The Astronomy Thread

It wasn't till very recently in 2012 that the IBEX mission proved that the heliosphere bowshock frontdoesn't existfor Sol, which is what that plasma wavefront is called. BUT there's still enough of a plasma wave to disperse the energy of 99% of all outgoing radio signals though.

And THAT was in 2012... 3 years AFTER aCornell team quantified the likelihood of radio transmissions of contemporary civilizations reaching each otherwithin cosmologically reasonable timeframes. Their conclusion was pretty damning for SETI even then:

Smith et al_sl said:

This paper develops a detailed quantitative model which uses the Drake equation and an assumption of an average maximum radio broadcasting distance by an communicative civilization to derive a minimum civilization density for contact between two civilizations to be probable in a given volume of space under certain conditions, the amount of time it would take for a first contact, and whether reciprocal contact is possible. Results show that under certain assumptions, a galaxy can be teeming with civilizations yet not have a guarantee of communication between any of them given either short lifetimes or small maximum distances for communication.

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So given an "optimistic" non-anthropic evaluation of the Drake equation that comes out with 300 concurrent civilizations (which is extremely unlikely considering the Carter Catastrophe qualification), their USABLE radio traffic that escapes their star's bow wake would be extremely unlikely to reach other civilizations anyway. Because physics.

And remember, IBEX also notes that Sol is actually travelling far FAR slower than most main-sequence yellow stars of the same age---the vast majority of m-congruent stars WOULD have a bowshock front that diminishes radio transmissions even more.

Yea, I don't have any of the facts or science stuff, but ever since I heard about fields surrounding solar systems I've been curious whether they're affecting interstellar communication.

That's the thing. The most earth-like exoplanet we've found so far isKepler-62f....

...and it's 1,200 light years away. The energy to send a coherent radio signal past the heliosphere's bow wave isn't crazy, but its way WAAAY more than the most powerful commercial transmission coming off Earth to date.

And most importantly, for them to hear it TODAY we would've had to transmit it back when Charlemagne was crowned the Holy Roman Emperor.

Yeah hubble's caught some pretty awesome ones:



The heliosphere actually sheathes the star's system from interstellar stuff. Most folks assumed Sol had a plasma bow shock front since our neighboring stars did, butIBEX showed that we're moving much slower and we dont.

1. Once mankind got to the point of starting our tech tree some 6-10 thousand years ago we've advanced dramatically to where we are now.

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It's difficult to quantify "dramatic" without a point of comparison, but ok.

2. Any pace that keeps up with our current one will have us continuously populating the galaxy in the next million years.

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This assumption is huge. We know that in human history the pace of discoveries varied dramatically for cultural reasons alone. We even know it went backward at times, so assuming this will no longer happen is in itself pretty big. That's not even touching the fact that we might hit knowledge walls or even physical walls that will prevent us from finding viable solutions to populate the galaxy.

3. There are 100 billion stars in the milky way.

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Ok.

4. Even a very conservative estimation of how unlikely it is for an Earth-level inhabitable planet to exist would still result in many Earth like planets.

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The article touches on the fact we are not sure how "earth-like" a planet must be to sustain life, but the range of biotopes on our planet alone tend to favor the idea that there is some wiggle room.

5. In a habitable planet, life has a chance of springing up over billions of years.

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My understanding is that we can reasonably assume that, because life was found on earth in totally isolated biotopes, or something similar?

6. In planet with life, civilization has chance of springing up over billions of years.

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We know there is a chance, because we know we exist, but we really have no way to quantify how big that chance is because we have a sample of one.

7. Once that planet establishes a civilization, it has a chance of colonizing the milky way.

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Again, even assuming a civilization, even assuming that human civilization as we know it today could lead to colonizing the milky way, we have no way to quantify how likely it is for a civilization to follow that same path.

8. We have not seen any life colonizing the milky way, why not?

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At the core of your assumptions, I feel there is the idea of a linear and continuous walk toward the better. The idea that today is better than yesterday and that tomorrow will be better than today and that, as such, whatever we can dream now will be a reality in the future, no matter how distant. When I see some of the theories in the linked article about the different types of civilizations and the graphs about the different steps and filters civilizations might have to go through, I feel they share that vision. I don't. For two simple reasons:

1) "Better" is not an universal notion. It is very much a cultural one. In the name of "better" men walked on the moon, but in the same name books were burned, knowledge forgotten, researches halted, political systems changed back and forth, etc. Civilizations are also well able to rise and fall from their own doing.

2) Predicting scientific progress (even if not hindered by cultural forces), is a perilous exercise, because while we are ingenious, reality does not care, so we depend on breakthroughs that might or might not happen. On top of that, we know there are things we can't know within the aseptic confines of our own mental constructions (I guess G?del killed my childhood dreams), so it seems more than a little presumptuous to think we (or anyone for that matter) can understand everything and solve all problems in our reality given enough time.


The other part of the argument is comparing a very big number of stars with a likeliness of the existence of Type II and above civilizations. The problem is that on one side of this comparison we have some material to make reasonably educated guesses, while on the other we really do not. And while the number of stars is indeed really really big, it is also a lot smaller than the number of legal chess games, so really, given the number of factors needed to reach Type II (if at all possible), it could very well be that the big number is just not big enough (and again, it's not touching the perennity - or lack of thereof - of a Type II and above civilization).

khorum_sl said:

The heliosphere actually sheathes the star's system from interstellar stuff. Most folks assumed Sol had a plasma bow shock front since our neighboring stars did, butIBEX showed that we're moving much slower and we dont.

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Is that good or bad news? Or neutral news because the lack of plasma bow does not hinder the sheathing effect?

Neither really... I just mentioned it in response to that paper from 1993 which assumed (like everyone else did) that there we had a plasma bow shock front since alpha centauri and tau ceti does. I suppose it's good for SETI and the James Webb telescope guys, though.

Well it also seems like a sufficiently advanced civilization could translate the willing members of their civilization into a digital form and exist almost entirely virtually. The Matrix basically. So you could have an infinitely diverse and expanding civilization without actually dealing with the issues of relativistic delays in communication and the logistics of galactic resource exploitation. Just look at our own MMOs as an example. What if the majority of humanity "lived" there rather than meatspace, and multi-tasked their brainpower to collectively operate the meatspace element of our society. You could also handle much greater levels of acceleration if you did need to move the server for resource reasons (a billion years passes and the sun you're based around isn't as favorable anymore perhaps) as the hard/wetware would be built to withstand G forces in double digits.

Yeah those are considered Kardashev-2 type civilizations. They'd live in dyson swarms or matrioshka brains, either way they'd live in some kind of post-biological closed loop collecting the total output of their star.

Thing is both are moribund, end-state malthusian dead-ends and they'd still be subject to outer bounds of the carter catastrophe. The carter equation figures the expansion of an civilization by whatever means, it just uses existing empirical data to asses the final bounds of the civilization growth (bayesian inference, like theGerman tank problem). We'd prolly be Kardashev-2s in 9,120 years too, then we all just kinda get bored and fuck off. Hell, some of the leading biologists today are saying some people alive today will live to 1,000.

I just googled the carter catastrophe, and that seems wildly implausible. It looks like mathematical wankery with no allowances for psychological development or physical transformations.

It's a probabilistic equation for predicting where the maximum bounds of a population is based on empirical data. Like the Drake Equation, you can tweak it if you like, but the bayesian inference behind it is just statistical math. If you adjust the median age to 1,000 years youd bump it up to 180k years like I mentioned earlier.

That particular branch of "mathematical wankery" has been around for decades and is used to accurately predict everything from quant fund algorithms that manage pension funds to how many tanks Israel makes in secret. In fact, in world war 2 we used it to accurately predict how many tanks the Nazis would have ready for D-Day, and it was off by 1. Nowadays it's basically the heart of control theory and runs everything from Amazon's warehouse stocking to google's self-driving cars.

No, I accept it's a useful way to model things. I just don't think it applies to the growth of humanity. There are a handful of rebuttals listed on the wikipedia page related to how it predicts human population growth, many of which I sympathize with.

khorum_sl said:

That's the thing. The most earth-like exoplanet we've found so far isKepler-62f....

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So someone negged me for this post. That's fine, but at least explain your reasoning. I was only commenting on the "most earth like planet" when in reality, all we know about it is how much light it dims from its parent star. The video goes into a better explanation than I could.

You're just not thinking with portals.

Nt