# Question about light speed. **URL:** \ **Category:** In My Humble Opinion\ **Created:** [April 28, 2014, 11:22pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224 "2014-04-28T23:22:39Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Space\_Trucker](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Space\_Trucker](https://boards.straightdope.com/u/Space_Trucker)\ **Post date:** [April 28, 2014, 11:22pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/1 "2014-04-28T23:22:39Z")
😃 ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [April 28, 2014, 11:51pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/2 "2014-04-28T23:51:18Z")
Other: no, you don’t need FTL to go to other stars…but the time dilation factor from relativity isn’t the solution. Generation ships and a LOT of patience is the solution. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 29, 2014, 7:25am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/3 "2014-04-29T07:25:00Z")
I voted yes, even though it looks like it’s impossible to achieve. Generation ships aren’t the answer, because that involves building a completely self-sustaining environment with machines and facilities that will keep functioning for tens/hundreds of thousands of years with no external support. This is analogous to us today still using the first flint axes ever made by humans. Not similar axes. The same ones. ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [April 29, 2014, 1:59pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/4 "2014-04-29T13:59:05Z")
Yes and no. You can go to the stars at sublight speeds; it will just take a loooooong time. However, if you want an interstellar society, you need to go faster. ---
**Author:** ![Mr\_Quatro](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@Mr\_Quatro](https://boards.straightdope.com/u/Mr_Quatro)\ **Post date:** [April 29, 2014, 4:42pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/5 "2014-04-29T16:42:16Z")
There is another option that by the time you get there … what you were headed for is not even still there due to the fact that it took X amount of light years for the light to get to you and X amount of light years for you to reach the light that you thought was light. That light might not even still be there. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [April 29, 2014, 8:52pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/6 "2014-04-29T20:52:02Z")
> [@Mangetout](#): > > . . . Generation ships aren’t the answer, because that involves building a completely self-sustaining environment with machines and facilities that will keep functioning for tens/hundreds of thousands of years with no external support. Yeah. So what’s the problem? > [@](#): > > This is analogous to us today still using the first flint axes ever made by humans. Not similar axes. The same ones. How so? Where are your technological parameters? How do you know we won’t have advances in materials tech in the future? We might find ways to create force fields, or to stiffen electron bonds in solids. It’s as if you’re insisting we use stone axes…when we have carbon fibers. How can you know we won’t discover something that is a similar jump upward in performance? I didn’t say we, today, at 21st Century tech levels could build generation ships. I said “we,” the human race, might do so. (I can also quibble, just a little, with “no outside support.” The ramscoop model relies on refueling from interstellar hydrogen. Or, you might build a fleet of generation ships, so that, if the frammistat on one breaks, you share veeblefetzers with the other ships. “Outside support” comes from the fleet.) ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [April 29, 2014, 8:55pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/7 "2014-04-29T20:55:45Z")
> [@Mr\_Quatro](#): > > There is another option that by the time you get there … what you were headed for is not even still there due to the fact that it took X amount of light years for the light to get to you and X amount of light years for you to reach the light that you thought was light. > > That light might not even still be there. “Do you think we are fools? We will go at night, when it is not so hot!” Most reasonable destinations would be main-sequence stars which are relatively likely to still be there after a lengthy voyage. Going to Rigel might not be quite as wise. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 29, 2014, 10:15pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/8 "2014-04-29T22:15:17Z")
> [@Trinopus](#): > > How so? Where are your technological parameters? How do you know we won’t have advances in materials tech in the future? We might find ways to create force fields, or to stiffen electron bonds in solids. > > It’s as if you’re insisting we use stone axes…when we have carbon fibers. How can you know we won’t discover something that is a similar jump upward in performance? I think you misunderstood my intent. The interval between setting off from Earth and arriving at the destination, for a generation ship, is similar to the interval between the middle stone age and today. - So I was actually wrong to say ‘the first flint axes’ by quite a margin (the first flint tools were made millions of years ago), but the point is that the journey time for a generation ship is orders of magnitude greater than the working lifetime of any technology we have ever devised. We don’t make things that last that long. > [@](#): > > I didn’t say we, today, at 21st Century tech levels could build generation ships. I said “we,” the human race, might do so. I think it’s far more likely that we would reinvent ourselves as machines and spend the journey in some sort of dormant state - although I still doubt machines that durable can be made. > [@](#): > > (I can also quibble, just a little, with “no outside support.” The ramscoop model relies on refueling from interstellar hydrogen. This point is not in dispute. > [@](#): > > Or, you might build a fleet of generation ships, so that, if the frammistat on one breaks, you share veeblefetzers with the other ships. “Outside support” comes from the fleet.) Redundancy is good - but the fleet still has no outside support. Can we build anything that works for hundreds of thousands of years? After a fraction of that time, _all_ the veeblefetzers on _all_ ships have stopped working, as have all the veeblefetzer manufacturing machines, and there’s nobody coming to the rescue. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [April 29, 2014, 10:26pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/9 "2014-04-29T22:26:39Z")
Assuming that technology on earth will continue to evolve . . . no matter how we go, our descendants will greet us there when we arrive. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 29, 2014, 10:47pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/10 "2014-04-29T22:47:42Z")
To me it is obvious, FTL travel is not only possible but our destiny, already written, signed, sealed and delivered. It is already done, we just have to walk it out. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [April 29, 2014, 10:51pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/11 "2014-04-29T22:51:56Z")
> [@panache45](#): > > Assuming that technology on earth will continue to evolve . . . no matter how we go, our descendants will greet us there when we arrive. That’s the kicker. No one is about to set off on a trip at the speeds the Voyager probes (tada!) achieve today. You’d want to get fairly close to the maximal achievable speed to even begin. When you get to .9 c you are good for reasonably close stars at least. ---
**Author:** ![ThisUsernameIsForbidden](https://avatars.discourse-cdn.com/v4/letter/t/b4bc9f/32.png) [@ThisUsernameIsForbidden](https://boards.straightdope.com/u/ThisUsernameIsForbidden)\ **Post date:** [April 29, 2014, 11:56pm UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/12 "2014-04-29T23:56:01Z")
Not in our lifetime. Bah! Get off my lawn! ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [April 30, 2014, 1:42am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/13 "2014-04-30T01:42:33Z")
> [@panache45](#): > > Assuming that technology on earth will continue to evolve . . . no matter how we go, our descendants will greet us there when we arrive. Uh oh… now we have a Xeno’s paradox of space travel. An infinite number of colony ships will all arrive in the final fractions of a second. 🙂 Hmmm… and an infinite number of ships would create a singularity. Thus, black holes are proof of interstellar travel. 🙂 More seriously, I don’t know how to answer the OP’s poll. I don’t think FTL is required, but I don’t think it’s because of the travel time diminishing. I do believe that generation ships are feasible within certain parameters. The comparison someone made to flint axes is a bad comparison because flint is not recyclable. It only shows that we need a different technology. An iron axe is a better example - melt it down, make a new axe. Or a glass bottle, as another example. You lose some of the material at different stages in the manufacture, use and recycling process, at least with current technology. But I don’t think nano tech that can filter out atoms is so far-fetched. If a team of nanobots scour our generation ship gathering stray atoms of iron and silicon, then nothing ever becomes truly lost. We just need enough energy inputs for the system to continue. The only resource the nanobots can’t retrieve is anything lost outside the ship, which would include hull ablation. But then we just have a math equation. If hull ablation happens at rate X, then we need X\*time of replacement material in storage. And now that we’re talking about resources outside the ship, there is a certain amount of interstellar material we can suck up and put to use. So now we have a rate Y of accumulation. Thus, we only need to pack (X-Y)\*time in replacement material. While these are not simple problems to solve, I don’t see them as insurmountable. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [April 30, 2014, 2:30am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/14 "2014-04-30T02:30:51Z")
> [@Mangetout](#): > > I think you misunderstood my intent. The interval between setting off from Earth and arriving at the destination, for a generation ship, is similar to the interval between the middle stone age and today. > > - So I was actually wrong to say ‘the first flint axes’ by quite a margin (the first flint tools were made millions of years ago), but the point is that the journey time for a generation ship is orders of magnitude greater than the working lifetime of any technology we have ever devised. We don’t make things that last that long. My apologies; far from the first time I’ve misread a post. That said, I still don’t think anyone can know enough to be certain. We, ourselves, might be the stone axe guys, saying, “No one could ever cross the desert, because you’d have to carry all the needed food and water on your backs. That simply can’t be done.” And then someone domesticates cattle, and you have ox-carts…and then someone else invents the internal combustion engine, and you have jeeps… Who knows what’s next? The proposal is certainly at risk for being leapfrogged, as in the old SF story where the generation ship arrives, only to learn that mankind invented FTL drive in the meanwhile. This was also a motif in the (excellent) Manga series “2001 Nights.” All I’m saying is that generation ships are a third alternative that the OP and poll didn’t include, and I think should have. I believe that working generation ships are more likely than FTL. But who the hell knows what will happen? (“In this town, don’t we love it now? Everyone’s waiting for the next surprise.”) > [@](#): > > I think it’s far more likely that we would reinvent ourselves as machines and spend the journey in some sort of dormant state - although I still doubt machines that durable can be made. . . . I like this answer also. I can’t quite agree that it’s “more likely” because it depends on future scientific discoveries, some of which may be wholly unforseeable. As extrapolations of what we know now, I will agree. ---
**Author:** ![ThisUsernameIsForbidden](https://avatars.discourse-cdn.com/v4/letter/t/b4bc9f/32.png) [@ThisUsernameIsForbidden](https://boards.straightdope.com/u/ThisUsernameIsForbidden)\ **Post date:** [April 30, 2014, 3:16am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/15 "2014-04-30T03:16:00Z")
I think a time dilation experiment on a small scale with a person travelling near c would be an interesting one. Have him travel for a year (our time) at that speed and live on the ship, upon returning, what would his watch say? Well, it would say less than a year, but how far could he get in a year his time? To follow up, how long, his time, would it take him to get to the nearest inhabitable planet? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 30, 2014, 6:22am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/16 "2014-04-30T06:22:13Z")
> [@ThisUsernameIsForbidden](#): > > I think a time dilation experiment on a small scale with a person travelling near c would be an interesting one. Have him travel for a year (our time) at that speed and live on the ship, upon returning, what would his watch say? Well, it would say less than a year, but how far could he get in a year his time? To follow up, how long, his time, would it take him to get to the nearest inhabitable planet? It would be interesting, but there is nothing ‘small scale’ about such a proposal. It would take enormous amounts of resources to do this - and in doing it, you would have to solve nearly all of the same problems that a larger scale interstellar voyage would present. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [April 30, 2014, 6:46am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/17 "2014-04-30T06:46:57Z")
> [@ThisUsernameIsForbidden](#): > > I think a time dilation experiment on a small scale with a person travelling near c would be an interesting one. Have him travel for a year (our time) at that speed and live on the ship, upon returning, what would his watch say? Well, it would say less than a year, but how far could he get in a year his time? To follow up, how long, his time, would it take him to get to the nearest inhabitable planet? Why do you think his watch would say anything different from what relativity says it would say? There is plenty of experimental evidence already. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [April 30, 2014, 6:59am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/18 "2014-04-30T06:59:12Z")
> [@Mangetout](#): > > Generation ships aren’t the answer, because that involves building a completely self-sustaining environment with machines and facilities that will keep functioning for tens/hundreds of thousands of years with no external support. We know that’s possible because we live on one that’s lasted for _billions_ of years not just thousands. We just can’t steer it. > [@Mangetout](#): > > Redundancy is good - but the fleet still has no outside support. Can we build anything that works for hundreds of thousands of years? After a fraction of that time, _all_ the veeblefetzers on _all_ ships have stopped working, as have all the veeblefetzer manufacturing machines, and there’s nobody coming to the rescue. Actually the solution to that is simple: you bring along enough technology to repair or rebuild everything, including the repair & manufacturing machinery; you don’t try to haul along several thousand years worth of spare parts. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 30, 2014, 7:11am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/19 "2014-04-30T07:11:16Z")
> [@Trinopus](#): > > My apologies; far from the first time I’ve misread a post. That said, I still don’t think anyone can know enough to be certain. We, ourselves, might be the stone axe guys, saying, “No one could ever cross the desert, because you’d have to carry all the needed food and water on your backs. That simply can’t be done.” And then someone domesticates cattle, and you have ox-carts…and then someone else invents the internal combustion engine, and you have jeeps… Who knows what’s next? True, but analogies about how we may be as ignorant as our ancestors contain an inherent contradiction, as well as plain factual inconsistencies. For example, I’ve heard it said that we will probably be able to travel faster than light in the future - and that our current view of its impossibility is like the prediction of 19th Century scientists, who asserted that people would suffocate if the speed of railway trains exceeded some trivial value. But really, it’s nothing like that. They pulled that idea out of their asses, and it was subsequently overturned by experiment. c as a fundamental speed limit, on the other hand, is not only _not_ pulled out of asses, it’s also been very substantially supported by experiment, not to mention the implementation of many technologies. The contradictory part is where the argument says (essentially): our ancestors were ignorant, but we know better, but actually, we don’t know better, because our predictions could be completely false. For FTL to be possible, we have to discover that not only were we wrong about a huge swathe of science, but also, that all the things we did (and that worked) with that science, _worked for completely unknown reasons_. For generation ships to be possible, we have to build stuff that lasts, and keeps working longer, than the whole of human civilisation. It’s a tall order - I’m not saying it’s absolutely impossible, just that I think most people who propose it enormously underestimate its difficulty. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [April 30, 2014, 9:06am UTC](https://boards.straightdope.com/t/question-about-light-speed/687224/20 "2014-04-30T09:06:34Z")
> [@Mangetout](#): > > For generation ships to be possible, we have to build stuff that lasts, and keeps working longer, than the whole of human civilisation. It’s a tall order - I’m not saying it’s absolutely impossible, just that I think most people who propose it enormously underestimate its difficulty. I on the other hand think you are creating a problem that doesn’t exist. The technology doesn’t have to be especially durable, it just needs to be repairable. [Next page](https://boards.straightdope.com/t/question-about-light-speed/687224.md?page=2)