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The Fermi Paradox -- Where is everybody?
- Thread starter pharmakos
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I have a degree in econ and studied econometrics under a Nobel laureate. As a practical matter, Econometrics is just a fancy name for forecasting with linear regression. Cliometrics is an exercise in hand-picking historical data that generates a model confirming the conclusions you want to publish. It has its uses, but is definitionally just correlative extrapolation and doesn't carry a lot of explanatory power outside of scenarios with heavily-vetted parameters. Any claims about the future of the universe made on the back of this methodology should be taken with heavy doses of salt.
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khorum
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You're the one having some difficulty with this after I've responded with citations and even some videos. If you're nursing some counterfactual when we've already sent a spacecraft that weighs more than a metric ton that will arrive at proxima centauri in 78,000 years with 1970's rocket propulsion, then YOU show it.
The ion thruster on Dawn beat Voyager's speed record halfway through the first leg of its journey and that was first conceived in the late 60's. It then had to flip around and decelerate, maneuver into an insertion orbit around Ceres, accelerate and decelerate again to orbit Vesta months later until it finally ran out of propellant last October.
If it had been purpose-built to generate 12 more years of constant accelration it would've achieved about 2% of lightspeed before it ran out of propellant, which is already twice as fast as the lowest bounds on Hair and Hedman's simulation which modelled seedships going from 1% to 25% of C.
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Sentagur
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I never said that we cant litter junk around the galaxy or launch things outside our solar system. Scaling that up to be actually useful to the meat bags infesting this planet on the other hand is still outside our reach. After New horizons is out of comms range it just becomes another piece of space debris floating around until it crashes into something.
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khorum
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Then dose cliometrics with all the salt you want. Are you objecting to the notion that the compulsion to address the unequal distribution of resources in any given society would inevitably diminish capital formation in those regions which would be best equipped and/or motivated to colonize beyond the planet?
I don't even remember anyone objecting to that point. Your original objection was to whether or not some civilizations "finding peace" with extinction should be evaluated as a "failures" or "suicides" when I more or less agreed that's a credible resolution to the Fermi Paradox, regardless of their reasons.
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khorum
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Addendum: If we could usekhorum 's rustled jimmies as fuel we could have colonized Pluto already
ROFL "my" rustled jimmies?! You're the guy who kept smashing out butthurt "I DISAGREE" posts because 1969 rocket technology can't seem to fulfill your star trek fantasy of laying pipe on green-skinned Andromedan strippers.
We don't even need to accelerate at a constant 1g since we won't have any living humans on that ship who needs the fake gravity. Without even going into magnetoplasma engines, which weren't around in 1969, Dawn's measly 0-60 in four days acceleration would've been enough to get to 2 million km/sec after a few years of constant acceleration.
If we DID accelerate at 1g it would only take three months of acceleration to get to 25% of c.
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Burns
Golden Baronet of the Realm
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Here is the study in question, if anyone wants to read the original:
Spoiler for size
Second direct link to source:
Spatial dispersion of interstellar civilizations: a probabilistic site percolation model in three dimensions | International Journal of Astrobiology | Cambridge Core
Spatial dispersion of interstellar civilizations: a probabilistic site percolation model in three dimensions - Volume 12 Issue 1
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Let’s say we had a 10,000kg 1GW Fusion power plant that we could put in a ship. Is there a payload calculator that could show what such a power plant could move in a accelerate to .25c, coast, decelerate to orbital velocity scenario?
Are there any models for what sort of power would be needed to accelerate propellant to relativistic velocities? At a certain point wouldn’t you get a lot more bang for your buck on propellant because your propellant would attain relativistic mass as well thus boosting its force?
Since we spend approximately zero dollars researching space propulsion I wouldn’t be surprised if thats all theoretical.
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khorum
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I dunno about a calculator but the math has been around since, well at least 1969. I'm not sure we can EVER develop a reaction-less drive that isn't a lightsail though, and even with the laser-propelled lightsails you'd still need to bring enough propellant for deceleration until you build a laser at the destination.
The most efficient engines so far are photonic/ion thrusters like the ones Dawn had. It's super slow acceleration (0-60 in four days lol) but with less than 600 pounds of xenon it was able to sustain constant acceleration for 5.9 years. It broke the record in the first six months.
High specific impulse drives like the VASIMR also use noble gases as propellant but it needs big (prolly fissile) generator to produce the 100 kilowatts for the magnetic bottle that will contain and shoot the gas plasma out the back. So you'd have to figure in the mass of the reactor, the drive and propellant. Would still be at least an order of magnitude more efficient than kerolox engines and the specific impulse of the plasma makes it possible to accelerate fast enough to get to Mars in 39 days.
They're saying a Mars mission would need several VASIMR engines and a ~50MW generator at least. NASA's also got a homegrown plasma Hall-Effect thruster called the X3 but I dunno how far along it is. VASIMR finished a 100-hour continuous burn trial last year.
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Magnetically accelerating individual atoms to 99.999999999% of the speed of light should be workable although the power requirements would be ridiculous. Same as how the particle accelerators work now, we CAN do this, it's just not energy efficient...
and at a certain point you get secondary benefit from the particles relativistic state...
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khorum
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Right but at that speed even the momentum imparted by red-shifted photons start pulling back on your velocity exponentially. If you hit a particle with mass, then it's catastrophic. So you'd either want to sweep the space in front of you with something well ahead of time or factor in the weight of impact shielding or something.
OR you can just accept that the only reason folks would risk catastrophic interstellar impacts at 99% of c is because we're human and our lifespan tilts that risk/reward calculation towards something that we can appreciate within our lifetimes. But we don't need to move at 99% of c or even 50% of c or even 25% of c to colonize whole galaxy.
OR you can just accept that the only reason folks would risk catastrophic interstellar impacts at 99% of c is because we're human and our lifespan tilts that risk/reward calculation towards something that we can appreciate within our lifetimes. But we don't need to move at 99% of c or even 50% of c or even 25% of c to colonize whole galaxy.
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I'm not talking about accelerating the ship to 99.9999% c I'm talking about accelerating your propellant to that so it provides a greater impulse per mass carried
re-read plz
yerm
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God I hate to jump in, but let me try a hopefully more rational objection.
Let's agree that modern propulsion is sufficient to allow us to both accelerate and then reverse the acceleration of a reasonably massive object, such that given no time constraints we can put an object around any/every celestial body we want to. Maybe several of em for good measure.
How does this translate into colonising anything, given current (nevermind 1969) levels of technology? What exactly are we sending across the universe that will result in humanity's conscious existence outside the solar system? I keep hearing seed ships or AI etc. What is any of this doing exactly? Are we hurling earthborne organic matter hoping for eventual evolution? Are we content to merely send digital recordings of humanity without means of replicating organic human life (or really any propogation of the species) and calling it a win?
I am not looking for some hypothetical to-be-invented tech, even if I personally think for sure it's coming. I want modern tech. Real existing proven cause we have it today no further innovation needed tech. Assume cost is no barrier here. Do we have what is needed to put, recreate, breed, clone, grow, or in any otherwise way end up with living humans existing on extra-solar celestial bodies?
Tldr - assume propulsion is a given, cost is no issue, but must use only currently-invented/discovered tech. Can we seed the galaxy/ies? How?
Let's agree that modern propulsion is sufficient to allow us to both accelerate and then reverse the acceleration of a reasonably massive object, such that given no time constraints we can put an object around any/every celestial body we want to. Maybe several of em for good measure.
How does this translate into colonising anything, given current (nevermind 1969) levels of technology? What exactly are we sending across the universe that will result in humanity's conscious existence outside the solar system? I keep hearing seed ships or AI etc. What is any of this doing exactly? Are we hurling earthborne organic matter hoping for eventual evolution? Are we content to merely send digital recordings of humanity without means of replicating organic human life (or really any propogation of the species) and calling it a win?
I am not looking for some hypothetical to-be-invented tech, even if I personally think for sure it's coming. I want modern tech. Real existing proven cause we have it today no further innovation needed tech. Assume cost is no barrier here. Do we have what is needed to put, recreate, breed, clone, grow, or in any otherwise way end up with living humans existing on extra-solar celestial bodies?
Tldr - assume propulsion is a given, cost is no issue, but must use only currently-invented/discovered tech. Can we seed the galaxy/ies? How?
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Sentagur
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Can you clarify this? Does it mean constant thrust with static fuel usage or constant acceleration as in x m/s/s for 5.9 years? Doesnt the latter require exponential fuel usage as the speed of the object increases? The former means the thrust is same but acceleration is negative exponential or whatever its called.
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I think what they're postulating is sending AI ships with numbers of human embryos that would be unfrozen and grown once the AI ship lands and establishes base camp.
The AI being able to do all this completely autonomously considering it would be years (perhaps tens of years) round trip communication time seems pretty ambitious. You'd need some pretty solid advancements in AI.
khorum
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Dawn's ion thruster had enough propellant to provide for constant acceleration for 5.9 years. That was about 600 pounds of Xenon and it was juuuust enough to complete its orbital insertion to Vesta. It's expressed as 5.9 years of delta-v since it had to accelerate, decelerate, maneuver etc to go from Earth to Ceres and finally to Vesta. But yes, it was basically constantly accelerating in one direction or another for almost six years.
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The acceleration was so small that the velocity of the spacecraft didn't change "that" much. So the increasing fuel usage to maintain acceleration wasn't really an issue.
khorum
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No idea. Dunno if there's a calculator out there but it kinda sounds like it would tip over Tsiolkovski's limits on rocket efficiency. Boosting all the propellant for the mission wouldn't be the most efficient anyway, even in multistage rockets. Maybe do something like have additional fuel stages orbiting Jupiter and Saturn at matching velocities for the outbound ship to grab during its gravity assist flyby?
Been meaning to try that in Kerbal.
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I'm talking past you somehow, and I apologize I'm probably being obtuse.
So you're carrying your xenon in a tank on the ship. Or whatever your propellant is. You magnetically accelerate some of it to 99.999% c and shoot it out the back. Just like, for example, in a chemical rocket, you accelerate shit (via energetic chemical reaction) to 4km/sec or whatever for your chemical rocket. The impulse is provided by shit going out at high speed. The force imparted to push it out, pushes you forward.
If we accelerate our propellant to 99.9999999%c, thats a LOT of force even for small amounts of propellant, so we get a correspondingly bigger forward force.
I'm not saying anything about accelerating the ship or any propellant store to relativistic velocities. I agree with your above post about shielding being a real problem as you get to those velocities.
For rockets in a vacuum that only starts being true if you're trying to accelerate your object faster than the exhaust velocity of your propellant. So yes, that would apply if you're shooting for significant factions of c, unless you're ejecting your propellant at ~c, in which case you have to get your huge power source to c, etc, etc.
It doesn't especially apply for "practical" versions of interstellar transit on scale of 10^several years.
Relevant:
"Relativistic rocket refers to any spacecraft that travels at a velocity close enough to light speed for relativistic effects to become significant. The meaning of "significant" is a matter of context, but often a threshold velocity of 30% to 50% of the speed of light (0.3c to 0.5c) is used... There is no known technology capable of accelerating a rocket to relativistic velocities. Relativistic rockets require enormous advances in spacecraft propulsion, energy storage, and engine efficiency which may or may not ever be possible. Nuclear pulse propulsion could theoretically achieve 0.1c using current known technologies, but would still require many engineering advances to achieve this. "