# Is there ANY realistic mode of interstellar travel? **URL:** \ **Category:** Factual Questions\ **Created:** [July 1, 2006, 12:38am UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818 "2006-07-01T00:38:39Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![TreacherousCretin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/treacherouscretin/32/476_2.png) [@TreacherousCretin](https://boards.straightdope.com/u/TreacherousCretin)\ **Post date:** [March 23, 2015, 4:56pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/41 "2015-03-23T16:56:34Z")
I’m confussed. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [March 23, 2015, 5:02pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/42 "2015-03-23T17:02:12Z")
It is nowhere set in stone that sentient beings have to grow old and die on a fixed timescale of a handful of decades. Want interstellar travel? 1. Put more money (trillions) into human brain research. Develop a brain emulator that uses non-biological parts. The emulator would use digital state files that can be checked for errors and backed up, therefore the emulated beings would be essentially immortal. 2. Send a starship that is the minimum size possible. Use antimatter, synthetic black holes, or just be happy with only reaching 2% of the speed of light and use a nuclear salt water engine. 3. Wait decades. Long travel times are no obstacle to beings that don’t age and can adjust their perceived rate of time. It doesn’t matter if the trip to alpha centauri takes 200 years if you can make it seem to take only 5 minutes to yourself. 4. Everyone who didn’t ride the ship (it would probably be really small and have limited onboard memory) can be beamed over as data packets via a laser communication system. Then beamed back once they are done exploring. FTL travel is just a science fiction crutch to tell the classic Hero’s Journey story, where the protagonist is a young man. It isn’t realistic or necessary. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [March 23, 2015, 5:03pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/43 "2015-03-23T17:03:56Z")
> [@Hermitian](#): > > Before you prematurely build your antimatter drive and blast off toward the direction of space, maybe you should determine a good landing spot. I don’t think the list of planets that are earth-like enough to live on them is very long True, but the cool thing is, you don’t need a star drive to get there. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [March 23, 2015, 5:10pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/44 "2015-03-23T17:10:23Z")
> [@Q.E.D](#): > > Oh, I don’t know about that. I wouldn’t rule out some form of suspended animation, like cryogenic storage. Granted, such a system would require an extremely high degree of reliability and would therefore be horrendously expensive, but it’s at least a possibility in theory. If such a system were workable, our astronaut(s) could return, although Earth would be practically unrecognizeable to them. Yes, I think sleepships. But soon, we could have cyber-ships. Again, this doesnt quite meet the OP, since here’s more or less asking for FTL, which pretty much is impossible. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [March 23, 2015, 5:11pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/45 "2015-03-23T17:11:46Z")
If only we could figure out how to manipulate Time And Relative Dimensions In Space… Jelly Baby? ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [March 23, 2015, 5:12pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/46 "2015-03-23T17:12:54Z")
> [@DrDeth](#): > > Yes, I think sleepships. But soon, we could have cyber-ships. > > Again, this doesnt quite meet the OP, since here’s more or less asking for FTL, which pretty much is impossible. If you got a reply from him, this really would be a zombie thread! :eek: ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [March 23, 2015, 5:55pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/47 "2015-03-23T17:55:51Z")
> [@DrDeth](#): > > Yes, I think sleepships. But soon, we could have cyber-ships. Solving the problem of “interstellar travel that takes less than a human lifetime” by making “human lifetime” longer is a much more tractable problem then finding a way to do FTL travel. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [March 23, 2015, 6:32pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/48 "2015-03-23T18:32:09Z")
Ok, old thread but why not move it forward. Alcubierre drive is theoretical and sexy, but I have to assume it would use approximately one gob of energy to bend even several lightyears of spacetime to make it practical as a means of transportation. Has the requisite “one gob” ever been quantified? And does it work in reverese for a substantially lower energy requirement? Rather than contract the spacetime between points A & B, just stretch the spacetime occupied by the starship as needed. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [March 23, 2015, 6:45pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/49 "2015-03-23T18:45:24Z")
> [@The Great Sun Jester](#): > > Ok, old thread but why not move it forward. Alcubierre drive is theoretical and sexy, but I have to assume it would use approximately one gob of energy to bend even several lightyears of spacetime to make it practical as a means of transportation. Has the requisite “one gob” ever been quantified? > > And does it work in reverese for a substantially lower energy requirement? Rather than contract the spacetime between points A & B, just stretch the spacetime occupied by the starship as needed. The Bloater Drive, from _Bill the Galactic Hero?_ It just might work… ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [March 23, 2015, 6:53pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/50 "2015-03-23T18:53:28Z")
Gawdammit, why do I even try to come up with new ideas? Not only do I fail every time, but by half a frikkin century. I should just stick to stringing beads like my father did, and his father before him. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [March 23, 2015, 7:38pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/51 "2015-03-23T19:38:16Z")
Faster-than-light travel would mean a helluva lot more zombie threads on this board. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [March 23, 2015, 7:59pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/52 "2015-03-23T19:59:09Z")
Yeah, but if you travel fast enough that you go back in time, than you can post in the threads while they’re still current. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 23, 2015, 9:56pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/53 "2015-03-23T21:56:42Z")
> [@](#): > > Quoth **The Great Sun Jester** : > > Ok, old thread but why not move it forward. Alcubierre drive is theoretical and sexy, but I have to assume it would use approximately one gob of energy to bend even several lightyears of spacetime to make it practical as a means of transportation. Has the requisite “one gob” ever been quantified? > > And does it work in reverese for a substantially lower energy requirement? Rather than contract the spacetime between points A & B, just stretch the spacetime occupied by the starship as needed. The “gob” has been quantified, and it is in fact possible to do it with substantially lower energy than “one gob”. That’s not the problem. The problem is in doing it with a _higher_ energy, since the “gob” is negative. As for the bit about launching early and being beat by those who launched later with better tech, I think that’s quite plausible; I just don’t think that the “better tech” involved will be total conversion tech (at least, not for the closest destination stars). When we do eventually launch an interstellar craft, it’ll probably be fusion powered. But like any technology, fusion will be progressively developed and refined, such that the fusion systems of year X+50 will be better than those of year X. So even just sticking to fusion as a power source, one might still be able to overtake the original explorers. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [March 23, 2015, 11:30pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/54 "2015-03-23T23:30:43Z")
> [@Francis\_Vaughan](#): > > One assumes someone has seen the vague idea of the Alcubierre drive and mixed that up with the somewhat common misconception that antimatter has negative energy, and thus maybe negative mass, and somehow stumbled on from there to the idea that there is a viable warp drive just waiting to be built. Well, this is just the sort of insight that is needed to devise unique new technologies. When it works, it’s genius! When it fizzles, everyone just laughs. Now, if we’re going to contemplate _theoretical_ solutions, regardless of the practical obstacles, let’s just suppose that we have unlimited hamsters. Could we reach even .9c then? How much hamster fuel would we need to bring aboard? Could we devise better (e.g., more energy-dense) hamster fuel? Could we breed arbitrarily efficient hamsters, or is there some theoretical limit to that? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [March 25, 2015, 5:13pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/55 "2015-03-25T17:13:47Z")
> [@Chronos](#): > > The “gob” has been quantified, and it is in fact possible to do it with substantially lower energy than “one gob”. That’s not the problem. The problem is in doing it with a _higher_ energy, since the “gob” is negative. > > As for the bit about launching early and being beat by those who launched later with better tech, I think that’s quite plausible; I just don’t think that the “better tech” involved will be total conversion tech (at least, not for the closest destination stars). When we do eventually launch an interstellar craft, it’ll probably be fusion powered. But like any technology, fusion will be progressively developed and refined, such that the fusion systems of year X+50 will be better than those of year X. So even just sticking to fusion as a power source, one might still be able to overtake the original explorers. That’s a plausible scenario, although not the one the old-time SF writers laid out. They always, to my knowledge, came up with a breakthrough that cut time by orders of magnitude. Just to show how far back the basic idea goes, here’s a summary of the Bernhard Kellermann novel, [Der Tunnel](http://en.wikipedia.org/wiki/Der_Tunnel_%28novel%29): > [@](#): > > Allan, an idealistic engineer, wants to build a tunnel at the bottom of the Atlantic Ocean connecting North America with Europe within the space of a few years. The idealist’s scheme is thwarted for financial reasons, and the tunnel construction (in particular a segment dug under a mountain) experiences several disasters. A fiasco seems inevitable, the army of workers revolt, and Allan becomes a figure of universal hatred throughout the world. After 26 years of construction, the tunnel is finally completed; however, the engineering masterpiece is outdated as soon as it opens, as aeroplanes now cross the Atlantic in a few hours. The book was filmed four times, with the last version released in the U.S. in 1935 as _Transatlantic Tunnel_. I’d be surprised if most Golden Age SF writers weren’t familiar with the novel and its ending even if they hadn’t read it. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [March 25, 2015, 7:07pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/56 "2015-03-25T19:07:07Z")
> [@Senegoid](#): > > Now, if we’re going to contemplate _theoretical_ solutions, regardless of the practical obstacles, let’s just suppose that we have unlimited hamsters. Could we reach even .9c then? How much hamster fuel would we need to bring aboard? Could we devise better (e.g., more energy-dense) hamster fuel? Could we breed arbitrarily efficient hamsters, or is there some theoretical limit to that? There are two problems with even hypothetical “hamster” powered sources for an interstellar spacecraft. One is that regardless of what power source you have, as long as you’re using rocket propulsion (e.g. momentum transfer using a propellant) you are tied to the so-called tyranny of the (Tsiolkovsky) [rocket equation](http://www.braeunig.us/space/propuls.htm#impulse); in essence, the efficiency at which you use propellant is dependent up the speed at which it is ejected. This is measured in what is termed “specific impulse” or I[SUB]sp[/SUB] and typically shown in units of seconds, although it is actually the amount of thrust per unit weight of propellant flowing through the exit plane over an interval. (Pedants will note that it would be more correct to speak in terms of mass flow and result in units of force/(mass×time), but for historical reasons propellant weight as measured at Earth’s surface is used.) This can be used to determine the ratio of propellant mass to payload mass (including the inert mass of the spacecraft and propulsion system). Even assuming very high temperatures (~10[SUP]8[/SUP] K) for fusion for a thermal rocket using hydrogen as the propellant, the I[SUB]sp[/SUB] comes out to be around 10,000 to 20,000 seconds to achieve a speed of 0.01c (1% of the speed of light, which would take over four centuries to visit the nearest star system) requiring a payload to propellant mass ratio in the millions or billions, so even nuclear fusion doesn’t provide temperatures sufficient to attain sufficient exhaust velocity and specific impulse for interstellar transit in a human lifetime. Of course, we could dispense with the thermal rocket and power some kind of higher specific impulse system propelling particles via a magnetically confined plasma, or an electrostatic grid, or even pure light, in which the efficiency is governed by your power conversion process. If an I[SUB]sp[/SUB] of around 80,000 s were achievable it would give a mass ratio of 45:1 to get to 0.01c, although if you wanted to decelerate at the destination the ratio is then (roughly) squared, giving a final ratio of greater than 2000:1. Realistically, if you wanted to transit even short interstellar distances in a human lifetime, you’d need an I[SUB]sp[/SUB] exceeding 100,000 seconds, for which there is no plausible system using any proposed propellant and power source, a point science fiction authors tend to gloss over or be ignorant of. The only solution to this is to either leave the propulsion system off the vehicle (e.g. beamed propulsion) or collect propellant as you travel through space (e.g. Bussard fusion ramjet), both concepts having immense practical problems that will likely not be solved by any foreseeable technology. The other problem is even more fundamental, and that is governed by thermodynamics; that is, no real world energy process can convert one source of energy into another without entropic losses, and those losses are thermal in nature. In colloquial terms, you will generate waste heat, and the higher power (energy per unit time) that your power operates at the greater the waste heat problem will be. Heat dissipation in space (where there is no atmosphere to convect away heat, so radiation is the only heat transfer mechanism) is a major problem even with low power systems used in present spacecraft. With a very high power propulsion system, heat energy will build up rapidly and will require some kind of thermoregulatory system and a massive radiating surface to reject the heat to the background of space. Even with the large absolute difference between the spacecraft thermal environment and the 2.7 Kelvin microwave background, it just isn’t plausible that a high power source could be used to propel a spacecraft for decades or centuries without exceeding its capacity to store excess generated heat, even if the thermal efficiency of the propulsion process were only a fraction of a percent. This leaves you with “hamsters” that have to be able to violate the laws of thermodynamics, which against puts us outside the realm of the practicable unless you have Maxwell’s demon in your pocket, in which case you can forget about interstellar travel and start doing some really impressive conjuring tricks like causing all of the fast moving molecules in the room to rush to one side. But in general we like to obey the rules of statistical mechanics and not posit schemes that require us to throw all of the fundamental laws on which our understanding of physics is based without a satisfactory replacement. Realistically, when we decide to start exploring beyond our own solar system, we’ll do so via proxy, with autonomous, self-maintaining probes that can operate for millennia and replicate themselves or any tools they need upon reaching another star or other interesting destination and then relay information back to us. Granted, it isn’t as sexy as swooping through space blasting away at xenomorphs, but barring practical wormholes or some other means of circumventing transit through normal space that is the only practical means of exploration. Stranger ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [March 31, 2015, 6:11am UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/57 "2015-03-31T06:11:37Z")
> [@Stranger\_On\_A\_Train](#): > > There are two problems with even hypothetical “hamster” powered sources for an interstellar spacecraft. Stranger, did you forget about antimatter when writing this post? Or do you consider it “speculation” that it is possible to produce positrons and antiprotons via spontaneous pair production reasonably efficiently, forming antihydrogen. Like certain experiments have demonstrated. Frozen antihydrogen would be hard to carry, but you could probably run a fusion reactor (it doesn’t have to be energy positive!) and produce heavier anti-elements. Produce an anti form of a solid type 1 superconductor and it would be much easier to carry. And, there you go. ISP of [10 million](http://www.projectrho.com/public_html/rocket/enginelist.php#id--Antimatter--Beam_Core). Now we’re talking. The second glaring flaw in your post is you refer to sending out self-replicating machinery at whatever velocity is physically achievable. Do you simply not believe you could bring human minds along this way (by scanning them and converting them to non-biological emulation hardware of some sort) or did you simply forget? A centuries long journey isn’t a big deal if you are a being that can self repair itself indefinitely, safeguarding it’s internal data with lots of parity bits. The third glaring flaw - I think you forgot about liquid droplet radiators when you were covering the problems with heat dissipation. Go check the math on those, they improve performance by several orders of magnitude. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 31, 2015, 8:41am UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/58 "2015-03-31T08:41:38Z")
Antimatter is far from an ideal method of propulsion. Stranger might like to elaborate upon this, as he has in the past, but the simple fact is that most of the products of antimatter annihilation(neutrinos, gamma rays) are pretty much useless for creating momentum in a spaceship. Gamma rays are pretty dangerous, too. To get round this, Robert Frisbee tried to optimise the design for an antimatter ship by extracting as much thrust from the annihilation products as possible, while keeping the reaction as far away from the payload as possible. Here’s his design study > **[ANTIMATTER\_ROCKET\_FOR\_INTERSTELLAR\_MISSIONS.pdf](https://www.relativitycalculator.com/images/relativistic_photon_rocket/ANTIMATTER_ROCKET_FOR_INTERSTELLAR_MISSIONS.pdf)** > > 364.19 KB …the ship is hundreds of kilometres long, and requires at least 40 tonnes of antimatter for propulsion. In short, antimatter is not the wonder fuel one might imagine. Every high energy propulsion system is going to have similar problems - the energies involves are so great, that the ship has to remain just below melting point, for example. One day maybe we’ll meet these engineering demands- but the ships probably won’t include accomodation for active human bodies. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [March 31, 2015, 4:30pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/59 "2015-03-31T16:30:01Z")
> [@eburacum45](#): > > Antimatter is far from an ideal method of propulsion. Of course it’s not so great. It also pretty much means very low thrust - you can only react a little antimatter at a time, and would need gigantic droplet radiators to vent the waste heat. So yeah, it’s still going to probably take centuries - but you wouldn’t need mass ratios of thousands : 1, and you could ultimately reach somewhere between 0.1 and 0.9 C for longer trips. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [March 31, 2015, 4:33pm UTC](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818/60 "2015-03-31T16:33:51Z")
> [@Habeed](#): > > And, there you go. ISP of [10 million](http://www.projectrho.com/public_html/rocket/enginelist.php#id--Antimatter--Beam_Core). Now we’re talking. The heat buildup problem still applies. > [@](#): > > The second glaring flaw in your post is you refer to sending out self-replicating machinery at whatever velocity is physically achievable. Do you simply not believe you could bring human minds along this way (by scanning them and converting them to non-biological emulation hardware of some sort) or did you simply forget? He might not consider that the same as “us” being there. As I said in the other thread, if we do get to other star systems, I doubt we’d be recognizable to us (today) as “us”. [Previous page](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818.md?page=2) [Next page](https://boards.straightdope.com/t/is-there-any-realistic-mode-of-interstellar-travel/362818.md?page=4)