Quote:
Originally Posted by DBryan
Summary
=======
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.
|
You are right. I say there is a difference between what I call the Observable Universe (OU) - probably the same as yours - and the rest of it, or what I call, the Universe as a Whole (UAW) and just to say the UAW is expanding because the OU is expanding is unscientific, since there is no evidence for this.
Quote:
The fundamental difference between the Observable Univese and the
Current Universe
================================================== ==
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
size ?
|
What radius? Is this about the Big Bang? What if it never happened - what if NASA's COBE satellite's photograph of the Universe as it Started was exactly that - a photo of the Universe at birth?
This infra-red snapshot that COBE took showed a 'hot smooth soup', with no sign of any Big Bang anywhere. Maybe the Cosmos came that way - already expanded.
You seem to show a certain level of understanding... and yet you're a Big Banger..?
Quote:
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.
|
They all do.
Quote:
|
Why does the Observable Universe appear to be expanding ?
|
Because it's falling..?
Quote:
=============================================
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
light !
Note again that this relates only to the OU and not to the CU.
|
If you say so.
Quote:
Note also that the observed expansion of the OU has
nothing to do with a (supposedly explosive) initial event.
|
Quite right, and so we should be looking for
other reasons. To me, this sounds like there is hope...
Quote:
|
The 'Big Bang' may have happened
|
Or maybe it didn't.
Quote:
|
...but it has no relevance to the expansion of the Observable Universe.
|
Well said.
Quote:
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.
|
I always thought the behaviour of the OU was the same as the behaviour of any falling body - accellerating due to gravity, into the center of mass of the UAW.
I suppose, just the fact that the Cosmos is falling - can tell you quite a bit about what it must be falling into.
Look around, in Space - we see lots of things falling. When they fall, they do certain things, things that falling bodies do in Space. There's no shortage of evidence, surely?
Quote:
Any hypothesis that the CU is expanding is unscientific since the CU
cannot be observed.
|
It is unscientific - with no evidence - I agree.
Quote:
|
Any hypotheses about the CU are metaphysical hypothoses - not Scientific hypotheses.
|
The OU can teach us much about the UAW, if we will just let it.