Why Doesn't Light from the Big Bang Get Stretched Out?

[leonstavros]

One of the proofs that there was a Big Bang is the measurement of microwave backround radiation. It has been measured to be around 2.7 degrees kelvin and the explanation given why it's that the BB created a spectrum of frequencies and they have been stretched out by space expansion over time to lower frequencies(microwaves).

My question is why doesn't this stretching occur to the light that is measured to be as old as the universe (13.8 billion years)? According to that theory there should not be any light frequencies from that time. Help me out I'm confused.

 

[mathman]

One of the proofs that there was a Big Bang is the measurement of microwave backround radiation. It has been measured to be around 2.7 degrees kelvin and the explanation given why it's that the BB created a spectrum of frequencies and they have been stretched out by space expansion over time to lower frequencies(microwaves).

My question is why doesn't this stretching occur to the light that is measured to be as old as the universe (13.8 billion years)? According to that theory there should not be any light frequencies from that time. Help me out I'm confused.

There is no light that old. The oldest "visible" radiation is the microwave background. There are old stars and their light is greatly redshifted.

 

[leonstavros]

There is no light that old. The oldest "visible" radiation is the microwave background. There are old stars and their light is greatly redshifted.

Quote from wikipedia "As the universe expands, more distant objects recede from the Earth faster, in what is called the Hubble Flow. The light from very distant galaxies is significantly affected by the cosmological redshift. While quasars with high redshifts were known, very few galaxies with redshifts greater than one were known before the HDF images were produced.[10] The HDF, however, contained many galaxies with redshifts as high as six, corresponding to distances of about 12 billion light-years. Due to redshift the most distant objects in the HDF (Lyman-break galaxies) are not actually visible in the Hubble images; they can only be detected in images of the HDF taken at longer wavelengths by ground-based telescopes."

I'm still puzzled by the fact that Hubble picked up images(wavelength of 400-800nm) of galaxies 12 billion years old. If the BMR is 13.8billion years old and its frequency is 160.2 GHz, corresponding to a 1.9 mm wavelength why such a big difference in wavelength?

 

[Calimero]

Why would you expect that cmb (bmr) light has the same wavelength as light from distant galaxies?

 

[leonstavros]

Why would you expect that cmb (bmr) light has the same wavelength as light from distant galaxies?

Not exactly the same wavelength but somewhat closer. The BB created visible as well as non-visible light but the visible light has been stretched by space expansion to mm wavelength size. Why isn't the 12 billion year old light from Hubble deep view also stretched to a similar amount?

 

[Calimero]

First, cmb was not exactly created by the bb event. It originates from some relatively short time after, from what is called decoupling event. It has almost perfect black body spectrum and thus can't really be compared that way to light coming from various sources within galaxy.

Rest assure that light coming from same distance is stretched for the same amount, no matter is it coming from galaxy or from alien light bulb. Of course if wave lengths are not the same at the time of emission, they will not be the same at the time of detection.

 

[leonstavros]

First, cmb was not exactly created by the bb event. It originates from some relatively short time after, from what is called decoupling event. It has almost perfect black body spectrum and thus can't really be compared that way to light coming from various sources within galaxy.

Rest assure that light coming from same distance is stretched for the same amount, no matter is it coming from galaxy or from alien light bulb. Of course if wave lengths are not the same at the time of emission, they will not be the same at the time of detection.

quote from wikipedia "The CMBR is well explained as radiation left over from an early stage in the development of the universe, and its discovery is considered a landmark test of the Big Bang model of the universe. When the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it, grew cooler. When the universe cooled enough, stable atoms could form. These atoms could no longer absorb the thermal radiation, and the universe became transparent instead of being an opaque fog.The photons that existed at that time have been propagating ever since, though growing fainter and less energetic, since the exact same photons fill a larger and larger universe. This is the source for the term relic radiation, another name for the CMBR."
I'm talking about the photons that existed at that time and have been propagating ever since. These photons have been stretched to a larger wavelength by space expansion. The same space expansion should have affected the photons from the Hubble deep view images to a similar but not same wavelength.

 

[Calimero]

I'm talking about the photons that existed at that time and have been propagating ever since. These photons have been stretched to a larger wavelength by space expansion. The same space expansion should have affected the photons from the Hubble deep view images to a similar but not same wavelength.

I re-read your second post. You are talking about galaxies with redshift z=6. Redshift of cmb is z=1090.

 

[Ich]

The same space expansion should have affected the photons from the Hubble deep view images to a similar but not same wavelength.

To get the proportions, don't use time before now, use time after Big Bang. Then, CMB originated after 380,000 years, the first galaxies after 1,700,000,000 years. That's a ratio >4000, and you find approximately the sqare root of it in the ratio of the redshifts.

 

[Calimero]

Leon, what are you probably missing is this:

1+z=\frac{a_{now}}{a_{then}}

From the time of cmb event to the time of first galaxies forming scale factor (a) - grew some 1090/7=156 folds (thus stretching the wavelengths for the same amount), and from the time of first galaxies forming until now - only 7 folds.

 

[leonstavros]

Thanks I'll check it out.