Hypothetical question on Inertia

[novaa77]

If we could imagine an object in space which does not obey the law of inertia ( ie it offers no resistance to motion) how would it react to a force applied to it? Since it offers no resistance to a force the concept of accleration would no longer apply (There would be no rate of change of motion). Does this mean it would instantaneously attain a certain velocity and what would that velocity be?

 

[G01]

An object that has no inertia is essentially an object that had no mass. We know what speed massless particles such as photons travel at. They always travel at the speed of light in a vacuum. They can't be slowed down in empty space. So, yes, they don't have a rate of change of velocity, since they always travel at a constant speed.

 

[novaa77]

Yes I am aware that mass implies inertia, that's why I said its hypothetical. myquestion is assuming it has mass and yet has no inertia how would it behave?

 

[genneth]

If a duck wasn't a duck, but was a duck, how would it behave?

 

[ZapperZ]

Yes I am aware that mass implies inertia, that's why I said its hypothetical. myquestion is assuming it has mass and yet has no inertia how would it behave?

You can't invoke mass while ignoring one of its property. This makes it a meaningless question. You have no ability to pick and choose what property of an object with a mass should have.

Zz.

 

[arildno]

Well, you MIGHT conceivably have had a universe in which that property of an object that determines the strength of the gravitational force between itself and some other object was wholly unlinked from the same object's inertial properties.

But that is a type of universe we don't live in, probably fortunately so.

 

[G01]

Yes I am aware that mass implies inertia, that's why I said its hypothetical. myquestion is assuming it has mass and yet has no inertia how would it behave?

As everyone else said, you can't have mass without inertia, so this question is meaningless. You can still ask it, I guess, but giving an answer is going to be impossible, since you want an answer in terms of the physics you're disregarding by asking the question in the first place.

 

[ok123jump]

You can't invoke mass while ignoring one of its property. This makes it a meaningless question.
Zz.

No! Bad ZapperZ! The regime of application of our models may be limited by the scope of our experience of phenomena.

You can still ask it, I guess, but giving an answer is going to be impossible, since you want an answer in terms of the physics you're disregarding by asking the question in the first place.

NO! BAD G01! Consider that Euclidean Geometry is fairly applicable to reality even though it make impossible assumptions of points, lines, planes, distances, ect..., and these shapes are purely abstract and never occur exactly in nature. The fractal geometric shapes of Mandelbrot are more accurate models of nature as we experience it [1][2], but this disregards the fact that Euclidean Geometry works. Inertia is only tangentially intertwined with Physics as we currently understand it.We do not know "what" inertia is! At this current moment, our experience reinforces the fact that inertia is a result of mass, but that is not to say that view is correct. We must be open to the questions "What if..." questions if we are to see through the incorrect models which we have anchored our knowledge upon (which ever they may be).

"There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy." - Hamlet (I, v, 166-167)

Following along the lines of Einstein, these thought experiments can sometimes be more meaningful as experiments.

Now, to hint at an answer, I offer the following.

Let's take a simple example of the absence of inertia applied to motion. Richard Feynman was once giving a lecture in Brazil (see [3]). His topic was the "lack of experimentation in the Brazil's science curriculum". He started out by taking a copy of one of the most widely used undergraduate physics books in the country and opening it to a page that gave an example of how to calculate the position of a sphere that had rolled down an tilted plane. His remark was (I don't have the book in front of me, I must paraphrase), "No! This is all wrong! These calculations neglect the fact that rolling spheres possesses rotational inertia, which means that there is a slight delay in movement from the time of experiencing acceleration. The ball would be located slightly behind the ideal position. If your curriculum focused on experimentation then you would have experienced such this delay and would realize the limited scope of these equations!"

If a macroscopic physical object lacks inertia, then it immediately responds to a change in acceleration. A rough interpretation of inertia is a "resistance to change".

I know that this is an active topic in the String Theory, Particle Physics, Astrophysics and Condensed Matter Physics communities at the moment. Certainly, if you are interested in these views, you can visit http://www.arXiv.org/ to read some e-prints on it.

References:

[1] Mandelbrot, B. B. "How long is the coastline of Britian? Statistical self-similarity and fractional dimension" Science (156), pp. 636-638 (1967)

[2] Mandelbrot, B. B. "The Fractal Geometry of Nature" W. H. Freeman and Company, San Fransisco, CA (1982) ISBN 0-7167-1186-9.

[3] Feynmann, R. P. "Surely You're Joking, Mr. Feynman! (Adventures of a Curious Character)" W.W. Norton & Company Inc., New York, NY (1985)

 

[Danger]

NO! BAD OK123JUMP!
We don't deal with 'what if?' here; that's what Science Fiction is for. Keep in mind that a lot of the people here probably wrote some of the papers that you like to paraphrase. You're dealing with world-class experts here (myself excluded), so second-guessing them is not a good idea. Challenge, by all means, but don't pretend to know more about their areas of expertise than they do.

 

[ok123jump]

Danger,

I have to heavily disagree, this is not relegated to the realm of "Science Fiction" any more than restricting the domain of a function to a subset and thereupon studying its behavior. There is absolutely nothing unscientific about that method, or this question. You are making reference to a heavily studied area of physics in which there are many theories, and yet, none adequately answer the question that Nova77 has posed (if one disregards the last two sentences).

The "world-class experts" can do the following:

Define inertia. Define it with String Theory, QFT, QED, QM, maybe even reach into the framework of Relativity and describe the nature of inertia. If any can do that, I assure you, there'll be a Nobel Prize waiting for them.

I remind you that at one point in time, the "world-class experts" widely believed that the Earth floated through Aether. Professors, researchers, technicians and students developed highly detailed annals of Chemistry, Physics, Astrophysics, Biology and a host of other technical works, predicated upon the idea that this "substance" existed. Through and through, the Scientific Method has whittled away at those theories which were too divergent from reality - it will continue to do so.

Lastly, if I have been untruthful about my facts, or I am incorrect in my statements, I implore everyone to point that out - that is the essence of the Scientific Method.

 

[novaa77]

Danger don't be a danger to progress. A hundred years ago the thought of a man on the moon would have been called science fiction. To be a "world class expert" (what ever that means) within the field of the known is no big deal. If you stop questioning you aren't going anywhere. As for inertia (as I'm sure you know) we don't have an explanation.
Now to get back to my question does anyone have an answer, "science fiction" is acceptable!

 

[lugita15]

Let's say that an object had a nonzero gravitational mass but no inertial mass. What would happen to it? I believe that was the original question.

 

[Doc Al]

Now, to hint at an answer, I offer the following.

Let's take a simple example of the absence of inertia applied to motion. Richard Feynman was once giving a lecture in Brazil (see [3]). His topic was the "lack of experimentation in the Brazil's science curriculum". He started out by taking a copy of one of the most widely used undergraduate physics books in the country and opening it to a page that gave an example of how to calculate the position of a sphere that had rolled down an tilted plane. His remark was (I don't have the book in front of me, I must paraphrase), "No! This is all wrong! These calculations neglect the fact that rolling spheres possesses rotational inertia, which means that there is a slight delay in movement from the time of experiencing acceleration. The ball would be located slightly behind the ideal position. If your curriculum focused on experimentation then you would have experienced such this delay and would realize the limited scope of these equations!"

Feynman was complaining about bad physics in the textbooks--a simple error that would have been detected if they did the experiment. Or if they had a clue about basic Newtonian mechanics. What does this have to do with the question at hand?

Now to get back to my question does anyone have an answer, "science fiction" is acceptable!

No, I'm afraid "science fiction" is not acceptable here.

 

[genneth]

Let's say that an object had a nonzero gravitational mass but no inertial mass. What would happen to it? I believe that was the original question.

Then the equivalence principle wouldn't be true, and the whole of GR would come crashing down. Then you're left with the problem of finding a field theory of gravity that doesn't violate special relativity (unless you're throwing that out too?)

 

[capnahab]

This question is not plausable. It is like asking the old Superman Comics book question. If a immovable mass is hit by a mass that can not be stopped what happens? Standard theory would say they would form a black hole due to the huge increase of mass due to the conservation of energy.

 

[ok123jump]

Capnahab, that may not be true.

Until the Manhattan Project, the question of whether there was an exact conservation of energy and momentum in the quantum realm was widely debated. A Quantum Theory of Optical Phenomena was formulated by J.C. Slater, in collaboration with Bohr and Kramers in 1925[1] that formulated a framework where these two concepts need not always apply. Somewhat recently, R. Pakula has used this framework and published an e-print[2] showing that the reasons leading to the assumption that a photon has mass 0, also attributable to the standardization of Quantum Theory from the Manhattan Project, are flawed. If he is correct in his framework, then, this is a situation where other processes take effect and there is not an exact conservation of energy and momentum in QM.

I relate this to the current topic by saying that there are credible views that exist contrary to the of the main viewpoints. Due to the fact that we do not know what causes inertia, we cannot assume that it is inherently generated by mass - we only have tangential evidence of their connection. If you assume that this is not the case, you fall into the post hoc ergo proctor hoc fallacy. We need direct evidence and a concise theory that links the two - I claim that both are lacking.

Thus, let us deeply consider what inertia is, rather than skipping this whole topic by making some half-baked reference to Science Fiction.

References:

[1] Slater, J.C. "A Quantum Theory of Optical Phenomena" Phys. Rev, Vol. 25, No. 4, pp. 395-428

[2] Pakula, R. "A realistic model for radiation-matter interaction" arXiv e-Print archive, June, 2004 http://arxiv.org/abs/quant-ph/0405055

 

[genneth]

Okay, so the problem of gravitational charge vs inertial mass is exactly the one addressed by the equivalence principle. Specifically, the weak equivalence principle, or uniqueness of free fall. This has been experimentally tested, through a series of very accurate experiments by Eoetvoes, Dicke, Braginsky, and that's only up to the late 1970's. Misner, Thorne and Wheeler, in Gravitation, gives the following figures:

5 parts in 10^9 that the Earth imparts the same acceleration to wood, platinum, copper, asbestos, water, magnalium (90% Al, 10% Mg), copper sulphate and tallow.

7 parts in 10^10 for Earth on platinum, copper, bizmuth, brass, glass, ammonium fluoride and an alloy of 30% Mg, 70% Cu.

1 in 10^11 of Sun on aluminium and gold.

1 in 10^12 of Sun on aluminium and platinum.

From this, it's possible to infer the response of neutrons, protons, electrons, virtual electrons-positron pairs, nuclear binding energy, electrostatic energy, etc. So we get 1 in 10^10 for neutron and proton, 2 in 10^7 for electrons vs nucleons, 1 in 10^4 for virtual pairs, 1 in 10^7 for nuclear binding energy and 3 in 10^9 for electrostatic energy.

The full details are, like I said, in Gravitation by MTW, 38.3.

Does this answer the question?

 

[ok123jump]

Okay, so the problem of gravitational charge vs inertial mass is exactly the one addressed by the equivalence principle. Specifically, the weak equivalence principle, or uniqueness of free fall. This has been experimentally tested, through a series of very accurate experiments by Eoetvoes, Dicke, Braginsky, and that's only up to the late 1970's. Misner, Thorne and Wheeler, in Gravitation, gives the following figures:

5 parts in 10^9 that the Earth imparts the same acceleration to wood, platinum, copper, asbestos, water, magnalium (90% Al, 10% Mg), copper sulphate and tallow.

7 parts in 10^10 for Earth on platinum, copper, bizmuth, brass, glass, ammonium fluoride and an alloy of 30% Mg, 70% Cu.

1 in 10^11 of Sun on aluminium and gold.

1 in 10^12 of Sun on aluminium and platinum.

From this, it's possible to infer the response of neutrons, protons, electrons, virtual electrons-positron pairs, nuclear binding energy, electrostatic energy, etc. So we get 1 in 10^10 for neutron and proton, 2 in 10^7 for electrons vs nucleons, 1 in 10^4 for virtual pairs, 1 in 10^7 for nuclear binding energy and 3 in 10^9 for electrostatic energy.

The full details are, like I said, in Gravitation by MTW, 38.3.

Does this answer the question?

I believe that your post is a great place to start. Good one.

Have these results been experimentally verified for particles?

 

[genneth]

I would say that these experiments are about particles. What do you have in mind?

 

[ok123jump]

As an example, if one could take a free particles, such as a free-electron beam, and experimentally verify the inertial inferrance from MTW, that would be a verification for particles.

Since I began my focus on Laser Physics, I have not come across such a report - that is not to say that one does not exist. Are you aware of any?

 

[genneth]

I am similarly ignorant of such tests. As it happens, I asked a similar question a while back on spr: http://groups.google.com/group/sci....read/thread/5ba054ba561be64b/86ac692f43b6e7b1

Perhaps you can find something useful from that.

However, personally, I find the existing tests perfectly acceptable. A violation of them would put much of the things we know about physics onto shaky ground -- the composition of atoms and molecules for one. I would think it unlikely, to put it mildly.

 

[Wonderballs]

It would behave exactly as you described, no resistance to motion. Happy??

 

[novaa77]

+ :uhh: =

 

[TVP45]

If we could imagine an object in space which does not obey the law of inertia ( ie it offers no resistance to motion) how would it react to a force applied to it? Since it offers no resistance to a force the concept of accleration would no longer apply (There would be no rate of change of motion). Does this mean it would instantaneously attain a certain velocity and what would that velocity be?

This is easy. Think of a shadow. It has no mass. It has no inertia. If we apply a force to it, it doesn't react at all. It can accelerate without a force and can quickly achieve almost any velocity (including speeds in excess of c). This, of course, is based on simple anecdotal observations and awaits a fully developed theory of dark.

 

[ok123jump]

It can accelerate without a force and can quickly achieve almost any velocity (including speeds in excess of c).

Certainly, this is not true. Take the conditions of a stationary sole source generator (say a giant candle, suspended in mid air) and a flat surface (similar to 2D slices of the xyz plane). Then, we arrive at two conclusions:

1. A shadow is the output of function of incident radiation (EM) onto the surface over which it's projected; furthermore, the amount of radiation absorbed by the surface is directly proportional to the amount of radiation emitted by the surface (the reason we can see objects). Therefore, the material will continue to fluoresce and re-emit EM radiation in direct proportion to the amount of EM radiation it receives - no photons = no feedback.

2. Similarly, if the shadow is considered the output of a function, it can be seen that the generating conditions of that function (namely the object that blocks the EM) bind the translational movement (defined as movement without change to the length of the shadow) to the surface is bounded by the speed at which the generating conditions evolve (the speed at which the blocking-object moves across the plane); accordingly, the traversal movement (defined as movement causing a change to the length of the shadow) is bounded by the velocity of the EM radiation provided by the source generator (the shadow cannot grow faster than then last packet of EM radiation which is to travel to the surface after it was blocked).

Consider this thought experiment: How long does it take light from the sun to reach the earth? If I were to build a giant solar reflector, and perfectly position it between the Earth and the sun so as to totally block out the light, how long would it take for you to notice that I blocked the sun?

As evidenced by the above statements. One can clearly see that shadows are bounded by the velocity of EM radiation (c in a vacuum) and due to the fact that they are the output of functions, they have no existence outside of their generating conditions, which happens to be an object which experiences force and is limited in velocity.

Although, I do give you credit for thinking outside of the box.

 

[Doc Al]

shadows moving faster than light

As far as shadows (and light spots) moving faster than light: sure they can. But shadows are not physical objects. Read this: Trivial FTL travel

 

[TVP45]

Doc Al,
Good call. I understood that to be a question when I posted, but you see the original question was about a "hypothetical object", which most would agree is anything that we can imagine being perceived by our senses. Thus, the edge of a shadow qualifies as such an object.
I suspect one might spend many an evening (and untold pints) debating whether such things as phase are "real" objects. And that is one of the great joys of science. Wouldn't it have been wonderful to take one of those long walks on the beach with Bohr et al?
Tom

 

[Doc Al]

I understood that to be a question when I posted, but you see the original question was about a "hypothetical object", which most would agree is anything that we can imagine being perceived by our senses. Thus, the edge of a shadow qualifies as such an object.

I disagree. A shadow is not any kind of a physical "object" and I doubt that that's what the OP had in mind. What's the mass of a shadow? How would one exert force on a shadow, even hypothetically? (And, as the title of that link suggests, having such non-objects travel FTL is trivial.)

 

[ok123jump]

Please explain to me why a shadow is more than a difference in emitted radiation over a particular surface...

 

[Doc Al]

Please explain to me why a shadow is more than a difference in emitted radiation over a particular surface...

And your point would be what? When we talk about the speed at which a shadow moves, realize that we're talking about its sideways motion across a surface. (Did you read the link?)

 

[easttiger2007]

If we could imagine an object in space which does not obey the law of inertia ( ie it offers no resistance to motion) how would it react to a force applied to it? Since it offers no resistance to a force the concept of accleration would no longer apply (There would be no rate of change of motion). Does this mean it would instantaneously attain a certain velocity and what would that velocity be?

The discussion goes too far. The question is simple, but need to be clarified by classifying into following two cases.
Case 1. Just the NSL changes its form, say f=m^2*a or or f=sin(m)*a etc. This will be a problem of mathematical deduction.
Case 2. Inertia just vanish completely. Then it can be regard as a limit of some real situation. For example, a light bead on a horizontal frame which can response to any significant horizontal force with nearly infinite acceleration.

 

[TVP45]

Sim Wa.
The OP insisted on a hypothetical object with at least one of it's commonly understood properties suppressed. An object is commonly understood to be anything capable of being perceived by our senses. A hypothetical object is thus anything which we can imagine being perceived by our senses. I have seen the edge of a shadow. QED.
If one asks a question about a hypotetical object, then one should expect an answer containing a hypothetical object. In fact, I suspect there is great similarity between a shadow and the hypothetical object posited, i.e, how does an object not subject to a field interact with a field?
Bohr had a great line which may apply here:
It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we say about Nature.
Tom

 

[vanesch]

If I may add something to this sometimes hallucinating thread
The OP asked essentially what happens if an object's inertial mass is zero, and if we exert a force on it. But the problem is: what does it mean to "excert a force" on an object ? Usually, this results from an interaction with a given prescription of how the momentum of the object changes, but this object doesn't have any !
Does the object have a position in space at a given instant, or is it position-less too ?
So you cannot ask what would happen if we exert a force on it, because that would mean that we should give a law saying how its momentum is changing, while it hasn't gotten any. In other words, it is meaningless to talk about exerting a force to an object for which momentum doesn't have a meaning, as force is change in momentum.
You could just as well ask what would happen to a position-less object when we apply an acceleration to it. Force is change in momentum. If there's no momentum, it cannot change it.

 

[novaa77]

So you cannot ask what would happen if we exert a force on it, because that would mean that we should give a law saying how its momentum is changing, while it hasn't gotten any. In other words, it is meaningless to talk about exerting a force to an object for which momentum doesn't have a meaning, as force is change in momentum.
You could just as well ask what would happen to a position-less object when we apply an acceleration to it. Force is change in momentum. If there's no momentum, it cannot change it.

All matter (physical substance as defined by the Oxford dictionary) is capable of accleration. The question is, is inertia an inherent property of matter, or is it a result of external influences that cause inertia and thus give us the "effect" of mass.

 

[tabchouri]

i would say the first hypothesis. inertia is inherent to mass.-----------------------------------------------------
Correct me if I am wrong.
http://ghazi.bousselmi.googlepages.com/présentation2