Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Relativistic Spaceship

dmytry.github.io

Post reply on HN
Print view View original

181–190 of 500 posts

Re: Relativistic Spaceship

#181

Post by pests »

naikrovek wrote: post #158
carpdiem wrote: post #105

Earlier quoted context omitted.

Doesn't really work this way. A lot of the wonkiness in SR is tied to the fact that the speed of light is the same, measured in _any_ reference frame. So, say you're on earth and you measure the speed of light... you find that it's c (~3x10^8 m/s). Now you get on a spaceship and accelerate to 0.5c with respect to earth, and you measure the speed of light relative to your spaceship... still c! In this way, you can't r…

So depending on how you measure, you’re always stationary or moving near light speed, or somewhere in between, depending on your measurement reference (the thing you’re moving relative to)? How is there a speed limit at all, if that’s the case? You can accelerate to 0.5c and then toss an apple out the window and say you’re moving at the speed of an apple tossed out of the window, relative to the apple. You have all o…

There is no underlying reference frame. All motion is relative. Everyone, no matter how fast they are already going, will measure the speed of light as c. Accelerate to .99c and shine a flashlight in front of you. That light is moving ahead of you at the speed of c. Because to you, you are not moving.

Re: Relativistic Spaceship

#182

Post by JumpCrisscross »

ithkuil wrote: post #175
JumpCrisscross wrote: post #161

Earlier quoted context omitted.

> takes the same amount of time to slow down as it did to speed up Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.

That is doable for "normal" speeds, not one where you accelerate 1G for twenty years, reach relativistic speeds that make you travel for hundreds of thousands of light-years in merely 20 years ship time

> doable for "normal" speeds, not one where you accelerate 1G for twenty years

It's still a lot of energy you can bleed off, particularly if you're aiming for a system with gas giants. I'm not suggesting one only rely on passive deceleration. But especially given it's fuel saved at the very end of the journey, fuel you no longer need to accelerate and decelerate for the entire duration of the trip, the savings could be sizeable.

Re: Relativistic Spaceship

#183

Post by JumpCrisscross »

dylan604 wrote: post #164
JumpCrisscross wrote: post #161

Earlier quoted context omitted.

> takes the same amount of time to slow down as it did to speed up Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.

Right, because space is known to be full of atmospheres to use to slow down. ???

> space is known to be full of atmospheres to use to slow down

The places people talk about travelling to tend to have atmospheres and gravity, yes.

Re: Relativistic Spaceship

#184

Post by amelius »

abhibeckert wrote: post #152
MilStdJunkie wrote: post #26

Earlier quoted context omitted.

Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…

> Every proton would have the energy of a baseball I wonder if you could capture that energy and use it to generate thrust. Most of the energy is coming from your thrust so it'd be a lossy process however if you're able to capture all of the energy then there won't be anything left to damage the ship.

This is a bit like driving into a brick wall, and then asking if you could use the released energy to go faster ...

Re: Relativistic Spaceship

#185

Post by [deleted] »

ithkuil wrote: post #173
JumpCrisscross wrote: post #160

Earlier quoted context omitted.

> always face the exhaust in that direction! It's not rocket science! You don't see a problem with trying to accelerate with two exhaust streams at 180º to each other?

What if the front one is only a small fraction of the thrust at the rear? Would that be enough to "clear the path". Surely it would cost some efficiency but it may beat he alternative

[deleted]

Re: Relativistic Spaceship

#186

Post by robbomacrae »

crazygringo wrote: post #80
robbomacrae wrote: post #20

This is something I've wanted to try in VR one day. Does anyone know if there is an app/game available for one of the popular headsets? Is there a technical limit to how realistic the effect could be?

You won't be able to perceive anything "3D" if you're aiming for accuracy. Even though we can perceive the "depth" of the stars through motion in this simulation, every star is still going to look equally far away, because their positions won't change between the left and right eyes. The same way we can't perceive the sun as further away than the moon -- depth perception merely tells us they're both "max far away". Y…

Yeah I figured that would be the case. I still think it would be really cool effect to see anyway if you could go fast enough and experience the motion parallax of the stars. No offense to this project as it's really impressive.

Re: Relativistic Spaceship

#187

Post by stavros »

naikrovek wrote: post #158
carpdiem wrote: post #105

Earlier quoted context omitted.

Doesn't really work this way. A lot of the wonkiness in SR is tied to the fact that the speed of light is the same, measured in _any_ reference frame. So, say you're on earth and you measure the speed of light... you find that it's c (~3x10^8 m/s). Now you get on a spaceship and accelerate to 0.5c with respect to earth, and you measure the speed of light relative to your spaceship... still c! In this way, you can't r…

So depending on how you measure, you’re always stationary or moving near light speed, or somewhere in between, depending on your measurement reference (the thing you’re moving relative to)? How is there a speed limit at all, if that’s the case? You can accelerate to 0.5c and then toss an apple out the window and say you’re moving at the speed of an apple tossed out of the window, relative to the apple. You have all o…

> You can accelerate to 0.5c and then toss an apple out the window and say you’re moving at the speed of an apple tossed out of the window, relative to the apple. You have all of c available as headroom again? You can accelerate up to 0.5c again, relative to the apple you tossed out the window?

Yes you can. You can even do it with 0.6c for both those speeds.

Re: Relativistic Spaceship

#188

Post by goblinux »

CobrastanJorji wrote: post #169
A_D_E_P_T wrote: post #39

~850 years of ship time at max acceleration and the universe is 10^30 years old. At this point, only white dwarfs, neutron stars, and various stellar remnants remain. Galaxies have dissipated, and stars like our Sun are a distant memory. (If any still exist to remember them. Which is, I'll add, not out of the question. Life can cling to structures built around black holes, white dwarfs, etc., and extract energy from…

You could imagine a technically advanced society using it as a sort of penal death sentence. "You were not safe around our people, so we are sending you to the end of time."

Isn’t that the plot of Skyrim?

Re: Relativistic Spaceship

#189

Post by savef »

I don't care so much about the physics side, it's just so bloody pretty. Is there anything like this that will play infinitely, with similar sliders to tweak the visuals? It'll look so good on an OLED.

Re: Relativistic Spaceship

#190

Post by wiml »

abhibeckert wrote: post #152
MilStdJunkie wrote: post #26

Earlier quoted context omitted.

Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…

> Every proton would have the energy of a baseball I wonder if you could capture that energy and use it to generate thrust. Most of the energy is coming from your thrust so it'd be a lossy process however if you're able to capture all of the energy then there won't be anything left to damage the ship.

The old Bussard ramjet concept was to capture these high velocity protons (with some kind of magnetic field), cause them to fuse, and use the fusion energy for propulsion.

There are a few engineering difficulties with the idea but it makes for some good SF stories...

Post reply on HN