1. May 27, 2006

### eggman

What is 'redshift' ?

one poster says depending on the color you see it will tell you which way the picture is moving..

ex:either away from the observer or towards the observer..

please explain in SIMPLE terms what these 'shifts' are...

is there a green shift or a blue shift in science?

..(i hope i put this idea in the proper area of the forum)

2. May 27, 2006

### Danger

There is indeed a 'blue' shift, which is the opposite of the 'red' shift. Both occur because the speed of light is constant. An object approching you is travelling at speed a, for instance. Since the speed of light is c, the logical first thought is that the light would then be approacing you at a + c. That can't happen, though, because the light is restricted to c. Instead, the light waves become 'compressed' (sort of like a spring). The waves get closer together (shorter wavelength), which raises the frequency (in the case of visible EM, toward the blue end of the spectrum).
A redshift is the opposite, wherein a receding object has the light waves behind it 'stretched' to a longer wavelength (red end of the spectrum).

3. May 27, 2006

### eggman

Look at this logic and see if it makes sense?

I look out my kitchen window...there is a green shrub/tree in the distance..

Is it moving away from me...or towards me?

..or is this apparent movement a 'trick of the light'?

This is very complex I feel because of the 'observers' question can be

false....that is to say not a True Scientific Question..

Needless to say I am not good at science...

4. May 27, 2006

### Danger

I think that you're misinterpreting the use of colour words in Doppler terms. Whatever the initial frequency of the EM is, it will be either increased or decreased according to a specific formula related to its motion. 'Red' and 'blue' are simply used to indicate that because they're the extreme ends of the EM spectrum that humans can see. Something that's blue to start with, approaching you fast enough, will be shifted up to ultraviolet or even gamma, which aren't visible. Something that starts out in ultraviolet will climb to x-ray or gamma status.
The bush is green due to the pigmentation of its cells, and has nothing to do with whether or not it's moving. (It isn't, by the way, unless you have an alien in your yard.) If someone were to uproot that bush and throw it at you at a good percentage of light speed, it would then grow bluer.

Last edited: May 27, 2006
5. May 27, 2006

### eggman

I think I see the idea...

The next time I see one of those trees vanish I will know its moving fast and could possibly wack me! :rofl:

Thanks for your help Danger :tongue2:

...the moral of the story...'Watch out for things that suddenly dissappear..it will indicate a 'shift' in the continuum and sh*t is
in the process of hurling itself about SpaceTime!! :surprised

6. May 27, 2006

### Danger

I wouldn't go putting that on an exam paper, but it sounds good to me.

7. May 27, 2006

### Mk

And watch out for SpaceTigers!!!

8. May 27, 2006

### Danger

Oh, yes! They're the worst! Bengals are timid little pussycats compared to the Space variety.

9. May 27, 2006

### Staff: Mentor

The names redshift and blueshift are used because red and blue are on opposite ends of the spectrum. If the wave is shifted longer, it is "redshift", if it is shifted shorter, it is "blueshift".

Doppler shift also works on sounds. When a train passes you and the pitch of its whistle changes - first rising, then falling, that's the same as blue then red shift - just with sound instead of light.

Last edited: May 27, 2006
10. May 28, 2006

### eggman

Thought Experiment

1)..If a man had a baseball attached to a wire and began to

spin it in a circle above his head what would you see as the ball

approached the speed of light...

11. May 28, 2006

### Mk

You would see a spinning ball. I assume you mean what color, if so, because it is spinning, one side would be red, and the other blue as it approached the speed of light. One side is relatively moving toward you, and the other, relatively moving away.

12. May 28, 2006

### eggman

If the ball achieved 'c' (speed of light) would it dissappear?

or what would you observe?

13. May 28, 2006

### Mk

The ball wouldn't achieve the speed of light.

14. May 28, 2006

### eggman

I put some stuff about speed and vibration over in the metaphysics section...I was attempting to understand what would occur
if an 'object' were capable of remaining intact and going lightspeed.

I am attempting to wrap my brain around Time Travel...and its different perceptions

Its very hard to grasp

Last edited: May 28, 2006
15. May 28, 2006

### Staff: Mentor

You would notice nothing out of the ordinary, regardless of the speed of the ball.

16. May 28, 2006

### Danger

And nothing with mass, be it a ball, a bat, or an umpire, can achieve light speed. There's no point in trying to visualize what would happen if it did, because it's flatly impossible.

17. May 28, 2006

### Mk

Are you dismissing my conjecture?

18. May 28, 2006

### Hootenanny

Staff Emeritus
Why would the baseball be 'spinning'?

~H

19. May 29, 2006

### Danger

I think that he means revolving around the anchor of the string, not rotating on its own axis.

20. May 29, 2006