Hypothetical combat with a five-dimensional weapon

Question

Let's imagine a handheld, five-dimensional melee weapon: 3 dimensions of regular ol' space, 1 of time, and an extra dimension of space. Its "hilt" is anchored in our usual 4-dimensional spacetime, so that we can wield it, but its "edge" is tethered in 5-dimensional spacetime. Perhaps also the "edge" can phase down to 4 dimensions when the wielder decides to "collide" with an object in our space.

How would this weapon function? What unexpected advantages would it have for the wielder? Unexpected dangers?

• One possible function I can imagine is that you would be able to strike people with the weapon at long distance, since it could "shortcut" through our space.
• I also imagine it could slice through things to strike objects. Say, stab someone from behind a wall without cutting through the wall.

Useful visualization if you are unfamiliar with higher dimensions: A 5-dimensional object passing through our space would be analogous to a 3-dimensional sphere passing through a 2-dimensional world sheet. Imagine a basketball passing through a sheet of paper. The cross-section of the ball, which is the only thing comprehensible to sheet-dwellers, can be visualized by them as a circle appearing out of nothing, shrinking, growing, then shrinking again before it disappears, as it passes through the 2 dimensional sheet.

Commenter Questions:

• The weapon can be smart or dumb.
• Some question whether the hilt can be affected by the edge (that is, whether it is possible to move the edge by the hilt at all, since 2d objects are not known to exist). This implies the weapon is artificial in its construction, and thus we must assume interaction is possible in order to be able to speculate, so it just is.
• To be clear, moving the hilt moves the 5d edge; rotating the hilt rotates the 5d edge; squeezing the hilt makes the edge 4d so that it can strike objects in lower dimensional space.

Relevant:

Graphically represent (map) multiple spatial dimentions

Answer 1

Ok, it's probably good to turn this into a Flatland problem.

So let's imagine what a 3D weapon anchored to a 2D world would look like.

There are a few options.

1: The hilt is anchored in 2D Realspace by a 2D plane and cannot rotate in 2D space and is solidly attached to a solid 3D object in 3D space

This would have almost no effect since the 3D object can't change its intersection with 2D space. Imagine a Flatlander holding, from their point of view a spike but from ours the corner of a triangle which cannot move further into flatworld or rotate but can float around on the surface at the same intersection. The weapon would likely have incredible inertia/mass since it's tied to a far more massive object. Instead of an atom-thick or no-thickness it would have either massively more or infinitely more mass.

EDIT, an exception: a complex 3D shape like a donut with the 2 arms of the loop passing through the 2D plane would manifest as 2 objects within flatland which would push and pull together. From inside it would look like the hilt wasn't connected to the "blade" but the 2 parts would act like one object because they are one object in 3D space.

2: The hilt is bound to 2D realspace along a 1D axis but the "blade" and the rest of the shape can rotate in 2D and 3D space around that axis.

This would be far more dangerous but probably more useful as a weapon and far harder to control. Imagine the flatlander holding the handle of a flail. They can partly control the "swing" in 3D space by squeezing the handle just right. Once they give it a little swing first to get it moving/rotating, from our point of view the flatlander is holding one corner of a shape which is bound by a 1D line to flatland. It swings in and out of flatland around that axis. The "blade" need not appear sharp in 3D space since it would always past into 2D space starting from an infinitesimal point and expanding outwards.

Depending on the shape it would be possible for edges to appear inside objects. From the point of view of a flatlander, the 3D flail holder would shake and squeeze their weapons hilt and then their head could explode as a 2D shape appears within it, expands and finally the connecting portion of the weapon would pass through the 2D plane.

3: The hilt is bound to a single point in 2D space, no axis....

this is not a usable weapon. It is dangerous to anyone within reach of it and would be almost impossible to control.

Turning back to your 5D (4D unless you want it to also be able to rotate in time and hit things in the past and future which I have no idea how to model)

If you go with option 2 then it might manifest as a weapon which, when the user swings it just right and squeezes the hilt just right, can be used to make apparently unattached lumps of metal appear briefly inside the people and objects in front of the hilt.

A dangerous weapon indeed to the point that you'd be very lucky to survive learning how to use it without killing yourself.

Answer 2

Any question that involves dealing with higher dimensions that what we, as humans living in three dimensions, are used to is tricky. There is a great video out there that describes what each dimension up to ten is like, and how it corresponds to the two dimensions around it. The basis of this video, at least from my perspective is that dimensions sort of repeat themselves: line, branch, fold. 1D is a line, it has no depth or width, only length. 2D is a branch, it has length and width but not depth. 3D is a fold, it has length, width and depth. Honestly, the video does a much better job explaining this: https://www.youtube.com/watch?v=p4Gotl9vRGs

Moving to the fourth dimension, duration, you again have a line. Expect it's not a line without width and depth, it's a line of three dimensions. Moving up and down the line would be like looking at yourself as you aged from birth to death.

The fifth dimension, then, is a branch off the line in the fourth dimension. You can visualize this as paths not taken in your current life. Choices not made, roads not walked down, are all visited in the fifth dimension.

Since your 5D weapon stops there, we certainly don't need to break out the 6D time folding machine.

How would this weapon function?

This weapon functions in five dimensions, yikes.

Let us try to draw a comparison to something that we know: I have no skill with a flail. I know how a flail works (a weighted ball on the end of chain attached to a stick) but I have no experience using a flail and therefore could not accurately predict what will happen when I use it this way or fling it that way.

So, your question of functionality comes with two answers.

1. To an amateur, the weapon will look like a three-dimensional weapon (as it will have an appearance to you and I has a normal looking thing because we can't see the 4th and 5th dimensions). It will function then just like you expect it to, it will strike, slash and hit. Only... weird things will start happening. You'll slash at something... and it won't be slashed right away. Maybe it will take years to be slashed. You don't know because the edge is in a 5th dimension you have no comprehension of and no control over.

2. To an expert, this weapon will be of amazing power.

   Scenario: Hitler walks up to the podium in Nuremberg. He starts speaking his grand speech, inspiring Germans to fight in WW2. Suddenly, blood pours from his chest and he slumps to the ground, dead. There are no persons near him, only a fatal stab wound to his chest.

   Fast forward to present day, where our 5D blademaster is standing at the exact spot where Hitler once gave his speech. The weapon is poised before him at a sharp upward angle as if it were thrust into a body. History is now forever changed. This brings me to the next question:

What unexpected advantages would it have for the wielder? Unexpected dangers?

You have invented a weapon that can essentially travel through time. So long as the wielder can perceive and successfully manipulate an object in the 5th dimension, he or she could conceptually stand in one place and stick the weapon into that place at every point in time that place has existed.

Pretty much, this weapon is capable of changing events at one point in the third dimension. If the edge where in the 6th dimension, it could change events at any point in the third dimension.

At least, I think so. Higher dimensions are hard.

Edit: But now, after thinking for a minute on this, I realize that this might not be quite correct, as the 5D blade would actually have to move through the 6th dimension to manipulate the 5th dimension so that we could actually perceive the change in the 3rd dimension.

Answer 3

Manipulation:

The hilt and the edge of the weapon are physically linked like any other weapon. Consequently, by waving the hilt in our 4-dimensional spacetime, the edge will move in its 5-dimensional spacetime, occasionally colliding into our space.

But the part in the fifth dimension is not or partially visible in our dimensions, we can only see the part that collide in our plan. Basically, the weapon will look like a flying blade that can teleport, move and phase through space according to the hilt's manipulation.

Advantages:

The main advantage for this kind of weapon is being able to make the blade appear behind the opponent or through his armour.

Dangers:

The main risk is failing to manipulate correctly the blade, due to the fact you have to take account of the fifth dimension when using the blade, making it appear on your body and injure yourself when you make an error.