In Portal, using the portal gun to get to the moon is the obvious space travel usage, but I think people are overlooking how it’d let you trivially break the rocket equation.
Hell, you could build a >1g torchship using nothing but the ocean.
@[email protected] drop a magnet in a cylinder with a portal at the top and bottom, and you have a free infinite-power generator (assuming the portals take nearly no power, and you’re in an accelerating reference frame)
Take your >1g water-torch ship, use it to kickstart the generator above, use the power from that to accelerate ions in a cylinder (with a portal at top and bottom). Eventually, your ion-based thrust is enough to cutoff the ocean portal. Reactionless thrust! + Particle beam cannon on-demand
@[email protected] Would you even get thrust, and not just a hole in the universe spewing water out? That mass isn’t actually part of the ship at any point, it’s in the ocean and then out in space. So the momentum of the ship doesn’t actually change
@[email protected] does the atmosphere (or vacuum) crosses portals? Because it would be a kind of problem…
@[email protected] yep! It does.
@[email protected] Infinite energy too by perpertual motion.
Portals break everything…
@[email protected] You say it’s obvious, but the first time I played Portal 2, I was rushing to finish it and wasn’t listening to the Cave Johnson dialog closely, didn’t put two and two together that portal paint was made with moon dust, and at the end of the final boss, I hesitated long enough before figuring out that I was supposed to shoot the moon that any tension in that moment was ruined as the game just sat and waited for me.
@[email protected] Yes, but if everyone built 1g torchships pretty soon there’d be no oceans! Much better to use Jupiter instead: nobody will miss it, right?
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I seem to recall Jupiter is the reason we only have planet destroying asteroids every half a billion years or so…@[email protected] @[email protected] planet destroying asteroids are the kind of thing that only civilizations without relativistic impactors have to worry about.
@[email protected] @[email protected] good point!
@[email protected] @[email protected] most of the water harvested from Jupiter would be burned getting away from Jupiter and eventually be recaptured by Jupiter because Jupiter is fucking massive
@[email protected] @[email protected] not if you’ve got portals! you can harvest remass from the bottom of a gravity well and transport it anywhere, for free!
@[email protected] @[email protected] oh, put the planteside portal low in the gravity well where the atmospheric pressure matches your requirements and have the shipboard aperture vent directly into space, won’t even need to torch it
…it would very slightly suck the gas giant towards the planetside portal though
@[email protected] @[email protected] As long as you only use it sparingly, climate change induced ocean level increase isn’t an issue. Probably doesn’t help with the rest of climate change, and when we inevitably don’t use it sparingly we get fun new environmental crises, but hey.
@[email protected] @[email protected] unfortunately the Half Life universe has the oceans already having dropped by a significant amount, because someone else (The Combine) is already draining the oceans. So using the ocean as remass is not the best idea, as easy as it is.
But yeah: you could use it just enough to get to Jupiter or some other source.
@[email protected] yeah!
Or there’s that possibility that Europa has more ocean water than earth, why not drain that? You can get there pretty easy with a torch ship…Or hell, with free thrust let’s just deorbit all the comets in the oort cloud into Mars and use the new Barsoom Ocean as our remass.
@[email protected] (I did think about jupiter more seriously but the problem is that you’d have to build a structure that could withstand the pressures of Jupiter’s atmosphere as it falls into the planet. That’s way harder than something that can survive the earth’s oceans, even if you would get more thrust out of it)
@[email protected] @[email protected] Why not just open a portal into the Sun?
@[email protected] @[email protected] Don’t drain Europa! It will anger the hyperintelligent squid there!
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that just provides an episode for our Torchship Explorers show. Captain Laser has to go help some ice miners working to set up a portal farm on the bottom of the European ocean, when their drills keep getting attacked, and the crew has to learn to communicate with the squids and figure out how to stop the miners from just going “fuck it” and poisoning the whole ocean.
@[email protected] Well, unless you want an empty ocean afterwards, you’d need some tricky engineering to make the backfeed portal work properly
I’d do the math on how much thrust you’d get out of sticking one portal at the bottom of the Mariana Trench and the other in a ship, but I think it’d maybe be slightly tricky because you’ve got yourself an inertialess thruster right there, which is slightly illegal according to physics.
The Einstein cops are gonna show up and impound your spaceship
@[email protected] I don’t think mass exiting through a portal imparts any thrust to the surface the portal is on, so not sure this works. but the remote fuel tank and the “infinitely falling object continuously pulls on gravitational partner” both seem legit to me. as well as the time travel implications.
And that’s just thinking about a static arrangement of portals. You could also use a dynamic arrangement where you use gravity to accelerate mass to arbitrarily high speeds and then fling it out the back
@[email protected] This is (spoilers!) one of the weaponizations of space magic in The Paranoid Mage indeed.
I think - I am a physicist but not a rocket engineer - that a portal wouldn’t propel anything.
Putting a portal on the underside of the spaceship and another in the deep ocean just makes the two of those places adjacent. The water would spray into space (and probably immediately freeze) but the reaction force wouldn’t be on the ship: there’s no water pushing back against it, after all. If there’s any reaction force it would be against the ocean.
If you could make portals bigger you could also have a fun setup where you build your spaceship and then just let gravity accelerate it though a portal-loop.
You get going as fast as you want, then just swap the portals so you’re now aimed at Mars.@[email protected] I seem to recall Larry Niven played with this stuff in his teleportation short stories in the 70s (notably “All the bridges rusting”). And I had fun with it in “Glasshouse”.
@[email protected] @[email protected] Peter F. Hamilton also uses the idea in a lot of various ways in his Salvation books. E.g. why deal with complicated propulsion systems when you can chuck the ingress end of a portal into a star and stick the egress end on the back of your ship.
@[email protected] @[email protected] A portal gun (with the other end of the portal inside the photosphere of a blue-white supergiant) makes a really neat blaster!
@[email protected] @[email protected] @[email protected] Backblast might make it a weapon of last resort, though.
@[email protected] @[email protected] @[email protected] true, but the fun part of a portal-ship is that there’s really no difference between a crewed lander and a remote-controlled doomsday missile.
if you land somewhere uninhabited and/or friendly, you can drop a portal and then send people through. if it’s unfriendly, you open the supergiant portal, and have the portal gun throw itself through a return-home portal that instantly closes. you build another ship
@[email protected] thread a rope with a weight through two vertical portals so the rope is pulled through infinitely as the weight drops.
Now you have infinite rotational energy to run a generator and the thermodynamics police are definitely going to break down your door
@[email protected] I get the feeling it would be amazing for some fraction of a second before either:
Relativity smacked you in the face
Friction did it’s thing
Physics gets angry and stops the earths rotation around the sun
Or
The people running this simulated universe turn it off and patch that bug before starting over.Anyway the lazy, boring way to use a portal and pretend you aren’t violating a bunch of physical laws is to just use it for fuel transport.
You have a bunch of fuel on the ground, a tiny tank on your rocket, and you keep topping off the rocket’s tank by piping in the fuel.@[email protected] The Pierson’s Puppeteers did this to fuel probes in Ringworld. The only difference was their technology required a physical teleportation device to be placed at the destination instead of just opening a portal anywhere, & transmission was limited to the speed of light.
BTW, as a variant on the kzinti lesson, the portals are extremely dangerous as a weapon, because of how good they are as a weapon.
Ignoring the obvious ways to fight with them like opening a portal on the enemy’s hull, shoving out a nuke and then closing the portal…
You could also just have a rock that you’re letting accelerate to arbitrary speeds in a vacuum. That’s free unbounded kinetic energy, the only limitation being the “charge” time.
@[email protected] I love this, just for the “Variant of the Kzinti lesson” reference.
@[email protected] k’chee u’riit maraai, indeed.
@[email protected] I recall Peter F. Hamilton doing just that in one of his books. The nuke part at least. Not sure about the space rock yeeting.
This isn’t a ship-destroying weapon, this is a civilization-ender if not planet-killer.
You’ve got a projectile moving at a significant fraction of the speed of light. This is a relativistic weapon: it’s going to hit harder than if it was a nuke.
You can also make it bigger by not using a roughly round rock and instead using a long rod of the densest material you can get your hand on.
But mass you pay for, speed you don’t.
Like, the worked example from Atomic Rockets has 7 kilograms of cat litter moving at 90% of lightspeed hitting a stationary target with 195 megatons of kinetic energy.
https://www.projectrho.com/public_html/rocket/spacegunexotic.php
@[email protected] honestly, a baseball at a significant fraction of c is sufficient - you don’t need a tungsten crowbar
@[email protected] yup. Doc Smith level planet busters are near trivial with portals
@[email protected] there are no unarmed spaceships
@[email protected] The hard part will be aligning the (“outgoing”) portal so perfectly, that you do not end up anywhere but your far away target.
@[email protected] That raises a question: Are portals subject to reaction forces? If not, a deflector would still be required and solid ‘fuel’ may be less usable.
@[email protected] I believe it’s also illegal according to the game, in that a portal can only be placed on a stationary surface.
I believe the portal would break as soon as the ship moved.@[email protected] you could already make perpetual motion machines with the mechanics you have available in-game so i think that’s probably fine in this scenario
@[email protected] xkcd did most of that math already, just need to multiply by density of water I believe: https://xkcd.com/969/
@[email protected] @[email protected] Portal also added more fun ways to break physics by giving Chell the magic inertia-canceling boots.
Not addressed in the game: What happens when the relative velocity between the ends of a portal is very high and something bigger than a molecule gets dropped through it.
@[email protected] Portals can’t move, so it wouldn’t be able to function as a propellant. What you’d have there is a high volume water cutter.
@[email protected] Einstein cops are no joke. They’ll put you in a cell with no external references and you won’t be able to tell if it’s even on Earth vs constantly accelerating in deep space.
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I think Niven once wrote an essay on this, in the context of teleportation booths. He posited that conservation of energy would be satisfied by temperature changes. In this example, the water would come out of the portal at cryogenic temperatures.@[email protected] every time I see inertialess thrusters discussed I always end up thinking it would be great to have a Skylark show made. I always enjoyed those books when I was a kid.
