What is Length contraction: Definition and 475 Discussions

Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length, which is the length as measured in the object's own rest frame. It is also known as Lorentz contraction or Lorentz–FitzGerald contraction (after Hendrik Lorentz and George Francis FitzGerald) and is usually only noticeable at a substantial fraction of the speed of light. Length contraction is only in the direction in which the body is travelling. For standard objects, this effect is negligible at everyday speeds, and can be ignored for all regular purposes, only becoming significant as the object approaches the speed of light relative to the observer.

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  1. P

    Exploring Quantum Entanglement Paradoxes: Length Contraction Clue?

    Could any of the experts here say whether there could be a clue here as to how to resolve the apparent paradoxes of quantum entanglement? I mean if a distance is reduced to zero, in a photon' s frame, then we should not be surprised that measurements made on one of a pair should be reflected...
  2. V

    Length Contraction & Galaxies: Time Dilation Adjustments

    Since galaxies are moving away from us, shouldn't they be contracted in length than they would be if they were at rest (wrt us)? In other words, are we observing increasingly shrunken galaxies as we look deeper into space? When measuring supernova light curves, we do adjust for time dilation...
  3. M

    Length Contraction of Bridge rotated 30 degrees

    Homework Statement A Train is driving with a uniformed velocity. v=1/4 c. The train is driving under a bridge, which is rotated \theta=30 degree in relation to the railway. The bridges length is 20 m long in a reference frame of the bridge (stationary bridge). Calculate the length of the...
  4. I

    Special Relativity - time dilation and length contraction

    Homework Statement The highest energy protons have gamma factors around ##1.0*10^{12}##. (a) Our galaxy has a disk diameter of 30 kpc, which is ##9.3*10^{20}m##. If a photon and one of these high energy protons start traversing the galaxy at the same time, by how long will the arrival of the...
  5. D

    Relativity time dilation and length contraction

    Homework Statement can somebody help my figure out what t0 l0 l and t is? For instance: A girl an her dad are in an airplane, the girl starts running 20m in 8 seconds. There is also a boy standing beneath the plane (lets pretend that the airplanes floor is seethrough. Homework EquationsThe...
  6. m4r35n357

    I Is it time to "retire" time dilation and length contraction?

    Considering the enormous number of questions posed on this forum and other places, the concepts seem fundamentally flawed (because both are formally and practically unobservable). The calculations themselves (together with the Lorentz Transform) are highly error-prone and the results misleading...
  7. T

    Does Length Contraction affect measured velocity?

    First, let me clarify if my understanding of length contraction is correct. Is it accurate to say that relativistic velocities not only affect the measured length of an object in the direction of motion, but also the distance to the object from an observer in the direction of motion? For...
  8. E

    Speed of Light: Length Contraction & 20AU Paths

    traveling at the ~speed of light leads to length contraction. based on that wouldn't a 20AU path be shorter if traveled at speeds near the speed of light ?
  9. fluidistic

    Length contraction via Lorentz transformation matrix

    1,2,3. Homework Statement I tried to derive the length contraction using the Lorentz transformation matrix and considering 2 events. I reached the correct result but there's a step that I had to assume that I don't understand. Consider a ruler of length L along the x-axis for an observer at...
  10. Justice Hunter

    Why does length contraction not cause Black holes?

    So i was watching this video : And it got me thinking... i began wondering why, when space contracts from someones frame of reference (In the video, this would be the frame of reference of the cat), why is it that the protons don't become black-holes when the space contracts? If the density...
  11. R

    A question on length contraction

    Just wondering if someone could check that I am understating this aspect of length contraction correctly... I am in a spaceship moving at say a speed of 0.6c relative to some imaginary ruler in space which has increments set 1 meter apart. (1 meter in the ruler's rest frame.) I am moving along...
  12. J

    When current flows through 2 parallel wires (same amount of current)

    when current flows through 2 parallel wires (same amount of current); the protons in the first wire would see the electrons drifting in a direction and also in the other wire (in the same direction). They would appear to be contracted in the direction which they flow due to length contraction...
  13. K

    Length Contraction & Relativistic Aberration: Is 1 Formula Enough?

    I have been coding a speed of light simulator and I am having a bit of trouble with a few aspects of the project. My first question is: Are the length contraction and relativistic aberration formulas BOTH needed in my calculations or does the relativistic aberration formula already account for...
  14. Ookke

    Distant stars and length contraction

    Please see the picture. Red dots are stars, lines are the path that light takes, our observer is at center. Assuming that stars are somewhat uniformly spread around us, I suppose that stationary observer (left picture) sees about as many stars in every direction, but an observer moving in...
  15. Kairos

    Time dilation, length contraction, but velocity invariant

    If a frame is moving at constant velocity relative to an observer, this observer perceives a time dilation and a length contraction. But in this case how the velocity (length/time) can appear constant ? It is expected to be contracted.. Thank you in advance for the explanation
  16. Mentz114

    Length contraction and the speed of light

    I hope to lay to rest two of the misconceptions about special relativity that are evident in the many questions asked here. 1) Why is the speed of light a constant ? Everybody believes Pythagoras's theorem that the length of the hypotenuse of a right angle triangle is ##\sqrt{s_1^2+s_2^2}##...
  17. Amr Elsayed

    Length contraction and direction of tavel

    Hi all, I want to make sure of a particular information. Length is contracted only in direction of motion. If I am on a spacecraft moving with high speed, I shall see the universe is contracted just in front of me that I am going to, but there would be no contraction If I look to regions that...
  18. Stephanus

    Exploring Twins Paradox & Length Contraction

    Dear PF Forum I want to know about these questions that are still bothering me, Does the universe have preferred frame of refference? Why there's twins paradox? Motion is relative, why 1 clock experiences time dilation while the other doesn't? V = \sqrt\frac{3}{4} ≈ 86.6\% If V define ratio of...
  19. A

    Muon length contraction confusion

    Muon created by fast cosmic ray has speed 2.99X10^8 m/s and life time 2.2 micro sec. According to this numbers muon should travel only 0.66Km with respect to Earth in his life time. however it travels more than 10 km (10.4km) due to time dilation. in muon frame of reference, Earth travels only...
  20. saadhusayn

    Length contraction at an angle

    Hi, My question concerns the following problem from chapter 4 of Special Relativity by A.P. French. A statement of the problem: 4-15 A flash of light is emitted at point O and is later reabsorbed at point P. In frame S, the line OP has a length l and makes an angle θ with the x axis. In a...
  21. Nick666

    Length contraction, train along a line, and a detector

    I was reading a closed thread here about the length contraction being real or not. The best I could understand my self is that space is the one that contracts, the final post by an experienced forum member saying something like its the space-time that changes, it rotates. But I still have to...
  22. E

    Length contraction test in electrical circuits

    As I am sure everyone is aware, there are still folks who don’t believe SRT and GRT. While 99.9% of them are nut-jobs, there is at least one that I respect – Tom Phipps specifically. I am not familiar with any of his writing before the advent of the GPS satellites. In any case, he now accepts...
  23. BTBlueSkies

    Will the Earth Observers See a Burning Spaceship?

    I had this though back in collage and asked my professor and he gave me a very short attempt to answer the question then said he was never quite sure about all this relativistic stuff... I didn't get my answer though but I have not forgot my question. Say a spaceship was headed toward the sun...
  24. V

    Understanding length contraction in SR

    I seem to be missing something fundamental about length contraction in SR. I would be grateful if someone can point out the error in the following logic. Suppose I have a method to measure lengths of objects in the following manner: I place a mirror at the right end of the object, send a light...
  25. Ookke

    Direction of length contraction in combined motion

    Left picture: There are two moving rails that cross at center (red dot) which itself doesn't move. The rails speeds are close to c, so that they are length contracted by factor 10 (roughly 0.995c). There are markings in rails at interval 10 length units in rails rest frame, so the interval is...
  26. L

    Are force fields deformed by length contraction?

    Imagine you have an electron traveling at high speeds... would you expect it´s EM field to be contracted following the Lorentz transformations?? If the answer is no, please explain why fields and their shape don´t deform when space-time does. How they retain their shape in a space that is not...
  27. Ganesh Ujwal

    Why isn't length contraction permanent even though time dilation is?

    Why isn't length contraction permanent even though time dilation is? It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that object goes back to "rest", it...
  28. ubergewehr273

    Length Contraction in Special Relativity

    Could somebody explain the logical reasoning behind lorentz contraction when an object travels faster and faster ?
  29. B

    Time Dilation/Length Contraction Qs: Exploring SR Basics

    It pains me to even type these out. I realize how many threads there are with very similar questions and to someone well versed in these topics, these questions probably all seem the same. But after reading what seems like all the questions, I feel I'm still confused. 1) In regards to the light...
  30. F

    Does Length Contraction Imply Superluminal Speeds?

    Assume a rocket sets off from Earth accelerating to 0.8c within 1 second. The distance to a star originally 1000 light years away contracts thus to 600 lightyears within 1 second. This means the star moves 400 lightyears in one second in the travelers frame. I make this an average speed of more...
  31. M

    Length contraction of particles

    As an object moves, it is contracted in the direction of it's motion. Why wouldn't each individual subatomic particle be contracted rather than the object as a whole?
  32. M

    Length Contraction of Electrons

    If you have a still wire with electrons moving through it, to an outside observer at rest relative to the wire, would the space between the electrons contract? I would think that special relativity causes the electrons to contract, (not the space between them) but the contracting of the...
  33. applestrudle

    Special Relativity Time Dilation Santa question

    I am doing a presentation and want to make sure I'm not misunderstanding something very fundamental. My argument goes like this: t0 = ϒt Santa is moving very fast and from his point of view he is in proper time. This means that if it takes him t0 seconds to deliver a present, the amount of...
  34. Q

    Length contraction and time dilation in spacetime

    Observers that pass each other with a relative speed close to the speed of light will observe length contraction and time dilation at the other observer. In a spacetime diagram, this would be represented by two worldlines making an angle, right? Some textbooks suggest that some of the length...
  35. Ookke

    Length contraction in diagonal motion and something strange?

    Object A goes horizontal line and object B diagonal line in 45 degrees angle (Fig 1). A and B have the same velocity ##v## in x-direction. In y-direction, B has velocity ##v##, A has none. The magnitude of ##v## is not very important, but the total speed of B must be below ##c##. In their own...
  36. R

    How does one get time dilation, length contraction, and E=mc^2 from spacetime metric?

    How does one get time dilation, length contraction, and E=mc^2 from the spacetime metric? Suppose all that you are given is x12 + x22 + x32 - c2t2 = s2 How do you derive time dilation, length contraction, and E=mc^2 from this? What is the most direct way to do this?
  37. Pezz

    Length Contraction: Why Must dx be Measured in the Prime Frame?

    The Lorentz transformation for motion in the same direction along the x-axis of two frames can be used to derive the length contraction formula. Say we are converting from dx to dx'. The t would obviously have to be 0. That would leave us with dx'=gamma(dx). My question is why dx here has to be...
  38. C

    Special Relativity as a source of Power?

    Hey guys, I've recently learned that magnetism is an electric field viewed from a different frame of reference and that the mathematics of electrodynamics describes this. However something raised my eyebrow which I wasn't quite clear on. If energy is put into a net flow of electrons, the...
  39. L

    Length Contraction: Sally & Sheldon's Meter Stick

    Homework Statement Sally and Sheldon have identical meter sticks. Sally is on earth, and sheldon is in a spacecraft that moves at 0.5c relative to sally. Sheldon leaves the spaceship at 0.1c relative to the spacecraft in a launch pad, moving away from sally. according to sally, what is the...
  40. T

    Solving Lorentz Transform problem using only length contraction

    Homework Statement A traveler in a rocket of length 2d sets up a coordinate system S' with origin O' anchored at the exact middle of the rocket and the x' axis along the rocket’s length. At t' = 0 she ignites a flashbulb at O'. (a) Write down the coordinates t'_F, x'_F, and t'_B, x'_B for...
  41. C

    What are the physics of length contraction?

    Objects in motion relative to an inertial frame S are measured to have contracted lengths in S in the direction of motion. How does Special Relativity view this contraction physically? For a concrete example, suppose I have a bar of steel moving lengthwise and, as it moves past me (in frame...
  42. H

    Questions on length contraction in train light clock experiment?

    Hi guys, I've been thinking about this experiment for the last few hours and I have a few questions which I am deeply confused about. 1) In the light clock experiment, where light clock is set up so that light travels vertically, and the train carrying the clock travels horizontally, wouldn't...
  43. H

    Short question about length contraction

    The at rest distance between Betty the astronaut and a flag in open space is 1 unit. If Betty approaches the flag at constant speed while laying out metre rulers, will she have laid out 1 unit of at rest rulers when she reaches the flag? Or will the number of rulers laid out exceed 1 due to...
  44. T

    Why are time dilatation & length contraction infinite at light speed?

    Considering that speed of light is constant and finite, then why are the time dilatation and length contraction infinite to a frame of reference moving at the speed of light? We know that a moving frame of reference experiments time dilatation and length contraction from the point of view of a...
  45. BiGyElLoWhAt

    Is "length contraction" an illusion?

    I've read a lot of places about length and time dilation or length contraction of an object relative to an observer, but what I haven't found is whether the space that the object occupies is actually being altered. It makes more sense to me that it would only appear as though the length changed...
  46. Erland

    Length contraction of rotating wheel

    Suppose that a wheel is rotating around its axis in free space with no friction, with no external forces acting on it. In theory, the wheel will rotate forever with constant angular velocity. This velocity is assumed to be small (essentially non-relativistic). Now, consider an observer O...
  47. A

    Lorentz triangle and length contraction perpendicular to propagation

    Consider a pole of 1 light second long in the ##y## direction (the vertical line(s) in the enclosed figure). It is moving in the ##-x## direction. According SR, the pole's length is not contracted because its length is not parallel to the propagation direction. However, given the time of flight...
  48. B

    Length Contraction Paradox Scenario

    Hi! I have been pondering a scenario involving a paradox with length contraction. I brought it up with my physics professor, and I somewhat understand what is supposed to happen, but I'm still somewhat confused, so I was wondering if you could help me figure out what is going on. In this...
  49. H

    Confusion over length contraction

    I understand why an object in a moving frame would be longer, but not why one in a stationary frame would be shorter. Wouldn't one in a stationary frame be the same as the object would be in the rest one? I understand the time dilation behind it, it's just that the rest of the reasoning makes no...
  50. A

    Distance dilation and length contraction

    I am trying to get another insight in what I think is currently for me a contradiction. I have searched the forums, and the web but come to the following assertion: The coordinate distance is the computation of the proper distance times the gamma-factor, while the "coordinate" length is a...
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