## Maximum efficiency when doing work over a distance

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sevenperforce
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### Re: Maximum efficiency when doing work over a distance

Yakk wrote:The claims that there is no way to bound it away from 100% efficiency seem wrong, as there is going to be an entropic cost to aiming at the target (picking that target, and not others, to apply your energy to), no? And that cost increases with the distance of the target (given a fixed size), as your aim has to be more precise?

Typically, the entropy cost of "setting up" a system is counted separately from the energy used within the system. The OP asks whether there is any intrinsic energy inefficiency proportional to distance when moving from the nonfictional realm of pushing on an object and the fictional realm of action at a distance. To be sure, the chosen telekinetic mechanism (whether it involves aiming or some sort of lossy particle beam or whatever) may indeed involve distance-dependent inefficiencies, and we've seen how the concept of moving something in a nonlinear direction will introduce torquing and thus decrease effective strength, but neither of those things are energy inefficiencies intrinsic to physics itself.

Depending on how the telekinesis works, my stick figure in the diagrams above could conceivably use a third object somewhere as a fulcrum or anchor of some kind and thus be able to exert greater sideways force than he otherwise would have been able to.

This cost (on first approximation) doesn't seem high, but it seems to be non-zero.

When the energy costs of an action can be made arbitrarily low by making the action arbitrarily slow, they can be dismissed for the purposes of evaluating the system itself.

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### Re: Maximum efficiency when doing work over a distance

gmalivuk wrote: There's always some other way of doing those things efficiently

Yes, but those other ways require energy sources that are located in different locations with respect to the object being acted on. If you are given a fixed location for an energy source, would it require work to transfer this energy into the appropriate location to implement these "other ways"?
This is the heart of the telekinesis problem. In one model of telekinesis, the answer is no. In a different model the answer is yes. If telekinesis could exist, it has to be one or the other. Can we determine which one?

Of course, there is also the issue of can telekinesis theoretically be possible. I don't think there is anything in the current model that says it can't. I could very well be wrong, which is why I asked this question.

gmalivuk wrote:You do know that conservation laws are not the only physical laws, right?

Please give me some examples of physical laws that make telekinesis impossible. Lack of evidence does not prove impossibility.
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sevenperforce
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### Re: Maximum efficiency when doing work over a distance

gmalivuk wrote:You do know that conservation laws are not the only physical laws, right?

Please give me some examples of physical laws that make telekinesis impossible. Lack of evidence does not prove impossibility.

I think you'd need to define telekinesis more specifically.

Like, if you're using the definition people typically think of -- that is, psychokinetic telekinesis or lifting/manipulating objects at a distance solely using your mind -- then no, that's not physically possible. None of the transient electromagnetic fields produced by the brain are sufficiently intense enough to produce any significant field more than a few inches away from your skull, and even if they could, they wouldn't be able to produce the kind of effects typically depicted as telekinesis.

If we're talking about something more like the Utility Gauntlets used by Syndrome in The Incredibles, then we're verging on the realm of remote possibility, though there would be plenty of specifics which would still result in it being shot down.

Now, if you expand "telekinesis" so broadly as to include ANY sort of "action at a distance" which allows the "invisible" manipulation of objects by any means possible (e.g. a tractor beam) then we're moving into the realm of actual research. Hell, I've used optical tweezers before, and you could call that "telekinesis" if you wanted to.

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### Re: Maximum efficiency when doing work over a distance

sevenperforce,
That's the thing. Telekinesis could be defined by something outside of our current knowledge. By assigning a mechanism to it, you implicitly apply restrictions to how it behaves. The question is would evidence of such "action at a distance" ability violate what we currently know about physics? Assume we cannot identify the mechanism, but we can see energy consumption, entropy increase, momentum conservation, etc. What patterns should we expect to observe in these quantities?
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FancyHat
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### Re: Maximum efficiency when doing work over a distance

In an attempt to clarify what's meant by 'telekinesis', I have produced the following illustration:-

An image seeking to illustrate the essential difference between telekinesis and, well, non-telekinesis, with reference to Newton's third law of motion.

This isn't supposed to completely define 'telekinesis', but it does seem to be the essential feature in the simplest terms.

There is then the question: does, or should, telekinesis violate Newton's third law of motion?

If it does, then, depending on what else might be true of telekinesis, it could violate other things in current science. Perhaps Yakk's point about aiming telekinetic abilities over greater and greater distances might stand, but that depends on what the details of telekinesis might be. There doesn't seem to be any certain reason why efficiency, or whatever, would have to be anything other than 100%. But there also doesn't seem to be any certain reason why telekinesis wouldn't or couldn't have an efficiency of over 100%. If it contradicts current science, then pretty much anything goes.

But if it doesn't violate Newton's third law of motion, or anything else in current science, then there must be some more forces present that aren't depicted in the second diagram, "With Telekinesis". Each force depicted would have to be paired with an equal and opposite force. But on what would they act? That would depend on how telekinesis would work. But if telekinesis doesn't contradict current science, and is only in addition to it, it seems the possibilities would then be constrained, and those constraints could be described.

I think the main question of this thread would then be: What, then, would be the most general form of those constraints?

Does that work?

Edited to add: I can think of something that could be added to the second diagram to make it comply with Newton's third law, and which would involve extra mass-energy being used. Whether or not that would be optimal in mass-energy requirement terms, I don't know.

This is based on the idea that the telekinetic should feel the same forces when using telekinesis as when not using telekinesis and acting directly, then-and-there. I thought I should explicitly say that.

There's an alternative, which doesn't have the telekinetic feeling the same forces when using telekinesis. That's different to the second diagram in the illustration. That would probably be like the first diagram, but, somehow, telekinesis would have to transfer any necessary mass-energy to the remote object, and then, remotely, do something like elasto's rocket device to remotely apply the force with equal and opposite reaction.

Whether telekinesis is like in the diagram, or more like elasto's rocket device, there seems to be a need to send some mass-energy to the remote location. Actually, I think that's probably the more basic idea than what I've incompletely illustrated, since what I illustrated can be achieved with two telekinetic acts combined: one to achieve the act of telekinesis itself, and one to provide the telekinetic with the experience of an equal and opposite, but displaced, reaction.
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elasto
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### Re: Maximum efficiency when doing work over a distance

FancyHat wrote:But if it doesn't violate Newton's third law of motion, or anything else in current science, then there must be some more forces present that aren't depicted in the second diagram, "With Telekinesis". Each force depicted would have to be paired with an equal and opposite force. But on what would they act? That would depend on how telekinesis would work. But if telekinesis doesn't contradict current science, and is only in addition to it, it seems the possibilities would then be constrained, and those constraints could be described.

One way that springs to mind would be that telekinesis actually opens a worm-hole that brings the points that were far apart into direct contact via a very short but non-zero length 'solid' medium.

To avoid ftl/timetravel implications (that don't contradict current science, but, still, better not to make our telekinetic into a god...) maybe forces are transferred through this solid medium at a speed much less than c - such that a prod at one end of the wormhole reaches the other end at the same time as light would take when travelling 'the long way' (ie. through our universe).

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### Re: Maximum efficiency when doing work over a distance

There goes any efficiency gain.
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sevenperforce
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### Re: Maximum efficiency when doing work over a distance

gmalivuk wrote:There goes any efficiency gain.

I think there would be a significant efficiency gain in my daily life if I was capable of exerting force on objects at a distance, regardless of whether there was a lightspeed delay in doing so. I could, for example, reach across the room and pick up a glass of water and bring it over here, without getting up. That's more efficient, lightspeed delay or no.

gmalivuk
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### Re: Maximum efficiency when doing work over a distance

I don't mean the delay, I mean the opening up a wormhole.
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FancyHat
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### Re: Maximum efficiency when doing work over a distance

Another, different illustration:-

Another image seeking to illustrate a possible, essential difference between telekinesis and, well, non-telekinesis, with reference to Newton's third law of motion.

This time, the telekinetic doesn't feel an equal and opposite reaction force. Instead, the telekinetic sends some mass-energy in a suitable form to the remote object. This is like elasto's rocket device, and requires good aim as Yakk observed. When the mass-energy gets to the remote object, it interacts with it in such a way as to exert a force on it, with an equal and opposite reaction force exerted on whatever becomes of what's left of the mass-energy. The object being acted on may well acquire some energy from the mass-energy sent to it, or might even lose some energy to it (if, say, it's being telekinetically slowed down).

For the telekinetic to feel an equal and opposite force acting on that telekinetic, more mass-energy can be expelled by the telekinetic in the appropriate direction. (This has not been illustrated in the illustration.) The result would be like the previous illustration, and without Newton's third law of motion being violated.

I guess this is now a question of optimisation in Special Relativity, where the rate of mass-energy to be emitted by the telekinetic is to be minimised for an arbitrary force remotely acting on an arbitrary mass. Given an intended force F (a vector) acting on a remote object with mass M, what's the minimum rate at which mass-energy needs to be emitted by the telekinetic towards that remote object? This can be expressed as a combination of mass rate, , for the (inertial) mass part of it, and power, P, for the kinetic energy part of it. The interaction at the remote object should be such that P+c2 is minimised. The interaction can involve as much mass-energy conversion as required. (I hope the 'm' with a dot above, '', is coming out okay.)

Though unlikely to be optimal, the interaction could involve chemistry. Before the interaction, a tiny amount of the mass being directed at the object would be chemical potential energy. It's included as mass, because it's not in the form of kinetic energy when it's on its way to the remote object. After the interaction, after whatever chemical reactions take place to liberate it, it would be kinetic energy instead (I'm assuming 100% efficiency for the chemical reactions). That would be a tiny amount of mass-energy conversion, but I hope it illustrates what I'm thinking.

Does that make sense?
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elasto
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### Re: Maximum efficiency when doing work over a distance

gmalivuk wrote:There goes any efficiency gain.

Well, I was assuming we were allowed to posit new science that wasn't in opposition to current knowledge but merely in addition to it. Are there no methods of wormhole generation that we have no evidence for but could work to create a wormhole without using much energy from this universe? If not I'm happy to assume the telekinetic has sources of energy outside of this universe

What I myself was visualizing though was to think of the universe as like a 2D piece of paper and the telekinetic and his target as 2D objects within it. Then the telekinetic acts by bending the paper universe until he is touching the other object and then doing whatever he likes to it. Noone else would see the bending of the universe through external dimensions as their line-of-sight is limited to the two dimensions of the paper. And so long as forces like gravity etc. also only propagate through the paper and not the extra dimensions (until the moment of contact which could be infinitesimal in duration) noone would notice anything different in how the universe evolves.

Might get messy (or fun!) if there is more than one telekinetic bending the universe at the same time though

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### Re: Maximum efficiency when doing work over a distance

Love the diagrams FancyHat! They make the question more clear.
I favor Elasto's description of space bending, This preserves Newton's laws but without introducing the need of other objects. In this model, the amount of "extra" work needed to be done is the work needed to do the space-bending.
In the model with mass-energy, the telekinetic needs to transport some "package" of energy to the target where it then interacts. The method of doing this is unknown. If the method of energy transport cannot be affected by intervening fields, it could very well be the energy is sent through another dimension.

gmalivuk,
Efficiency depends on how you define "required work". The required work is supposed to be the theoretical minimum energy needed to perform the action.
Compare the minimum amount of energy required for you to lift a dumbbell sitting next to your computer to the minimum energy required to lift an identical dumbbell sitting on the surface of the moon. The moon's gravitational field is weaker, so lifting the dumbbells by the same distance requires less work for the dumbbell on the moon. Yet, it is much more difficult for you to lift the dumbbell on the moon because you are not sitting next to it.
Effectively, the "required work" to lift the dumbbell on the moon also includes the work needed to transfer your energy (eg. your physical body) to the moon.
For a telekinetic, the "required work" is comparable to that for lifting the dumbbell on earth.

The required work for a telekinetic is the true theoretical minimum*, so anything short of telekinesis cannot achieve 100% efficiency. No matter how efficient your method is, any work done to transporting energy to the moon is unnecessary work when it comes to lifting the dumbbell on the moon.

*Assuming telekinesis doesn't break physics.
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gmalivuk
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### Re: Maximum efficiency when doing work over a distance

Efficiency depends on how you define "required work". The required work is supposed to be the theoretical minimum energy needed to perform the action.
Compare the minimum amount of energy required for you to lift a dumbbell sitting next to your computer to the minimum energy required to lift an identical dumbbell sitting on the surface of the moon. The moon's gravitational field is weaker, so lifting the dumbbells by the same distance requires less work for the dumbbell on the moon. Yet, it is much more difficult for you to lift the dumbbell on the moon because you are not sitting next to it.
Effectively, the "required work" to lift the dumbbell on the moon also includes the work needed to transfer your energy (eg. your physical body) to the moon.
For a telekinetic, the "required work" is comparable to that for lifting the dumbbell on earth.
Yes, I understood all that the first time you explained it.

My point was that opening up a wormhole is almost certainly far more energy-intensive than "simply" going to the moon in the first place.
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### Re: Maximum efficiency when doing work over a distance

Ah okay. Does it have to be though? Is there a law that gives a minimum amount of energy needed to rip a hole in space time?
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sevenperforce
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### Re: Maximum efficiency when doing work over a distance

Cradarc wrote:Ah okay. Does it have to be though? Is there a law that gives a minimum amount of energy needed to rip a hole in space time?

If "rip a hole in spacetime" is taken to have the same order of energy consumption as creating a black hole, then yes, and the law is a derivation from the Schwarzschild equation:

E = c4√A/2G√π

where E is the total energy required, c is the speed of light, A is the area of the hole you want, and G is the gravitational constant.

Just as an example: if you wanted a hole the size of a soda straw, you'd need roughly 3e41 Joules of energy.

FancyHat
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### Re: Maximum efficiency when doing work over a distance

Cradarc wrote:I favor Elasto's description of space bending, This preserves Newton's laws but without introducing the need of other objects. In this model, the amount of "extra" work needed to be done is the work needed to do the space-bending.

That sounds a bit like building a space elevator in order to avoid having to deal with rocketry.
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gmalivuk
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### Re: Maximum efficiency when doing work over a distance

Like building a space elevator every time you want to launch something, perhaps.
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lorb
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### Re: Maximum efficiency when doing work over a distance

Maybe the question can be better answered from an engineering perspective than from a purely (abstract) scientific one. If there is some job to do, and the required energy is available at a distance, what is the most efficient available way to get that energy there. For example how would you get the energy to charge a phone to the ISS? (suppose astronaut mike is no longer allowed to charge his phone by means available at the station itself because he is only using it for silly games)
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