Okay let’s establish something first:
I may have faulty reasoning. My question stems from this thought of mine:
When you move in object you’re only moving SOME of the pieces of it, which (depending on how/where you grip) “pull” and “push” other particles via various attractive/repulsive forces binding them together. Kind of like trailing a bunch of beads along on a string.
Now in everyday object, even when looking at a mighty carrier (in slow-mo even) you don’t see the front move and the rest “stretch” and then “move along” (nor do you see it "scrunch and then “push along”). So maybe my reasoning is flawed here, but with it I came up with a question.
Given the following:
I’m Herakles or Superman or something, I can EASILY lift and pull this pole.
I have a display that has 0 time delay between point A (my location) and point B. If you want to think of it this way I’m in Pac-Man world and the end of my pole comes into my field of vision as it “loops” around.
All things (air resistance, gravity etc) are perfectly uniform along the test field.
The pole I’m using is ideal and the internal structure is as simple as possible (though also magically enchanted not to bow or break under its own weight/length of course).
What would be the time delay (if any) if I pulled a 1 Lightyear long pole between the part I pulled visibly moving and the other side “reacting.”
Would it be noticable at all? If not how long would I probably need to make it to have an observable delay?
Assume whatever distance and structure etc between the molecules/atoms/whatever would be easiest for calculations if there are any calculations that could be reasonably done to calculate this. Otherwise just give me ballpark numbers or concepts (“noticable” or “tiny” etc).
Given you are positing an impossibly strong person to move the pole, and a (magically) impossibly strong pole, no answer would make any sense in the real world.
In real life, with a very long pole, either the pole breaks, or motion at one end travels as a wave along the pole at something like the speed of sound in the pole’s material.
All real world objects flex. Inertia will act on the entire length of the pole, slowing its movement anywhere where you’re not directly pressing on it, and so cause it to flex.
The closer the object is to not flexing, the more energy you will have to exert to move its length (counteract inertia.) Subsequently, as the flex amount nears zero, the amount of energy equals what it would take to propel the mass of the object to light speed. That is of course infinite for any object that has mass, and so…
For a rod or wire 6,000,000,000,000 (trillion) miles long, I honestly can’t see any material that would be able to overcome inertia. It will stretch then snap at your end, and I think the other end wouldn’t even budge at all.
I asked this of my friend’s physics-major dad when I was in high school, except I asked it about a Known Space-style variable sword, a wire encased in a “stasis field” that makes it perfectly rigid. He said “Well, motion travels at the speed of sound in the object, so in an infinitely rigid object, it would travel at the speed of light. Of course, in a real-world object, infinite rigidity would be impossible.”
Well, the speed of light is relevant, in so far as, for any real material whatsoever, the speed of sound is always strictly less than the speed of light. There are actually materials for which they’re very close, but steel is not one of them.
I interpretted the OP as hypothesizing that the speed of propagation would be c almost regardless of material and then wondering of that was true. i wanted to nip that idea right off.
Clearly there is no possible dynamics problem in which c is truly absolutely 100% irrelevant.
I didn’t mean to have the question have anything to do with light/FTL stuff. I used Lightyear because I figured it was a sufficiently large distance to have a noticable difference. I talked about it being unnoticable normally because I knew it was FAST I just wasn’t sure HOW fast. I also admit I did neglect the fact that the rigidity of the structure (making it unbreakable) would cause issues with the problem. So the rest “reacts” at the speed of sound in the medium then?
Is this because it would act as a “vibration” travelling along the object and then the density and Youngs Modulus of the object would be called into play to dictate how much there is to move and how much elasticity/freedom there is between the individual “pieces”?
That is to say, we’ve never had a sample of neutronium in a laboratory, but one can make indirect observations of the speed of sound in neutronium by watching the aftermath of starquakes in pulsars.
Another material with an impressive speed of sound is a photon gas, which has a sound speed of precisely 1/3 c. I don’t know whether that’s ever been directly measured in a laboratory, though (it’s certainly more plausible than neutronium). And I don’t know offhand what the typical sound speed is in a quark-gluon plasma, but I would expect that it would be impressively high, as well.