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B Why is interstellar travel so hopelessly difficult?

  1. Jun 3, 2017 #1
    So, I have been thinking about TRAPPIST-1 and how far away that system is from us. It is 40ly away from Earth, according to our frame of reference. This is often put in a way that makes one think that even at speeds close to that of light, it will take almost 40 years to get there.

    The muons in our upper atmosphere, on the other hand, show something different. Even though they are short lived, unstable particles they often make it to the surface of the Earth just because of their high velocities. Here length contraction/ time dilation makes them survive long enough( Or brings us closer to them).

    Won't the same argument work for human subjects, travelling at relativistic speeds?
    The distance between them and TRAPPIST-1 would be so small that they may finish it in a couple of years, depending on their precise speeds.

    I don't know, if I am missing something here, except the Earth's reference frame where it is inevitably 40 years, but the astronaut might not be that discomforted by the journey, at the end of the day. (Feel free to throw quantitative arguments and maths to make your point, if you want to)
    Last edited by a moderator: Jun 7, 2017
  2. jcsd
  3. Jun 3, 2017 #2


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    You have it right - the traveller can experience arbitrarily short time if they can tolerate the acceleration. But the energy requirements to accelerate even a small mass to near light speed are horrific. Google for "relativistic rocket" if you want the depressing details - even total conversion drives need (from memory) millions of times the mass of the payload in fuel.
  4. Jun 3, 2017 #3
    I live in horrific details, thanks for that ;)
    However, what used to confuse me were the articles claiming, it would take me almost 40 years to get there even at light speed or 99.9% of it. I don't even care if my rocket gains so much mass because of high velocity that it turns to a black hole, tbh :P
  5. Jun 3, 2017 #4


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    You can get there and back in arbitrarily short time by your own clocks, but it will inevitably have taken 80+ years by Earth's clocks. Whether that means that it takes 80 years or no time at all depends on your application. If you ask your love to wait for your return (you'll only be gone a few minutes!) you may be disappointed.

    A word of advice - forget you ever heard the phrase "relativistic mass". It causes all sorts of confusion. For example, the idea that your rocket might turn into a black hole. http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html
  6. Jun 3, 2017 #5
    Thanks, it actual cleared a lot of air. It raises more questions too, but I guess, I might have to crack open a few books and sort them out for myself.
  7. Jun 3, 2017 #6
    Another issue is that at high relativistic speeds, collisions with small particles in the interstellar void could be catastrophic. Then there is the need for shielding from cosmic gamma rays. Etc. ... Many impediments for our current state of technology.
  8. Jun 7, 2017 #7
    A ship using a constant 1g acceleration half-way toward its destination, and then applying the same 1g acceleration to slow down for the other half can travel 40 light years in about 7.3 years of traveler time. If you made a round trip, You'd experience about 14.6 years, but about 83.8 years would pass on Earth. Rockets that can apply 1g of acceleration are well within our grasp. Rockets that can do this for years at a time, however, are far beyond reach at this point. So, the main problem we have to tackle for relativistic space travel is the ability to apply a useful amount of thrust for long periods of time practically. Even a highly efficient fusion torch drive would have a hard time doing this.
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