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@[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] 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
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
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.
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.
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.
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
But yeah this is the ultimate doomsday weapon. You can accelerate indefinitely for free, you just have to wait.
(and if you can put your portals in orbit of a more massive object, you get faster acceleration than 1g)
So you don't need more than a portal gun, a tungsten rod, and some time to blow the atmosphere off a planet.
Sir Isaac Newton may be the deadliest son of a bitch in space, but the deadliest son of a bitch in the Half Life universe is Cave Johnson.
The Nihilanth could teleport an entire army to earth, the combine can conquer a planet in hours, the g-man has control over time and space, but Cave Johnson's invention could put a hole in a planet
Alternate ending to Half Life Alyx where it turns out the scary thing the Combine has locked up in the vault is Chell.
There's also the gravity interaction: an infinitely falling object that never reaches the bigger body is also accelerating the bigger body.
Your forever falling object is shoving the earth upward, very slowly. That could matter in the long enough term... But it seems kinda meaningless compared to the other ways you could use a portal.
Still, might be handy if you need to adjust the orbit of a planet and are willing to wait.
It would be a very Cave Johnson thing to try to fix global warming by pushing the earth away from the sun.
The only thing more Cave Johnson would be using relativistic weapons to blow up the sun
The lab boys tell me that if you dump enough iron into a star, it'll turn off. Well, we don't have that much iron on hand, but what if it's moving at 99% the speed of light?
They told me that wouldn't help, but I said pack your bags: We're doing it anyway
Portal 2 does establish that the portal-placing shot moves at the speed of light, but that just raises the question of how fast you move through the portals themselves.
It basically can't be slower than light, or you'd chop yourself in half if you moved halfway into one and then backed out.
So it has to be lightspeed: which means, if relativity is still correct, that it's also a time machine.
Maybe not one that lets you trivially violate causality but with moving portals or multiple portals, whoops...
Anyway once you're flying around the universe with your FTL portal-rockets the next question is what happens if the two ends of a portal are moving at different speeds through time. What if you drop one end into a black hole?
And what if you put one end on an enemy planet and the other end in low orbit around Betelgeuse when it finally goes supernova?
How many gamma rays will come through a hole in space about a meter across?
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@[email protected]
In a book (Bobiverse) two moon sized bodies were accelerated to very close to speed of light, and hit a star, coming at it from opposite directions.
Result was described as basically a nova.
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@[email protected] One wonders what kinds of electromagnetic interaction tricks you can do with portal technology as well. At the very least, you can build a computer that's physically enormous while being linked together through portals as if it's microscopically adjacent.
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@[email protected] boring "explanation" that the energy which can cross a portal is limited by the power of the portal generator - so you can only accelerate to c if your generator can output that much juice - it's not free just super efficient
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@[email protected] That passage out of The Killing Star when the Relativistic projectiles hit Earth...
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@[email protected] yup. Doc Smith level planet busters are near trivial with portals
@[email protected] honestly, a baseball at a significant fraction of c is sufficient - you don't need a tungsten crowbar
@[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.
@[email protected] I love this, just for the "Variant of the Kzinti lesson" reference.
@[email protected] k'chee u'riit maraai, indeed.
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@[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] 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".
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@[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
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@[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] This is (spoilers!) one of the weaponizations of space magic in The Paranoid Mage indeed.
@[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] 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.
@[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] xkcd did most of that math already, just need to multiply by density of water I believe: https://xkcd.com/969/
@[email protected]
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] 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.
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@[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] 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?
@[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)
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this post was submitted on 16 Jan 2024
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