| 1 "Axel Boldt" |
Size of observable universe? | maandag 18 februari 2002 22:13 |
| 2 "Boyan" |
Re: Size of observable universe? | donderdag 21 februari 2002 15:01 |
| 3 "george todd" |
Re: Size of observable universe? | woensdag 6 maart 2002 9:22 |
| 4 "Bill Nelson" |
Re: Size of observable universe? | donderdag 7 maart 2002 7:21 |
| 5 "Henry Wilson" |
Re: Size of observable universe? | donderdag 7 maart 2002 23:58 |
| 6 "Bill Nelson" |
Re: Size of observable universe? | vrijdag 8 maart 2002 2:18 |
| 7 "Jeff Root" |
Re: Size of observable universe? | vrijdag 8 maart 2002 8:07 |
| 8 "Joseph Lazio" |
Re: Size of observable universe? | vrijdag 8 maart 2002 15:27 |
| 9 "Martin Gradwell" |
Re: Size of observable universe? | vrijdag 8 maart 2002 17:37 |
| 10 "Henry Wilson" |
Re: Size of observable universe? | zaterdag 9 maart 2002 0:35 |
| 11 "Jan Panteltje" |
Re: Size of observable universe? | zaterdag 9 maart 2002 0:38 |
| 12 "Jeff Root" |
Re: Size of observable universe? | zaterdag 9 maart 2002 0:39 |
| 13 "Henry Wilson" |
Re: Size of observable universe? | zaterdag 9 maart 2002 1:26 |
| 14 "Jeff Root" |
Re: Size of observable universe? | zaterdag 9 maart 2002 1:49 |
| 15 "David Evens" |
Re: Size of observable universe? | zaterdag 9 maart 2002 8:52 |
| 16 "Nicolaas Vroom" |
Re: Size of observable universe? | zaterdag 9 maart 2002 12:47 |
| 17 "Joseph Lazio" |
Re: Size of observable universe? | zaterdag 9 maart 2002 15:49 |
| 18 "Jan Panteltje" |
Re: Size of observable universe? | zaterdag 9 maart 2002 16:53 |
| 19 "George Dishman" |
Re: Size of observable universe? | zondag 10 maart 2002 10:20 |
| 20 "Mark Q" |
Re: Size of observable universe? | zondag 10 maart 2002 10:34 |
| 21 "George Dishman" |
Re: Size of observable universe? | zondag 10 maart 2002 12:20 |
| 22 "George Dishman" |
Re: Size of observable universe? | zondag 10 maart 2002 12:26 |
| 23 "Martin Gradwell" |
Re: Size of observable universe? | zondag 10 maart 2002 13:47 |
| 24 "George Dishman" |
Re: Size of observable universe? | zondag 10 maart 2002 15:24 |
| 25 "Martin Gradwell" |
Re: Size of observable universe? | zondag 10 maart 2002 22:07 |
Hello,
I often find claims on the internet like this: "since the universe is ~15 billion years old, the observable universe must be ~15 billion lightyears in radius". I don't think this is correct since the universe was expanding for all those years.
Are there any estimates for the radius of the observable universe, based on the currently best values of Hubble's constant, cosmological constant, mass density etc.?
(When I say "radius", I mean "radius *right now*", i.e. put a sequence of observers in a straight line on adjacent galaxies, let them use their cosmological clocks and at 0:00 am January 1 2003 GMT they all measure the distance to their nearest neighbor, then we add all those numbers up.)
Axel
As far I know Universe expands faster than the speed of light...
And this is still within rule that nothing can travel fastr than
the speed of light, since, universe expands in "empty" medium.
If not correct I'd be glad to hear expert's explanation on this.
Boyan
"Axel Boldt"
I often find claims on the internet like this: "since the universe is
~15 billion years old, the observable universe must be ~15 billion
lightyears in radius". I don't think this is correct since the
universe was expanding for all those years.
Are there any estimates for the radius of the observable universe,
based on the currently best values of Hubble's constant, cosmological
constant, mass density etc.?
(When I say "radius", I mean "radius *right now*", i.e. put a sequence
of observers in a straight line on adjacent galaxies, let them use
their cosmological clocks and at 0:00 am January 1 2003 GMT they all
measure the distance to their nearest neighbor, then we add all those
numbers up.)
Axel
"Boyan" wrote:
Since the most distant objects are about 14 billion light years away
you might think that they had to take more than 14 billion years to
get there from the big bang, making the universe some 30 billion years
old. But all sorts of observations say this isn't so. Astronomers get
around this by employing the inflation therory which says that the
universe expanded to almost it's current size in the first seconds of
the big bang.
In sci.astro george todd
Look at it this way. Forget how long it took for the objects to get
where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
--
On Thu, 7 Mar 2002 06:21:00 +0000 (UTC), Bill Nelson
Look at it this way. Forget how long it took for the objects to get
where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
--
Can you not see George's point?
If there was a big bang, which I doubt, then the objects we see as 14
billion years old must have taken at least another 14 billion years to get
where we are observing them now.
Henry Wilson, Henry Wilson's free thought Laboratory,
In sci.astro Henry@the.edge(henry wrote:
Look at it this way. Forget how long it took for the objects to get
where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
Sure, but it does not mean much. We cannot see back to within a short
time of the formation of the universe. All we can go on is what we can
observe and make conjectures.
So what? See above.
--
George Todd wrote:
Bill Nelson replied:
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
Henry Wilson replied to that:
Turn Bill's statement around: If the Universe is 14 billion
years old, then light from the earliest thing we can see, the
cosmic microwave background radiation, which was emitted about
300,000 years after the Big Bang, has been travelling toward us
for 13,999,700,000 years. It took the matter which emitted the
light 300,000 years to reach the positions from which the light
was emitted.
Light from galaxies which appear to be 10 billion light-years
away was emitted 4 billion years after the Big Bang, and has
been travelling toward us for 10 billion years. It took the
matter which emitted that light 4 billion years to reach the
positions from which the light was emitted.
Light from galaxies which appear to be 1 billion light-years
away was emitted 13 billion years after the Big Bang, and has
been travelling toward us for 1 billion years. It took the
matter which emitted that light 13 billion years to reach the
positions from which the light was emitted.
Light from the computer monitor in front of you was emitted
just now, and took a tiny fraction of a second to reach you.
It took the matter which emitted the light 14 billion years
to reach the positions from which the light was emitted.
-- Jeff, in Minneapolis
.
"JR" == Jeff Root
If the furthest objects we can see are 14 billion light years
away, and assuming that it is not an intrinsic intensity problem,
then the age of the Universe is 14 billion years - at least the
stars that produced the light we are now viewing started doing so
14 billion years ago.
The statements by Jeff Root, George Todd, and Henry Wilson seem to be
based on a misconception of the Big Bang. The BB did not occur at a
central point in space, away from which everything has been moving
since. The BB occurred at a point in time, but everywhere in space.
Those distant galaxies didn't have to move to some distant point,
they've always been distant.
--
Henry Wilson
In sci.astro george todd
Look at it this way. Forget how long it took for the objects to get
where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
That only makes sense if we see only the first light coming
from those stars. What if they were already old at the time
when they emitted the light which we see today?
I presume that Bill considers the stars to be young; they will
have experienced very little proper time, at the time when they
emitted the light which we see today, because of the effects
of time dilation. This is a very SR-oriented approach, and
there is no reason to suppose that the entire universe can be
encompassed in a single SR-style reference frame.
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. Regardless of the proper time
experienced by those distant stars, in our own reference frame
they were 14 billion light years distant from us, 14 billion years
ago, and they were receding from us at almost lightspeed then.
Extrapolating backwards, and assuming constant speed, they
were in our own vicinity 28 billion years ago. So, bearing in mind
these assumptions, our own timeline should be 28 billion years
long, or thereabouts.
--
Can you not see George's point?
If there was a big bang, which I doubt, then the objects we see as 14
billion years old must have taken at least another 14 billion years to get
where we are observing them now.
This would be true if there was a single SR-style frame of
reference which included both ourselves and the distant objects,
in which light travelled at constant speed in straight lines and
all material objects travelled more slowly than light.
However, consider the consequences if one or more of these
assumptions is invalid.
1) There is not a single applicable SR-style frame:
SR only works where gravitational effects are negligible.
On a universal scale the gravitational effects of a universe-full
of matter need to be taken into account.
2) Light does not travel at a constant speed.
Actually light does travel at a constant speed c, by definition.
If c seems to vary, it is because our clocks or measuring rods
are unreliable, and there is no such thing as a reliable clock or
measuring rod; but this definition is like defining "a foot" to be
the length of the reigning monarch's foot, and establishing by
decree that this does not change. As the monarch gets older,
the world around him shrinks for no obvious reason.
Light, it has been established, is affected by gravitation in
much the same way that matter is. It is bent by passage close
to the sun. for example. Why should we not interpret this
as an acceleration in the direction of the sun, and assume that
light heading directly towards the sun is similarly accelerated
i.e. it speeds up? In this interpretation, the speed of light will
vary from place to place according to depth in a gravitational
well.
The alternative, that light speed is constant everywhere,
is only viable if we decree it to be the case, and say that it is
everything else that varies, not the light speed. This leads to
a non-Euclidean concept of space which can easily tie itself
in knots. Why do we do it? Because we can, and because
we are hopelessly addicted to the idea of c being everywhere
the same. C has only ever been measured in one tiny corner
of the cosmos, i.e. on or very near the earth's surface, and
the earth's depth in a gravitational well has not varied
significantly in the time since measurements began.
3) Light does not travel in straight lines.
So the orbit of a planet is "maximally straight", but in
our lucid intervals we can see that it is an ellipse (in space,
or an elliptical spiral in spacetime). So, similarly, the fact
that light travels along "maximally straight" paths does not
prevent it from following closed orbits. That is what in fact
happens, in a closed universe. We can imagine these
orbits as simple ellipses, or as maximally straight paths
in a spacetime which is curved and wraps around,
depending on our degree of attachment to GR principles
and/or on our degree of masochism.
In either case, the galaxies which we see at an apparent
distance of 14 billion light years could actually be our
own galaxy and its neigbours, seen at an earlier stage
in their development. Or they could be precursor galaxies
which have long since ceased to exist, with our galaxy
and its neigbours formed from the remnants.
4) Material objects can travel faster than light.
If they could, then they could easily have got to where
they are observed to be in 300,000 years, even though
they seem to be 14 billion LY away from us.
I'm just mentioning this possibility for completeness.
I don't intend to address it in any depth, since I
can't imagine any mechanism which would propel
matter at a speed sufficient to overtake the light in
its vicinity. However, I will say that the SR rule about
nothing travelling faster than light applies only to
a SR inertial reference frame, and only locally in GR.
For an accelerating observer, distant objects will seem
to approach or recede at speeds much greater than
the local speed of light. For a rotating observer, with
a corotating reference frame, distant stars appear to
follow circular orbits (as in the Ptolemaic system), and
to do so with extreme rapidity.
Henry Wilson, Henry Wilson's free thought Laboratory,
Martin Gradwell, mtgradwell@btinternet.com
On 7 Mar 2002 23:07:53 -0800, jeff2@freemars.org (Jeff Root) wrote:
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some
30 billion years old. But all sorts of observations say this
isn't so. Astronomers get around this by employing the inflation
therory which says that the universe expanded to almost it's
current size in the first seconds of the big bang. I think it's
all a big conspiracy to confunse us Junior Collage graduates!
Bill Nelson replied:
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
Henry Wilson replied to that:
Can you not see George's point?
If there was a big bang, which I doubt, then the objects we see as
14 billion years old must have taken at least another 14 billion
years to get where we are observing them now.
Turn Bill's statement around: If the Universe is 14 billion
years old, then light from the earliest thing we can see, the
cosmic microwave background radiation, which was emitted about
300,000 years after the Big Bang, has been travelling toward us
for 13,999,700,000 years. It took the matter which emitted the
light 300,000 years to reach the positions from which the light
was emitted.
Light from galaxies which appear to be 10 billion light-years
away was emitted 4 billion years after the Big Bang, and has
been travelling toward us for 10 billion years. It took the
matter which emitted that light 4 billion years to reach the
positions from which the light was emitted.
Light from galaxies which appear to be 1 billion light-years
away was emitted 13 billion years after the Big Bang, and has
been travelling toward us for 1 billion years. It took the
matter which emitted that light 13 billion years to reach the
positions from which the light was emitted.
Light from the computer monitor in front of you was emitted
just now, and took a tiny fraction of a second to reach you.
It took the matter which emitted the light 14 billion years
to reach the positions from which the light was emitted.
-- Jeff, in Minneapolis
.
If the most distant objects we see are 14 billion lightyears away, then it
must have taken them much longer than 14 billion years to get to the
positions in which we see them now.
More likely, all matter traveled on average at much less than c, making the
universe possibly many hundreds or even thousands of billions of years old.
Henry Wilson, Henry Wilson's free thought Laboratory,
Joseph Lazio wrote :
Are you alright?
J.P. Commander of Space Police
--
George Todd wrote:
Bill Nelson replied:
If the furthest objects we can see are 14 billion light years
away, and assuming that it is not an intrinsic intensity problem,
then the age of the Universe is 14 billion years - at least the
stars that produced the light we are now viewing started doing so
14 billion years ago.
Henry Wilson replied to Bill Nelson:
Jeff Root replied to Henry Wilson:
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
Joseph Lazio replied to Jeff Root:
I can't speak for the others, but my reply did not involve the
notion that the Big Bang occurred at a point in space.
However, all matter DID have to move to the locations where we
see it now. It has spread out a lot since the Big Bang. A few
seconds after the Big Bang, all the matter which is now in the
Milky Way galaxy was squeezed into a volume smaller than a star
like Betelgeuse.
If the Big Bang was 14 billion years ago, then the matter in
your body took 14 billion years to reach the positions in which
you see it now, and the matter in a galaxy a billion light-years
away took 13 billion years to reach the positions in which you
see it now.
-- Jeff, in Minneapolis
On 08 Mar 2002 09:27:30 -0500, Joseph Lazio
George Todd wrote:
Bill Nelson replied:
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous
information.
If the furthest objects we can see are 14 billion light years
away, and assuming that it is not an intrinsic intensity problem,
then the age of the Universe is 14 billion years - at least the
stars that produced the light we are now viewing started doing so
14 billion years ago.
Henry Wilson replied to that:
Can you not see George's point? If there was a big bang, which I
doubt, then the objects we see as 14 billion years old must have
taken at least another 14 billion years to get where we are
observing them now.
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
The statements by Jeff Root, George Todd, and Henry Wilson seem to be
based on a misconception of the Big Bang. The BB did not occur at a
central point in space, away from which everything has been moving
since. The BB occurred at a point in time, but everywhere in space.
Those distant galaxies didn't have to move to some distant point,
they've always been distant.
I like it!
--
Henry Wilson, Henry Wilson's free thought Laboratory,
Bill Nelson wrote:
(I deleted parts of what Bill wrote which are not essential.)
Martin Gradwell replied to Bill Nelson (in part):
No, all wrong. :-)
I want to start with an assumption that is similar to but not
the same as Bill's. If the Universe is 14 billion years old,
then the most distant things we can see must appear to be less
than 14 billion light-years away.
The most distant thing we can see is the cosmic microwave
background radiation (CMBR). Since it is reliably calculated
to have been emitted about 300,000 years after the Big Bang,
that light must have travelled for about 13,999,700,000 years
(over a distance of about 13,999,700,000 light-years) to reach
us. When the CMBR we see now was emitted, the matter which
emitted it may have been only one or two hundred thousand
light-years away from our current position. (A more precise
figure may be available.) The expansion has carried us and the
matter which emitted the CMBR much farther apart, during which
time the CMBR was travelling from the locations that it was
emitted from (all around us) to our current position.
-- Jeff, in Minneapolis
.
On Fri, 08 Mar 2002 23:35:04 GMT, Henry@the.edge(Henry Wilson) wrote:
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some
30 billion years old. But all sorts of observations say this
isn't so. Astronomers get around this by employing the inflation
therory which says that the universe expanded to almost it's
current size in the first seconds of the big bang. I think it's
all a big conspiracy to confunse us Junior Collage graduates!
Bill Nelson replied:
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous information.
If the furthest objects we can see are 14 billion light years away,
and assuming that it is not an intrinsic intensity problem, then the
age of the Universe is 14 billion years - at least the stars that
produced the light we are now viewing started doing so 14 billion
years ago.
Henry Wilson replied to that:
Can you not see George's point?
If there was a big bang, which I doubt, then the objects we see as
14 billion years old must have taken at least another 14 billion
years to get where we are observing them now.
Turn Bill's statement around: If the Universe is 14 billion
years old, then light from the earliest thing we can see, the
cosmic microwave background radiation, which was emitted about
300,000 years after the Big Bang, has been travelling toward us
for 13,999,700,000 years. It took the matter which emitted the
light 300,000 years to reach the positions from which the light
was emitted.
Light from galaxies which appear to be 10 billion light-years
away was emitted 4 billion years after the Big Bang, and has
been travelling toward us for 10 billion years. It took the
matter which emitted that light 4 billion years to reach the
positions from which the light was emitted.
Light from galaxies which appear to be 1 billion light-years
away was emitted 13 billion years after the Big Bang, and has
been travelling toward us for 1 billion years. It took the
matter which emitted that light 13 billion years to reach the
positions from which the light was emitted.
Light from the computer monitor in front of you was emitted
just now, and took a tiny fraction of a second to reach you.
It took the matter which emitted the light 14 billion years
to reach the positions from which the light was emitted.
-- Jeff, in Minneapolis
.
If the most distant objects we see are 14 billion lightyears away, then it
must have taken them much longer than 14 billion years to get to the
positions in which we see them now.
Sure, if they had traveled at the speed of light to their presently
observed positions, we could say the big bang (if any) occured something
like 24 billion years ago, depending where we sit in relation to the big
bang's center.
The intersting thing is how much Henry is working to demonstrate his
total refusal to read any post he responds to, in this case by making
precisely the same error corrected by the post he replies to.
Henry Wilson, Henry Wilson's thought-free Lavatory,
"Joseph Lazio"
George Todd wrote:
Bill Nelson replied:
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous
information.
Please explain.
If the furthest objects we can see are 14 billion light years
away, and assuming that it is not an intrinsic intensity problem,
then the age of the Universe is 14 billion years - at least the
stars that produced the light we are now viewing started doing so
14 billion years ago.
Henry Wilson replied to that:
Can you not see George's point? If there was a big bang, which I
doubt, then the objects we see as 14 billion years old must have
taken at least another 14 billion years to get where we are
observing them now.
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
The statements by Jeff Root, George Todd, and Henry Wilson seem to be
based on a misconception of the Big Bang. The BB did not occur at a
central point in space, away from which everything has been moving
since. The BB occurred at a point in time, but everywhere in space.
Those distant galaxies didn't have to move to some distant point,
they've always been distant.
What is the difinition of everywhere in space ?
(What is the difinition of always been distant ?)
The subject we are discussing is explained at the following two Faq's
If the Universe is only 10 billion years old, why isn't the most distant
object we can see 5 billion light years away?
IMO it is important to make a disctinction between:
We do not see an object where the object is Now.
On the other hand we can calculate where this
object is Now.
This whole controversy started with observations Now
that z (redshifts) can be larger than 1 which is
an indication of the speed of the object in the past.
Nick
--
"JR" == Jeff Root
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
The following is going to sound really counter-intuitive, but, no,
nothing has moved. A picture will illustrate it better than words.
If this is the present situation
[1] This statement ignores any "peculiar" motions of galaxies, but
those produce only small differences compared to the distances being
discussed here.
--
Jeff Root replied to Henry Wilson:
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
Joseph Lazio replied to Jeff Root:
The statements by Jeff Root, George Todd, and Henry Wilson seem to
be based on a misconception of the Big Bang. The BB did not occur
at a central point in space, away from which everything has been
moving since. The BB occurred at a point in time, but everywhere
in space. Those distant galaxies didn't have to move to some
distant point, they've always been distant.
I can't speak for the others, but my reply did not involve the
notion that the Big Bang occurred at a point in space.
However, all matter DID have to move to the locations where we see
it now. It has spread out a lot since the Big Bang. A few
seconds after the Big Bang, all the matter which is now in the
Milky Way galaxy was squeezed into a volume smaller than a star
like Betelgeuse.
If the Big Bang was 14 billion years ago, then the matter in your
body took 14 billion years to reach the positions in which you see
it now, and the matter in a galaxy a billion light-years away took
13 billion years to reach the positions in which you see it now.
The following is going to sound really counter-intuitive, but, no,
nothing has moved. A picture will illustrate it better than words.
If this is the present situation
[1] This statement ignores any "peculiar" motions of galaxies, but
those produce only small differences compared to the distances being
discussed here.
--
JP Commander of Space Police
The importance of coordinate system being used seems to be
getting missed in some of these discussions.
"Jeff Root"
Martin Gradwell replied to Bill Nelson (in part):
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. Regardless of the proper time
experienced by those distant stars, in our own reference frame
they were 14 billion light years distant from us, 14 billion years
No, in SR coordinates, they were just under 7 billion light years
distant, 7 billion years ago. Looking at the figures in this section
of Ned Wright's tutorial may help:
http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD
The second figure is where values like 14 billion years come from
but the third figure is the same thing plotted in SR coordinates.
No, all wrong. :-)
I want to start with an assumption that is similar to but not
the same as Bill's. If the Universe is 14 billion years old,
then the most distant things we can see must appear to be less
than 14 billion light-years away.
The most distant thing we can see is the cosmic microwave
background radiation (CMBR). Since it is reliably calculated
to have been emitted about 300,000 years after the Big Bang,
that light must have travelled for about 13,999,700,000 years
(over a distance of about 13,999,700,000 light-years) to reach
us. When the CMBR we see now was emitted, the matter which
emitted it may have been only one or two hundred thousand
light-years away from our current position. (A more precise
figure may be available.)
In SR coordinates, the matter would have been about 7 billion
light-years away and moving so fast it had only experienced
300,000 years of proper time. When we look at that matter we
are seeing material as it was 300,000 years after the BB so
it can be described as "seeing the universe as it was
13,999,700,000 years ago". This is described from our frame
of reference.
True, but we are not moving in our frame of reference, that
applies if you consider the frame of the matter that emitted
the radiation. When the CMBR was emitted, we were 300,000
light-years away and moving near to the speed of light. In
the matter's frame, by the time the light had caught up with
us, we had experienced 14 billion years of proper time.
Jan Panteltje wrote in message ...
Why should the universe be "sane"? Why should it meet with the expectations
of you, a mere "speck in the inifinity"?
You comprehend a lot more of it by using "defect math" than by being "sane".
Mark Q
"Nicolaas Vroom"
The statements by Jeff Root, George Todd, and Henry Wilson seem to be
based on a misconception of the Big Bang. The BB did not occur at a
central point in space, away from which everything has been moving
since. The BB occurred at a point in time, but everywhere in space.
Those distant galaxies didn't have to move to some distant point,
they've always been distant.
Joseph is right on the button. The BB theory does not include the
concept of an origin. When you talk of "origin of the BB", you are
inventing your own theory. That version may then have the problems
you describe.
This is somewhat over-simplified but should give you a start in
the right direction towards finding out more: BB theory does not
include t=0 but starts at a fraction of a second thereafter. At
that time space was infinite (based on current measurements). At
t=1 microsecond, the part of space we can now see was a few
hundred metres in diameter and the plasma in it was pretty
uniformly dense throughout. Beyond that was the same. A patch of
plasma one light year away from ours at that time probably had a
similar density. Since then, everything has expanded.
The phrases you quote mean that, from the earliest instant
covered by BB theory, space was infinite and uniformly filled
with matter (or more accurately the radiation which was later
converted to matter).
Since everything was uniform, no part is any more 'the origin'
than any other part, and trying to incorporate that concept (plus
mixing of coordinate systems) seems to be at the bottom of most
of the problems in this thread.
I have snipped other parts of your post as they tend not to be
relevant once you discard the erroneous 'origin' concept.
"George Dishman"
I have snipped other parts of your post as they tend not to be
relevant once you discard the erroneous 'origin' concept.
Looking again at your post, I was thinking of these comments:
Please explain.
Your other comments on where the object is now etc. are valid.
Sorry for any confusion.
George Dishman
"Jeff Root"
Martin Gradwell replied to Bill Nelson (in part):
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. Regardless of the proper time
experienced by those distant stars, in our own reference frame
they were 14 billion light years distant from us, 14 billion years
No, in SR coordinates, they were just under 7 billion light years
distant, 7 billion years ago. Looking at the figures in this section
of Ned Wright's tutorial may help:
http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD
The second figure is where values like 14 billion years come from
but the third figure is the same thing plotted in SR coordinates.
The web is full of statements like the following
(from http://www.astro.ubc.ca/people/scott/faq_email.html):
"The CMB photons we see today are coming to us from way
across the Universe (about 13 billion light years away, if for
example the Universe is 13 billion years old). That's true no
matter what direction in the sky we look."
The implication of these statements is that the age of the
CMBR is the same as the age of the universe (give or take
300,000 years or so), and the CMBR photons have been
following straight paths ever since they were emitted.
Therefore, these photons come from approximately N light
years away, where N is the age of the universe in years as
measured by a local observer.
All the documentaries I have seen which bear on this
issue seem to make a similar claim.
In contrast, we have the diagrams in Ned Wright's tutorial.
You say that "The second figure is where values like 14
billion years come from but the third figure is the same
thing plotted in SR coordinates."
However, none of these figures is labelled with times or
distances, and if they were then presumably the observer's
timeline would be 14 billion years long in both the second
and the third figure. In neither figure is anything observed
to be fourteen billion light years distant, though in the SR
representation the distant galaxies, which are observed
to be 7 billion light years distant and receding at nearly the
speed of light, can be *inferred* to be 14 billion light
years distant "now" (whatever "now" means).
In the SR representation it is remarkable that we can only
see back 7 billion years, and the things we see happening
7 billion years ago are supposedly the first observable
things that ever happened in our universe, even though
our universe is 14 billion years old.
Or, maybe we *can* see a distance of fourteen billion
light years in any direction. That is the way most people
seem to interpret the situation, and the lack of proper
labelling on the diagram means that it can support
either interpretation. But then our own timeine would be
28 billion years long
In the second diagram, the one with the pear-shaped
past light "cone", the light from supposedly "distant" galaxies
actually originates fairly locally. It moves outward, carried
by the "expansion of space", then back again. Remarkably,
it then seems to stop. Well, the diagram does only depict
the past light cone of a single current event, but why should
we suppose that this light has diverged and reconverged
only once in the history of the universe? What is so special
about the current moment, that makes light converge now
for the first time? Obviously, nothing. When light converges
at a point, and there is no observer or other obstacle located
at that point, the light continues, re-diverging. It can orbit the
universe several times before being intercepted. Past events,
even those early in the universe's history, will have pear-shaped
past light cones, and pear-shaped future light cones too.
There is no logic that says otherwise, only a questionable
diagram. Therefore the apparently distant galaxies, at various
apparent distances, can all be images of more local galaxies
or their precursors.
..
Martin Gradwell, mtgradwell@btinternet.com
"Martin Gradwell"
George Dishman
"Jeff Root"
Martin Gradwell replied to Bill Nelson (in part):
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. Regardless of the proper time
experienced by those distant stars, in our own reference frame
they were 14 billion light years distant from us, 14 billion years
No, in SR coordinates, they were just under 7 billion light years
distant, 7 billion years ago. Looking at the figures in this section
of Ned Wright's tutorial may help:
http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD
The second figure is where values like 14 billion years come from
but the third figure is the same thing plotted in SR coordinates.
The web is full of statements like the following
(from http://www.astro.ubc.ca/people/scott/faq_email.html):
"The CMB photons we see today are coming to us from way
across the Universe (about 13 billion light years away, if for
example the Universe is 13 billion years old). That's true no
matter what direction in the sky we look."
The implication of these statements is that the age of the
CMBR is the same as the age of the universe (give or take
300,000 years or so), and the CMBR photons have been
following straight paths ever since they were emitted.
Therefore, these photons come from approximately N light
years away, where N is the age of the universe in years as
measured by a local observer.
All the documentaries I have seen which bear on this
issue seem to make a similar claim.
Yes, I agree, but you have to realise that these are trying
to convey something complex in a simple manner. If you say
to the average layman "The CMBR originated at a distance
of 300k light years, and has been travelling towards us for
the last 13.997 billion years. It travels at the speed of
light relative to all local matter it passes on the way."
you are only going to create confusion.
If these pages just said the CMBR was emitted 300k years
after the start of time and didn't comment on distance,
I think it would be much simpler.
Of course you are going beyond the simplistic presentations
and looking in more detail so you have to appreciate that
things are actually more complex.
However, none of these figures is labelled with times or
distances, and if they were then presumably the observer's
timeline would be 14 billion years long in both the second
and the third figure. In neither figure is anything observed
to be fourteen billion light years distant, though in the SR
No, you are right, and I did say "14 billion years" in that
paragraph, not "14 billion light years". Going on from that
to say the light originated 14 billion light years away is
a way of defining a distance scale but it is not the SR
definition of distance.
I should have also mentioned the diagrams on the next page
http://www.astro.ucla.edu/~wright/cosmo_03.htm
in particular http://www.astro.ucla.edu/~wright/cosmo230.gif
which is a way of showing the same as the SR diagram on
the previous page. To see why SR coordinates are inadequate,
consider how
http://www.astro.ucla.edu/~wright/cosmo240.gif
would be represented. That is the diagram that I think
conveys the model best, but the scales are non-linear
so as you say "14 billion light years" is I think still
a misleading way of stating it.
Yes, they can be considered slightly less than 14 billion
light years away if now means a horizontal through our 'now'
on the chart (neglecting the change of slope with the Earth's
orbit), and things 15 billion light years away would be
happening before the start of time. It is a problem with the
way the times and distances are plotted. Consider Ned's
comments on Mercator projection below the conformal chart.
On the other hand, a surface of equal cosmic age is the
parabola at the top of the chart and in that 'now' the matter
that emitted the CMBR is even further away. You pays your
money and you takes your pick.
Exactly, and SR cannot represent matter beyond that. That
is one limitation of that representation. You said in your
first post
and
1) There is not a single applicable SR-style frame:
SR only works where gravitational effects are negligible.
On a universal scale the gravitational effects of a universe-full
of matter need to be taken into account.
In those statements you put your finger on the problem. It
really needs GR, not SR.
Right, look again at
"The CMB photons we see today are coming to us from way
across the Universe (about 13 billion light years away,
if for example the Universe is 13 billion years old)."
If our measurements suggested our own timeine was
28 billion years long, that would read:
"The CMB photons we see today are coming to us from way
across the Universe (about 28 billion light years away,
if for example the Universe is 28 billion years old)."
The usual statement would be "At that time, space between
here and there was expanding at exactly 1 light year per
year." You should be able to pull that comment to shreds,
but there is no simple way to put GR into words and you
need to ask someone who understands it a lot better than I.
Simply the fact the the author illustrated the path of the
light we are seeing now. There is of course a whole family
of curves converging at every point on our timeline but
showing them all would make a solid red sheet of paper.
"Orbiting the universe" is only applicable if it is closed.
If as we suspect it is open, the light would pass us and
continue on to infinity. Even in a closed universe AIUI,
the time taken for a single orbit is twice the time from big
bang to big crunch. (I remember this from the relativity or
cosmology FAQ but I haven't checked recently.)
There are some people looking at that possibility but simple
shapes for the universe do not allow it.
George Dishman
I don't see that. People know that, according to the BB
hypothesis, the local matter which the light passes on the
way is receding from us, so they will understand how
light might be "swept along" by the matter and recede from
us even when it is directed towards us. They might make
an analogy with a fish, swimming upstream, which might
get further from the head of the stream if the flow is
too strong for it. It will only make progress when it
enters a region of calmer water, where the flow is not
so strong.
Regardless of the validity or otherwise of this analogy,
it is less confusing to to say what a theory actually says
than to pretend that it actually says something else.
But then, people would assume that the CMBR originates
at a great distance. That might be better than them being
explicitly told that it originates at a great distance, but not
much better.
...
I should have also mentioned the diagrams on the next page
http://www.astro.ucla.edu/~wright/cosmo_03.htm
in particular http://www.astro.ucla.edu/~wright/cosmo230.gif
which is a way of showing the same as the SR diagram on
the previous page.
This diagram *looks* like a SR diagram, because the
past light "cone" is actually depicted as a cone, with the
sides having a 45 degree slope; but the similarity is
superficial. The diagram was made by taking a diagram
in which space is depicted as expanding, with a "pear-
shaped" past light cone, and pummelling it into shape
through coordinate transformations. It is still a depiction
of a non-SR universe. In fact, the untransformed
diagram is one in which the universal expansion slows
down, because of the lambda parameter (as opposed
.to a universe like the one we observe, where the
"expansion" is accelerating).
When the expansion is "divided out", it means that
light which originated locally is depicted as if it came
from a great distance (and travelled, initially, much
faster than light travels locally). When we stretch the
time axis then in addition to the previous distortion
we make it look like things moved more slowly in
the past. This avoids the embarrassment of having
distant light seeming to travel faster than local light;
but why shouldn't light have travelled at a different
speed in the past, if conditions were greatly different
then? Why are we so wedded to the idea of c being
constant that we establish it by decree, and adjust
everything else to make it come about?
http://www.astro.ucla.edu/~wright/cosmo240.gif
would be represented. That is the diagram that I think
conveys the model best, but the scales are non-linear
so as you say "14 billion light years" is I think still
a misleading way of stating it.
I would disagree that this diagram conveys the
model best, and I don't see how it is possible
to use this diagram without being misleading; but
I am not a proponent of the model, so perhaps
I am missing something.
..
The usual statement would be "At that time, space between
here and there was expanding at exactly 1 light year per
year." You should be able to pull that comment to shreds,
but there is no simple way to put GR into words and you
need to ask someone who understands it a lot better than I.
Actually, when I said "it seems to stop" I meant that the
pear-shaped past light cone is not extrapolated into the
future to produce a (possibly pear-shaped) *future* light
cone. The remarkable thing, in my opinion, is that light
is never depicted as completing a single orbit, or even
a full half-orbit. As you say below: "Even in a closed
universe AIUI, the time taken for a single orbit is twice
the time from big bang to big crunch". In other words,
even moments before the big crunch no light will have
completed even just half of an orbit.
When the universe was much younger, an observer
could still have seen CMBR in every direction. The
CMBR photons he could have observed would have
almost completed half an orbit. Suppose that the
observer, instead of observing these photons, had
stood to one side and let them pass by. Would these
photons not, shortly afterwards, gain the distinction
of having completed more than half an orbit?
I know that the answer is "no" in the standard big bang
scenario. This is because the CMBR light is always,
in a sense, approaching the observer who ultimately
intercepts it, even as it seems to recede (in the fish
analogy, it is always "heading upstream" against the
flow of the expansion). After it has passed it is a
receding light front, and always will be thereafter.
In fact, it will recede at an accelerating rate.
I understand this, but I am sceptical about it.
The reasons why light cannot come around for a
second or third pass are tied in with the assumed
homogeneity of the universe. IMO the universe is
not homogeneous, and contains concentrations of
mass sufficiently large to draw light into closed orbits.
In an absolutely homogeneous universe light can
only approach an observer from the direction of the
source of the light. Given inhomogeneity, this ceases
to be true.
..
I've tried to deal with this point above. Yes, in a
*completely homogeneous* closed universe light
can only complete half an orbit in the time from big
bang to big crunch, and yes, the standard theory
assumes homogeneity. I just don't think it should,
given the observed *in*homogeneity.
even those early in the universe's history, will have pear-shaped
past light cones, and pear-shaped future light cones too.
There is no logic that says otherwise, only a questionable
diagram. Therefore the apparently distant galaxies, at various
apparent distances, can all be images of more local galaxies
or their precursors.
There are some people looking at that possibility but simple
shapes for the universe do not allow it.
In GR, it is unlikely that a universe with any mass to
speak of will have a simple shape, unless it is rather more
homogeneous than our universe appears to be.
I am now touching on my own pet theories, as described
on my website, which you may consider to be excessively
speculative. They work for me, but I'll understand if you
don't wish to go in that direction.
Martin Gradwell, mtgradwell@btinternet.com
Back to my home page Contents of This Document
>
Hello,
3 Size of observable universe?
Van: "george todd"
Onderwerp: Re: Size of observable universe?
Datum: woensdag 6 maart 2002 9:22
>
As far I know Universe expands faster than the speed of light...
I think it's all a big conspiracy to confunse us Junior Collage
graduates!
4 Size of observable universe?
Van: "Bill Nelson"
Onderwerp: Re: Size of observable universe?
Datum: donderdag 7 maart 2002 7:21
>
Since the most distant objects are about 14 billion light years away
you might think that they had to take more than 14 billion years to
get there from the big bang, making the universe some 30 billion years
old. But all sorts of observations say this isn't so. Astronomers get
around this by employing the inflation therory which says that the
universe expanded to almost it's current size in the first seconds of
the big bang.
I think it's all a big conspiracy to confunse us Junior Collage
graduates!
Bill Nelson (billn@peak.org)
5 Size of observable universe?
Van: "Henry Wilson"
Onderwerp: Re: Size of observable universe?
Datum: donderdag 7 maart 2002 23:58
>
In sci.astro george todd
>>
Since the most distant objects are about 14 billion light years away
you might think that they had to take more than 14 billion years to
get there from the big bang, making the universe some 30 billion years
old. But all sorts of observations say this isn't so. Astronomers get
around this by employing the inflation therory which says that the
universe expanded to almost it's current size in the first seconds of
the big bang.
I think it's all a big conspiracy to confunse us Junior Collage
graduates!
>
Bill Nelson (billn@peak.org)
At the frontier of scientific invention.
www.users.bigpond.com/rmrabb/HW.htm
6 Size of observable universe?
Van: "Bill Nelson"
Onderwerp: Re: Size of observable universe?
Datum: vrijdag 8 maart 2002 2:18
>>
>
Can you not see George's point?
>
If there was a big bang, which I doubt, then the objects we see as 14
billion years old must have taken at least another 14 billion years to get
where we are observing them now.
Bill Nelson (billn@peak.org)
7 Size of observable universe?
Van: "Jeff Root"
Onderwerp: Re: Size of observable universe?
Datum: vrijdag 8 maart 2002 8:07
>>>
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some
30 billion years old. But all sorts of observations say this
isn't so. Astronomers get around this by employing the inflation
therory which says that the universe expanded to almost it's
current size in the first seconds of the big bang. I think it's
all a big conspiracy to confunse us Junior Collage graduates!
>>
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous information.
>
Can you not see George's point?
If there was a big bang, which I doubt, then the objects we see as
14 billion years old must have taken at least another 14 billion
years to get where we are observing them now.
8 Size of observable universe?
Van: "Joseph Lazio"
Onderwerp: Re: Size of observable universe?
Datum: vrijdag 8 maart 2002 15:27
>
George Todd wrote:
>>>>
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some 30
billion years old.
>
Bill Nelson replied:
>>>
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous
information.
>
Henry Wilson replied to that:
>>
Can you not see George's point? If there was a big bang, which I
doubt, then the objects we see as 14 billion years old must have
taken at least another 14 billion years to get where we are
observing them now.
>
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
>
Light from galaxies which appear to be 10 billion light-years away
was emitted 4 billion years after the Big Bang, and has been
travelling toward us for 10 billion years. It took the matter
which emitted that light 4 billion years to reach the positions
from which the light was emitted.
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
9 Size of observable universe?
Van: "Martin Gradwell"
Onderwerp: Re: Size of observable universe?
Datum: vrijdag 8 maart 2002 17:37
>
On Thu, 7 Mar 2002 06:21:00 +0000 (UTC), Bill Nelson
> >
> >>
Since the most distant objects are about 14 billion light years away
you might think that they had to take more than 14 billion years to
get there from the big bang, making the universe some 30 billion years
old. But all sorts of observations say this isn't so. Astronomers get
around this by employing the inflation therory which says that the
universe expanded to almost it's current size in the first seconds of
the big bang.
I think it's all a big conspiracy to confunse us Junior Collage
graduates!
> >
> >
Bill Nelson (billn@peak.org)
>
Actually it travels along "geodesics", which are said to
be "maximally straight". So does anything else which is
in "free fall", subject only to gravitational influences.
This is because nowadays gravitation is not considered to
be a force, but a warping of the geometry of spacetime.
>
At the frontier of scientific invention.
www.users.bigpond.com/rmrabb/HW.htm
http://www.btinternet.com/~mtgradwell/
10 Size of observable universe?
Van: "Henry Wilson"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 0:35
>
George Todd wrote:
>>>>
>
>>>
>
>>
It's worse than that. Assume there WAS a big bang.
>
Sure, if they had traveled at the speed of light to their presently
observed positions, we could say the big bang (if any) occured something
like 24 billion years ago, depending where we sit in relation to the big
bang's center.
At the frontier of scientific invention.
www.users.bigpond.com/rmrabb/HW.htm
11 Size of observable universe?
Van: "Jan Panteltje"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 0:38
>
The statements by Jeff Root, George Todd, and Henry Wilson seem to be
based on a misconception of the Big Bang. The BB did not occur at a
central point in space, away from which everything has been moving
since. The BB occurred at a point in time, but everywhere in space.
Those distant galaxies didn't have to move to some distant point,
they've always been distant.
Or is this the new Bush US disinformation take of?
>
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
12 Size of observable universe?
Van: "Jeff Root"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 0:39
>>>>>
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some 30
billion years old.
>>>>
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous
information.
>>>
Can you not see George's point? If there was a big bang, which I
doubt, then the objects we see as 14 billion years old must have
taken at least another 14 billion years to get where we are
observing them now.
>>
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
>
The statements by Jeff Root, George Todd, and Henry Wilson seem to
be based on a misconception of the Big Bang. The BB did not occur
at a central point in space, away from which everything has been
moving since. The BB occurred at a point in time, but everywhere
in space. Those distant galaxies didn't have to move to some distant
point, they've always been distant.
13 Size of observable universe?
Van: "Henry Wilson"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 1:26
>
"JR" == Jeff Root
>>
>>>>>
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some 30
billion years old.
>
>>
>
>>>>
>
>>
>
>>>
>
>>
>
>>
>
>
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
At the frontier of scientific invention.
www.users.bigpond.com/rmrabb/HW.htm
14 Size of observable universe?
Van: "Jeff Root"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 1:49
>>
If the furthest objects we can see are 14 billion light years
away, ... then the age of the Universe is 14 billion years ...
>
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. Regardless of the proper time
experienced by those distant stars, in our own reference frame
they were 14 billion light years distant from us, 14 billion years
ago, and they were receding from us at almost lightspeed then.
Extrapolating backwards, and assuming constant speed, they
were in our own vicinity 28 billion years ago. So, bearing in mind
these assumptions, our own timeline should be 28 billion years
long, or thereabouts.
15 Size of observable universe?
Van: "David Evens"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 8:52
>
On 7 Mar 2002 23:07:53 -0800, jeff2@freemars.org (Jeff Root) wrote:
>>
George Todd wrote:
>>>>>
>>
>>>>
>>
>>>
>>
>
It's worse than that. Assume there WAS a big bang.
>
More likely, all matter traveled on average at much less than c, making the
universe possibly many hundreds or even thousands of billions of years old.
At the frontier of antiscientific evasion.
www.users.bigpond.com/rmrabb/HW.htm
16 Size of observable universe?
Van: "Nicolaas Vroom"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 12:47
>
"JR" == Jeff Root
> >
> >>>>
Since the most distant objects are about 14 billion light years
away you might think that they had to take more than 14 billion
years to get there from the big bang, making the universe some 30
billion years old.
>
> >
>
> >>>
> >>>
>
> >
>
> >>
>
> >
>
> >
>
http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN
If the Universe is only 10 billion years old, how can we see objects
that are now 30 billion light years away?
http://www.astro.ucla.edu/~wright/cosmology_faq.html#ct2
The position where an object is Now.
Versus
The position where we see an object Now.
If we claim that an object (galaxy) is now further away
from the origin of the BB (our galaxy ?)
than the age of the universe *3 than that object
has travelled a tremendous distance at a tremendous
rate.
(In principle we can also be at this same distance
from the origin of the BB, which I doubt)
The question is if we can use that speed to calculate
the distant Now (the present distance).
Maybe quasars only have large speeds for a certain
period and than slow down.
>
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
17 Size of observable universe?
Van: "Joseph Lazio"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 15:49
>
Jeff Root replied to Henry Wilson:
>>>
Turn Bill's statement around: If the Universe is 14 billion years
old, then light from the earliest thing we can see, the cosmic
microwave background radiation, which was emitted about 300,000
years after the Big Bang, has been travelling toward us for
13,999,700,000 years. It took the matter which emitted the light
300,000 years to reach the positions from which the light was
emitted.
>
Joseph Lazio replied to Jeff Root:
>>
The statements by Jeff Root, George Todd, and Henry Wilson seem to
be based on a misconception of the Big Bang. The BB did not occur
at a central point in space, away from which everything has been
moving since. The BB occurred at a point in time, but everywhere
in space. Those distant galaxies didn't have to move to some
distant point, they've always been distant.
>
I can't speak for the others, but my reply did not involve the
notion that the Big Bang occurred at a point in space.
>
However, all matter DID have to move to the locations where we see
it now. It has spread out a lot since the Big Bang. A few
seconds after the Big Bang, all the matter which is now in the
Milky Way galaxy was squeezed into a volume smaller than a star
like Betelgeuse.
>
If the Big Bang was 14 billion years ago, then the matter in your
body took 14 billion years to reach the positions in which you see
it now, and the matter in a galaxy a billion light-years away took
13 billion years to reach the positions in which you see it now.
* - - - + - - - + - - - + - - - *
1 2 3 4 5
with galaxies at locations 1 and 5, then in the past these same
galaxies were at the following locations
*---+---+---+---*
1 2 3 4 5
They were still at 1 and 5. Nothing has moved[1]. The distances
between galaxies increase over time, but the galaxies do not move to
different positions.
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
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18 Size of observable universe?
Van: "Jan Panteltje"
Onderwerp: Re: Size of observable universe?
Datum: zaterdag 9 maart 2002 16:53
>
"JR" == Jeff Root
>>
>
>>>>
>
>>
>
>>>
>
>>
>
>>
>
>>
This sucks, I respect your postings, in fact I always read these, they are
a great source of knowledge and I learn from that, but here it is not only
my intuition that starts screaming.
>
* - - - + - - - + - - - + - - - *
1 2 3 4 5
with galaxies at locations 1 and 5, then in the past these same
galaxies were at the following locations
*---+---+---+---*
1 2 3 4 5
They were still at 1 and 5. Nothing has moved[1]. The distances
between galaxies increase over time, but the galaxies do not move to
different positions.
Lt. Lazio, HTML police | e-mail: jlazio@patriot.net
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
You COULD say: 'nothing has moved', and visualizing that,
if you say your yardstick shrunk, then perhaps, using this yardstick, as an
observer INSIDE (the same reference frame) as that bang (big), OK, indeed
leaving out any 'not smoothness' in the expansion.
But there are several things wrong with that line of thought:
First of cause I want to look at it from an 'outside' point, with MY yardstick,
from MY frame of reference, and then, things move.
Second, taking your reasoning, not only is information never lost, but you
could keep processing backwards to zero (approaching size), and still make
that claim?
Obviously things would break down.
Also, there may have been many big bangs, and then it would be a good idea to
take a different point of view then the one in the center of one bang,
So, I am (obviously) not a SR expert.
But keep it sane right?
I see 'space being created' close to the 'flat earth' and sun orbiting the
earth stuff, long ago, things get much simpler if you assume space existed,
and the stars moved away from a center point in a super explosion, big bang,
of which there may have been / may be many.
So, not very scientifically, but a lot more sane then taking some defect math
and doing a divide by zero and multiply by n on both sides of the equations,
putting yourself at the center 'universe', well, don't you see we are but a
speck in the infinity, we this what we can see and call out universe, is not
but a scratch at the surface of something so great and beautiful, you can not
comprehend and capture with math.
19 Size of observable universe?
Van: "George Dishman"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 10:20
>
> >
> >
ago, and they were receding from us at almost lightspeed then.
Extrapolating backwards, and assuming constant speed, they
were in our own vicinity 28 billion years ago. So, bearing in mind
these assumptions, our own timeline should be 28 billion years
long, or thereabouts.
>
>
..The expansion has carried us and the
matter which emitted the CMBR much farther apart, during which
time the CMBR was travelling from the locations that it was
emitted from (all around us) to our current position.
--
George Dishman
The arrow of time points in many directions.
20 Size of observable universe?
Van: "Mark Q"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 10:34
>
So, not very scientifically, but a lot more sane
>
you can not comprehend and capture with math.
21 Size of observable universe?
Van: "George Dishman"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 12:20
>
"Joseph Lazio"
> >
>
>
If we claim that an object (galaxy) is now further away
from the origin of the BB (our galaxy ?)
>
(In principle we can also be at this same distance
from the origin of the BB, which I doubt)
>
What is the difinition of everywhere in space ?
(What is the difinition of always been distant ?)
--
George Dishman
The arrow of time points in many directions.
22 Size of observable universe?
Van: "George Dishman"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 12:26
>
> > >>>
Look at it this way. Forget how long it took for the objects to
get where they are - that is unnecessary and extraneous
information.
>
>
If we claim that an object (galaxy) is now further away
from the origin of the BB (our galaxy ?)
than the age of the universe *3 than that object
has travelled a tremendous distance at a tremendous
rate.
--
George Dishman
The arrow of time points in many directions.
23 Size of observable universe?
Van: "Martin Gradwell"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 13:47
>
The importance of coordinate system being used seems to be
getting missed in some of these discussions.
> >
> > >
>
>
George Dishman
The arrow of time points in many directions.
http://www.btinternet.com/~mtgradwell/
24 Size of observable universe?
Van: "George Dishman"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 15:24
>
> >
The importance of coordinate system being used seems to be
getting missed in some of these discussions.
> > >
> > > >
> >
>
>
In contrast, we have the diagrams in Ned Wright's tutorial.
You say that "The second figure is where values like 14
billion years come from but the third figure is the same
thing plotted in SR coordinates."
>
representation the distant galaxies, which are observed
to be 7 billion light years distant and receding at nearly the
speed of light, can be *inferred* to be 14 billion light
years distant "now" (whatever "now" means).
>
In the SR representation it is remarkable that we can only
see back 7 billion years, and the things we see happening
7 billion years ago are supposedly the first observable
things that ever happened in our universe, even though
our universe is 14 billion years old.
>
Be that as it may, I will (temporarily) assume the applicability
of SR, just to see where it leads. ..
>
However, consider the consequences if one or more of these
assumptions is invalid.
>
Or, maybe we *can* see a distance of fourteen billion
light years in any direction. That is the way most people
seem to interpret the situation, and the lack of proper
labelling on the diagram means that it can support
either interpretation. But then our own timeine would be
28 billion years long
>
In the second diagram, the one with the pear-shaped
past light "cone", the light from supposedly "distant" galaxies
actually originates fairly locally. It moves outward, carried
by the "expansion of space", then back again. Remarkably,
it then seems to stop. ...
>
.. Well, the diagram does only depict
the past light cone of a single current event, but why should
we suppose that this light has diverged and reconverged
only once in the history of the universe? What is so special
about the current moment, that makes light converge now
>
for the first time? Obviously, nothing. When light converges
at a point, and there is no observer or other obstacle located
at that point, the light continues, re-diverging. It can orbit the
universe several times before being intercepted. Past events,
>
even those early in the universe's history, will have pear-shaped
past light cones, and pear-shaped future light cones too.
There is no logic that says otherwise, only a questionable
diagram. Therefore the apparently distant galaxies, at various
apparent distances, can all be images of more local galaxies
or their precursors.
--
George Dishman
The arrow of time points in many directions.
25 Size of observable universe?
Van: "Martin Gradwell"
Onderwerp: Re: Size of observable universe?
Datum: zondag 10 maart 2002 22:07
>
If you say
to the average layman "The CMBR originated at a distance
of 300k light years, and has been travelling towards us for
the last 13.997 billion years. It travels at the speed of
light relative to all local matter it passes on the way."
you are only going to create confusion.
>
If these pages just said the CMBR was emitted 300k years
after the start of time and didn't comment on distance,
I think it would be much simpler.
>
>
To see why SR coordinates are inadequate,
consider how
> >
In the second diagram, the one with the pear-shaped
past light "cone", the light from supposedly "distant" galaxies
actually originates fairly locally. It moves outward, carried
by the "expansion of space", then back again. Remarkably,
it then seems to stop. ...
>
>
"Orbiting the universe" is only applicable if it is closed.
If as we suspect it is open, the light would pass us and
continue on to infinity. Even in a closed universe AIUI,
the time taken for a single orbit is twice the time from big
bang to big crunch. (I remember this from the relativity or
cosmology FAQ but I haven't checked recently.)
>
> >
>
>
--
George Dishman
The arrow of time points in many directions.
http://www.btinternet.com/~mtgradwell/
Created: 26 March 2002
