Expansion of universe

If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

On Apr 19, 9:50*pm, Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

Distance is growing in all of space. Galaxies were smaller.

Mitch Raemsch

Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

If it's expanding then the separation rate will increase
over time (the further away it gets, the faster it will go).

On 4/19/10 11:50 PM, Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

H_o = 71 km/s/Mpc

No Center
http://www.astro.ucla.edu/~wright/nocenter.html
http://www.astro.ucla.edu/~wright/infpoint.html

Also see Ned Wright's Cosmology Tutorial
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html
http://www.astro.ucla.edu/~wright/CosmoCalc.html

WMAP: Foundations of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni.html

WMAP: Tests of Big Bang Cosmology
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html

Sam Wormley wrote:
On 4/19/10 11:50 PM, Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

H_o = 71 km/s/Mpc

I just wished they'd used some more 'natural' units. Mixing
two different units of length in the same parameter just obscures
what it really says:

H_o = 1/(age of the universe) or H_o = c/(radius of the universe).

Much clearer, no?

Jeroen Belleman

On 4/20/10 9:49 AM, Jeroen Belleman wrote:
Sam Wormley wrote:
On 4/19/10 11:50 PM, Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

H_o = 71 km/s/Mpc

I just wished they'd used some more 'natural' units. Mixing
two different units of length in the same parameter just obscures
what it really says:

H_o = 1/(age of the universe) or H_o = c/(radius of the universe).

Much clearer, no?

Jeroen Belleman

Convenient units of measure for astronomers might not be best
for you, Jeroen.

Do you like this better?
71 ± 2(stat) ± 6 (systematic) km/s/Mpc = 2.30095131 × 10^-18 hertz

"Lax" wrote in message
...
| If the expansion of the universe is causing some galaxy to move away
| from us at some velocity and if the expansion of the universe stays
| constant, will the galaxy always be moving away from us at that
| velocity (if nothing abnormal happens)?
|

Surprising as it may seem, the galaxy concerned will appear to accelerate
away! This is the way we currently measure large distances in the
universe - the further away galaxies are, the faster they appear to move
away from us. This is measured by the Doppler effect on the wavelengths of
light we see - the "red shift". Spectral lines emitted / absorbed by
various elements should be at a definite wavelength - if they appear
elsewhere then the light must be appearing redder or bluer depending on
whether the object concerned is receding or approaching. This is the same
principle which makes the noise from a moving object appear to drop in pitch
as it passes you or how Doppler radar spots the unusual wind patterns
accompanying tornadoes.

Google "Hubble's Law" to find out the story of how this was discovered - it
is no coincidence that the most poweful telescope we currently have - the
Hubble Space Telescope - is named after this gentleman.

All this also means there is an "event horizon" - galaxies more than a
certain distance away will appear to be moving away faster than the speed of
light so no information from them can ever reach us unless...

The rate of expansion may not be constant, and that depends on how much mass
there is in the universe. If there is more than a certain amount, the
expansion will eventually be slowed and reversed, with a "big crunch" in the
far distant future. Long before the "big crunch" the now blue-shifted light
from the sky will vapourize all matter.

But the smart money is on there being not enough mass, so the universe will
expand indefinitely. There may also be an energy field which opposes
gravity and is actually accelerating the expansion. If this is the case
then eventually any remaining objects in the universe will have a very
lonely end as everything else will have been carried beyond the "event
horizon" by the relentless expansion.
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

Sam Wormley wrote:
On 4/20/10 9:49 AM, Jeroen Belleman wrote:
Sam Wormley wrote:

H_o = 71 km/s/Mpc

I just wished they'd used some more 'natural' units. Mixing
two different units of length in the same parameter just obscures
what it really says:

H_o = 1/(age of the universe) or H_o = c/(radius of the universe).

Much clearer, no?

Jeroen Belleman

Convenient units of measure for astronomers might not be best
for you, Jeroen.

Do you like this better?
71 ± 2(stat) ± 6 (systematic) km/s/Mpc = 2.30095131 × 10^-18 hertz

Yes, if I were to use H_o in a publication, I might indeed state its
value as being 2.30 aHz. SI rules. Perhaps I'd use 2.30 as^-1, to
avoid the suggestion the universe is periodic at that rate. ;-)

The remainder of the figures after the decimal point are rubbish,
of course.

Jeroen Belleman

"Jeroen Belleman" wrote:
Sam Wormley wrote:
Jeroen Belleman wrote:

Sam Wormley wrote:
H_o = 71 km/s/Mpc

Jeroen Belleman wrote:
I just wished they'd used some more 'natural' units. Mixing
two different units of length in the same parameter just obscures
what it really says:
H_o = 1/(age of the universe) or H_o = c/(radius of the universe).
Much clearer, no?
Jeroen Belleman

Sam Wormley wrote:
Convenient units of measure for astronomers might not be best
for you, Jeroen.
Do you like this better?
71 ± 2(stat) ± 6 (systematic) km/s/Mpc = 2.30095131 × 10^-18 hertz

Jeroen Belleman:
Yes, if I were to use H_o in a publication, I might indeed state its
value as being 2.30 aHz. SI rules. Perhaps I'd use 2.30 as^-1, to
avoid the suggestion the universe is periodic at that rate. ;-)
The remainder of the figures after the decimal point are rubbish,
of course.

hanson wrote:
Well whatever your H preference is... the editor will dis- or a-gree.
But you are right about "the figures after the decimal point "
H and G are related, and G is still not accurately measured.
Maybe b_r, some 5.5*10^-8 times smaller than "g" maybe
be measurable with greater accuracy and put some veracity
into the 1234 cosmic envelope equation concatenate:
||||||| c = (GM/R)^1/2 = (GMH)^1/3 = (GM*b_r)^1/4 ||||||| see:
http://tinyurl.com/1234-cosmic-envelope
Have fun, dude... ahahahaha... ahahahahanson

"Jeroen Belleman" wrote in message
...
Sam Wormley wrote:
On 4/19/10 11:50 PM, Lax wrote:
If the expansion of the universe is causing some galaxy to move away
from us at some velocity and if the expansion of the universe stays
constant, will the galaxy always be moving away from us at that
velocity (if nothing abnormal happens)?

H_o = 71 km/s/Mpc

I just wished they'd used some more 'natural' units. Mixing
two different units of length in the same parameter just obscures
what it really says:

H_o = 1/(age of the universe)

That's not the case if the expansion is accelerating (as seems to be the
case)

H_o = c/(radius of the universe).

Not really, as that assumes that the universe is completely within our
cosmological horizon (I think!)