Red shift question

[the_id]

What is the minimum relative speed two objects must be moving away from each other in order for the red shift effect to be detected?

 

[newtonian]

The_Id - Good question and I don't know.<br /><br />However, I do know gravitation can also cause an effect, though tiny - it has apparently been measured so that sensitive a spectrometer should detect slow motion, relatively speaking.<br />"Relativity predicts that light will be red-shifted and time will pass more slowly in a strong gravitational field, and observation and experiment have confirmed both of these predictions." -"The World of Science," 1991, Volume 8, The Universe, page 104.<br /><br />I also know that examination of distant quasar light shows a series of spikes in the spectrum indicating various clouds - it is called the lyman-alpha forest in the light spectrum where the spikes are different due to the different red-shifts of the different clouds between us and the quasar.<br /><br />I'll let someone else post estimates for the actual answer you are looking for.<br />BTW, light can also be blue shifted for approaching objects like Andromeda.

 

[the_id]

Thanks.<br /><br />Ok, I’ll simplify my question. Would a red shift be detectable at 25 % <i>c</i>?<br />

 

[alokmohan]

I thing 70%will be nice.

 

[siarad]

lyman-alpha forest show that Space is expanding. Saiph pointed me to this when I asked how could we tell space was expanding.<br />There are 3 Redshifts:<br />recessional<br />gravitational<br />space expansional

 

[vogon13]

What is the lowest speed Doppler police speed radar can detect? I believe devices can catch you coming or going, and are frequently used in school zones. Such devices are frequently calibrated with a tuning fork and I seem to recall 600 Hz as a number used to describe such. When radar bounces off moving object, carrier frequency is increased (blue shifted) for approaching object, and decreased (red shift) for receding object. Seems to me, technique could be applied to solar system objects for orbit calculations, and deep space objects, if containing natural maser (a stable oscillator), would appear to be candidates for technique also. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

Siarad - Yes indeed.<br /><br />Here is some detail from the following article on the IGM, intergalactic medium, and one source of evidence, namely the lyman-alpha forest absorption lines in quasar spectral analysis, which is now very precise.<br /><br />Scientific American, 10/02, article The<br />Emptiest Places Space By Evan Scannapieco,<br />Patrick Petitjean<br />and Tom Broadhurst<br /><br />Here is an excerpt from pages 58,59.<br /><br />The exerpt concerns evidence about the nature of the IGM, the intergalactic medium. As shown below, the evidence proves the IGM is highly ionized or magnetized, and, in fact, means that magnetism played an important role in structure formation in the early universe - a fact usually ignored. <br /><br />In fact, the hundreds of intergalactic clouds causing the lyman-alpha forest in quasar spectra are all no more than one part in one million neutral hydrogen, they are mostly ionized hydrogen; etc.<br /><br />More on thread theme, note the increase in sensitivity of spectral analysis allowing this detailed study of varying red shifts of hydrogen absorption lines in quasar spectra, as well as other element absorption lines.<br /><br />See Sciam.com for the article for additional detail and diagrams.:<br /><br />"The second type of evidence involves quasars. Thought to be powered by young supermassive black holes, these extremely bright objects act as lighthouses that illuminate narrow stretches<br />of intergalactic space. Material between us and a quasar ab-sorbs<br />light of specific wavelengths, leaving a telltale imprint on<br />the quasar spectrum. Interpreting such spectra requires a de-gree<br />of care. They contain lines at wavelengths that do not ap-pear<br />to correspond to any known substance. This discrepancy<br />is thought to be a product of the expansion of the universe,<br />which, by stretching the light waves, causes the spectral lines to<br />move from their usual positions to longer wavelengths?a pro-cess known as redshifting. The

 

[the_id]

There’s a lot of helpful information here. Thank you, everyone.

 

[vogon13]

Speed difference across Saturn's rings is spectroscopically detectable from earth. Proved Maxwell's assertion rings not a solid object. Speed difference between adjacent resolvable ring elements is quite small.<br /><br /><br /><br />The females will become very restless....<br />Heloise <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

Steve, The_Id- what is cee?<br /><br />Good post- note that spectrographs have become more precise in time, which is how the lyman-alpha forest has been studied so extensively as in the Sciam article I quoted.<br /><br />Vogon- Thank you

 

[Saiph]

it really depends on the detector. For astronomical redshifts, I'd say hundreds of kph or more.<br /><br />In reality, especially with police laser radar systems, you can get a lot better than that, since you can control the light signal, and the signal stregth, etc. Police radars can get to a few miles per hour accuracy, especially the laser ones (those might get well below 1mph).<br /><br />Police radars work a bit differently though. They send out a specific wave, and recieve an altered one. They then combine the two and analyze the "beat" pattern that arises.<br /><br />You can't really do that with starlight. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[newtonian]

Saiph- Agreed.<br /><br />Note the thread on exciting atoms.<br /><br />The link between research lines has to do with the detection of hyperfine structure in light spectra caused by nuclear spin of protons and neutrons in a net effect - which requires 1000 times more sensitivity than the detection of fine structure caused by electron spin and causing dual lines in hydrogen spectral lines corresponding to the spin of 1/2+and 1/2 - respectively.<br /><br />That is very precise spectral analysis!