Talk:Bucket argument

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[edit] Absolute vs Relative

so... is this true then or what? does this prove there is an absolute frame of reference? i have been wondering this since i was like 12 so it would be nice to know why nobody ever discusses it... -plasticlax

It appears that rotation is absolute, but translation is still relative. pstudier 08:12, 2004 Apr 1 (UTC)

(William M. Connolley 21:42, 18 Oct 2004 (UTC)) I think the variant is due to Ernst Mach. But OTOH the variant I'm used to is an otherwise empty universe featuring two spheres joined together by a rope. If you measure the tension in the rope you can find out if they are spinning. Mach's principle says that there is no tension. I think.

Einstein's theory of general relativity does not need the assumption of absolute space. Of course, Einsteins theory of gravity and motion does need to provide a mechanism that is telling matter whether it is accelerating or not, the bucket thought experiment proves that.
According to the theory of general relativity there is a universal inertial field. This universal inertial field is transparant to velocity, so all velocities are indistinguishable, but whenever an object accelerates, there is interaction with the universal inertial field, opposing (but not preventing) the acceleration, hence the formula of proportion: F=ma. In a universe without matter the inertial field would be identical to minkowsky space-time everywhere. But matter deforms the inertial field in its neighbourhood, and wherever the universal inertial field is deformed only limited volumes of space are effectively indistinguishable from minkowski space-time. The part of this deformation of space-time geometry that counts the most is the gravitational time dilation. When matter moves through deformed space-time geometry, the line of travel is seen to be curved when looked at from a sufficient distance. Unlike electromagnetic interaction, that is mediated by a "carrier" that travels in space, gravitational interaction is mediated by deformation of the very fabric of space-time itself. Deformation of the gravito-inertial field and deformation of the space-time geometry are one and the same thing in the theory of general relativity.
Rotation is not absolute, but according to general relativity it is exceedingly rare to see significant rotation of local space-time geometry with respect to the universe. Hence rotation measured against the locar space-time geometry and rotation with respect to distant stars are invariably seen to match. General relativity does predict under what (extreme) circumstances significant local rotation of space-time geometry with respect to the Universe will occur.
When two spaceships are co-accelerating, then their relative velocity is zero. However, when they want to communicate, for example by radio signals, they observe the signals are distorted. Their interaction with space-time affects the signals. It is only when both space-ships are moving inertially that the laws of special relativity apply. When the spaceships are both accelerating they must each take their individual interaction with the universal inertial field into account. --Cleon Teunissen | Talk 18:19, 19 Mar 2005 (UTC)
(William M. Connolley 21:44, 19 Mar 2005 (UTC)) The bucket argument proves nothing. Its something to ponder, but no-one has drawn any defendable physical theory from it.
Well, Einstein did draw a conclusion from the thought experiment. To Einstein it showed a severe condition that any theory of motion must meet. Einstein agreed with Mach's objection against newtonian absolute space. Newtonian absolute space acts on matter but it is not acted upon, wich, argued Einstein, is profoundly unsatisfacty. Einstein's physics intuition told him that a theory of physics that wants to really represent Nature should describe Nature as interactions between physical things that act upon each other and that are being acted upon.
To illustrate the condition that any theory of motion must meet Einstein devised the rotating liquid spheres thought experiment. Einstein argued that this thought experiment proves that there must be an interaction of local matter with distant matter. The problem of taking account of inertia is a problem of information. Independent of the choice of coordinate system, either rotating with respect to the liquid sphere floating almost alone in space, or a coordinate system that has zero rotation with respect to the liquid sphere floating in space, it must be recognized that some mediator is providing the information that determines exactly how much the liquid sphere is bulging at the equator.
Any theory that lays claim to being a good representation of Nature must describe a mechanism that relays that information. Einstein believed that general relativity achieves this aim, and the scientific consensus in the community of physicists is that general relativity indeed achieves that aim. Mach's original proposal was that any theory of motion and in particular inertia should not refer in any way to space, Mach argued that it should be about interactions of matter only. Einstein did not follow that proposal of Mach. --Cleon Teunissen | Talk 09:13, 20 Mar 2005 (UTC)

[edit] The bucket and the floating globes (new article)

I wrote a new article, after reading Newton's Scholium.

I concentrated on the physics, and I avoided the philosophy. Newton's rotating bucket is not situated in empty space; the two globes, connected by a cord under tension had been situated by Newton in otherwise empty space. The bucket argument is not a thought experiment, it is an inference from something seen in daily life; the two-globes-connected-by-a-cord is a thought experiment. It is understandable that the two have been merged into a bucket-with-water-in-empty-space, but I feel the article should be historically correct.

The globes-and-cord thought experiment is by far the most interesting line of thought, it is wider in scope than the rotating bucket argument.

I decided not to write about Mach's philosophical objections against the tacit assumptions in newtonian dyanamics. --Cleon Teunissen | Talk 18:45, 20 Mar 2005 (UTC)

[edit] Category; Classical mechanics

Sebastian (talk) had added [[Category:Kinematics]] to the article, commenting:

maybe should be dynamics, but there is no such cat as of now Sebastian (talk) 10:11, 2005 May 20 (UTC)

The current article on Kinematics opens with:

In physics, kinematics is the branch of mechanics concerned with the motions of objects without being concerned with the forces that cause the motion. In this latter respect it differs from dynamics, which is concerned with the forces that affect motion.

So the category 'Kinematics' is certainly inappropriate for the bucket argument. The bucket argument is about the philosophy of Classical mechanics. Newton is justifying his concept of laws of motion, he is very much concerned with the forces that are at work. Therefore I have removed the 'Kinematics' category, and replaced it with [[Category:Classical mechanics]]
--Cleon Teunissen | Talk 15:00, 20 July 2005 (UTC)

"Here Newton tacitly assumes the weight of the globes is known." Shouldn't that be mass??--Hobx 05:36, 3 September 2005 (UTC)

[edit] Something wrong?

This page is profoundly confusing, utterly useless for a beginner. I found an older version much more useful to understand things.(http://en.wikipedia.org/w/index.php?title=Bucket_argument&oldid=24025492) Please don't make things complicated just to give them the appearance of 'scientific rigour'. 59.163.146.5 09:04, 20 February 2006 (UTC)

I wrote the version that you prefer. My version was replaced, with the comment: 'amateur viewpoint removed'.
I have no trouble understanding the current version, being a physicist, and I know the relevant history of physics reasonably well. But I agree with your criticism that the current version is only understandable for people who already have a solid grasp of the subject matter; the current version assumes a lot of prior knowledge in the reader. The current version of the article is written for people who won't look up the article, since they already know.
In my version I focused exclusively on Newton's thinking and on translating concepts from newton's time to present day concepts, to make it an article that newbies to the subject can learn from. Maybe a merger should be attempted. Newton was very keen to debunk Descartes. --Cleonis | Talk 11:17, 20 February 2006 (UTC)
A few of that version are IMO misreadings, eventhough I base myself on the same translation of Newton. In particular, I think that he did not claim that motion under the influence of a force is true motion.
Neverheless there is much of value in that version, and reinserting some of it in the article may improve it for sure - as it is, the article is rather short anyway, so it will be a welcome complement. Harald88 22:35, 7 September 2006 (UTC)
The version of article that I wrote does not attribute to Newton a claim that 'motion under the influence of a force coincides with true motion'.
What I intended to convey in the version that I wrote is the following: 'true motion (as Newton conceived it) can be thought of in terms two components that add up to a single true motion. The two components are: a true uniform motion, that is unknowable, and accelerated motion (for example: orbiting around the Sun), that is observable.' --Cleonis | Talk 09:03, 10 September 2006 (UTC)
Good! Formulated like that, it is much clearer. Harald88 09:11, 10 September 2006 (UTC)

[edit] A newtonian style defence of absolute space

I'd like to present a line of reasoning, in spirit similar to the rotating bucket and the orbiting spheres. The purpose of presenting this line of reasoning is to show how I think Newton and his contemporaries were thinking.

A mill is built above a little stream of water, the water drives a waterwheel. The miller cannot directly see the stream from his living quarters, and he has build a device for monitoring the flow of water. An airtight sac is floating on the water, the sac has enough buoyancy to support a long pole. The pole extends through the floor of the miller's living quarters, and from the height of the pole the miller can see whether it is worthwile at all to go down and try to get some milling done.

If the pole does not move at all, then presumably the stream is dry. If water is flowing, then fluctuations in the flow of water will make the pole go gently up and down. The miller cannot see the water itself, what he can observe by watching the pole is change in the flow of water. In order for a thing to be changable, the thing itself must exist; water is flowing.

Change of velocity is physically manifest. When a carriage suddenly moves faster, the passengers feel the lunge. Change of velocity exists, we observe it. In order for a thing to be changable, the thing itself must exist. This proves the existence of velocity with respect to absolute space.

As I announced: the above depicts a line of reasoning that I think Newton or a contemporary might have offered.

It is sometimes suggested that Newton was naive in asserting absolute space. But it is the other way round: it is a sign of ignorance to accuse Newton of underestimating the range of options. --Cleonis | Talk 09:58, 10 September 2006 (UTC)

I was also impressed by Newton's reasoning. Note that we can only include in the article what has been published. Still, I think that Newton himself made his line of reasoning sufficiently clear, it's just a matter of highlighting and clearly paraphrasing the pertinent passages of his "Scholium". Harald88 10:45, 10 September 2006 (UTC)
Of course, I presented the line of reasoning only to offer a guideline of highlighting and paraphrasing pertinent passages of the 'Scholium'.
In the version of the article that I wrote it ends with a section that switches to a modern point of view. In the definitions (definition III) Newton defines a concept of 'vis inertia' which today would be called 'reactive inertial force'. If a force is impressed on an object, then due to inertia there is a reactive inertial force that is exerted by object. Newton follows the habit of his time (a habit that is just as current today) to describe inertia as a property of the object in and of itself. In Newton's time the usual name is 'vis insita' the 'life within' the object. The modern point of view is that Newtonian absolute space must be conceived of as acting upon objects, opposing change of velocity. In this view the assumed absolute space is conceived of as the underlying cause of the phenomenon of inertia. It seems it cannot be ascertained for sure whether Newton thought of inertia as an innate property of objects, or as a consequence of absolute space acting upon matter. --Cleonis | Talk 11:30, 10 September 2006 (UTC)

[edit] Statement of Descartes' position not understandable

The article proposes:

that space is nothing other than the extension of matter, and that the true motion of a body consists in its transference from the vicinity of bodies immediately surrounding it to the vicinity of other bodies.

The use of "it" and "its" which may refer to any of a number of different nouns occurring earlier in the sentence render the meaning obscure. Here are some options:

that space is nothing other than the extension of matter, and that the true motion of a body consists in the body's transference from the vicinity of bodies immediately surrounding the body to the vicinity of other bodies.

that space is nothing other than the extension of matter, and that the true motion of a body consists in the transference of motion from the vicinity of bodies immediately surrounding the body to the vicinity of other bodies.

that space is nothing other than the extension of matter, and that the true motion of a body consists in transference of space from the vicinity of bodies immediately surrounding the space of one body to the vicinity of other bodies.

And so on. Can this sentence be cleared up? It also would be helpful later on to have Descartes' theory as applied to the bucket, so we can see that in fact the bucket experiment contradicts his theory. Brews ohare (talk) 14:11, 12 May 2008 (UTC)