The Astronomy Thread

Lambourne · Sep 27, 2019

We may also have been overestimating the useful lifetime (to a civilization) of high power radio transmissions. Even at our current level of technology they are being phased out already. Older radio wave navigation systems like LORAN had transmitter power in the megawatt range, now replaced by GPS satellites which operate at a few hundred watt. Radio and tv signals are shifting to low power digital too.
We didn't start sending out high power radio signals until the 1930s and it looks like they may be all be gone by the 2030s. That leaves only a very tiny window where a civilization is detectable via radio waves, so even if many are nearby it would be very unlikely for us to catch them at just the right moment.

Cybsled · Sep 27, 2019

Plus you have to factor in moving past radio eventually. Even in The Expanse, they start to use laser "tight beam" communication over radio. And that doesn't even get into possible modes of quantum communication. Radio is potentially a stepping stone, but it doesn't mean it continues to get used for an extremely long period of time. And your point about high power transmissions is a good one.

Ukerric · Sep 27, 2019

Aldarion said:
Why cant it be "We're the first" and "there is no great filter"?

Not saying thats my position, but wouldnt that also explain the observed state?

Not entirely, because we appear to be latecomers. The Universe is nearly 14 billion years old, our sun and Earth appear to be 5. So, if you want us to be the first but without a great filter, you have to figure out a mechanism by which absolutely no life could develop for the first 9 billion years of the Universe, but that mechanism no longer applies, and all civilizations are now just starting to appear all around.

"We're the first" is shorthand for "we're the first species to pass every great filter until advanced technical civilizations."

If you assume that life-capable planets are extremely rare => great filter at planetary formation
If you assume that complex life is rare => great filter at apparition of life or complex life
If you assume that intelligence is rare => great filter at the intelligence stage of evolution
etc...

Basically, since a naive-numbers Drake Equation leads to an overcrowded galaxy chock-full of intelligent species, we have concluded that at least one parameter in the equation is horribly small vs expected. That parameter is a Great Filter (because it divides the equation in two realms - the hopeful and the heir to the stars). All of the real debate these days is "which one".

We're close to exclude the planetary formation one, because exoplanets are dime a dozen, and we still suffer from bias in that the non-viable ones are the easiest to detect currently. All of the rest are... still possible.

Which is why native life on Mars (as opposed to a panspermia between Earth & Mars) is a terrible news. The fact that we're alive doesn't let us deduce anything about the probability of life itself, since the conditional probability is always 1. Having life on Mars, Europa or anywhere else in the Solar Systems makes it very likely that apparition of life is not a Great Filter... which makes all other Great Filters more likely, including the one on our species/civilization lifetimes. And if you find anything more complex than a simple bacteria, it gets worse because you knock down two Great Filters for the price of one.

Ukerric · Sep 27, 2019

Cybsled said:
In theory vs practicality. If they are a limited life span species, then your only options are a) stasis tech b) artificial augmentation (ie, cyborgs c) generation ships. In all scenarios, there has to be a strong drive to basically abandon your life as you know it and everyone you know (or to expand in such a fashion if they aren’t beholden to individualistic desires)

Remember: "it only takes one".

Gavinmad · Sep 27, 2019

Maybe the Reapers are the great filter.

Ukerric · Sep 27, 2019

Gavinmad said:
Maybe the Reapers are the great filter.

In Drake equation scholar circles, you usually call them Berserkers (thanks Fred Saberhagen).

Aldarion · Sep 27, 2019

Ukerric said:
Not entirely, because we appear to be latecomers. The Universe is nearly 14 billion years old, our sun and Earth appear to be 5. So, if you want us to be the first but without a great filter, you have to figure out a mechanism by which absolutely no life could develop for the first 9 billion years of the Universe, but that mechanism no longer applies, and all civilizations are now just starting to appear all around.

"We're the first" is shorthand for "we're the first species to pass every great filter until advanced technical civilizations."

If you assume that life-capable planets are extremely rare => great filter at planetary formation
If you assume that complex life is rare => great filter at apparition of life or complex life
If you assume that intelligence is rare => great filter at the intelligence stage of evolution
etc...

Basically, since a naive-numbers Drake Equation leads to an overcrowded galaxy chock-full of intelligent species, we have concluded that at least one parameter in the equation is horribly small vs expected. That parameter is a Great Filter (because it divides the equation in two realms - the hopeful and the heir to the stars). All of the real debate these days is "which one".

We're close to exclude the planetary formation one, because exoplanets are dime a dozen, and we still suffer from bias in that the non-viable ones are the easiest to detect currently. All of the rest are... still possible.

Which is why native life on Mars (as opposed to a panspermia between Earth & Mars) is a terrible news. The fact that we're alive doesn't let us deduce anything about the probability of life itself, since the conditional probability is always 1. Having life on Mars, Europa or anywhere else in the Solar Systems makes it very likely that apparition of life is not a Great Filter... which makes all other Great Filters more likely, including the one on our species/civilization lifetimes. And if you find anything more complex than a simple bacteria, it gets worse because you knock down two Great Filters for the price of one.

I didnt explicitly say it in my post, but when I propose "we're the first" I am really proposing "life is exceptionally rare in the universe, bordering on unique".

If the emergence of life, or the emergence of intelligent life, are sufficiently rare that would explain the observed state without any great filter. I dont see how its useful to talk about a filter that applies before a species exists. We should confine that term to things that prevent species from achieving interplanetary civilizations, not things that prevent species from existing in the first place.

khorum · Sep 27, 2019

Well the point is to inventory those circumstances that may explain the Fermi Paradox of "Where is everybody". In which case the extreme rarity of biogenesis WOULD qualify as a potential Great Filter.

As he said, other components of the Drake equation's predicted factors have been observed. Since the Kepler observatory has gone live we've confirmed thousands of exoplanets orbiting main sequence stars in the habitable zone. So that filter is off the table. Now we still haven't confirmed if any of those planets might have harbored multicellular life, so THAT filter is still a distinct possibility.

Ukerric · Sep 27, 2019

Aldarion said:
If the emergence of life, or the emergence of intelligent life, are sufficiently rare that would explain the observed state without any great filter. I dont see how its useful to talk about a filter that applies before a species exists.

That's a matter of semantics. When we talk about civilizations in this galaxy, every factor counts. Every factor that is near-zero is equally useful to explain why there's no civilization around. Just because we've crossed it does not mean it's not a filter - it's merely a filter that we overcame already. And thus, we're the first (at least in the observable neighborhood), and we inherit the stars.

So, when you say "life is exceptionally rare", you're making a statement that is semantically equivalent to "the great filter is at the creation of life".

And it's useful, because once you make that statement, then yes. There's nothing anymore mandating a further filter, and a long and prosperous future for our civilization becomes the probable case.

khorum · Sep 27, 2019

Lambourne said:
We may also have been overestimating the useful lifetime (to a civilization) of high power radio transmissions. Even at our current level of technology they are being phased out already. Older radio wave navigation systems like LORAN had transmitter power in the megawatt range, now replaced by GPS satellites which operate at a few hundred watt. Radio and tv signals are shifting to low power digital too.
We didn't start sending out high power radio signals until the 1930s and it looks like they may be all be gone by the 2030s. That leaves only a very tiny window where a civilization is detectable via radio waves, so even if many are nearby it would be very unlikely for us to catch them at just the right moment.

Scientists DON'T just factor in radio communications since we know our own high powered radio communications degrade over cosmic distances. As I mentioned earlier Shermer uses the infrared shift produced by urbanization, which could come from city lights to infrastructure to agriculture. Using historical models he puts Drake's L at around 600 to a thousand years. Carl Sagan preferred to use the window in which a civilization would have access to nuclear technology, since between using it and storing it or exploding it a planet would emit gamma and xrays that would not otherwise be there. Sagan's figure would put L at 50,000 years---which is what SETI uses since radiation generated by industry could potentially be distinguishable from cosmic background radiation.

And lastly there's Kardashev's expression of the total energy utilization of advancing civilizations. As civs advance their demand for energy increases proportionally. So they'd first capture all the available energy from their planet, then capture all the available energy from their star. Once they can do that then it's only a matter of letting solar radiation escape out one hemisphere of their dyson shell to turn their star into a shkadov engine---which would accelerate so long as the star shines and so reach relativistic speeds within a few thousand years. This is why people are using Kepler to investigate weird stars with strange orbits and wobble as if a megastructure is orbitting it, like Tabby's star.

But even WITHOUT Shkadov stars, a civilization using our own clunky technology travelling at chemical rocket speeds could have colonized the entire Milky Way in 5 to 50 million years....but we don't see anything like that at all.

Cybsled · Sep 27, 2019

Ukerric said:
Remember: "it only takes one".

You're right, it just takes one. But on a cosmic scale, you need more data. You can't draw a conclusion with 50 years of extremely limited data/observational capabilities out of billions.

A civilization could have been hypothetically beaming transmissions to us for 5,000 years, but if those 5,000 years were during the Neolithic period, or heck even up until the Victorian era, then we missed the evidence.

Cybsled · Sep 27, 2019

khorum said:
But even WITHOUT Shkadov stars, a civilization using our own clunky technology travelling at chemical rocket speeds coukd have colonized the entire Milky Way in 5 to 50 million years....but we don't see anything like that at all.

But it wouldn't be practical to expand with that level of tech in most cases if the lifeform has a limited lifespan on par with a human, plus it would require engineering technology that could deal with centuries of deep space travel without support. It's not impossible, but neither is rowing around the Earth in a kayak. It's just at a level of impracticality without sufficient technologies that offset the massive hurdles with space travel on that time scale.

khorum · Sep 27, 2019

Cybsled said:
But it wouldn't be practical to expand with that level of tech in most cases if the lifeform has a limited lifespan on par with a human, plus it would require engineering technology that could deal with centuries of deep space travel without support. It's not impossible, but neither is rowing around the Earth in a kayak. It's just at a level of impracticality without sufficient technologies that offset the massive hurdles with space travel on that time scale.

AGAIN it's not a matter of practicality, but NECESSITY.

You're anthropomorphizing hypothetical civilizations which is what Kardashev successfully avoided. You don't need to imagine lifespans or biological limits, he simply measured the total energy production and consumption rates of any given civilization regardless of what the individuals in it may or may not regard as "practical". Millions of humans questioned the practicality of the steam engine, or the necessity of electricity when whale oil worked just fine, or the need for nuclear power when coal plants worked fine. But our demand for more energy grew beyond our capacity so we kept growing that capacity---regardless of whether individuals thought "nah this is fine".

That relationship between demand and supply is universal and serves to predict the behavior of humans or little green mushroom people from Zorbat IV.

pharmakos · Sep 27, 2019

Time for a bump?

The Fermi Paradox -- Where is everybody?

Fermi paradox - Wikipedia The Fermi paradox or Fermi's paradox, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates, e.g., those given by the Drake equation, for the existence of extraterrestrial civilizations. The basic...

www.firesofheaven.org

pharmakos · Sep 27, 2019

Couple recent news articles from earlier this week that were lost in the Fermi Paradox discussion:

Troubled Times for Alternatives to Einstein’s Theory of Gravity | Quanta Magazine

New observations of extreme astrophysical systems have “brutally and pitilessly murdered” attempts to replace Einstein’s general theory of relativity.

www.quantamagazine.org

Russia Won't Tell NASA What Caused Mystery Leak on ISS

Roscosmos had previously suggested a man-made hole in the Soyuz spacecraft caused an air leak on board the International Space Station in August 2018.

www.newsweek.com

Particularly that second one is wtf/ugh/sigh

Cybsled · Sep 27, 2019

khorum said:
AGAIN it's not a matter of practicality, but NECESSITY

Right, a civilization that has completely exhausted/is close to exhausting all local resources basically has to look elsewhere or die/risk collapse.

So if we look at vast timescales, eventually you have to look outside your solar system, although such a move with limited speed would be more like exodus than expansion.

khorum · Sep 27, 2019

Cybsled said:
Right, a civilization that has completely exhausted/is close to exhausting all local resources basically has to look elsewhere or die/risk collapse.

So if we look at vast timescales, eventually you have to look outside your solar system, although such a move with limited speed would be more like exodus than expansion.

Sure, but again we can't anthropomorphize the motives of hypothetical aliens. We can't assume their need for lebensraum or planets with liquid water or whatever. So the idea is to use systems that are universal to predict behavior. Things like how the laws of thermodynamics would apply to all civilizations and it scales into thermoeconomics, which predicts how things redistribute energy, from sub-cellular organelles to big corporations to civilizations.

WE might want to colonize Alpha Centauri because cow farts destroyed our ecosystem, but aliens might just be attracted to shiny space lights.

Aldarion · Sep 27, 2019

Ukerric said:
That's a matter of semantics.

I agree. I just find it an important semantic distinction. The filter metaphor only makes sense for factors that end species. But no disagreement about its impact.

khorum · Sep 27, 2019

Aldarion said:
I agree. I just find it an important semantic distinction. The filter metaphor only makes sense for factors that end species. But no disagreement about its impact.

A key point is that the Fermi Paradox ASSUMES the mediocrity principle. It begins with the assumption that the conditions that allowed human brains to observe this universe IS NOT unique. It simply asks why there aren't other intellects.

So answering it with a proposal built upon the Anthropic Principle, like the simulation hypothesis and others---although effective---is kinda missing the point.

Oldbased · Sep 27, 2019

It is fairly safe to assume many worlds have some form of life on them. Maybe even trillions.
What is crazy to me is when you think how much life exists on Earth, yet only 1 type can create iPhones.

The Astronomy Thread

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