Seeing old galaxies

Just been listenin to "In Our Time"


If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Wouldn't the universe be a maximum of 1 billion light years across when
this light was created and it therefore would have gone past us 12 bn
years ago? I thought that the speed of light is an absolute limit, so
to repeat the obvious it would have been produced when the universe was
1bn years old, but 13 bn light years across (mimimum).

Please answer ASAP as I need to sleep.

Thanks.

PS No maths please.

PPS This probably a really stupid question and the 1bn light years bit
is more to illustrate the question rather that being a real figure.

nous a donc écrit :

Just been listenin to "In Our Time"


If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Wouldn't the universe be a maximum of 1 billion light years across
when this light was created and it therefore would have gone past us
12 bn years ago? I thought that the speed of light is an absolute
limit, so to repeat the obvious it would have been produced when the
universe was 1bn years old, but 13 bn light years across (mimimum).

Please answer ASAP as I need to sleep.

OK, as this seems to be an emergency, I suggest you to read this short page
http://www.atlasoftheuniverse.com/redshift.html

PS No maths please.

PPS This probably a really stupid question and the 1bn light years bit
is more to illustrate the question rather that being a real figure.

There is no stupid question.
Only stupid answers )

--
Norbert. (no X for the answer)
======================================
knowing the universe - stellar and galaxies evolution
http://nrumiano.free.fr
images of the sky http://images.ciel.free.fr
======================================

wrote in message
ups.com...
Just been listenin to "In Our Time"


If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Wouldn't the universe be a maximum of 1 billion light years across when
this light was created and it therefore would have gone past us 12 bn
years ago? I thought that the speed of light is an absolute limit, so
to repeat the obvious it would have been produced when the universe was
1bn years old, but 13 bn light years across (mimimum).


Thank you for posing that question.

I have often wondered about this apparent paradox, but I haven't asked the
question for fear of ridicule.


The lack of answers suggests that you may have a very good point.


Regards


Donal
--

Donal wrote:
wrote in message
ups.com...
Just been listenin to "In Our Time"

If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Because it happens to have been the right distance away for light that
left it 13bn years ago to reach the earth now. Common sense
definitiions of time and space do not work well on cosmological time
scales.

Wouldn't the universe be a maximum of 1 billion light years across when
this light was created and it therefore would have gone past us 12 bn
years ago? I thought that the speed of light is an absolute limit, so
to repeat the obvious it would have been produced when the universe was
1bn years old, but 13 bn light years across (mimimum).

By the time the universe was 1bn years old its extent was effectively
inifinite. The the current favoured explanation of early inflation is
widely accepted by most astrophysicists as matching the observations
very well. Refinements will doubtless improve on it.

A short intro to inflation by John Gribbin (sans maths) is online at:
http://www.lifesci.sussex.ac.uk/home...bbin/cosmo.htm

And another set of cosmology FAQs that eschew the mathematics by Eric
Linder:
http://supernova.lbl.gov/~evlinder/umass/faq.html

And a slightly harder more modern treatment with pictures from DAMPT
http://www.damtp.cam.ac.uk/user/gr/p...nf_lowden.html

Ned Wright's cosmology FAQ deals with another more common variation of
your question:
http://www.astro.ucla.edu/~wright/co...y_faq.html#ct2

Unfortunately the precise answers become rapidly mathematical. Natural
language is not good for describing abstract concepts like these with
anything like adequate precision.

Thank you for posing that question.

I have often wondered about this apparent paradox, but I haven't asked the
question for fear of ridicule.

There are no stupid questions. It is better to ask a question than
remain ignorant. You would be amazed how often apparently stupid
questions lead to progress.

The lack of answers suggests that you may have a very good point.

Amateur astronomers tend not to follow cosmology of the early universe
very closely so your pool of respondents in here is a bit limited.

And sadly sci.astro where you could try asking the question is overrun
with demented netkooks. You might well find more in the FAQs for
sci.astro.research or on Ned Wright's cosmology FAQ. Most academic
research sites will have reasonably mainstream views on the topic but
very few of them are non-mathematic treatments.

And without the underpinning of a mathematical formalism it can easily
look like an ad hoc handwaving explanation.

Regards,
Martin Brown

"Donal" wrote in message
...

wrote in message
ups.com...
Just been listenin to "In Our Time"


If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Wouldn't the universe be a maximum of 1 billion light years across when
this light was created and it therefore would have gone past us 12 bn
years ago? I thought that the speed of light is an absolute limit, so
to repeat the obvious it would have been produced when the universe was
1bn years old, but 13 bn light years across (mimimum).


Thank you for posing that question.

I have often wondered about this apparent paradox, but I haven't asked the
question for fear of ridicule.


The lack of answers suggests that you may have a very good point.


Regards


Donal
--





Martin Brown gave an excellent reply, but I will add something else. The
question was posed in a simple way, but the answer is a bit more
complicated; for example, it was said that we see the light now which was
generated 13 billion years ago by the galaxy; however if that is so, of
course the galaxy must be hugely further away by now.
Ned Wright explains this stuf rather well, but I will warn you that you will
not look at his web page for twenty minutes and understand all, it takes a
lot of time and a large number of visits to begin to get the hang of it.

wrote in message
ups.com...
Just been listenin to "In Our Time"


If Hubble captures the light of galaxies (not just background
radiation) that are 13 bn years old and the universe is approximately
14 bn years old, how come we can see it?

Wouldn't the universe be a maximum of 1 billion light years across when
this light was created and it therefore would have gone past us 12 bn
years ago? I thought that the speed of light is an absolute limit, so
to repeat the obvious it would have been produced when the universe was
1bn years old, but 13 bn light years across (mimimum).

Please answer ASAP as I need to sleep.

Thanks.

PS No maths please.

PPS This probably a really stupid question and the 1bn light years bit
is more to illustrate the question rather that being a real figure.

It would be easier with a diagram but here goes.
The speed of light isn't an absolute limit to the rate of expansion of
the universe. 13 Bn ly is the
"lookback time" of Hubble, it can see galaxies as far back/away as 13Bn
years ago. There may be more
to see further back, or space may have expanded enough to shift really
old/distant light out of the
visible.
================================================== =============================
http://zebu.uoregon.edu/~js/ast123/lectures/lec14.html

Expanding Universe:

A common question in cosmology is "why are all the galaxies receding
from each other?" In other
words, the cosmological principle requires that we not be at a special
place in the Universe. Since
all the galaxies are moving away from us, then they must all be moving
away from each other. This is
explained if the Universe, as a whole, is expanding.

In a real sense, Hubble's law, the recession velocity of galaxies, is
an illusion. The galaxies are
not moving, the space between them is literally expanded.

Lookback Time:
The large size of the Universe, combined with the finite speed for
light, produces the phenomenon
known as lookback time. Lookback time means that the farther away an
object is from the Earth, the
longer it takes for its light to reach us. Thus, we are looking back in
time as we look farther
away.


The galaxies we see at large distances are younger than the galaxies we
see nearby. This allows us
to study galaxies as they evolve. Note that we don't see the
individuals evolve, but we can compare
spirals nearby with spirals far away to see how the typical spiral has
changed with time.

http://www.citebase.org/cgi-bin/cita...tro-ph/9306002

We present explicit expressions for the calculation of cosmological look back time, for zero
cosmological constant and arbitrary density parameter ?, which, in the limit as redshift becomes
infinite, give the age of the universe. The case for non-zero cosmological constant is most
easily solved via numerical integration. The most distant objects presently known (approaching
redshift z = 5) have implied ages of ? 1-2 Gyr after the the Big Bang. The range of such age is
narrow, in spite of a variety of cosmological models one might choose. We give a graphical
representation of a variety of cosmological models and show that a wide range of Hubble constants
and values of the age and density of the universe compatible with modern studies are consistent
with adoption of a positive cosmological constant.