A paradox inside Newtonian world

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    Newtonian Paradox
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The discussion revolves around a paradox in Newtonian mechanics concerning gravitational forces and the behavior of masses. Participants debate the calculations and assumptions regarding how gravitational forces act on a system of masses arranged in a specific configuration. Key points include the assertion that the net force on certain masses is directed leftward, while others argue that the center of mass may not actually move left due to the dynamics of the system over time. The conversation highlights the complexities of infinite mass distributions and the implications for conservation laws in physics. Ultimately, the paradox challenges traditional interpretations of gravitational interactions in a Newtonian framework.
  • #451
Tomaz Kristan said:
No, it is not always correct just to extrapolate that way. For example, every finite set of naturals have a maximum element. But there is not so for an infinite set of them. Never.
But extrapolating from finite sets is the only way we have of evalutating convergent sums. Without this extrapolation, all infinite sums are undefined.
 
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  • #452
Tomaz:
But why insist that Newton's theory has to apply to infinite sets of masses?
Newton proposed a physical theory. Infinite sets are not within that scope.
Your "paradox" may be entertaining but I don't see it as any challenge to the theory.
 
  • #453
ObsessiveMathsFreak said:
But extrapolating from finite sets is the only way we have of evalutating convergent sums. Without this extrapolation, all infinite sums are undefined.

I respect this. Gave you several examples, related to this case.

The infinite sum of forces, all converge to a finite value.
 
  • #454
Eli Botkin said:
But why insist that Newton's theory has to apply to infinite sets of masses?

Be cause there is no rule to forbid that. It is allowed, and it's enough.
 
  • #455
I skipped over like 15 pages here cause it was getting tedious, but did you ever show WHY you believe the collective masses on the left (of the ball +jupiter experiment) do not move toward jupiter? I don't understand that.
What would keep them from moving as a whole? The collective forces acting on one of the masses is all of the surrounding masses plus jupiter. While the near masses may keep it from moving, each one has some effect from Jupiter that I don't see how gets canceled out. Each one would have an effect, that would press it a little more on the one to its right, which in turn would result in a normal on the next one toward the left, which would move it to the right, all the way down the chain. What am i missing?

Also we're assuming an infinite number of balls? Because each ball would have a resultant force to the left EXCEPT the left-most one. It would have the resultant force to the right, and it would be great, correct? Basically the force of all balls to its right. By making the system infinite its almost like looking at the whole picture, minus the leftmost ball. Right?
 
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  • #456
Healey01 said:
What would keep them from moving as a whole?

It's the same thing. You can look every subsystem as a whole, or only the "whole system", it's motion would be the same.

For example, you may cut the Moon into 777 pieces in your calculation and still the orbit must be the same.

Also we're assuming an infinite number of balls?

Yes, we do. Here in this construction. (Maybe I should call it Kristan's complex :blushing: ).

I don't think - no, I am quite sure in fact! - that nothing like this lives in the real world. It's just a problem inside the abstract Newtonian world.

It would have the resultant force to the right, and it would be great, correct?

Correct. In the finite case, it's all okay.
 
  • #457
Healey01 said:
WHY you believe the collective masses on the left (of the ball +jupiter experiment) do not move toward jupiter?

They (each and every ball) have the only liberty to move in the accordance to the resulting force. And the resulting force is a finite force to the left, for any ball you choose.

Still, I do not necessarily insist in a moving thing. The fact, that at the moment t=0, when all the velocities are still zero, when the third Newton's law is already not obeyed -- is enough.
 
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  • #458
Healey01 said:
I skipped over like 15 pages here cause it was getting tedious

Same here :rolleyes:

I smell a problem in setting up the original configuration...
(i.e. related to the unbounded density of the progressive balls and... oh yeah! we need infinity balls! If they start packed together, how could we unpack them? If they start separated, how do we move them to their final positions?)
 
  • #459
Tomaz Kristan said:
They (each and every ball) have the only liberty to move in the accordance to the resulting force. And the resulting force is a finite force to the left, for any ball you choose.
As I've read in previous pages, Newtonian physics allows for infinite particle masses, correct? Or even non-particle. Does it allow for infinite spatial dimensions?

What if instead of having them go farther to the left, you say, there are an infinite number of them with the same pattern as stated, from some distance X=-D to X=0. So the infinite particles are not the endpoints but rather the inbetweens. Does the same problem occour? I would imagine not and the system of balls would move together toward Jupiter in the expected manner. The problem is lying not that its just an infinite series or the number of items, which seems trivial, but that the dimensional distance is infinite as well. At least that's what it looks like. But I am no PhD mathematician.
 
  • #460
xnick said:
If they start packed together, how could we unpack them? If they start separated, how do we move them to their final positions?)

Doesn't matter. You can't even "separate" two mass points. But you can always set the original position every way you want.
 
  • #461
Tomaz Kristan said:
And the resulting force is a finite force to the left, for any ball you choose.
But the force on the center of mass is infinite.
 
  • #462
ObsessiveMathsFreak said:
But the force on the center of mass is infinite.

Not true. The mass center is at 10/19 and the force there is of course finite.
 
  • #463
Tomaz Kristan said:
Three weeks ago I have constructed this apparent paradox inside the Newtonian world.



http://critticall.com/alog/Antinomy_inside_mechanics.pdf"

Am I wrong or not? What's your say?

- Thomas

Yeah.

For every mass particle you can take the combined force of all the particles left from it, acting as a force to the left relative to the center of mass of all particles on the left side, and all the particles right from it, acting as a combined force to the right relative to the particles to the right. This holds true for every mass particle, except the right most one.

But at the same time, the center of mass of all the masses on the left side, will move to the right, and the center of mass of all the masses on the right side, move to the left.

This then however makes clear that, while at first we say that for every particle it moves to the left, it also belongs to a constellation of particles which center of mass moves to the right.

So, your initial hypotheses that ALL masses move to the left, is not true.

This could be shown also by in advance calculating the center of mass of all particles, and calculate the nett force from every particle as acted upon by that center of mass. So, most part of the particles move to the right.
It's center of mass doesn't move.
 
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  • #464
Nothing moves at t=0. What happens later, I don't even care that much. Situation is illegal already.

At t=0, all net forces, to every ball, point left. And that's bad enough.
 
  • #465
Tomaz Kristan said:
Not true. The mass center is at 10/19 and the force there is of course finite.
What, the force field? That's not the force on the center of mass. The force on the center of mass is a divergent sum of the forces on every particle.
 
  • #466
You know what? I don't even care for that. All I need is the situation at t=0, and the finite (all negative!) forces to every ball.

What may going on later, is irrelevant. The paradox has already happened at zero time.
 
  • #467
I've just noticed this thread, and I haven't read the whole thing. So apologies if this has already been brought up. But it seems to me that there is a very basic problem with this. Tomaz, you describe your scenario as "a mass of 2^{-N} kg 10^{-N} for every N". So each mass point can be indexed by a natural number.

You then go on to talk about "the rightmost mass point". But what would its index be? It can only be the largest natural number. But there is no largest natural number. So it seems to me that you can't say anything about the rightmost mass point. It simply doesn't exist.
 
  • #468
The whole thread is silly.
OP simply doesn't understand that using conditionally convergent distributions is unphysical to start with; he insists that his own unphysicality is Newton's fault.

I haven't bothered with this nonsense for a long time.
 
  • #469
Tom,

I describe it as a mas of 2^-N kg at position 10^-N meter for every natural N, 0 included.

So the rightmost ball is at 1 meter, has 1 kg. The whole system has of course 2 kg.

And the leftmost ball does not exists.

That's how I describe the damn thing.
 
  • #470
Tomaz Kristan said:
You know what? I don't even care for that. All I need is the situation at t=0, and the finite (all negative!) forces to every ball.
You don't even care about the force on the center of mass? Isn't that the whole point of this entire thread? Everything I have said applys exclusively at t=0.

Tomaz Kristan said:
What may going on later, is irrelevant. The paradox has already happened at zero time.
You still haven't proven that mathematically.
 
  • #471
OMF ...

Do you agree, that a finite force is to every mass point?

Do you agree, that every one of those forces is directed toward the left?

(At t=0, of course!)

It would be enough, thank you.
 
  • #472
Resume?

So, here we are. This simplified version, at t=0, with no moving (yet), is sky clear and nobody can raise an objection?

Good.
 
  • #473
Im sorry, have you gotten around to doing any of the math so I could see what you're stating?
 
  • #474
The left pointing component of the force is equal to 0.992*G*(m/d)^2 for every ball. Where d is the distance to the nearest left ball.

The right pointing component is always smaller. It's also always a finite sum of a finite number of finite right pointed forces.

The resulting force is always negative, for each ball.

Need to be even more specific?
 
  • #475
Tomaz Kristan said:
The right pointing component is always smaller. It's also always a finite sum of a finite number of finite right pointed forces.

The resulting force is always negative, for each ball.

Yes and the resulting sum of all such forces is undefined.

Consider the force on each ball simply from the one to the left of it.

The mass of the right ball is 2^{-N}. The mass of the ball to its left is 2^{-N-1}. The distance between the two balls is 10^{-N}-10^{-N-1}.

For the left pulling (negative) force on the Nth ball due to only the ball to its immediate left is

F_N = \frac{G 2^{-N} 2^{-N-1}}{\left(10^{-N}-10^{-N-1}\right)^2}= \frac{G 2^{-2N-1} }{10^{-2N}\left(1-10^{-1}\right)^2}
F_N = G\frac{5^{2N}}{2 \left(\frac{9}{10}\right)^2}=\frac{100 G}{162} 5^{2N}

So the sum of all these leftmost forces(a sum less than the total leftmost forces is:

S = \sum_{N=0}^{\infty} F_N = \sum_{N=0}^{\infty} \frac{100 G}{162} 5^{2N}
S = \frac{100 G}{162} \sum_{N=0}^{\infty} 5^{2N}

5^{2N} is obviously, no immediately obviously a divergent sum. In case you don't believe me, here's the first terms 1, 25 , 625 , 15625, 390625, 9765625, 244140625. This isn't going to diverge.

What more do you want? The force on the center of mass is not defined. It doesn't have a mathematically defined motion.
 
  • #476
Your calculation is wrong, OMF.
 
  • #477
Tomaz Kristan said:
Your calculation is wrong, OMF.
Words fail me.
 
  • #478
I know that, already. But do try!

Do you agree, that the sum of masses on the left side of every ball is equal to the mass of that ball?

1/2+1/4+... =1.

Yes?
 
  • #479
If it's wrong, then you could certainly point out a specific error now, couldn't you?


Incidentally, if I may guess where you're going next, you should remember that the gravitational field exerted by a system of particles is usually not equal to the gravitational field exerted by a hypothetical point particle located at their center of mass whose mass is the sum of the individual masses.
 
  • #480
Shall we bet around this?

I am all for, are you also?
 

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