Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: CliffordK on 02/06/2014 19:50:33

Title: Are light spectral lines constant?
Post by: CliffordK on 02/06/2014 19:50:33

As I understand it, each element/compound creates specific spectral lines of light when heated.

Are these always constant so the Hydrogen spectral lines will be the same on every star?

Red-shifting and blue-shifting is considered the shifting of these lines due to a star's relative motion with respect to Earth (or the observer).

However, if you were actually orbiting a star a billion light years from Earth, would it be emitting the same spectral lines as our own sun?

I suppose my question is regarding thinking about atomic clocks.  An atomic clock might be defined as the frequency that causes the hyperfine transition of the target atom, hydrogen, cesium, or rubidium. 

This is susceptible of shifting with changes in gravity or velocity. 

So, would we conclude that the emission of light spectra would also be affected by velocity and gravity?

Title: Re: Are light spectral lines constant?
Post by: evan_au on 02/06/2014 21:53:19

There have been attempts to test whether fundamental constants are the same across the universe.

Some groups have suggested that there is a small variation in the fine-structure constant (http://en.wikipedia.org/wiki/Fine-structure_constant#Is_the_fine-structure_constant_actually_constant.3F).

Title: Re: Are light spectral lines constant?
Post by: RD on 02/06/2014 22:24:27

Magnetic and electric fields can alter spectral lines ...

http://en.wikipedia.org/wiki/Zeeman_effect
http://en.wikipedia.org/wiki/Stark_effect

Title: Re: Are light spectral lines constant?
Post by: CliffordK on 03/06/2014 05:27:07

Quote from: RD on 02/06/2014 22:24:27

Magnetic and electric fields can alter spectral lines ...

http://en.wikipedia.org/wiki/Zeeman_effect
http://en.wikipedia.org/wiki/Stark_effect

Thanks,
So, in the presence of an electrical or magnetic field, the spectrum is shifted slightly, but also changed in a way that should be able to be detected.  Broadened, split, etc.

Title: Re: Are light spectral lines constant?
Post by: JP on 03/06/2014 11:31:25

Quote from: evan_au on 02/06/2014 21:53:19

There have been attempts to test whether fundamental constants are the same across the universe.

Some groups have suggested that there is a small variation in the fine-structure constant (http://en.wikipedia.org/wiki/Fine-structure_constant#Is_the_fine-structure_constant_actually_constant.3F).

Indeed, and this would have huge implications.  A major assumption in much of modern physics is that the laws of nature are the same everywhere in the universe.  This includes the values of constants and the form of physical laws.  Under this assumption, the photons emitted locally (i.e. if you stand at rest next to the atom of interest) should have the same spectrum anywhere in the universe, assuming the local conditions are the same (same background electric and magnetic fields, same background tidal forces, etc.)

The spectrum can change due to various laws of physics: Doppler shifts, Zeeman/Stark effects, gravitational red/blue shift, but these are also known, predictive laws that assume the photons emitted locally in the atom's rest state (with the same background conditions) have an identical spectrum anywhere in the universe.