Are Photons the Particle Associatid with the CMB?

[Anomalocaris]

I have nothing to add...

Until I ask the next question.

since the CMB is isotropic, how do scientists use it to chart the history of the universe? What do they look for?

Vorlon mentioned a peak. How can something that's isotropic have a peak?

The peak refers to the distribution of the frequency of the individual CMB photons.   CMB comes as mix of photons of all wave lengths.   But the distribution of wave lengths in the mid is not random.  It follows a particular curve closely mimicking the ideal black body curve, which sort of looks like a skewed bell curve, with the largest percentage of photos falling into a narrow frequency band around the middle, and fewer and fewer photons falling into bands on either side.  The frenquecy vor referred to is the peak frequency of the distribution. The peak frequency of CMB is the same as the peak frequency of the thermal radiation from a black body object with the temperature of 3 degrees kelvin.

Isotrophy of CMB refers to the fact that no matter which direction you look, CMB photons all have almost exactly that same distribution, peaking at the same frequency.

Also.  CMB is almost isotopic, but not quite.   There are very subtle but detectable patterns in it.   The largest pattern, which manifest in CMB being hotter in the direction of the constellation of Leo, grading systematically to being colder 180 degrees away, is  from the motion of the earth.  Other smaller patterns come from  gravitational lensing caused by massive foreground abject.   This second pattern reflects the megastructures of the universe, like superclusters of galaxies.   So this pattern provide information on how the largest gravitational megastructures evolved since The Big Bang.   But subtract these patterns out, and there are still seem to be more unevenness in the CMB not explainable by effects of foreground objects.   this remaining unevenness could be the remains of unevenness in the Big Bang itself.