Reason the early Universe was opaque?

[PeterPeter]

Apparently the early universe was opaque because the atoms were ionized.

I'm wondering, why do electrons scatter photons but atoms don't?

I'm presuming it's the electrons that do the scattering.

 

[phinds]

Apparently the early universe was opaque because the atoms were ionized.

I'm wondering, why do electrons scatter photons but atoms don't?

I'm presuming it's the electrons that do the scattering.

Atomic nuclei formed at about 3 minutes after the singularity but entire atoms didn't form until about 400,000 thousand years after so until that time there were no full atoms to even BE ionized. This was all because the energy plasma that was the early universe was SO energetic.

http://en.wikipedia.org/wiki/Chronology_of_the_universe#mediaviewer/File:History_of_the_Universe.svg

 

[sophiecentaur]

Atomic nuclei formed at about 3 minutes after the singularity but entire atoms didn't form until about 400,000 thousand years after so until that time there were no full atoms to even BE ionized. This was all because the energy plasma that was the early universe was SO energetic.

http://en.wikipedia.org/wiki/Chronology_of_the_universe#mediaviewer/File:History_of_the_Universe.svg

But there must have been equal numbers of + and - charges (I'm assuming here) so there would have been ions and electrons - even if they had never met up with each other before.

 

[Drakkith]

Apparently the early universe was opaque because the atoms were ionized.

I'm wondering, why do electrons scatter photons but atoms don't?

I'm presuming it's the electrons that do the scattering.

Atoms are electrically neutral overall and, thanks to their quantized energy levels, don't react very well to electric fields compared to free charges like you find in a plasma. In other words, an electric field cannot cause a whole atom to move since it's neutral, but it can cause an electron and a proton to move when they are unbound in a plasma. It's only when the frequency is just right that an electronic/nuclear transition can take place and the atom can absorb a photon.

 

[sophiecentaur]

The basis of the quantum mechanical model for atoms is that an isolated atom can only exist in certain energy (quantum) states. EM can be emitted or absorbed by transitions between these discrete states - i.e. only specific, characteristic wavelengths. When white light is shone through a gas, the gas will absorb only the wavelengths corresponding to its emission spectrum.
A free electron can have any energy state so it can transition from its present state to any other - absorbing any wavelength.
A bit of repetition there - sorry.