Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Cosmic Microwave Background
Name: Jack H.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 9/30/2003

How is it that we can "see" the cosmic microwave background radiation? It seems to me that, no matter which way its photons were heading when they started on their way in the year 380,000, they must surely have left the matter of the universe behind by now. They travel at the speed of light and we do not even come close, (do we?). So why are they still around here?

Understanding the "Big Bang" is not at all in line with our intuition. It is not as if we are sitting "over here" on Earth and "it" happened "over there" about 13 billion years ago. Except for the predicted (and observed) fine structure, it occurred in all directions in space simultaneously -- it is the very creation of space itself. So our intuition fails us, and must be disregarded. The experimental observation is that no matter what direction we look into space, other galaxies are receding from us. From the Doppler shift in the wavelength(s) of light we are able to tell how far these sources are, and how fast they are receding from us. The observation is that not only are they moving away from us (and one another) more recent observations suggest that the furthest (i.e. oldest) sources may even receding at an increasing rate.

No one (even the experts, not just us poor mortals) has a good explanation for why this is and so there are tags that we put on the observations "dark matter", "dark energy" etc., but that is not an explanation, it is a name tag. The "Universe" the "All" is weird indeed.

Vince Calder

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory