Length Contraction Explained Simply

• bhsmith
In summary, length contraction is a phenomenon observed when an object is in motion relative to a reference frame. It explains how the length of an object appears shorter to an observer in a different reference frame due to the effects of time dilation and relativity of simultaneity. The 1888 Michelson-Morley experiment and subsequent experiments have indirectly proven the existence of length contraction. Although there is no direct experimental proof, theories such as the MMX setup and isotropy of light speed support the concept of length contraction.
bhsmith
I'm having a hard time understanding length contraction. can anyone explain it to me in simple terms?

just remember that the length of an object in one reference frame is the distance between the front and back at one simultaneous moment so relativity of simultaneity enters into it.

Alright, I understand that. I have been researching Length Contraction and i have found that there is no real evidence to prove length contraction. is this correct?
Also a lot of places state that since time dilation is true then length contraction is true as well because they are concurrent. I don't understand this statement. How are these two phenomena concurrent?

Somehow you seem to have missed the point. Length contraction and time dilation are effects that are observed by someone moving relative to some clocks and rulers ( yours, for instance).

So if I cruise by your spaceship in mine, I will see your clocks running slowly and your rulers appear shorter than mine. But nothing has actually happened to any clocks or rulers. Naturally, you will think the same about my clocks and rulers.

I think length contraction was initially proven by the 1888 experiment of Michelson-Morley.

Go https://www.physicsforums.com/blog.php?b=1959 for an explanation by starthaus "MMX.pdf."

Later backed up by Lorentz-?Fitzgerald?

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Actually, if I got it right: if a train is 100m long at rest in the stationary frame, it will still be 100m long when it starts to move, when observed from the stationary frame. But the observer in the train will experience contracted lengths along the path of movement.

stevmg said:
I think length contraction was initially proven by the 1888 experiment of Michelson-Morley.

Go https://www.physicsforums.com/blog.php?b=1959 for an explanation by starthaus "MMX.pdf."

Later backed up by Lorentz-?Fitzgerald?

No, MMX doesn't have anything to do with length contraction. Check https://www.physicsforums.com/showthread.php?t=229034". At this point there are no direct experimental proofs of length contraction.

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psmitty said:
No, MMX doesn't have anything to do with length contraction. Check https://www.physicsforums.com/showthread.php?t=229034". At this point there are no direct experimental proofs of length contraction.

The MMX has everything to do with length contraction. Consider an inertial apparatus has two orthogonal arms x and y that are equal length in the rest frame of the apparatus, such that a omnidirectional signal propagating from the origin reflects off mirrors at the ends of the arms and return simultaneously to the origin. In an inertial reference frame moving parallel to the x arm the simultaneous return of the signals to the origin can be explained if the moving observer measures the x arm to be shorter than the y arm, if we insist that the speed of light is the same for all observers and independent of the velocity of the source. Changing the clock rate of a clock co-moving with the origin cannot make the signals return simultaneously. The MMX result can alternatively be explained in terms of time dilation like this. The observer at rest with the apparatus can take the point of view that the clock of the moving observer is time dilated and out of sync and so this causes the moving observer to incorrectly measure the length of the x arm to be shorter.

psmitty said:
Actually, if I got it right: if a train is 100m long at rest in the stationary frame, it will still be 100m long when it starts to move, when observed from the stationary frame. But the observer in the train will experience contracted lengths along the path of movement.
This is not quite right either if I understand you correctly. The observer in the stationary frame (the frame at rest with the track that does that does not accelerate) will measure the train to be shorter than 100m when it has velocity relative to the track. The observer onboard the train will still measure the length of the train to be 100m after it has accelerated and returned to inertial motion and after he has resynchronised all his clocks. The observer on the train after it has accelerated will measure objects at rest with the track to length contracted.

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psmitty said:
No, MMX doesn't have anything to do with length contraction. Check https://www.physicsforums.com/showthread.php?t=229034". At this point there are no direct experimental proofs of length contraction.

This is false, in the frame of an observer wrt which the Earth (with the lab and the MMX setup) are moving, length contraction is the correct explanation of the null result.
In the frame of the lab, the isotropy of light speed is the explanation of the null result.

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psmitty said:
No, MMX doesn't have anything to do with length contraction. Check https://www.physicsforums.com/showthread.php?t=229034". At this point there are no direct experimental proofs of length contraction.

starthaus said:
This is false, in the frame of an observer wrt which the Earth (with the lab and the MMX setup) are moving, length contraction is the correct explanation of the null result.
In the frame of the lab, the isotropy of light speed is the explanation of the null result.

You've been educating me (stevmg) about this for a long time... I assume the false statement from psmitty is the statement that "MMX doesn't have anything to do with length contraction." (in this thread there have been too many negatives so that it becomes convoluted.)

Of course textbook explanations and your blog on MMX referred to above establish this.

stevmg

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stevmg said:
No, MMX doesn't have anything to do with length contraction.

Sure it does, read my statement again.

Check this thread. At this point there are no direct experimental proofs of length contraction.

There is no DIRECT test for length contraction. This doesn't mean that MMX is not an INDIRECT proof of length contraction.

Of course textbook explanations and your blog on MMX referred to above establish this.

stevmg

My blog (and textbooks) show how length contraction explain the null outcome of MMX.

starthaus -

I was backing you... Your blog makes that point. My previous post must have been a quote without the
. I understand your MMX.pdf quite well.

stevmg said:
starthaus -

I was backing you... Your blog makes that point. My previous post must have been a quote without the
. I understand your MMX.pdf quite well.

I see, you can go back and edit your post to fix that.

SH

Check it out (post 10) again - it looks right now but I am not used to going back before the last post to edit a prior post and the subsequent replies may be based on the "wrong" info in that prior post.

SMG

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stevmg said:
SH

Check it out (post 10) again - it looks right now but I am not used to going back before the last post to edit a prior post and the subsequent replies may be based on the "wrong" info in the that prior post.

SMG

yes, this makes sense

1. What is length contraction?

Length contraction is a phenomenon in which objects appear shorter in the direction of motion when observed from a reference frame in which they are moving at high speeds. This is a consequence of Einstein's theory of special relativity.

2. How does length contraction occur?

Length contraction occurs because time and space are relative concepts and are affected by the speed at which an object is moving. As an object moves at high speeds, its length in the direction of motion appears to decrease from the perspective of an observer in a different reference frame.

3. What are the implications of length contraction?

The implications of length contraction are significant in the field of physics and have been confirmed through numerous experiments. It helps explain why objects appear to be shorter when traveling at high speeds, and it also plays a crucial role in understanding the behavior of particles at the subatomic level.

4. Is length contraction observable in everyday life?

No, length contraction is only noticeable at extremely high speeds, close to the speed of light. In everyday life, the effects of length contraction are too small to be observed by the human eye. However, it is a fundamental principle in understanding the behavior of objects at high speeds.

5. How can length contraction be explained simply?

Length contraction can be explained simply by understanding that time and space are relative concepts and are affected by an object's speed. As an object moves faster, its length in the direction of motion appears to decrease, but its overall volume remains the same. This is due to the fact that the speed of light is constant for all observers, regardless of their relative motion.

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