6 ms·

Only for those left behind, time dilation is magic. As per wikipedia: > a constant 1 g acceleration would permit humans to travel through the entire known Univ

Only for those left behind, time dilation is magic. As per wikipedia: > a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime So it's really only a challenge of propulsion. You're not making a return trip to any recognizable civilization though.

jandrese 6y ago
Yeah, but have you ever worked out the rocket equation for a spaceship that accelerates at 1G for a full year? There literally isn’t enough mass in our solar system, even with a ridiculous engine with an ISP of 5000 and perfect alchemy to convert all raw mass in the solar system to rocket fuel.
- yread 6y ago
  Project Orion could do ISP of 100,000. Even nuclear thermal engine could reach 5000
  - jandrese 6y ago
    As far as I know Nuclear Thermal rockets have topped out around 1000. Project Orion is entirely theoretical and the ISP calculations should be taken with a grain of salt.
d_silin 6y ago
The amount of energy required to keep that 1g acceleration though...
- brutt 6y ago
  Sun have lot of energy, so it can be used as energy source. If you plan to travel at % of c, you will need strong enough radiation and thermal shield anyway. And if you have such shield, why not just dive into Sun for refueling? Humans can stay at high orbit, when interstellar locomotive refuels.
  - kzrdude 6y ago
    At the speed you are going, the sun will quickly be a pale white dot
    - fabiospampinato 6y ago
      Potentially you could bring the sun along with you.
      - misnome 6y ago
        Where does the energy to accelerate the sun at 1g come from?...
        fabiospampinato 6y ago
        From the sun itself, potentially it might be doable
        cgriswald 6y ago
        From the sun: https://en.m.wikipedia.org/wiki/Stellar_engine https://en.m.wikipedia.org/wiki/Stellar_engine
        misnome 6y ago
        The sun is _really_ _really_ heavy. From that article the best case scenario is a billionth the acceleration you are looking for. And you can’t take a billion stars because then you have more mass... Edit: the interesting part of discussing the 1g is probably less a realistic proposal and more how about how the concept of acceleration quickly runs up against our mental constructs of what acceleration and distance means. I don’t know the source, but it’s probably an enlightening to discuss what it means in the context of relativity.
        kzrdude 6y ago
        Ok, it would be exciting to move the whole solar system to a nicer place in the galaxy. But how many years are we not going to use to evaluate the ethics and technical risks of the experiment? :)
- z3t4 6y ago
  Particles accelerate to light speed all the time though. So it is possible, we have not yet discovered a way to do it at larger scale.
  - airstrike 6y ago
    Particles also don't care so much about how quickly they stop...
    - egeozcan 6y ago
      “Speed has never killed anyone. Suddenly becoming stationary, that's what gets you.” Jeremy Clarkson
  - cocoa19 6y ago
    "Particles accelerate to light speed all the time though" No.
  - dragonwriter 6y ago
    > Particles accelerate to light speed all the time though. No, they don’t, as far as we know. There are particles that are always slower than light, and particles that always go at exactly light speed, but no particles that accelerate to (or decelerate from) light speed.
olvy0 6y ago
Explored in Paul Anderson's novel Tau Zero. https://en.wikipedia.org/wiki/Tau_Zero https://en.wikipedia.org/wiki/Tau_Zero
- cure 6y ago
  Nitpick, it's Poul Anderson. Yes, that is an odd spelling of his first name.
  - ochrist 6y ago
    Not in Denmark where his family came from.
- kwhitefoot 6y ago
  Brilliant book! I recommend it highly.
dylan604 6y ago
And you're also never stopping anywhere, so it would only ever be a permanent sight seeing tour.
empath75 6y ago
Stopping is sort of a problem.
hellofunk 6y ago
> a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime Wow that is actually very fascinating, it never occurred to me that it works that way. I’m always thinking of 11 light years as too far away for someone to achieve in a lifetime, but I am of course thinking about that from the perspective of the person who is not traveling.
- cmehdy 6y ago
  I'm not sure how they calculate the 1g thing past the speed of light (which takes you something short of a year to get to by classical mechanics). But say we just break physics as we know it, and somehow the prophesized amount of time to travel is accurate. You're still going in a straight line and not stopping, unless you want to take another lifetime or be crushed by forces that would hurt just a little bit. So don't turn, only decide to stop in the first half of your life (or you won't live to see the end of the journey), beat light and physics by the end of year one of your life, and enjoy the ride. I'm not sure what you'll "see" outside of your spaceship though, and I do hope for you that there's not a single speck of dust in your path and no wall at the end.
  - californical 6y ago
    I didn't read their idea, but you wouldn't ever need to go faster than the speed of light for this to work -- just approaching it infinitely close would be enough. Sure it might take a hundred million years for your journey from an observer watching you on earth, but thanks to time dilation, it could still be less than a lifetime for the person on the ship
    - cmehdy 6y ago
      Well then how do you get to the parts of our universe that are receding at a speed faster than light due to space expansion? I'm not nearly as comfortable with relativity as I'd like to be, but too much in this hypothetical "woahdude" scenario ends up being a logical roadblock to me.
deleted 6y ago
[deleted]
mikro2nd 6y ago
> only a challenge of propulsion Also a challenge of ablation. At any reasonable fraction of c your spacecraft has a serious erosion problem.
- TheOtherHobbes 6y ago
  Possibly also the challenge of getting baked by the Unruh Effect.
philipkglass 6y ago
This substitutes the challenge of inventing a warp drive with the challenge of inventing a limitless free energy machine. An antimatter fueled rocket can't keep up with what "1G, indefinitely" demands. Not even beamed power propulsion driven by a Dyson swarm can do that. I like the Revelation Space universe, but its fictional Conjoiner drive and the near-light-speed Lighthugger spacecraft powered by it are no closer to realization than any of Star Trek's technobabble. The same goes for the forever-accelerating Bussard ramjet vessel of Tau Zero.
bryanrasmussen 6y ago
what is one human lifetime? that seems an uncertain measure. Also most astronauts I've seen look like they're halfway through one human lifetime when they first get off planet.

jandrese 6y ago

Yeah, but have you ever worked out the rocket equation for a spaceship that accelerates at 1G for a full year? There literally isn’t enough mass in our solar system, even with a ridiculous engine with an ISP of 5000 and perfect alchemy to convert all raw mass in the solar system to rocket fuel.

yread 6y ago
Project Orion could do ISP of 100,000. Even nuclear thermal engine could reach 5000
- jandrese 6y ago
  As far as I know Nuclear Thermal rockets have topped out around 1000. Project Orion is entirely theoretical and the ISP calculations should be taken with a grain of salt.

d_silin 6y ago

The amount of energy required to keep that 1g acceleration though...

brutt 6y ago
Sun have lot of energy, so it can be used as energy source. If you plan to travel at % of c, you will need strong enough radiation and thermal shield anyway. And if you have such shield, why not just dive into Sun for refueling? Humans can stay at high orbit, when interstellar locomotive refuels.
- kzrdude 6y ago
  At the speed you are going, the sun will quickly be a pale white dot
  - fabiospampinato 6y ago
    Potentially you could bring the sun along with you.
    - misnome 6y ago
      Where does the energy to accelerate the sun at 1g come from?...
      - fabiospampinato 6y ago
        From the sun itself, potentially it might be doable
      - cgriswald 6y ago
        From the sun: https://en.m.wikipedia.org/wiki/Stellar_engine https://en.m.wikipedia.org/wiki/Stellar_engine
        misnome 6y ago
        The sun is _really_ _really_ heavy. From that article the best case scenario is a billionth the acceleration you are looking for. And you can’t take a billion stars because then you have more mass... Edit: the interesting part of discussing the 1g is probably less a realistic proposal and more how about how the concept of acceleration quickly runs up against our mental constructs of what acceleration and distance means. I don’t know the source, but it’s probably an enlightening to discuss what it means in the context of relativity.
        kzrdude 6y ago
        Ok, it would be exciting to move the whole solar system to a nicer place in the galaxy. But how many years are we not going to use to evaluate the ethics and technical risks of the experiment? :)
z3t4 6y ago
Particles accelerate to light speed all the time though. So it is possible, we have not yet discovered a way to do it at larger scale.
- airstrike 6y ago
  Particles also don't care so much about how quickly they stop...
  - egeozcan 6y ago
    “Speed has never killed anyone. Suddenly becoming stationary, that's what gets you.” Jeremy Clarkson
- cocoa19 6y ago
  "Particles accelerate to light speed all the time though" No.
- dragonwriter 6y ago
  > Particles accelerate to light speed all the time though. No, they don’t, as far as we know. There are particles that are always slower than light, and particles that always go at exactly light speed, but no particles that accelerate to (or decelerate from) light speed.

olvy0 6y ago

Explored in Paul Anderson's novel Tau Zero. https://en.wikipedia.org/wiki/Tau_Zero https://en.wikipedia.org/wiki/Tau_Zero

cure 6y ago
Nitpick, it's Poul Anderson. Yes, that is an odd spelling of his first name.
- ochrist 6y ago
  Not in Denmark where his family came from.
kwhitefoot 6y ago
Brilliant book! I recommend it highly.

dylan604 6y ago

And you're also never stopping anywhere, so it would only ever be a permanent sight seeing tour.

empath75 6y ago

Stopping is sort of a problem.

hellofunk 6y ago

> a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime Wow that is actually very fascinating, it never occurred to me that it works that way. I’m always thinking of 11 light years as too far away for someone to achieve in a lifetime, but I am of course thinking about that from the perspective of the person who is not traveling.

cmehdy 6y ago
I'm not sure how they calculate the 1g thing past the speed of light (which takes you something short of a year to get to by classical mechanics). But say we just break physics as we know it, and somehow the prophesized amount of time to travel is accurate. You're still going in a straight line and not stopping, unless you want to take another lifetime or be crushed by forces that would hurt just a little bit. So don't turn, only decide to stop in the first half of your life (or you won't live to see the end of the journey), beat light and physics by the end of year one of your life, and enjoy the ride. I'm not sure what you'll "see" outside of your spaceship though, and I do hope for you that there's not a single speck of dust in your path and no wall at the end.
- californical 6y ago
  I didn't read their idea, but you wouldn't ever need to go faster than the speed of light for this to work -- just approaching it infinitely close would be enough. Sure it might take a hundred million years for your journey from an observer watching you on earth, but thanks to time dilation, it could still be less than a lifetime for the person on the ship
  - cmehdy 6y ago
    Well then how do you get to the parts of our universe that are receding at a speed faster than light due to space expansion? I'm not nearly as comfortable with relativity as I'd like to be, but too much in this hypothetical "woahdude" scenario ends up being a logical roadblock to me.

deleted 6y ago

[deleted]

mikro2nd 6y ago

> only a challenge of propulsion Also a challenge of ablation. At any reasonable fraction of c your spacecraft has a serious erosion problem.

TheOtherHobbes 6y ago
Possibly also the challenge of getting baked by the Unruh Effect.

philipkglass 6y ago

This substitutes the challenge of inventing a warp drive with the challenge of inventing a limitless free energy machine. An antimatter fueled rocket can't keep up with what "1G, indefinitely" demands. Not even beamed power propulsion driven by a Dyson swarm can do that. I like the Revelation Space universe, but its fictional Conjoiner drive and the near-light-speed Lighthugger spacecraft powered by it are no closer to realization than any of Star Trek's technobabble. The same goes for the forever-accelerating Bussard ramjet vessel of Tau Zero.

bryanrasmussen 6y ago

what is one human lifetime? that seems an uncertain measure. Also most astronauts I've seen look like they're halfway through one human lifetime when they first get off planet.