# Acceleration insulation: I can build the Moon cannon, now what?

This is steampunk, so assume a non-relativistic, non-quantum world (but more on that shortly).

I want a material that insulates against acceleration but not gravity.

Full explanation:

This is the material one would use to line the walls of a cannon-launched spacecraft.

Let's assume that the insulation is not perfect. It reduces the acceleration felt by occupants, and a thicker layer provides better insulation. After all, I don't need complete inability to feel acceleration, it just has to be feasible to reduce accelerations of 1000g or more to something a human can survive. I expect the not-100% protection won't matter much to the physics, just mentioning it for completeness.

I haven't determined what happens if you don't insulate all sides of a capsule, or what happens if you bore a hole in the insulation.

Note in what sense I mean "insulates against acceleration". It doesn't mean "objects inside the container cannot be accelerated". It means "objects inside the container are accelerated along with it without feeling a force from the walls". That is, the insulation (if it were perfect) causes the interior to be an inertial reference frame regardless of its motion.

Because it insulates against acceleration, it also insulates against free-fall. If you were in orbit in such a spacecraft, you could walk on the floor; that is, the direction of the Earth would feel like down. But your weight pressing on the floor must not affect the trajectory of the spacecraft; how? I want to replicate how gravity worked in From the Earth to the Moon. The crew felt gravity except at the point where the gravity of the Earth and Moon cancelled.

As that points out, occupants are not insulated against the gravity of bodies outside. I assume that the outside world is also not insulated against the gravity of objects inside.

This material doesn't make accelerating the whole spacecraft any easier. As the previous paragraph notes, the craft as a whole affects and is affected by gravity in the same way a craft of the same mass without the insulation would be. Also, the inertial mass of objects placed inside the container can still be detected from the outside.

Clarification: The material does not just damp large accelerations. You can move inside normally. That is, a force exerted by one object inside on another object inside has the same effect it normally would. Only forces exerted on the outside of the container cause the specified effects inside.

The material is passive; it does not require a power source.

What are the unintended consequences of this?

I don't want this material to permit perpetual motion. It should be valuable, but not THAT valuable. A material that insulates against gravity would allow a perpetual motion waterwheel. I've avoided that, but I expect there may be other weird ways to get there.

That is, forget about Einsteinian relativity. This does weird things relating to Galilean/Newtonian relativity.

To restate, since I don't know if I got through: I'm looking for an interpretation of this material based on a 19th century understanding of acceleration and gravity, not a modern one. This is a world where the ether exists - not that I know exactly what that means, given that 19th century concepts of it were inconsistent and unclear. Giving something a name doesn't explain it. So I don't know whether I'm hoping for an explanation tied into the properties of ether or one that doesn't depend on them. I could express my goal as "I want something that, in a 19th century physics context, is more unobtainium than handwavium. And then I want to know the logical consequences." I know that isn't very technical.

• Repeat with me: You cannot separate gravity and acceleration. Gravity is a **force**, acceleration is the result of a force (gravity or other) Commented Mar 7, 2015 at 18:03
• If the astronauts inside your capsule were not to feel the acceleration, they would move slower than the capsule, so they would end outside of it (somehow, probably not in good health). Commented Mar 7, 2015 at 18:08
• You're essentially asking for the inertial dampeners from star trek in the form of a material Commented Mar 9, 2015 at 2:54
• Maybe. Do Star Trek or Star Wars inertial dampers shield against free-fall? I don't know, nor do I care in this context. Commented Mar 11, 2015 at 19:39
• I recommend removing the goal of "feeling gravity" in orbit/freefall. That particular goal is so far outside the realm of physics that you are better off either using magic or rewriting the laws of physics, from the ground up, to suit your needs. Choosing Newtonian physics over Einsteinian doesn't help either -- Newton's laws are responsible for the behaviors of free fall and weightlessness. Commented May 10, 2015 at 2:17

First, an "acceleration shield" in the true sense of the word is impossible. However, one could imagine something close to it:

The reason why acceleration affects you is that it actually doesn't affect you: When the car accelerates, you don't accelerate with the car, and therefore the car presses against you, and indirectly accelerates you that way. On the other hand, when you are directly accelerated (as in free fall), you actually do not feel any weight; indeed it is exactly free fall where you feel weightless.

So the material could simply transfer all acceleration also to anything enclosed by it. So if your capsule is accelerated with 1000g, then so is every single atom of the people inside, and therefore the acceleration is not felt by the people inside, exactly because it does affect them. In some sort, the material holds all the enclosed atoms (but of course it not really can hold them, or else any movement inside would get killed; probably the effect would need to be limited to large accelerations).

However you'll not get walking in the gravitational field during orbit that way; free fall is and remains weightless, sorry.

• What does "directly accelerated" mean? Free fall is when all parts of the object feel the same forces (v.g., only the gravity), so they all have the same accelerations and not have to exert forces one into the other to keep their respective positions (on Earth, your feet must exert force on the floor to compensante for gravitatory accelaration) Commented Mar 7, 2015 at 18:07
• @SJuan76: With "directly accelerated" I mean exactly the situation of free fall: The force applies to every single atom. Unlike when accelerating your car where the force is only applied to your back, and your atoms then transfer it throughout your body. Commented Mar 7, 2015 at 18:11
• Actually he would get the walking in orbit, the explanation would be too long for a comment here - if you want to know while feel free to ask it as a question or take it to chat :) Commented Mar 7, 2015 at 19:26
• @TimB: So how do I take it to chat? Commented Mar 8, 2015 at 7:05
• Commented Mar 8, 2015 at 17:19

Instead of acceleration insulation this could be done another way: Your cannon generates gravity. If the driving force is gravitic you will not feel it, you'll just be accelerated. (Consider an astronaut in orbit. He's really being accelerated at almost 1g all the time.)

As far as I know this doesn't violate any laws of physics although we do not have the foggiest notion of how to go about it in a practical fashion. (For an impractical fashion, consider a machine that has two wheels, each with two opposite very heavy masses. Start with the masses all in a line, the ship heads between them. As it gets close you turn the wheels, the masses head away and out. The ship will experience some acceleration from this. To get a meaningful acceleration you'll need degenerate masses, incredible amounts of energy to turn the wheels, wheels made of unobtainium and you'll probably end up destroying the ship with the tides anyway.)

• Interesting, but not the question I'm asking. I'm asking Given this technology, how does it work, and what else can be done with it? Commented Mar 19, 2015 at 23:56

How does it work?

If I knew all the details, I'd make a fortune, wouldn't I? One reasonable way is that the material, when suddenly compressed, generates a field on the side of the force that envelopes a given volume and transmits an equivalent force evenly to all normal matter within that volume.

You're not exactly asking about shielding from acceleration. You want the passengers to accelerate, after all, you just would rather they didn't feel it. You want the passengers (or cargo) to be protected from the stresses of acceleration. If, as my above hand waving should do, the accelerating force were felt by every particle of their bodies evenly, they wouldn't feel the acceleration, but they would be accelerating. As to what this mysterious force is... It's unknown to our science. Maybe it is a side effect of your aether.

I don't see how the above would be usable to build a perpetual motion machine or violate any conservation laws. It could be used to make a very effective substitute for a wooden mallet. A long shaft of it might be a murder weapon by forcing movement within the body, but a long shaft of wood's been an effective murder weapon for some time now.

With some mechanism to compress it, it might be used to simulate gravity. With several banks of it aligned in the same direction, being compressed in turns. As far as naturally procuring 1g except at the waypoint between the earth and the moon, sorry. Not a clue as to how it could do that.

We're going to start with Einstein. You don't want Einsteinian physics, and that's fine by me. However, his thought experiments involving reference frames give you something important to work with: you actually cannot measure the acceleration of an object in isolation. The classic example is free-fall in an elevator. You cannot tell the difference between floating off into space and plummeting towards the ground because your acceleration is the same as that of the elevator (at least until the elevator hits terminal velocity). This is why we often confound the terms "free fall" and "weightless."

Of course your hypothetical thought elevators aren't free falling at the times you are worried about: they're crammed into a barrel with a whole lot of explosives behind it. I have to hand it to steampunk characters. They're gutsy. Almost as gutsy as real world medical patients who get a PET scan, which involves the repeated collision of matter and antimatter a few feet from your head.

So the thing that crushes people under high-G forces is not the acceleration, per se, but how that acceleration is applied. In this case, it is applied by large explosive strapped to a rigid plate behind people's backs. The explosives gently prod the rigid plate forward. Unfortunately for our frequent fliers, the rigid plate also prods the passengers, and while the rigid plate may have considered the effects of the explosives to be "gentle," when put on human terms, that adjective ceases to quite describe the mess that the custodians will have to clean up afterwards.

One classic solution is a hammock, which can flex to help accelerate the body evenly. For the sorts of accelerations you are looking at, that's not going to be good enough. However, it is worth recounting the work of Captain John Paul Stapp who voluntarily subjected himself to up to 46Gs of deceleration in a rocket-sled. His work points to the weak part of the body: the eyes. His largest issue was white out or red-out as the blood was forced from or into his retina. Capillary bursts were common.

Beyond that, we can revisit the real issue: we need everything in the cabin to accelerate at the same rate. If they do this, it doesn't matter how much kick you receive. We know that doing this properly and physics-like doesn't work. If it did, we'd have shot our way to the moon already. We're going to have to handwave.

Non-newtonian fluids provide an interesting basis to build a mythical material from. Materials like ooblick act fluid until subjected to strong forces; they then act more like a solid. Non-newtonian fluids are real physics, but we could consider a fictional version which works in non-local ways to accomplish your goals. What if, a day before you fly, you are given a strange vial of liquid to drink. A day later, it has permeated your body. When you fly, technicians coat the capsule with material from the same batch as the liquid you drank. You settle in, and get comfortable. When the explosive charges are finally detonated, not only does this material stiffen like ooblick, but it engages in a highly fictitious process which stiffens the stuff you drank as well, keeping it rigid with respect to the material outside (this is a non-local behavior... decidedly not science fact). This effect keeps the different parts of your body accelerating at the same rate, so no one part of the body receives undue stresses. Once the initial acceleration is over, the material returns to "liquid," which is good because things like moving blood through your body were really hard when the material was preventing anything from moving in different directions.

• PET scan subjects are even more gutsy than you describe, they are getting matter-antimatter annihilations inside their head (or other body part) Commented Mar 14, 2021 at 15:55