# Speed of light makes space travel pointless **URL:** \ **Category:** Factual Questions\ **Created:** [March 26, 2001, 4:11am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494 "2001-03-26T04:11:32Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![samboy](https://avatars.discourse-cdn.com/v4/letter/s/cdc98d/32.png) [@samboy](https://boards.straightdope.com/u/samboy)\ **Post date:** [March 26, 2001, 4:11am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/1 "2001-03-26T04:11:32Z")
I have come to the conclusion that all space exploration is pointless unless we can find a way to exceed (and by many times) the speed of light. Looking through astronomy books it appears that the nearest star to us is about 4 light years away. Im sure you all realise this means that even if we have a space ship traveling near the speed of light it would still take about 4 years to get there. And that is only the nearest star in our Galaxy which is 75000 light years across and is one of billions of Galaxys which are millions of light years away. Faced with these astronomical distances, shouldn’t we all give up on space travel until we can move faster? Also since the C limitation applied to everything this also means that we can’t communicate with distant worlds either because our signals would take forever to reach anyone else. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [March 26, 2001, 4:14am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/2 "2001-03-26T04:14:39Z")
And the general question here is what? Relativistic concerns don’t even factor in to the space travel we do today. The Mars missions were plotted using only Newtonian physicw; why should we stop existing space exploration when the SOL doesn’t even apply to what we’re doing now? ---
**Author:** ![Lawmill](https://avatars.discourse-cdn.com/v4/letter/l/ecc23a/32.png) [@Lawmill](https://boards.straightdope.com/u/Lawmill)\ **Post date:** [March 26, 2001, 4:19am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/3 "2001-03-26T04:19:43Z")
Your view seems very short sighted. Unless we try, humankind will never know whether the speed of light can be exceeded or there are other methods of traveling faster than light. Heavier than air flight would probably have seemed like a ridiculous form of transportation a few centuries ago, it’s a good thing we didn’t write that off. I can think of several scenarios where people would willingly travel long distances across space. -this solar system is so bad that life on a ship is as good or better -people live much longer or can be put into a state where they don’t age much or at all, this wouldn’t make a 1000 year trip seem quite as bad -an “Australia” scenario, convicts or either people without much to live for in this system decide that starting a voyage of colonization/discovery is worth devoting their lives ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [March 26, 2001, 4:47am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/4 "2001-03-26T04:47:14Z")
but wouldn’t the Theory of Relativity dictate that the subjective time of the astronauts would be less than the actual time here? I mean, as long as you have no problem with time passing more quickly for everyone back here on Good Ol’ Terra than for you, why not take the trip? Does anyone know how much subjective time would pass at say, .75LS for a 4-LY trip? As far as communication, yeah. At this point in our knowledge of the way the universe works, we’d be f—ed. ---
**Author:** ![hansel](https://avatars.discourse-cdn.com/v4/letter/h/6bbea6/32.png) [@hansel](https://boards.straightdope.com/u/hansel)\ **Post date:** [March 26, 2001, 4:49am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/5 "2001-03-26T04:49:41Z")
I don’t have a cite, but I’ve read articles in reputable science journals that are extremely speculative about theoretical means of FTL travel, having to do with different dimensions and such (one such theory speculated about creating an envelope of a different dimension around a ship - theoretically untroublesome, but practically undoable, right now). As I recall, it’s nothing that violates the physics we know today. Some of it is based on assumed discoveries or hypothesis being proven true. They’re so abstract as to be currently useless for actual research. But they do explore extreme possibilities that suggest that C is a barrier to be overcome, not an absolute limit. ---
**Author:** ![Bean\_Counter](https://avatars.discourse-cdn.com/v4/letter/b/db5fbb/32.png) [@Bean\_Counter](https://boards.straightdope.com/u/Bean_Counter)\ **Post date:** [March 26, 2001, 6:03am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/6 "2001-03-26T06:03:46Z")
How long did it take Columbus to cross the Atlantic Ocean? How long does it currently take a jet airplane? 400 years + and we are still trying to find ways to do it faster. First wind powered ships. Then steam powered ships. Then Jets. The Concorde. Speculation/dreams of sub-orbital flights. First the human race got there. Then we worked on getting there faster. It took 400 years to widdle down the time to cross the Atlantic from months down to hours. That was only a few hundred miles in the rather friendly environment of our planet. How much time do you think is necessary to cross the vastness of space in the inhospitable void? Also, if we do not go to the stars, what of our race and cultures? It will be thousands, if not millions of years in the future, but our sun will eventually grow old and die. If we do not go to the stars, everything will be lost. Not just the inhabitants of the planet at that time, but all of the work and dreams of previous generations will be gone as well. Our space program has taken a few baby steps in the marathon necessary to bridge the vastness of space. But the journey of a thousand miles begins with but a single step. Yeah, it’s a pretty optimistic view colored by a lifetime of science fiction fandom, but if no one dreams the dream, how can it come true? ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [March 26, 2001, 6:26am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/7 "2001-03-26T06:26:54Z")
Current opinion is that we need some way to “cheat” even to get to the nearest stars. Ideas along this theme always seem to be based on manipulating the space-time continuum, overcoming the need for transporting unfeasibly huge amounts of fuel. Seems to me that there is another problem which nobody ever seems to mention. Manipulating of the continuum, using wormholes or whatever, seems to be the only way it can be done. Imagine we suddenly find that Einstein was wrong - we _can_ travel faster than light. Imagine further that we discover some easy method of attaining these speeds. We then have a situation where we aren’t messing with the physics of space and time; we are simply going bloody fast! Now then, what about the G forces on board the ship? How does Captain Picard stand there sipping a coffee as the _Enterprise_ accelerates into Warp 9? Unless there is some way of providing some sort of artificial isolation from onboard G forces, sheer speed won’t be the way to the stars. Trekkies, how do the script writers tackle this? ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [March 26, 2001, 10:29am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/8 "2001-03-26T10:29:05Z")
First of all the traveler CAN get to the nearest star 4 light years away in under 4 years due to time/space dialation. The time for people on earth woud be much longer though. The biggest problem to travel at light speed is fuel. Im not sure it this is exactly true but it’s something I’ve been considering for some time: You would need an equal mass of fuel to the weight of your ship to accelerate to 1/2 the SOL if that mass leaves your ship at the SOL and is 100% efficent. If that is true I think to travel 4 lightyears in about 3 years (for the traveler, not for the observer) accelerating at apx 1g for 1/2 the trip and decelerating for the other 1/2 you would need a ship that is 64:1 fuel:ship using antimatter/matter assuming you carried all fuel with you. ---
**Author:** ![Badtz\_Maru](https://avatars.discourse-cdn.com/v4/letter/b/e36b37/32.png) [@Badtz\_Maru](https://boards.straightdope.com/u/Badtz_Maru)\ **Post date:** [March 26, 2001, 10:33am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/9 "2001-03-26T10:33:25Z")
Well, maybe someone will build a Bussard ramjet someday - gather your fuel on the way with a big hydrogen scoop. Or leave your fuel at home and propel the ship by light pressure from an array of huge lasers. I imagine a ship could carry enough antimatter to propel itself to near lightspeed too, we just need to work on making enough of it. ---
**Author:** ![Fern\_Forest](https://avatars.discourse-cdn.com/v4/letter/f/71c47a/32.png) [@Fern\_Forest](https://boards.straightdope.com/u/Fern_Forest)\ **Post date:** [March 26, 2001, 10:42am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/10 "2001-03-26T10:42:42Z")
that light sail idea is a good one. I think if you were on a light ship that experienced an acceleration/decceleration of 1g to the Centauri systerm you’d notice that 45 years have passed. I could do the math precisely but those equations are a real pain in the wahosits. But I don’t think interstellar space travel is useless without “cheating.” I believe that if human kind set there mind to populating the galaxy we could do it in a couple million years easy. Based on technology we know already. All we have to do is to perfect what we have now and we could do it. ---
**Author:** ![Astroboy14](https://avatars.discourse-cdn.com/v4/letter/a/df705f/32.png) [@Astroboy14](https://boards.straightdope.com/u/Astroboy14)\ **Post date:** [March 26, 2001, 10:55am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/11 "2001-03-26T10:55:35Z")
> [@](#): > > Does anyone know how much subjective time would pass at say, .75LS for a 4-LY trip? I’m confused: 😕 See? Isn’t the subjective time of a 4 light year trip, at relativist speeds, close to 4 years? What am I missing? _Help! Former physics student turned booze-addled English teacher puling in agony here!_ ---
**Author:** ![Badtz\_Maru](https://avatars.discourse-cdn.com/v4/letter/b/e36b37/32.png) [@Badtz\_Maru](https://boards.straightdope.com/u/Badtz_Maru)\ **Post date:** [March 26, 2001, 11:02am UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/12 "2001-03-26T11:02:24Z")
> [@](#): > > \*Originally posted by brother rat \* > **that light sail idea is a good one. I think if you were on a light ship that experienced an acceleration/decceleration of 1g to the Centauri systerm you’d notice that 45 years have passed. I could do the math precisely but those equations are a real pain in the wahosits. But I don’t think interstellar space travel is useless without “cheating.” I believe that if human kind set there mind to populating the galaxy we could do it in a couple million years easy. Based on technology we know already. All we have to do is to perfect what we have now and we could do it.** > > I actually did the math once, and at 1G acceleration it only takes a month or two to reach 99% of C. For the folks on the ship (assuming they accelerated to 99% of C at 1 G, coasted, then decellerated at the same rate) it would take them well under a year, for the folks at home a few months longer than 4 years. > > \*\* ---
**Author:** ![Akatsukami](https://avatars.discourse-cdn.com/v4/letter/a/ea666f/32.png) [@Akatsukami](https://boards.straightdope.com/u/Akatsukami)\ **Post date:** [March 26, 2001, 12:32pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/13 "2001-03-26T12:32:09Z")
**blessedwolf** asks: > [@](#): > > Does anyone know how much subjective time would pass at say, .75LS for a 4-LY trip? _Assuming_ that we’re not doing any accelerating (there are equations for that, too, but I don’t have them in my head) the subjective time is: t[sub]s[/sub] - t[sub]r[/sub] \* sqrt(1-(v[sup]2[/sup]/c[sup]2[/sup])) Thus, assuming that we travel at .75 of light speed over 4 ly, the time experienced by the travellers is: 4 \* sqrt(1-(.75[sup]2[/sup])) = 2.65 years. **k2dave** writes: > [@](#): > > Im not sure it this is exactly true but it’s something I’ve been considering for some time: You would need an equal mass of fuel to the weight of your ship to accelerate to 1/2 the SOL if that mass leaves your ship at the SOL and is 100% efficent Not quite. The non-relativistc mass-ratio equation is: d **v** = **v** [sub]e[/sub] \* ln (m[sub]0[/sub]/m) Again, there _is_ a relativistic version, but I don’t feel like looking it up at this hour. Note that change in velocity (dv) _is_ directly proportional to the exhaust velocity of the propellant, v[sub]e[/sub]. Note also that this is a _vector_ equation (that why the "v"s are bolded), so that jinking around will reduce the speed (_i.e._, velocity component on the line between source and destination), and that if you want to _de_celerate from your peak velocity[sup]1[/sup], you either reduce that peak velocity by two, increase your mass ratio by e[sup]2[/sup] (about 7.39), or use some other means of braking, such as a magnetic drag. [sup]1[/sup][sub]Personally, I think that it’s a bad idea to go zipping through Alpha C system at .75 of light speed[/sub] ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [March 26, 2001, 4:06pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/14 "2001-03-26T16:06:30Z")
> [@](#): > > Imagine we suddenly find that Einstein was wrong - we can travel faster than light. First of all Einstein’s field equations do not prohibit wormholes (Einstein - Rosen bridges) which in effect would allow FTL travel without locally exceeding c. Second, exceeding c in normal space-time would involve effects preceding causes and in the extreme case you could be everywhere in the universe at the same time. Also at the speed of light, the electric and magnetic fields of a light wave would not be time varying and therefore there could be no light. I can’t write out the equations here but if you’re interested in accelerational time dilation and fuel consumption do a search on “The Relativistic Rocket” ---
**Author:** ![justinh](https://avatars.discourse-cdn.com/v4/letter/j/9fc29f/32.png) [@justinh](https://boards.straightdope.com/u/justinh)\ **Post date:** [March 26, 2001, 4:49pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/15 "2001-03-26T16:49:59Z")
light year definition? is it the distance traveled by light in one year (where time is from the light’s perspective)? I thought that if a star was 4 light years away then it would take me 4 years (of my time) traveling at the speed of light to reach it. ---
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [March 26, 2001, 4:55pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/16 "2001-03-26T16:55:56Z")
What kind of society would commit itself to funding a prohibitively expensive interstellar exploration program without being fairly certain that the final destination had sufficient merit to justify the huge public investment? If we found something “interesting” within, say, 30 light years of Earth–and be able to travel at 80% of light–you’re still talking about almost a century passing before the scientific results would be known back here on Earth. That requires an exceptionally foward-looking taxpayer base, especially given the possibility that this mission would yield little if anything of practical value. Would taxpayers (or a mega-corporation) be willing to finance pure research or exploration for the sake of exploration? I doubt it. Imagine even deeper-space exploration taking 1,000 years on Earth before payback is received. What taxpayer would be willing to finance that? I love the idea of discovery, but financing it would be difficult. ---
**Author:** ![SuaSponte](https://avatars.discourse-cdn.com/v4/letter/s/67e7ee/32.png) [@SuaSponte](https://boards.straightdope.com/u/SuaSponte)\ **Post date:** [March 26, 2001, 5:21pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/17 "2001-03-26T17:21:18Z")
> [@](#): > > \*Originally posted by TheLoadedDog \* > Now then, what about the G forces on board the ship? How does Captain Picard stand there sipping a coffee as the _Enterprise_ accelerates into Warp 9? > > Unless there is some way of providing some sort of artificial isolation from onboard G forces, sheer speed won’t be the way to the stars. > > Trekkies, how do the script writers tackle this? You poor, ignorant fool. Picard drinks **tea** , not coffee. The script writers tackle the gravity problem with inertial stabilizers - they keep inertia constant, thereby cancelling the effects of acceleration. Presumably, this is the same as anti-gravity, which they mention on occasion, but don’t use all that often. Sua ---
**Author:** ![Akatsukami](https://avatars.discourse-cdn.com/v4/letter/a/ea666f/32.png) [@Akatsukami](https://boards.straightdope.com/u/Akatsukami)\ **Post date:** [March 26, 2001, 5:22pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/18 "2001-03-26T17:22:31Z")
**tsunamisurfer** asks: > [@](#): > > What kind of society would commit itself to funding a prohibitively expensive interstellar exploration program without being fairly certain that the final destination had sufficient merit to justify the huge public investment? Pharaonic Egypt? Qin China? Medieval Catholic Europe? I agree that it is implausible (not to mention a bad idea) to assume that United Earth will send off a colonizing expedition to Tau Ceti without first learning whether there _is_ something to colonize there. By that same token, however, an exploratory (and presumably unmanned) mission need not be as expensive as a full-fledged colonization effort. ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [March 26, 2001, 6:37pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/19 "2001-03-26T18:37:01Z")
> [@](#): > > \*Originally posted by \*\*\*Astroboy14 \*\* > Isn’t the subjective time of a 4 light year trip, at relativist speeds, close to 4 years? What am I missing? I don’t like the term “subjective time”. It makes it sound like there is some “objective time” to compare subjective time to. The only time is what we can measure and it’s _not_ subjective. As you approach the speed of light relative to a reference frame that you designate as stationary, your time slows relative to the stationary system. > [@](#): > > \*Originally posted by \*\*\*Ring \*\* > First of all Einstein’s field equations do not prohibit wormholes (Einstein - Rosen bridges) which in effect would allow FTL travel without locally exceeding c. > > Second, exceeding c in normal space-time would involve effects preceding causes and in the extreme case you could be everywhere in the universe at the same time. Any time you travel faster than light, you will have cause and effect violations even if you obey the local speed limit. If I arrive at my destination before light could travel the distance, there will be reference frames where I arrive before my departure. Passing through a wormhole does not give you any special dispensation to violate causality. Allowing information to pass through a wormhole intact has the same cause-effect paradoxes that any other method of faster-than-light travel has. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [March 26, 2001, 7:20pm UTC](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494/20 "2001-03-26T19:20:00Z")
DrMatrix: Would you therefore propose that FTL travel is impossible, even with “cheating”, because of the cause-effect paradoxes it creates? I trust your opinion on this, as you seem to be very knowledgeable in this area, but it sure sucks as far as exploring the universe goes. -b [Next page](https://boards.straightdope.com/t/speed-of-light-makes-space-travel-pointless/59494.md?page=2)