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wolfekeeper:"Yes, that's partially true, all the effects are due to distortions when something accelerates."Length contraction advocates insist that it does not involve any force applied to 'contracted' objects or distances between objects. So acceleration is not a factor.
Quote from: old guy on 24/09/2012 21:25:27Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?Please, can you write down the physics law which states this? Hint: there isn't any.If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.If you still think there have to be a force, state the physics law.
Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
Nope )There are so many thing explainable by introducing length contractions as real from the frame measuring it, from the muon's 'point of view/reality' to how 'forces' behave (had a really good one on that, but as usual I can't seem to find it when I need it:)
This one might do though? What is a magnetic field? although when speaking of both time dilations and lorentzFitzGerald contractions the text assume that one understand that the descriptions are frame/observer dependent.
But the bottom line (?) is that using lenth contractions and time dilations you get a new view on a lot of phenomena, although it do take some time to melt.
Quote from: David Cooper on 24/09/2012 21:39:16Within SR (and I'll restrict this reply to that since that's what I was talking about in the box at the top), I don't think there's any real contraction of the object at all - all you're getting is apparent contraction Please *define* "real" and "apparent" in this context.
Within SR (and I'll restrict this reply to that since that's what I was talking about in the box at the top), I don't think there's any real contraction of the object at all - all you're getting is apparent contraction
Quote from: old guy on 24/09/2012 21:25:27David Cooper:QuoteIn SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?Yes, that's partially true, all the effects are due to distortions when something accelerates.
David Cooper:QuoteIn SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.Since Earth is a solid object and my "probe" is a rigid metallic craft, and since no force is applied, how do you explain their changes in shape/ length /diameter without applying a force... other than apparent changes as very distinct from changes in the objects themselves?
In SR there is no force applied, but there seem to be many different explanations as to what happens - my reading of it is that you simply get a different view of them from other frames where they appear to contract in their apparent direction of travel because part of their length is expressed in the time dimension, and the result is that they are effectively shortened from the point of view of observers moving at other speeds.
... in the twin paradox, the one that accelerates is the one that ends up ageing, not the one that just sits there.)
There are forces that cause this (actually the acceleration directly causes it), but they always act within the object that accelerates. (Note that there is a real physical difference between an accelerating object and a non accelerating object; a mass on a spring can tell you which is which for example).
In physics, to change the shape of a physical object, a force must be applied. Do you understand?
Quote from: wolfekeeper on 25/09/2012 21:04:29There are forces that cause this (actually the acceleration directly causes it), but they always act within the object that accelerates. (Note that there is a real physical difference between an accelerating object and a non accelerating object; a mass on a spring can tell you which is which for example).I'm beginning to think you may not understand the mechanism fully. If you accelerate an object to 0.866c it will be length contracted to half its original length. Now turn it sideways without slowing it down and the length contraction will be removed from the object's length and transferred to its width (which is now aligned with the direction of travel). The acceleration force does not compress the object to a shorter length other than temporarily - any compression will be removed when the acceleration force stops. You can see more easily why this is the case if you imagine pulling the object up to high speed by towing it behind a rocket - the acceleration will now stretch it a little, but the object will still length-contract as it travels faster, and when the acceleration force is removed, the tiny bit of stretching will be removed.
In physics, to change the shape of a physical object, a force must be applied. Do you understand? Observation does not change the shape of physical objects. See what I mean? To crush a stone, the molecular bonds within the compounds must be broken, which requires physical force. Same for Earth as a whole. It can not be flattened without application of a huge force, which would then destroy it anyway, not just compress its diameter to the 1000 miles (in the direction of an observer's pass-by) suggested for the extreme of an Earth with a length contracted diameter.
Quote from: lightarrow on 25/09/2012 19:32:58Please, can you write down the physics law which states this? Hint: there isn't any.If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.If you still think there have to be a force, state the physics law.When SR speaks of "for observer A, at rest with Earth"... Earth is spherical (almost), while "for observer B
Please, can you write down the physics law which states this? Hint: there isn't any.If an object contract *while staying in the same frame of reference* you do need a force for it, but it's not this the case.If you still think there have to be a force, state the physics law.
, flying by very fast" Earth is severely oblate (to say a 1000 mile diameter in the direction of the observer's travel),... this is about how Earth is observed from different frames, not about Earth actually changing shapes as it is seen differently. Do you understand this difference?
This is my point.In physics, to change the shape of a physical object, a force must be applied.
Quote from: lightarrow on 25/09/2012 11:52:03Please *define* "real" and "apparent" in this context.I'm using "real" to mean the shape that things might actually be (if external factors aren't adding undetectable distortions, such as would occur if the universe was rolled up in another dimension). I'm using "apparent" to mean the shape that things appear to be when observed from other frames where you don't get a proper picture of them. It's perfectly possible though within SR to have a different take on things and declare all possible views of things shapes as being equally real such that there is an infinite range of shapes for each object and you simply see different ones from different frames. What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
Please *define* "real" and "apparent" in this context.
Even the same word "observer" is misleading. It's not just an "observation", it's a *measurement*. It could be done from an authomatic instrument, in the absence of any living being.
The question is, do different frames of reference determine various realities
like different shapes of objects, etc.? Does observation
determine 'the shape of things' or do they have their own shapes?
The answer is that they do,
If you have a problem with this, remember that what is a fast travelling bullet against you and so a great danger, is a still bullet if you move at the same speed of it, and so a harmless one... Speed, momentum, energy, wavelenght and frequency, are examples of frame-dependent quantities. "realities" do change, changing the frame.
Define "their own". Does it mean: "in their proper frame"? Yes, they have their own shape. Do you understand it's definition? In physics you can't do anything without definitions
...but you are not aware that it's a your idea that has never become a definition. I have no problem in being in agreement with this definition, but I can't accept that you pretend to give it as granted.
Me: “The question is, do different frames of reference determine various realities”
Quote from: old guy on 26/09/2012 18:47:50 Me: “The question is, do different frames of reference determine various realities”Me: of course they do. Because for me "reality" means "what I measure".What follows is just your definition of "intrinsic property of a body", on which I can even agree, but it's nothing else than that.Since I have enough of this discussion, I will not reply to your next post.Regards.--lightarrow
What doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.
The job of science is to determine what objective reality is in each case, not subjective differences in observational points of view. Earth and its distance from the Sun, etc. has an objective reality as it is, not depending in differences in how it can be observed and measured from different frames.
QuoteWhat doesn't work is the idea that things physically change their shape to accomodate with how they're being observed, but I'm not sure if anyone actually holds that position in the way that I mean it.Who here holds that position? I can quote a few. That issue remains the essence of this thread's challenge.