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Author Topic: Is red-shift caused by width contraction of the moving body?  (Read 731 times)

Offline Thebox

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relative to an observer an object moving away will contract in dimensions, it is said an object red shifts moving away from an observer at the near speed of light,

are the two connected?


(no father ted jokes please)



The reflected light becomes narrower?
« Last Edit: 03/02/2016 11:02:23 by Thebox »


 

Offline evan_au

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Quote
are the two connected?
Short answer: No.

Quote
an object moving away will contract in dimensions ...at the near the speed of light
This is true. It is called Lorentz contraction, but you have to be going very fast for it to be detectable.

At "normal" speeds (< 1 million km/h), it can be effectively ignored.

c:  3.00E+08   m/s   
         

v/c   v (m/s)   v (km/h)   Lorentz Factor

0.001   3.00E+05   1.08E+06   0.9999995
0.01    3.00E+06   1.08E+07   0.999949999
0.1     3.00E+07   1.08E+08   0.994987437
0.5     1.50E+08   5.40E+08   0.866025404
0.75    2.25E+08   8.09E+08   0.661437828
0.9     2.70E+08   9.71E+08   0.435889894
0.99    2.97E+08   1.07E+09   0.14106736
0.999   3.00E+08   1.08E+09   0.044710178

Quote
it is said an object red shifts moving away from an observer
This is true. It is called Doppler shift, and it is quite detectable even at the speed your car travels in residential areas (maybe 40km/h to 60km/h). That is how police use radar and laser to check your speed.
It is also used to measure the wobble on a massive star due to the orbit of its much smaller planets - a disturbance that equates to a walking speed.
At these low velocities, Lorentz contraction can be totally ignored.

Quote
are the two connected?
Long Answer: Yes and No.
No: When objects are approaching you, Doppler effect gives a "blue shift". Time dilation can only produce a red shift. So the effects are quite separate (and opposite).

Yes: There is a relativistic version of the Doppler shift which takes into account time dilation of the moving object which emitted the light.
- This is not the length contraction of the object which emitted the light.
- Time dilation follows the same Lorentz factor as length contraction.

The relativistic correction would only really matter in particle accelerators and distant cosmological objects that are traveling faster than 0.1% of the speed of light relative to us.

See: http://en.wikipedia.org/wiki/Relativistic_Doppler_effect
 

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