Question about the COBE results and othe cosmic questions

[bdewoody]

I was watching a program tonight on the Science Channel about the birth of the universe and the discovery of the cosmic background radiation that supports the Big Bang Theory. The discussion went on to the results obtained by the COBE satellite which finally found the clumpiness in the background radiation they were looking for. They stated that the clumps resulted in the clusters of galaxies that are visible today. But that seems to indicate that we are seeing the same objects twice (as was discussed in the circular universe thread).

Something else I am curious about and I hope I am stating this correctly. When we see computer images of the universe does the computer project objects current locations or their locations as we would see them from earth on any given night. For example we see objects on the other side of the milky way where they were a few hundred thousand years ago not where they are now (if now makes any sense at that scale) On the other hand when we look at a galaxy such as Andromeda from the top we are seeing the stars in their true relative positions as they are all approximately the same distance away. I hope that made sense.

 

[MeteorWayne]

I was watching a program tonight on the Science Channel about the birth of the universe and the discovery of the cosmic background radiation that supports the Big Bang Theory. The discussion went on to the results obtained by the COBE satellite which finally found the clumpiness in the background radiation they were looking for. They stated that the clumps resulted in the clusters of galaxies that are visible today. But that seems to indicate that we are seeing the same objects twice (as was discussed in the circular universe thread).

Hi bdew, I'll take a shot at it. In a sense we are seeing it twice but in two different forms. The COBE (and more precise, more recent WMAP, and soon to be even more precise Planck) data shows the density of matter shortly after the Universe was created (~ 380,000 y after the BB), when it became transparent to radiation. It's the "food" from which galaxies were created over the next billion years or so. In the "hotter" areas (a few millionths of a degree warmer), the matter was more dense, so galaxies formed there later on.

Something else I am curious about and I hope I am stating this correctly. When we see computer images of the universe does the computer project objects current locations or their locations as we would see them from earth on any given night. For example we see objects on the other side of the milky way where they were a few hundred thousand years ago not where they are now (if now makes any sense at that scale) On the other hand when we look at a galaxy such as Andromeda from the top we are seeing the stars in their true relative positions as they are all approximately the same distance away. I hope that made sense.

As far as I know, we see everything in the positions where they were when the light was emitted. There really is no way to know exactly where stars on the other side of the Milky Way, or Andromeda, or other galaxies in the Universe are "now", we can only collect data that gets here at the pokey ol' speed of light.

So we see the stars of Andromeda in their relatively correct positions where they were ~ 2.54 +/- 0.06 million years ago (for the center), +/- 0.11 million years for the for the near and far edge since we see it more or less from the side.

Hope that helps

Wayne

 

[csmyth3025]

The COBE (and more precise, more recent WMAP, and soon to be even more precise Planck) data shows the density of matter shortly after the Universe was created (~ 380,000 y after the BB), when it became transparent to radiation. It's the "food" from which galaxies were created over the next billion years or so. In the "hotter" areas (a few millionths of a degree warmer), the matter was more dense, so galaxies formed there later on.

Wayne

This idea that "hotter" spots in the CMB indicate more matter had me scratching my head. A read of the Wikipedia article on the CMB explains it as follows:

There are two fundamental brands of density perturbations—called adiabatic and isocurvature. A general density perturbation is a mixture of both, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures.

Adiabatic density perturbations
the fractional overdensity in each matter component (baryons, photons ...) is the same. That is, if there is 1% more energy in baryons than average in one spot, then with a pure adiabatic density perturbations there is also 1% more energy in photons, and 1% more energy in neutrinos, than average. Cosmic inflation predicts that the primordial perturbations are adiabatic.

Isocurvature density perturbations
the sum of the fractional overdensities is zero. That is, a perturbation where at some spot there is 1% more energy in baryons than average, 1% more energy in photons than average, and 2% less energy in neutrinos than average, would be a pure isocurvature perturbation. Cosmic strings would produce mostly isocurvature primordial perturbations.
The CMB spectrum is able to distinguish these two because these two brands of perturbations produce different peak locations. Isocurvature density perturbations produce a series of peaks whose angular scales (l-values of the peaks) are roughly in the ratio 1:3:5:..., while adiabatic density perturbations produce peaks whose locations are in the ratio 1:2:3:...[61] Observations are consistent with the primordial density perturbations being entirely adiabatic, providing key support for inflation, and ruling out many models of structure formation involving, for example, cosmic strings.

If I'm reading this passage correctly, "hotter" spots in the CMB equate to "more energy in photons" which, in turn, means similarly more energy in baryons (more matter). Does this sound about right?

Chris