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Relativistic Spaceship

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Re: Relativistic Spaceship

#261

Post by pants2 »

ryandrake wrote: post #27
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.

Sure, there are plenty of practical problems that would make the trip impossible. The fuel mass alone that would have to be shot out the back to make that trip would be something on the order of 800 million times the mass of the payload (you). So a 100kg person sitting in a 100kg spaceship would require something like 160 billion kg of fuel, assuming zero energy loss in burning the fuel. Relativistic rocket calculato…

Fun fact: if you got 250 MPG in a space car loaded up with as much gasoline as there is water in the ocean, you could could drive to the edge of the observable universe.

Re: Relativistic Spaceship

#262

Post by huytersd »

tempestn wrote: post #235
huytersd wrote: post #214

Earlier quoted context omitted.

Time travel seems so easy and we could do it with the tools we have now for the most part. Maybe we’ll never go into the past but relatively contemporary humans are going to be all over the future in all kinds of places. After the first time it happens people in the future can start to expect a human from the past to keep visiting every so often.

If that did start happening, it's not like the people from the past would just pop up suddenly. We would be aware of their journey. It's not like a time machine where someone just disappears from the past and appears in the future.

Sure, and we would probably be able to tell when they were from based on the approaching crafts. It’s going to be amazing to be able to step 50,000 years into the future to see how humanity has turned out. I’d give up anything to have a chance at that.

Re: Relativistic Spaceship

#263

Post by Dylan16807 »

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.

> 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.

If we're still talking about Star Trek, then on a solar scale those ships can stop on a dime. They're not going to hit an unmapped planet while putting around.

Re: Relativistic Spaceship

#264

Post by Terr_ »

AlexAndScripts wrote: post #15
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.

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.

I wonder how fast the interstellar medium of gas etc. drifts and flows... could sacrificial sweeper-ships drill out a less-dense-holes for other traffic on a reasonable timescale?

Re: Relativistic Spaceship

#265

Post by timschmidt »

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

Whipple shields [1] don't weigh much, and don't involve negative acceleration of any kind.

1: https://en.wikipedia.org/wiki/Whipple_shield

Re: Relativistic Spaceship

#266

Post by chuckhend »

JumpCrisscross wrote: post #161
dylan604 wrote: post #159

Earlier quoted context omitted.

Or stopping. It takes the same amount of time to slow down as it did to speed up. Presumably, you'd have to rotate 180° so you are now thrusting in the opposite direction. So at the speeds you've reached to get there in 20 years (ship time), you'd just race on by.

> 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.

We'd still be limited by however many Gs human body can handle right?

Re: Relativistic Spaceship

#267

Post by scubbo »

eru wrote: post #201
hotpotamus wrote: post #144

Earlier quoted context omitted.

From memory, photons are massless, otherwise they could not move at light speed. They do have momentum though.

Photons have mass, but no rest mass. (Or something like that.)

Momentum but no mass, if I recall my physics correctly (low certainty).

Wait, hang on, we have access to an appreciable-chunk of the world's knowledge at our fingertips...

https://en.wikipedia.org/wiki/Photon - "Photons are massless[...]In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p[...]Current commonly accepted physical theories imply or assume the photon to be strictly massless"

Re: Relativistic Spaceship

#269

Post by TaylorAlexander »

MilStdJunkie wrote: post #26
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.

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…

What do you mean “the energy of a baseball”? A baseball at what speed?

Re: Relativistic Spaceship

#270

Post by tempestn »

huytersd wrote: post #262
tempestn wrote: post #235

Earlier quoted context omitted.

If that did start happening, it's not like the people from the past would just pop up suddenly. We would be aware of their journey. It's not like a time machine where someone just disappears from the past and appears in the future.

Sure, and we would probably be able to tell when they were from based on the approaching crafts. It’s going to be amazing to be able to step 50,000 years into the future to see how humanity has turned out. I’d give up anything to have a chance at that.

You could always take a flier on cryonics.
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