[heads]

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 instead. A kiloton of TNT is 4GJ, so it’s also like a 500 kiloton bomb going off every second.

Dropping 5e5kg of rock into the worlds biggest dumpster truck at 10m/s yields 25MJ of chaos so it’s also like a parking lot of 80,000 of those being filled with a continuous stream of rubble. That’s probably the best analogy given that we’re talking about machinery — your spaceship needs to have the build resilience of tens of thousands of dumpster trucks but condensed into the cross sectional area of a dinner table.

[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.

[khazhoux]

> How do I get an idea for what 20 billion baseballs (2TJ) feels like?

In the 90s, the show Special Relativity’s Funniest Home Videos would often have guys getting hit in the crotch 20B times with a baseball. Honestly, it never gets old.

[mattmaroon]

They all started to look staged after the first billion though.

[kaashif]

> A kiloton of TNT is 4GJ, so it’s also like a 500 kiloton bomb going off every second.

Funnily, my first reaction to this comparison is that it makes it seem more plausible to me that this is possible. After all, a Star Destroyer can take gigaton level hits!

But the problem with that is Star Destroyers are fictional.

I've been spending too much time on spacebattles.com.

[MilStdJunkie]

The canon energy levels given for Star Wars weaponry are so inconsistent with the presentation that one either ignores canon or accepts that the Star Wars galaxy has fundamentally different physics.

Extreme geek caution: I've been running a Star Wars pen and paper RPG since . . oh dear. . 2015, in an ancient simulationist[1] game system, and the only way I've been able to make anything consistent is dialing everything down to WW2 levels. 7.62x5X, .50 BMG, 46 cm/45 Type 94 capital ship weapons. All except for exceptional plot items, like lightsabers and doomsday weapons, which behave . . well, they're magic. Sensors are likewise pretty primitive, enhanced with canon exotics like Kronau radiation, so engagement ranges are (relatively) piddling, hostiles zip by each other all the time. Electronics and technology in general must be barely understood by literally anyone, with the powerful assemblies - hyperdrive cores, droid motivators, repulsorlift "sand" - being exotics, possibly xenotechnology from the deep past mined by xenoarchaeologists[2], but hooked together by varying degrees of "competent 1950s electrician".

In short, it's a fantasy setting with guns that players get excited about. And a community of worldbuilders that is, let's not dice words here, insane. That second point is huge if you're not 24 or otherwise gifted with a combination of hubris and spare time.

[1] All the kids today with their streamlined narrative-focused games! Seriously, though, I get it. The physics simulationist in me that brings me to HERO System says more about me as a person than my players.

[2] Archaeology a much more valuable degree in the Star Wars universe.

[ben_w]

Your description reminds me of Star Fleet Battles. As a young teen I made the mistake of treating SFB like Star Trek, while also making the mistake of not realising that Star Trek itself was just doing space combat as ${year of filming}-era naval battles with latex and lightbulbs.

SFB is 1900-1945 naval warfare, but themed with every plot point from TOS and TAS and probably some novels too, so has the Kzinti, Tholian webs, Klingon stasis field generators, and two distinct weapons where the TV series uses just photon torpedoes.

[heads]

The numbers are big but they don’t seem “big big” like Sagittarius A* is big or the distance to Andromeda is big.

[lstodd]

Distance to Andromeda isn't big.

Galaxy filaments are big.

[greggsy]

Could you repeatedly send disposable ‘dozer’ drone ships towards your destination to help clear the way, and potentially devise a means of keeping the clearing free of stray atoms?

[bufferoverflow]

No, interstellar atoms (or other particles) aren't static, they aren't just hanging in one place. Everything is moving. Some particles are moving very fast.

[soco]

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

[heads]

I’m British with, funnily enough, a Duke’s County cricket ball on my desk.

My nephew is Californian and I gave him one for his sixth birthday. Mine felt a bit lighter so we did an experiment over Zoom together to measure the density. He’s certainly a bit young for that — “it’s the same size but yours is heavier” — but there’s no harm in influencing them from an early age.

Of relevance to your comment: I made a point of doing it in grams and millimetres.

[kreeben]

>> baseball

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

[AlexAndScripts]

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

[db48x]

Actually, the American SOP is the original because the British changed the definition of the gallon in 1824, which you will notice is long after the Revolutionary War. No one in America cared, so we kept on using our customary units.