Hey there! Sign in to join this conversationNew here? Join for free
    • Aston Villa FC Supporter
    Offline

    3
    ReputationRep:
    Aston Villa FC Supporter
    (Original post by AlbertXY)
    Only if you don't look at it closely, I have read his papers of relativity and SR, that is why I know he was wrong and was able to work out where he was wrong using a train analogy and creating a physical test that shows it does not happen.
    does happen
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    A motorway will do.
    That doesn't specify which reference frame.


    (Original post by AlbertXY)
    light length between eye and object is visual contraction,
    I don't think there is a sensible distinction to be drawn. If you are simply referring to the length as measured by somebody moving to be a 'visually contracted' length, then you are just agreeing with SR but giving things a different name.

    In relativity there is a concept of 'proper length', which is defined to be the length of an object in its own reference frame. This does not contract by definition (since it specifies a reference frame), so if that's what you mean by 'physical length' then okay, but it's not exactly revelatory!


    And my model and physical real life experiment shows there is no physical length contraction.
    How so?
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    Only if you don't look at it closely, I have read his papers of relativity and SR, that is why I know he was wrong and was able to work out where he was wrong using a train analogy and creating a physical test that shows it does not happen.
    With your level of mathematical knowledge there is an approximately zero chance you understood what was said. The language of physics is mathematics.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Implication)




    How so?

    You will find relative to an inertia reference frame a proper length is referred to as it's rest length also used in relativity.


    In imagination, imagine standing on a central platform between two trains, one train on the left and one train on your right. We measure both trains to be an equal rest length of lets say 50 meters. Now if the trains travel at the same speed away from you and parallel to each other, the observer on the platform witnesses a length contraction of both trains, people on the trains still measure the trains to be at rest length relative to each other. The train the people and their ruler have contracted , so they still measure 50 meters.


    Ok so far?
    • Aston Villa FC Supporter
    Offline

    3
    ReputationRep:
    Aston Villa FC Supporter
    (Original post by Implication)
    With your level of mathematical knowledge there is an approximately zero chance you understood what was said. The language of physics is mathematics.
    :ahee: :lol:
    Offline

    17
    ReputationRep:
    (Original post by Implication)
    With your level of mathematical knowledge there is an approximately zero chance you understood what was said. The language of physics is mathematics.
    burrrrrrrrrrn :rofl:
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    You will find relative to an inertia reference frame a proper length is referred to as it's rest length also used in relativity.
    Indeed.


    In imagination, imagine standing on a central platform between two trains, one train on the left and one train on your right. We measure both trains to be an equal rest length of lets say 50 meters. Now if the trains travel at the same speed away from you and parallel to each other, the observer on the platform witnesses a length contraction of both trains, people on the trains still measure the trains to be at rest length relative to each other.
    Yep. We measure the trains to have contracted because we're moving relative to them. The people on the first train aren't moving with respect to the train so still measure its rest length. The same holds for the second train.


    The train the people and their ruler have contracted , so they still measure 50 meters.
    Let's make that a little more precise. In their reference frame the people on the train haven't contracted and nor have their rulers, so they still measure 50m. If we watch them measuring their train, it will look to us as if both their rulers and the train have contracted so we'll see the train hit the 50m mark on their ruler - it just won't match our ruler.

    No real disagreement so far!
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Implication)
    Indeed.




    Yep. We measure the trains to have contracted because we're moving relative to them. The people on the first train aren't moving with respect to the train so still measure its rest length. The same holds for the second train.




    Well in their reference frame the people on the train haven't contracted and nor have their rules. But yes if we watch them measuring their train, it will look to us as if both their rulers and the train have contracted so they'll measure 50m.

    No real disagreement so far!
    Ok, so half way through the journey one of the trains breaks down, and the other train continues its journey. The observer on the platform gets on his bicycle and decides to travel tot he broken down train to confirm his original measurement of 50 meters, He arrives to confirm the rest length is 50 meters, but was curious about the contraction they had just observed, So in being a scientist , the observer placed two sensors on the stationary train , one at the front and one at the rear to record the returning passing trains measurement by sensor alignment What do you think the result was?

    Name:  einy.jpg
Views: 21
Size:  20.5 KB
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    Ok, so half way through the journey one of the trains breaks down, and the other train continues its journey. The observer on the platform gets on his bicycle and decides to travel tot he broken down train to confirm his original measurement of 50 meters, He arrives to confirm the rest length is 50 meters, but was curious about the contraction they had just observed, So in being a scientist , the observer placed two sensors on the stationary train , one at the front and one at the rear to record the returning passing trains measurement by sensor alignment What do you think the result was?

    Name:  einy.jpg
Views: 21
Size:  20.5 KB
    Can we clarify precisely what the sensors are measuring?
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Implication)
    Can we clarify precisely what the sensors are measuring?

    The sensors are measuring alignment , but we already know they will align because the trains travelling parallel in motion measured the same .
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    The sensors are measuring alignment
    In what sense? What exactly are they measuring?


    but we already know they will align because the trains travelling parallel in motion measured the same .
    The fact that they are the same length (which is what I assume you mean by alignment i.e. check that when the fronts are aligned the backs are also aligned) when they are stationary with respect to each other does not necessarily mean that they are the same length when one is moving relative to the other. We need to check this; otherwise we are presupposing that there is no length contraction.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Implication)




    The fact that they are the same length (which is what I assume you mean by alignment i.e. check that when the fronts are aligned the backs are also aligned) when they are stationary with respect to each other does not necessarily mean that they are the same length when one is moving relative to the other. We need to check this; otherwise we are presupposing that there is no length contraction.

    Yea you got this, you understood, I already know there will be no contraction you can check,
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    Yea you got this, you understood, I already know there will be no contraction you can check,
    If you have legitimately performed this experiment and think you have found no length contraction, I have two things for you to consider. First, think very carefully about precisely how you measure the 'alignment'. It's very easy to say things like 'oh we'll just use a lightgate and measure the time it spends clicked off', but you have to be very careful to ensure you consider everything relativistically. It's very easy to forget this when you consider the time taken for light signals to move between sensors and objects etc. More importantly, to what precision did you run the experiment? The factor by which lengths contract and times dilate is denoted by \gamma, and is given by

    \gamma=\dfrac{1}{\sqrt{1-\frac{v^2}{c^2}}}.

    The UK high-speed trains go at a maximum of 300kmph, which is roughly 85 m/s. So even if you ran the experiment with trains that went this fast, you'd be looking at a gamma factor of

    \gamma=\dfrac{1}{\sqrt{1- \Big(\frac{85}{300,000,000} \Big)^2}}.

    It's very unlikely that your calculator will be powerful enough to even compute this number, and will just tell you that there is no change. The exact factor by which the train would contract at such a high speed is 1.0000000000000402. For a slower speed this would be even closer to 1 (no change). Was your equipment sensitive enough to notice this? Was it the change outside your error tolerances? For equipment that measured values to a precision of 1 in 1,000,000,000,000, you wouldn't measure a difference even if there was one! Your equipment just wouldn't be good enough for the job! You'd need much higher speeds or much better equipment.
    • Aston Villa FC Supporter
    Offline

    3
    ReputationRep:
    Aston Villa FC Supporter
    (Original post by AlbertXY)
    The sensors are measuring alignment , but we already know they will align because the trains travelling parallel in motion measured the same .
    The detectors will see that the trains will not be perfectly aligned.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Implication)
    If you have legitimately performed this experiment and think you have found no length contraction, I have two things for you to consider. First, think very carefully about precisely how you measure the 'alignment'. It's very easy to say things like 'oh we'll just use a lightgate and measure the time it spends clicked off', but you have to be very careful to ensure you consider everything relativistically. It's very easy to forget this when you consider the time taken for light signals to move between sensors and objects etc. More importantly, to what precision did you run the experiment? The factor by which lengths contract and times dilate is denoted by \gamma, and is given by

    \gamma=\dfrac{1}{\sqrt{1-\frac{v^2}{c^2}}}.

    The UK high-speed trains go at a maximum of 300kmph, which is roughly 85 m/s. So even if you ran the experiment with trains that went this fast, you'd be looking at a gamma factor of

    \gamma=\dfrac{1}{\sqrt{1- \Big(\frac{85}{300,000,000} \Big)^2}}.

    It's very unlikely that your calculator will be powerful enough to even compute this number, and will just tell you that there is no change. The exact factor by which the train would contract at such a high speed is 1.0000000000000402. For a slower speed this would be even closer to 1 (no change). Was your equipment sensitive enough to notice this? Was it the change outside your error tolerances? For equipment that measured values to a precision of 1 in 1,000,000,000,000, you wouldn't measure a difference even if there was one! Your equipment just wouldn't be good enough for the job! You'd need much higher speeds or much better equipment.

    All the maths in the world doe's not explain reality, I have not tried this experiment, but there is without an uncertainty I know I am correct. Physical contractions involve forces, I do not consider air is an equal and opposing force to contract molecular structure that is dense. There may be some expansion and contraction in the overall form involving thermodynamics, but there is cert is not the way you imagine. You are correct I should hold judgement until something like this is tested, but I am sure I am right.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Kyx)
    The detectors will see that the trains will not be perfectly aligned.

    And by what external and opposing force do you perceive contracts the solid ?
    • Thread Starter
    Offline

    2
    ReputationRep:
    How would you try to explain this -

    For an object to contract in length. the rear has to be travelling faster than the front.
    • Aston Villa FC Supporter
    Offline

    3
    ReputationRep:
    Aston Villa FC Supporter
    (Original post by AlbertXY)
    How would you try to explain this -

    For an object to contract in length. the rear has to be travelling faster than the front.
    Now this is a good idea
    Offline

    18
    ReputationRep:
    (Original post by AlbertXY)
    All the maths in the world doe's not explain reality, I have not tried this experiment, but there is without an uncertainty I know I am correct. Physical contractions involve forces, I do not consider air is an equal and opposing force to contract molecular structure that is dense. There may be some expansion and contraction in the overall form involving thermodynamics, but there is cert is not the way you imagine.
    If you are defining a physical contraction to be one involving forces, then indeed special relativistic length contractions are not 'physical contractions'. But this is not a definition used by anyone else in physics so isn't very useful. In fact, we really do observe that the molecules making up a solid are closer together when viewed from a reference frame in which the solid is moving. If you like, you can pass this off as a 'visual distortion' - which in some sense it is. But these distortions are a fundamental part of space and time, and the fact is that in frames where certain objects are moving, those objects interact with the rest of the universe as if they are shorter than they are in their own frame. It isn't just humans who 'see' a difference.


    You are correct I should hold judgement until something like this is tested, but I am sure I am right.
    The problem is that SR has been tested and confirmed many times. Maybe not using an experiment identical your own, but the same principles have been used and special relativity confirmed.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Kyx)
    Now this is a good idea
    I know lol,

    Name:  101.jpg
Views: 58
Size:  22.7 KB

    Phys 101
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Have you ever participated in a Secret Santa?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.