Where is the center of the universe?

[Catastrophe]

Does the visible edge of the universe disappear at the same rate regardless of which direction one looks? Should this not be the case it is possible to determine the position where it first began.

By "visible edge", I assume you mean limit of observable universe?
I have never, to my knowledge, used the term myself.

I assume that the limit(s) of the observable universe would simply be the furthest points from which one receives light (or other signal, if any). They are not otherwise distinct locations.
They are not marked by any visible wall or edge, and, in fact, I have stated that "the universe has no edge".

Cat

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Here, I replied to the question:

"So why don't you think there is a boundary (edge) and a beyond for the universe?"

 

[Unclear Engineer]

A couple of thoughts about whether the universe is expanding equally fast in all directions:

1. The Cosmic Microwave Background Radiation does have a discernable red shift in one direction and blue shift in the opposite direction. Astronomers attribute that to the velocity of our galaxy through space, as it orbits in the local group of galaxies. But, I have never seen a test of that based on orbital mechanics of the known local galaxies. I even wonder if we know enough about what is on the other side of our own galaxy to do that calculation reliably.

2. I have not seen a test of the Hubble Factor done in discrete directions. I suspect that the observations are not numerous enough to build "ladders" in individual directions that would have enough precision to make a reliable conclusion about any differences.

Still, it is sort of intriguing to think that the CMBR could provide a frame of reference for what is "still" in the universe and what is moving in a specific direction at a specific speed.

 

[Classical Motion]

ALL EM stimuli is detected as a symmetric stimuli because of the mass action-reaction dynamic of inertia.

And this has blinded everyone to the true nature of light. EM radiation. Light is intermittent with a duty cycle, it is not a wave…… only the detection response is wavy. Mass waves, not light.

And that wave is distorted with relative motion because of inertial response. The duty cycle is smeared. Because of “equal bounce” of matter. This equal bounce is super-imposed on the UNEQUAL stimulus of motion light.

And we think it’s a natural wave shift.

Spacetime and space expansion come from this error.

THE EQUAL RATE OF MASS RESPONSE DISTORTS THE TRUE (changing)RATE OF STIMULUS.

 

[Helio]

A couple of thoughts about whether the universe is expanding equally fast in all directions:

1. The Cosmic Microwave Background Radiation does have a discernable red shift in one direction and blue shift in the opposite direction. Astronomers attribute that to the velocity of our galaxy through space, as it orbits in the local group of galaxies. But, I have never seen a test of that based on orbital mechanics of the known local galaxies. I even wonder if we know enough about what is on the other side of our own galaxy to do that calculation reliably.

Google the CMB dipole and you'll have hundreds of articles on this.

The motions of the Earth/Sun/galaxy/local cluster became somewhat known in the 1930's IIRC, when redshifts were deemed extragalactic. Redshifts of almost 10% c were found by folks like Humason in the early 30's. The expansion rate, however, required great improvements to distance calculations before refinement since the very first rate was 575 kps/Mpc (Lemaitre; 1927) followed by Hubble (500 kps/Mpc; 1929). It took folks like Baade to discover Cepheid variables come in two flavors and RR Lyrae variables are Pop II to correct Hubble's estimates. Dust extinction measurements were also improved to tweak the expansion rate.

It later took the observations of the Type 1a SN to get a clearer picture of the "Hubble Flow" as the larger redshifts made any local kinematic errors mor trivial.

2. I have not seen a test of the Hubble Factor done in discrete directions. I suspect that the observations are not numerous enough to build "ladders" in individual directions that would have enough precision to make a reliable conclusion about any differences.

There could easily be very accurate spectral redshift measurments on a million or more galaxies. I recall the 9 m telescope at McDonald Obs. was designed for spectral data. They upgraded to fiber optics to allow, IIRC, up to 25k spectrums per image.

 

[Unclear Engineer]

There could easily be very accurate spectral redshift measurments on a million or more galaxies. I recall the 9 m telescope at McDonald Obs. was designed for spectral data. They upgraded to fiber optics to allow, IIRC, up to 25k spectrums per image.

Redshift measurements alone would not produce a measure of the Hubble Parameter, it also requires independent distance measurements. And that requires Cepheid variables, SN1a measurements, etc. to build the "distance ladder".

What I am asking is whether the distance ladder has been built in several directions using only observations in those directions, so that a comparison could be made among Hubble Parameter estimates as a function of direction. What I typically see is a compilation of all available measurements, which effectively provides an average of all directions.

Considering the recent goal of reducing the uncertainty in the measurements so that there is no overlap of the confidence intervals for the "ladder" version of the Parameter vs the CMBR version, it is understandable that it would be done that way. But, it does not address the question about whether there is a difference in the expansion rate in different directions as seen from Earth - I think that it is still an assumption that it is invariable with direction. And, I would not be surprised if the number of available observations in specific directions were not numerous enough to produce uncertainty bands that do not overlap for differences that are on the order of the differences in the CMBR vs direction.

 

[Helio]

What I am asking is whether the distance ladder has been built in several directions using only observations in those directions, so that a comparison could be made among Hubble Parameter estimates as a function of direction. What I typically see is a compilation of all available measurements, which effectively provides an average of all directions.

There could be a paper using accurate expansion rates as a function of spherical angle, but there is a chance there are none, as well.

The 1 part in 100k in variation in the CMBR is one reason why there might be some reluctance to do a major study. But it wouldn't be hard to do given today's greatly improved accuracy for distances. There are additional techniques used to test those distances including the magnitude of B stars, galaxy magnitude with angular size, etc.

Einstein's GR, along with others including Lemaitre, assumes (requires) homogeneity. But I know almost nothing of the guts to GR, only how elegant it seems to be on the surface.

The Type Ia, no doubt, are the best markers for huge redshifts, which is necessary for what you're asking.

There have been a few competent folks that have suggested something might be found that would tweak the Type 1a data enough to make a difference. AFAIK, nothing has caused much of a dent.

Perhaps resolving the Hubble Tension will bring more. [I still can't get an answer from either forum why acceleration doesn't explain the tension since the slower rate tied with the CMBR would be necessarily slower than today's H-L constant.]

Statistical analysis of the motions of thousands of galaxies and clusters likely allows for a fairly accurate model for the Hubble Flow.

 

[Unclear Engineer]

Helio, isn't the "acceleration" the explanation offered for the "tension" between the CMBR and the "ladder" of distance vs apparent recession velocity of stars and galaxies? The plots of the "ladder" velocities seem to be a straight line to me. I have not seen one with an arrow that says "spatial acceleration starts here - but I think I have read some texts that say it started 8 billion years ago. I did not find that when I searched, though.

Wikipedia has a write-up on the Hubble Parameter interpretation as a function of time here https://en.wikipedia.org/wiki/Hubble's_law that I suspect you have already read more times than me, and probably understand better than I do. But, it doesn't seem to address any variation in the Hubble Parameter with time or distance in the ladder data.

it does have some discussions about how the age of the universe could be different than current consensus, based on various interpretations of the available data. It also seems to further muddy the waters with some new data from different methods.

Maybe the best interpretation is that "nobody really understands it well enough to explain it clearly."

 

[Gibsense]

They are not marked by any visible wall or edge, and, in fact, I have stated that "the universe has no edge".

The size of the universe as it expands is defined by the time (that you size it). Therefore we might consider the edge to be time. Observable or otherwise

 

[Helio]

Helio, isn't the "acceleration" the explanation offered for the "tension" between the CMBR and the "ladder" of distance vs apparent recession velocity of stars and galaxies?

That's actually my question. I haven't seen where the tension is explained with acceleration, but I only ask at times when I see an article that ducks this viewpoint. I suspect I'm missing something since it's so obvious that acceleration would demand an expansion rate difference. Even Lemaitre postulated acceleration in his 1927 paper, complete with graph. [I think there were two reasons for this: vacuum energy, which he and others never abandoned unlike Einstein, implied from the cosmological constant by Einstein and that stars and the Earth may have had ages at that time that would be older than the universe. ]

The plots of the "ladder" velocities seem to be a straight line to me. I have not seen one with an arrow that says "spatial acceleration starts here - but I think I have read some texts that say it started 8 billion years ago. I did not find that when I searched, though.

That's interesting, but the tension difference isn't that much so either the acceleration is rather recent in its effects or it was never that great. The general view, I think, is that DE will have greater and greater accelerating effect as it overcomes the weakening constraining gravity due to an expanding universe. But DE is not hard science yet. The evidence for acceleration, however, seems reasonably strong... so far.

Wikipedia has a write-up on the Hubble Parameter interpretation as a function of time here https://en.wikipedia.org/wiki/Hubble's_law that I suspect you have already read more times than me, and probably understand better than I do. But, it doesn't seem to address any variation in the Hubble Parameter with time or distance in the ladder data.

it does have some discussions about how the age of the universe could be different than current consensus, based on various interpretations of the available data. It also seems to further muddy the waters with some new data from different methods.

Maybe the best interpretation is that "nobody really understands it well enough to explain it clearly."

Thanks for looking. It still strikes me as odd that I have yet to see anyone use acceleration to explain the tension. But, again, there could be a dozen articles and papers doing so.

 

[Gibsense]

Helio,​

The point here is to imagine that we are the 'Flatlander' (Spacelander) trying to interpret 4-dimensional space. In the case where our universe might be a hypersphere.
The diagram attempts to show that our 'Flat' interpretation of space (the tangental line in the diagram) would lead to an interpretation of distance that was increasingly distorted as t=0 was approached. Maybe this is equivalent to your 'acceleration' idea.
The idea here is that 'acceleration' does not exist it is a misinterpretation due to our 'Spacelander' perspective.

 

[Gibsense]

How are we to know that the rate of expansion of the universe is the same in every direction? This is the usual assumption, but if it is slower in particular directions this would suggest that its center was further from this direction than from places that has a greater speed of change..

I agree. However, in this context, the Centre of the universe is only valid in a 4-dimensional space. That is there is no fixed point within 3D space - it is everywhere.

 

[Unclear Engineer]

I agree. However, in this context, the Centre of the universe is only valid in a 4-dimensional space. That is there is no fixed point within 3D space - it is everywhere.

But, that is also an assumption. Finding differences in direction for astronomical parameters would not only violate that assumption, it would throw cosmological theorizing into a major tizzy.

So, my suggested approach is to check on the validity of the underlying assumptions whenever possible.