5
   

blue shift and speed of light

 
 
dalehileman
 
  1  
Reply Thu 6 Mar, 2014 01:48 pm
@rosborne979,
Quote:
Even though both doppler shifts "look" the same, they are the result of two very different causes.
Thanks Ros for that input, something entirely new to me. However I am wondering how it might impact on Bev's q
rosborne979
 
  1  
Reply Thu 6 Mar, 2014 02:42 pm
@Romeo Fabulini,
Even the spin doesn't happen that fast, so you don't see any distortion.
0 Replies
 
rosborne979
 
  1  
Reply Thu 6 Mar, 2014 02:43 pm
@dalehileman,
It doesn't.
dalehileman
 
  1  
Reply Thu 6 Mar, 2014 02:55 pm
@rosborne979,
Quote:
It doesn't.
Okay Ros but do you now better understand the gist of Bev's q
Romeo Fabulini
 
  1  
Reply Thu 6 Mar, 2014 03:27 pm
Quote:
Rosborne said: Even the spin [of Andromeda] doesn't happen that fast, so you don't see any distortion

Modern astronomical instruments are very sensitive.
But anyway the fact remains we're seeing the farther half of the galaxy as it appeared thousands of years before the nearer half..Smile
Zarathustra
 
  1  
Reply Thu 6 Mar, 2014 03:51 pm
@Romeo Fabulini,
It is because you are looking back in time. You do not see the stars on the near side as they are today you see them as they were 2.54 million years ago. You do not see the stars on the far side as they are today nor as they were 2.54 million years ago but 2.54 + 0.26 = 2.8 million years ago. The Andromeda of today will not be visible for over 2 1/2 million years.

So of course we are not seeing each edge simultaneously we are seeing them 260,000 years apart in time.
0 Replies
 
Romeo Fabulini
 
  1  
Reply Thu 6 Mar, 2014 05:16 pm
Quote:
Zarathustra said: So of course we are not seeing each edge simultaneously we are seeing them 260,000 years apart in time

Yes I know, that's why I find the oliquely-angled Andromeda pic interesting because time is "stretched" from the front to the back throughout the pic..Smile
Zarathustra
 
  1  
Reply Thu 6 Mar, 2014 06:03 pm
@Romeo Fabulini,
No you actually said the EXACT opposite "which means we're simultaneously seeing the rim furthest away from us and the rim nearest to us at the same time"

So I'll let Ros chase you and Deihl around as you constantly change your positions and pretend you cannot understand something when you just won't accept it so as to create all the "personal paradoxes", he seems to enjoy it while I find the tactics childish.
0 Replies
 
Romeo Fabulini
 
  1  
Reply Thu 6 Mar, 2014 06:23 pm
Quote:
Zarathruster said:@RF- No you actually said the EXACT opposite "which means we're simultaneously seeing the rim furthest away from us and the rim nearest to us at the same time"

Hmm..I was in two minds whether to post such a complex fun observation in case i wasn't able to find the words to describe what i was trying to say.
Remember, when we look at a photo of Andromeda, THAT's what I meant when I said we're seeing the front and rear rims 'simultaneously' on a flat page in a book or on a monitor screen.
Look-
The farther half (B) is is light-years further away than the nearer half (A), so we're 'looking back in time' from front to rear in the picture.
It's no big deal, just a fun observation like I said..Smile

http://i53.photobucket.com/albums/g64/PoorOldSpike/Photos%20Three/andromeda-galaxyb_zps80a33e29.jpg~original
rosborne979
 
  1  
Reply Thu 6 Mar, 2014 07:45 pm
@Romeo Fabulini,
Romeo Fabulini wrote:
But anyway the fact remains we're seeing the farther half of the galaxy as it appeared thousands of years before the nearer half..Smile

And we see the whole thing as it was 2.5million years ago.
0 Replies
 
rosborne979
 
  1  
Reply Thu 6 Mar, 2014 07:51 pm
@Romeo Fabulini,
Romeo Fabulini wrote:
The farther half (B) is is light-years further away than the nearer half (A), so we're 'looking back in time' from front to rear in the picture. It's no big deal, just a fun observation like I said..Smile

It is interesting to recognize that we're looking "back in time" across the disk. I'll give you that. But there's no mystery associated with it in regards to distortions of what we see (which is what you mentioned in an earlier post).
0 Replies
 
rosborne979
 
  1  
Reply Thu 6 Mar, 2014 07:54 pm
@dalehileman,
dalehileman wrote:
Quote:
It doesn't.
Okay Ros but do you now better understand the gist of Bev's q

I always understood it, and I have answered it in several different ways. It's only you who are not understanding the subject material. And we've been through this before so I'm not investing much time into trying to break down your misunderstandings. If bevinp wants to interact then I may devote a bit more time to this.
dalehileman
 
  1  
Reply Fri 7 Mar, 2014 10:44 am
@rosborne979,
Quote:
If bevinp wants to interact then I may devote a bit more time to this.
Bev where are you, and how have I misinterpreted your q
0 Replies
 
dalehileman
 
  1  
Reply Sat 8 Mar, 2014 12:08 pm
@bevinp,
Bev let me try again, however haltingly: Looking at a burst of light as a "package" containing a fixed number of cycles of fixed wavelength, then you're asking, if this package (say, one light-second) always passes you at the same speed no matter how fast you try to go, then if it always contains the same number of pulsations why isn't it always the same color

The reason is, in effect when you change your speed you're looking at a different "package". Assuming it's a red light from a distant source; if you take off toward it, in effect your clock slows down so that its light appears more nearly blue. But you're now wondering how more cycles could suddenly find their way into the same span: it's because you and your yardstick have seemingly shrunk in the direction of motion; so your "package:" is much longer than mine--even though to you it's still 1 light-second in length

You'll note Bev my use of "in effect" and "seemingly". That's because the changes that take place in you and your rocket ship are relative to me, who remains behind, stationary with respect to the red light. ('Cause exactly the same circumstances as described above would apply if it were not you in motion but me and the light source. As they say, "It's all relative")

I am still wondering, Bev, whether Ros interprets your original q in the same way as I and if so whether he might yet better respond than I


Again however, this posting doesn't address the puzzling intuitive aspects of relativistic changes in the moving object, a subject still open to speculation. Presently merely attempting clarification of Bev's q and a possible response thereto
0 Replies
 
bevinp
 
  1  
Reply Mon 10 Mar, 2014 07:10 pm
@dalehileman,
Dale,
Sorry to be so long in replying. I am new to this forum and I thought I would receive an email when my topic received posts.
So now having read all the posts (I'm impressed with the number), yes you are exactly correct. Your explanation of my query is clearer than mine.

As someone mentioned, perhaps time dilation is the cause (or one of them) or it may be, once again, good old quantum mechanics.

By the way Wikipedia states "blue shift" means either a red shaft or a blue shift. Which explains the other aspect that puzzled me. Since the universe is expanding then we must see the galaxies receding from us. That's fine but if there is the doppler shift in the light we see, then the colour change should be to the longer wavelengths; ie, the red end not the blue end? It seems unusual that the accepted scientific label of the observed phenomenon is not exact; it would be just as easy to say red shift.

Anyway, I am glad that others have a similar problem with understanding why there is a doppler shift.

Bev
PS. Yes the doppler effect is obvious and easily understood in sound but there the speed of a specific sound wave is relative to the medium not the observer.

bevinp
 
  1  
Reply Mon 10 Mar, 2014 07:30 pm
@rosborne979,
rosbourne,
Surely the expansion of the universe involves movement and hence velocity. How can something expand and not have relative motion, one side to the other?
Or are you saying that relative motion is different when that motion/velocity is travelling near to speed of light (relativistically)? If so then at what velocity does this change occur?

Bev
Brandon9000
 
  1  
Reply Mon 10 Mar, 2014 07:38 pm
@bevinp,
bevinp wrote:

rosbourne,
Surely the expansion of the universe involves movement and hence velocity. How can something expand and not have relative motion, one side to the other?
Or are you saying that relative motion is different when that motion/velocity is travelling near to speed of light (relativistically)? If so then at what velocity does this change occur?

Bev

I think rosborne was saying that the phenomenon consists of the expansion of space itself rather than movement through space. There is relative velocity to us, though, nonetheless.
bevinp
 
  1  
Reply Mon 10 Mar, 2014 08:12 pm
@Brandon9000,
So Brandon, Ros says space is expanding, implying that the motion of the stars is not related. This raises the question of how do we know, if it is not by viewing the motion of the light emitting objects in space? Or is the expansion of space alone a consequence of the theory of space and the universe?

But back to my question, your inputs nor ros's have not provided any explanation of why we perceive a doppler effect. I don't doubt that it is seen, I just want to know why. One line answers are not likely to provide that information.
Bev.
rosborne979
 
  1  
Reply Mon 10 Mar, 2014 08:33 pm
@bevinp,
bevinp wrote:

rosbourne,
Surely the expansion of the universe involves movement and hence velocity. How can something expand and not have relative motion, one side to the other?

Or are you saying that relative motion is different when that motion/velocity is travelling near to speed of light (relativistically)? If so then at what velocity does this change occur?

A couple of points related to both of your posts:
* Expansion of the Universe does result in longer wavelengths which is Red Shifted. So the deeper we look into space the redder things look.
* Objects which are expanding away from us do have relative velocity (to us), but that is not what is causing the Cosmological Red Shift. As the Universe expands the wavelength of light expands with it and that produces the Red Shift.
* A similar Red Shift also occurs when an object moves away from you due to relative motion as opposed to expansion. But that Red Shift is caused by the doppler effect rather than expansion. Both look similar but the cause it different.
* * Wiki Describes it this way: Distinguishing between Cosmological Red Shift and Doppler Red Shift can illustrated by the "Expanding Rubber Sheet" Universe, a common cosmological analogy used to describe the expansion of space. If two objects are represented by ball bearings and space-time by a stretching rubber sheet, the Doppler effect is caused by rolling the balls across the sheet to create peculiar motion. The cosmological redshift occurs when the ball bearings are stuck to the sheet and the sheet is stretched.
rosborne979
 
  1  
Reply Mon 10 Mar, 2014 08:38 pm
@bevinp,
bevinp wrote:
But back to my question, your inputs nor ros's have not provided any explanation of why we perceive a doppler effect. I don't doubt that it is seen, I just want to know why. One line answers are not likely to provide that information.

I actually answered that in my first post. We perceive a doppler effect because the wavelength of the light is changed (Red or Blue Shifted) due to the effect of relative velocity on light. The speed of the light isn't changing. The wavelength of the light (and its frequency) that we perceive, is.
0 Replies
 
 

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