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Background: 600-ish years into the future. Humanity finally managed to make Earth uninhabitable and now lives in space. Some humans shed their flesh bodies and are now reduced to brains, their "bodies" being space ships. I am looking for a futuristic, but still science-based explanation which allows such a spaceship to use an acceleration of around 50g for long periods of time (up to 20 hours), and 100g for a few seconds, in extreme cases, without obviously turning the brain it hosts into mush. My imagination created some sort of rotating sphere filled with an electrically-permeable gel, which turns slowly, with the brain inside it, acting as a cushion, but I am not fully satisfied. Any other ideas?

EDIT: I was asked to provide constraints.

  1. The device which protects the brain in the spaceship should be rather small, no more than twice the size of a human head.
  2. The space ship is fusion-powered, therefore plenty of power available, but we need to limit the amount of power the device would use, or make the power usage exponentially higher, the higher the protected volume would be.
  3. „Magical” Forcefields, non-inertial systems or exotic matter usage („MumboJumbonium”, to quote someone) are to be avoided.
  4. Inertial dampeners are OK, as long as there's some drawback attached to them (see constraint 2 as an example) and they have some background explanation (they work and can be used because...?)
  5. Acceleration in real space/time is a prerequisite. Propulsion methods which avoid acceleration are not allowed in this context.
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    $\begingroup$ Oh, simple - it works due to MumboJumbonium. $\endgroup$
    – VLAZ
    Commented Nov 4, 2022 at 8:31
  • $\begingroup$ Would it be an option to use bioengineering to change the brains themself to make them physically more sturdy? $\endgroup$
    – Philipp
    Commented Nov 4, 2022 at 12:11
  • $\begingroup$ Inertial dampening/suppression is likely off the table for any reasonably hard sci-fi. I've been trying to shoehorn them into my sci-fi for years but as it turns out, messing around with inertia breaks just about every aspect of physics in the most horrible ways. $\endgroup$
    – BMF
    Commented Nov 4, 2022 at 12:39
  • $\begingroup$ Sounds reminiscent of The Ship Who Sang. $\endgroup$
    – John Bollinger
    Commented Nov 4, 2022 at 15:00

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The gel the brain is stored in reinforces the brain. It seeps into the brain and makes its internal structure sturdier, which makes the whole brain more resistant to acceleration.

This could be done by nanites which builds stabilizing micro-structure within the brain which greatly enhance its structural integrity. Or it could be done purely biochemically by an agent which reacts with the cell walls of the neurons and hardens them with a protective shell. Neither of that must affect the natural processes of the neurons and their ability to form synapses, so the natural thinking processes of the human remain unaffected.

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  • $\begingroup$ Thank you, that's actually wonderful, and fits perfectly within the greater worldbuilding framework I am thinking about. That is indeed the solution I was looking for. $\endgroup$
    – Eduard B
    Commented Nov 4, 2022 at 12:29
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    $\begingroup$ This is how they restore old boats, I went to a viking ship museum in Denmark and they found pieces of old viking boats that they reassembled - removing them from the water they would dry out and be destroyed, so they injected a clear polymer into them that reinforced them without changing their appearance so they could be reassembled and displayed. $\endgroup$
    – NibblyPig
    Commented Nov 4, 2022 at 18:58
  • $\begingroup$ For a fun plot twist, let the protective shell allow the neurons to still function, but interfere with forming and dropping of synapses. Your ship can't learn new things well and forgets where it puts the keys. $\endgroup$
    – Wayne Conrad
    Commented Nov 4, 2022 at 20:13
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    $\begingroup$ @WayneConrad I already have a plot twist, the brain(s) enter reduced functionality while subjected to high accelerations, e.g. sensor range is greatly reduced, all sensitive sensors are off, the brain is kind of paralyzed. $\endgroup$
    – Eduard B
    Commented Nov 5, 2022 at 16:08
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Liquid immersion does this by itself

The physics stack exchange question referenced below indicates that a full bodied human with liquid breathing can sustain around 100 g's by doing no more than suspending the body in a liquid. From your question, it isn't far fetched to imagine a brain suspended in liquid, and whatever breathing replacement system it uses can just be rated for the high g forces. I don't think you have the problem you think you do.

https://physics.stackexchange.com/questions/141030/does-liquid-immersion-protect-against-g-forces

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    $\begingroup$ To avoid differential pressure on the brain-skull-liquid boundary you would want the liquid density to closely match the brain density since at 40g pressure can quickly build up along the direction of acceleration. $\endgroup$
    – philn
    Commented Nov 4, 2022 at 17:56
  • $\begingroup$ Yes, but for how long? I am talking about 50g for up to 24 hours in a relatively straight line, or sudden accelerations of up to 100g for several (up to 30) seconds. None of the articles mention for how long is that acceleration sustainable. They most likely assume it's sudden and stops very quickly, in a matter of seconds. $\endgroup$
    – Eduard B
    Commented Nov 4, 2022 at 19:09
  • $\begingroup$ @philn The original source article actually states that (plural) presumably hundreds of G can be withstood, with the limiting factor being breathing. They also site a that they were testing sustainable acceleration, not instantaneous. $\endgroup$
    – Mathaddict
    Commented Nov 8, 2022 at 16:54
  • $\begingroup$ @EduardB I can't think of why this wouldn't work for a long time period. Scuba diving exposes the body to similar pressures just without as sharp of a pressure gradient. When scuba diving the pressure gradient is just a function of regular gravitational acceleration whereas at 40g it is 40x larger. I did some googling and scuba divers conventionally go down to 130ft. That would expose much more pressure than shallow water immersing a brain; if we take the head to be 1ft in diameter you'd only be exposed to 40ft of pressure at one part of the skull if using water as the liquid. $\endgroup$
    – philn
    Commented Nov 8, 2022 at 17:32
  • $\begingroup$ @philn While that's true, remember acceleration is not the same as pressure. Pressure exerts force from all directions equally, while acceleration is unidirectional. Think of an egg, you can squeeze it from all direction with a LOT of force before it bursts, but place it on a hard surface and accelerate one way, it would pop pretty easily. Hence my idea of rotating the brain in dense liquid. Acceleration/jerk/snap/crackle/pop effects are visible in real life in car accidents (car hits tree, car hits wall). Let's just say they're not something human bodies manage to sustain. $\endgroup$
    – Eduard B
    Commented Nov 9, 2022 at 18:23
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Alcubierre Drive

enter image description here

The king of Pseudo-science around here is the Alcubierre Drive. It avoids the problem of huge acceleration by having the spaceship stay still relative to the nearby spacetime, only pushing and pulling the spacetime in a bubble around the ship.

The reason it's pseudo-science -- it's suspected to be impossible to create. We know that if god was to coil up space around his wrist in the correct manner and then let 'er rip, the result would be a self-perpetuating Alison Cuthbert spacetime bubble. But coiling up space that way to begin with requires something called "negative energy density" or "negative mass".

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  • $\begingroup$ I am familiar with that, but acceleration is a prerequisite, therefore I have added rule #5 to the original post. Apologies, I had thought it obvious that acceleration is a must and the method to deal with it is being the main topic. $\endgroup$
    – Eduard B
    Commented Nov 4, 2022 at 12:03
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Store the Brain as Energy

enter image description here

Before the ship accelerates, the brain or the entire person is scanned, and the data is absorbed into the transporter pattern buffer. The buffer is a mechanical system built to be much more resilient to strong acceleration than a squishy meatbag.

When the spaceship comes to speed, the brain or entire person is reconstituted as if nothing happened. From their point of view the ship instantly jumped to top speed and all the clocks jumped forward a few hours.

Bonus points for hijinks!

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    $\begingroup$ It's a good possible solution, however the ship maneuvers at those accelerations. It's not solely "accelerate in a straight line towards a distant, known destination". Think dogfights, battles, following an object which changes trajectory, etc. The brain needs to be active and in control. $\endgroup$
    – Eduard B
    Commented Nov 4, 2022 at 12:31
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    $\begingroup$ @EduardB you might want to use the tag [science-based] in your Q next time to disuade answers like these (that try to bypass your entire problem with fairy physics irrelevant to your worldbuilding). $\endgroup$
    – BMF
    Commented Nov 4, 2022 at 12:46
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    $\begingroup$ @BMF Fairy physics are appropriate when the question asks for pseudo-science by name. $\endgroup$
    – Daron
    Commented Nov 4, 2022 at 13:27
  • $\begingroup$ @EduardB This is information you should include in the question, to avoid rejecting answer for reasons that were in your head but not written down. $\endgroup$
    – Daron
    Commented Nov 4, 2022 at 13:29
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    $\begingroup$ The OP's world uses fusion power and has concerns about hard accelerations. IMO that places the scope of its science outside Star Trek's. $\endgroup$
    – BMF
    Commented Nov 4, 2022 at 17:51
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Entirely digital brains is the best idea I can think of.

If you're getting rid of fleshy bodies, why not also get rid of fleshy brains and go with a digital mind? A digital mind could easily pull this kind of acceleration, as the computers inside of missiles often do so. A digital mind would also have the sort of reaction time you'd ideally want for space combat, because instead of nerves that move far below the speed of sound you have electricity that moves at nearly the speed of light.

However, this does lead to the question of how people aren't using this ability to cheat death, which is a can of worms that is problematic from a storytelling standpoint because it inherently reduces the stakes of the story. If you can download your brain into a spaceship, why can't you also download it to multiple robot(or even clone/cyborg) bodies? Eclipse Phase has this problem.

Probably the best idea you can go with is to embrace the(likely incorrect) Roger Penrose idea of quantum computing inside the brain and say that this level of quantum uncertainty allows brain transfer but does not allow replication. If you wanted a bit of tragedy you could also raise the question as to whether these minds are really the original person or just an AI loosely based on someone who is now dead due to this "upload" process. Is it worth becoming Maverick if you sort of die in the process?

You also need to have limits on the development of synthetic AI, because this process is pointless if you can churn out synthetic AIs that are built for nothing but flying spaceships. Fears of the risks of conventional AI are probably workable enough here, especially with the brain interface tech required for these sort of uploads in the first place allowing organic or uploaded brains to do more of the work.

Though for a frame challenge I still would say that Expanse-style space travel and combat with conventional human pilots is generally the best option if you want plausibility. This is also true because going at 50-100g is extremely unlikely with any sort of even semi-plausible rocket design(with even the Expanse cheating). Anything more than 10-15g that a person can at least temporarily survive with the right equipment is going to be implausible anyway.

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  • $\begingroup$ My story contains brain-only factions, heavily modified human being factions (brains, bodies), AIs (solo, multiplicity and grand AI), traditional fanatics (unchanged bodies and minds) and so on. There are limits in place for AI space travel. To keep it brief, FTL travel (jump drives) mangles AI functionality unless it's paired with a biological brain, which is immune to jump drive corruption and keeps the AI stable through a cyberlink (quantum entanglement communication). AIs need brains to travel and for abstract thinking, humans need AIs for computing power and tech research. $\endgroup$
    – Eduard B
    Commented Nov 5, 2022 at 17:39
  • $\begingroup$ Considering the above, a brain can, in my work, be digitalized, but loses abstract thinking and ability to travel freely. Some old brains (centuries old) choose this path to achieve immortality. Everything is about to change, though... my question is aimed to clarify technical aspects which lead to this pivotal story point. $\endgroup$
    – Eduard B
    Commented Nov 5, 2022 at 17:41

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