There is a fundamental difference between the Observable Universe (the
universe we see) and the Current Universe (the universe as it is now).
The maximum outer limit of the Observable Universe must be expanding
at the speed of light !
Any hypothesis that the Current Universe is expanding is a
metaphysical claim (an Unscientific assertion) since the Current
Universe cannot be observed.
The fundamental difference between the Observable Univese and the
There seems to be a failure even by senior Cosmologists to properly
distinguish between the Current Universe (lets call it the CU) and the
Observable Universe (the OU). The CU is the universe as it is now -
not as we see it but as it actually is now. The OU on the other hand
is the universe as we see it. Because of the finite speed of light,
when we look out into space we see back through time. The further out
we look, the more 'distorted' must be our view as compared to the CU
(the universe as it is now).
We know that the size of the OU is proportionate to its age ie Age x c
= Radius (where c is the speed of light). However the size of the CU
is not so easy. The CU is not observable so how can we know its
In Ned Wright's Cosmology FAQs, he regularly extrapolates from the OU
to the CU as if there were no difference; as if looking at the past
and speculating about the (unobservable) Present are factually
equivalent. For example, if the OU is observed to be expanding,
Wright assumes that the CU is also expanding.
Why does the Observable Universe appear to be expanding ?
If the universe had a beginning then the speed of light sets the
maximum possible size for the OU eg if the age of the universe is 14
billion years then the maximum possible distance to the outer limit of
the OU is 14 billion light years (radius). This is simply because the
light which we observe from the outer reaches of the universe cannot
have travelled further than 14 billion light years since the
beginning. Note that we are talking about the OU which is unlikely to
bear any resemblance to the CU.
Continuing the previous example, after another billion years have
elapsed, the outer limit of the OU will be 15 billion light years.
So the maximum outer limit of the OU must be expanding at the speed of
Note again that this relates only to the OU and not to the CU.
Note also that the observed expansion of the OU has
nothing to do with a (supposedly explosive) initial event. The 'Big
Bang' may have happened but it has no relevance to the expansion of
the Observable Universe.
So how fast is the Current Universe expanding ?
We cannot say of the CU that it is expanding. If it were expanding
how would we know since we cannot observe it? We can make guesses
about what the CU is doing but that is all that they are - guesses.
Any hypothesis that the CU is expanding is unscientific since the CU
cannot be observed. Any hypotheses about the CU are metaphysical
hypothoses - not Scientific hypotheses.