# Shortening of objects (Lorentz contraction)

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How do objects get shorter? Do they get shorter beginning from the point which is towards the direction of the object's displacement to the opposite end of that point on the same object? If a car was driving forward extremely fast, then the car will get shorter at the front and back? So what about the top and bottom?

Which raises the question, is it possible for something to move in all directions at once without splitting itself up (Does this deal with the uncertainty principle about inability to locate exact position and movements of electrons?)?

Also, is the decrease of an object's length a proportional decrease based on the object's stable length or is it a constant decrease based on how fast something is moving?

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Length contraction is a result of how we observe/measure things and the finite speed of light. The fractional shortening is dependent on the speed.

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How do objects get shorter? Do they get shorter beginning from the point which is towards the direction of the object's displacement to the opposite end of that point on the same object? If a car was driving forward extremely fast, then the car will get shorter at the front and back? So what about the top and bottom?

Which raises the question, is it possible for something to move in all directions at once without splitting itself up (Does this deal with the uncertainty principle about inability to locate exact position and movements of electrons?)?

Also, is the decrease of an object's length a proportional decrease based on the object's stable length or is it a constant decrease based on how fast something is moving?

Objects contract with relative motion along the direction of motion. Perpendicular to the direction of motion, there is no contraction. In between the contraction is a function of I believe the cosine of the angle.

The object contracts per the factor: Square root ( 1 - v^^2) where v is relative velocity as a percentage of the speed of light. So for an object which is not moving relative to you, v is zero. So the factor is one and you measure no contraction. If the object is moving at 87% the speed of light, v = 0.87. Here the factor calculates as 0.5. So you measure the object's length in the direction of motion contracted to half what it would be at rest.

Edited by I ME
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• 2 years later...

The generally given answer is that the object length contracts in the observer's reference frame from the object's rear forward. A good way to think about it is to use the relativity of simultaneity and an object already in motion relative to the observer. The object accelerates simultaneously along its length in its own frame. That is not simultaneous in the observer's frame. The acceleration at the rear occurs first in the observer's frame, then the accelerations of each remaining part of the object occur successively later and serially from back to front. So the farther back along the object, the greater the head start in acceleration in the observer's frame. So the contraction occurs from the rear forward.

If you want the object to start at rest and then accelerate, here is a good illustration of the rear forward contraction:

http://www.mathpages.com/home/kmath422/kmath422.htm

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• 2 months later...

The length contraction of an object was first theorised in ether theory.

The length of an object can be measured by the time it takes for light to travel the length of it. (point A and point B)

The ether has the speed of light going in all directions at c.

If you move relative to the ether then the time for light to travel from point A to point B would be different than from point B to point A

If you take the average of those measurements then you get the Lorentz factor.

In experiments where length was measured by light travelling the length of a distance moving at different speeds compared to the ether, there was an expected "relative length expansion" by the lorentz factor.

There was no detected "relative length expansion", so it was theorised that the actual length measured was shortened as it moved through the ether.

Relativity theory took this theory and took out the ether and predicted that any object would "appear" to contract by the lorentz factor corresponding to the relative speed that object would move to an observer.

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It's really quite simple. "Velocity" in 3d+1 can be represented as "rapidity" in 4d, that is, the angle by which the subject of observation has rotated in the x-t, y-t, and z-t planes.

The foreshortening, then, is identical to the foreshortening we see when a motionless object is rotated from broadside-on to head-on. Ordinary objects around us just don't move that fast, so we never notice it; we only notice the kind that happens with the motionless object because that's all we've ever seen.

Edited by Schneibster
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Is the travelling object contracting or the space, in which the travelling object exists, is contracting?

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