# The Naked Scientists Forum

### Author Topic: Length contraction is a mathematical convenience.  (Read 612 times)

#### jeffreyH

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##### Length contraction is a mathematical convenience.
« on: 23/09/2016 17:17:23 »
In general relativity we can actually detect the effects of gravity on time. The Lorentz factor leads to the conclusion of length contraction. However, unlike time dilation, this is only a mathematical convenience. You cannot actually detect a change from any point of observation. This takes away the issue of length contraction during rotation. Where the radius would have to contract in order for the spinning object to not disintegrate.
« Last Edit: 23/09/2016 17:27:15 by jeffreyH »

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #1 on: 23/09/2016 22:24:42 »
In general relativity we can actually detect the effects of gravity on time. The Lorentz factor leads to the conclusion of length contraction. However, unlike time dilation, this is only a mathematical convenience. You cannot actually detect a change from any point of observation. This takes away the issue of length contraction during rotation. Where the radius would have to contract in order for the spinning object to not disintegrate.

In reality  we can actually detect the effects of gravity on the rate of the Caesium atom which we use to measure time.

Of course objects do not contract in length although spin can make an object contract at its ,,poles,,

#### jeffreyH

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##### Re: Length contraction is a mathematical convenience.
« Reply #2 on: 25/09/2016 18:35:57 »
In general relativity we can actually detect the effects of gravity on time. The Lorentz factor leads to the conclusion of length contraction. However, unlike time dilation, this is only a mathematical convenience. You cannot actually detect a change from any point of observation. This takes away the issue of length contraction during rotation. Where the radius would have to contract in order for the spinning object to not disintegrate.

In reality  we can actually detect the effects of gravity on the rate of the Caesium atom which we use to measure time.

Of course objects do not contract in length although spin can make an object contract at its ,,poles,,

Those are very pertinent observations.

Say Fred plans his journey to star x. He knows it is l lightyears away and calculates that with enough fuel he can reach it in n years at velocity v. He knows nothing of relativity. When he actually undertakes the journey he finds that he reaches star x in 1/2n years. So now he concludes that his distance measurements must have been in error and the star was only 1/2l light years away. He has experienced length contraction without being able to detect it. Due to time dilation. In which case time dilation must relate to the amount of inertia in the moving mass.

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #3 on: 25/09/2016 22:26:01 »
In general relativity we can actually detect the effects of gravity on time. The Lorentz factor leads to the conclusion of length contraction. However, unlike time dilation, this is only a mathematical convenience. You cannot actually detect a change from any point of observation. This takes away the issue of length contraction during rotation. Where the radius would have to contract in order for the spinning object to not disintegrate.

In reality  we can actually detect the effects of gravity on the rate of the Caesium atom which we use to measure time.

Of course objects do not contract in length although spin can make an object contract at its ,,poles,,

Those are very pertinent observations.

Say Fred plans his journey to star x. He knows it is l lightyears away and calculates that with enough fuel he can reach it in n years at velocity v. He knows nothing of relativity. When he actually undertakes the journey he finds that he reaches star x in 1/2n years. So now he concludes that his distance measurements must have been in error and the star was only 1/2l light years away. He has experienced length contraction without being able to detect it. Due to time dilation. In which case time dilation must relate to the amount of inertia in the moving mass.

Sorry Jef for being argumentative, If Fred knows star X is l light years away, knows means prior information ,

If Fred has prior calculated the distance , he does not know the accuracy of his calculation until he tests his calculations are accurate by making the journey.

I do not 'see' how or why you are suggesting a contraction or time dilation of the journey experience, the error would be in the calculation, nothing more than that?

#### GoC

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##### Re: Length contraction is a mathematical convenience.
« Reply #4 on: 26/09/2016 13:31:15 »
The box

You are not understanding the deeper meaning of time as it relates to SR. JefferyH on the other hand is confusing length contraction with time dilation. In SR your synapsis slow with all biological processes in the body. The electron makes its cycle but has to also add the distance through space into its cycle. So your clock slows. Your also a biological clock so you age slower.

Length contraction is only a visual phenomenon and not physical. It is the competition between the speed of light and the speed of an object. At relativistic speeds light cannot reflect off the entire length of an object. This is due to the finite speed of light. Many believe it to be physical but they do not understand relativity correctly. They only understand relativity math without the physical reason. Rotation is due to light being independent of the source. Those who consider light in an inertial frame as being perpendicular are not following relativity but there own version of relativity. You need to consider a sphere of light when created and you approach a vector from the past position from where light came. That angle causes the contraction viewed. Geometry will follow the Lorentz contraction when using light independent of the source. Those that just follow math without understanding the math come to a different conclusion.

JefferyH has the better idea on relativistic affects and deeper understanding.

#### phyti

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##### Re: Length contraction is a mathematical convenience.
« Reply #5 on: 26/09/2016 17:20:53 »
1.
In reviewing the MM experiment, on the left, the path in the x direction was assumed equal to the path in the perpendicular direction, x = p. The transit time for x was calculated to be > that for p. The results were negative. Lorentz and others proposed a contraction in the x direction to explain the results, as shown on the right.
The lab speed of .6c is exaggerated for clarity, since the lower limit of the effective speed was only 30 m/s.
On the left, there are 2 returning signals from Rx and Rp. Applying time dilation assigns each an earlier time, but does not make them simultaneous. Only length contraction does that. SR which appears 15 yrs later only assigns a longer length (R) to x, i.e.
t=x/(c/γ)=γx/c. Notice it's just a question of which value you associate with γ.
2.
The anaut uses the earth based distance 1 ly to calculate transit time. Moving at .6c his arrival time t is 1/.6=1.67 yr. He and his clock rate are .8 (earth normal). He arrives at 1.33 yr ship time. He hasn't made any errors  even if he is familiar with SR. He assumes a pseudo rest frame (allowed by SR) and explains the early arrival of his destination (the effects of his time dilation) as the contraction of the universe as it passes by in the opposite direction at .6c.  He can't detect his length contraction since his measuring devices contract proportionally. His length contraction is a deformation of material, a motion induced phenomena. The universe contraction is a deformation/altering of his perception, also a motion induced phenomena. He can also choose to interpret the scenario as his time dilation, based on his acceleration from earth.
When physicists accelerate particles to high speeds, no one sees the rest of the world contract. Likewise, an anaut moving at high speed cannot cause such an event.
The observer is not exempt from the effects of high speed, the same as any material object.

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #6 on: 26/09/2016 18:54:15 »
The box

You are not understanding the deeper meaning of time as it relates to SR. JefferyH on the other hand is confusing length contraction with time dilation. In SR your synapsis slow with all biological processes in the body. The electron makes its cycle but has to also add the distance through space into its cycle. So your clock slows. Your also a biological clock so you age slower.

Length contraction is only a visual phenomenon and not physical. It is the competition between the speed of light and the speed of an object. At relativistic speeds light cannot reflect off the entire length of an object. This is due to the finite speed of light. Many believe it to be physical but they do not understand relativity correctly. They only understand relativity math without the physical reason. Rotation is due to light being independent of the source. Those who consider light in an inertial frame as being perpendicular are not following relativity but there own version of relativity. You need to consider a sphere of light when created and you approach a vector from the past position from where light came. That angle causes the contraction viewed. Geometry will follow the Lorentz contraction when using light independent of the source. Those that just follow math without understanding the math come to a different conclusion.

JefferyH has the better idea on relativistic affects and deeper understanding.

Well! there is nothing I do not understand on the subject of time or contraction.

I understand why you think ''time'' slows down but quite clearly you do not understand that time does not slow down. Time is not motion or a rate, time is timeless and just is.

It is not totally true that an object cannot contract in length, i.e a car hitting a brick wall at high speed certainly contracts in length as the momentum continues to take the rear of the vehicle forward while the front of the vehicle is stopped by the wall.

Interpretation is the key to understanding anything, without interpretation being precise it is nothing more than mumbo jumbo.

#### jeffreyH

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##### Re: Length contraction is a mathematical convenience.
« Reply #7 on: 26/09/2016 21:09:17 »
To get the subtleties of the subject it would be useful to read up on the lifetimes of muons and how time dilation affects them.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html

Does the sky contract to accommodate the muons or do they simply travel further?

#### GoC

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##### Re: Length contraction is a mathematical convenience.
« Reply #8 on: 26/09/2016 22:22:43 »
I am a realest so for me of course the reaction availability at 0.98c is much less than a relative rest frame. Space does not contract to my mind. There are no worm holes. We live in a three dimensional universe with motion. You cannot create a perfect circle in a three dimensional universe. Point to point can get closer and smaller but still not create a perfect circle.

Your understanding affects your interpretation of observation. We cannot view a Photon or Muon to understand the processes and are stuck with just guesses. Relativity and relativistic math appear to be accurate with observation. It is the subjective interpretations that are suspect. Is there a medium? If you say no there is nothing to work with to know why the electron always cycles to the photon distance traveled in every frame. If you say yes to a medium we have to consider energy is in the medium and not in mass because of the MMX.

Since I am a realest something makes the electron move relative to the photon distance traveled. The Muon reaction time is related to relativity also. It cannot react at the same distance through space at relativistic speeds but be sure in the view of a realest its a slow reaction possibly caused by compressed space and not contracted space causing the increased distance.

#### David Cooper

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##### Re: Length contraction is a mathematical convenience.
« Reply #9 on: 27/09/2016 19:41:46 »
In general relativity we can actually detect the effects of gravity on time. The Lorentz factor leads to the conclusion of length contraction. However, unlike time dilation, this is only a mathematical convenience. You cannot actually detect a change from any point of observation. This takes away the issue of length contraction during rotation. Where the radius would have to contract in order for the spinning object to not disintegrate.

How do you know a change can't be detected? If you put eight rectangular objects round the edge of a circle such that each is touching the next one "head to tail", what happens if you then rotate them round the circle at 0.866c? They will all contract to half their rest length and gaps will open up between them such that you could fit twice as many of these objects into the same space. See http://magicschoolbook.com/science/ref-frame-camera.htm - click on the button on the left and then type "d" to select an illustration of something close to this. The initial view shows the eight rectangles length already contracted to half their rest length, as required by their speed of travel. If you type "2" you'll see the same thing from the frame of reference of the lowest red rectangle on the screen, at which point it is shown at its rest length. If you type "3" you'll see the same for the red rectangle on the right with that rectangle displaying its rest length. "1" gets you back to the original view. Pressing "s" (for "start/stop") will run time, although it actually shows these objects passing the circle on tangents to it rather than going round it, but it is easy to see that if they were going round it you could have twice as many in that space as the rest length of the rectangles would ordinarily force them to take up, and the 16 objects would then be forming a chain contacting the whole way round, thereby showing that the contraction is real.

No one's done the experiment because the speeds are too high and a small disc rotating fast enough would hide what happens by flying apart long before any length contraction can show up, but a huge disc could hold together and would behave as I've described.

#### jeffreyH

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##### Re: Length contraction is a mathematical convenience.
« Reply #10 on: 27/09/2016 22:04:53 »
You need to think in terms of mass flow dm/dt in relation to the gamma function. This falls in line with both the increase in relativistic mass and dilation of time with no resort to a physical change in length. I could go through a full proof but I have other issues to contend with at the moment.

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #11 on: 28/09/2016 09:58:41 »
You need to think in terms of mass flow dm/dt in relation to the gamma function. This falls in line with both the increase in relativistic mass and dilation of time with no resort to a physical change in length. I could go through a full proof but I have other issues to contend with at the moment.

Not quite true, an object that gains more ''mass'' expands in all directions, an object that loses ''mass'' contracts back to equilibrium entropy.

Relativistic ''mass,, is an increase in speed and not an increase in ''mass''.

An object falling that is 1 kg will remain 1 kg in free fall, but the acceleration of G gives the object relativistic  weigh and force.

The actual mass of any object is m=0,  because m=g

Without g an object has no mass, it is mass less and weightless.

Time dilation is not a time dilation, it is a timing synchronisation offset, time ''flows'' constantly externally of the Caesium atoms that you use to measure time.

added- I have added a real simple diagram with 4 lines that show why you are wrong about time dilation and contraction.

The first two lines are of external space and equal in length.

The third and 4th lines being internal synchronous unless the 4 th line is in in motion.

p.s understand the bottom two lines are internal relative to the top two lines and do not affect the top two lines.

added- oh no, I can't quite believe I have started to discuss this again, so why I am it I might as well tell you what time dilation actual is.

Time dilation is thermodynamics and the affect of a bodies entropy emit/gain ratio, when a body is in motion or moves away from a larger mass, the object emits less because of distance and speed to the other body. It will always lose and gain entropy at a rate, motion/distance changes this rate.

I have told you  before that things extract ''things'', ''energy'' that is greater than the S will emit and attract to things with a lesser S.

All things want to be the same. All things want to remain at ''room'' temperature.

>E will always ''find'' a way to travel to things with <S than an equilibrium.

Imagine this, the electricity that comes into my home is pulled along the wire, it is pulled along the wire because the wire is less energy than the electricity, the electricity reaches the element where it is then pulled/stretched across space to the wall. If the wall was to contract in distance to the end of the wire the stretch would compress and red shift, if it were to contract even further it would eventually become compressed to blue.

White light is beyond 750nm, less distance = less nm and greater magnitude.

What you see in the above video, the plasma is being pulled, you can not see this effect between bodies with your eyes but I assure you it is there but invisible.

« Last Edit: 28/09/2016 10:54:38 by Thebox »

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #12 on: 28/09/2016 11:00:54 »
To get the subtleties of the subject it would be useful to read up on the lifetimes of muons and how time dilation affects them.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html

Does the sky contract to accommodate the muons or do they simply travel further?

Or do they fall into a denser medium and gain life from the medium to sustain their extension period......

#### Thebox

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##### Re: Length contraction is a mathematical convenience.
« Reply #13 on: 28/09/2016 11:17:01 »
I am pulled to the ground because I have less entropy and energy than the ground, the ground is also pulled to me because I have less energy than the ground.

That is what gravity is.

added- Because the ''outer space'' is ''cold''  the energy from ''inner space'' is attracted to the ''outer space''and is stretched/pulled outwards.

« Last Edit: 28/09/2016 12:25:32 by Thebox »

#### jeffreyH

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##### Re: Length contraction is a mathematical convenience.
« Reply #14 on: 28/09/2016 14:13:31 »
OK so mass flow is basically m/t. If we look at time dilation we have

[ tex ]\Delta t' = \frac{\Delta t}{ \sqrt{1 - \frac{v^2}{c^2} } }[ /tex ]

For a relativistic mass flow we can define the equation

[ tex ]f' = \frac{m_0 \sqrt{1 - \frac{v^2}{c^2}}}{\Delta t}[ /tex ]

So as velocity increases the flux of energy slows. Hence time dilation. I did not have to resort to using length at all.

OK So basically latex is screwed. To see what the equation looks like go here https://www.codecogs.com/latex/eqneditor.php and copy and paste the stuff in between [ tex ] and [ /tex ] into the equation editor. You might learn something.
« Last Edit: 28/09/2016 14:20:04 by jeffreyH »

#### GoC

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##### Re: Length contraction is a mathematical convenience.
« Reply #15 on: 28/09/2016 19:44:46 »
the box,

You are new to the rabbit hole.

jeffreyH,

You have the advantage of knowing what to expect when you go from room to room in the rabbit hole using math.

There is mechanics behind the math that is elusive and most are satisfied by knowing what to expect in each room.

When you try to go past the math we are in a subjective nightmare and are told to stop because it is unfathomable. I would disagree. Why do we view the cat larger in one room and why do we only see the Cheshire's teeth in another? We have to build the mechanics to reproduce the entire rabbit hole and not just one room. The current subjective understanding is not coherent to form the mechanics.

#### jeffreyH

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##### Re: Length contraction is a mathematical convenience.
« Reply #16 on: 28/09/2016 20:23:24 »
the box,

You are new to the rabbit hole.

jeffreyH,

You have the advantage of knowing what to expect when you go from room to room in the rabbit hole using math.

There is mechanics behind the math that is elusive and most are satisfied by knowing what to expect in each room.

When you try to go past the math we are in a subjective nightmare and are told to stop because it is unfathomable. I would disagree. Why do we view the cat larger in one room and why do we only see the Cheshire's teeth in another? We have to build the mechanics to reproduce the entire rabbit hole and not just one room. The current subjective understanding is not coherent to form the mechanics.

You give me much more credit than I deserve.

#### GoC

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##### Re: Length contraction is a mathematical convenience.
« Reply #17 on: 28/11/2016 16:06:05 »
No, you have a thinkers mindset and not just a follower mindset.

dt changes but c remains the same for GR. c has to travel a greater distance in a more dilated environment. We measure time by cycle distance  of the electron or light distance of the photon while c remains the same.

#### The Naked Scientists Forum

##### Re: Length contraction is a mathematical convenience.
« Reply #17 on: 28/11/2016 16:06:05 »