# How does a body "know" how to move??!!

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Think of a body moving as in Newton's first law - in a straight line at a fixed speed say. I have been wondering where is the information for the body to "know" how to move? One could argue that the motion itself is the "information", but that is somewhat unsatisfactory from an information theory point of view.

I understand that information theory is being suggested as a possible way of looking at fundamental physics, so my question might be relevant, even though I am only a novice student of theoretical physics.

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When a body experiences a force, it moves, i.e., it accelerates. According to Newton's First Law, a body in a uniform state of rest or motion continues to do so, until and unless an external force acts on it. From this we deduce, that motion or rest is independent of getting information about the reference frame. Any body will be in such a state until external force acts on it. However from a body's motion, we can get some information. Suppose a body is showing accelerated motion- in such a case we infer that some external force must have acted upon it.

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Any inertial frame is as good as any other, so a body can always say it is at rest and everything else is in motion. These frames are simple linear transformations of each other, so that's where the constant velocity comes in.

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Sure, I know about inertial reference frames, relativity etc but I think there might be some mileage in exploring ways in which the information about motion is stored. For example, where is the information stored - "in" the object or "in" space?

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Sure, I know about inertial reference frames, relativity etc but I think there might be some mileage in exploring ways in which the information about motion is stored. For example, where is the information stored - "in" the object or "in" space?

I am very much subject to correction but Is the information encoded in the whole environment? Is that what the gravity field is ?
Every point in spacetime has "instructions" as to where a macro level body should go and this set of instructions is provided by the global distribution of mass-energy wrt that point.
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The gravity field holds information about acceleration once an object is there but I cannot see how this is related to the information about individual objects' different velocities.

It's a conundrum to me, and it seems that nobody has considered the problem ever!

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Think of a body moving as in Newton's first law - in a straight line at a fixed speed say. I have been wondering where is the information for the body to "know" how to move? One could argue that the motion itself is the "information", but that is somewhat unsatisfactory from an information theory point of view.

I understand that information theory is being suggested as a possible way of looking at fundamental physics, so my question might be relevant, even though I am only a novice student of theoretical physics.

Newton postulated that motion is in reality with respect to Absolute Space (your teacher may have forgotten to inform you). According to Newton the body "knows" how to move even without external action, because that entity is no hindrance as long as the body doesn't accelerate with respect to it. Alternatively, Minkowski proposed a Block Universe. You can read ongoing discussions about those concepts in the General Philosophy forum (Is Space-Time a physical entity, physical space vs physical space-time).

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So that's " I don't know either then" is it?

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Sure, I know about inertial reference frames, relativity etc but I think there might be some mileage in exploring ways in which the information about motion is stored. For example, where is the information stored - "in" the object or "in" space?

So that's " I don't know either then" is it?

Anyone can be a smartass.

But have you studied Hamilton-Lagrangian mechanics and the principle of least action and the calculus of variations?

That is what you need to you to obtain an answer.

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Think of a body moving as in Newton's first law - in a straight line at a fixed speed say. I have been wondering where is the information for the body to "know" how to move? One could argue that the motion itself is the "information", but that is somewhat unsatisfactory from an information theory point of view.

I understand that information theory is being suggested as a possible way of looking at fundamental physics, so my question might be relevant, even though I am only a novice student of theoretical physics.

Although you appear to be asking for answer in physics, there are also physiological answers. If that is also your interest, you might want to consider how our cerebellum actually manages how our body moves and how our motor cortexes manage motor information, initiate and control our motor responses.

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I seem to have to touched a nerve!

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So that's " I don't know either then" is it?

Nope - we are in nearly the same position (but slightly better) than the ancient Greeks when they invented the atom concept. In fact they already found the answer, just not totally sure, and without details. And already somewhat better: the first law is about inertia. Thanks to people like Newton we can make sense of it, and thanks to people like Maxwell we know that self induction and inertia are related. The electron told us not only about electricity, but also about mechanics. What did you learn so far?

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Although you appear to be asking for answer in physics, there are also physiological answers. If that is also your interest, you might want to consider how our cerebellum actually manages how our body moves and how our motor cortexes manage motor information, initiate and control our motor responses.

I think he was referring to the generalized "object" definition of body rather than the human body.

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I think he was referring to the generalized "object" definition of body rather than the human body.

Oh...I see...nevermind

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Think of a body moving as in Newton's first law - in a straight line at a fixed speed say. I have been wondering where is the information for the body to "know" how to move? One could argue that the motion itself is the "information", but that is somewhat unsatisfactory from an information theory point of view.

I understand that information theory is being suggested as a possible way of looking at fundamental physics, so my question might be relevant, even though I am only a novice student of theoretical physics.

How is that "unsatisfactory from an information theory point of view"? Would you mind explaining the link to information theory you are claiming?

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I don't see any connection between information theory and Newtonian Physics.

Perhaps you have misunderstood this

Rasher Null

I understand that information theory is being suggested as a possible way of looking at fundamental physics, so my question might be relevant, even though I am only a novice student of theoretical physics.

Information theory is based on the idea that a system (real and physical or artificial and imaginary) can exist in a specific finite number of states.

This corresponds to quantum mechanics and statistical mechanics in theoretical physics which have a similar basis.

Newtonian physics allows an unlimited number of states'.

So for example the short answer is a body doesn't.

Consider a tank of water on the top of a hill.

Which way will it flow?

The answer is any way that you punch a hole in the side.

The water will flow out anywhere because it exerts pressure on all sides simultaneously.

How does that fit with your information theory?

Edited by studiot
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It's the issue of motion that I am trying to draw attention to. I'm not an information theory specialist - just a layperson. Perhaps my association of "information about motion" with "information theory" is misguided .. but certainly I am puzzled by motion in terms of how it is "coded for", as it were. It seems that the state of motion of an object can only be deduced through observation of that motion, but psychologically at least, this is bizarre and unsettling, I suggest. What is it about the state of matter and or space that "codes" velocity?

Has anyone ever considered what motion is at the quantum level?

Edited by Rasher Null
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I don't understand why you think there is any information, code or knowledge needed for motion to occur. The information only exists in our minds when we make some observation about it. It is not inherent, or required, for motion to happen.

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I'm sorry, what does coding have to do with my tank of water?

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I feel you guys are missing a trick by being so dismissive and unwilling to think about it. I mean, reputable scientists have even speculated that space could be granular and discrete at the quantum level. Quantum weirdness abounds and there are several mysteries - I feel a fresh look at motion might be make for an interesting discussion.

Sure motion can be successfully treated as a cut and dried concept in classical physics, but I was hoping to move away from that limited viewpoint.

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I feel you guys are missing a trick by being so dismissive and unwilling to think about it. I mean, reputable scientists have even speculated that space could be granular and discrete at the quantum level. Quantum weirdness abounds and there are several mysteries - I feel a fresh look at motion might be make for an interesting discussion.

I don't think anyone is being dismissive. People have engaged pretty well for an idea that is not well explained and appears to have no basis.

Perhaps you need to be a bit more specific about your ideas.

For example, what is the relationship between motion and information?

What is the relationship between knowledge and motion?

What is the relationship between coding and motion?

Why do you think information is required for movement?

Edited by Strange
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Thanks for that Strange.

OK, well I don't have many ideas - certainly not well formed ones, so I am unable to present a coherent model or theory merely air my thoughts and hope that others do likewise.

The "problem" I have is when I think about two rigid spheres that move differently in a perfect inertial reference frame. Conducting a thought experiment ... if one were to freeze each object and examine it in unlimited detail , would I be able to deduce in which direction, say, each object is moving? If I were to examine the space in and around each object would I be able to then?

If the answer is no, then what accounts for the difference in motion? If "nothing" accounts for the difference in motion, then the next question is "what does that say about motion...?"

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If you freeze them, then they are not moving. You need to observe their change in position over time; that is what define movement.

But perhaps you are thinking of something like Zeno's paradox. Which is largely resolved by Newton's (and Leibnitz's) work on calculus and limits.

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When I say "freeze" them I mean take an instantaneous snapshot, so they are still moving. (It is a thought experiment remember!)

No I'm not actually thinking about Zeno so far - that paradox is merely a mathematical one.

Edited by Rasher Null
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Essentially, you're saying "If we ignore all information about motion, what can we say about motion?"

Alternatively, you're asking for how to express the laws of motion as a first-order differential equation, where the way in which things change only depends on their current status. In which case, you may want to look into phase space.

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