Expanding Universe

1 Vignesh	Expanding Universe	maandag 12 november 2001 0:19
2 Greg Neill	Re: Expanding Universe	maandag 12 november 2001 0:55
3 PoorRichard	Re: Expanding Universe	maandag 12 november 2001 1:36
4 dlzc@aol.com (formerly)	Re: Expanding Universe	maandag 12 november 2001 3:23
5 Vignesh	Re: Expanding Universe	maandag 12 november 2001 5:49
6 Nicolaas Vroom	Re: Expanding Universe	maandag 12 november 2001 14:11
7 PoorRichard	Re: Expanding Universe	maandag 12 november 2001 15:13
8 Martin Hardcastle	Re: Expanding Universe	maandag 12 november 2001 20:36
9 George Dishman	Re: Expanding Universe	maandag 12 november 2001 22:29
10 PoorRichard	Re: Expanding Universe	maandag 12 november 2001 23:06
11 Nicolaas Vroom	Re: Expanding Universe	dinsdag 13 november 2001 20:23
12 retiche@home.com	Re: Expanding Universe	woensdag 14 november 2001 16:10
13 PoorRichard	Re: Expanding Universe	woensdag 14 november 2001 16:43
14 Joseph Lazio	Re: Expanding Universe	donderdag 15 november 2001 13:47
15 Jonathan Silverlight	Re: Expanding Universe	donderdag 15 november 2001 23:07
16 Joseph Lazio	Re: Expanding Universe	vrijdag 16 november 2001 1:08
17 William C. Keel	Re: Expanding Universe	vrijdag 16 november 2001 14:52

Hello

I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory?

Thanks

"Vignesh" iluvastro@yahoo.com wrote in message news:75e0808e.0111111519.6dfb141a@posting.google.com...

>

Hello I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory?

The Theory of Relativity states that nothing material can move as fast or faster than light *in* space. But no such restriction applies to space itself which may be growing larger or smaller, carrying the embedded objects along with it. With Hubble's law we have the case where space is expanding, that is, space is being created between objects at great distances.

So, yes it's possible for distant galaxies to be receding at or faster than the speed of light (although we wouldn't be able to see them as their light would be redshifted to undetectable energies, or they would be so far away that their light would not have been able to reach us over the age of the universe).

"Vignesh" iluvastro@yahoo.com wrote in message news:75e0808e.0111111519.6dfb141a@posting.google.com...

>

Hello I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory? Thanks

Dear Vignesh:

>	This would be true if redshift was strictly due to recession velocity. But there has been considerable evidence collected over the past 30 years which shows that there appears to be a 'non-velocity' component to redshifts. So, in other words, Hubble's relation is flawed.

Hubble also didn't like the redshift vs. distance relation being represented as velocity based. He just didn't have any other models at the time.

David A. Smith

> >

I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory?

"Greg Neill" wrote in message news:...

>	"Vignesh" iluvastro@yahoo.com wrote in message news:75e0808e.0111111519.6dfb141a@posting.google.com...

> >

Hello I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory?

>

The Theory of Relativity states that nothing material can move as fast or faster than light *in* space. But no such restriction applies to space itself which may be growing larger or smaller, carrying the embedded objects along with it. With Hubble's law we have the case where space is expanding, that is, space is being created between objects at great distances. So, yes it's possible for distant galaxies to be receding at or faster than the speed of light (although we wouldn't be able to see them as their light would be redshifted to undetectable energies, or they would be so far away that their light would not have been able to reach us over the age of the universe).

Hello Greg

Thanks.I am sorry if this question sounds prepostereous.If this explanation is true can,we as a part of one embedded space(galaxy) approach another galaxy with the speed of light or some super human speed close to that of light?will this take us any way near to other galaxies which may have some form of life?

(p.s) Can u suggest some material or book which explains the concept of space and time in a simple way?

Thanks

Vignesh iluvastro@yahoo.com schreef in berichtnieuws 75e0808e.0111112049.5ce54180@posting.google.com...

>	"Greg Neill" wrote in message

news:...

> >	"Vignesh" iluvastro@yahoo.com wrote in message news:75e0808e.0111111519.6dfb141a@posting.google.com...

> > >

Hello I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory?

> >

The Theory of Relativity states that nothing material can move as fast or faster than light *in* space. But no such restriction applies to space itself which may be growing larger or smaller, carrying the embedded objects along with it. With Hubble's law we have the case where space is expanding, that is, space is being created between objects at great distances. So, yes it's possible for distant galaxies to be receding at or faster than the speed of light (although we wouldn't be able to see them as their light would be redshifted to undetectable energies, or they would be so far away that their light would not have been able to reach us over the age of the universe).

>

Hello Greg Thanks.I am sorry if this question sounds prepostereous.If this explanation is true can,we as a part of one embedded space(galaxy) approach another galaxy with the speed of light or some super human speed close to that of light?will this take us any way near to other galaxies which may have some form of life? (p.s) Can u suggest some material or book which explains the concept of space and time in a simple way?

A very good book which discusses this subject is the book UNIVERSE by Kaufmann. I have the second edition
Chapter 27 is called: Quasars and active galaxies.
Box 27.1 is called: The realistic redshift. It explains that for slow speeds you can use the formula:
v = c*z For high velocities you must use the formula:
v/c = (z+1)^2 - 1 / { (z+1) ^ 2 +1} The text in the book explains why.
Using z=3.78 we obtain v/c = 0.92 Or v = 0.92 * c

This means that galaxies/quasars can not recede faster than the speed of light.

You should also study in Chapter 26 called: Galaxies Box 26-2: The Hubble law as a distance indicator.

The text near box 27.1 raises a different question: How can Quasar OH 471 (z=3.4) be 18 billion light years away while the image of the quasar that we see corresponds to the state of the Universe roughly 2 billion years after the Big Bang. My understanding is that 2 billion years after the Big Bang the size of the Universe was 2 billion light years.

IMO assuming that the Big Bang happend 20 billion years ago the maximum distance you can see something is 10 billion light years away when the Universe was already 10 billion years old.

"Nicolaas Vroom" nicolaas.vroom@pandora.be wrote in message news:3UPH7.22779

>

The text near box 27.1 raises a different question: How can Quasar OH 471 (z=3.4) be 18 billion light years away while the image of the quasar that we see corresponds to the state of the Universe roughly 2 billion years after the Big Bang. My understanding is that 2 billion years after the Big Bang the size of the Universe was 2 billion light years. IMO assuming that the Big Bang happend 20 billion years ago the maximum distance you can see something is 10 billion light years away when the Universe was already 10 billion years old.

In article <3UPH7.22779$XM4.1213@afrodite.telenet-ops.be>, Nicolaas Vroom nicolaas.vroom@pandora.be wrote:

>	Chapter 27 is called: Quasars and active galaxies. Box 27.1 is called: The realistic redshift. It explains that for slow speeds you can use the formula: v = c*z For high velocities you must use the formula: v/c = (z+1)^2 - 1 / { (z+1) ^ 2 +1}

Actually the recession speed is not well defined -- you should ask what sort of distance and what sort of time are appearing in v = dr/dt. Depending on your definition of distance, you can certainly get v > c. The relativistic Doppler shift, which is what's being used here if I'm not mistaken, does not give a meaningful answer.

The answer to this FAQ is here: http://www.astro.ucla.edu/~wright/cosmology_faq.html#FTL

>	The text near box 27.1 raises a different question: How can Quasar OH 471 (z=3.4) be 18 billion light years away while the image of the quasar that we see corresponds to the state of the Universe roughly 2 billion years after the Big Bang.

The answer to this FAQ is here: http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN

Martin
--
Martin Hardcastle Department of Physics, University of Bristol
Never attribute to malice what can adequately be explained by stupidity Please replace the xxx.xxx.xxx in the header with bristol.ac.uk to mail me

"PoorRichard" wrote in message news:xQEH7.16613$I6.3763793@typhoon.ne.mediaone.net...

>	This would be true if redshift was strictly due to recession velocity. But there has been considerable evidence collected over the past 30 years which shows that there appears to be a 'non-velocity' component to redshifts. So, in other words, Hubble's relation is flawed.

Since I have recently quoted:

http://arxiv.org/abs/astro-ph/0104382

in a number of posts as relevant to this question, I would be very interested to read the papers to which you refer. Can you please post the relevant citations. -- George Dishman The arrow of time points in many directions.

"George Dishman" wrote in message news:1005600631.15810.0.nnrp-10.9e989a91@news.demon.co.uk...

>	"PoorRichard" wrote in message news:xQEH7.16613$I6.3763793@typhoon.ne.mediaone.net...

> >	This would be true if redshift was strictly due to recession velocity.

But

> >	there has been considerable evidence collected over the past 30 years which shows that there appears to be a 'non-velocity' component to redshifts. So, in other words, Hubble's relation is flawed.

>	Since I have recently quoted: http://arxiv.org/abs/astro-ph/0104382 in a number of posts as relevant to this question, I would be very interested to read the papers to which you refer. Can you please post the relevant citations. -- George Dishman The arrow of time points in many directions.

Martin Hardcastle schreef in berichtnieuws GMpD4G.I5E@bath.ac.uk...

>	In article <3UPH7.22779$XM4.1213@afrodite.telenet-ops.be>, Nicolaas Vroom nicolaas.vroom@pandora.be wrote:

> >	Chapter 27 is called: Quasars and active galaxies. Box 27.1 is called: The realistic redshift. It explains that for slow speeds you can use the formula: v = c*z For high velocities you must use the formula: v/c = (z+1)^2 - 1 / { (z+1) ^ 2 +1}

>

Actually the recession speed is not well defined -- you should ask what sort of distance and what sort of time are appearing in v = dr/dt. Depending on your definition of distance, you can certainly get v > c. The relativistic Doppler shift, which is what's being used here if I'm not mistaken, does not give a meaningful answer. The answer to this FAQ is here: http://www.astro.ucla.edu/~wright/cosmology_faq.html#FTL

> >	The text near box 27.1 raises a different question: How can Quasar OH 471 (z=3.4) be 18 billion light years away while the image of the quasar that we see corresponds to the state of the Universe roughly 2 billion years after the Big Bang.

>	The answer to this FAQ is here: http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN

the "many distance definitions" FAQ at http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD starts with the following sentence: " With the correct interpretation of the variables, the Hubble law (v = HD) is true for all values of D, even very large ones which give v > c." which raises some doubts. IMO the Hubble law is "true" for all combinations of v and D for which we have performed observations and which all give the same value for H. (corrected ?)

For example Hubble Law is not true for Andromeda galaxy which approaches our gallaxy.

Question: For which stars ? and of galaxies have we calculated/measured both v and D. Is there an URL with this information ?

No, no part of the Universe exceeds the velocity of light, in fact, when analyzed correctly, the reverse is true, The Universe is actually contracting slightly andonly appears to be expanding due to relativistic effects. The subject is handled quite rigorously in http://members.home.net/retiche/grav0.htm without a resort to sophisticated mathematics.

On 11 Nov 2001 15:19:07 -0800, iluvastro@yahoo.com (Vignesh) wrote:

>

Hello I am new to Astro group.I have few doubts abt Hubble's law.It states that the velocity of a receding galaxy is directly proprotional to it's distance from us.So it implies that the farther the galaxy the faster it's velocity is.Does this situation give us a theoretical possibility that a galaxy may be receding at the speed of light, which violates Einstein's theory? Thanks

retiche@home.com wrote in message news:3bf2889b.4791256@news...

>	relativistic effects. The subject is handled quite rigorously in http://members.home.net/retiche/grav0.htm without a resort to sophisticated mathematics.

>>>>>

"NV" == Nicolaas Vroom nicolaas.vroom@pandora.be writes:

NV> Question: For which stars ? and of galaxies have we calculated/measured both v and D. Is there an URL with this information ?

No individual stars have measured Hubble recession velocities. An individual star at a sufficiently large distance to participate in the Hubble flow would be too faint to be detectable.

As for galaxies with measured values for v and D, I presume you mean those for which D has been measured independently of the redshift. I would start at the ADS, URL: http://adsabs.harvard.edu/abstract_service.html. Riccardo Giovanelli has done a lot of work on this topic, so I'd start with looking at his papers.

-- 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

In article , Joseph Lazio writes:

>>>>>>

"NV" == Nicolaas Vroom writes:

>

>>	NV Question: For which stars ? and of galaxies have we calculated/measured both v and D. Is there an URL with this information ?

>	No individual stars have measured Hubble recession velocities. An individual star at a sufficiently large distance to participate in the Hubble flow would be too faint to be detectable.

???

They can certainly resolve stars in the Virgo cluster. That's why they launched HST, surely? (yes, I know there were other reasons :-) Or are you saying they can't get useful spectra of those stars?

>>>>>

"JS" == Jonathan Silverlight writes:

JS> In article , Joseph Lazio JS> writes:

>>>>>>>

"NV" == Nicolaas Vroom writes:

>>

>>>	NV Question: For which stars ? and of galaxies have we calculated/measured both v and D. Is there an URL with this information ?

>>	No individual stars have measured Hubble recession velocities. An individual star at a sufficiently large distance to participate in the Hubble flow would be too faint to be detectable.

JS> ???

JS> They can certainly resolve stars in the Virgo cluster. That's why they launched HST, surely? (yes, I know there were other reasons :-) Or are you saying they can't get useful spectra of those stars?

I'm not sure if one could obtain a spectrum of an individual star in the Virgo cluster, though, I'd be inclined to doubt it. Even if one could, the Virgo cluster is not far enough away. There are galaxies in the Virgo cluster with *blueshifts*. That means that the peculiar velocities of the cluster are comparable to or exceed the Hubble flow at the distance of the Virgo cluster.

-- 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

Jonathan Silverlight wrote:

>	In article , Joseph Lazio writes:

>>>>>>>

"NV" == Nicolaas Vroom writes:

>>

>>>	NV Question: For which stars ? and of galaxies have we calculated/measured both v and D. Is there an URL with this information ?

>>	No individual stars have measured Hubble recession velocities. An individual star at a sufficiently large distance to participate in the Hubble flow would be too faint to be detectable.

>

???

>	They can certainly resolve stars in the Virgo cluster. That's why they launched HST, surely? (yes, I know there were other reasons :-) Or are you saying they can't get useful spectra of those stars?

I don't think there are any individual stars in Virgo (apart from the occasional supernova, which may count for this purpose) for which useful spectra can yet be obtained. However, from the ground, patience will yield a detection of the [O III] 5007-Angstrom emission line from planetary nebulae in Virgo which is sufficient to do dynamics, so that counts (in a way) as stellar spectra showing the Hubble expansion.

Bill Keel

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