Ask A Scientist© Astronomy Archive

name         Jean D.
status       educator
age          50s

Question -   If light travels through space, why is space dark?
This is a question that has been around for centuries. It is attributed to
an astronomer Heinrich Olbers, and bears the name Olbers' (sometimes called
Olber's) paradox. Your inquiry motivated me to do a web search -- I thought
the answer was simple, I was missing something obvious, and a quick
refresher would supply a profoundly simple answer. I was badly mistaken!

The paradox arises by assuming 1. The universe is an infinite Euclidian
space. 2. The age of the universe is infinite. 3. Matter is uniformly
distributed. 4. The universe is static.

The terms "infinite" and "static" not literally, but sufficiently large to
be approximated by these terms. None of these assumptions is exactly true
and some "explanations" just say the assumptions are wrong therefore there
is no paradox. Sorry, but that is just avoiding the issue. It is clear that
we do not "see" all the radiation in the universe and if we could see
everything from cosmic rays to microwaves, the sky would be uniformly
bright, but that too is only a conjecture because at the present time we
cannot "see" all the radiation in the universe at all wavelengths
(energies). Ronald Koster has proposed a resolution which may be correct,
that says that we are shielded from radiation originating very far away and
gives a simple calculation that he contends resolves the paradox, but I'm
not an astrophysicist, so I am not able to assess the correctness of his
arguments.

I will be interested to see what other Newton BBS responders have to say
about this, too.
I do not think the answer is simple.

Vince Calder
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