Not to my knowledge, but he should have. Science fiction authors have a bit of a love affair with ramscoop drives, and as with all love affairs, they have a tendency to overlook their beloved’s flaws. The problem with ramscoops is aerodynamic drag. Sure, the interstellar medium is pretty sparse, but it’s not a complete vacuum, a fact which the ramscoop relies upon in the first place. If you’ve got a big enough scoop that the fuel you gather is non-negligible, then you’ve also got a big enough scoop that drag is non-negligible. At some speed, you’ll eventually get to a point where the thrust you get from burning the hydrogen in your fusion reactor is equal to the drag from scooping up that hydrogen in the first place. The density of the ISM and the size of your scoop cancel out in the calculation of the speed, leaving it determined entirely by the efficiency of fusion. Assuming that your reactor is 100% efficient (which it won’t be, due to neutrinos, but we’re looking for an upper bound, so let’s ignore that), the speed works out to be 12% of c.
The biggest problem with interstellar travel is the ridiculous amounts of energy needed to attain even modest speeds. I read somewhere that at the trivial speed of a few miles per second, the kinetic energy of an object is equal to its mass in TNT. At (IIRC) 87% of lightspeed, the kinetic energy is equal to the converted rest mass of the object. In other words, spacecraft (and their occupants) are clouds of gas relative to the energies typical of space travel. Nuclear energy is needed even for reasonably fast interplanetary travel within a solar system. Interstellar travel… weill it’s telling that people start with presuming total conversion is available and THEN seek ways (like ramscoops, etc.) to bring the problem down to something even halfway managable. Lightsails eliminate the exponential ship mass problem but introduce headaches of their own.
Frankly the only way I see interstellar travel ever advancing beyond the “space ark” level of taking centuries to crawl a few light years, is if the laws of physics somehow allow for movement without acceleration- or equivalently, somehow temporarily setting aside the rest mass of a ship and crew. For which “speculative” isn’t a strong enough adjective; it makes antimatter drives look positively mundane.
Your friend is correct: it is not possible – given current technology.
But until the 1930’s and the jet engine, it would have been correct to say “it is not possible to build an airplane powerful enough to go faster than Mach 1”.
Until the 1950’s and nuclear-powered submarines, it was correct to say “it is not possible for a submarine to circumnavigate the globe underwater”.
It took a change from internal combustion to nuclear power to make those submarines work, which is changing to a whole new theory and a new branch of physics. To travel interstellar distances means developing either a workable suspended animation for humans, or a method of traveling faster than the Einsteinian lightspeed limit. (Or some completely new theory.) Neither of those are possible now, even in theory. So it’s a pretty big step. Maybe impossible.
The trouble with the notion that we might be wrong about faster-than-light travel is that it would imply we’re wrong about nearly everything else as well - but if we’re wrong about nearly everything else, how does all the wrong stuff happen to work for us now?
In order for the theory of relativity to be overturned, it would need to be explained as just a localised configuration of some larger-scale phenomenon, which is capable of different configurations in other circumstances.
I’m not sure whether that’s possible or if it has already been explicitly ruled out - something like it happened with Netwonian physics, which just happened to be a good enough approximation of relativity for use at everyday scales - but assuming relativity will be overturned on similar basis is just argument by analogy (as are all the other arguments involving heavier-than-air flight, etc)
Barring some sort of advance in physics I think there is little chance of any sort of interstellar travel anytime soon, and perhaps never.
There is a chart here from NASA (from this page) showing the required propellant to get to the centauri system in 900 years (and it’s NOT counting the mass/time required to turn around and stop - just fly past). As you can see, via chemical rockets like we currently use there is not enough mass in the whole universe to do it! Even using antimatter rockets (which is afaik the best we could possibly do period if our current understanding of physics is correct) using you’d need 10 railway tankers worth of antimatter. Just to get to the closest star in 900 years, and without saving any fuel to stop.
It’s sort of depressing to think about, really. Unless we are very wrong about something, or we can find a loophole that allows FTL travel and/or reactionless drives we’re pretty much stuck here on earth.
I knew it was bad, but I didnt think it was THAT bad. I have a suspicion somebody made an assumption to make it even worse than it really is. My first guess is a **one stage **chemical rocket.
I’ve havent run any numbers, but given that folks have proposed such “slow” probes in the past, me thinks something is afoot here.
How much worse? 10 x more mass required?
I don’t understand that. My calculation assumes I want to use all the extra matter on board to annihilate with antimatter. Why would I want to waste some of the energy on rest energy in the exhaust? Since the momentum of that exhaust is proportional to sqrt(E^2 - m^2*c^4), I get the most momentum for zero rest particles, like gamma rays.
Of course, the big disadvantage with gamma rays is that I have to figure out a way to get them to go in one direction. Since mirrors don’t seem plausible, perhaps I can make a stimulated emission gamma ray amplifier fueled by antimatter, but these are engineering details.
Well, the proposed probes are all very small (the chart I linked to is for a shuttle sized cannister) and none of them would actually use chemical rockets (Project Longshot would use a fusion engine for example).
Otherwise I don’t really know what to say, it’s very possible it is off somehow - my maths and physics skills are not nearly good enough to say. I just figured NASA is reasonably reputable and I have no reason to doubt them.
Edit: even if it’s off by a factor of 10, it still shows that it takes an unreasonable amount of reaction mass in every case.
I believe you are correct: matter + antimatter = gamma rays is the maximally efficient drive. Antimatter factory, antimatter containment, gamma ray mirror: minor engineering details.
Now, if you think outside the box a bit, things get just a bit less bleak. Like a nanoprobe, which can hopefully scavenge enough molecules of various sorts from the star system in question to build all sorts of things, perhaps a human from scratch. Being of very small mass, such a probe would (hopefully) avoid the large payload and life support issues with a living breathing crew. Von Neumann machines with a twist.
Chronos is correct here (not unusual, it seems). I was presuming sufficient magic in the propulsion system that only energy need be considered.
I think the general conclusion must be that interstellar travel is prohibitively impractical with current technology - we’ll need some sort of warp drive before it can reasonably be considered.
But that does violate the “embodied humans” question of the OP.
IMHO, it’s perfectly possible; you just have to take your time. Assuming you have a large essentially self contained ship or fleet of ships there’s no reason you couldn’t take thousands of years for each voyage, without having to spend immense amounts of energy to reach high speeds. The people who arrive might be the distant descendants of the ones who set out, but they wouldn’t care; as far as they are concerned they’ve been home the whole time.
Do the ideas in the OP actually make interstellar travel any easier? The proposal there is to build a very small spaceship which doesn’t carry human beings but just the information to build humans from the matter in the solar system reached by the ship. The mind of the humans would then be downloaded into those bodies. Is that really any easier? Don’t the objections from physics given in this thread apply to any size of spaceship? Isn’t the problem that you can’t send any physical object at a reasonable speed to travel interstellar distances? By reasonable speed, I mean while it’s possible to imagine a generation ship that takes thousands of years to travel to another star, it’s not possible to build a ship to travel within a single lifetime.
Well, yes. Smaller, lighter objects take less energy to get to high speeds. A one ton payload is going to take far less energy to accelerate than a ten thousand ton payload. And you eliminate all the practical problems of sustaining flesh and blood humans for so long, and the psychological problems of sending just a few people on a decades long journey.
I mulled this over during nighmares last night. Your right, its pretty bad for chemical rockets. As for the NASA part, I worked on government projects to know some real spin can be put on even technical stuff to make “your” project look so much better than anyone elses.
The answer to the OP is the same as the answer to every similar question that has ever been asked. It will remain strictly and provably impossible right up until the moment when someone finds a way to do it. At which point, people will find other things to declare to be impossible.
If you think I’m wrong, pick up a history book.
As noted above, it’s worth recognizing a difference between things (such as heavier-than-air flight) thought by some to be impossible simply because a longish series of attempts at them came to not very much, and things that would strain or violate physics.
Perpetual motion would be a good example of the second. Vast numbers of folks have expended vast effort on this tantalizing quest - more than a few of them have used words just like your second sentence above. But our best understanding of fundamental physics says all this was a complete waste of time. They should have waited for (or worked on) some theoretical breakthrough, without which their efforts were doomed.
Another consideration. Even if it is technologically possible, humans may never reach large enough numbers to make it economically possible to even try.
It might end up being like a tribe of 10 people wondering if they can build the pyramids. Doesnt seem impossible… not sure exactly how some of the problems to do it are to be solved… but where will we ever find enough time, money, and man hours to actually do this thing ?
How can there even be a fixed c, when all time and speed is relative?