Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.physics.relativity > #355773 > unrolled thread

Re: On length contraction and the length contraction paradox

Back to article view | Back to sci.physics.relativity

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: On length contraction and the length contraction paradox udr310515@gmail.com - 2015-07-04 17:19 -0700
    Re: On length contraction and the length contraction paradox "Dono," <sa_ge@comcast.net> - 2015-07-04 17:32 -0700
      Re: On length contraction and the length contraction paradox udr310515@gmail.com - 2015-07-04 17:40 -0700
        Re: On length contraction and the length contraction paradox "Dono," <sa_ge@comcast.net> - 2015-07-04 18:19 -0700
          Re: On length contraction and the length contraction paradox Poutnik <poutnik4nntp@gmail.com> - 2015-07-07 19:18 +0200
          Re: On length contraction and the length contraction paradox Odd Bodkin <bodkinodd@gmail.com> - 2015-07-08 08:05 -0500
            Re: On length contraction and the length contraction paradox Fritz Köhler <fritzk@notrenetwork.net> - 2015-07-25 16:41 +0000
            Re: On length contraction and the length contraction paradox Odd Bodkin <bodkinodd@gmail.com> - 2015-07-25 12:44 -0500
              Re: On length contraction and the length contraction paradox Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-07-25 21:40 +0200
                Re: On length contraction and the length contraction paradox Tom Roberts <tjroberts137@sbcglobal.net> - 2015-07-25 20:30 -0500
                Re: On length contraction and the length contraction paradox Ignorant Raving Crackpot <ignorantravingcrackpot@gmail.com> - 2015-07-25 23:50 -0700
                  Re: On length contraction and the length contraction paradox Ignorant Raving Crackpot <ignorantravingcrackpot@gmail.com> - 2015-07-27 17:24 -0700
                  Re: On length contraction and the length contraction paradox Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-07-28 13:33 +0200
                Re: On length contraction and the length contraction paradox Odd Bodkin <bodkinodd@gmail.com> - 2015-07-27 09:38 -0500

#355773 — Re: On length contraction and the length contraction paradox

On Saturday, July 4, 2015 at 6:11:08 PM UTC-4, shuba wrote:
> udr310515 wrote:
> 
> > https://www.youtube.com/channel/UCGxPzvWDpIp4cqIcaw2wx-A/videos.
> 
> > Any pertinent comments very much appreciated. Please keep in mind
> > that these presentations use standard special relativity and in
> > NO way do they try to rewrite any basic tenets. The issue at hand
> > is to provide better visualization and to make counterintuitive
> > concepts quasi-intuitive again, if at all possible.
> 
> Nice work, I enjoyed it. I can't say how well it might help new
> learners understand the subject, but it very well could for some.
> Focusing on spacetime and its symmetries is for sure the way to go.
> 
> A couple things. First, the video with the flashing rim lights
> contains a final frame providing mathematics to answer the question
> of whether the effect of independent pulses around the rim could
> actually be "observed". It seems to be correct (and interesting!)
> but it shows that unless the flash frequency is unrealistically
> short and/or the lab size is unrealistically huge, there is no
> chance of measuring even one pair of pulses around the rim of the
> moving lab, much less identifying multiple simultaneous pulses.
> 
> Secondly, the use of the term "observed" is always problematic and
> leads many learners astray. Using "measured" or "calculated" is
> generally better, as what is observed with our eyes or even cameras
> and other instruments contains other elements than time dilation
> and length contraction, e.g. Terrell rotations, Doppler shifts, and
> effects due to light travel time, which go beyond the presentations.
> 
> 
>          ---Tim Shuba---

Thanks for taking the time to watch and comment. 
About your 2nd point: you are right of course, made a note of it.
About the 1st point, which is a very good observation: 

No, I don't think the effect is just theoretic and too demanding to measure. I believe existing tech is actually just about good to observe something like this, provided we could make an object go at the necessary relativistic speeds. 

Lets take \beta = (√3)/2,  \gamma = 2 as in the videos, and 2R = 100m for a round figure. Then the proper-time differential along the direction of motion amounts to ∆t' = (\beta\gamma x 2R) / c = (50√3)/(3x10^8m/s) ~ 288x10^-9s = 288ns. This is well within the range of current ultra-high speed cameras, see for instance http://newsoffice.mit.edu/2011/trillion-fps-camera-1213 or https://www.youtube.com/watch?v=-fSqFWcb4rE. Now lets say the single pulse duration in the moving frame is \tau ~ 3ns, which is again well within range of current tech. Laser pulses are routinely 3 orders of magnitude shorter than this and possibly a lot shorter than that if the pulse is shaped right (quantum squeezing makes this possible). In the stationary frame this would give an observed spot of width ∆x = (c\tau)/(\beta\gamma) = (3x10^8m/s)x(3x10^-9s)/(2x(√3)/2) = .9/√3 m ~ 52 cm << 100m but absolutely visible. You can see that we could even take 2R = 10m for ∆t' ~ 28ns, and \tau ~ 1ns for ∆x = .3/√3 m ~ 17 cm and everything still works fine.

The real problem right now is to make an object go, or find one that already goes, at a velocity v = \beta x c. Anyway, the fun part is that such an experiment would provide another test of special relativity and a very interesting one at that. It would actually visualize the "flow" of proper-time in an object moving at relativistic velocity relative to the observer (camera). 

[toc] | [next] | [standalone]

#355774

On Saturday, July 4, 2015 at 5:19:03 PM UTC-7, udr3...@gmail.com wrote:
> 
> Lets take \beta = (√3)/2,  
> The real problem right now is to make an object go, or find one that already goes, at a velocity v = \beta x c. 


This is very tough (if not impossible) with today's technology. I thing that the highest \beta observed for a massive particle is 0.22 for the ions used in the Ives-Stilwell experiments.

[toc] | [prev] | [next] | [standalone]

#355777

On Saturday, July 4, 2015 at 8:32:53 PM UTC-4, Dono, wrote:
> On Saturday, July 4, 2015 at 5:19:03 PM UTC-7, udr3...@gmail.com wrote:
> > 
> > Lets take \beta = (√3)/2,  
> > The real problem right now is to make an object go, or find one that already goes, at a velocity v = \beta x c. 
> 
> 
> This is very tough (if not impossible) with today's technology. I thing that the highest \beta observed for a massive particle is 0.22 for the ions used in the Ives-Stilwell experiments.

And those are ions. So, yeah, that's the real problem. We do not have macroscopic objects moving at relativistic speeds yet.

[toc] | [prev] | [next] | [standalone]

#355779

On Saturday, July 4, 2015 at 5:40:38 PM UTC-7, udr3...@gmail.com wrote:
> On Saturday, July 4, 2015 at 8:32:53 PM UTC-4, Dono, wrote:
> > On Saturday, July 4, 2015 at 5:19:03 PM UTC-7, udr3...@gmail.com wrote:
> > > 
> > > Lets take \beta = (√3)/2,  
> > > The real problem right now is to make an object go, or find one that already goes, at a velocity v = \beta x c. 
> > 
> > 
> > This is very tough (if not impossible) with today's technology. I thing that the highest \beta observed for a massive particle is 0.22 for the ions used in the Ives-Stilwell experiments.
> 
> And those are ions. So, yeah, that's the real problem. We do not have macroscopic objects moving at relativistic speeds yet.

No, we don't and it will be a very long time before we do. 
On a different note, this forum is full of cranks ("alsor" is one of them, there are many more) so you'll need to learn how to ignore them.

[toc] | [prev] | [next] | [standalone]

#356147

Dne 07/07/2015 v 16:21 Thomas 'PointedEars' Lahn napsal(a):
> Poutnik wrote:
> 
>> On 07/07/2015 08:59 AM, Thomas 'PointedEars' Lahn wrote:
>>> Odd Bodkin wrote:
>>>> Yes.
>>>> And so what is your line for relativistic speeds that these are all less
>>>> than that line? 
>>> Certainly, for a relative speed to be called “relativistic” by me, it
>>> would have to lie well above about 0.000234 c.
>>
>> IMHO, it is not matter of speed itself,
>> but rather if level of SR effects
>> is higher then measurement error or acceptance threshold.
> 
> Yes.
> 
>> For LC wrt validity on EM laws under coordinate transform,
>> e.g. moving charges and wires,
> 
> We are not discussing “moving charges and wires”.  We are discussing
> *human-made spacecraft*.
> 
>> relativistic speed is very low
> 
> Why?
> 
That is the right question.
Try to answer it.

-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#356277

On 7/7/2015 8:05 PM, Thomas 'PointedEars' Lahn wrote:
> Odd Bodkin wrote:
>
>> On 7/7/2015 9:18 AM, Thomas 'PointedEars' Lahn wrote:
>>> Odd Bodkin wrote:
>>>> On 7/7/2015 1:59 AM, Thomas 'PointedEars' Lahn wrote:
>>>>> Odd Bodkin wrote:
>>>>>> On 7/6/2015 1:44 PM, Thomas 'PointedEars' Lahn wrote:
>>>>>>> Odd Bodkin wrote:
>>>>>>>> I assume you're discounting man-made interplanetary probes and
>>>>>>>> astronomical bodies, all of which are macroscopic objects moving at
>                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>>>>>>> relativistic speeds.
>          ^^^^^^^^^^^^^^^^^^^
>>>>>>> […]
>>>> […]
>>>> Relativity applies at ALL speeds, not just speeds above a certain
>>>> domain.
>>>
>>> Your logic is flawed.  We are not discussing if relativity applies to all
>>> speeds; that was never doubted.  We are discussing which speeds deserve
>>> to be called “relativistic”.
>>>
>>> If the term “relativistic speed” applied to all speeds, then it has no
>>> meaning.
>>
>> Exactly the point that physicists make.
>
> You have no clue what points physicists make.  You do not even know what you
> said just a few postings before.  There is a reminder above.

I see it. A ball rolling on a table is also moving at relativistic 
speeds for certain applications and measurements. What's your point?

>
>> There is no distinct meaning for "relativistic speeds".
>
> There is.  I have just told you.
>
>> It is vague, soft-boundaried, qualitative term that is generally avoided
>> as being without objective meaning.
>
> Assuming for a moment that would be true, you have used it in your argument.

What argument? You're always assuming that everyone must be making an 
argument. I made a comment.

>
> What does that tell you?
>
>
> PointedEars
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

[toc] | [prev] | [next] | [standalone]

#358608

Thomas 'PointedEars' Lahn wrote:

> Again, it was not debated that effects of special relativity come into
> play even at relative speeds we can observe in everyday life.  Instead,
> your use and understanding of “relativistic speed” was debated.  For if
> you are saying that everything moves “at relativistic speed”, even
> current “man-made interplanetary probes” which move at less than a
> thousandth of the speed of light in vacuum (c), then the term
> “relativistic speed” does not have a meaning different from “speed”, and
> “relativistic speed” can be dropped without loss from the vocabulary of
> science, which avoids any duplicates and ambiguities.

I don't know. What do you think?

[toc] | [prev] | [next] | [standalone]

#358627

On 7/25/2015 7:40 AM, Thomas 'PointedEars' Lahn wrote:
> Odd Bodkin wrote:
>
>> On 7/7/2015 8:05 PM, Thomas 'PointedEars' Lahn wrote:
>>> Odd Bodkin wrote:
>>>> On 7/7/2015 9:18 AM, Thomas 'PointedEars' Lahn wrote:
>>>>> If the term “relativistic speed” applied to all speeds, then it has no
>>>>> meaning.
>>>> Exactly the point that physicists make.
>>> You have no clue what points physicists make.  You do not even know what
>>> you said just a few postings before.  There is a reminder above.
>>
>> I see it. A ball rolling on a table is also moving at relativistic
>> speeds for certain applications and measurements. What's your point?
>
> Again, it was not debated that effects of special relativity come into play
> even at relative speeds we can observe in everyday life.  Instead, your use
> and understanding of “relativistic speed” was debated.  For if you are
> saying that everything moves “at relativistic speed”, even current “man-made
> interplanetary probes” which move at less than a thousandth of the speed of
> light in vacuum (c), then the term “relativistic speed” does not have a
> meaning different from “speed”, and “relativistic speed” can be dropped
> without loss from the vocabulary of science, which avoids any duplicates and
> ambiguities.

That is EXACTLY the point. As you said, relativistic speeds are those 
speeds that come into play, and those are speeds that occur in everyday 
life. Therefore there IS NO line of demarcation between "relativistic 
speed" and "speed". If you believe there is such a line that 
distinguishes the two, then by all means tell me at what value that line 
occurs.

>
> But what you are saying is evidentially not the case.  The term
> “relativistic speed” is used for speeds, and the term “relativistic” is used
> in general, when the effects of special relativity become *significant* (or
> *important*, if you can understand that better); _not_ other speeds, and
> _not_ other circumstances.  *WLOG*, speeds close to c, and effects of
> special or general relativity, are attributed with “relativistic” in the
> literature.
>
> The underlying problem here is that “relativistic speed” is a *popular*-
> scientific term that you and other blissfully ignorant people who know hard
> science only from mass media, are trying to fit into what they think would
> be a scientific framework, claiming it would have (a distinct) meaning in
> the real one.
>
>>> Assuming for a moment that would be true, you have used it in your
>>> argument.
>>
>> What argument? You're always assuming that everyone must be making an
>> argument. I made a comment.
>
> Your same old semantic fallacy.
>
>
> PointedEars
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

[toc] | [prev] | [next] | [standalone]

#358639

Odd Bodkin wrote:

> On 7/25/2015 7:40 AM, Thomas 'PointedEars' Lahn wrote:
>> Again, it was not debated that effects of special relativity come into
>> play even at relative speeds we can observe in everyday life.  Instead,
>> your use and understanding of “relativistic speed” was debated.  For if
>> you are saying that everything moves “at relativistic speed”, even
>> current “man-made interplanetary probes” which move at less than a
>> thousandth of the speed of light in vacuum (c), then the term
>> “relativistic speed” does not have a meaning different from “speed”, and
>> “relativistic speed” can be dropped without loss from the vocabulary of
>> science, which avoids any duplicates and ambiguities.
> 
> That is EXACTLY the point.

It is exactly *my* point; not yours.

> As you said, relativistic speeds are those speeds that come into play, and
> those are speeds that occur in everyday life.

I said the exact opposite.  Because in everyday life (that is, the life of 
the *average* person, unaware of relativity) the effects predicted by 
special and general relativity are *present* *but* *not* *significant*, and 
the relative speeds there are *too low* for them to become significant, i.e. 
noticeable by those people (without instruments).

> Therefore there IS NO line of demarcation between "relativistic
> speed" and "speed".

Utter nonsense.  And I am tired of explaining to you why.

> [tl;dr]


PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#358657

On 7/25/15 7/25/15   2:40 PM, Thomas 'PointedEars' Lahn wrote:
> Odd Bodkin wrote:
>> there IS NO line of demarcation between "relativistic
>> speed" and "speed".
>
> Utter nonsense.

Not so. Odd Bodkin is correct. Whether a given speed is "relativistic" or not 
depends on one's physical situation and measurement accuracy -- there _IS_ no 
"line of demarcation", it must be considered on a case-by-case basis.

	We use the term "relativistic speed" to mean that the
	effects of SR are important.

In our everyday lives, with measurement accuracies of ~ 0.1 second and ~ 1 mm, 
no speed we encounter is "relativistic" (including high-power rifle bullets, 
artillery rounds, jet airplanes, and anti-aircraft rockets).

But in a laboratory with clock accuracy ~ 10^-18, scientists at NIST were able 
to observe "time dilation" from a relative speed of a few cm/s -- slower than 
most people walk.


> And I am tired of explaining to you why.

Your "explanations" leave A LOT to be desired. But it's also true that you two 
are not really diametrically opposed (as your words imply)....


Tom Roberts

[toc] | [prev] | [next] | [standalone]

#358671

On Saturday, July 25, 2015 at 2:44:10 PM UTC-5, Thomas 'PointedEars' Lahn wrote:
> Odd Bodkin wrote:
> 
> > 
> > That is EXACTLY the point.
> 
> It is exactly *my* point; not yours.
> 
> > As you said, relativistic speeds are those speeds that come into play, and
> > those are speeds that occur in everyday life.
> 
> I said the exact opposite.  Because in everyday life (that is, the life of 
> the *average* person, unaware of relativity) the effects predicted by 
> special and general relativity are *present* *but* *not* *significant*, and 
> the relative speeds there are *too low* for them to become significant, i.e. 
> noticeable by those people (without instruments).
> 
> > Therefore there IS NO line of demarcation between "relativistic
> > speed" and "speed".
> 
> Utter nonsense.  And I am tired of explaining to you why.

Your semantic quibbles are making no sense, and your ongoing feud with
Odd is, quite frankly, incomprehensible to me.

[toc] | [prev] | [next] | [standalone]

#358848

On Sunday, July 26, 2015 at 11:57:22 AM UTC-5, Ignorant Raving Crackpot wrote:

> Who cares about USENET anymore? Haven't you noticed that the vast bulk
> of online discussion is currently carried on by other means? I use
> Google Groups because I don't care to spend money to access an 
> antiquated discussion system. For free, however, USENET is worth it.
> And yes, if it offends your sensibilities, I don't exactly care.

From Wikipedia:
  Over time, the amount of Usenet traffic has steadily increased. As
  of 2010 the number of all text posts made in all Big-8 newsgroups 
  averaged 1,800 new messages every hour, with an average of 25,000 
  messages per day. However, these averages are minuscule in 
  comparison to the traffic in the binary groups. Much of this 
  traffic increase reflects not an increase in discrete users or 
  newsgroup discussions, but instead the combination of massive 
  automated spamming and an increase in the use of .binaries 
  newsgroups in which large files are often posted publicly. 

Compare the TOTALITY of messages appearing in all Big-8 newsgroups
with the traffic in ONE single special-interest online community, 
DeviantArt, to which my daughter regularly posts:

From Wikipedia:
  As of March 2013, the site consists of over 25 million members, and 
  over 246 million submissions, and receives around 140,000 submissions
  per day. In addition, DeviantArt users submit over 1.4 million 
  "favorites" and 1.5 million comments daily. The domain deviantart.com
  attracted at least 36 million visitors annually by 2008 according to a
  Compete.com study. As of July 2011, it is the 13th largest social 
  network with 3.8 million weekly visits.

Newsreader-based text-only newsgroups have little future compared with
browser-based online communities.

[toc] | [prev] | [next] | [standalone]

#358880

Ignorant Raving Crackpot wrote:

> Who cares about USENET anymore?

(“Usenet” is not an acronym; it has been an abbreviation for “U(SE)NIX User 
Network”, but obviously it is not anymore.)

I do, many other people do, and you should as well.  Because you are using 
it just now, without even realizing it.  You have not visited the Usenet 
Improvement Project website I referred you to, have you?


Pointed'O tempora, o mores'Ears
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#358800

On 7/25/2015 2:40 PM, Thomas 'PointedEars' Lahn wrote:
> Odd Bodkin wrote:
>
>> On 7/25/2015 7:40 AM, Thomas 'PointedEars' Lahn wrote:
>>> Again, it was not debated that effects of special relativity come into
>>> play even at relative speeds we can observe in everyday life.  Instead,
>>> your use and understanding of “relativistic speed” was debated.  For if
>>> you are saying that everything moves “at relativistic speed”, even
>>> current “man-made interplanetary probes” which move at less than a
>>> thousandth of the speed of light in vacuum (c), then the term
>>> “relativistic speed” does not have a meaning different from “speed”, and
>>> “relativistic speed” can be dropped without loss from the vocabulary of
>>> science, which avoids any duplicates and ambiguities.
>>
>> That is EXACTLY the point.
>
> It is exactly *my* point; not yours.

Well, perhaps we agree then. :)

>
>> As you said, relativistic speeds are those speeds that come into play, and
>> those are speeds that occur in everyday life.
>
> I said the exact opposite.

I quote you above: "Again, it was not debated that effects of special 
relativity come into play even at relative speeds we can observe in 
everyday life." But if this is not what you meant....

> Because in everyday life (that is, the life of
> the *average* person, unaware of relativity) the effects predicted by
> special and general relativity are *present* *but* *not* *significant*,

Alright, then perhaps the boundary is what value you consider to be 
significant. What is the value where you would place the effects at 
being significant?

>  and
> the relative speeds there are *too low* for them to become significant, i.e.
> noticeable by those people (without instruments).
>
>> Therefore there IS NO line of demarcation between "relativistic
>> speed" and "speed".
>
> Utter nonsense.  And I am tired of explaining to you why.
>
>> [tl;dr]
>
>
> PointedEars
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

[toc] | [prev] | [standalone]

Back to top | Article view | sci.physics.relativity

csiph-web