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I printed out that article you posted. It is a real read all right. It will take me some time to get through it, but until then, there are some comments to be made from my very limited perspective. Think in terms of "space", and forget matter for a moment.

If space is infinite, then the universe is likely expanding into an infinite void. In this case I would have to say that Doppler is the most likely cause of redshift. Again, in my limited knowledge of this subject (and an oppressive tendency to think only with Newtonian physics), it would seem that both Doppler and space expansion represent similar phenomena. Does it really matter from the perspective of the observer how the redshift is generated - whether it is Doppler or expansion? Both would seem to have the same effect, and both could even be playing a role. So objects are moving away from the observer in both cases, only by a different mechanism. I don't see how either approach would effect the redshift, or how that redshift could define either mechanism (maybe something in that article I just printed out).

From a very simplistic view, the BB suggests that no matter where you are in the universe, everything appears to be moving away from everything else, and there is no center of the universe. This strongly suggests expansion of space. If, however, matter is expanding into an infinite void, it seems likely it would therefore have a point of origin, and an outer edge. I believe most high brows in Cosmology would suggest that this is simply not likely. It would require that our local space be the center of the universe. Otherwise, redshifts would not be the same for the most distant galaxies in all directions. Certainly our instruments are sensitive enough to pick up even a slight variance in such redshifts and none are seen, at least to my knowledge.

This is such a contentious issue that it is not possible for anyone to provide a "correct" answer. I would suggest if your considerations of the origin of the universe has a significant following of learned professionals, who can say that you are wrong? No one!
If space is infinite, then the universe is likely expanding into an infinite void.
The following are just my previous thoughts on that idea as it seems to be quite a common suggestion. There's nothing scientific about what I'm saying, it may even appear like waffle, in any case, science about what's beyond the universe is hard to come by.

Yes, infinite, but definitely not void. Everything that exists has some kind of connection to something else, or a chain of cause and effect to it. If there where just one universe in a void it would not have anything to connect with, it wouldn't belong to a chain of cause and effect. there would have been nothing to give rise to its existence or reason for its existence. A void can't provide a reason or basis for anything. You would be left with the question why just one universe. It would either have had to come from nothing, or something had been sitting there for an infinite amount of time and then with no cause just decided to explode 13.8 billion years ago (the way out of that, is to invoke the cyclic universe theory, but that's just as bizarre anyway).

Also, I suggest the laws of physics don't allow one-off phenomenon, if something can happen once, then it can always happen. The formation of a universe is a natural phenomenon, so if one can form then there must be an infinite number given an infinite space.
Again, in my limited knowledge of this subject (and an oppressive tendency to think only with Newtonian physics), it would seem that both Doppler and space expansion represent similar phenomena. Does it really matter from the perspective of the observer how the redshift is generated - whether it is Doppler or expansion? Both would seem to have the same effect, and both could even be playing a role. So objects are moving away from the observer in both cases, only by a different mechanism. I don't see how either approach would effect the redshift, or how that redshift could define either mechanism
With my also limited knowledge I would completely agree. No, second thoughts, they represent distinctly separate phenomenon but have the same result. No third thoughts, I think they have different results. In the case of doppler only redshift, the shift happens immediately and is only dependent on your relative speed and is independent of separation distance. You should see the same redshift from 1 light year away as 10 billion light-years, if you're still travelling at the same speed.

If the redshift were due to expanding space then it would depend on the distance. If you were nearby, space would not be stretched much, but the further you move away, the more space will become stretched, so you will see more redshift due to this effect the further away from the source you get.

So, if space is expanding, then I think you're right that it could be both playing a role.

Another thought comes to mind, I thought the Michelson and Morely experiment demonstrated that light wasn't travelling in any medium, so how come expanding space can affect it anyway, it must be travelling in something it can interact with?

As you can see, I'm in a pickle with this one, so please apply your limited knowledge to my limited knowledge, and let me know what you think :)

Got lots more to add to the rest of your interesting post, but I'll do that after I've given my brain a rest:).
 
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After this, my head is hurting more still:

"In one set of circumstances the proper interpretation of the redshift seems clear. When the curvature of spacetime is small over the distance and time scales traveled by a photon, it is natural to interpret the observed frequency shift as a Doppler shift. This interpretation is the reason that a police officer can give you a speeding ticket based on the reading on a radar gun. As far as we know, no one has successfully argued in traffic court that there is an ambiguity in interpreting the observed frequency shift as a Doppler shift.22 In the expanding universe, spacetime curvature is small over regions encompassing nearby objects, specifically those with z = ∆λ/λ ≪ 1. There should be no hesitation about calling the observed redshifts Doppler shifts in this case, just as there is none in traffic court. Surprisingly, however, many people seem to believe that the “stretching of space” interpretation of the redshift is the only valid one, even in this limit. We will examine the interpretation of redshifts of nearby objects more carefully in Sec. II."

Any comments? (Yes, it is from that very long article).

Sorry to repeat again, but this is the cause of my problem:
From Abstract:
, . . . . . . however, its validity is more uncertain on cosmological scales, or when dark matter is concerned.

Cat
 
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Mar 19, 2020
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Forgive my short answer here David, but I have read so much about all of this that it is difficult to dissect every nuance and try to make sense of it. But I must reply to a specific aspect of your post:

"Yes, infinite, but definitely not void. Everything that exists has some kind of connection to something else, or a chain of cause and effect to it. If there where just one universe in a void it would not have anything to connect with, it wouldn't belong to a chain of cause and effect. there would have been nothing to give rise to its existence or reason for its existence. A void can't provide a reason or basis for anything. You would be left with the question why just one universe."

As a scientist, I do not believe that everything must be connected to something else. This is an assumption without any compelling evidence to support it. While all of what we see might suggest it, there is no proof of an inherent connectivity. No doubt there are many who will disagree with this notion. Life would be boring if they did not!

Moreover, you bring up two major issues here: "How" and "why". They are very different concepts.

In their purest definition (which are most applicable for the issues at hand), "how" is what makes things work, or put together, etc. "Why" is a nebulous term indicating a "reason" for that "thing" that works, etc.

"A void can't provide a reason or basis for anything."

This is the biggest problem I have debating aspects of science, not just cosmology. Many scientists will tell you they do not believe there is a "reason" for anything. There does not have to be. The classic "Why are we here?" begs a "reason" which likely does not exist. Reasons are human inventions to explain the unexplainable. I submit that our existence, and all we see and think, has no explanation as to "why".

Science can explain "how" things happen in many cases. I do not believe it can provide a "reason" why they happen.
 
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Cat, many of our heads are hurting over all this. There are so many concepts and notions flying around that are so counter intuitive that only an idiot would not experience some form of mental duress.
 
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Nov 20, 2019
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After this, my head is hurting more still:

"In one set of circumstances the proper interpretation of the redshift seems clear. When the curvature of spacetime is small over the distance and time scales traveled by a photon, it is natural to interpret the observed frequency shift as a Doppler shift. This interpretation is the reason that a police officer can give you a speeding ticket based on the reading on a radar gun. As far as we know, no one has successfully argued in traffic court that there is an ambiguity in interpreting the observed frequency shift as a Doppler shift.22 In the expanding universe, spacetime curvature is small over regions encompassing nearby objects, specifically those with z = ∆λ/λ ≪ 1. There should be no hesitation about calling the observed redshifts Doppler shifts in this case, just as there is none in traffic court. Surprisingly, however, many people seem to believe that the “stretching of space” interpretation of the redshift is the only valid one, even in this limit. We will examine the interpretation of redshifts of nearby objects more carefully in Sec. II."

Any comments? (Yes, it is from that very long article).

Sorry to repeat again, but this is the cause of my problem:
From Abstract:
, . . . . . . however, its validity is more uncertain on cosmological scales, or when dark matter is concerned.

Cat
From Abstract:
, . . . . . . however, its validity is more uncertain on cosmological scales, or when dark matter is concerned.
Hi cat I would like to reply to this, I remember reading it but where did it come from?
 
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David

Search Results
Web results

I believe this is the reference to Abstract:

Search Results
Web results

Journal of Cosmology and Astroparticle Physics ... Camille Bonvin and Pierre Fleury. Published 25 May 2018 • © 2018 IOP Publishing Ltd and Sissa Medialab Journal of Cosmology and ... Part III: Test of the Equivalence Principle J. Cosmol.



. . . which you should find at the bottom.

Best

Cat :)
 
. . . . . . . . . . . .

and this is the search which provided it:

Whilst looking at (SEARCHING)
Cosmological redshift Equivalence Principle

I came across the following:

Journal of Cosmology and Astroparticle Physics
Testing the equivalence principle on cosmological scales
Camille Bonvin and Pierre Fleury
Published 25 May 2018 • © 2018 IOP Publishing Ltd and Sissa

If you hit the Article Information +
above the abstract you can download what appears to be a free copy (as opposed to the purchase printable) at:
BEWARE! You will need your best maths hat on.
I did a lot of math in my Chemical Engineering Degree but this makes it look like Modern Art gone wrong!

Cat

P.S. I am still looking for the source for the bit above the abstract which does NOT appear to be from the quoted article.
 
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On a completely different aspect of EXPANSION I have found the following reference "All About Space" Issue 052 June 2016 page 14 which may help to keep your grey matter ticking over (see how thoughtful I am) ;)

"A team of astronomers have used data collected from NASA's Chandra X-ray Observatory, ESA's Planck Satellite and a large list of optical telescopes to conduct the most thorough investigation into dark energy yet.
. . . . . . . . . . . . continues . . . . . . . . . . . .
Recent results from the study suggest that while the Universe is expanding, the amount of dark energy is not - it remains a 'cosmological constant'. "Although we've looked hard at other explanations," adds Ming Sun, also of the University of Alabama, "it seems dark energy behaves just like Einstein's cosmological constant".

Any views on this please?

Cat ;)
 
The original mentioned a glossary associated with NASA.

You can access the WHOLE of the Glossary, which you can save, for example, on your desktop (I have checked this works as an Internet Shortcut). It appears that free use is allowed subject to normal conditions. Permission for wider use should be requested. Cat :)

https://ned.ipac.caltech.edu/level5/Glossary/Essay_lss.html.


Please note the following and check any relevant additional requirements:
Unless otherwise stated, all material on the site was produced by NASA and STScI. Material on this site produced by STScI was created, authored, and/or prepared for NASA under Contract NAS5-26555. Unless otherwise specifically stated, no claim to copyright is being asserted by STScI and material on this site may be freely used as in the public domain in accordance with NASA's contract. However, it is requested that in any subsequent use of this work NASA and STScI be given appropriate acknowledgement. STScI further requests voluntary reporting of all use, derivative creation, and other alteration of this work. Such reporting should be sent to http://aas.org/directory.
 
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Nov 20, 2019
130
68
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. . . . . . . . . . . .

and this is the search which provided it:

Whilst looking at (SEARCHING)
Cosmological redshift Equivalence Principle

I came across the following:

Journal of Cosmology and Astroparticle Physics
Testing the equivalence principle on cosmological scales
Camille Bonvin and Pierre Fleury
Published 25 May 2018 • © 2018 IOP Publishing Ltd and Sissa

If you hit the Article Information +
above the abstract you can download what appears to be a free copy (as opposed to the purchase printable) at:
BEWARE! You will need your best maths hat on.
I did a lot of math in my Chemical Engineering Degree but this makes it look like Modern Art gone wrong!

Cat

P.S. I am still looking for the source for the bit above the abstract which does NOT appear to be from the quoted article.
Thanks for that Cat. All I can say in this case is agree that it looks like modern art gone wrong! I'll look at the "All About Space" article tomorrow.
 
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Forgive my short answer here David, but I have read so much about all of this that it is difficult to dissect every nuance and try to make sense of it. But I must reply to a specific aspect of your post:

"Yes, infinite, but definitely not void. Everything that exists has some kind of connection to something else, or a chain of cause and effect to it. If there where just one universe in a void it would not have anything to connect with, it wouldn't belong to a chain of cause and effect. there would have been nothing to give rise to its existence or reason for its existence. A void can't provide a reason or basis for anything. You would be left with the question why just one universe."

As a scientist, I do not believe that everything must be connected to something else. This is an assumption without any compelling evidence to support it. While all of what we see might suggest it, there is no proof of an inherent connectivity. No doubt there are many who will disagree with this notion. Life would be boring if they did not!

Moreover, you bring up two major issues here: "How" and "why". They are very different concepts.

In their purest definition (which are most applicable for the issues at hand), "how" is what makes things work, or put together, etc. "Why" is a nebulous term indicating a "reason" for that "thing" that works, etc.

"A void can't provide a reason or basis for anything."

This is the biggest problem I have debating aspects of science, not just cosmology. Many scientists will tell you they do not believe there is a "reason" for anything. There does not have to be. The classic "Why are we here?" begs a "reason" which likely does not exist. Reasons are human inventions to explain the explainable. I submit that our existence, and all we see and think, has no explanation as to "why".

Science can explain "how" things happen in many cases. I do not believe it can provide a "reason" why they happen.
Allow me to try and explain a bit better, as I'm not very good at putting thoughts to words.

Everything is from the same lego set or construction kit, which has the same universal rules of engagement everywhere. Also, everything is connected to something else by the rules of cause and effect. Nothing has a stand-alone isolated existence, it was created from this kit by its rules and engagement with its environment, and by cause and effect – which means a connection or relation to something else in the universe. This linage of cause and effect goes all the way back to the big bang i.e. everything has roots. For example, you and I are connected in the sense that we have a common ancestor.

Another possible reason for a universal connection is that our universe's empty space is not void, but is full of things such as quantum field/foam/fluctuations, aether, vacuum energy, dark energy or whatever. If it was void, then finding an object in it would be like finding a potato without a field. So for me, this full up space is as the field is to the potato.

Because of this kit and its rules, I believe everything has an explanation and a reason for its existence. The only dead end is when you get to the question 'why is there something rather than nothing'. Given that there is 'something' and its rules, then from there on, I believe everything is explainable and has a reason for its existence.

I see the universe as one whole deterministic mechanism and so has an explanation and reason right back to the 'why is there something rather than nothing question', then I give in :)
 
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David

Whilst I understand much of what you post, some I do not understand.

This: "I see the universe as one whole deterministic mechanism and so has an explanation and reason right back to the 'why is there something rather than nothing question', then I give in" sounds very Victorian. To loosely quote Laplace: "Give me the position and motion of every particle in the Universe and I will predict the whole of the future". Of course, this was quickly hit on the head by the Heisenberg Uncertainty Principle, which replied "No, you can't".

This seems to parallel your last sentence as if you are in agreement with Laplace, only to find your path is a cul-de-sac with the Uncertainly Principle scrawled as large graffiti on a blocking wall. Does this conclusion not indicate a conflict with your basic assumptions?


Cat :)
 
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David

Whilst I understand much of what you post, some I do not understand.

This: "I see the universe as one whole deterministic mechanism and so has an explanation and reason right back to the 'why is there something rather than nothing question', then I give in" sounds very Victorian. To loosely quote Laplace: "Give me the position and motion of every particle in the Universe and I will predict the whole of the future". Of course, this was quickly hit on the head by the Heisenberg Uncertainty Principle, which replied "No, you can't".

This seems to parallel your last sentence as if you are in agreement with Laplace, only to find your path is a cul-de-sac with the Uncertainly Principle scrawled as large graffiti on a blocking wall. Does this conclusion not indicate a conflict with your basic assumptions?


Cat :)
Not at all, Laplace has it right! I believe every quantum particle, even every quantum fluctuation, must be deterministic, all must obey cause and effect. I believe, that with the Uncertainty Principle the problem lies with the act of measuring. The 'measuring and observing' disturbs the system. Just because you cannot know the exact velocity and position of an electron, I suggest, that does not mean that it doesn't have an exact velocity and position. If I don't measure or observe the electron, I can imagine that it will continue with its exact parameters, unknowable, but still exact. So long as the system is unobserved, all its subsequent interactions will be precise and deterministic. For any of its properties to change by the smallest of amounts will require a cause.

So I still stand by my proposition that the whole universe, and indeed the whole of 'The Infinite' is deterministic and works like precise clockwork. At the same time, it's unpredictable because we could not provide Laplace with precise data without disturbing things, and hence changing the future. Heisenberg is only partly right in that you cannot predict the future, but his principle doesn't rule out a deterministic universe if you leave it alone.

For me, the only brick wall is as said - 'Why is there something rather than nothing'. It may still be possible to know everything about stuff, and all the laws of physics, but you don't need to know every last detail of the universe for that :)
 
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Hi David

I hope we are not going to fall out over what are only our opinions. I respect your opinions but still base mine on:

"To loosely quote Laplace: 'Give me the position and motion of every particle in the Universe and I will predict the whole of the future'. Of course, this was quickly hit on the head by the Heisenberg Uncertainty Principle, which replied "No, you can't".

There are other things which require my respect for the HUP.
I am prepared to modify the 'hit on the head' bit :)
Maybe I am wrong. So what? I have been wrong about plenty more things in my life. Can we just shake on it and carry on please?

Cat :)
 
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Hi David

I hope we are not going to fall out over what are only our opinions. I respect your opinions but still base mine on:

"To loosely quote Laplace: 'Give me the position and motion of every particle in the Universe and I will predict the whole of the future'. Of course, this was quickly hit on the head by the Heisenberg Uncertainty Principle, which replied "No, you can't".

There are other things which require my respect for the HUP.
I am prepared to modify the 'hit on the head' bit :)
Maybe I am wrong. So what? I have been wrong about plenty more things in my life. Can we just shake on it and carry on please?

Cat :)
Yes, of course, no problems :)
 
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Hi David
Just been re-reading posts and came upon this from above:
"everything has an explanation and a reason for its existence"
Has everything an explanation and a reason understandable by mankind?
Is this understanding arranged for us from 'above' or is it up to mankind to work it out? What would happen if we went the way of the dinosaurs?
Or is it just that if we "don't get it" we "don't get it?
Just got my anthropomorphic hat on and thinking of man as the centre
of the Universe. What is your take on this?
Cat :)
 
Nov 20, 2019
130
68
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Hi David
Just been re-reading posts and came upon this from above:
"everything has an explanation and a reason for its existence"
Has everything an explanation and a reason understandable by mankind?
Is this understanding arranged for us from 'above' or is it up to mankind to work it out? What would happen if we went the way of the dinosaurs?
Or is it just that if we "don't get it" we "don't get it?
Just got my anthropomorphic hat on and thinking of man as the centre
of the Universe. What is your take on this?
Cat :)
Just been re-reading posts and came upon this from above
Is this 'above' you're referring to the same as the 'above' lower down? :) sorry, couldn't resist that:)
Has everything an explanation and a reason understandable by mankind?
Possibly not. Instead of going the way of the dinosaurs, we might get (even) smarter:) and then yes. For now, most people struggle with relativity and quantum mechanics (I'm now thinking of your 'modern art gone wrong' description), so when or if a theory of everything comes to be, I think only a few would understand it anyway. I can't see it happening any time soon. Nature doesn't owe it to us to be understandable, I accept that as well.

On the positive side haven't we come along way in the last few hundred years of our ~ 6.4 million years of being human. For example, take the standard model of particles (16 is it), on one hand, it gives the impression that its almost done. Also, it looks like relativity and quantum mechanics might be combined one-day. You could be forgiven into thinking we're almost there, and that its just loose ends which need tidying up. With a thousand more years who knows, I think yes.

There's also the possibility that computers will outsmart us one day (have you heard of the 'singularity' by Ray Kurzweil) there are only a few years to go for that.
Is this understanding arranged for us from 'above' or is it up to mankind to work it out?
Definitely nothing from above. As you say "if we "don't get it" we "don't get it?"

The dinosaurs lasted 160 million years without even being smart, what could we achieve in that time?

I can conceive that its possible to know everything, but still except for that brick wall is as said above - 'Why is there something rather than nothing'.
 

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