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Relativistic Spaceship

dmytry.github.io

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Re: Relativistic Spaceship

#251

Post by ryandrake »

gosub100 wrote: post #222
naikrovek wrote: post #158

Earlier quoted context omitted.

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…

> so c relative to what? it's either "relative to any observer." or "relative to any inertial reference frame". no matter where you go (on the ship, on a planet you pass by, on another ship) you will never see the apple travel as fast as the photons coming out of your flashlight. Depending on where the observer is, they will see the apple accelerate to 0.5c (if they are aboard the ship) or they will see it gain mass…

If you want to explore/understand the velocities of these relativistic apples, look into the Velocity-addition formula[1].

1: https://en.wikipedia.org/wiki/Velocity-addition_formula

Re: Relativistic Spaceship

#252

Post by wholinator2 »

bhickey wrote: post #236
steffenfrost wrote: post #234

Earlier quoted context omitted.

Couldn't you shoot an electron bream ahead of the ship to ionize the atoms and the deflect them with a magnetic field?

Briefly: No. I read a paper on the topic a few years back. My recollection is that once you go faster than about 0.3c it becomes impossible to shed heat faster than you gain it from collisions with Helium. I'll try to dig it up.

I'm interested if that's physically impossible or just currently technologically impossible

Re: Relativistic Spaceship

#253

Post by qsi »

caturopath wrote: post #93
AlexAndScripts wrote: post #15

Earlier quoted context omitted.

I suppose you would also have to worry about surviving the trip - every atom in the interstellar medium would damage your ship, likely penetrating the entire way through, and electromagnetic repulsion would only work with charged particles.

Why not just increase power to the main deflector?

Because you need to reverse the polarity first.

Re: Relativistic Spaceship

#254

Post by jtriangle »

caymanjim wrote: post #150
jtriangle wrote: post #17

Earlier quoted context omitted.

~9.8 m/s sounds pretty comfortable.

You're accelerating at 9.8m/s^2 toward your chair right now, so it depends on how comfortable the chair is.

Bold of you to assume I'm not standing on a Uline rubber anti-fatigue mat

Re: Relativistic Spaceship

#256

Post by badosu »

eh_why_not wrote: post #107

Beautiful! For the comments saying we "just" need to maintain a 1G acceleration, should point out that as the ship approaches the speed of light, its mass increases [0]. And as the mass increases, so does the thrust required to maintain that acceleration. So that engine better be able to tap into some magical energy source, otherwise it can't maintain the acceleration at the higher speeds. :) [0] https://en.wikipedia…

The "increasing mass" stuff is more to make it easier for calculations and learning (with imo terrible consequence to physical intuition) than an actual physical concept.

This video does a good job talking about the issue: https://www.youtube.com/watch?v=6HlCfwEduqA

Re: Relativistic Spaceship

#257

Post by dtgriscom »

jcadam wrote: post #125
ryandrake wrote: post #12

Great visualization of the unintuitive nature of special relativity. It's kind of mind blowing to realize that if we could accelerate our spaceship at a mere 1G continuously, we could visit the center of the Milky Way in under 20 years (spaceship time), totally do-able in a human lifespan. Of course 27900 years would have passed on Earth, so you wouldn't be able to tell anyone about your vacation.

Could use such a ship as a time machine (well, that only goes one way).

My comfy chair is a one-way time machine.

Re: Relativistic Spaceship

#258

Post by StevePerkins »

cameron_b wrote: post #225
eru wrote: post #199

Earlier quoted context omitted.

Planets are tiny compared to the vastness of space. So you would never accidentally warp inside a planet.

If we’re talking about the known universe, the odds of your near-light navigation accidentally clipping a not-mapped-yet planet are certainly not zero. Our gaze into the heavens is much better at spotting stars than their dark orbiting bodies, and we have fingers left over from one hand counting the number of observation platforms observing deep space from above our shimmering atmosphere.

Indeed. We can't even agree on whether or not there's an extra Neptune-sized gas giant out beyond the orbit of Pluto, and that's right here in our OWN solar system!

Re: Relativistic Spaceship

#259

Post by EA-3167 »

eru wrote: post #211
EA-3167 wrote: post #168

Earlier quoted context omitted.

It would be cheaper in every sense to turn something like a giant asteroid into a rotating habitat ship than achieve a constant 1g to even the closest systems. Realistically interstellar travel is not a thing that (biologically modern) humans will ever be suited for, robotic probes don't need thousands of kg of food and water to stay alive, don't need artificial gravity, air, or entertainment. The fact that the trip…

You are right. One addendum: many humans would be bothered by one-way trips, but humanity is large, and in absolute numbers there are still plenty of volunteers for one-way trips to the planets and stars.

When talking about how efficient a given reaction mass engine, such as a rocket, can be the unit is specific impulse in seconds. That unit represents how long a given engine carrying a given propellant can maintain 1g acceleration.

For context, the most powerful chemical rockets peak around 450s-530s. A nuclear rocket of the sort we can build today would be more than twice that value, and super-efficient ion thrusters can have IspS in the tens of thousands of seconds.

But we're talking about an engine with a specific impulse measured in decades, and as far as anyone knows that means having catastrophic amounts of antimatter. I don't think plucky explorers on a one-way trip are going to have access to a small moon's worth of antimatter, and if they did, imagine how many more interesting things they could do with it than fly to nowhere?

Re: Relativistic Spaceship

#260

Post by sriku »

The viz shows visible light, but you'll be basking in gamma and more energetic photons as they've all shifted up. It does note that infra red shifts into visible light. I wa swondering whether the perspective change is accurate as the length contraction should've brought everything much closer.
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