Is cosmic back ground radiation able to somehow not dissapate?

In summary, the scientists say that radiation from a point source, such as a radio antenna or a pulsar, goes thru ever larger spherical areas as the radius of transmission increases...so the "intensity" or strength per unit area dissipates. The radiation from the Big Bang was spread out over a large area, so it has weakened over time.
  • #1
land_of_ice
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It says in numerous books that radiation dissipates after about a distance of from the Earth to the sun, and also when the scientists sent the radio signal of the Beatles's music into outer space a while ago, that , even though they did that through SETI, or whatever program they did that through, that the signal will dissipate after a certain distance and not reach any aliens. If radiation dissipates and behaves this way, then how is cosmic back ground radiation evidence of the big bang? Are they saying that cosmic back ground radiation is radiation that was somehow able to not dissipate (or be absorbed)?
 
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  • #2
Well, if by dissipate you mean scattered in its travel, of course it can be scattered, there are many processes for that, like inverse compton scattering which creates the famous SZ effect.

Now, if you mean that cmb looses energy, well, that does happen too. The wavelength of radiation gets stretched by a factor of a(t) because of cosmic expansion.

You might also be wondering what happens with energy conservation if photons go to larger (and hence less energetic) wavelengths as the universe expands. To make a long story short, energy conservation in its "naive" form (dE/dt=0) doesn't holds in general relativity.
 
  • #3
I think what land_of_ice is describing is simpler than what lasm2000 is talking about: radiation gets less intense as it spreads out into a larger volume of space from a particular point. It's just being spread more thinly. The CMB didn't come from a particular point, because the Big Bang wasn't an explosion at a particular point in space. The Big Bang occurred in all parts of the universe at once. Therefore the CMB wasn't spreading out into previously empty space from one point.
 
  • #4
As crowell explains CMBR is everywhere so it doesn't disippate in a traditional sense...but does in others.

In a nutshell, electromagnetic radiation (photons) remains constant but space does not; Each photon continues at lightspeed, c, but their concentration and frequency changes.

Radiation from a point source, such as a radio antenna or a pulsar, goes thru ever larger spherical areas as the radius of transmission increases...so the "intensity" or strength per unit area dissipates...a fixed number and concentration of photons at the point of emission gets "thinner and thinner" as more area is encountered. Like a light, such as a star, at a great distance looks really dim...few photons enter you eye...but such a star would burn you in an instant up close, such as local star, "the" sun...

On the other hand the CMBR has weakened due to the expansion of the universe: At the time the first CMBR passed thru where Earth would have been back then, about 380,000 years after the bang, it would have been about 454,000 K...pretty hot...today it's only about 2.7 K..."empty" space is pretty cold these days. Over eons, that same expansion effect will also weaken our radio signals a bit, but in the few years we have been around I doubt it would be measureable...

Check this out: http://en.wikipedia.org/wiki/CMBR#Temperature
 
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  • #5
We missed the really hot epoch. Our solar system is merely 4.5 billion years old. The CMB temperature has only dropped around 20 degrees since then.
 
  • #6
Chronos said:
We missed the really hot epoch. Our solar system is merely 4.5 billion years old. The CMB temperature has only dropped around 20 degrees since then.

And a damned good thing we did too, or we'd be proto-nuclear soup. :smile:
 

1. What is cosmic background radiation?

Cosmic background radiation refers to a type of electromagnetic radiation that is uniformly present throughout the universe. It is a remnant of the Big Bang and is one of the strongest pieces of evidence for the Big Bang Theory.

2. How does cosmic background radiation relate to the dissipation of energy?

Cosmic background radiation is not able to dissipate because it is the energy that was created during the Big Bang. As the universe expanded, this energy spread out and cooled, but it has not dissipated completely. This is why it is still detectable today.

3. Is cosmic background radiation evenly distributed?

Yes, cosmic background radiation is evenly distributed throughout the universe. This is because it originated from the Big Bang, which is thought to have happened in a single point and then rapidly expanded, spreading the radiation uniformly.

4. Can cosmic background radiation be blocked or absorbed?

Cosmic background radiation is a type of electromagnetic radiation, so it can be blocked or absorbed by certain materials. However, due to its low energy and long wavelength, it can pass through most materials without being absorbed. This is why it is able to permeate the universe and reach us on Earth.

5. What is the significance of cosmic background radiation?

Cosmic background radiation is crucial in helping us understand the origins and evolution of the universe. By studying its properties, we can gather information about the Big Bang and the early stages of the universe. It also provides evidence for the expanding universe and supports the theory of cosmic inflation.

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