Evidence for large scale length contraction?

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #50 on: 07/09/2012 20:19:16 »
The idea of absolutes in time and space, of a universal reference frame, of immutability have been shown to be incorrect.

They haven't all been shown to be incorrect, but length contraction certainly must happen in one way or another, as has been demonstrated by the Michelson Morley experiment. Anyone who wants to deny length contraction would really be better off joining the Einstein camp rather than attacking it, because SR at least provides a way for the contraction to be apparent rather than actual, even if it then leads to endless arguments about whether the contraction then counts as an illusion or not.

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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #51 on: 07/09/2012 21:11:34 »
This particular thread was so interesting to me, because for such a long time I tried to train my intuition to see the length contraction. And I visited this forum (and some others) specifically because I could find some line of thinking different from text-book, and some freedom of users to express whatever they wanted.

You have decided - on the basis of zero evidence - that earth has an essential, absolute shape that forms part of a natual universal truth;

To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths. 
Why should not some real object have a form of itself? Why an object cannot be something by itself?

the products of special relativity threaten your preconceptions therefore you reject the proven science and embrace your intuitions
It is not that I reject proven science, actually I really want to get there but myself and in my own way.
In this process I asked myself many of the questions you have seen in this thread or in other related threads.

I hope @imatfaal will not close this topic. Why should be closed? Isn't special relativity an interesting topic?

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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #52 on: 07/09/2012 21:22:01 »
..  SR at least provides a way for the contraction to be apparent rather than actual.

To me looks quite "actual", otherwise how could muon decay so little while passing through atmosphere? The little decay of muon is quite actual and not apparent. Note that In muon frame it has to travel a smaller distance that the observer on Earth measure.

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #53 on: 07/09/2012 21:30:07 »
To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths. 
Why should not some real object have a form of itself? Why an object cannot be something by itself?

That's a good point, flr.  The problem is that intuition only works when you're so familiar with something that it becomes intuitive!  It can also be very misleading in science, since many effects are counterintuitive.  A far better guide in science is logic.  Once you know something is true (by observing or measuring it), you can logically figure out its consequences. 

That's the case in special relativity.  Length contraction is very counterintuitive, but we know that the speed of light is constant for all observers from experiments.  Once you know that's true, you can logically work through the consequences, and find that lengths have to contract.  Our intuition fails because we hardly ever experience relativistic effects in daily life.  You can definitely train your intuition by studying something thoroughly, but it takes a lot of effort to actually learn a subject so well that it becomes intuitive, especially when its as abstract as relativity theory.

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #54 on: 08/09/2012 00:07:44 »
This thread is now continued in the New Theories section, by order of imatfaal.

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #55 on: 08/09/2012 00:27:07 »
At this point I will repeat my previous message.

SR does not rob an object of its intrinsic properties.

The properties that we measure and ascribe to an everyday object: its mass, size and shape, are its intrinsic properties. The Earth is an oblate spheroid of revolution, with minor radius 6353 km and major radius 6379 km, and mass 5.98 E 24 kg. Those are absolute and immutable properties.

If a traveller moving at speeds where SR effects exceed the precision of measurement makes observation of the Earth's properties, then s/he will observe a set of properties different to this, and different to those observed by another such observer moving at a different speed and direction. But none of this directly reflects the Earth, which can blissfully retain its intrinsic properties.

When we refer to such observations, it is quite usual to use the term "rest mass". Perhaps the logic of the situation would become clearer if we were also to use terms like "rest shape" for the other intrinsic properties of an object.

If, however, the Earth interacts with another object moving at such speeds, then the interaction will, from the point of view of the other object, be determined by the "distorted" properties of the Earth, as measured in its own reference frame. From an Earthbound point of view, though, the interaction will be governed by the intrinsic properties of the Earth and the "distorted" properties of the other object as observed from the Earthbound frame of reference. And the mathematical detail of the SR formulation will ensure that both observers will get the same result when the actual consequences of the interaction are calculated -- relative to the particular frame of each observer, of course.

The other laws of physics are likely to ensure that neither of these observers is still around to make the actual measurements, of course [;D]
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #56 on: 08/09/2012 15:37:52 »
This particular thread was so interesting to me, because for such a long time I tried to train my intuition to see the length contraction. And I visited this forum (and some others) specifically because I could find some line of thinking different from text-book, and some freedom of users to express whatever they wanted.

You have decided - on the basis of zero evidence - that earth has an essential, absolute shape that forms part of a natual universal truth;

To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths. 
Why should not some real object have a form of itself? Why an object cannot be something by itself?

the products of special relativity threaten your preconceptions therefore you reject the proven science and embrace your intuitions
It is not that I reject proven science, actually I really want to get there but myself and in my own way.
In this process I asked myself many of the questions you have seen in this thread or in other related threads.

I hope @imatfaal will not close this topic. Why should be closed? Isn't special relativity an interesting topic?

It's no illusion friend :) And I like the way you think btw, but neither will you ever see it locally. The only way a length contraction can be expressed is in a measurement between 'frames of reference'. If you use what I call 'locality' as your guiding principle OG is right. A object has the form you find it to have being at rest with it and the proofs for that is simple. Just become 'at rest' relative whatever you want to measure. Damocles hit the nail spot on with that one.

To further the discussion :) All of this has to do with what you think you observe. A 'whole undivided SpaceTime', or 'frames of reference' mediated by and through 'radiation'. Using your own unique frame you can define yourself and your closest environment as, loosely speaking again :) unchanging, aka 'invariant', no matter where you are or how 'fast' you go.

I believe in 'frames of reference' and 'locality', and there you will find things to have a consistency. Using a 'undivided SpaceTime the concept becomes trickier to me in that, what we have, still must relate to those 'frames of reference' 'joining it up'. Then defining it as 'one reality', the degrees of freedom we find it to have (dimensions) becomes 'unbreakable definitions´, defining a 'bubble' of sorts called SpaceTime. It's not like that to me, SpaceTime is a (very) partial 'bit' of something more/less, and it all coexists. What we see use radiation.
=

Can you see what I mean there? That when we find those length contractions contradict common sense. we all assume that 'one SpaceTime to bind us all'? ahem. If we let locality define a SpaceTime it will use frames of reference, radiations constant, 'gravity/mass', 'energy'. And we can leave the 'space' as it is, 'empty', at least classically, locally definable as 'invariant' too. Our problems arise with our preconceptions of how 'things always have been, and always must be'. Those change with knowledge, but each generation somehow still presume that their 'level' defines 'what is', don't they :)

When it comes to the question of 'motion' as uniform/accelerations?
That's tricky, but in locality all (uniform) motion must by definition become relative. Although we still have that constant frame radiation binding together 'locality', to measure a 'motion' against, using lights blue/red shifts. Accelerations will then be equivalent to 'gravity' as I think.
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Sorry, I write too slow, and my brain seems to assume that my fingers have brains of their own, as I keep missing those letters and small binding words. Also, you can always polish it a bit, can't you ::))
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And OG, please stop being so hard on the mods. It's definitely not easy being one, and? I find Imatfaal a quite good one.
« Last Edit: 08/09/2012 16:37:42 by yor_on »
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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #57 on: 08/09/2012 19:50:56 »
..  SR at least provides a way for the contraction to be apparent rather than actual.

To me looks quite "actual", otherwise how could muon decay so little while passing through atmosphere? The little decay of muon is quite actual and not apparent. Note that In muon frame it has to travel a smaller distance that the observer on Earth measure.

That's a different aspect of it - it travels further through our frame, but it itself appears to be (or is) shortened in length. You're now talking about it travelling further in our frame due to time dilation making it longer-lived in our frame. To make sense of it without SR, the internal mechanical mechanisms of the muon would have to be slowed down by its movement through the fabric of space such that it lasts longer. Alternatively, to make sense of that in SR you have to eliminate all ideas of Newtonian time such that the most genuine length of time for the muon to last is the one as measured in its own frame, while in any other frames where the measurement is different it will appear to last for longer than that.

What this means is that both the shape and time are probably best measured from the same frame as the thing being measured, while other frames may contract the apparent length in one direction and extend the apparent lifespan of the thing in question. But we're always trying to describe things in terms which shouldn't be applied to a universe with Newtonian time removed from it. If we attempt to remove Newtonian time properly, everything in the universe ends up being effectively simultaneous (because you end up with an eternal block universe) and there is no longer any speed of anything - not even a speed of light. Time is transformed into a kind of distance instead, and the future was never generated out of the past in cause-and-effect order.

Those are the necessary consequences of removing Newtonian time, and I hope there's no one here who wants to have their cake and eat it by smuggling a Newtonian time back in by the back door to try to make SR sound more compatible with common sense, because it won't fit.

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #58 on: 08/09/2012 23:24:47 »
Lightarrow said:
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Physics concerns measures; if an object's measure changes, then the object changes.
(Also):You always have to specify a frame of reference, it *doesn't exist* a "lenght" independent of it.

This claims that things have no length (shape, etc.) on their own, intrinsically, independent of measurement.
Me:
"Does this claim that Earth changes shape as it is measured from different frames of reference?"
Lightarrow:
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Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?

The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it. It is in fact nearly spherical. As I said: "This, of course, is impossible and has never been empirically observed." (A flattened Earth, for instance.)
When you say "in the real world" you are actually saying "in the Earth's frame of reference".
Do you want to postulate the existence of a preferred frame of reference in relativity (that is, the "proper" frame, which in this case is the Earth frame )? Then you should explain how could Einstein base his theory on the fact that a preferred frame doesn't exist.
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You're wrong for both assertion. Maybe you still haven't totally grasped what "measure of lenght" means, read again my first post. A measure of lenght *is* frame-dependent, and so is, as consequence, an object's shape.

I grasped it just fine. You are wrong to assert that an object's shape (like Earth) depends on how it is observed/measured, as if it had no reality, no intrinsic properties of its own.
Say 1000 ships pass by Earth going 1000 different (but near 'c') velocities, all going in 1000 different directions. Does Earth change into 1000 different shapes with its diameter contracting variously in all those directions? Of course not!
See up. You are still talking of the Earth's shape in a preferred one of the frames.
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Wiki on Realism (my bold):
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In philosophy, Realism, or Realist or Realistic, are terms that describe manifestations of philosophical realism, the belief that reality exists independently of observers.
"Observers" here in the context of this thread includes abstract points of view, all possible "frames of reference... no living "subject" required.
You asked me to define "actual." That would be that "reality exists independently of observers."
Earth is actually nearly spherical. AC is actually 4.37 light years from Earth. The distance to the Sun is actually about 93 million miles, which would not change if it were measured by a ship flying by very fast. The probe in my example is not actually 10 meters long, as observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)
In all of those cases we refer to distances and dimensions in the "proper" frame, because is the simpler one; but is it always possible to find such a frame?
Imagine a massive neutron star, which is composed of two concentric parts spinning along a same axis but in opposite directions, so that the outer edges of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?
« Last Edit: 08/09/2012 23:28:25 by lightarrow »

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #59 on: 08/09/2012 23:55:39 »
From Lightarrow:
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Imagine a massive neutron star, which is composed of two concentric parts spinning along a samr axis but in opposite directions, so that the outer bords of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?

We would have to imagine something a little different to that, because in SR length contraction operates only in the direction of motion, and rotation only describes motion perpendicular to the radius. So the intrinsic radius would be easily and unambiguously determined in an inertial frame that is stationary relative to the centre-of-mass of the neutron star.

Nevertheless it is possible to think of an "intrinsic" property that is ill-defined for a complex object -- in fact such properties are legion. What is the rest mass of the solar system? If we try to measure it in the frame of the centre-of-mass of the solar system, the orbital motion of each of the planets would ascribe to it a mass slightly greater than its own rest mass. So we are faced either with an object that has a mass somewhat greater than the sum of the parts or a mass that cannot be directly measured.

For a physicist, this creates a contradiction and a crisis, that can only be ultimately resolved with a denial that anything has "intrinsic" properties. For a chemist, though, there is no problem. We are forever ascribing an "intrinsic" weight to an atom which (for quite different reasons) is quite significantly different to the sum of masses of its protons, neutrons, and electrons.

Even in a Newtonian universe, the solar system does not have a shape. The concept of "intrinsic" properties does not collapse as a result. A house or a raindrop still has an intrinsic shape. In the chemist's world an object may or may not have a particular intrinsic property. A benzene molecule has an intrinsic shape, a butane molecule does not.
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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #60 on: 09/09/2012 02:31:58 »
A benzene molecule has an intrinsic shape, a butane molecule does not.

 Note that, although in benzene is no free rotation of some chemical group(at  room T), the benzene also changes its [instantaneous] shape (on fs time-scale) due to all sort of  vibrations/deformations. But that has nothing to do with Lorentz contraction.

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #61 on: 09/09/2012 09:10:47 »
You are quite right of course flr. I had wandered a long way from the original topic. The point that I was trying to establish in my post was that the fact that some objects did not have some intrinsic properties was not an argument against rest properties (Lorentz contraction) as genuinely intrinsic properties.
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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #62 on: 09/09/2012 11:56:02 »
From Lightarrow:
Quote
Imagine a massive neutron star, which is composed of two concentric parts spinning along a samr axis but in opposite directions, so that the outer bords of these parts are moving at relativistic speeds.
1. Which would be the measured radius of the star?
2. Which would be its "intrinsic" radius?

We would have to imagine something a little different to that, because in SR length contraction operates only in the direction of motion, and rotation only describes motion perpendicular to the radius. So the intrinsic radius would be easily and unambiguously determined in an inertial frame that is stationary relative to the centre-of-mass of the neutron star.
Yes, you're right. Then we could substitute "radius" with "circumference", even if this quantity it's not so immediate to measure...
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Nevertheless it is possible to think of an "intrinsic" property that is ill-defined for a complex object -- in fact such properties are legion. What is the rest mass of the solar system? If we try to measure it in the frame of the centre-of-mass of the solar system, the orbital motion of each of the planets would ascribe to it a mass slightly greater than its own rest mass. So we are faced either with an object that has a mass somewhat greater than the sum of the parts or a mass that cannot be directly measured.
I have written a lot of times that the term "rest mass" is misleading and you have found now a perfect example of this (apart  the case of a massless object as a photon).
The right concept is "invariant mass" m, and it's very easy to compute it: you find a frame of ref. where the total momentum p is zero, then m = E/c2 where E is the total energy of the system. Of course invariant mass is not additive: the solar system's mass is not the sum of the planets masses (as for an atom, as for a nucleus, as for a gas in a box).
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For a physicist, this creates a contradiction and a crisis, that can only be ultimately resolved with a denial that anything has "intrinsic" properties. For a chemist, though, there is no problem. We are forever ascribing an "intrinsic" weight to an atom which (for quite different reasons) is quite significantly different to the sum of masses of its protons, neutrons, and electrons.

Even in a Newtonian universe, the solar system does not have a shape. The concept of "intrinsic" properties does not collapse as a result. A house or a raindrop still has an intrinsic shape. In the chemist's world an object may or may not have a particular intrinsic property. A benzene molecule has an intrinsic shape, a butane molecule does not.

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Offline simplified

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Re: Evidence for large scale length contraction?
« Reply #63 on: 09/09/2012 12:14:49 »
To be honest, my intuition tells me that objects deserve an absolute shape, and I find it hard to train my intuition to believe otherwise. Maybe from here arise my difficulty in accepting the relativity of lengths. 
Why should not some real object have a form of itself? Why an object cannot be something by itself?

That's a good point, flr.  The problem is that intuition only works when you're so familiar with something that it becomes intuitive!  It can also be very misleading in science, since many effects are counterintuitive.  A far better guide in science is logic.  Once you know something is true (by observing or measuring it), you can logically figure out its consequences. 

That's the case in special relativity.  Length contraction is very counterintuitive, but we know that the speed of light is constant for all observers from experiments.  Once you know that's true, you can logically work through the consequences, and find that lengths have to contract.  Our intuition fails because we hardly ever experience relativistic effects in daily life.  You can definitely train your intuition by studying something thoroughly, but it takes a lot of effort to actually learn a subject so well that it becomes intuitive, especially when its as abstract as relativity theory.
Our logic should use what laws of measurement of speeds?

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #64 on: 10/09/2012 20:41:35 »
imatfaal, post 44:
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OK - Enough.  This is a semi-official note that we either return to accepted ideas or the thread gets closed.

There have been 18 posts here since this warning. Are they all based on “accepted ideas” or are my criticisms of mainstream large scale length contraction the only ones censored?
I tried to move the discussion to “New theories,” as you demanded, but none but one joined in there, and it continues here.
I have replies to many of those posts since your warning, but I am gagged while no one else is. I need some guidance here, preferably from a moderator not so prejudiced against me.
imatfaal:
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It is clear that many of you regard Special Relativity and/or its implications as a convenient fiction - This thread is rapidly descending into a melange of arguments from personal incredulity and ignorance of the subject and that is against the ethos of this Q&A forum.


No, I do not regard SR as a “convenient fiction.” You continue to intentionally misrepresent me. Clocks do slow down when accelerated to higher velocities, and adjustments to the GPS system (and other applications) compensate for the differences precisely and effectively. Yet there is still no empirical evidence for large scale length contraction, and insisting that it is a logical consequence of the math, as a reciprocal of “time dialation” still doesn’t make earth’s diameter or the distance to the sun contract.

Imatfaal From post 49:
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Frame dependence, special and general relativity, and a privileging of observation, modelling, and mathematics mean that your false division into intrinsic and extrinsic is meaningless.

That division is the core of the issue, as far from "meaningless" as it gets.
Yet you have not replied to any of the very cogent arguments by others here, let alone mine, here or in “New Theories,” explaining the central relevance of the internal vs external properties distinction to the difference between actual, real, naturally occurring properties and the differences among observational effects due to differences in frames of reference.

I am bound and gagged here and need of some help from someone who is willing to address these issues on behalf of the forum admin and let me speak freely in reply.

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #65 on: 10/09/2012 22:15:32 »
Hi Old Guy,

Hopefully I count as a less prejudiced moderator.  :)

First, the moderators did discuss this as a team, and we support Imatfaal's decision. 

The reason why is that this forum is primarily a science Q&A and discussion forum to answer questions and foster follow-up discussion about mainstream science.  Unfortunately, if we regularly allowed posts on non-mainstream science, we would confuse the many users who come to the site to get answers in terms of the main stream!

'Mainstream' in terms of length contraction is Einstein's special relativity, which does predict length contraction.  Criticisms of that idea should be kept to New Theories, as mentioned above. 

As you note, the New Theories forum is not an incredibly active part of this site.  This is probably because our primary purpose as a forum is science Q&A.  While we're happy to accommodate non-mainstream ideas in 'New Theories', if your primary goal on the site is to discuss outside-the-mainstream ideas, then you might find it more productive to seek out another forum.

Finally, I've posted this publicly because you've posted your complaint publicly.  If you don't find this a satisfactory response, please PM me or another moderator, but please do not post your response here so that this thread stays on topic.

Thanks!

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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #66 on: 11/09/2012 00:13:16 »

But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower? 

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #67 on: 11/09/2012 00:28:20 »

But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower?
Good questions, fir. I hope you get some answers. So far, I haven't.

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #68 on: 11/09/2012 16:10:08 »
It is as if Skulls in the Stars were reading this thread!  His latest blog addresses this question with spooky accuracy
http://skullsinthestars.com/2012/09/10/relativity-ten-minutes-to-alpha-centauri/

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This warping of space and time is the most shocking part of special relativity when one encounters it for the first time.  It is important to note that I use words like “perceive”, “observe” and “point-of-view” to describe the changes in time and space, but these are real changes — no physical experiment or measurement of any kind will disagree with the results.
There’s no sense in being precise when you don’t even know what you’re talking about.  John Von Neumann

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #69 on: 11/09/2012 17:24:12 »

But how came the moun finds a shorter path in its way through atmosphere? By which mechanism its path is shorter than what I observe from Earth?
Is our universe made of multiple "realities" that are superimposed? In each such "reality" length is shorter or longer and time "flow" faster or slower? 

Now you're venturing into philosophy, flr.  What physics can tell you, as imatfaal said, is that distance is something we measure.  We know that for the same Newtonian (non-relativistic) path, from the sun to the earth, the distance measured does in fact depend on how fast the observer is moving along that path.  This is what the theory of special relativity tells us and is in accordance with experiments and observations.

Science restricts itself to predicting the results of measurements, however.  If you want to ask about what it means for two observers going from the sun to the earth to measure two different distances, that's getting into philosophy.  Science can guide your inquiries by telling you that any philosophical interpretation you come up with has to match validated theories, but building some reality that exists beyond those theories is beyond science.

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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #70 on: 11/09/2012 17:24:49 »
The relativity of lengths and time on the frame of reference is barely a reformulation of "speed of light is invariant to observer".
In my opinion the invariance of "c" does not explain the length contraction and time dilation just - because they are 2 sentences with the same meaning but put in different wording.

I am not sure I found a satisfactory answer to the question: "what makes space and time be relative?" or its equivalent "what makes c be invariant?"
Instead I found in many places the argument that the invariance of c is immediately equivalent with relativity of space and time.

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #71 on: 11/09/2012 17:32:12 »
I am not sure I found a satisfactory answer to the question: "what makes space and time be relative?" or its equivalent "what makes c be invariant?"
Instead I found in many places the argument that the invariance of c is immediately equivalent with relativity of space and time.

I don't think there is a satisfactory answer to why the speed of light is constant.  It's a postulate of special relativity, which means we take it as a fact.  We have plenty of measurements that establish it as a fact, but we don't have some deeper theory that tells us why it is.  The other postulate of special relativity is that the laws of physics are the same for all observers in inertial (constant velocity) reference frames.
(See: http://en.wikipedia.org/wiki/Postulates_of_special_relativity#Postulates_of_special_relativity)

Once you take those two to be true (and we do so based on observations) then special relativity follows.  You can further validate special relativity by checking its specific predictions against reality, which has also been done.  So we're pretty sure it's true because the postulates have been checked, and the theory follows from those, and the theory itself has been checked.

As for why the postulates are true, we don't know.  Some deeper theory may come along to explain that, or it may be something we never know.  The fact that we don't know means there's plenty of future work to be done.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #72 on: 11/09/2012 22:30:33 »
There is a clear divide here between two sides, one of them being mainstream (physics) and the other being mainstream (common sense). Each side frequently claims things to be facts when they are not facts at all, but merely assumptions made by the theory they have already aligned themselves with. For example, if a theory says that there is no preferred frame of reference, then that is a "fact" within that theory, but not a real fact. A rival theory which assumes that there is a preferred frame of reference could likewise have the existence of a preferred frame as one of its "facts", but it is not a real fact either. People on both sides here are promoting "facts" as facts, and that is simply not moral. If you want to educate people, you have absolutely no right to indoctrinate them by pushing "facts" as facts while doing so on the basis of any kind of authority (such as being some variety of mainstream, whether that be of the physics or common sense variety).

Here's an example of the problem:-

Quote
I don't think there is a satisfactory answer to why the speed of light is constant.  It's a postulate of special relativity, which means we take it as a fact.  We have plenty of measurements that establish it as a fact, but we don't have some deeper theory that tells us why it is.

So, we take something as a fact because it is a postulate of a theory. That does not make it a real fact - it's only a "fact" within a theory. This is then backed up by a claim about measurements establishing it as a fact, but there are no measurements that can be made which can do anything of the kind - the speed of light can only be measured on a round trip, thereby completely hiding any actual variation that may be there. To call things facts when they are not facts is wrong, and it's absolutely wrong to mislead the public in this way.

Special Relativity is a theory and not a fact. The things taken as facts within SR are not automatically facts outside of SR. I had to take my questions about relativity to another forum because I was not allowed to ask them here as I was daring to question Einstein's relativity. You are not supposed to be a church defending a religion here by excluding people who ask awkward questions which challenge your own beliefs. Your job is to explain theories and to word things carefully so as not to make claims which go beyond what can be justified.

On the other side we have a claim that there's no real length contraction, but ironically that could only be true in any absolute sense if Einstein's Special Relativity is true - any other way of interpreting the Michelson Morley experiment requires actual length contraction to account for the only real fact which can be measured here (that light always completes the journeys along the arms of the MM apparatus and back in the same length of time [assuming they're exactly the same length - they don't actually have to be, but that's a detail that doesn't need to be explored]).

I myself made some assertions here a while back when asking a question about the mechanism behind time dilation and was banned from posting here for ten days on the basis that I was evangelising. I could have backed up those assertions and demonstrated them all to be correct, but I wasn't allowed to. The moderators, however, are allowed to make assertions without backing them up, and they refuse to engage in any discussions which are in danger of showing them to be false - it all gets pushed into a backwater instead where they can ignore it and where no one will see it.

I've arranged for some people at a couple of radio stations to watch what happens to this post because the way it is dealt with will be very revealing to them about the nature of a certain forum which they promote through their connections with a certain person who has already failed to deal with my fully-reasonable complaints about the way I've been treated here. I want to discuss science, and science has to be open to question. If this is actually a Church of Einstein, it should say so at the top and not claim to be a science forum.

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #73 on: 11/09/2012 22:58:01 »
David, you're right that you can't prove anything is 100% fact.  Fortunately, science doesn't work that way, or we'd be in serious trouble doing it!  It's a fascinating subject how theories get accepted as mainstream, but its also well beyond the scope of this forum. 

Our scope is, as I said above, science Q&A and discussion in terms of mainstream theories.  We're a site staffed mostly by volunteer moderators and provided freely to our members as a place to do just this.  Your previous posts were moved because they were simply beyond the limited scope of this forum.  As I mentioned to Old Guy, we're not trying to stifle your ideas--we just have a very limited scope: science Q&A and discussion in terms of mainstream science.  Topics that stray too far from that are moved to the appropriate sub-fora (generally new theories for non-mainstream science). 

If you are eager to discuss non-mainstream ideas, we do provide the New Theories forum for this.  However, as you can see it's a small part of this forum and not our focus.  If you would like an in-depth discussion of non-mainstream theories, there are other science fora on the net which are far broader in scope and content that might generate livelier discussions. 

Again, due to our limited scope and time, and to keep this thread on topic, I'll be moving all further off-topic posts to the appropriate sub-fora.

Thanks,
JP moderator

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #74 on: 12/09/2012 00:31:02 »
Discussing Einstein's SR and trying to help people understand it properly is not something that can be classed as non-mainstream ideas. Most ordinary people find SR downright weird, and that automatically makes it interesting to them and well worthy of serious discussion on any science forum. It isn't beyond them either. Having explored it extensively myself, I now understand why physicists make the claims they do about it, and it actually makes a lot of sense in many places where I previously thought it was completely barking. Most, if not all of the apparent contradictions disappear when you completely eliminate Newtonian time from the model. This ultimately leads though to a point where the cause-and-effect pattern of events which is written through everything that happens in the universe cannot have taken place in order of cause followed by event because that would automatically bring back in a Newtonian kind of time which is not allowed in SR, so that means that within SR events are not caused by their causes. There is a rival interpretation (that of Lorentz) which fits the actual facts every bit as well as SR while lacking the cause-and-effect problem, so we are clearly dealing with "facts" here which aren't anywhere near to being 100% fact and which may not even be 50%, and that's why it's so important that people aren't given a misleading impression as to what is a fact. [There is a problem for the Lorentz theory too in that its preferred frame of reference cannot be detected, though it is also the case that it shouldn't be possible to detect it through any of the experiments which have ever been carried out.] I cannot see how it is acceptable for anyone to push one theory while banning discussion of the other given that the banned one is arguably at least as likely to be true as the allowed one. If the mainstream common sense theory of Lorentz is not to be allowed here in discussions, the only fair thing to do would be to be even-handed and ban all discussion of SR from this forum as well so that the public is not misled by any bias. I don't see any need to do that though - the subject is well within the capability of ordinary people to follow the arguments and it's just a matter of stamping on anyone who makes an assertion of any kind and demanding that they either back it up or shut up. Relativity is one of the most interesting aspects of science, and I think it ought to be possible to handle it here fairly.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #75 on: 12/09/2012 06:49:55 »
I think it's fairly simple what the mods want. We can all soar, but that's for 'New theories', (although) it's quite hard not to put in your own interpretations in this Physics, Astronomy & Cosmology forum and we're all failable. This site was once constructed for giving people the chance to have in depth discussions, but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions, and to be perfectly strict also the math behind the reasoning. And the last demand is definitely the hardest. But that is if one want people to take one seriously, and then one probably publish elsewhere :)

« Last Edit: 12/09/2012 06:53:25 by yor_on »
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #76 on: 12/09/2012 20:02:26 »
This reply will be appropriate to the parameters of the forum stated in yor-on's last post:
yor_on:
Quote
...but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions,...
(my bold.)

There seems to be an exception made for large scale length contraction of objects as a theory with no empirical evidence to support it, since, as JP pointed out, no one has yet observed Earth, for instance, from that ubiquitous, thought-experimental near 'c' fly-by frame. But Einstein loved a good thought experiment, and I thought I presented one as a reasonable test of length contraction in reply 17.
Quote
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.
Also, from my reply 34:
Quote
The probe in my example is not actually 10 meters long, as (it was) observed from Earth's frame. Proof: It will not fit in the shuttle's 10 meter cargo bay. (Much too long, actually.)

The above was not directly addressed here the first time around. I hope it will generate relevant replies this time.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #77 on: 12/09/2012 20:44:31 »
I think it's fairly simple what the mods want. We can all soar, but that's for 'New theories', (although) it's quite hard not to put in your own interpretations in this Physics, Astronomy & Cosmology forum and we're all failable. This site was once constructed for giving people the chance to have in depth discussions, but when it comes to state for example that a length contraction isn't 'real' it automatically drops into New Theories. Einstein defines it as 'real' from the frame measuring, and so did Lorentz too. To prove it wrong must then belong to New Theories, and doing it one need to present testable predictions, and to be perfectly strict also the math behind the reasoning. And the last demand is definitely the hardest. But that is if one want people to take one seriously, and then one probably publish elsewhere :)

There was a long argument caused by people using different interpretations of the word "real". Length contraction is absolutely real for Lorentz (though it's impossible to tell whether something's really been contracted as you can't tell if it's moving), while for Einstein it's real as a measured phenomenon. We can argue as much as we like about the degree to which Einstein considered it to be real in any other sense, but none of that makes any difference to his theory. Some people even think that objects are physically changed in shape by being observed by moving observers, and they can think that if they like, but so far as I am aware it is not a requirement of SR that you believe such a thing. It may be that Einstein considered all possible observed shapes of things as being absolutely real at the same time and that the one which maximised all its dimensions not to be superior - I haven't seen enough evidence to know what he believed on that point, but I certainly don't think it's crucially important to SR. Regarding the case where the dimensions of an object are all maximised as the real shape of that object would simply be a slightly different interpretation of a trivial detail of SR and not a new theory.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #78 on: 12/09/2012 21:01:33 »
Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.)
Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”
The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.

Is it Groundhog Day? This has already been answered. It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger. This allows you to decelerate the ship without a pile-up, and maybe it should be applied inwards from the sides of the cargo bay to avoid the force acting on one end of the ship before the other. You would close the rear door just as the end of the alien ship has entered the cargo bay (which is theoretically possible if the ship is very thin), and then you apply the force to stop the ship. The ship is completely contained in the cargo bay for a moment and is still moving at high speed, but that speed is completely removed in the next instant, thereby preventing it from crashing into the end wall. What will happen next? Well, all the atoms are too close together in the direction in which the ship was moving a moment earlier, so they will push out against each other and the ship will lengthen, either breaking its way through the wall and the door, or the ship will buckle badly in order to lengthen without exceeding the 10m space available to it.

I hope that helps.
« Last Edit: 12/09/2012 21:06:12 by David Cooper »

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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #79 on: 12/09/2012 22:03:16 »
David Cooper:"I hope that helps."
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:
Quote
It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.

Quote
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.

This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.

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Offline David Cooper

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Re: Evidence for large scale length contraction?
« Reply #80 on: 12/09/2012 23:06:27 »
David Cooper:"I hope that helps."
No, it only confuses the experiment, as I laid it out, with your own conditions.
The rules of engagement for a thought experiment are set by its author's conditions.
You say:
Quote
It will fit in the cargo bay for a moment, but it has to keep moving relative to the cargo bay in order to do so, with the result that it will only fit in it for a moment, so you're going to need a cargo bay with open doors at both ends. If you slow it to a halt or accelerate the shuttle to its speed so that you can capture the alien ship, it will then be too big to fit.

I said that the shuttle pulls alongside of the probe and finds that it is way longer than the 10 meters it was measured to be from earth. Yes, it will "be too large to fit", which was my point illustrating that its "contracted length" is much shorter than its actual length, as observed from its own frame of reference "alongside" it. The bay is a standard shuttle bay, not "open at both ends" for a brief fly-through by the probe. It either will fit in a 10 meter bay or it will not.

I answered the question. It's up to you to interpret the results. While they were moving at different speeds, it did fit, and once they aren't, it won't.

Quote
Quote
Actually, there may be a better way to illustrate things: you could do away with the door at the far end of the cargo bay and have some kind of device to decelerate the whole ship in an instant without crushing it, this being done by applying a levitation kind of force to it (as has been done with a frog), but obviously much stronger.

This is blatant obfuscation of the thought experiment as I presented it.
The project was to retrieve the probe. The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

It was a very clear way of looking at how things work and it will allow the shuttle to retrieve the probe.

Quote
... And your 'evangelism' above is not helping the credibility of this thread. I expect it will be closed primarily because of your continuing rants, like about "The Church of Einstein" and such. You are hijacking this thread with your radical opinions.
I am still hoping for an intelligent replies to my experiment as I presented it.

My radical opinions? I'm trying to be neutral about things, not pushing any theory forward as being correct, but making it clear where the failings of different theories lie so that people can make up their own minds, or better still, not make up their minds but continue to be open to all reasonable possibilities. I'm not interested in hijacking your thread - I'm only still posting here because I thought you were looking for help in understanding this, but you clearly aren't. You've had the answers you need from various people, but you simply reject them every time. I'm now being won over by the mods - they read you absolutely right. Goodbye.

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #81 on: 13/09/2012 00:32:30 »
My last contribution to this thread, and an emphatic re-iteration of my previously stated position. My only reservation in the very definite statements I am about to make is that I know little of general relativity and its consequences, but I am well versed in special relativity.

Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.

This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.

Both of these assertions are a matter of definition -- you cannot deny either of them unless you can establish that there is some ambiguity or indeterminacy in my definitions.

It is only through the operation of these definitions that we are able to make tables of atomic mass, Earth's shape and size, and 100,000 other intrinsic properties that are listed in the CRC Handbook of Chemistry and Physics.

It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.

There is one other matter that I think needs to be cleared up:
Any idea that mentions "large scale" suggests a theory that treats large scale and sub-microscopic systems differently. If that is what is intended, then we need a smooth boundary condition at the swap-over scale. This is consistently achieved for quantum theory as a "sub-microscopic theory". I do not see how it could be for a Lorentz transformation that is well-established for sub-microscopic objects, but would become "switched off" for macroscopic ones.
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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #82 on: 13/09/2012 04:26:04 »
Hi Damocles,

I admit this thread has so many different subjects being discussed that I haven't kept up on all of them.  I tend to agree with you that a lot of properties of an object can be, and are in practice, defined in its center-of-mass rest frame.  And we definitely know when something is in our inertial reference frame.  It's center of mass won't be moving with respect to us, which is easy to observe. 

So we can define the properties of a known object by specifying them in its rest frame, but we cannot practically redefine our definitions of measurement of length and time in such a way.  If we did so, our clocks and meter sticks would have to change length to match the speed anything was moving with respect to us. 

What I've also argued against is the idea that length doesn't contract simply because we can define the length of an object in its center of mass reference frame.  Just as the laws of physics say a planet should be (roughly) spherical in it's COM frame, they also say it should be squashed if you're moving with respect to it.  Unless you choose to completely redefine how we make measurements, you're going to measure the planet as squashed and all physical laws formulated in your reference frame are going to treat it as squashed.  Of course, special relativity also allows you to formulate the laws from the planet's COM frame, in which case it's spherical and you are squashed.  Neither is more correct than the other because they both describe physical reality as measured by observers. 

-----------------------------------

The following isn't addressed at you, Damocles, but there's so many viewpoints being expressed in this thread that I feel I should make my point of view clear.

What I've also argued against  is the introduction of extra complexity to special relativity in order to preserve some preconception about the universe.  Science doesn't work that way.  We can always hold an infinite number of preconceptions about the universe and introduce extra hidden variables into a model to preserve them.  Obviously no one's arguing something this far out, but if I were more comfortable with unicorns causing length contraction, I could always introduce unicorns who zip about the universe shrinking our rulers with magical pony power.  As long as the unicorns are undetectable by measurement, and their pony power works identically to Lorentz contraction, I can claim that my results are completely in line with observations.  That doesn't this viewpoint valid science, nor does it make other viewpoints with far less absurd preconceptions valid science.  Science is generally about using the simplest possible model to describe some phenomenon, not choosing the more complex model because it fits your preconceptions.

A far more real point than the unicorns is that many scientists are also deeply religious and believe that a deity or deities play an important role in the universe.  Their personal view probably involves a complex theory that allows the deity to act but remain undetectable.  However, they also generally realize that good science does not involve complicating a theory with undetectable variables that have no influence on measurement, so when they present their work to other scientists, they present the 'mainstream' version of the theory. 

Einstein's special relativity is the mainstream scientific explanation because it is the simplest model which introduces the fewest extraneous variables and preconceptions and explains observations.

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #83 on: 13/09/2012 04:37:00 »
There is no disagreement JP; I was simply wanting to defend the notion and status of intrinsic properties, because without them we lose an enormous amount of clearly correct, convenient, and valid science.

I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #84 on: 13/09/2012 04:44:28 »
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.

Are intrinsic and extrinsic the usual technical terms used here?  It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #85 on: 13/09/2012 04:49:55 »
Quote
Are intrinsic and extrinsic the usual technical terms used here?  It's been a while since I studied special relativity, but I don't recall ever learning terms other than "rest ____" to describe properties measured in the rest frame.

Probably not, but their meanings are fairly clear, they are much loved of philosophers, old guy had already used the terms, and someone in the earlier posts in this thread had objected to the use of "rest ..." properties.
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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #86 on: 13/09/2012 11:07:10 »
I was up till two this morning re-reading my Wolfgang Rindler - couldn't sleep.  I don't remember him using the words.  He tends to talk about rest frame, inertial frame, etc.  I must admit that in a discussion regarding Special Relativity I think they are potentially misleading in that they may lead to a misconception that the length contraction is not "real" - ie that it is merely an artifact of vision/observation rather than an actual consequence of frames in relative motion. 
There’s no sense in being precise when you don’t even know what you’re talking about.  John Von Neumann

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Offline lightarrow

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Re: Evidence for large scale length contraction?
« Reply #87 on: 13/09/2012 13:02:39 »

Any object does have intrinsic properties. That is not a matter that hinges on any observational result -- it is a matter of definition. An intrinsic property of any object is one that is measured in or calculated to an observation in the inertial frame of reference that is stationary with respect to that object's centre-of-mass.

This definition automatically gives rise to the fact that an inertial frame of reference that is stationary with respect to the centre-of-mass of an object is a privileged frame in that it allows an observer to directly measure the object's intrinsic properties.
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.
« Last Edit: 13/09/2012 13:04:28 by lightarrow »

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Offline damocles

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Re: Evidence for large scale length contraction?
« Reply #88 on: 13/09/2012 13:23:58 »
I am sorry to have caused more confusion in what was already a confused and confusing discussion. Intrinsic is not a recognized technical term in the SR field.

It is purely and simply a term that I chose to define and use because there were a couple of problems with "rest" properties
(1) An objection to "rest mass" that Lightarrow expressed that I did not quite understand but attempted to accommodate. He suggested "invariant" but I had my problems with that particular term because I would want to restrict that term to quantities like c0 that are genuinely the same to all observers. The rest mass is indeed the same to all observers, but only privileged observers in the rest frame can measure it directly. Others have to deduce its value from the measurements they make of a non-invariant related property.
(2) A rather more trivial, but possibly confusing ambiguity in a rest property of a complex object: The rest property should be taken as the value of a physical quantity in the frame of the centre-of-mass of the complex object, but could be confused with a very different property that would be measured if all of the parts of the complex object were brought to rest relative to one another. This particular problem seemed about to come to the fore when someone -- lightarrow? -- started talking about neutron stars with incoherent internal motions at relativistic relative speeds.

I chose the words "intrinsic" and "extrinsic" because their normal meanings in the English language seemed very apt for the flavour I was trying to give them. The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape because local application of the laws of physics say that the equipotential surfaces in its gravitational field will be shaped as oblate spheroids of revolution, and it is plastic enough as a planet to have its surface adopt an equipotential shape (to a very close approximation). Basically, if the Earth were an observer, the intrinsic shape of the Earth is the one that it would know it had, in spite of whatever others may observe. It is a part of the Earth's nature. The opposite of intrinsic -- extrinsic -- means something that belongs to a thing only by virtue of a relationship with an external force or object. Extrinsic properties are every bit as "real" as intrinsic ones, but they can and do vary according to different relationships with different external objects.

But these terms are not SR technical terms. They are simply English words that I have chosen that in their normal English meanings capture the character that I see operating in properties of objects under SR conditions. The meanings are also congruent with those that several philosophers give them as technical terms.

From lightarrow:
Quote
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.
Oh, and lightarrow, i have already in an earlier post in this very long thread, pointed out that an argument that a particular object might not possess a particular intrinsic property is not an argument against intrinsic properties per se. If the monochromatic light that it emits at a particular time is a property of a star, then it did have a unique rest frame at the time it emitted it; if we can no longer determine what that frame was that does not deny its existence, and nor does the fact that the star might since have died. And if the light is regarded as a property of the photons, then it cannot be intrinsic, because the photons themselves have no rest frame.
1 4 6 4 1
4 4 9 4 4     
a perfect perfect square square
6 9 6 9 6
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1 4 6 4 1

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Offline flr

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Re: Evidence for large scale length contraction?
« Reply #89 on: 13/09/2012 15:25:26 »
Ok. So, which is the intrinsic property of a monocromatic light (or X-ray, or gamma ray) beam coming from a very distant star? If you say "the frequency", I ask you "in which frame?" And if you reply "in the source frame" I can reply that the star which have emitted it, now can be non existing anylonger, and its ancient position can be  non identifiable.

Interesting point, but I have a quick question.
Let's assume there is a distant source (like our Sun) that emits harmless visible light for an Earth observer.
The observer take a  relativistic ship (0.9999c)  and travel toward the source. His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light. Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.
My question is: Will the observer on ship get hurt by gamma rays? Or in his ship those penetrating gamma rays (that on Earth were visible light) have the same impact as the visible light on Earth frame, i.e. they will be harmless?
« Last Edit: 13/09/2012 15:29:44 by flr »

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #90 on: 13/09/2012 16:00:33 »
SR definitely has invariant quantities, which may be defined in terms of some formula entirely in terms of local measurements (in any inertial reference frame), and which turn out to be constant, no matter which reference frame is chosen. 

Rest properties seem a bit different, since they require a reference frame to be fixed.  However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.

However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic.  Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic.  It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).

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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #91 on: 13/09/2012 16:14:39 »
His ship screen out all radiation except those wavelengths that for the Earth frame were harmless visible light.
 Due to Doppler Effect the light that penetrates the ship will be now gamma-ray.

What type of shielding are you using?  Most shielding will only care about how fast the light wave peaks hit its surface, i.e. the frequency.  Let's say the sun emits only one wavelength of visible light when your ship is at rest with respect to the sun.  The light wave's peaks hit your shielding at a slow enough rate that they pass through the shielding. 

Now you start flying really fast towards the sun.  Because you're flying into the peaks, they'll start hitting your shield faster.  Since your shield only cares about how fast the peaks hit it, it blocks the light and no light gets into your ship. 
« Last Edit: 13/09/2012 16:16:32 by JP »

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #92 on: 13/09/2012 16:25:16 »
SR definitely has invariant quantities, which may be defined in terms of some formula entirely in terms of local measurements (in any inertial reference frame), and which turn out to be constant, no matter which reference frame is chosen. 

Rest properties seem a bit different, since they require a reference frame to be fixed.  However, it seems at first glance that (aside from light) you could always use local measurements to figure out the required transformation into a rest frame of the measuree and then transform whatever measurements you make to that rest frame.

However, Lightarrow's example of light certainly causes a bit of an issue for this definition of rest properties=intrinsic.  Light has no rest frame, yet a photon clearly has invariant mass which seems to be intrinsic.  It also has spin, which certainly meets the criteria most folks would set for intrinsic (and indeed, it is technically termed an intrinsic property in relativistic QM).

Now I am getting confused - a single photon has no invariant mass, it must be zero. Spin - yep
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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #93 on: 13/09/2012 16:37:30 »
Zero is still a number!   :)

I meant that having an invariant mass of zero still counts as having an invariant mass in the case of a photon, even though it has no rest frame.  You can calculate it from the length of it's energy-momentum four vector in any reference frame and get zero as a result.

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Offline imatfaal

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Re: Evidence for large scale length contraction?
« Reply #94 on: 13/09/2012 16:42:38 »
You had me worried there for a moment JP!
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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #95 on: 13/09/2012 18:34:10 »
A really nice discussion.
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Offline old guy

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Re: Evidence for large scale length contraction?
« Reply #96 on: 13/09/2012 18:52:06 »
While y’all are sorting out the semantics of technically acceptable language for describing length contraction... “rest frame, inertial frame, invariant or not”... and answering unrelated “trick questions,”
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.

A very brief recent summary from my post 79, edited (...) for clarity of detail:
Quote
The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

 As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”

Damocles:
Quote
The dictionary definition of "intrinsic" is "belonging to a thing by its very nature". The Earth has an "intrinsic" shape ...

So does my alien probe: its shape as it was built, obviously “at rest” with it.
Substitute “as it was originally formed by gravity” and you have the intrinsic shape of Earth.

Damocles said:
Quote
It is only through the operation of these definitions that we are able to make generalizations such as "the (intrinsic) shape of any sufficiently large and plastic planet must be an oblate spheroid of revolution", and similar issues that were quite legitimately worrying old guy around posting #30 of this thread.

The core of my “worry” as expressed in post 30:
Me:
Quote
Does this claim that Earth changes shape as it is measured from different frames of reference?
Lightarrow:
Quote
Certainly. In a frame of reference which is still with respect of our planet, the Earth is spherical...; in another, moving, frame, it's not (and of course every human being is flattened too). Where is the problem?
Me:
Quote
The "problem" is that, "in the real world" Earth does not change shape with every different possible measurement of it.

Damocles:
Quote
I fully agree that any property like the shape of an object measured by an observer in a moving frame is totally valid, and the extrinsic shape that s/he observes must be regarded as the actual shape of the object by such an observer who wishes to do consistent physics in their own frame, but it clearly differs from its intrinsic shape.
(my bold)

Very contradictory! The “contracted length” of the probe or shape of Earth’s diameter is NOT the “actual” length/shape in either case.

Imatfaal:
Quote
...misconception that the length contraction is not "real" - ie that it is merely an artifact of vision/observation rather than an actual consequence of frames in relative motion.

My thought experiment illustrates what is “real” about the length of the probe as compared with the “vision/observation”/measurement of it from Earth’s frame. It “really” will not fit into a 10 meter bay!


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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #97 on: 13/09/2012 19:14:56 »
"The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built."

If you think of it OG. To retrieve that probe it will have to be in its so called 'rest frame'. And in that frame of reference the probe will have its 'rest properties', if you like. Assuming that the cargo bay is built to the dimensions we found the probe to have before joining up with it, becoming 'still' relative it, it will be found not to fit. The whole idea with a length contraction is that frames of reference will differ when compared, not that you will find length contractions being in the same frame of reference, 'at rest' with what you measure. As you are, approximately, on any planet.

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Offline yor_on

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Re: Evidence for large scale length contraction?
« Reply #98 on: 13/09/2012 19:20:59 »
You still don't get it OG? We measure, and from there construct what is 'real'. There is no better way. Doing so we find that from the frame of the muon, if it could measure a distance, that distance must be contracted. You mix 'rest frames' with comparisons between frames, and somehow seem to assume that they are the same, always?

That's wrong.
=

What you can do is to assume that locally (locality) must be the preferred frame, just as the idea of 'invariant mass' have a same property assumed, no matter where it is measured. But the discussion about what is more 'real', comparisons between frames of reference, or comparisons being at rest with what you measure, is meaningless. They are both as real from the frame measuring. Instead of complaining, embrace it :)
« Last Edit: 13/09/2012 19:30:59 by yor_on »
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Offline JP

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Re: Evidence for large scale length contraction?
« Reply #99 on: 13/09/2012 20:09:47 »
I still have received no unequivocal answer to the “will it fit?” question, illustrating the difference between the intrinsic length of the probe measured from at rest with it and the extrinsic , contracted length measured from Earth’s frame.

A very brief recent summary from my post 79, edited (...) for clarity of detail:
Quote
The project was to retrieve the probe. (Traveling near ‘c’’ toward Earth and measured, from Earth to be 10 meters in length.) The question was, will a shuttle with a 10 meter cargo bay contain it? The answer is no, and the reason is that the "contracted length" of the probe as measured from earth is not its actual, intrinsic length, as it was built.

 As I said, “I am still hoping for intelligent replies to my experiment as I presented it.”

You've received plenty of replies, Old Guy.  You haven't received any that you happen to like, but that's now this forum operates.  :)

I think it's clear from almost every poster in this forum that the 'rest length' of the probe is longer than the 'rest length' of the cargo bay, while the measured length of the probe as it passes through the cargo bay in motion will be exactly as long as the cargo bay. 

You're engaging in evangelism of your viewpoint by continually restating the same arguments without engaging in discussion.  That is not acceptable on this forum.

If you do want to discuss what 'rest length' means vs. length measured in non-rest frames, there is an interesting discussion going on about that and you're welcome to engage in it, so long as you keep it a discussion.