I recall reading one way is that the outer ring of the solar sail detaches and continues on. It reflects the LASER light back at the inner portion of the solar sail on the ship which has turned around so it’s backing into its target now.
It’s been a while since historian Sid Meier addressed this important question. Memory is hazy. But I faintly recall that “industrialization” had many precursors - you have discovered the secret(s) of: agriculture, archery, architecture, astronomy, banking, bronze working, cavalry, chemistry, chivalry, compass, construction, currency, education, electricity, engineering, feudalism, gunpowder, horseback riding, iron working, masonry, mathematics, metallurgy, mining, navigation, optics, philosophy, physics, printing press, steel, universities…. There was also a boost to emphasizing research and building “Copernicus’ Observatory” and “Darwin’s Voyage”.
(In short, it didn’t happen because the Greeks were invaded by Montezuma, Mao Tse-tung and Shaka. As is my limited understanding.)
Late to this thread, but I wanted to throw in a plug for Steven Johnson’s book (and PBS documentary series) “How We Got to Now.” It’s his premise that a handful of innovations caused great leaps forward… including glass lenses, refrigeration, artificial light, etc.
The nice part about an artificial ship as opposed to a natural planet is that you live INSIDE it, rather than on the surface. Blocking cosmic rays is a question of engineering, not new science.
Except that it isn’t. You’re doing a bunch of things we already do. Sure, the numbers are a couple orders of magnitude bigger than anything we have now. The engineering problem is a monumentally DIFFICULT one. But it doesn’t require metamaterials, or nanotechnology, or fusion power, or anything else that we don’t yet know can be done.
Yes, it’s the synergy effect. Each piece fed the next. Two precursors make four more possible, which make 8 more things possible, then 16. Not unlike that sort of geometric progression… We just happen to live in a world where that’s reached a huge number.
An interstellar trip will last thousands of years. How is it going to be powered without fusion? I doubt they could take along enough fusion fuel to last that long.
The US used 176,791,667 MW-D of power in 2022.
A breeder reactor can get 900 MW-D of energy out of 1 KG of uranium (it reuses the output of the reactor in another rector, and so on, to get the most energy out possible).
So it would take about 200,000 kg to power the energy requirements of the US for a year. If our interstellar spaceship uses as much energy every day as the whole US, then a 1,000 year journey would need 200,000 tons of Uranium.
The ability to share information and, therefore, the printing press, cannot be underestimated, and this is an example of that. Had this information been shared with the world, someone would have made that connection even though he did not.
It WAS shared with the world, hence why you know about it.
The problem isn’t the lack of a connection. It’s that at the time there was no economic incentive to create labor saving devices, because most societies relied on a social structure where warriors were praised and placed in charge, and whose incentives were based around fighting and conquering and enslaving others for labor.
In such a system, creating a labor saving device weakens the ruling class, and so there is no incentive for it to be done.
Yeah, but now do the energy requirements for taking a large mass to anywhere near the speed of light.
It takes about 10^20 J of energy to accelerate 1,000 kg to .9 C. I believe that’s about 100 years of current U.S. energy production. Aside from issues of propulsion efficiency and such, that’s just the sheer kinetic energy an object would have at that speed.
If you wanted to send a ship with people, food, shielding, etc, You’re probably into the millions of kg for the ship. You’d need 100,000 years of annual energy production per million kg to impart that much energy to the ship. For reference, a fully loaded SpaceX Starship is about 5 million kilos.
So let’s be realistic and say we want to send a ship the size of Starship to Alpha Centauri, and the trip can take no more than 1,000 years. We would need to accelerate our ship up to about 1300 km/s. Relativistic effects don’t matter at these speeds. It would take about 3.4 X 10^18 J to accelerate the ship to that speed. So about an entire year’s worth of U.S energy production to get a Starship up to a speed that would get it to our nearest neighbor in 1,000 years,
If you want to take 10,000 years, we can cut that down to about 3 x 10^16 J.
Now, this doesn’t include the energy required to brake at the other end, so double the energy requirements. And it doesn’t include the propulsive inefficienes. Also, the hard math of the rocket equation means that even with efficient fusion power, the fraction of mass that is payload would be under 10%. With fission, maybe .1%-1%. And with conventional fuels it’s impossible.
Travelling between stars is just incredibly difficult, Science fiction makes it sound easy, but that’s fiction.
So it’s still the case that one answer to the Fermi Paradox is that sending functioning ships between stars is so incredibly difficult that it’s extremely rare. And self-replicating probes that have to refuel at each star system may be so difficult that none of the possible civilizations in our galaxy have managed to build such things.
Why? We’re talking about a thousand year long sub-light journey. And potentially the acceleration is coming from lasers back home anyhow.
Read the rest of my post. I started at speed of light to show how ridiculous it was, then went on to show different lower speeds, including speeds that would take a ship 1,000 years to get to Alpha Centauri.
And those numbers were absolute best cases. How much drag is there in interstellar space? There are about 10^6 particles in a cubic meter of interstellar space. It’s not completely empty. Those molecules will add drag to the spaceship. I believe that was the problem with the Bussard Ramjet - if they made the scoop big enough to draw in enough fuel, it was overcome by drag. But in any ship energy will be lost to drag and have to be replaced.
Those particles will also cause heating, as will reflected energy from the exhaust. That’s a non-trivial problem. Another is that even at 1% the speed of light, hitting a particle massing 1g would impart about 4500 MJ of energy to your spaceship. That’s roughly a ton of TNT equivalent.
We actually don’t know all that much about tye interstellar medium, other than in large averages. We can measure stellar extinction and figure out the average density of the gas between us and the star. But for discrete objects like rogue planets, black holes, junk blasted off of planets or from supernovae, material disturbed and flung into interstellar space in clumps, we have very little information. We are using microlensing to find rogue planets, but for objects on the order of a gram to a million kg, all we can do is extrapolate from what we see around us, and that’s not very good.
It may be that any journey to another star carries with it an extremely high chance of hitting particles from 1g to 1kg or more. Hitting a 1 kg object at .1C would be like having a nuke go off on the nose of your spaceship. It would be extremely hard to protect against particles even 1/100 that size. And over thiusands of years there would be heavy erosion of the spacecraft just from the gas and dust in the interstellar medium evennif you didn’t hit any big pieces.
It gets much worse if you are in a molecular cloud. The galaxy is filled with molecular clouds. It might be that you can’t travel through them in any reasonable amount of time, which could further limit any civilizations that developed on a planet in or near them.
The Bussard ramjet is a good example of what I would call ‘recency bias thinking’. Robert Bussard came up with the concept of the Bussard Ramjet in 1960, and immediately we started talking about them as if they were an obvious tech that aliens would have.
For the first couple of decades of my adult life, if someone would ask about travelling to the stars, the answer was, “Use a Bussard Ramjet!” We talked about means for finding them, people worked seriously on plans for building them, etc. It was a staple in hard Science Fiction. This went on for probably a few decades.
Then we found out a little more about the interstellar medium and discovered that the ramjet concept could not work. Oh well.
We have just barely entered the interstellar medium with the Voyager probes, and they’ve already made discoveries we didn’t know about before. For example:
We are babes in the woods with this stuff. The honest answer to questions about travelling to other stars should always include the caveat that we know almost nothing about it. Maybe dark matter, primordial black holes, or cosmic debris or something else we have yet to discover makes it impossible or nearly so to travel above a very slow speed between stars.
Maybe there is a form of ‘cosmic speed limit’ having to do with the ability to avoid objects that limits travel to the kinds of speeds we’ve seen with interstellar objects that have passed us by, like Oumouamoua. Or something else about interstellar travel we have not yet discovered that explains why the aliens aren’t here.
Our solar system is protected from a lot of interstellar stuff by the light pressure from the sun. Solar radiation dominates. But once you get past the ‘bow shock’ where the interstellar medium domionates, things may be very different, and in ways we have yet to understand. Like the ‘plasma hum’ we recently discovered.
To make the twenty-four trillion nine hundred eighty-four billion ninety-two million eight hundred ninety-seven thousand four hundred seventy-nine mile journey, Breakthrough Starshot is doing the most serious research to date WRT lasers and sails.
The Australian National University (ANU) reports the team is developing a tiny probe, about the size of a smartphone [with a lightsail] that will be powered by a powerful laser array from Earth. That laser array will concentrate millions of beams on the sail throughout its interstellar journey, allowing it to reach Alpha Centauri in about 20 years. Dr. Ward, from the ANU Research School of Physics, says. “To achieve this, we estimate the number of lasers required to be approximately 100 million.”
For a cellphone. Now imagine powering a ship big enough to live on for the rest of your life, because this would surely be a one way journey.
They admit they haven’t worked out the sail design. Or being able to keep the lasers trained on the sail. And there will need to be some inflight corrections - you can’t reliably aim at a spot in the sky and hit something that will be there in 20 years.
The point of all of this is that it’s easy to say, “oh, we’ll just point a laser at our spaceship and push it to Alpha Centauri.” Doing it in practice is not just building bigger versions of the technology we already have.
Also, as I understand, lasers are not that efficient. (on the order of a few percent). To power X watts of laser power will likely require 15X input (i.e. for CO2). LED’s are more efficient but not collimated enough for long distances? Then presumably these will be in orbit or on the moon, so what do you do to dump the other 85% of the power that’s waste? Where do you get the fuel (fusion) to run 100M lasers? And power plants? etc. etc.
As for generation ships, you have to think big. How many people to colonize Alpha Centauri? How much prebuilt equipment and raw materials? Even for a simple hypothetical 430 year journey, how much spare air and water, and heavily protected life forms in case of a disaster on the way? What about slow leaks? Even the smallest leak over 430 years could be disastrous, and there’s no resupply depot.
And so on, and so on…
And just imagine - if that ship were arriving at Alpha Centauri today, we’d have been relying all this time for the fuel and technicians’ wages to keep those lasers running for 1000 years - on either the Holy Roman Empire or the Vatican. Or the Byzantine Empire.
What are you talking about? You use the lasers to get up to speed, not the whole time.
I think you guys are arguing against a point that I am not making.
I’m not saying we’ll do it any time in the forseeable future, or even that it’s more likely that we’ll do something like that than go extinct.
However, if at some point we end up living in space habitats all around the solar system, and we have been doing so for thousands of years without going extinct, then giving a large habitat the boost it would need to slowly coast over to another star would not be an unimaginably difficult task.
…did you actually read the article that you linked? I’m confused as to what possible relevance it has to this discussion. The article mentions that the interstellar medium, which is basically a very (very very veryx10^…) diffuse plasma of particles in the void between stars, is so diffuse that we thought that it’s basically impossible to even measure, aside from at times when the solar radiation flares up. When this happens the solar wind pushes out past where Voyager currently is, disturbing the interstellar medium with a shockwave. We can measure the density of the interstellar medium during this shockwave, based on the interaction between the diffuse plasma particles and the solar wind.
The unexpected discovery that the article talks about - this “hum” - is simply the fact that Voyager’s instruments are able to detect a faint measurement from the interstellar medium even between pulses of solar wind, allowing them to measure the density of the medium at all times.
Again, I’m extremely confused as to what relevance you think this would have?
TL;DR. the best explanation anyone seems to have is that typically development seems to follow a slow curve where very little change is apparent for a long, long time. Then an inflection point is reached followed by exponential change, at least until a leveling-off point rounds off the curve.
It’s been pointed out that that pattern goes all the way back to the beginning of life on Earth. Billions of years before cyanobacteria and archaea got ambitious enough to form eukaryota. Maybe another billion or two years before multicellular animals and plants took off in a big way. A couple of hundred million years before multicellular life adapted to land. One or two hundred million years more before organisms whose behavior wasn’t 100% pre-programmed. The first rudiments of human intelligence one-to-three million years ago. The first artifactually sophisticated cultures forty thousand years ago; dabbling in agriculture maybe eight thousand years ago; writing six thousand years ago. The scientific method five hundred years ago, the industrial revolution two hundred years ago; the first Turing-Complete computers seventy-five years ago.
The increase in complexity almost follows a straight line when graphed on a logarithmic scale. Which leads to speculation about what sort of singularity might be coming up in just the next century.