It seems it would be, no? I know I have seen examples of relativity that seem to use Doppler-type explanations. i.e. the one where the space ship takes off and is sending flashes of light that reach the earth further apart on outbound and quicker on inbound flight. It’s been a few years since i read Relativity, but I don’t recall any mention of the Doppler Effect or vice-versa. What’s the dope?
The doppler effect applies to things traveling through a medium such as sound. This doesn’t apply to light as there is no medium but relativistic effects on time and space make for similar results to the doppler effect. The Michelson-Morley (sp?) interferometer experiment showed that there is no “ether” to propegate light waves. Do some seaches on that experiment to learn more. http://users.powernet.co.uk/bearsoft/MickM.html is a good starting point.
Ummmm, correct me if I’m wrong, but wouldn’t saying there’s no doppler effect on light mean that the entire basis for modern astronomy is invalid? As far as I know, our entire currently accepted model of the universe was formed to explain the red/blue shift of stars, galaxies, etc. This is where we got the idea that the universe is expanding, how distances are estimated, etc.
ugghhhhh trying to remember physics class. Too hard, remember drawing stick figures, remember taking apart batteries, wait, wait, somethings coming, remember physics teacher talking about red and blue shift, coming back to me, red and blue shift are caused by the different wavelegnths of red and blue light. Yeah it is has something to do with the doppler effect. Well it was no good I couldn’t remember, but I did find a relevent website.
http://www.angelfire.com/az/BIGBANGisWRONG/index.html
Joe, you’re not wrong, but the red shift in light or the function of police speed radar has completely different mechanics than the sound of a train whistle shifting as it passes you. Sound travels through a medium, EM waves do not. The M-M experiment was done to see if there was an otherwise undetectable “ether” for light to propegate through.
I know that, but the OP didn’t ask anything about a medium for light. The doppler effect most definitely does affect light (or at least your perception of light), and I think it figures rather intimately into relativity effects. But of course I’m no physicist, so I’m getting a little out of my expertise here.
Sorry, Padeye, but you’re wrong on this one. The Red Shift that’s seen with retreating galaxies IS the Doppler shift, and is called this in the literature. The cause is exactly the same as the cause of dopple shifting of sound waves – the motion of the observer relative to the source, which causes a shift in perceived frequency. Ain’t got nothin’ to do with the presence or absence of a medium. Michelson-Morley and other experiments were looking for differences in propagation of light in different directions with a FIXED source and observer.It was the medium that was supposed to be moving, as you correctly note.
As for Relativistic effects, I’m, not sure what you mean. Certainly the frequency is shifted, but you’d expect that in any case. Some very large frequency shifts have been observed, in which emission spectra normally in the UV have been shifted up to the visible. But I dont know that I’d qualify it as “relativistic”.
There ARE frequency shifts due to the curving of space, I believe. “Gravitational red shuifts” might answer your need for relativistic doppler effects, since you need the theory of relativity to explain them.
The Doppler Effect is not relativistic.
The Doppler Effect has to do with the frequency of the received wave. Relativity has to do with the velocity of the received wave.
Sound is not relativistic so the speed of sound depends on the relative motion of the two observers. The speed of light, being relativistic, does not.
Considering that Christian Doppler discovered this effect studying the frequency change in light, it would seem that Joe has it right. If you calculate the Lorentz transformation of the light’s frequency, you wind up with the same equation as the Doppler equation for a moving observer.
Cartoongod, careful with that site. (Generally it is good advice to be critical of anything labelled “Big Bang is Wrong!”. Of course it’s good to be critical with any information learned over the internet.)
I’ve talked with John Kierein on another message board. He has some interesting ideas, but by no means has proved them. Most astronomers don’t agree about the Compton effect being involved.
Wrong. Dangit. I made a copy error when deriving the relativistic frequency shift. Sorry.
Classical Doppler shift: f’ = f(1 + v[sub]o[/sub]/v)/(1 - v[sub]s[/sub]/v)
Relativistic Doppler shift: f’ = f * sqrt[(1 + v/c)/(1 - v/c)]
There are non-Doppler shifts in light frequency due to General Relativity, as CalMeacham notes.
Arrgh. Wrong again. Of five sources, only one (of course, the only one I checked before the first post) says he discovered it for light. All others claim he discovered it for sound. Considering that Lorentz’s equations came out in 1853, and Doppler’s equations came out in 1842 (and he died in 1853) Occam’s Razor means I’m probably 0 for 2 today.
Punoqllads has the right formula for relativistic Doppler shift a couple of posts up there. This formula must be used if the relative motion of sourse and observer is near c, but the non-relativistic form is a decent approximation for low speeds. Note that it’s possible to get a redshift of more than one (wavelength more than doubling), which would imply speeds faster than the speed of light, by the classical equation.
Now, if we’re talking general relativity, then there’s at least two other possible causes of red/blue shift. The first, already mentioned, is gravitational redshift: If light is leaving a gravity well, it’ll appear redder at the top than at the bottom, and conversely, if it’s going down, it’ll get bluer. This is a very small effect for a weak field like the Earth’s, but it has been measured. The other redshift in GR, which is often confused with the Doppler effect, is cosmological redshift. This is the cause of the redshift of distant galaxies and quasars, and it’s due to the space in between the source and observer expanding while the light is en route, thereby stretching the wavelength of the light.
Not that anyone here likely knows who Young Song is, but …
Of course the Doppler Effect works with light : It’s why the lights on cars are white when coming towards you and red when they’re driving away from you.
An the new Infinitis and Lexii are faster so the headlights appear blue?