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Comment by marcyb5st

12 hours ago

Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms.

If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you reach what today is considered the edge of the observable universe.

By the time you get there you are basically traveling at a rounding error from C.

36 comments

marcyb5st

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ExoticPearTree  11 hours ago

> If you accelerate at 1g constantly for 1y you travel 0.5 light years

Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

  • TheOtherHobbes  10 hours ago

    We can't do it with any rocket-like propulsive technology. By the time you get anywhere close to c the front of your spacecraft is being abraded into nothing by interstellar gas, larger particles of dust will kill you, and colliding with anything bigger creates an explosion that can be seen for light years. You need to be flying a large asteroid to even think about surviving it - you still won't for long, but you will have time to think about it - and the energy requirements are wildly impractical.

    Magic warp bubble tech is the bare minimum, and we're nowhere close to inventing that.

  • myrmidon  10 hours ago

    Sadly there is no realistic approach to get there (even assuming fantasy-levels of technology).

    Chemical rockets are currently the only thing that allow sustaining such accelerations briefly for human-size payloads, but the low exhaust velocity and exponential reaction mass requirement make sustaining it for days/months/years completely impossible.

    You'd have to supply the energy externally (i.e. some sort of beam propulsion), but getting any significant fraction of g out of such a system (with human-sized payloads) seems unlikely within the next centuries, especially as the distance increases.

    • consp  10 hours ago

      > You'd have to supply the energy externally (i.e. some sort of beam propulsion), but getting any significant fraction of g out of such a system (with human-sized payloads) seems unlikely within the next centuries, especially as the distance increases.

      Or some form of ram scope, plenty of H everywhere, but those also have the issue of you collecting things while going at relativistic speeds.

      1 reply →

  • wallst07  11 hours ago

    We can easily accelerate past 1g... 1g is just chosen for human comfort, but running any rocket engine continuously for a year requires an impossible amount of fuel.

  • 40four  8 hours ago

    Not with current technology. That was kind of the physics “trick” in the book ‘Project Hail Mary’, where the astrophage provided enough energy and propulsion to be able to sustain 1G of acceleration.

  • jdjfbfbdbfnf  11 hours ago

    We need a massive rocket to escape the earths gravity (1g). That takes us minutes and a crap ton of fuel. The issue is to keep doing that with fuel and oxidiser constantly for 1, 2 or 10 or 25 years is a monumental amount of energy, which is a monumental amount of weight, which is a monumental amount of volume... Also you also need the exact same amount of fuel to stop again.... So yeah ... We don't got it yet

  • SideburnsOfDoom  1 hour ago

    > Can't we accelerate past 1G constantly?

    It's hard to accelerate at or beyond 1G for very long with current technology. Roughly speaking, the rocket runs out of fuel soon. Packing more fuel makes the rocket heavier, meaning diminishing returns when using the fuel. The mass required grows exponentially. See "The tyranny of the rocket equation"

devld  6 hours ago

> You do that for 10.5 years and you reach the center of the milky way

But that would be pretty pointless without taking the time to decelerate :)

rrr_oh_man  11 hours ago

> math get's really counterintuitive to grasp

People always say that about speed of light stuff, but I don’t get it. Do you have any more examples of counterintuitive math?

Because what you’re describing is basically the equivalent to compound interest in finance. (e.g. investing $100 at 10% interest over 10 years results in $260)