Where is the center of the universe?

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The center point of a sphere, or a ball, no matter which, is the set 'Point' of all points of the surface of the sphere or ball. a form of quantum entanglement, the countless many into the one. "All roads lead to Rome" (lead to the center). Once more into the breach, Hawking's "Grand Central Station of the Universe" and that other center to the GCS of the U, "The (timeless (t=0)) Clock."
 
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Catastrophe

"Science begets knowledge, opinion ignorance.
For the Navy.
For Astronomers there is the Horizon Problem.

I think the most common interpretation of Observable Universe would be the volume to the Event Horizon. Some might suggest a Hubble Sphere, others a Particle Horizon.

When used in a technical Cosmology sense the choice of telescope does not define the Observable Universe Limits, more likely would be the Past Light Cone limits for example at t=0

Thank you for the correction to your blank space problem! :)
 
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Catastrophe

"Science begets knowledge, opinion ignorance.

It seems quite simple English to me.

Observable Universe = all that can be observed by any and all means.

Of course, it depends on the ability and technology of the observer.

In this case, it may be qualified as



Cat :)
What is observable today is a lot more than what was observable a hundred years ago; a thousand years ago....

What may be considered as observable if and when we travel to interstellar, and maybe intergalactic, space, will be enormously more. "The map is not the territory."
 
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This seems to confirm exactly what I posted.

Cat :)
Yes, its just the word 'theoretically' which allows for theory however if we delve a little deeper then you may well turn out to be correct. Say, that we were to travel (thought experiment) at near 'c' then we would (if my stated theory were correct - in Flatlander) then the current boundary at t=0 would be extended, similarly a longer wavelength telescope might extend the 'reach' beyond the theoretical limit.
Anyway this - definitions - is your area of expertise so back to you!
 
To take a page out of COLGeek's book ("The only thing larger than the universe is one's imagination"), the only other thing larger than the universe is the individual behind the imagination (thus, the individual at the center of the universe, everywhere the center of the universe is, period)!
 

Catastrophe

"Science begets knowledge, opinion ignorance.
To take a page out of COLGeek's book ("The only thing larger than the universe is one's imagination"), the only other thing larger than the universe is the individual behind the imagination (thus, the individual at the center of the universe, everywhere the center of the universe is, period)!

IMHO being geographially at the centre of one's observable universe does not make one the most important in the universe. These are mixed idioms.

Cat :)
 

Catastrophe

"Science begets knowledge, opinion ignorance.
Yes, its just the word 'theoretically' which allows for theory however if we delve a little deeper then you may well turn out to be correct. Say, that we were to travel (thought experiment) at near 'c' then we would (if my stated theory were correct - in Flatlander) then the current boundary at t=0 would be extended, similarly a longer wavelength telescope might extend the 'reach' beyond the theoretical limit.
Anyway this - definitions - is your area of expertise so back to you!

What location of theoretically are you referring to, please?

Unfortunately, t = 0 seems to being now for all different things.
My use is for the beginning, or transition, before the BB, or the nexus between phases.

Cat :)
 
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IMHO being geographially at the centre of one's observable universe does not make one the most important in the universe. These are mixed idioms.

Cat :)
Tell me what is more important, Cat. I agree with Thomas Jefferson that the individual is just as important as the government (the communal)! "You cannot possibly have "one world" without two worlds (or, as some physicists and philosophers say about the physics, "many worlds")...!"
 
Wouldn't an expanding sphere have the same expansion rate at all locations? And at the same time. Wouldn't the surface of an expanding sphere have the same time too? And every part of the surface the length would be the same at all locations.

No matter which way you work it, an expanding sphere solves nothing about mass distribution.

But it does explain light distribution. And the inverse square law. A field property, not a mass property.

The shifts you see are not Doppler shifts, they are inverted duty cycle shifts. Sequential concentric discrete expanding shells. Duty cycle shells.

And time and length are constant. Because the length or amount, of e, is constant.

Sequential concentric discrete shells can not be produced without constant length and constant time.

Unlike modern dogma, the true dynamic of light insists on constant length and constant time.

Modern science, of course, has it backwards.
 
Going back a ways in these posts:

The concept that the universe can be thought of as a 3-dimensional surface in a 4-dimensionals "space-time" mathematical space does work mathematically, and that math is the Lorenz equations of Special Relativity Theory. The "time" dimension is the radius from the center of the 4-dimensional sphere to everything definable with x,y,z coordinates in our currently observed universe. So, it is "time" that is expanding the universe in this analogy. (And doing so at the speed of light, because the length dimension is "ct".)

But, that doesn't try to actually explain the physics - it is just the logical mathematical interpretation of the fact that we cannot seem to measure any difference in the apparent speed of light when we know that our velocity has changed, which is what the Michelson-Morley experiment established as a fact.

But, General Relativity Theory tells us that the apparent rate of time passage is not constant throughout the universe. It is slower in the vicinity of large masses.

And the red/blue dipole in the redshift of the cosmological microwave background radiation does seem to indicate a frame of reference against which we can measure "peculiar' velocities, which we assume are related to our gravitational attractions to other galaxies and resultant motions through space.

Trying to make sense of the observations falls into 2 distinct realms of physics.

One is the observations of astronomy, which, so far at least, are limited in time and distance to the cosmological microwave background radiation emission time/place. (And even that is an assumption about how that microwave background was created.)

The "observations" for earlier times and greater distances are all from high energy particle accelerator collisions in experiments conducted here on Earth, combined with assumptions about how those could be relevant to the behavior of the universe at earlier times than astronomy can observe, when the prevailing theory extrapolates the density backwards in time to create high temperatures and particle energies that are similar to the particle accelerator experiments.

And in that Big Bang Theory, the predicted effects from General Relativity need to be over-ridden by an assumption that some unknown "dark" energy source caused expansion when GRT would otherwise predict collapse to a singularity due to the extremely high density. Or, that consideration is deflected with rhetoric about how there is nothing outside the universe, so there is no way to measure a collapse of the universe. Yet, the theory does talk about the expansion of the universe, which is the opposite of collapse.

There are plenty of hypotheses about how all of this fits together into a physics level understanding. (I use the word "hypothesis' instead of "theory" because these hypotheses are apparently not testable with today's knowledge and equipment.)

There is even the "block universe" hypothesis that posits that the past and future times are already in existence in some way, and that we "observers" are simply being transported through it all (at the speed of light) along that radius from the "beginning of time" at the center of the 4-dimensional mathematical space. Which would tend to imply that we have no "free will" because we are simply being moved through those predetermined conditions of the future at larger time radii.

Personally, I am not a believer in the "block universe" and prefer to think that it is things that happen in the past and present that determine what will occur in the future through physical laws that we can partly understand today and can hope to understand better tomorrow, and take the opportunity to use now to improve tomorrow.
 
'MOND' is a possibility that is still debated. But the principle it states - that variation by direction - is a real possibility. if I recall correctly, in my "Hubble Tension" I used relativity as a possible explanation but differently: Stars and galaxies have speed therefore their clocks will differ from Cmb clocks i.e. the time element (age of the universe) will differ when comparing 1a Supernova with the Cmb.
This has to be 'plugged into' my calculation involving a geometric distance to the 'Age of the Universe' As set out in my Hubble Tension post.
Hubble Tension is still an issue. MOND is one possibility.
MOND only helps diminish DM in galaxies, IIRC. But it still requires DM to explain high velocities in galactic clusters.

I don’t know much on this topic. I’ve yet to see anyone explain why there is a “tension”. The slower H-L rate at the CMBR period should necessarily be less than the local time H-L rate, given spacetime acceleration.

What good is acceleration if you never go faster?
 
Yep, but imagine if there was a debate on why the gravity rate of 9.8m/sec^2 was less long before Theia hit? The impact/merger solved that hyperbolic "tension".
Helio, I am not following your reasoning.

The gravitational acceleration rate on Earth' surface (small "g") is 9.8 m/sec^2 ( or 32.2 ft/sec^2) because of the mass and radius of the Earth.

If Theia did strike the Earth, it would likely have affected Earth's mass and radius, so I would expect that Earth's surface gravitational acceleration value would have been different before such a strike, without any change in the underlying physics since before that time.

But, I think you are wondering about the more general Gravitational Constant, "G" which sets the attraction between any 2 masses, based on their mass values and the distance between their centers of mass. "G" is equal to 6.6743×10^−11 N⋅m^2/kg^2. In English units, that is 3.436x10^-8lb-ft^2/slug^2. G is used in the formula F = G M1 x M2 / R^2 to compute the force attracting 2 masses, denoted as M1 and M2.

There is some theoretical attempt to relate G to the Hubble Factor (no longer a "constant"), as described here: https://arxiv.org/abs/2306.05450.

And, there are other attempts at resolving the "Hubble tension", including MOND.

The problem I have with these approaches is that it is always mathematically possible to "fit" calculated results to observations if you are willing to allow "constants" to become variables, and/or introduce entirely new and unconstrained parameters into the equations. So, in order to be taken seriously, it is essential that the fitting be shown to work for different types of observations - preferably all observations (which MOND has not done).

So, I think studies of the type described in the link I provided are useful examinations of the data and might lead to better understanding if they hold up under extensive testing. But, I would not take these results as fact at this point in their development. It is an interesting result, however.
 
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The constant of "Big 'G'" is a property of entangling (including "quantum entangling") concurrent REALTIME NOW instant and has no relationship whatsoever to light's coordinate points' past-future histories SPACETIME.
 
UE, the Theia crude analogy was only about the change in a gravity (acceleration). I would expect we would see a change in the H-L rate given the acceleration claim for the expansion. The then and now effects should necessarily be different.
 
Isn't the apparent H-L change the reason that people think there was an acceleration in the rate of space expansion? Space/time expansion and any acceleration is a theory based on observation, not a fact that has been proven by the observations.

And, its relationship to the gravitational constant "G" possibly also changing with time is even more hypothetical.

Might be true, but not a proven fact at this point in our development of understanding.
 
Isn't the apparent H-L change the reason that people think there was an acceleration in the rate of space expansion?
You're thinking logically. :) But we have to go back to 1995 for this. There's a cool story behind all this.

The few articles addressing the tension, which is the small differences between the two expansion rates (today vs. 13.8 Gyrs ago via the CMBR) cause me to infer that the "surprise" is because they are not the same rate. Also of note, the differences are outside their respective margins of error. So it seems that the earlier rate (13.8 Gyrs ago) was actually a little less than today.

The original acceleration finding was big news in 1995. The two independent teams (Berkley & Harvard Obs.) studying Type 1a SN were conducted to improve the value of the expansion rate.

Berkly, comprised mainly of physicists, apparently had more clout and got the best telescopes and times to acquire a lot of SN data for distant galaxies. Harvard's team consisted mostly of astronomers. They wisely chose to use filtered imaging to improve their fit for their fewer data points. This gave them a more accurate result -- quality vs. quantity.

As a result, perhaps, Adam Reiss with the Harvard team broke the news that the universe is accelerating. Berkly announced it as well very shortly thereafter, perhaps the same or next day, IIRC.

This is when DE was born. Though no one then, nor today, knew the cause, it was easy to make the jump to an energy source since the cosmological constant -- a little DE from Einstein, if you will, to keep the cosmos from collapsing under its own "weight" -- never truly was discarded by all cosmologists. Recall that Edington, Lemaitre and, perhaps, de Sitter never tossed it, though Einstein felt it was too ad hoc and shown, in his view, to be superfluous once he recognized the elegance in Lemaitre's dynamic view of GR vs. his static model, which couldn't explain Slipher's redshifts. Also, Lemaitre's model actually included acceleration in his 1927 paper!

The recent studies, giving us "tension", of the acceleration rate at the time of the CMBR is slightly less. But no one I've seen so far has argued that a slower expansion rate should not have been predicted. I assume my lack of understanding is the reason, but how?

Space/time expansion and any acceleration is a theory based on observation, not a fact that has been proven by the observations.
Well, I like to reserve facts to represent objective evidence. Wishful thinking, suppositions, conjecture, hypotheses, theories come from these facts. The more facts, the stronger the theory, at least until the facts either force correction or destruction.

I'm guessing that a lot of people try to swallow too much when they first look at BBT. Thus, when I can present it, I prefer to simplify it and start with how it was found and work back from there.

Recall that Lemaitre had only two "facts": GR and galactic velocities/distance. [Three if we separate velocities and distances.]

In 1925, he started seeing error in deSitter's GR model, and began realizing that a dynamic model made more sense. [Weyl and Robertson also had dynamic models, but they didn't see the expansion, reportedly.] Lemaitre simply matched the galaxies having both Slipher's redshift velocities and Hubble's distance measurements, thus deriving the first linear relationship for galactic distance and recessional velocities. He labeled this expansion rate, ironically, H. ;) [When he translated the paper two years later into English, he left his expansion rate calculations out since, per his comments, Hubble had already improved the science on this. This likely is why Hubble has received so much of the credit, but a little too much, IMO.]

[Hubble took credit for this relationship, and he even blasted (Aug, 1930) de Sitter when he published his own, more advanced, linear relationship without giving enough credit, in Hubble's view, to Mt. Wilson (ie Hubble).]

And, its relationship to the gravitational constant "G" possibly also changing with time is even more hypothetical.

Might be true, but not a proven fact at this point in our development of understanding.
Perhaps, but if G is altered even a tiny, tiny, tiny bit in the earliest times, then either stars won't form (sllightly less G) or the Universe collapses.
 
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The difficultly in explaining implies incoherence. Why must the universe include all? Why can't it have a boundary? What if different speeds were being miscalculated as distance? How can we be sure of what other galaxies see? Why have we found no other life like our own? The existence of these questions allows participation by those who sing, "He got the whole world in His hands." And we know with utmost certainty we can't allow that. 🤣
 

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