Coming here from another star system in a reasonable time would require more energy than they'd get by turning every planet in the solar system to energy with perfect efficiency. There are no exotic elements here that aren't present everywhere in the universe.
What resources could a space-faring civilization need that earth has?

Well, maybe they'll want to build a hyper-space bypass through here.

[–] Ludicrous0251@piefed.zip 7 points 17 hours ago (1 children)

Coming here from another star system in a reasonable time would require more energy than they'd get by turning every planet in the solar system to energy with perfect efficiency.

... I'm not sure that's right. If you're in the convert matter to energy game, you can go a long way with just a little bit. That c^2 bit of e=mc^2 is obscenely massive, and most importantly, since your kinetic energy is 1/2mv^2, efficiency and relativistic limitations aside, to get something going close to the speed of light you need to convert roughly the same amount of mass to energy for propulsion.

There's some nuance there, but even 100:1 means you could get a ship the size of Manhattan traveling at near light speed for a good sized asteroid of mass. No need to fuck with planets.

[–] mech@feddit.org 3 points 17 hours ago (2 children)

The rocket equation is a bitch.
If you want to accelerate close to c, brake at earth, then do the same thing again on the way back, you'll need to carry a planet mass worth of fuel at launch, just to propel a small craft.
And then you still haven't done anything productive in our solar system.

[–] OwOarchist@pawb.social 5 points 15 hours ago

The rocket equation assumes you need to bring all your fuel with you.

But with things like laser-propelled light sails, you might be able to propel the ship with energy the ship doesn't need to carry.

[–] MalReynolds@slrpnk.net 4 points 15 hours ago* (last edited 15 hours ago) (1 children)

Look at Bussard Ramjet. Why would you carry your fuel with adequately advanced technology (let alone zero point quantum stuff)

Shields are much more interesting near c.

[–] mech@feddit.org 3 points 15 hours ago (1 children)

Shields are another thing: How do you protect your hull from the protons that hit it at relativistic speed?

[–] sunnie@slrpnk.net 3 points 11 hours ago

Any problem is solvable with unlimited energy at your disposal. Protons are charged so you divert them with an electric field. If you’re using a ramjet for propulsion, you collect them to fuse. The incoming velocity could be a benefit there.

[–] OwOarchist@pawb.social 1 points 15 hours ago* (last edited 15 hours ago)

in a reasonable time

What a 'reasonable' time is may depend heavily on perspective.

If the aliens are robotic/electronic in nature (perhaps having long ago replaced their biological predecessors), long timescales may mean nothing to them. Simply go into 'sleep mode' until the ship arrives. Or not ... a robot might have no concept of 'boredom' and no problem remaining fully conscious for however long it takes to slowly cross the distance.

If the aliens naturally have very long lifespans, they may view a travel time of 500 years as 'reasonable' for such an important voyage.

If they have some sort of 'hive mind', where a large group of them can consider themselves a single individual (or even just a very collectivist culture), then they may see no issue in crossing interstellar distances in a 'generation ship' where only the eventual descendants of the original crew will reach the destination.

If they've perfected some sort of anti-aging technology and/or the ability to freeze themselves in stasis, they might see a long travel time as relatively unimportant. If they live indefinitely long and are already thousands of years old, what's a few hundred years of spaceflight? If they can freeze themselves (literally or figuratively) and wake up when they're about to arrive so that the subjective travel time is only a few hours, they may see that as worthwhile.

would require more energy

... if done by any technology we know or could dream up with our current understanding of physics.

But we already know our understanding of physics is fundamentally incomplete. We don't know what dark matter or dark energy are. We don't have a reliably working theory of quantum gravity. We haven't managed to join quantum physics and relativity together yet in any functional way.

It's highly speculative, of course, but we can't rule out the possibility that aliens with a better understanding of physics might be able to develop a way to travel at extremely high speeds without needing as much energy as our current physics suggest it would require.

The amount of energy required also greatly depends on the mass of the ship making the journey. It's possible they could reduce the energy requirement by miniaturizing their spaceship. Say, a very small robotic probe capable of self-replication, and carrying blueprints for building more macro-scale technology and possibly rebuilding the aliens themselves. The tiny spaceship can then be accelerated to very high speeds with relatively little energy. When it arrives (say, on the far side of the moon), it can then harvest local resources to replicate itself into an army of builder bots, and then use more local resources for those builder bots to assemble a proper alien ship/base, complete with aliens inside. With this strategy, all you need to carry is enough machinery to build a copy of the probe + data storage to contain all the blueprints. Conceivably, that could all be achieved in a very small package, perhaps even microscopic -- after all, self-replication and data storage are things that microscopic single-celled organisms can do on earth. In theory, there's no reason a microscopic robot couldn't do the same things. You could achieve extremely high velocities with relatively little energy if your spaceship was, say, 1cm in diameter and weighed less than half a gram.