enormous set of entities of such incredible mutual alieness that meeting another set of such entities from another biological base may be of no particular note, locally exciting, globally ho-hum.

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.

Let's find out!

All in the name of technology..

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.

If there are no ETs within the bubble how can they discover the signal?

Sorry, I meant discover as in through our bubble's reaching them in the future (ensuring they're at least 100ly away).

Ha. So, we don't even rate a single pixel on the blank, white screen that is the Universe? Sounds about right.

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