Question

What is the earliest point in the universe that we can observe? Why can’t we see back further than this?

If the cosmic microwave background was generated by a 3000 K plasma why does it have a blackbody spectrum of a 2.73 K object?

Which fundamental force is the first force to separate from the other forces? What is the second?

Plz answer all questions i posted, it's my last question can be posted in this month, or i definitely will report ur answer

Answer 1

1.) If you think about it, we can use light to look at distant objects because light propagates freely from the matter which emitted it. This was not always the case: when the Universe was less than 100 000 years old, the matter and radiation were so densely packed that light was "coupled" to the matter. This means that light which was emitted when the Universe was less than 100 000 years old couldn't "go anywhere", and hence can't reach us today. Observationally, this means that when we try to look at higher and higher redshifts, we hit a "wall" corresponding to the redshift when the Universe was 100 000 years old. This wall is the cosmic microwave background, or CMB.

2.)The CMB temperature is 2.73 K and it is a constant value irrespective of the direction it is measured. The spectrum of CMB is extraordinarily close to an ideal blackbody spectrum (spectrum is the measurement of how much radiation is emitted by an object at different wavelengths). The peak of this curve is completely determined by the temperature is the object. The image below shows a theoretical blackbody curve of an object with temperature 2.73 K and the points are data of CMB taken by COBE telescope. The data falls on the theoretical curve so precisely that the error bars on the data smaller than the thickness of the black line. Thus CMB is the most ideal natural blackbody radiation in nature.

The CMB gives a snapshot of the universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thereby making the universe nearly transparent to radiation because light was no longer being scattered off free electrons. When it originated some 380,000 years after the Big Bang—this time is generally known as the "time of last scattering" or the period of recombination or decoupling—the temperature of the universe was about 3000 K.

Since decoupling, the temperature of the background radiation has dropped by a factor of roughly 1,100 due to the expansion of the universe. As the universe expands, the CMB photons are redshifted, causing them to decrease in energy. The temperature of this radiation stays inversely proportional to a parameter that describes the relative expansion of the universe over time, known as the scale length. The temperature T_r of the CMB as a function of redshift, z, can be shown to be proportional to the temperature of the CMB as observed in the present day.

3.) Gravity is the first force to separate from the other forces. The second is strong nuclear force.