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Author Topic: How was light produced by the Big Bang?  (Read 2292 times)

Offline Spacetectonics

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How was light produced by the Big Bang?
« on: 29/12/2012 12:36:24 »
Following the Big-bang Theory!

One which I haven't found an answer is,base on this theory Electromagnetic radiation(light?) had happened many years after the initiation of Big-Bang ,so what about  light ?if there was a bang then was there any light ?and if yes what happened to it ?(considering the universe temperature reaches 10 billion Centigrade at the first second!)
How first light emitted in the universe anyway?

« Last Edit: 01/01/2013 22:25:09 by chris »


 

Offline Phractality

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Re: BigBang- light?!
« Reply #1 on: 29/12/2012 19:00:51 »
According to Big Bang theory, the CMBR is the light that was being emitted when space first became transparent. Before that, the light was being reabsorbed before it could travel any great distance. The whole universe was like the interior of the sun; lots of light with nowhere to go.
 

Offline evan_au

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Re: BigBang- light?!
« Reply #2 on: 30/12/2012 04:14:30 »
Light can be emitted from any accelerated charge, such as the protons & electrons zipping past each other in the sun, or by the hot gas produced by the big bang.

In theory, all frequencies can be emitted, but the spectrum puts out most energy in a band which is related to the temperature of the gas. Really hot material puts out energy in the X-Ray band or higher frequencies. The sun puts out most energy in the visible band, while cooler objects like Jupiter put out most energy in the infra-red band.The shape of this spectrum is called the "black body radiation".

Depending on the chemical makeup of the gas (and its temperature) there is sometimes an additional "line spectrum" visible, where certain light energies are emitted more strongly (or absorbed more strongly) than the black body radiation theory would predict, as the energy levels of the atoms favour these energies.
 

Offline imatfaal

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Re: BigBang- light?!
« Reply #3 on: 30/12/2012 11:21:19 »
Further to Phractality and really only to mention the name - the time when the Cosmic Microwave Background Radiation was emitted has the poetic and meaningful name "The Era of Last Scattering" or "The Surface of Last Scattering".  Whilst it sounds as if the physicists were waxing lyrical it actually tells you what was happening; before that point all the light that emitted (and it would have been huge amounts) was very quickly scattered and reabsorbed by the very hot and opaque plasma that filled the universe.  But when hydrogen started to form as neutral atoms the light started to be able to travel without being absorbed by the charged plasma - it is this light from the universe we still see as the CMBR; it was emitted at the vital point at which the universe was still hot enough to emit light everywhere almost completely homogenously, but was cooling enough that some of this light was not immediately reabsorbed.  This was a mere 300k years after the bigbang - in a history of over 13billion years - that is very early in the life of our universe.
 

Offline Spacetectonics

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Re: BigBang- light?!
« Reply #4 on: 06/01/2013 06:49:12 »

 before that point all the light that emitted (and it would have been huge amounts) was very quickly scattered and reabsorbed by the very hot and opaque plasma that filled the universe. 

Thanks For the information,

"the very hot and opaque plasma that filled the universe"

was Scattering  and re-absorption  due to gravity? or the physical conditions,if any ;what were they? and the other thing I wish to ask is :

If light could not scape ,then what we shall expect for "time " in the first 200.000-370.000 years (before light could scape)?I am mostly relating this to the Special relativity !

Cheers

 

Offline evan_au

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Re: How was light produced by the Big Bang?
« Reply #5 on: 06/01/2013 09:55:56 »
Light is an electromagnetic wave; it is influenced by any particle(s) with electric charge, such as electrons, protons, muons, quarks, etc which would have filled the early big bang universe.

When matter is very hot, protons & electrons are not bound to each other, but are floating around in a ionised plasma (much like the Sun today). This produces (and absorbs and scatters) wideband radiation http://en.wikipedia.org/wiki/Bremsstrahlung

However, as the Big Bang expanded, it cooled, eventually to the point where electrons and protons could enter stable orbits, forming an atom (ie it is no longer ionised). An atom produces (and absorbs and scatters) only specific frequencies, allowing all of the other radiation to continue with the energy it had from its last scattering encounter with an ionised plasma.

So, no, the scattering was not due to gravity, it was due to scattering from an ionised plasma.
  • In a hot, dense plasma, the energy of photon travels only a very short distance before it encounters other charged particles, where it is scattered again.
  • In a cooler, atomic gas, photons can travel a considerable distance without scattering (unless they happen to match the energy in the line spectrum).
  • The fact that light could not escape had more to do with the finite speed of light (and the potentially finite volume of the universe) than with Special Relativity.

I think "time" could be considered to run normally in these first 300k years, just as it does in some very hot and dense stars today. [What happened in the first 1 millisecond of the Big Bang is still a matter of some conjecture, which was one reason we needed the LHC at CERN: http://en.wikipedia.org/wiki/A_Large_Ion_Collider_Experiment#August_2012_highest_temperature_experiments ]
 
 

Offline imatfaal

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Re: How was light produced by the Big Bang?
« Reply #6 on: 07/01/2013 17:19:58 »
The last paragraph of evan's post - especially this "just as it does in some very hot and dense stars today" is crucial.

The whole universe was kinda like this before the era of last scattering.  Bear in mind that the energy generating bit of the sun is way in the middle - what we see as light is the result of a couple of thousand years worth of emission, scattering, absorbtion, and re-emssion before a photon leaves the sun.  In the early universe it took 300k years before the matter cooled down for photons to actually travel without bumping into a charged particle.
 

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Re: How was light produced by the Big Bang?
« Reply #6 on: 07/01/2013 17:19:58 »

 

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