Astronomy / Space Astrophysicist Describes A Stellar Engine That Can Move The Solar System
- Thread starter Manticore
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Yes, hence moving the whole solar system is rather silly.
Let's do a comparison, for an (very) upper estimation let's assume the sum of the mass of all exodus ships is that of the biosphere of the Earth. Assuming that's 1.15 x 10^16 kg, the energy requiered to accelerate that mass up to 10% of the speed of light is (according to newtonian mechanics, the difference is still negligible compared to relativistic calculations) is 1.035 x 10^31 J already taking into acount the deacceleration on arrival.
Assuming the mass of the Sun is 2 x 10^30 Kg, to accelerate the Sun to 100 Km/s or 10^5 m/s would take 10^40 J.
Mind you, I'm very sure you don't need to move a mass comparable to that of the biosphere to transport all humans, I merely used it to demonstrate how big of a difference there is between moving the whole Sun and just migrating.
Ah so we are talking about events affecting all of our solar system (not sure GRBs fit that description though), you are certainly overestimating the energy requiered to migrate at decent speeds.
And moving the Solar System is not something you do until you are already a K2 civilization.
There are many plausible (even if far-fetched) ways of going interstellar and lifting things out into orbit, then again, this paragraph is rather vague.
What futurists and more importantly, in what papers?
After some reading, I saw how ridiculously slow all proposals are, active engines talk about a displacement of 10 parsecs per million years.
Shouldn't do anything since our sun is currently spiralling through the galaxy.
I get the feeling that we're having two different conversations, but I just wanted to respond to this part, primarily because I like doing back of the envelope calculations. 
I actually felt that your "(very) upper estimation" seemed to be a bit low, so I did my own estimation. The best calculations of an O'Neill Cylinder I could find quickly online (including one from Isaac Arthur's reddit) all agreed that "island three" would have a mass of around 3x10^12 kg. It would take about 2x10^4 such cylinders to evacuate the current population of the Earth, or about 6x10^16 kg... again a difference which is negligable at these scales.
Of course, my argument was always once you start moving into the K2 range of energy consumption, its very likely that a civilization already has a Dyson Swarm, and if it has a Dyson Swarm, then it makes little sense not to bring that infrastructure along with you. Especially when you consider that if you do have a Dyson Swarm, then the planet-bound population probably represents a tiny fraction of percent of the system's total population. After all, our civilization currently consumes about 4x10^12 J/s, and the sun produces 3.84x10^26. Assuming that a K2 civilization uses only 10% of that power to sustain habitats, we're still talking about a population that is 10^13 bigger than it is currently.
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True. But since we're talking about a disaster (a nearby supernova) that we should have at least a million year warning about, that's all we need. A nearby gamma-ray burst, since we're essentially talking about a (relatively) narrow beam, doesn't require a displacement nearly as huge to avoid the disaster.
The total energy emitted by the sun is about 3.84 x 10^26 J/s. So launching your exodus fleet would require about 2.7x10^4 seconds (7.5 hours) of the sun's total energy output. Half of would need to take the form of fuel, but assuming whatever is stopping your fleet is about as efficient as the sun (very unlikely IMO), the mass of the fuel would about 8.4x10^15 kg, so even if we assume the typical 10% efficiency rate, the difference is negligable, given that the we've broken out the exponents here.
I actually felt that your "(very) upper estimation" seemed to be a bit low, so I did my own estimation. The best calculations of an O'Neill Cylinder I could find quickly online (including one from Isaac Arthur's reddit) all agreed that "island three" would have a mass of around 3x10^12 kg. It would take about 2x10^4 such cylinders to evacuate the current population of the Earth, or about 6x10^16 kg... again a difference which is negligable at these scales.
Of course, my argument was always once you start moving into the K2 range of energy consumption, its very likely that a civilization already has a Dyson Swarm, and if it has a Dyson Swarm, then it makes little sense not to bring that infrastructure along with you. Especially when you consider that if you do have a Dyson Swarm, then the planet-bound population probably represents a tiny fraction of percent of the system's total population. After all, our civilization currently consumes about 4x10^12 J/s, and the sun produces 3.84x10^26. Assuming that a K2 civilization uses only 10% of that power to sustain habitats, we're still talking about a population that is 10^13 bigger than it is currently.
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True. But since we're talking about a disaster (a nearby supernova) that we should have at least a million year warning about, that's all we need. A nearby gamma-ray burst, since we're essentially talking about a (relatively) narrow beam, doesn't require a displacement nearly as huge to avoid the disaster.
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Wouldnt it be easier to move the star thats about to go nova to a safer place, rather than risk making one single mistake that wrecks the solar systems current equilibrium.
I must admit that on reading the OP I immediately thought that perhaps this scientist needs to be eliminated ASAP.
Why take the effort to move a planet we ourselves try to destroy in the first place.
As far as I understood we greedy human apes are doing our best to kill the planet as quickly as we can via death by a million cuts. Just look how far we already got in just a few centuries of human technical development. I feel we are almost done. Just give us a few more centuries and we will have created a beautiful new Venus.
I guess in some future we might try to move our solar system, including its dead, mostly desolate, plastified planet Earth (aka Venus 2), to avoid some potential cosmic disaster, but I do not see the point. The biggest cosmic disaster lives on this very planet and it is called... humanity.
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A full Dyson's sphere is far in excess of what would be needed to move the solar system and no, I don't imagine the thin shell of material that would make one up would provide much protection from the threats envisioned.
Getting to a viable system with any significant portion of humanity would be the problem.
Moving the solar system may be comparatively easy because the sun it self is the main engine and source of fuel, while Earth is already an excellent life support system.
Maybe like a super, hyper, giant, mega nuclear bomb ?
That's what it's doing right now, has been doing for almost 5 billion years and is likely to continue doing for another 5 billion. The sun converts roughly four million tons of matter to energy per second. And the sun is also already moving at ~200km/s in it's orbit around the galaxy.
In this proposal, we'd just be directing a fraction of this energy released to shift it's trajectory slightly.
It will take hugely more energy to move the sun than to move the entire population of Earth, many orders of magnitude more. That's never been in dispute.
Still simpler to move the whole solar system, because the same tools that would let you evacuate Earth could move the solar system, and we already have a pretty good planet here. Making a new home, almost from scratch, while allowing this one to be destroyed, would be phenomenally wasteful.
To evacuate earth, you'd need essentially double the resources needed to move the solar system, because you'd need the same infrastructure at the destination to decelerate incoming vessels that you used to accelerate them in that direction in the first place. Against any of the threats envisioned, it would be much simpler to stay put and divert the solar system enough to avoid them, than to abandon this system and start over elsewhere, unless we already knew of some place better.
Moving the other star would present many of the same hurdles as evacuation. You'd have to colonize that system, build massive infrastructure, then start moving it...rather than being able to utilize the resources of an already inhabited system. Even if there was time, doing this to a system you don't expect will survive seems almost as wasteful as abandoning Earth to start over somewhere else, to me.
There is also a smaller subset of threats that could be moved than ones that could possibly require moving Earth. A likely supernova could probably be moved, probably even easier than the Sun, at least if there were enough resources in orbit of that star to construct what was required, as it's luminosity vs. mass ratio would almost certainly be higher. However, there are other potential threats that would not provide enough energy we could harness to move them.
There would also not be any one single mistake that could wreck the solar system. Even the more rapid proposal would take geologic time scales; if problems were noticed, the project could be adjusted, or abandoned.
We are certainly the most pressing threat to our survival in the here and now...but this may not always be the case, and nothing is lost by imagining a future where those times are past.
The total energy emitted by the sun is about 3.84 x 10^26 J/s. So launching your exodus fleet would require about 2.7x10^4 seconds (7.5 hours) of the sun's total energy output. Half of would need to take the form of fuel, but assuming whatever is stopping your fleet is about as efficient as the sun (very unlikely IMO), the mass of the fuel would about 8.4x10^15 kg, so even if we assume the typical 10% efficiency rate, the difference is negligable, given that the we've broken out the exponents here.
7.5 hours plus the time needed to accelerate is much less than 1 million years.
I can't find immediate sources of the population of O'Neil Cylinders.
You are of course, assuming a linear relationship between energy consumption and human population, throught modern history every person has been increasingly consuming more and more energy individually. You are also assuming such populations can actually be sustained within our own Solar System.
From some simple reading, the main threat of those stellar events is the depletion of the ozone layer caused by excessive UV irradiation. Is there really no way to prevent such effects? Remember, terraforming is well within our hands by this point and replacing a small part of the atmosphere is even simpler than that.
The Sun being it's own engine? You are talking about the passive engine right? That one is not deemed fast enough as to avoid stellar hazards. There's also the fact that having such a massive reflector within the Solar System would highly alter the solar irradiance on Earth. Active stellar engines are deemed fast enough though they consume a lot of the star's mass, thus, altering it's brightness and mass which again, would actively mess up with the Earth.
Why is that? Even though making arks is a very large endeavour, it's certainly not comparable to the scale of the engines proposed.
Except, when you evacuate the Earth you do not pull the whole Sun after you. This is a complete non-sequitur.
You also have to deal with the reality of anyone going forgetting what they were sent for and never accomplishing the task. That is the single biggest issue potentially. Same with anything built over a generation. For all we know our ancestors destroyed a previous planet and lived on mars and use it to make earth as a better home and we have no clue now.
If you built a dyson sphere poeple may never know it wasn't natural and then not know the threat is coming anymore. Data doesn't go on endlessly like people presume. The reality is far more complex. If it wasn't done in a single generation it likely won't get done. Human knowledge doesn't just go on endlessly. There are ebs and flows. It's basically use it or loose it. Once it's built(assuming you can get it built without loosing knowledge to do it) you will forget in a few generations how becuase you exist on it and don't do the things to have to pontially. The knowledge will vanish to some extent. Maybe a lot. The likely hood is more than less also. Any mechanical advantages added during a generation literally make you do less reducing those things it doesn't make you have to do anymore be known less later because of the mechanical advantage and not doing those things anymore. Knowledge is just sensory data from our 5 or whatever senses being processed in our brains. Anything you don't do isn't known by the machine taking in inputs over their life and hence won't be carried on to the exact degree it isn't carried on.
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This depends on the timescales involved.
Not significantly, because you aren't directing any of them at Earth. The sun's surface temperature would increase slightly, which would slightly increase it's irradiance, but if that caused any issues, the Earth could be easily shaded.
The amount of mass consumed would be largely arbitrary and dependent on the acceleration desired. Only in the most extreme scenarios would any significant fraction of the sun's mass be consumed.
I'm not convinced that arks needed to protect and sustain billions of people for thousands of years would be a lesser endeavor, and even if it were, it's not the main problem...accelerating them is.
How do you propose to get all of these people and all of this stuff to a suitable system on a practical timescale without being able to harness a significant fraction of solar irradiance? I cannot think of any practicable propulsion mechanism that would be independent of a star that would suffice.
You need to accelerate in the opposite direction to stop at the destination and i don't see any good way to do this with only the resources you could bring with you. Proposals for photogravitational assist that have been floated in relation to missions like Breakthrough Starshot are highly dependent on the right configuration of the destination system and would likely be wholly insufficient for any manned mission, even for generation ships.
Not pulling the sun after you is precisely the problem. It's a giant ball of fuel and a stable fusion reactor. It also has Earth in tow, which will offer better protection and sustenance than almost any other conceivable vessel.
That number wasn't about the amount of time it takes. That number was an attempt to get you to realize the scale of what you're talking about. According to your own estimates, the energy needed to evacuate the current population of the Earth is in the order of 10^31 J. The current population of the Earth generates on the order of 10^12 J/s.
To again try to put these numbers in perspective, the amount of power you estimated was needed to evacuate the current population of the Earth is 10,000,000,000,000,000,000 times what we have available today. It would take 317 billion years, about 23 times the current age of the universe, to evacuate the Earth... assuming that we used no power at all to do things like survive ourselves.
The numbers are similarly bad for a K1 level civilization. They would have access to power on the order of 10^17 J/s, or about 100,000 times the amount of power we have today, so it would only take them about 3 million years to evacuate the current population of the Earth's population... which would be a bit like evacuating ten people out of a large city, and declaring everyone saved.
Your own estimates of the power needed to evacuate the current population of the Earth are at a level achievable only by K2 civilizations, or those well on their way to becoming one. Evacuating the current population of the Earth would be a bit like cutting off the tip of someone's pinky and evacuating it, and declaring everyone saved.
The sources I found was about 300,000, assuming that the interior surface area is used to replicate conditions on Earth, including how we grow our crops. The population could be denser, of course, but an O'Neill Cylinder is designed to take maximum advantage of that huge and efficient fusion power generator at the center of our system. Take that away, and you have to replace it with another form of power generation... and the fuel to operate it for hundreds, if not thousands, of years.
I actually assumed that the average inhabitant of our hypothetical K2 civilization uses ten times the power than we do today, which I consider a gross overestimation, because power consumption per capita in developed countries has remained stable for decades despite standards of living having increased, thanks to increasingly efficient appliances. It wouldn't surprise me at all to see power consumption start to drop in developed countries, as economies of scale continue to make green living more affordable. I just assumed such a civilization would devote considerable resources to other pursuits.
As for how such populations could be sustained within our own Solar System:
Let's face it, if we want to live in this solar system in the very long term, we're going to need to reduce the mass of the sun to do so.
This is why I feel like we were having two separate conversations. You're thinking in terms of a planetary civilization, one that isn't even a K1 yet if you're worried about "ozone depletion," and everyone else, including the OP, is talking about a K2 civilization, one that dwarfs a K1 by an order of magnitude greater than a K1 dwarfs the hunter gatherers hypothesized to have survived the Toba eruption.
Isn't one of the problems with GRBs that they basically are electromagnetic radiation moving at the speed of light, meaning that information about their existence travel through the Universe at the same speed?
That makes them hard to predict. However, from what I know, the chances of Earth being hit by a GRB is very limited, even though I read that if Betelgeuse goes supernova, it might be possible to measure an effect in the ozone layer. It probably won't blow up in the foreseeable future. I hope not. It's one of my favorite stars.
The conditions necessary for a GRB to be a threat to us are kind of hard to miss: namely the death of a massive star, the collision of two neutron stars, or the collision of a black hole and neutron star; that is within ten thousand light years of us; with the pole pointin right at us. IIRC, there’s only one candidate for a GRB to be a potential threat to us, that threat is low, and it’s not likely to be a danger to us for a million years in any case.
As for Betelgeuse, at 650 ly away, it’s too far away to be a threat to us.