Time dilatation and redshift

[Jacques]

Time dilation will redshift the spectrum of an radiating object moving relative to the observer.

Also the motion of the object will redshift (if the object is moving away) or blueshift (if the object is moving closer) it spectrum because of the Doppler effect.

 

For an object moving toward the observer, is there a speed where the redshift cause by time dilatation will be compensated exactly by the Doppler blue shift ?

[J.C.MacSwell]

Time dilation will redshift the spectrum of an radiating object moving relative to the observer.

Also the motion of the object will redshift (if the object is moving away) or blueshift (if the object is moving closer) it spectrum because of the Doppler effect.

 

For an object moving toward the observer' date=' is there a speed where the redshift cause by time dilatation will be compensated exactly by the Doppler blue shift ?[/quote']

 

I like this question and noone has answered so I will blurt out a guess and hope someone will correct or add incite:

 

My thought is no because if any speed matched/compensated then all speeds would.

 

Having said that there must be some angle (perpendicular component) such that it would work out where the blueshift is exactly compensated for by the total speed.

 

What is that angle? I think it would be somewhat profound if it was 45 degrees so that is my guess.

[Johnny5]

Jaques, would you mind deriving the formula for 'doppler effect' for me?

 

I seem to have trouble remembering it.

 

Thank you

 

PS: I know it resembles the effect that happens when a car is coming towards you with its horn on.

[Jacques]

Here is a link that explain relativist redshift.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html#c1

 

The only solution for source equal observed frequency is for v=0

 

I think also that there might be some solution for source going with an angle toward the observer.

Thanks for your answers

[tskaze]

correct me if i dont have any idea what im talking about (it's quite possible) but if an object is moving away it has no blue shift to speak of?

 

edit: disregard that i understand now.

[Jacques]

Maybe I should start a new thread on that but looking at the equation on the redshift bring an other question in my mind:

 

In other thread I read that distant galaxies doesn't have proper motion, there apparent motion is caused only by the expansion of space. My question is why does the time dilatation component is include in the redshift equation ?

[geistkiesel]

I like this question and noone has answered so I will blurt out a guess and hope someone will correct or add incite:

 

My thought is no because if any speed matched/compensated then all speeds would.

 

Having said that there must be some angle (perpendicular component) such that it would work out where the blueshift is exactly compensated for by the total speed.

 

What is that angle? I think it would be somewhat profound if it was 45 degrees so that is my guess.

If I read Jacques ques tion correctly, if one moves at a speed equal to the oncoming speed of thelight source, the blue shift effect would be nulled out by the observer's motion in the same direction as the source. Hence the observer would observe the absolute rest photon spectrum emanating from the photon source.

 

Geistkiesel

[Johnny5]

Here is a link that explain relativist redshift.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html#c1

 

The only solution for source equal observed frequency is for v=0

 

I think also that there might be some solution for source going with an angle toward the observer.

Thanks for your answers

 

 

Jacques' date=' I looked at the link, and saw the diagram, all the circles.

 

Does this bear any relationship to the Mach effect... Mach cone?

 

Let me see if I can find something on it.

 

Mach cone

 

Let the Mach number be 1.22 in the Java applet, and you see the Mach cone forming.

 

Can this effect be tied into the Doppler effect formulas?

 

Regards

[J.C.MacSwell]

If I read Jacques ques tion correctly' date=' if one moves at a speed equal to the oncoming speed of thelight source, the blue shift effect would be nulled out by the observer's motion in the same direction as the source. Hence the observer would observe the absolute rest photon spectrum emanating from the photon source.

 

Geistkiesel[/quote']

 

Jacques' question had the source moving toward the observer. You just described a stationary light source relative to the observer.

[geistkiesel]

Jaques' date=' would you mind deriving the formula for 'doppler effect' for me?

 

I seem to have trouble remembering it.

 

Thank you

 

PS: I know it resembles the effect that happens when a car is coming towards you with its horn on.[/quote']

Johnny5,

See feynman's "Lectures on Physics" Vol I, ch 34-7.undergraduate textbook, very informative.

 

Geistkiesel

[Johnny5]

Johnny5' date='

See feynman's "Lectures on Physics" Vol I, ch 34-7.undergraduate textbook, very informative.

 

Geistkiesel [/indent']

 

Yes I just ordered it, will have it in two weeks.

 

Thank you

[Jacques]

Can this effect be tied into the Doppler effect formulas?

 

No. The Mach effect is a case of the Doppler effect. The applet is cool!!! Remark that it illustrate very well the Cherenkov radiation. To understand the Doppler effect set a speed < 1 and imagine that you are a stationary observer on the screen. If you are to the right of the screen you will see the source moving toward you and you will see wave front reaching you by unit of time (blue shift). If you imagine yourself to the left of the moving source less wave front will reach you by unit of time (red shift)

 

 

My original question was about the combination of 2 effects of a moving source of wave:

1 Time dilatation: time in a moving source slowdown for an outside stationary observer. So the frequency of a radiation will look lower or redshifted. Note that the slowdown is independent of the direction of the moving source relative to the observer.

2 Doppler effect: the frequency of a source will look lower when the source is moving away (redshift) and it will look higher when the source is moving toward the observer (blue shift).

 

So I was wondering if the combination of the two effects (redshift of time dilatation and blueshift of Doppler effect) could cancel each other in the case a moving source toward the observer.

From the equation we can see that the Doppler effect is always bigger than the time dilatation so the cancellation of the 2 effect is impossible.

Thanks again for your answers