Why do people assume the speed of light can be exceeded? This would really seem to be a nessecery component of establishing some kind of star empire.
Not on a medium-sized length of time by galactic standards. Instead, you merely need the somewhat implausible scenario of creatures with an intergenerational desire to populate the galaxy, the means to conserve their knowledge of how to do so, and millions of years to move around themselves or their machines.
The Fermi Paradox is only really a paradox if you believe some science fiction concepts are not just plausible but inevitable. It really doesn’t require FTL but it does require belief in concepts that are beyond current accepted physics.
Also note Fermi never suggested that aliens don’t exist. Fermi concluded that interstellar flight may be impossible, or not worth the effort, or civilization doesn’t last long enough for it to happen.
To expand on my previous post.
Here is a link it Michael Hart’s 1974 metaphysical (abstract theory with no basis in reality) argument. Which is really the basis for what is better called research into the “Fermi–Hart paradox”
http://adsabs.harvard.edu/full/1975QJRAS..16..128H
Being a metaphysical argument it is philosophy and not science which allows for non-scientific ideas like faster than light travel.
Most of the confusion is from that philosophy needing a way to get around the fact that a galaxy wide civilization couldn’t exist without prompt communication. The philosophical requirement is that within known limits posed by the speed of light that you couldn’t have an empire at a galactic scale without a way to communicate in a way that allowed you to maintain what people would call an empire.
Really it relates to the implications of General Relativity and the fact that the entire concept of “now” breaks down. There is no objective concept of “now” that even works between earth and our nearest neighbor of Alpha Centauri.
“What is happening right now at Alpha Centauri” is actually an absurd nonsensical statement. The concept of “now” just doesn’t even exist at that scale let alone across the galaxy. So most people thinking about this “paradox” invoke some form of FTL communication or travel to work around that inconvenient reality.
As the structures required under the thought experiment require this level of galactic organization some arguments resort to FTL while others try to adjust to a more organic outspread but still have to make other assumptions that are counter to our current understandings of physics.
*To be clear I don’t think it is wrong for people to consider this idea, I am just trying to communicate the reasons people writing about it have to resort to science fiction concepts. *
No, just some plausible fraction of the speed of light.
The universe is billions of years old. Even if there are reasons that life could not have evolved during the first several billion years, conditions have not significantly changed in at least the last billion years or so. So if intelligent life is common, we’d expect many civilizations to have started developing technology at least hundreds of millions of years ahead of us. The diameter of the milky way is about 100,000 light years, so that gives plenty of time for civilizations limited by c to spread throughout the entire galaxy.
So the Fermi “paradox” is simply the question - what is wrong with that account, what are we missing, why didn’t that happen?
You don’t need to imagine an empire to have an issue. Allow a civilization at star A 100,000 years to reach a new star (star B) and set up an advanced civilization there and allow the civilizations at stars A and B another 100,000 years to reach 2 new stars (and so on). Even at that pace, which does not take anywhere near FTL travel, and in less than 4 million years (a tiny fraction of the lifespan of a star), the whole galaxy is full.
The cost of developing the technology for a viable population of human to survive a trip that takes 100,000 years to a location which may not be viable for colonization and the social will to fund such a long shot becomes a problem. The energy requirements for such a mission also resort to people considering other sci-fi concepts like Dyson spheres. FTL travel gets a person past that practical issue of dedicating most of their energy production for multiple centuries for a long-shot mission. It also gets around the practical issues of barriers for long term travel like DNA’s issue with radiation exposure etc…
You have to work around Fermi’s concerns that interstellar travel and colonization may just not be practical and/or desirable for most civilizations.
I was thinking of 100,000 years as an upper limit on the time to set up a new civilization capable of colonizing on its own. I’m not suggesting that this is one really long project requiring a 100,000 year commitment.
This all makes my head hurt. A lot. But I can grasp the ton of filters between “Monkeys with opposable thumbs” and a Mega-large detectable object. And a lot of them arn’t even destructive. (Depending on your definition I guess). Simulation or holograph technology being so advanced, why bother with the real thing…etc…
Another angle i don’t see get enough lip service (Or maybe it does and I watch the wrong videos) There could be an entire Federation, Romulan and Klingon Empire out there and going by Trek tech we’ve seen…we don’t have the means to detect them.
Yes, there are a number of possible solutions. But nobody knows which one applies, and none of them seem particularly likely, so it’s still an interesting puzzle.
The speed of light is only a limit for creatures who have short lifespans and live life at some ridiculous pace tied to the rotation of their homeworld.
The Great Immortal Slow Star Lords don’t concern themselves with ephemera like “generations” and “radio signals” - you can have a personal convo with Blort 2 systems over next millennium, when your slow ship gets there. Said convo will take 500 years, but then you *did *just see them 65 million years ago, when you helped them clear that vermin infestation. Let’s hope it hasn’t recurred…
It does not take as long to populate the whole galaxy as you might think (even only going well below light speed) using generation ships. They’ve done the math and with some conservative numbers figured the galaxy can be populated in about 50 million years assuming a species intent on seeing it done. 50 million years is peanuts on an astronomical scale and, of course, you would have vast amounts of the galaxy populated long before you got the whole thing so it is not unreasonable to wonder where these aliens are.
You don’t move 100,000 light years, you move 10 light years, then the next generation moves another 10 light years, then the next generation moves another 10 light years, etc. Eventually, after several thousand generations, you have moved 100,000 light years.
While the nearest stars to Earth are not close, any decent percentage of C does get us to them, comfortably, within a human lifetime.
To get to 1/2 c at an acceleration of 1G with 1000 Kg of payload would require 250,000 KG of fuel and that isn’t with the fuel to stop.
If you assume you want to stop and 1000 Kg of payload and 250,000 Kg of fuel to do so, they would need 62,750,000 KG of fuel to accelerate. As you would need more than 1000 Kg of payload to create a colony it becomes larger and larger.
Even if you could invoke sci-fi like positron beams 1000 Kg would require ~6 Trillion Watts when the worlds total primary energy consumption is about 18 TW/year. So to accelerate a short ton to half the speed of light would take 1/3 of the worlds entire annual energy production.
Also what is the “human lifetime” when exposed to large amounts of radiation?
You don’t need to go that fast - a species could start to live in asteroids permanently, spreading out through the Oort cloud and slowly move from Oort cloud to Oort cloud, living more or less in steady state while in interstellar space and expanding population when a new Oort cloud allows the opportunity - and by moving at a ten-thousandth of c, the species still overwhelms the galaxy in a very short time (astronomically speaking).
The example in post #12 assumed around 0.25c speed.
Also, if it was me, I would send fuel ahead of me. Just great big unmanned tanks of fuel sent off at intervals along the line of travel albeit at a slower speed. Do that for 50 or 100 years then the colony ship will catch up and refuel en-route.
Also, for comparison, a US WWII battleship held around 9,250,000Kg of fuel so 250,000Kg doesn’t seem terrible.
Won’t help significantly. In order for the payload ship to rendezvous with the fuel ships, they have to be going the same velocity. A slower fuel ship may as well not be there at all. So you still have to accelerate the fuel as much either way.
The only way this could help is with some of the deceleration fuel. But only after the ship has partially decelerated from its maximum velocity.
Floating on the ocean is so much different than travelling through space that any comparisons are pretty useless.
Except I was choosing optimistic non-existent technologies, for our current best hydrogen/oxygen chemical rockets a (admittedly inefficient) single stage rocket would require the equivalent of the entire mass of the universe to hit 0.1 c for 1000 Kg.
Half the weight of an average car or 1000 Kg isn’t a lot of payload if you want to bring humans along.
With current chemical rocket technology within practical efficiencies most estimates are about 100,000 years to reach the nearest Earth-ish like planet. The Tsiolkovsky rocket equation being dependent on effective exhaust velocity, and 4,400 m/s for Liquid oxygen/hydrogen is the bummer.
Take the space shuttle as an example though, using my same numbers it would require around 4,706,250,000,000 kg of fuel but still isn’t large enough for interstellar travel.
The special relativistic rocket equation is:
Δv = c * tanh( v[sub]e[/sub]/c * ln(m[sub]0[/sub]/m[sub]1[/sub]))
Where:
v[sub]e[/sub]: velocity of the rocket exhaust from the rockets frame
m[sub]0[/sub]: initial mass of payload and fuel
m[sub]1[/sub]: final mass
So:
Delta v in km/s for various fuel loads + 1000 Kg payload (~2000 lbs) 4,000 m/s exaust:
14.33 : 25,000 kg
24.31 : 250,000 kg
34.42 : 2,500,000 kg
44.55 : 25,000,000 kg
54.68 : 250,000,000 kg
…
95.21 : 2,500,000,000,000 kg
…
500.46 : 2.5e52 (More mass than total mass of the visible matter ~6e51 kg)
784.14 : 2.5e80 Kg
1,594.64 : 2.5e160 kg
1,604.77 : 2.5e161 kg
3,012.94 : 2.5e300 kg
3,083.86 : 2.5e307 kg ~ 1% of the speed of light (highest I can calculate without overflow)
Note your problem there, using liquid oxygen/hydrogen you only gain about 10 km/s per order of magnitude more fuel. As 10% of c is 29,979.24 km/s you have a problem.
It takes 2500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 kg of liquid oxygen/hydrogen to get 1% of the speed of light.
We have an analogy right here on Earth. Man spread from Africa to all over the world and did not have to set up any Empires to do so. I’m not sure how long the expansion took, but it certainly took many thousands of years. Polynesia was settled relatively recently. The movement of a tribe to a new location probably didn’t take that much less time than movement to a new star at relativistic velocities. And probably a larger percentage of the average lifetime than it would be for an advanced civilization which would surely develop ways of prolonging life.
Our ancestors moved because of climate pressure, lack of food, or population pressure. Maybe our alien friends are satisfied where they are and don’t feel like expanding.