Exploring Redshift of Distant Galaxies - Experimental Data

In summary, the conversation discusses the possibility of using Doppler redshift to explain the observed redshift of distant galaxies, but it is argued that this would require them to be moving at speeds faster than the speed of light, which is not possible. Cosmological redshift is proposed as the true explanation, but the question is raised about how this can be reconciled with Hubble's Law and the deceleration of galaxies. The topic of Vera Rubin's anomalous measurements of galactic stars and the constant cosmic background radiation is also brought up, with some papers suggesting that the background radiation should have been absorbed by galaxies and dust. The conversation ends with a clarification about the relationship between cosmological redshift and recession speeds of galaxies.
  • #1
Kamil Szot
37
0
Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted?

Would the speeds of the galaxies necessary for Doppler redshift to explain all of the observed galaxies redshift be unreasonable or is there something else that prevents such explanation to be sufficient?

I noticed that distance to far galaxies are given in terms of their redshift rather than lightyears. Do we have any other way to tell how far these galaxies are?

What is the farthest data point of distance and redshift that we can use to verify how they should correlate?

Could you point me to some experimental data of this kind?
 
Space news on Phys.org
  • #2


This subject is brought up here so often that I'm sure others will respond (or you COULD just do a forum search), but I will simply point out that if you argue that all redshift is Doppler redshift instead of Cosmological redshift, you have to argue that distant galaxies are MOVING at much faster than the speed of light, which is silly. Cosmological redshift, the true reason, simply shows that they are receeding at faster than light, not moving at faster than light.
 
  • #3


phinds said:
This subject is brought up here so often that I'm sure others will respond (or you COULD just do a forum search),

I tried that. Failed. So I asked.

I'm very thankful for your answer (even more if the subject is brought here that often).

phinds said:
but I will simply point out that if you argue that all redshift is Doppler redshift instead of Cosmological redshift, you have to argue that distant galaxies are MOVING at much faster than the speed of light, which is silly.

Is there some maximum doppler redshift that can be achieved by shooting object away from us at almost the speed of light and we observed galaxies that exceed this limit?

How fast emmiter would have to move away from us to turn gamma photon into microwave background photon?
 
  • #4


I found some cool material on the subject: http://www.astro.ucla.edu/~wright/cosmo_01.htm

Calculators for things I don't understand included. :-)

I don't understand the part that says:

In special relativity we know that the redshift is given by
1 + z = sqrt((1+v/c)/(1-v/c)) so v = cz + ...
but the higher order corrections (the "...") in cosmology depend on general relativity and the specific model of the Universe.

especially: so v = cz + ...
because I'd rather think that v = (2cz+cz2) / (2+2z+z2) which gives you speeds lowen than c for all possible z.
 
Last edited:
  • #5


Kamil Szot said:
Is there some maximum doppler redshift that can be achieved by shooting object away from us at almost the speed of light and we observed galaxies that exceed this limit?

Google cosmological redshift
 
  • #6
  • #7


I understand that Hubble, De Broglie, and Enrico Fermi, passed away without believing in the expansion of the universe because the redshift of galaxies are the same for those that are at the same distance from earth.

This would imply the Earth is at the center of the universe in a big bang expanding universe.

Vera Rubin measured an anomalous cosmological redshift of peripheral galactic stars.

Her published claim to have measured anomalous speed of peripheral galactic stars is her personal opinion.Also, how does one explain the constant cosmic background radiation? Where does it get it's energy from?

A number of papers I've come across have established that it should have been absorbed by galaxies and intergalactic dust several billions of years ago because it is very faint.
 
  • #8


I've read that Z=1.4 is the red shift indicating a cosmological separation speed equal to the speed of light, and some galaxies have a red shift of Z = 8. So, does that mean they are moving away from at 5.7 times the speed of light? If so, this conflicts with something I read that said the fastest speed recorded so far is about twice the speed of light.
 
  • #9


marksesl said:
I've read that Z=1.4 is the red shift indicating a cosmological separation speed equal to the speed of light, and some galaxies have a red shift of Z = 8. So, does that mean they are moving away from at 5.7 times the speed of light? If so, this conflicts with something I read that said the fastest speed recorded so far is about twice the speed of light.

Objects at the very edge of the observable universe are receeding from us at about 3c but no speeding tickets are issued because they are really sitting still --- it's just that the distance between us is expanding. Google "metric expansion" for details.
 
  • #10


Yes, I know the difference between cosmological and Doppler red shift. The point is, the one's that are the farthest are Z = 8, and Z = 1.4 indicates a recession at light speed. So, 8 divided by 1.4 = 5.7 Does that mean that the galaxies are receding at 5.7 times the speed of light? Apparently that nust not be the correct way to compare the red shift numbers because you say the fastest are at 3c, not 5.7c.
 
  • #11


marksesl said:
Yes, I know the difference between cosmological and Doppler red shift. The point is, the one's that are the farthest are Z = 8, and Z = 1.4 indicates a recession at light speed. So, 8 divided by 1.4 = 5.7 Does that mean that the galaxies are receding at 5.7 times the speed of light? Apparently that must not be the correct way to compare the red shift numbers because you say the fastest are at 3c, not 5.7c.

that's true! the instantaneous recession (as of today or as of when the light was emitted or at whatever moment) is NOT proportional to the redshift!

as a rule you need a calculator to get the recession from the redshift, it isn't a simple linear relation.

The speed that the distance is increasing TODAY happens to be proportional to the DISTANCE today, so there is a very easy way to get it. Just go to Ned Wright's calculator which gives the today distance (labeled comoving radial) and find the distance for z=8 and for z=1.4 and take the ratio of the two distances.

That ratio of the two distances will be the speed of distance increase, as of today, as a multiple of c.

You can make that more accurate by using a more precise figure instead of 1.4, but 1.4 is good enough and good to know. More decimal places is not going to change things significantly. Google "wright calculator" and give it a try!
 
Last edited:
  • #12


You can, of course, translate redshift into an equivalent special relatistic velocity, but, the modern interpretation is based on general relativity. GR enjoys vast experimental confirmation. In fact, it has never failed a single test. SR simply cannot explain a myriad of evidence that is easily accommodated by GR.
 
  • #13


I noticed that distance to far galaxies are given in terms of their redshift rather than lightyears. Do we have any other way to tell how far these galaxies are?

We determine such distances indirectly: Turns out type 1A supernovas all have the same brightness and we can identify such characteristic brilliance:
http://en.wikipedia.org/wiki/Type_1a_supernova#Light_curve

So we determine a standard supernova 1A brightness, correlate with calculated distances to known galaxies and observed redshifts where they are found and then correlate redshifts z = ∆λ/λ to distances of other galaxies. Hubble correlated brightness and the parameter z.You might find this Scientific American article of interest:

Misconceptions about the Big Bang: Scientific American 6/14/08
http://www.sciam.com/article.cfm?id=misconceptions-about-the-2005-03

When the hot plasma of the early universe emitted the radiation we now see, it was receding from our location at about 50 times the speed of light.

This is when the surface of last scattering,the 'hot plasma', the origin of CMBR we observe, was about 42 mly from us...it's now about 46Bly distant.

oops..just noticed this is an old thread...oh well...
 
Last edited by a moderator:

1. What is redshift and how is it related to distant galaxies?

Redshift is a phenomenon in which light from an object appears to have a longer wavelength than it actually does. In the context of distant galaxies, redshift is caused by the expansion of the universe, which stretches the wavelength of light as it travels through space.

2. How is redshift measured in distant galaxies?

Redshift is measured using a unit called z, which represents the ratio of the observed wavelength to the rest wavelength of light. This can be calculated using a spectrograph, which separates light into its component wavelengths and allows us to measure the shift in the spectral lines of distant galaxies.

3. What can we learn from studying the redshift of distant galaxies?

By studying the redshift of distant galaxies, we can learn about the expansion rate of the universe and the distribution of matter in the universe. Redshift can also provide information about the age and distance of galaxies, as well as their movement and interactions with other galaxies.

4. How is experimental data collected for studying the redshift of distant galaxies?

Experimental data for studying the redshift of distant galaxies is collected through observations using telescopes and spectrographs. These instruments capture the light emitted from galaxies and provide data that can be analyzed to determine their redshift.

5. What are the potential implications of redshift on our understanding of the universe?

The measurement and study of redshift has led to significant discoveries about the universe, including the expansion of the universe and the existence of dark energy. It has also helped us understand the evolution and structure of galaxies, and continues to provide insights into the nature of the universe and its origins.

Similar threads

B What value of z (redshift) equals apparent superluminal recession?
    • Cosmology
Replies
28
Views
1K
I Have I got the right picture for cosmological redshift?
    • Cosmology
Replies
2
Views
2K
I Cosmic Event Horizon – Does it have any real effects?
    • Cosmology
Replies
9
Views
2K
I Problem interpreting a Distance-Redshift Plot
    • Cosmology
2
Replies
55
Views
8K
B Do we directly observe redshifted galaxies receding >c?
    • Cosmology
Replies
17
Views
2K
I Some redshift from prism effect of a gravitational lens?
    • Cosmology
Replies
18
Views
2K
B Exploring the Impact of a Supervoid on Hubble and Acceleration Parameters
    • Cosmology
Replies
1
Views
2K
B Clarification on how old the Universe is
    • Cosmology
Replies
11
Views
2K
I CMB creation, distance measurement question
    • Cosmology
Replies
7
Views
1K
B The accelerated expansion of the universe; redshift and time/distance
    • Cosmology
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top