Question regarding Newton's absolute space.

1. Jul 10, 2009

Shai-Hulud

I'm having a difficult time rationalizing the description that a book I'm currently reading has given of Newton's idea of acceleration relative to absolute space.

As I understand this description, it states that acceleration occurs relative to the whole of absolute space. I don't understand how one can make this statement, for it is not known, as far as I am aware, whether or not space is finite. If space is infinite, how can can one make the statement that any state of motion during acceleration is any faster or slower than any other state of motion during acceleration?

Acceleration requires a reference point just as well as any other state of motion, but a reference point would be meaningless in an infinite plain. Any one reference point is just as good as any other. The reference point could very well exist at any and all points during an objects acceleration. Unless it were given a relative position to some other reference point within space, in which case it would be distinguishable from any other reference point. It would make sense to me to say that acceleration occurs relative to the point of the origin of the force, rather than to an undefinable point in absolute space; such as the point at which an astronaut in space turns on his jet pack and starts accelerating, or a point in space that the axle of a rotating wheel takes up. In this case, two distinguishable reference points are given: the point of the origin of the force, and the point that is the accelerating object. But this still doesn't make sense, because each of the reference points could appear to be accelerating relative to the other, even though only one of them is.

This only really makes sense to me if space is given to have parameters and to be definably still (if the properties of absolute space can't be measured or observed, then what's to say that it isn't also undergoing some state of non-uniform motion?), thus making reference points distinguishable. I suppose one could argue that the whole of infinite space could be considered a parameter, but I don't personally believe that such would validly explain this dilemma.

So, is there anyone who could please help clear up my confusion?

2. Jul 10, 2009

turin

I don't know if I understand your confusion, but it sounds similar to my own, so I will try to explain what I think I have understood.

First of all, Newton's concept of space and time is not consistent with the mainstream physics concept of space and time today. I just want to make that disclaimer. Loosely, you can think of Newton's concept of space and time in terms of our contemporary understanding if the speed of light were infinite (and gravity were very weak on all relevant distance and time scales).

Given a background space, the concept of acceleration, and even the concept of velocity, can be well-defined, and there is no issue. However, even Galileo hundreds of years ago (and even before Newton) realized that absolute velocity may be a false concept. Newton had this idea of "the fixed stars". This allowed him to reason such concepts as rotational motion. However, Newton did conceive of a giant bucket with very thick massive walls containing some liquid, and pondered whether the whirling effect of the rotation of the bucket (as perceived by observers outside of the bucket) would be diminished by some sort of "shielding" from the outside universe by the thick massive walls. For instance, he wondered could the bucket walls be made so thick and massive that the externally observed rotation of the bucket would have no effect whatsoever on the liquid inside, as if the bucket were not rotating at all as perceived inside.

For more see Mach's principle.

3. Jul 10, 2009

tiny-tim

Hi Shai-Hulud !

Which book?

4. Jul 10, 2009

Shai-Hulud

So far I've read the first four books of the Dune series. Amazing books.

5. Jul 13, 2009

cfung

I read the brief history of time by Hawkings and somewhere in that book the author talks about exactly this idea of your concern. With great clarity, he points out the consequences of Newtonian absolute space time and explains how it is flawed with Einstein's theory. Let me see if i can bring that specific part up.

6. Jul 13, 2009

JCOX

The difference i believe is the fact that newton thought mass and time were absolutes, which we now know is false. We now know that gravity effects time(moreover the acceleration due to gravity) and C (speed of light) is the ultimate speed of the universe. Newton thought that their was such a thing called ether. "ether" was an idea that the universe had say some MAIN frame of reference. It was not until Einstein that we see their is no absolute frame of reference but rather RELITIVITE frames of reference...Hints General Relitivity and Special Relitivity.

7. Jul 13, 2009

Staff: Mentor

I wasn't aware that the Dune series could be considered as physics textbooks.

8. Jul 13, 2009

arildno

For committing blasphemy, jtbell is scheduled for demolition.

I would advise you not to approach any sand dunes, if you do not want to be gobbled up by irate worms.

9. Jul 13, 2009

Shai-Hulud

Oh, hah. I totally read that wrong.

The Fabric of the Cosmos.

10. Jul 14, 2009

tiny-tim

"The Fabric of the Cosmos"

uhh? you read The Fabric of the Cosmos, and you thought you were reading one of the Dune series? :rofl:

(watch out for wormholes! )
I see … there's a fairly clear summary of this at http://www1.kcn.ne.jp/~h-uchii/philsci/Newsletters/newslet_58.html
Sorry, I don't understand any of this …

what's the difference between an infinite plane and the surface of a sphere?

11. Jul 14, 2009

BobbyBear

Um, excuse me for butting in as I'm not sure if this is relevant, and I really am not into relativistic concepts, but I just wanted to point out that, as far as I understand, Newton's claim about the universe was of the existence of an inertial frame of reference (actually, an infinite number of them) (Newton's First Law). I don't know how the universe being finite or infinite affects this. Yes, motion, as far as velocity goes, is relative to the frame of reference, and there is nothing that can identify an object's velocity as being 'absolute', as I don't think one can point out any 'absolute frame of reference' in the sense of it being motionless . . . but acceleration is absolute with respect to inertial reference frames - that was Newton's claim as embodied in his laws of motion.

12. Jul 14, 2009

Staff: Mentor

For penance, I will go watch the movie Dune five times.

(I could use an excuse to take advantage of the HD DVD that I picked up cheap last year and haven't gotten around to watching yet...)

13. Jul 15, 2009

arildno

The worms of the earth are mollified.