[TheOtherHobbes]

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 of new physics might make all of this possible, but - by definition - we have no idea what that might be.

[db48x]

Worse, it has deleterious effects on the spacetime inside the bubble too. The leading edge of the bubble has exactly the same curvature as a white hole, and the back edge is exactly like a black hole. The result is a beam of Hawking radiation between them. Expect temperatures on the order of 10³⁵K if you manage to stabilize the bubble, but note that this amount of radiation is much more than enough on its own to destabilize it. <https://en.wikipedia.org/wiki/Alcubierre_drive#Survivability...>

So not only do you need “exotic” matter with negative mass to bend spacetime into a warp bubble, the bubble itself creates so much radiation that spacetime is flattened back out again.

[MilStdJunkie]

It's been literal decades since I saw it, but the premise of K-Pax always seemed neat: aliens move their consciousness around through some sort of superliminal signal[1], but it looks an awful lot like madness to us humans.

Until he starts solving cosmological problems . . I sort of felt like the truth of the matter should have been more ambiguous than was presented. More Shining, less Friday the 13th.

I remember the premise being far superior to the film, but maybe the novel is worth a look.

[ijustlovemath]

The theoretical Alcubierre drive basically collects all of the material you would intersect with in a gravitational well ahead of the vehicle as you travel, which is great!

...until you stop, releasing all of that mass as a gargantuan amount of energy at your landing site.

[lobocinza]

Would make an effective weapon.

[bilsbie]

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...

[foobarbecue]

I imagine you got "autocorrected" but to slow the error propagation I'll point it that it's a "Bussard" ramjet, not "buzzard."

[LorenPechtel]

Well, a Bussard ramjet has been shown to have a maximum possible velocity of .12c. No idea if a buzzard version can do better. :)

[kypro]

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...

[dsign]

There is so much we don't know. But I would happily engage in speculation:

- Without needing to make it to the closest star, we have big problems here. If we solve those problems before we leave our solar system, we may be changed beyond recognition. We may not be biological any longer, for example, or at least not forcibly so, and traveling as solid matter may seem silly to our future descendants.

- We don't understand well enough the nature of reality. For all we know, our machines and organisms made of atoms and molecules may be, by far, more inefficient and wasteful than an equivalent process at some other layer or scale. Like somebody who discovers themselves living inside a match box in a forgotten attic, we may decide to move to the more spacious main floor of the castle.

- A variation of the above: maybe space-time itself is something we use inefficiently. It could be that a way to stop being troubled by the slow speed of light is by lowering our own "life" speed, increasing our volume to span entire solar systems, and decrease our density so much that your ancestors would confuse us with sparse interstellar matter. Or, at the opposite end, it could be that we find a way to move our entire future civilization to a cubic centimeter of space and a few microseconds that feel like eons.

[hetman]

I don't think you need such extreme relativistic speeds to obtain the desired result though. The above assertion that every proton would have the energy of a baseball puts us at a rather incredible speed. A quick Google gives the energy of a baseball pitched at 90 mph to be around 117.4 J. For a proton to have the equivalent relativistic kinetic energy would put it at 99.999999999999999999999918% the speed of light!!

Now let's take a much more reasonable speed like 10% the speed of light. Assuming the 100 protons per cubic meter figure above, each square metre of ship now only needs to dissipate 2.27 mW of energy. 10% the speed of light is enough time to reach Alpha Centauri within a single lifetime (42 years). And fast enough to visit every part of the galaxy in less than a million years. We could even imagine generational ships travelling at 1% the speed of light (now the energy dissipation demands are 2.25 μW per square metre of ship surface). That's still under 10 million years to colonise the entire galaxy.

If intelligent life is abundant in the galaxy then I don't think the speed of spaceships at least offers a fundamentally insurmountable technical challenge for that life to spread everywhere.

[adrianN]

Sending humans across thousands of light years seems almost impossible , but sending von Neumann probes throughout the galaxy should be possible with some reasonable improvement to our technology.

[sydbarrett74]

Yes. That's my assumption: a sufficiently advanced race won't send members of its own species into the inhospitable furthest reaches of space, but rather probes that can report data back to the home-world. That was always my issue with the Kardashev Scale: isn't the technological level of a species better dictated by how little energy they use to accomplish some goal?

[db48x]

Von Neumann probes don’t just send information back, they reproduce themselves. Anything that can manufacture a copy of itself from materials scavenged in unexplored territory can probably build anything else you want as well. A Kardashev II civilization would build a Dyson swarm around it’s own star (or one near by if they are cautious) and use a fraction of its power to send self–replicating Von Neumann probes to a few hundred or thousand nearby stars and galaxies. Those probes would build not just copies of themselves but new Dyson swarms to launch them with. Once the Dyson swarm is built there is plenty of energy available to do all kinds of things, like moving planets around, terraforming them, and seeding them with life.

[tim333]

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