Close enough that we could probably develop a probe to get there in the next few centuries and check it out. What are the current popular candidates for propulsion systems capable of accelerating to near the speed of light?
Just going to recycle this comment I made in reply to an almost identical comment as yours. I don't think you folks realize how big space actually is.
The speed of light is 1079 252 848 km/h, the fastest space craft ever made was the Parker Solar probe (using a sling shot) clocking in at 692 000 km/h. So at that speed it would take, 1559 years to travel one light year.
This planet sits at a distance of 48 light years, so it would 74 832 years to get there. Just for good measure, when it gets there it would also take 48 years for us to know that since radio travels at the speed of light.
Note, that the speed of the spacecraft I mentioned was the peak speed. Space is big, really big.
Science fiction has entertained and inspired millions of people and we should all be grateful for that but it has also distorted what people think space really is.
When you consider the scale of space it becomes pretty understandable why the Milky Way isn't teeming with civilizations sending large amounts of mass all over the galaxy. A realization one comes to despite the facts that it has taken humans a blink of an eye (on a galactic timescale) to go from tools to rockets and the Milky way is billions of years older than the entire history of the Earth.
On a scale of probable -> less probable, you have:
Self-organizing chemicals -> replication -> evolution -> multi-cellular life -> creatures that move around -> intelligent life -> use of tools -> basic technology like wheels, steam engine -> industrialization -> advanced tech -> automation -> space faring -> capable of interstellar travel -> capable of intergalactic travel. Powered by energy sources of increasing complexity/sophistication & scale.
This whole evolution requires a stable environment. Dinosaur-killing asteroid & it's back to square 1. Also (for example) how would intelligent life on a waterworld (which basically excludes electronics as we know it) become space-faring?
So it's not unlogical to expect that microbial life could be 'everywhere', tool-using intelligent creatures are rare, and interstellar-capable civilizations are so few & far between that (on average) they're just too distant in space or time.
Doesn't matter who visits who if neither party can cross the ocean in between.
I blame Star Wars, kinda. Watching it with my kid, I can't help but notice that everywhere they travel in space -- even by accident -- they end up by a planet that can support human life in terms of temperature, atmosphere, and gravity. Mandalore (the Mandalorian home planet, natch) has a moon that doesn't only support life; it also has the exact same gravity as Mandalore!
Sentient life in hospitable environments is as unavoidable in the Star Wars universe as it is absent in ours.
Project Hail Mary does a pretty good job, although probably doesn't come across in the film. SF that doesn't even bother using wormholes or some other FTL travel (e.g. warp speed) is quite annoying, though.
I mean, even there they pretty use the Astrophage as a plot device to fill in the huge gap in technology needed to cover those distances. They make it clear that they would have no chance to cover those distances without the Astrophage, but it is very convenient.
If I understand correctly, time spent within this interstellar ship reference frame would be significantly less than 75k years. And at 1c speed, 48 years on Earth would be ~2 years of "flight" for the passengers, correct me if I'm wrong.
You are not wrong, but it still wouldn't make a whole lot of difference. First of all with any technology we currently have, including hypothetical proposals, we can't even get close to 1c. The best we can do, and this assumes purely hypothetical unproven ideas, is accelerate to a fraction of the speed of light. Acceleration itself will take up a significant amount of time and even then we are nowhere near the speed of light. Project Orion would in theory be able to do 3% to 10% of the speed of light. That's about the only proposed propulsion we actually have the technology for in the sense that we might be able to build it this decade.
So let's be optimistic and assume we can reach 10% of c (unlikely), that is 10 years for one light year, meaning that it takes about five centuries. Practically speaking 10% of c is unlikely, it takes about a month to accelerate to those speeds you'd need an insane amount of mass in the form of bombs to explode to just get up to speed. Which is why 3% is more "realistic". Oh, did I mention that there is no realistic way to slow down either? In theory it is just detonating the same amount of bombs in front of the craft, but in order to take that mass on your journey you'd need a lot more mass to get up to speed and the numbers get silly rather quickly.
So "realistically" at 3% of c we are talking about roughly 1500 years to just speed past our target.
Also, the original remark was about sending probes, not humans. But at 3% or 10% of c time dilation isn't much of a factor either so you'd need a generational craft if you want to send people.
Man, that’s not how intelligence works. Eventually if a civilization doesn’t blow itself up, it will achieve anything, and it’s not incremental steps. Speed has never been incremental steps. in 1810 you would’ve been thinking about faster horses or some shit like that. Def not rockets. OP said hundreds of years. In hundreds of years from now our rulers will definitely have that kind of tech, whatever tech it is.
Often technology is approaching an asymptotic limit that it will not go beyond. Know about a hand waving will change the laws of physics. There's every reason to believe that the speed of light is a maximum that we will never be able to choose because it requires infinite energy. While it is true we don't know everything, and there are certainly parts of it we don't know, the things we do know will have to obey and predict the things that we currently do know to be true. The laws of relativity, although annoying, are very good at describing things. If anything replaces relativity, it's going to replace it while still predicting exactly the same things that relatively does that we have verified. That doesn't leave much room for a theory that might and faster travel.
If we’re talking about human technology available in a few hundred years, don’t discount far more exotic options. I’ve heard people talk of theoretical terrestrial lasers pushing on tiny probes. With an absolutely gigantic laser and magical material at the back of the probe that won’t instantly vaporize there’s enough energy to get something the size of a smartphone up to a reasonable proportion of the speed of light.
I can’t prescribe this theoretical technology to the problem. But I also think it’s unreasonable to set the limit using known technology and then discount the idea altogether. We have no idea what will be possible in 300 years.
Note that you can't use these lasers to slow down the probe, which will dramatically limit the things the probe can do at the destination. I'm not even sure what kind of interesting things a probe the size of a smartphone could do, let alone phone home.
> you can't use these lasers to slow down the probe
You can, but you need a couple of solar sails. You beam the laser at the sails to accelerate, then at the halfway point one of the sails detaches and becomes a reflector, which lights up the now flipped probe and remaining sail to decelerate them.
send an unending chain of them and you solve the transmission problem _and_ they don't have to slow down as you'll always have another on the way past whatever you're targeting
How many times the Earth's materials would we consume doing that? And wouldn't it block ma lazor from reaching the previous probes and accelerating them?
Exactly. Imagine what would be possible after a billion year of technological evolution, heck even just 100'000 years. We already know that space time metric engineering is theoretically possible within our current understanding of physics, we don't have either the technology or access to energy density necessary to do it. And that's only within our limited understanding of how the universe works.
If you have a billion year long civilization, it would probably be easier to genetically/medically engineer humans to live forever, so that a 75,000 year space voyage doesn’t seem so long. Easier than near-lightspeed space travel at any rate.
The general idea is to deliberately shape the geometry of spacetime to allow for effects such as faster-than-light travel (relative to another region of spacetime).
Einstein's field equations link geometry to matter and energy:
G_μν = 8πG/c⁴ · T_μν
Left side describes how spacetime curves (the metric tensor). Right side represents what's causing the curvature (the stress-energy tensor): mass, energy, momentum. The usual approach is: you specify T_μν (what matter is where) and solve for the resulting curvature. Metric engineering takes the backward approach. You pick the geometry you want first: e.g a bubble that carries its contents faster than light relative to the outside universe. Then you work out what T_μν would have to be to produce that geometry: what distribution of energy and stress the equations demand.
The classic example of spacetime metric engineering is the Alcubierre drive.
The limitation with this is that the required T_μν has negative energy density in some regions (the bubble walls) which violate some assumptions about how "reasonable" matter behaves. But Quantum Field theory allows such local regions of negative densities and we have created such regions in labs experimentally already (Casimir effect). We "just" don't know how to sustain the effect at bigger (atomic) distances.
At the distances involved even the beam from a gigantic laser will be spread out enough not to vaporise anything — you won't need a magic material, just a very large, thin, and highly reflective solar sail.
The comment you replied to doesn't appear to be misunderstanding the size of the galaxy, they mention acceleration to near the speed of light so they're probably thinking 100 years to get there and another 48 to receive signals back. The missing part is the propulsion system capable of doing that.
> the fastest space craft ever made was the Parker Solar probe (using a sling shot) clocking in at 692 000 km/h…
After 44 days of acceleration. On a multi-millennia mission we’re talking a velocity likely 300x what the Parker Solar Probe achieved (while falling into the Sun).
> I want to know what future technologies could accelerate an object to a significant fraction of the speed of light.
With all due respect, this has been extensively debated online and is extremely easy to look up.
> Could those breakthroughs be achieved in the next 2 or 3 centuries?
Any predictions on future scientific breakthroughs are wishful thinking. Even directions that seem promising at some point can end up being dead ends and we simply don't know what we will or will not achieve.
With current technologies, even hypothetical ones we can't get there in a time period that is under a few centuries at best and over a millennium at worse. Even for the centuries figure we'd require technologies we haven't been able to crack yet.
Probably more likely that we work out how to fold spacetime than we get there in anything like a high enough percentage of the speed of light - the fastest object we ever made travelled at something like ~0.064% * C so we are looking at ~750 years with current technology and presumably we'd need to switch on the probe in 3/4 of a millennium and figure out how to slow it down and get it into some sort of orbit around the planet.
750 years is hard for me to get excited about even as a vampire.
It’s highly unlikely we’re ever getting FTL. We should become comfortable with that and let go our fantasies. Let theoretical physicists chug away at this, we should get underway with projects that are possible with known science.
Depends on who you mean as "we". The speed of light isn't a speed limit. If you can create a ship that is capable of 1g acceleration, it doesn't just stop accelerating as it reaches the speed of light relative to some stationary object, like Earth. Instead you start getting relativistic effects and things start getting very weird with time and distance doing some funky stuff. You keep zooming along just fine from your perspective, but an at-rest observer on Earth would see your ship asymptotically approach the speed of light, but never exceed it. The universe is very weird. In any case you could viably travel billions of light years in a single human lifetime, but for an observer at rest billions of their years would genuinely pass. In other words, traveling into the future is very much a real thing, so far as our current understanding of the universe goes.
The search term on this is 'relativistic starship.' Here's [1] a calculator to see what the math works out to for a ship capable of accelerating at 1g indefinitely. So for instance you could travel to Andromeda, some 2 million light years away, in about 28 years. But 2 million years would really pass for those at relative rest, such as those on Earth. So if you came back, the humanity you found (if any) would be unimaginably different.
And this isn't some just some weird fringe theoretical/mathematical thing. For instance GPS satellites have to compensate for time dilation because relativistic effects would otherwise have a substantial effect. Another example is at things like the large hadron collider. As a convenient effect of relativistic effects, emergent unstable particles exist far longer than they 'normally' would before decaying due to the fact they're moving at relativistic rates.
Relativistic starships are impossible because they require impossible amounts of fuel. "If you can create a ship that is capable of 1g acceleration" is doing a lot of heavy lifting. The rocket equation means you need to take along exponentially increasing amounts of fuel
Even antimatter rockets top out at 50% of light speed. Laser boost like with Dyson Swarm could get similar speeds because time dilation slows down the acceleration.
This isn’t gonna work, space isn’t truly empty. Even with antimatter propulsion the interstellar medium will start to vaporize your ship at speed above 0.2c.
Even if FTL is achievable (which I agree, highly unlikely), it's still extraordinarily slow on cosmic scales. The closest star is a little over 4 ly away!
And probing the universe outside the Milky Way? Forget about it.
1. if FTL is achievable, then presumably it isn't limited to 1.00000000001 x C
2. I like to think about the size of the universe by always remembering that with the naked eye, on a good night, there's only a single object in the entire night sky that isn't in our galaxy (M3, the Andromeda Galaxy).
I think you mean M31 instead of M3, and assuming northern hemisphere viewing only. I think the Magellanic Clouds are visible in the southern hemisphere.
The entire universe seems to be inside a giant black hole, anyway, and the more it goes, the more evidence is found to support that. Might as well find a black hole and visit other universes than explore our own.
It would help if our science wasn’t distracted by things like global warming and nazi governments though. There are definitely ways we can help the process * right now *
Was it my comment you really wanted to reply to? My point is that there are things we can do right now/today in order to heal our society from the sort of malignancies that distract us from advancing as a race.
Scientists and engineers with an interest in such things would have an easier time working on it, if the broader economic and civic context they work in wasn't being messed with by demagogues.
They shouldn't be drafted to resolve the rise of petty tyrants. It's a waste of their time.
With variations on nuclear propulsion we could plausibly get to up to around 12% the speed of light. At least that's the number quoted for Project Daedalus [1], which is using nuclear fusion for the first stage and nuclear-powered ion engines for the second stage. With the cruder but more realistically achievable right now Project Orion design (riding the shockwaves of nuclear bombs) you could still get to ~3% the speed of light
But even at 0.12c, we are looking at 400 years to get there. And we'd be zooming by at 12% the speed of light. If we want to slow down a bit that'd add hundreds of billions to the cost.
It might be worth waiting another century to see if we can come up with a faster design in that time. Not like closer targets like Alpha Centauri, where the thing stopping us is mostly just the absurd cost
> But even at 0.12c, we are looking at 400 years to get there. And we'd be zooming by at 12% the speed of light. If we want to slow down a bit that'd add hundreds of billions to the cost.
That’s the really hard part. If it’s almost science fiction to accelerate to 0.12c, it’s certainly much more difficult to slow down. At that speed we’d travel and pass this small system in mere minutes.
You just turn around halfway and use your main drive to decelerate. Yes, that does double the travel time, but it's the only way to do it. The hard part is then finding ways to get to a faster speed at turnaround time.
In most realistic settings it's even easier. For example a Project Daedalus probe only accelerates for four years before running out of fuel. So you could decelerate in just four years. Maybe a bit more, since you only have the smaller second stage engines. But essentially you are accelerating for four years, coasting for 392 years and decelerating for another four years. Accelerating for the whole time and turning around in the middle would be faster, but we don't have the fuel for that
The issue is that in the original architecture without breaking you burn 50k tonnes of fuel to get 1k tonnes of payload up to 12% lightspeed. If you want to break all the way back to zero, you need to 50k tonnes of fuel to break. But that means you need to accelerate another 50k tonnes of fuel up to speed.
Which means you need 50 times for fuel to get from 0.11c to 0.12c, and you need to accelerate that fuel to 0.11c, so you need more than 50 times the fuel for the step from 0.10c to 0.11c, and an even larger factor more to accelerate from 0.09c to 0.10c, etc. So you don't just require another 50*50k = 2M tonnes of fuel, but an exponentially larger amount. The tyranny of the rocket equation
I think the only way political will can fund nasa to realize these 1960 design ideas is an infinite capacity arch rival that threatens/render irrelavent either the dollar's supremacy or american power (and just those two, because apparently these days there is no "threat"/need to defend a higher cause, like the neo-liberal rules based system or democratic or human right values). Also that arch-rival that is probably/likely not china(practically speaking)
Those 190km/s of the Parker solar probe were, crucially, periapsis speed.
This is a bit like bouncing a rubber ball from a building, measuring its speed at ground level and then going: "Given our fastest achieved speed, we expect to hit the cloud level in <10s".
~200km/s sustained speed is already insanely optimistic for anything we could realistically build in the next half century, so your position is even more ironclad than it looks at first glance.
Yep. We haven't really figured out how to do a good government that lasts more than 200 years. Maybe unless you think monarchy is good, in which case I still don't want to share a spaceship with you.
The Tynwald evolved from a jury into a legislature, didn't admit its first elected member until 1866, its first few hundred years of existence are assumed rather than documented, and actual power resided with a mixture of kings (most of whom were also kings of other places or answered to kings in other places) for most of its existence. So not an ideal example :)
How much of that time did it spend fully sovereign over its territory? I'd love to learn otherwise, but my impression is that it has mostly been under the shadow of England, and the pressures of a government under those circumstances are not comparable to those for, frankly, one that's more responsible for its destiny as a starship crew would be. I bet you can find lots of long-running tiny local governments with very little power, both dominated and protected by a string of larger, more powerful, but more volatile governments.
I have no doubt that even the most republican of cultures launched from Earth would end up thoroughly monarchistic by the time the generation ships arrived at their destination. At best monarchistic - who knows what savage new forms of society could evolve in that sort of context?
There is a lot of precedent for this. Even on Earth, in 2026, international maritime law states that there is no such thing as a vessel with "democracy" and that a captain always has supreme command. Ships, airplanes, etc are all in a category that operate as strict autocracies.
More optimistically, you might see some kind of "choosing a chief by consensus" type of situations that you see in some small hunter-gatherer societies (being careful with the word "savage", which is... usually misleading). It'll depend a lot on the size of the crew.
> Perhaps, but it is horrifically long in terms of human stuff.
Not really, unless you're obsessed with the idea that great works need to happen within your lifetime. Europe is chock full of cathedrals that took 400-600 years to build, worked on by countless generations who would never live to see them completed.
The difference there being that at the end of your day, having spent it masoning, you could leave the cathedral and go back to your family and have a walk in the fields and drink and be merry with people loved and new. The project wasn't the entiriety of your existence, it was merely the means to pay for it.
Unless we have generational ships the size of small countries, I'm not sure the human brain - unaided and non-forcedly evolved to do so - would be able to handle essential incarceration in a series of metal tubes for its own and its descendents existences.
Generational ships would of course need to be very large, but I doubt it would need to be as large as you think. And it doesn't need to look like metal tubes. Many northern cities have extensive underground or between-building pedestrian bridges and large shopping malls, etc that can provide quite a lot of variety and the feeling of open and green spaces that is pretty attractive during long cold winters. Whether that's 'enough' to avoid mental health issues in a permanent setting is of course a different story, but that's just one of thousands of problems that would need to be solved before that ever comes close to reality :)
Yeah, this is the problem though - ironically highlighted by my still-maintained love and hope for Starship: Beyond Earth orbit, the energy requirement to move even small tens of tons of useful life-sustaining mass is incredibly expensive.
Like, to get a useful amount of people to Mars would be... the wealth of a first world nation for tens of years. Even using nuclear engines.
A generational megaship travelling at some small percentage of c to a nearby useful star (not even the nearest ones, which are all a bit shit)?
There's just nothing within our current projected reality that could even begin to accomodate that possibility.
Never mind the fact you'd need redunancy, and at least a few hundred years of testing to ensure that whatever mega project you could ultimately send wouldn't simply get vaporised halfway through, from realities unknown.
Maybe I'm over-thinking things. It seems like a lot of people's existences essentially revolve around a pocket-sized glowing rectangle.
Future AI and a database of all of humanity's experience before launch might be enough to keep the generational populace amused and distracted for the entiriety of their meagre, trapped existence... .
Back yard meaning we can see it but never touch it. If the ship to get there was ready today, it would get there in the year one-million? Back yard is Mars, Venus, moon. And I'm being generous with Mars and Venus.
Yeah, if your username is any indication of your age, you've possibly taken much the same trajectory of pessimism that I have. As a youth, I assumed we'd be hitting multiple Cs or bending space time when I was an adult; As an adult I thought we might get a percentage of C and conquer the solar system; Now I realise Just How Much Effort it would be to accomplish much of any value on our own Moon, never mind Mars.
I still hold on to the idea that very long term we might make strides in our own solar system, but it is a depressingly-longer timescale than I always used to believe.
Unless we have some magic-level shift in our understanding of physics, we're never getting anything beyond Von Neumann probes to other stars, and even then we're talking thousands of years.
laser propelled solar sails are the only plausible solution at the moment and it is not a given that even that is possible. Lots of engineering challenges there that may not have solutions.
other ideas:
1. be way more patient
2. anti matter based propulsion (more out there than solar sails)
3. nuclear bomb based propulsion
One issue is as you get to these speed little bits of dust will anhillate the probe, so you need some kind of shielding, raising the mass budget, making it all the harder. A solar sail has to be able to survive holes getting poked it in it and still working, etc.
Interstellar travel is probably not ever going to happen. Even if we have antimatter propulsion (which is still probably not practical even under ideal circumstances), we’re still talking hundreds of years of travel time to get to somewhere like this star.
This also goes for aliens visiting Earth. Interstellar travel is just so impractical that I don’t think anyone has come on safari to Earth.
A generation ship is probably doable with some level of conceivable technology. We just have to figure out how to be self sufficient out there then we have all the time in the world, or universe. That's a big "just", I know.
One of the Voyager probes measured the density of the interstellar vacuum at 80,000 protons (and the same number of electrons) per cubic meter. A proton going through a piece of aluminum foil delivers a roughly constant amount of energy regardless of speed; a relativistic proton will pinch through and carry most of its energy with it.
(No punchline; I just think that's cool. I understand that the real problem is the rare dust grain, not the ubiquitous gas.)
The political challenge of funding a laser program just for research for centuries seems just as daunting - lacking the capability for some self repairing, self healing devices, the automated or (lobster-ai) probe going to stars is just as far away as when Charles Stross first wrote about it in Accelerando some twenty years ago. Given the collapse of political norms, looking back, the decades long research projects of the US space program appear to be soon relics of the past.
I wouldn't bet on and as I understand theory allows a shorter routes. Major caveat is weve never observed them and their existence doesn't guarantee they're traversible.
What's exciting to me is that the existence of such a planet provides fuel for more research into the field.
If we design a probe that travels at speed of light it would reach there in 48 years and it would send back what it's seen after another 48 years. It would take multiple generations of scientists to work on this project. The longest we have worked on, are Voyager projects. Can we expect that level of commitments from our governments or corporations? Voyager became successful because people could see distant futures. We can barely plan few years ahead.
If you could solve propulsion enough to accelerate and decelerate a spaceship at just 1G, you could forget the probe and just send people there. While it would take ~50 years of earth time, it would only take ~7.5 years for the astronauts. They could reach the planet with most of their lives free to go to work studying or even colonizing it.
This is indeed an interesting perspective, but "constant 1g rocket acceleration" is not even an engineering pipedream, it's strictly fantasy territory.
I had this realization in high school. At the time I did not appreciate how impossible it is to accelerate at 1G for that long. Absent some entirely new physics becoming available. All signs point to it not being possible, so not even likely new physics could exist.
This is where English’s defective subjunctive makes life harder: The point wasn’t about the practicality of the probe from a scientific position, but rather pointing out that even in a best-case scientific scenario, the political-economic-cultural forces are against us.
> Can we expect that level of commitments from our governments or corporations?
Clearly, right now we cannot. This is one of the worst obstacles to progress in these areas that I see, and I don't see any obvious way to fix it.
The situation we're currently in would've been utterly unfathomable to me 30 years ago. I have lost a great deal of the hope and optimism I held in the past. Interstellar exploration is but one of many fields where we are suffering due to short term thinking.
Small fusion reactors don't really solve any of the key challenges. You need reaction mass to accelerate, you run out of reaction mass way too quickly even with a magical energy source on board to throw it out the back of the ship really fast.
why, so they can watch corporate news from earth to get depressed? /s
Actually, it's a great question. Even if we have single photon sensitivity detectors, just what kind of power would a laser need? Or would it be some other area of the emf spectrum? Or some other kind of communication? Sci fi ventures into gravitational waves sometimes
Close enough that we could probably develop a probe to get there in the next few centuries and check it out. What are the current popular candidates for propulsion systems capable of accelerating to near the speed of light?