What is background radiation caused by??

Question

What is background radiation caused by??

Answer 1

You need to clarify.  Cosmic microwave background radiation or some other background radiation?

Answer 2

There is the microwave background radiation that is the remaining radiation from the big bang, as explained by Kes.

There are high energy particles such as neutrinos that stream from space and travel pretty much through us us the earth itself.

There are high energy particles and waves that interact with our upper atmosphere to create other types or radiation or particles.

I think these particles are called cosmic rays - http://en.wikipedia.org/wiki/Cosmic_ray

The background radiation we detect is a mix of the three above.

I am not perfectly sure what your question was asking for, my answer explains what radiation we could receive on earth that originates from space.

Answer 3

Because stars (and their planets) are light years apart within galaxies separated by far more light years within the near perfect vacuum of outer space, radiation (photons) can travel at the speed of light and rarely strike an object to become absorbed.  Therefore, following the Big Bang there was an initial quantity of energy (radiation) traveling through a relatively confined space that could be measured (if anyone had been there?) as heat energy (similar to solar rays on your arm).  In the past (perhaps) 15 billion years the universe has continued to vastly expand with most galaxies racing away from each other like raisin within a loaf of rising bread dough.  The original radiation from the Big Bang is now confined within a vastly larger volume and spread so thin that its heating effect (compared to the sun) is only a few degrees above absolute zero.  Because this very weak radiation is detected in every direction from space it forms a background radiation (rather than a beam, etc.).