Contraction Definition and 689 Threads

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...

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...

So my textbook definitions of the ricci tensor and ricci scalar are: ##R_{ab}=R_{acbd}g^{cd}## - I note the contraction is over the 2nd and 4th index. and the 1st and 3rd. ##R=R_{ab}g^{ab}## Now, I'm trying to show that...

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...

I just got to know about this concept, "Lorentz contraction". It says The size(measure) of objects decrease as we approach the speed of light(I think, I'm right!). If this is true, then the size of our sun should be slightly smaller, as the Earth races around the sun, at a speed of one-tenth of...

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...

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...

What do they mean by 'Contract ##\mu## with ##\alpha##'? I thought only top-bottom indices that are the same can contract? For example ##A_\mu g^{\mu v} = A^v##.

As you approach c time slows. Relative to an observer. But it is an actual thing. A material thing can be seen to have not aged as the observer did, right? Well if time slows then an atom cannot vibrate at the same frequency as 'normal'. It must be slowed. An atom vibrating at an...

Hello, Onhttp://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html website it says in the section "below the rocket, something strange is happening" that the distance of an object which passes the accelerating observer never increases -c2/α. I think this means, that the Rindler Horizon...

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...

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...

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

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...

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...

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?

Hey guys, So in my notes I've got this statement written: If tensor with no symmetry properties, A^{\mu\nu}, contracts to a_{\mu\nu}, we can write this as A^{\mu\nu}a_{\mu\nu}=\frac{1}{2}a_{\mu\nu}(A^{\mu\nu}-A^{\nu\mu}) as a_{\mu\nu} (A^{\mu\nu}+A^{\nu\mu}) = 0. So I don't see how the...

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...

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...

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...

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?

I already know the solution to this problem, but I'm not sure exactly why it works out the way it does, so I'm looking for an explanation. Homework Statement A particle accelerator accelerates electrons at 40 GeV in a pipe 2 miles (3218.69 metres) long, but only a few cm wide. How long is the...

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...

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...

A quick question. It's been a long time since I had anything to do with special relativity, so I really can't remember much. But last night I was thinking about the "proof" of special relativity with the case of muons. So basically: Muons are created when particles hit the atmosphere. They...

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...

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...

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...

Hello. I'm learning about Lie derivatives and one of the exercises in the book I use (Isham) is to prove that given vector fields X,Y and one-form ω identity L_X\langle \omega , Y \rangle=\langle L_X \omega, Y \rangle + \langle \omega, L_X Y \rangle holds, where LX means Lie derivative with...

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...

In order for the light to take the same amount of time for both paths in the interferometer, simple geometry implies that the ratio between length and width will have to decrease. A straightforward derivation gives L/W=Sqrt(1-v^2/c^2) where the velocity v is in the direction of the length...

Hi Just wondering about the orbital path of a high speed particle - eg electron in orbit. Is it length contracted? Then how do we manage nλ=2.π.r ? Neil

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...

I have encountered a difficulty which arises from my attempt to combine non collinear Lorentz transformations in analyzing the following problem: A thin rod is cut from a metal plate leaving a slot of exactly the same size. The two are separated and set in motion thus: the rod lies along x...

My question is essentially a variation of the Ehrenfest paradox in SR. But hopefully with some experimental data. In the LHC, for example, a fixed number of particle bunches with some length are injected into the main ring. Now, as the velocity of the particles increases, the bunches would be...

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...

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...

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...

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...

Length contraction velocity question. Suppose there are two sets of binary neutron stars in mirrored synchronous orbits one light year apart with zero differential velocity between the orbits center of mass. Both sets of binary stars are orbiting very fast causing velocities with respect...

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...

We have a few posters struggling with this, I thought I'd post a step by step guide, to see if it would help. That seems easier than trying to untangle the confused threads we have. We'll see if it works... Setup and notation: We have a rocket, which has a front and a back. We have a...

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...

Let's suppose that we have a rod which is 2 meters long in its rest frame. Its rest length can be defined as a set of points which do not occupy the same place, measured in a frame which is at rest with the rod as a whole. Now if we travel relative to the rod, it gets length contracted, I...

Since many authors call simultaneity between events a convention, and that under the specific set of rules we may choose a convention or a coordinate system relative to an IRF (or non-inertial) to describe space time, I wonder what's the relation between this and the effects of length...

If a spaceship travels a distance of one light year as measured from Earth in one year's time as measured from the spaceship what is the relative velocity for earth-ship. Also how far did the pilot travel according to the pilot and how long was the trip according to an earth-clock? I found...

Homework Statement A relativistic conveyor belt is moving at speed 0.5c relative to frame S.Two observers standing beside the belt, 10 ft apart as measured in S, arrange that each will paint a mark on the belt at exactly the same instant (as measured in S). How far apart will the marks...

Homework Statement Consider the metric space (R^{n}, d_{∞}), where if \underline{x}=(x_{1}, x_{2}, x_{3},...,x_{n}) and \underline{y}=(y_{1}, y_{2}, y_{3},...,y_{n}) we define d_{∞}(\underline{x},\underline{y}) = max_{i=1,2,3...,n} |x_{i} - y_{i}| Assume that (R^{n}, d_{∞}) is...

I am given this function $f(x)=\langle (1/9) \cos(x_1+ \sin(x_2)) , (1/6) \arctan(x_1+ x_2) \rangle$ where $x_1= \langle 0,-1 \rangle$. may I please get hints on how to prove that this function is a contraction map

The three main effects of SR occur in inertial frames and change the description of space-time relative to a particular observer. My question here is how do these effects occur on Earth, since we know that motion on Earth is non-inertial. I know that we travel at small speeds and that we can't...