Challenges to the Redshift Method and Hubble's Law

[xhu2688]

TL;DR Summary

In computing Hubble's constant, discords arise. But no serious doubt on Hubble's Law yet. What if Hubble's Law is a special of a different Law and Doppler's Redshift is not a major redeshift?

Since Hubble's Law has been around a long time, so, after almost 100 years, to challenge its validity looks like dumb and stupid. So let me be that
dumb guy, or maybe the bad boy that spoils the whole thing.

Here let me start with the Redshift in general. There are three Redshifts proposed till this date: 1. Doppler Redshift; 2. Cosmologic Redshift; 3. Gravitational Redshift.

1. Let's consider the Gravitational Redhsift. First of all, Grevitational Redshift is very small. Secondly, when photon leaves the gravitational field,
what is going to happen? Won't its frequency be restored back to before? If that's the case, when we observe light from stars and when photon reaches Earth, the greatest gravity it endures is the gravity of Earth which has negligible gravitational redshift. And won't the gravitational effect of the emitting star has stronger gravitation than Earth?

So, for most observations (stars not near black holes), gravitational redshift may be ignored.

2. As for Cosmologic Redshift, first of all, it is based on the assumption that Universe is expanding. But how do we know it is expanding (I mean by observational facts, not by theories like general relativity)? From Hubble's Law. Now if Hubble's Law is an incorrect interpretation of the observationnal redshift data, then the major evidencial support of Universe Expansion may be gone. I know this is a big claim and I may be blundered, but this is the whole point I am going to make later in this post.
Secondly, if Cosmologic Redshift indeed is a major contributor to the redshift values observed, won't the Cosmologic Redshift has a single value
for all stars (otherwise how can you have a Hubble's Law)? And won't the Cosmologic Redshift be istropical (same along different directions)?

But we observed redshifts of value from 5.2, all the way to 1809. How can a single Cosmologic Redshift explain this?

3. Now let's come to the Doppler's Redshift. This Redshift for a star moving along line of sight is given by
Z = Sqrt ((1 + v/c )/ (1- v/c)) - 1 , (1)
Now, with v = 0.1c, it gives only a redshift of Z = 0.1055, and for a star speed v = 0.6c,
it gives only a redshift of Z = 1. A speed of 0.6c is enormously fast for any star! Too fast to be reasonable.

According to this article:
https://www.newsweek.com/hypervelocity- ... tar-631870
The fastest speed of an observed star in our Milkway (out of Milkway it is difficult to record speed directly,
I guess) is 2x10^6 miles per hour, or 3.2x10^6 km/H, or 8.89x10^3 km/s, which is barely 0.0296c, where c is the light speed.

This would mean, for redshifts that are larger than 5, Doppler Redshift cannot be the major contributor of the redshift values
astronomers observed, otherwise the speed of the stars have to be >0.99999c. That's too fast to be true.

To my understanding, in deriving Hubble's Law, there are two assumptions:
(1) The redshift is mainly due to Doppler Redshift;
(2) the velocity of the star is small such that v = c Z.

Now, as we have shown above, for a v = 0.1c, the redshift value from Doppler Redshift is only 0.1055,
far less than most redshift values observed (from 5.2 to 1809). This would mean, Doppler Redshift cannot explain large redshift values. As such, Hubble's Law cannot be applied to large redshift values as well, in addition to the fact that it cannot be applied to fast moving stars (due to the non-relativisitic assumption v = cZ).

So I hope the discuss above are meaningful. If I missed anything, please correct me. I'll continue a little later. If the above discussions are nonsenses, then I may have goofed somewhere, then there is no need to continue to waste people's time.

 

[Orodruin]

Summary: In computing Hubble's constant, discords arise. But no serious doubt on Hubble's Law yet. What if Hubble's Law is a special of a different Law and Doppler's Redshift is not a major redeshift?

Here let me start with the Redshift in general. There are three Redshifts proposed till this date: 1. Doppler Redshift; 2. Cosmologic Redshift; 3. Gravitational Redshift.

Wrong. There is just redshift. These names have been given to coordinate dependent interpretations of different cntributions to redshift. Mathematically they all have the same origin.

First of all, Grevitational Redshift is very small.

This depends on the situation. Also note that a photon in itself does not have a frequency, it has 4-frequency. To interpret that as a frequency requires reference to an observer and is observer dependent.

The rest of your post is full of similar misunderstandings. There are too many for me to go through them all. I suggest taking a GR course if you want to know what the theory actually says instead of relying on popular scientific description. Popular science may be good to make the general public interested in science, but it is often written to produce awe and twist your mind. It certainly is not written to teach you science and it is generally a very bad starting position to try to deduce things and do actual science however tempting that may be.

 

[xhu2688]

Thanks. Now I got it: the cosmologic redshift is given by
Z = R_to / R_te - 1 = (R_to- R_te) / R_te
R_to the expansion coeffient of at observer time, and R_te the expansion coefficient of emitting time.

Now this is considered to be the main redshift in Hubble's Law:
(R_to- R_te) / R_te = （H_0 / c ） D
This looks better, but still I have other questions. But I'll think it more before I put things out,
so to avoid stupid mistakes.

 

[xhu2688]

I am actually reading GR, but frankly, I need to be convinced first (by observational data with convincing physical explanation) that the Universe is indeed expanding, otherwise, all the complicated math is useless if the Universe is not expanding, but some other things produced the redshift. The cosmologic redshift indeed can explain this but there is a logic issue：if we assume the Universe is expanding, then we did find something to fit the model.
Do we have other evidences except Hubble's Law to show the Universe is indeed expanding?

 

[Orodruin]

Hubble’s law is just the linear approximation of the general cosmological redshift for small distances. It is not the full story.

I am actually reading GR, but frankly, I need to be convinced first (by observational data with convincing physical explanation) that the Universe is indeed expanding, otherwise, all the complicated math is useless if the Universe is not expanding, but some other things produced the redshift.

This is backwards. You cannot be convinced of something without learning what that something is.

 

[mfb]

The cosmologic redshift indeed can explain this but there is a logic issue：if we assume the Universe is expanding, then we did find something to fit the model.

An expanding universe is the only model we have that fits to all the observations. There was no shortage of other models that were considered historically (look up tired light for example), but they all didn't fit to observations and were refuted over time.

Do we have other evidences except Hubble's Law to show the Universe is indeed expanding?

Galaxy evolution, gravitational waves from a neutron star merger, the cosmic microwave background, the abundance of the elements, ...