- #1
Dmstifik8ion
- 206
- 1
On a sheet of paper draw four concentric circles, one outside the other.
Fill the innermost circle with dots. This is the CMB photons at the point in time when they were scattered throughout the early universe and first became liberated from the spreading dense matter cloud that scattered them.
At some point on the second circle mark the current position of the Earth 13 billion years later (but not necessarily 13.7gly from the point of the big bang)
The third circle is to indicate a distance of 13.7gly from the big bang and is only to illustrate the point that due to the expansion of space itself the universe is much larger than would be allowed by the velocity of light if space had not expanded as well.
The fourth outermost circle roughly illustrates the current size of the universe.
In the approximately thirteen billion years the universe has been expanding since the CMB photons were first liberated (the innermost circle) these photons have spread out uniformly throughout the current universe and are moving in all directions, predominately outward but some toward and some away from the Earth (and some back toward the big bang itself but very few actually returning to the point of the singularity). Of those that originally had a trajectory toward the Earth, some of them will arrive at this moment in time and contribute to the Wmap picture we see today.
As the universe continues to expand they also become more and more spread apart and fewer and fewer will arrive at any given time yielding a cooler and cooler picture of the CMB to any given point within the universe.
Is there any validity to this simplified view of how we witness the CMB we observe today?
Fill the innermost circle with dots. This is the CMB photons at the point in time when they were scattered throughout the early universe and first became liberated from the spreading dense matter cloud that scattered them.
At some point on the second circle mark the current position of the Earth 13 billion years later (but not necessarily 13.7gly from the point of the big bang)
The third circle is to indicate a distance of 13.7gly from the big bang and is only to illustrate the point that due to the expansion of space itself the universe is much larger than would be allowed by the velocity of light if space had not expanded as well.
The fourth outermost circle roughly illustrates the current size of the universe.
In the approximately thirteen billion years the universe has been expanding since the CMB photons were first liberated (the innermost circle) these photons have spread out uniformly throughout the current universe and are moving in all directions, predominately outward but some toward and some away from the Earth (and some back toward the big bang itself but very few actually returning to the point of the singularity). Of those that originally had a trajectory toward the Earth, some of them will arrive at this moment in time and contribute to the Wmap picture we see today.
As the universe continues to expand they also become more and more spread apart and fewer and fewer will arrive at any given time yielding a cooler and cooler picture of the CMB to any given point within the universe.
Is there any validity to this simplified view of how we witness the CMB we observe today?