Understanding Acoustic Peaks Beyond Last Scattering

In summary, the first acoustic peak is from the acoustic oscillations at last scattering, and the next one is about 0.4 of a degree past last scattering. Then the rest of the acoustic peaks get there as the oscillations spread out because there was no more plasma to oscillate.
  • #1
superg33k
96
0
I am supposed to have a qualitive knowledge of acoustic peaks for my exam, so none of the maths. After reading around I am still left with a few questions.

Is the first acoustic peak from the acoustic oscillations at last scattering? I imagine there were many oscillations before then but we just won't know about them. The first acoustic peak is about 2 degrees in the sky, which is the same size as the particle horizon since last scattering so it would make sense it happened then. (I used 'particle horizon' meaning the distance photons could have traveled since last scattering, I hope I used it right).

If this is right: How did the rest of the acoustic peaks get there? The next one is about 0.4 of a degree and that must be waaay past last scattering, so there would be no plasma to oscillate!

Thanks for any help. And if what I said above doesn't make any sense, don't blame me, blame my useless course text!
 
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  • #2
Accoustic peaks are radiation shocks in the CMB. Does that help?
 
  • #3
Chronos said:
Accoustic peaks are radiation shocks in the CMB. Does that help?

Nope sorry. Acoustic peaks are due to gravitation vs photon pressure causing plasma oscillations in the early universe (when it was all plasma). Then last scattering happened, so no more plasma to oscillate and and we see the evidence as fluctuations in the CMB (radiation shocks from the oscillating plasma).

The first peak is 2 degrees in the sky, agreeing with the particle horizon since last scattering. How oh how did the other smaller peaks get there? The second peak covers 0.4 of a degree, anything that happened at last scattering should have spread to 2 degrees in the sky. If it happened after last scattering then what caused the peaks (as there was no plasma to oscillate)?
 
  • #4
My google searches for answers took me back to my post! That can't be a good sign.

Thinking further I'm staring to think I'm wrong saying:

superg33k said:
The first acoustic peak is about 2 degrees in the sky, which is the same size as the particle horizon since last scattering so it would make sense it happened then.

superg33k said:
The first peak is 2 degrees in the sky, agreeing with the particle horizon since last scattering.

These don't make sense. I doesn't matter what size the particle horizon is SINCE last scattering. It matters what the particle horizon was AT last scattering. So the first peak corresponds to the biggest sound horizon from the earliest oscillation, and the other peaks from later times and their sound horizon won't be as big. Then when last scattering happened they were released at their current size as fluctuations in the CMB.

Well this makes more sense to me, but it is just me taking a logical informed guess. And it disagree's with some other things I've read. :(
 
  • #5
Well it seems that these smaller (angle, and hence size) peaks are the harmonics of the big (sound horizon size) oscillations. And their smaller temperature fluctuations is due to diffusion at recombination that thermalized a little which effected the smaller sized peaks more than the bigger.
 
  • #6
superg33k said:
Well it seems that these smaller (angle, and hence size) peaks are the harmonics of the big (sound horizon size) oscillations. And their smaller temperature fluctuations is due to diffusion at recombination that thermalized a little which effected the smaller sized peaks more than the bigger.

Right. See, for example,

http://nicadd.niu.edu/~bterzic/PHYS652/Lecture_20.pdf.
 

1. What is the meaning of "acoustic peaks beyond last scattering" in cosmology?

The term "acoustic peaks beyond last scattering" refers to the pattern of fluctuations in the cosmic microwave background (CMB) radiation that can be observed in the universe. These peaks are caused by the sound waves that traveled through the early universe before it became transparent, which is known as the last scattering surface. The peaks provide important information about the composition and structure of the universe.

2. How do scientists study acoustic peaks beyond last scattering?

Scientists study acoustic peaks beyond last scattering by analyzing the fluctuations in the CMB radiation using satellites and ground-based telescopes. These instruments detect the temperature and polarization of the CMB radiation, which can reveal the location and intensity of the peaks. Scientists also use mathematical models and computer simulations to understand the physical processes that give rise to the peaks.

3. What does the presence of multiple acoustic peaks in the CMB indicate?

The presence of multiple acoustic peaks in the CMB indicates that the universe is homogeneous and isotropic on large scales. This means that it looks the same in all directions and at all locations, and the distribution of matter and energy is uniform on large scales. The positions and heights of the peaks also provide information about the density and composition of the universe, as well as the effects of gravitational interactions.

4. What can we learn from the acoustic peaks beyond last scattering?

The acoustic peaks beyond last scattering provide important insights into the history and evolution of the universe. By studying the positions and heights of the peaks, scientists can determine the age and size of the universe, as well as the amount and nature of dark matter and dark energy. They can also test theories of cosmology and fundamental physics, such as the theory of inflation and the standard model of particle physics.

5. How do acoustic peaks beyond last scattering support the Big Bang theory?

The presence and characteristics of the acoustic peaks beyond last scattering provide strong evidence for the Big Bang theory, which states that the universe began as a hot and dense singularity and has been expanding and cooling ever since. The peaks are a direct consequence of the early universe being hot and dense, and their positions and heights match the predictions of the Big Bang model. This is one of the key pieces of evidence that support the Big Bang theory as the best explanation for the origin and evolution of the universe.

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