Why can we see the CMB in every direction we look?

[cosmictide]

Hi guys,

As you can probably tell this is my first post, so I thought I ask a question that I've had trouble getting my head round. I think I know the reason but I'm not a 100% certain.

Why is it that we see the CMB radiation from every direction we look? I would really appreciate if someone could explain this to me, even better if there was a diagram to go along with it to help me understand our position in the universe.

Thanks in advance.

 

[Bandersnatch]

Hi cosmictde, welcome to PF!

Imagine a large volume of space, perhaps even infinite if you can do that. Now, imagine that at a certain point in time each and every point in that space emits a photon in some random direction.

Wait some time for the photons to travel around in straight lines.

Now pick a random point in the volume of space. Imagine it's the Earth, and look around.

There will be photons coming at you from every direction. Wait some more. The photons you saw previously had already passed you by, but you still see other photons that only now had the chance to reach you. It'll go on like that forever, whichever point in space you choose to look from.

What you should gather from the above, is that the emission of Cosmic Background Radiation was an event that happened everywhere at a single point in time, rather than an even that happened somewhere in particular.

 

[bapowell]

Have a look at http://tangentspace.info/Articles/cmb1.php. The section "Getting Situated" should answer your question.

 

[cosmictide]

Have a look at http://tangentspace.info/Articles/cmb1.php. The section "Getting Situated" should answer your question.

Hi cosmictde, welcome to PF!

Imagine a large volume of space, perhaps even infinite if you can do that. Now, imagine that at a certain point in time each and every point in that space emits a photon in some random direction.

Wait some time for the photons to travel around in straight lines.

Now pick a random point in the volume of space. Imagine it's the Earth, and look around.

There will be photons coming at you from every direction. Wait some more. The photons you saw previously had already passed you by, but you still see other photons that only now had the chance to reach you. It'll go on like that forever, whichever point in space you choose to look from.

What you should gather from the above, is that the emission of Cosmic Background Radiation was an event that happened everywhere at a single point in time, rather than an even that happened somewhere in particular.

Thank you so much. That makes things much more clear.

 

[sardar]

The Cosmic Microwave Background (CMB) is the leftover radiation from the Big Bang, which occurred approximately 13.8 billion years ago. This radiation is present in all directions because it is the remnant of the initial explosion that created the universe. As the universe expanded and cooled, the radiation was stretched out and became the microwave background that we can detect today.

To understand why we see the CMB in every direction, we need to first understand the concept of the observable universe. The observable universe is the portion of the universe that we can see and detect, and it is limited by the distance that light has had time to travel since the beginning of the universe. This distance is approximately 46.5 billion light years in all directions.

Now, imagine that we are at the center of a sphere with a radius of 46.5 billion light years. This sphere represents the observable universe. The CMB radiation is present in all directions because it is evenly distributed throughout this sphere. This means that no matter where we look within this sphere, we will see the CMB radiation.

Additionally, the CMB radiation is also known as the "afterglow" of the Big Bang. This means that it is the oldest light in the universe and has been traveling through space since the beginning of time. As a result, it has had enough time to reach us from all directions, filling our observable universe with this background radiation.

In summary, we see the CMB in every direction because it is the oldest light in the universe, evenly distributed throughout our observable universe. This is a key piece of evidence for the Big Bang theory and helps us understand our place in the universe. I hope this explanation helps and feel free to ask any further questions.