# Length Contraction Evidence?

Homework Helper
So does there exist any evidence to support the theory of length contraction? I am aware of the overwhelming evidence to support time and mass dilation, but none for length.

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russ_watters
Mentor
Time dilation and length contraction are two parts of the same thing, so when you observe one you are also observing the other. For example, when a particle in a particle accelerator takes longer to decay because of relativistif effects, it also travels a longer distance than it "should", based on the same effect. But in the frame of the particle, it does not travel a longer distance than it should.

I'm not an expert, but I'm quite sure length contraction follows directly from time dilation. A nice example are muons that come from the atmosphere. They have a very short lifetime, so without relativity you would assume that they would never be able to travel the, say, 10km in that time, but because of time delation it can. If you, however, look at the case from the perspective of the muon, the time is going at a 'normal' rate. The only way for the muon to reach the earth is if the distance were smaller (i.e. length contraction).

For the muon experiment, click:
http://hyperphysics.phy-astr.gsu.edu/HBASE/Relativ/muon.html

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Dale
Mentor
So does there exist any evidence to support the theory of length contraction?
Yes, particle accelerators work. The bunch length is contracted as predicted. Plus russ_watters and ImAnEngineer are correct.

Homework Helper
Yes I'm aware that mass dilation and length contraction both originated from time dilation, which in turn is a bi-product of the assumption that the speed of light is always constant from any frame of reference.

russ_watters said:
Time dilation and length contraction are two parts of the same thing, so when you observe one you are also observing the other.
There is much evidence to support time dilation which would explain many phenomena. Following from this, in order to obey the law of conservation of energy, mass must also be affected. These are also two parts of the same thing.
However, there is also evidence to support mass dilation without using this link between the two. Similarly, I'm just in search for any evidence to support length contraction without making it an assumption by the observation of the others.

dalespam said:
Yes, particle accelerators work. The bunch length is contracted as predicted. Plus russ_watters and ImAnEngineer are correct.
Could you please expand on this
How were they able to detect the contractions in length?

Thanks for the help everyone.

Dale
Mentor
Could you please expand on this
How were they able to detect the contractions in length?
The total amount of charge in a bunch increases as the length contraction increases. Basically, because of length contraction you can squeeze in more charged particles in a single bunch than you could without length contraction. The design of the particle accelerator takes this length contraction into account, and the accelerator functions as designed.

Homework Helper
The total amount of charge in a bunch increases as the length contraction increases. Basically, because of length contraction you can squeeze in more charged particles in a single bunch than you could without length contraction. The design of the particle accelerator takes this length contraction into account, and the accelerator functions as designed.
Ahh thankyou for the explanation. I could've guessed the first evidence to be posted would have something to do with the particle accelerator
That same machine gave me the first, indesputable evidence of mass dilation too.