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Relativistic Spaceship

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Re: Relativistic Spaceship

#401

Post by tsimionescu »

ben_w wrote: post #397
tsimionescu wrote: post #384

Earlier quoted context omitted.

Your fuel still gets consumed, so you still can't rely on your fuel as the main form of shielding. Towards the end of your journey, your rocket is approximately 0% fuel. And at the point of highest speed, before you start decelerating, it is roughly 50% fuel. And you are entirely wrong about the isotopes of hydrogen. Tritium is highly radioactive, with a half life of ~12 years. And it is not just hard, but virtually…

> And you are entirely wrong about the isotopes of hydrogen. Tritium is highly radioactive, with a half life of ~12 years. And it is not just hard, but virtually impossible to isolate tritium out of water. On the contrary, it's quite easy to do if there is any significant fraction of tritium present. The proportional mass difference of ³H vs. ¹H is x3, which alters the chemistry enough to make separation easy. You ca…

Oops, looks like reading the first Google result I could find wasn't the best way to research this topic... Sorry and thank you for the correction.

Re: Relativistic Spaceship

#402

Post by kypro »

TheOtherHobbes wrote: post #374
heads wrote: post #313

Earlier quoted context omitted.

If you’re doing 2e8 m/s, your ship is long and thin with a 1m3 nose cone, and space has 100 baseballs per m3 then you’re being hit by 2e10 baseballs a second. How do I get an idea for what 20 billion baseballs (2TJ) feels like? Apparently bullets are about an order of magnitude more energetic than baseballs (800J vs 80J) so I guess I could try to build my intuition based on being shot ~2 billion times a second instea…

It's clearly not a solvable problem with current ideas about technology. No amount of ice, rock, magnetism, or Magic Unobtanium is going to make this practical. I'm not even sure about warp drives. Bending spacetime one way means it has to squish back the other way. The energy released might not affect the ship - possibly - but I'd be surprised if it didn't affect the spacetime it had just passed through. Some kind o…

Am I wrong to think it seems probable that such things aren't realistically possible given the fact that the universe seems to be so lifeless?

If the practical limits of rocket technology don't allow life to much beyond their own solar system then given the vastness of space that would be a good reason why we don't see any evidence of intergalactic civilisations or large feats of engineering. All other explanations for why the universe seems to lifeless seem to rely on elaborate hypotheticals like us being an early civilisation, us being extremely lucky/improbable in other ways, or that alien life is anti-social. But it always seemed to me that the best explanation is probably just that such things are not possible.

I mean there's a chance there's some new physics out there, but you'd think if there was star wars level tech out there (warp drives, etc) then something out there would have built one already and would rather quickly spread outwards...

Re: Relativistic Spaceship

#403

Post by monkeydust »

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.

Its a true mind f*. A round trip would take the best part out of a normal human lifetime but it would appear that you have travelled over 55 thousand years into the future when you return the earth...assuming it's still there.

Re: Relativistic Spaceship

#404

Post by zardo »

function_seven wrote: post #174
abhibeckert wrote: post #152

Earlier quoted context omitted.

> 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.

Isn't this kinda like mounting a fan on your car's roof to charge the battery? You have accelerated your spaceship to 0.995C (or whatever) and now you are encountering space dust at a phenomenal rate. Some of that dust is moving away from you, some of it toward you, some of it is at rest. On average it's all just sitting there unaware that your vessel is about to smack into it. The energy is in the difference between…

I think in principle you should be able to generate thrust greater than drag orthogonal to the particle flow. That's what wings do.

Re: Relativistic Spaceship

#405

Post by bilsbie »

TheOtherHobbes wrote: post #374
heads wrote: post #313

Earlier quoted context omitted.

If you’re doing 2e8 m/s, your ship is long and thin with a 1m3 nose cone, and space has 100 baseballs per m3 then you’re being hit by 2e10 baseballs a second. How do I get an idea for what 20 billion baseballs (2TJ) feels like? Apparently bullets are about an order of magnitude more energetic than baseballs (800J vs 80J) so I guess I could try to build my intuition based on being shot ~2 billion times a second instea…

It's clearly not a solvable problem with current ideas about technology. No amount of ice, rock, magnetism, or Magic Unobtanium is going to make this practical. I'm not even sure about warp drives. Bending spacetime one way means it has to squish back the other way. The energy released might not affect the ship - possibly - but I'd be surprised if it didn't affect the spacetime it had just passed through. Some kind o…

Hydrogen is diamagnetic (1) so you’d just need the right level of magnetism to repel it (or slightly redirect it)

Or if we shape the field into a buzzard ramjet then you actually take advantage of the interstellar material for fuel.

(1) https://sciencing.com/magnetic-properties-hydrogen-7648446.h...

Re: Relativistic Spaceship

#406

Post by AlexAndScripts »

kreeben wrote: post #368
soco wrote: post #357

Earlier quoted context omitted.

There we go again, Americans using anything but the metric system :) scnr

>> baseball How large is one of those, even? I much prefer to work with perfectly spherical Olympic swimming pools.

Would that be the original British Imperial SOP or the closely-related but not-quite-the-same American SOP?

Re: Relativistic Spaceship

#407

Post by tim333 »

kypro wrote: post #402
TheOtherHobbes wrote: post #374

Earlier quoted context omitted.

It's clearly not a solvable problem with current ideas about technology. No amount of ice, rock, magnetism, or Magic Unobtanium is going to make this practical. I'm not even sure about warp drives. Bending spacetime one way means it has to squish back the other way. The energy released might not affect the ship - possibly - but I'd be surprised if it didn't affect the spacetime it had just passed through. Some kind o…

Am I wrong to think it seems probable that such things aren't realistically possible given the fact that the universe seems to be so lifeless? If the practical limits of rocket technology don't allow life to much beyond their own solar system then given the vastness of space that would be a good reason why we don't see any evidence of intergalactic civilisations or large feats of engineering. All other explanations f…

It seems reasonable, although we may still be able to send messages with radio, lasers etc. Though even that isn't easy.

Re: Relativistic Spaceship

#408

Post by canadianfella »

heads wrote: post #313
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…

If you’re doing 2e8 m/s, your ship is long and thin with a 1m3 nose cone, and space has 100 baseballs per m3 then you’re being hit by 2e10 baseballs a second. How do I get an idea for what 20 billion baseballs (2TJ) feels like? Apparently bullets are about an order of magnitude more energetic than baseballs (800J vs 80J) so I guess I could try to build my intuition based on being shot ~2 billion times a second instea…

[dead]

Re: Relativistic Spaceship

#409

Post by hnuser123456 »

lloeki wrote: post #325
jemfinch wrote: post #305

Earlier quoted context omitted.

It's impossible for your fact and the fact you're replying to both be true. Water is denser than butter, and the nearest star to the sun is about 4.3ly away; if your fact were true, the universe would be a black hole. A cubic lightyear is about 8.468e+50 liters, and butter weighs 911 g/L, giving the mass of a cubic lightyear of butter to be 7.714348e+50, whose Schwarzchild radius is about 121,103,293 lightyears, abou…

> if your fact were true, the universe would be a black hole ... maybe it is? Hear my pet theory out. Extrapolating backwards from the expansion of our universe, the Big Bang model posits a hyperdense state that exceeds black hole levels originating from a singularity, yet it's thought that somehow it did not collapse back, handwaving it as "physics as we know it did not apply". But maybe physics as we know it does a…

schwarzschild radius of mass of the universe (3.4 * 10^54 kg) = 5.05 * 10^24 km

radius of universe = 4.4 * 10^23 km (47b ly)

mass required to have schwarzschild radius of 4.4 * 10^23 km = 2.96 * 10^53 kg

Surely we are still discovering the implications of these numbers being so close.

I like your time-reversed black hole framing, thanks for that.

https://www.wolframalpha.com/input?i2d=true&i=+schwarzschild +radius+of+mass+of+the+universe

https://www.wolframalpha.com/input?i=radius+of+universe

https://www.wolframalpha.com/input?i2d=true&i=+schwarzschild +radius+of+2.96*Power%5B10%2C53%5D+kg

Re: Relativistic Spaceship

#410

Post by ben_w »

tsimionescu wrote: post #401
ben_w wrote: post #397

Earlier quoted context omitted.

> And you are entirely wrong about the isotopes of hydrogen. Tritium is highly radioactive, with a half life of ~12 years. And it is not just hard, but virtually impossible to isolate tritium out of water. On the contrary, it's quite easy to do if there is any significant fraction of tritium present. The proportional mass difference of ³H vs. ¹H is x3, which alters the chemistry enough to make separation easy. You ca…

Oops, looks like reading the first Google result I could find wasn't the best way to research this topic... Sorry and thank you for the correction.

Happens to us all, thank you for being gracious about it :)
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