Various methods of measuring Hubble Constant not quite in agreement - new physics?

[gary]

A 6 Feb 2019 article in Scientific American (https://www.scientificamerican.com/article/have-we-mismeasured-the-universe/) by Corey S. Powell discusses
how various methods of measuring the Hubble Constant are in agreement
within 10 percent or better, but that last 10 percent is proving somewhat
vexing.

The problem is that the errors bars for some of the methods aren't
overlapping with each other and there is an increasing confidence
that discrepancy is not due to experimental error alone.

There is a growing hunch by some researchers that the discrepancies
betray something fundamentally new that we don't understand yet.





Full article here :-
https://www.scientificamerican.com/article/have-we-mismeasured-the-universe/

Paper, "Sounds Discordant: Classical Distance Ladder & ΛCDM -based Determinations of the Cosmological Sound Horizon", by Knox et. al :-
https://arxiv.org/abs/1811.00537v1

[gary]

In a news release today from the University College London (https://www.ucl.ac.uk/news/2019/feb/gravitational-waves-will-settle-cosmic-conundrum), researchers
claim that gravitational wave measurements from approximately
50 neutron stars over the next decade will resolve an intense debate over
the Hubble Constant.




News story here :-
https://www.ucl.ac.uk/news/2019/feb/gravitational-waves-will-settle-cosmic-conundrum

Paper in Physical Review Letters (subscription required), "Prospects for
Resolving the Hubble Constant Tension with Standard Sirens" by Feeney et. al. :-
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.061105

[gary]

Meanwhile researchers at the Kavli Institute for the Physics and
Mathematics of the Universe have been attempting to map historical
changes in dark matter by analysing images of more than ten million
galaxies.





Story and video here :-
https://phys.org/news/2019-02-historical-dark.html

[madbadgalaxyman]

It is not required by every cosmological theory which is under current serious consideration, that the universe should be expanding at the same rate in every region that is within it.
(I am not talking here about relatively small regions of space , such as clusters of galaxies, where the expansion of the universe is (of necessity) slower due to a Strong local gravitational field)

Another untested assumption of most cosmologies is that the universe is isotropic (that is, it looks the same in every direction) and homogeneous (with matter on the largest scales being evenly distributed), but even the assumption of homogeneity is becoming dubious due to the Vast structures that have been revealed in redshift surveys......
there are known supergalactic structures up to a billion light years across!

Other assumptions which are not intrinsic to Big Bang and Expanding Universe models include:
- the idea that the universe had a beginning in time
- the idea that the universe began from an actual mathematical point.

I am not the biggest fan of the Big Bang concept, as its truth seems to rest on only a small number of observed facts.
BUT it would have to be regarded as an Observational Fact that::
(1) the universe is expanding
(2) the mean density of matter in the universe was much greater in its early years than it is now, and the density of the universe has got systematically smaller with the passage of time.

If we consider, for example, a Nearby low-surface-brightness Dwarf Irregular galaxy which is surrounded by little else but a cube of empty space that is 1 million light years on a side (as dIrr galaxies so often are, as they preferentially occupy lower-density regions of space), we can easily see that the current Matter Density of the universe must be exceedingly low......only one tiny patch of stars existing within a truly vast volume! (Note: an admixture of lots of "dark matter" is also necessary to account for the gravitational mass of one of these tiny galaxies)

So really, it Must be the case that the density of the early universe had - of necessity - to be very high; without this necessary Very High density, structures such as stars and galaxies could never have formed in our universe. In fact, it is very-well-known now that the time-rate at which stars formed was exceedingly high in the early universe;
naively, one may regard this very very rapid formation of stars as being due simply to the fact that much higher gas densities and gas pressures and gas masses existed then.

I am not a cosmologist or a physicist, but these facts seem to me be be evident even to the intelligent layperson.

[xelasnave]

Hi Robert
I am not a fan of the big bang either.
The first observation of an expanding universe was drawn upon to propose that the observed expansion could be extrapolated back to a "point" or I expect the "cosmic egg" that the Church seemed to be considering borrowing from the various pagan and other cosmologies that presented such in their attempts to explain creation.
And yet the observed expansion never could be extrapolated to a point when you consider that much later the theory of inflation was "invented" to get the theory over an annoying hurdle that failure to jump would see its demise.
So it seems to me that the only observational evidence is the background radiation which is supportive however it is not evidence that the theory of inflation has any footing.
And I find it simply impossible to accept what it tells us...I can not believe that the universe went from the size of a basket ball (perhaps) to certainly the size of the observable universe or larger in a zillionth of a zillionth of a zillionth of a second...that is an extrodinary claim and frankly I would expect that to buy the idea one could expect to require extrodinary evidence well past calculations that say that such was possible and in fact did occure.
Scientific theories require predictions to be validated.
As you observe this is not entirely the case...and I can add to that...the prediction of lighter elements falls down due to the observed absence of lithium. ..I have read a paper which basically sais...the litium was there but by such and such a process is now not there☺.
I sometimes wonder if the observed expansion tells the correct story...there was the tired light idea which suggets the expansion is not in fact occuring but that idea is seen as impossible...well if it turns out there is no expansion the cosmic egg idea must fail.
Personaly I dont like that the theory hints at creation whilst protesting that it does not deal with the creation of the universe but merely its evolution...original opponents to the big bang felt it was a mere religious ploy and given its creator U dont see such as unreasonable irrespective of being justified or not.
However steady staters have been sidelined ... I think the universe must be eternal simply because not to think such means one must take a point where there was nothing and things started from there...I cant believe that is possible and even the big bang theory, although hinting at such a situation, deals with something..a hot dense simething but a something nevertheless...so where did the hot dense something come from..if always there the universe can only be considered eternal.
Alex

[madbadgalaxyman]

hi Alex,
it has been a long while since I contributed to IIS, or even read any of your posts, but it is very good to hear from you again and it is very good to note how your thinking on scientific issues has progressively evolved to become very sophisticated.


I have mentioned, in my first post in this thread, a few of the 'elephants in the cupboard', that is, unknowns, in cosmology. But the "biggest elephant" may be the unanswered question of whether or not the universe is actually infinite, and the question of the true nature of what can be found beyond the part of the universe that is currently detectable by humans.



It is usually assumed that the universe is infinite, that it goes on for ever and ever in all directions, which of course would mean that, by definition, the currently observable (by people on planet Earth) region of about 20 billion light years in diameter is only the tiniest fraction of the entire universe. And this implies that conditions in some of the vast regions that lie outside of the observable region could conceivably be vastly different from those that are found inside the observable region;
in cosmological theorizing, there is currently no reason to have any certainty about the physical structures and physical laws existing in that part of space which is beyond the region of space that humans can currently observe.


cheers,
Robert

[raymo]

Whilst not blindly believing anything that has not been well and truly proven,
I am prepared to believe that because so many things about our universe
are so incredible [unimaginable speeds, densities, sizes, temperatures etc:]
that virtually anything is possible, including inflation. If I remember rightly,
quantum physics does not prohibit in principal, something being created from nothing. I personally tend to favour a finite universe with a definite beginning.
raymo

[RyanJones]

The idea of inflation is hard to get ones head around. The idea that everything is moving away from everything else at the same rate and that as such there is no central point from which everything is moving. Let's just go with that idea for a minute though and turn to the" observable universe " the key word being observable. All " observations " are taken from a central point, us, as it is us that is observing it. 13.5 billion years in every direction making the observer centre of the universe. This would hold true no matter where the observer was in the universe in which case it is inconceivable that there isn't more beyond what we can observe. Our " understanding " is only ever based on what we can observe though and all therories that have been tried and tested are under the assumption that with the technology or natural senses we possess that we can in fact observes everything that is possible. This to me sounds quite arrogant.

The other problem that I have with the idea of inflation is again that the universe and everything within it is expanding away from everything else. We as human beings are in that universe. Doesn't it make sense then that we are also, down to a subatomic level, expanding at that same rate ? And if so, how can we observe this expansion if we are part of it. Much like two people standing " stationary " on a train. For us to observe and measure the expansion of everything, if indeed this it what is happening, must we not be metophoically outside the train ? Or are we the only place in the universe that is not subject to this expansion ?

These theories are nice to a point of human comprehension but I am far from convinced they are " right ". Hence why we continually find holes in our own arguements. It may also be true that my personal thoughts are clouded by my ignorance on the subject matter, but then isn't that true for everyone expect the one person who does in fact " know " everything ?

[xelasnave]

What a wonderful discussion.

Robert you raise an interesting aspect about the universe being infinite or not.

The big bang has a feature I feel folk overlook when they suggest that it may be infinite.

The difficulty in my view must be that if we start with a finite object, and it would seem that the big bang starts with a finite object, we can not grow that object to infinity.

I think the theory of inflation basically suggest a rapid doubling of size and I suggest that no matter how many times you double the size you can never reach infinity.

As I understand the term it is a situation where adding subtracting or to multiply can not alter infinity.

I think the big bang can suggest the universe is very big but its premise of an intial finite state must preclude the big bang universe ever being infinite.

My understanding of the size of the observable universe is that it is approximately 90 billion light years in diameter..If I can find authority I shall post same.

Raymo

I also am not sure about the prohibitions that may be found in the Standard Model however I think one must remember that the suggestion that the Universe may have come from nothing has no basis in so far as the Big Bang Theory only takes us to a time a short time after "the big bang" and at that time the theory deals with a hot dense something often refferred to as a singularity but a something nevertheless.

Why folk jump from there to speculating that what ever it was that was hot and dense came from nothing I really dont know..

I think to arrive at that conclusion is driven by a need with humans to identify a creation point...the big bang certainly does not do that but certainly given the need or expectation that humans hold that there is a begining one can understand speculation will go that way.

But we have no science model to suggest something came from nothing.

And really even those folk who speculate upon where the "stuff" came from invoke quantum fluctuation which is something and certainly not a condition where we could reasonably say " well this condition is nothing."

As to accepting anything is possible I suggest the concept of inflation goes way beyond anything we can observe and perhaps the concept is beyond comprehension...but as I have said, for myself I find the proposition that the universe could grow from the size of a basket ball to a diameter of over 90 billion light years in a zillionth of a zillionth of a zillionth of a second...which for all reasonable analysis one can consider to be instantaneous...a period so short what else could you call it but instant??? ...to be highly unlikely particularly as there is no evidence at all...zip.

Now irrespective of what this initial stuff was that inflated I dont know how one can accept that such could be remotely possible ...it is even beyond god like...and yet no one seems to stop and say "hang on this is the most extrodinary claim that has ever been made in all of history should I accept it on the basis that someone has created this view by math alone with absolutely not one piece of observational evidence."


My concern is that such an acceptance has prevented any further developement of cosmology.

The idea was needed to fix the sameness problem...I expect hastely and in a panic for the problem as perceived threatened to bring the big bang theory down...and I get the impression the theory of inflation was presented and accepted with sighs of relief and the matter never visited again.

I think the sameness problem could be looked at differently..perhaps rather than requiring an external cause confinned to a small region there could be an inherent quality of matter that causes it to be the same as other matter even if that other matter is at the opposite end of the universe...and could not such and approach be more reasonable than requiring an instant growth of the Universe?

Personally I favour a static universe as did DrA and am inclinded to think a steady stste universe is probably more likely..the steady state has its problems granted but nothing like needing the theory of inflation.

But the proponents guard the theory because in my view it gives the thinking man the answer he wants (and what all humans through out time have wanted) and that is a point of creation.. .which ironically the bbt actually does not do...but it is a short leap (a quantum leap☺) to find creation if not god.

I dont think there could be such a point oppting for the belief there has always been something...meaning no start, no end, no top sides or bottom...and as you ponder that consider the saying "it is a wise man who can imagine a stick without ends"☺.

Hi Ryan
Although the universe is thought to be 13.5 billion years old that does not mean its diameter is 27 billion years...why? well one must include expansion since the inflation...the expansion is not limited by the speed of light you see☺ as it is space that is expanding and as such not confinned to loght speed...and here I note inflation and expansion are best thought of as two greatly different eras...or so I believe.

I will try and find authority for the size of the observable universe but I would encourage you to search as it will be so much more satisfying for you to work it out.

I hope our discussion can continue as it is an intetesting matter and somewhat tied to what we do...although I must admit I still regard cosmology as a sport where no particular view can be said to be certain...
Alex

[xelasnave]

I hope this link works.

https://en.m.wikipedia.org/wiki/Observable_universe

However it does seem to support the notion that the observable universe is approx 90 billion light years in diameter and why.
Alex

[RyanJones]

Indeed you are right about the 90 odd billion ly size Alex. This wiki though also moves to support the premise of my point regardless of the actual "size". It talks about a diameter. Diameter being defined as " a straight line passing from side to side through the centre of a body or figure, especially a circle or sphere " which directly suggests a central point of origin. Now to make that measurement, a central point needs to be defined. As we are the observer, the propostous and arrogant assumption is that that central point is us. And yet if expansion is correct, it is happening everywhere and no matter where it is observed, it is constant. So if we were somewhere else in the universe, it would appear the same. This leads to the idea of infinity. As you illuded to, infinity is not possible if it is presumed to be from a singularity ( single point of origin ).

I think this leads to what you were saying about these ideas being the limiting factor of cosmology. The only the way as, human beings, that we are capable of communicating these concepts is with current definitions such as diameter, time, volume, mass, velocity etc... Which despite being great to communicate ideas between one another, are all simply human constructs to that end. That need to define in order to communicate is the limiting factor at the very point of definition.

I'm not a religious man myself but the idea that a god exsis and is the creator of everything is actually no more propostous than any other idea. Despite all the scientific " measurements " of all that exsists, even these therories are subjective to the observer. It is quite arrogant of us to assume that we are even capable, with the senses we possess, to observe and difine everything that exists. Even exsistance itself is subjective to the observer.

It is no wonder then that no matter how hard we try to define the universe and its size, mass, contents..., we will always find something that doesn't add up. The earth was flat until it wasn't, the sun revolved around the earth until it didn't, we were the centre of the universe until we weren't and the universe is what we think it is now until it isn't.

[madbadgalaxyman]

By definition, if the universe is truly infinite, then the region of space that we humans have so far been able to detect of it with our available instruments , however grand it may seem to us in its physical scale, is by definition infinitely smaller than the Much Much More Vast regions of the whole universe. So it may be a fair analogy to think of the

so-far-observed part of the universe as being akin to a grain of sand in its size, as compared to a much larger section of the universe being like the entire Earth in its size.

By definition, the currently unobserved regions cannot be known about with certainty, though we can come up with many interesting theories about them; we cannot know for sure what precisely is beyond the observed region.....
volumes of space with differing expansion rates and/or differing physical laws? other universes? A supergiant wall of green cheese? Multiple copies of the Astrophysical Journal distributed throughout deep space? etc. etc.

(An entertaining and thought-provoking book on infinities of various sorts is "The Infinite Book" by John D. Barrow, who is one of the true Wild Men of physics and mathematics)

And we are to consider how often theory has proved to be Entirely in error when it comes to accurately describing and explaining a physical phenomenon, only to be later on Rescued and Corrected by the observations that are made of actual objects and phenomena,
e.g. nearly everything that theorists thought they reliably knew about the process of star formation has turned out to be Mostly Wrong now that Star Formation been turned into an observational science.


cheers, Robert

[xelasnave]

Hi Ryan
The wonderful thing about the observable universe concept means that each of us is the center of the ( observable universe).. .I certainly enjoy pointing out to folk who hint that I am self centered that well of course as I am at the center of the observable universe..after a little time I make them happy by showing they are also the center of their observable universe☺.

And although we cant talk about religion, which I point out that I am not☺, the prospect of an eternal universe with no creator appeals to me more than a finite universe (with necessarily a creation point and perhaps an entity responsible for creation as some will imagine) as the entity presumably and necessarily eternal would have to come out of eternity (a long time☺) to cause creation...I suggest this such merely to move on to consider the prospect of creation without an entity which in the same way forces us to consider how eternity existed before the big bang and then at some point eternity gave in to allow the universe to be created, somehow, and finite time start and to exist outside of eternity☺.

Something I find interesting, and U wonder what Robert may be able to input on this curious feature of gallaxies...observations seem to suggest that gallaxies line up like buttons on a string...the string being the jets that flow from the presumed central black hole of a gallaxy...if we look at the filament structure this is how the galaxies align...or so I believe.
I have tried many times to get discussions going on this most curious situation but annoyingly all I have got as a reply to a posting (elsewhere) is that such is entitely consistent with the big bang theory...as though we dont want to talk about it☺.

But it looks as if this line up exists and one must question why...its seems one galaxy passes material to the next on the string...
I find it extrodinary that no one finds this interesting.
Alex

[xelasnave]

Hi Robert
I am inclined to think your grain relationship is probably the way it is and we are even more insignificant than our observations to date tell us.

Folk speak about nothing but I suggest there can be no such thing because if there is indeed nothing there , wherever that may be☺, then there must be something.

So we get to the edge of the universe ☺ can we find that the universe sits in nothing? Well of course not as there can only be something..so does this not indicate the universe must be infinite.

But the problem with infinite not only means no limit in extent but may mean no limit in size☺ both larger and more astoundingly as to smaller...which translates to ideas that a single electron holds multiple universes☺.

Then perhaps the most alarming thing about infinite is everything and us perhaps is then infinite in replication and at larger and smaller scales..without limit☺.

So are you aware of the button on a string line up with gallaxies? And if so do you see anything interesting.
Alex

[RyanJones]

Alex,

The button on a string formation of galaxies does intrigue me and I will follow that up with some gsearch ( Google research ).

I know from my following of many of your posts that you are an astrophotographer also and I wonder if you have ever noticed as I have, the amazing number of groups of relatively evenly spaced groups of 3 stars that litter our images. I find that fascinating and often wonder if there's any reason for it ?

As far as the discussion for infinity. I refer to what I feel is the most perfect number in mathematics, PI. For as far as it is possible to calculate, there is no know pattern or order to is decimal places and yet in all that chaos it defines the most perfect shape with the smallest possible surface area per volume. The definition of natural efficiency. An equation that is perfectly independent of any number that is associated with it yet creates undeniable definition based on the associated number. So I put it to all that maybe the size ( volume ) of the universe can be defined as 4/3pi x infinity cubed ?

[xelasnave]

Ryan
There is a reason for everything.

I notice so many things that I find interesting but generally I keep stuff to myself mainly because when one makes an observation one is driven (at least I am) to explain why it may be so...and so rarely do you get folk happy to discuss the matter in somewhat a positive manner.

As to the three stars I suggest you get a 3d understanding of the relationship of all you notice and see if there is anything they hold in common...a big job so get started.

As Asimov I think it was said discoveries come from making the observation...isnt that interesting.

It is difficult to indulge "free" thinking or explore stuff on most science sites..I dont know if you know of Cosmoquest but its somewhat indicitive of the reception an armchair scientist receives..it is understandable to a large degree but I suspect causes many to give up trying to think of something new.

I spent years working out how gravity works only to find I was on the same track as Le Sage back in 1745.
I am convinced gravity works via a pressure and crudly can build a universe using that approach...and that is not to suggest I cast out GR etc...but to myself I find I can explain how everything works in that universe from a lens to an atomic bomb...its cool if you are not trying to convince others you understand things...I am convinced dark matter has no need to exist nor dark energy and happily I noticed a recent paper somewhat moving my way☺.

If you consider gravity as a pressure the need for datk matter disappears but as I cant express the idea with math I can only hold a internal belief that I know how the gallaxies rotate via an external rather than an internal influence.

I spend a great deal of time still thinking about this stuff but these days I keep it to myself as after all its my opinion and does not gain status by expressing it to others.
The galaxy line up I believe hints at something extremely grand ... I look forward to your thoughts.
Alex

[xelasnave]

And sorry Gary for cluttering your thread with musings...but as folk notice the activity they will at least get to notice what it was you posted...not my stuff thats for sure.
Alex

[RyanJones]

Feel free to PM me Alex if you need someone to bounce these ideas off. I too have found it difficult to find someone that is open enough to question what we " know "

I too don't feel that dark matter or dark energy are part of what is out there. I believe that both serve as a technical way of saying both we don't know and also we might be wrong.

I have therories that I don't often share around black holes and what is going on there. Far from the beliefs of many and probably well tied to your gravity pressure theory.

I feel we have taken this thread hostage but if anyone else feels like they like o chime in..... My mind is open

[xelasnave]

Certainly the mention of "dark" is a genuine recognition by science that the area is not totally understood..a placeholder is a good way to look at it...we onow there is something but we but know much at all☺.

Thanks for your offer Ryan I will keep your offer in mind.
Thank you.
Alex

[gary]

Hi Alex,

Thank you and absolutely no problem.

Muse away!

We're just glad the fires appeared to have dodged you.

[xelasnave]

Thank you for your understanding Garry.

Fortunately I am all mused out:D
alex

[sjastro]

It’s been awhile since I have posted here.
While we don’t have a sample size of fifty binary neutron stars to determine the Hubble constant, the current sample size of one allows us to gather information on the redshift.
How does the redshift of the gravitational wave source GW170817 formed by the neutron star merger compare to the cosmological redshift z calculated by “conventional” means?

By conventional means using the formula:
z = (λ – λ0)/ λ0

λ is the wavelength say of hydrogen Balmer lines in the spectrum of a distant galaxy.
λ0 is the wavelength of the Balmer lines in a rest frame such as a laboratory spectrum.
GW170817 fortunately originated in the galaxy NGC4993 the redshift of which is calculated by conventional means.

Determining the cosmological redshift of a gravitational wave is anything but straightforward.
Firstly we don’t have the benefit of a catalogue of gravitational wave laboratory spectra that serves as our rest frame.
Secondly the gravitational waves measured by LIGO and Virgo don’t explicitly measure a redshift in frequency as there is degeneracy issue.
This issue will be made clear a little later on.

We need to define the effective mass of a binary system to understand how the redshift is calculated.
Intuitively one might think this is simply the sum of the masses of the neutron stars or black holes making up the binary system but it is somewhat more complicated.
We are interested in the mass-energy of the binary system which also includes the energy contribution from the gravitational waves.

The effective mass or “chirp mass” CM for a binary system is defined as.

CM= (m1.m2)^0.6/(m1+m2)^0.2

m1 and m2 are the masses of the neutron stars.


Since the chirp mass includes energy which is a function of frequency that can be redshifted, the chirp mass itself can be redshifted according to the formula.

CM(redshifted) = (1+z)CM(rest frame)

The gravitational frequency data from LIGO and VIRGO allows us to calculate the redshifted chirp mass (CM(redshift)).
Here lies the problem, we don’t know the contributions of z and CM(rest frame) to the redshifted chirp mass.
This problem is known as the M, Z degeneracy.
If the CM(rest frame) can be determined then the redshift z can be calculated as CM(redshifted) is already known.

This is where LIGO stepped into to the picture.

sjastro said:
Congratulations on this significant discovery.
Has this discovery broken the mass-redshift degeneracy allowing the calculation of the redshift of GW170817?
If so how does it compare to the redshift of NGC4993?

Christopher Berry LIGO said:
Not directly, but you could if you are willing to assume a neutron star mass.

Since (i) we get masses consistent with known neutron stars, and (ii) we overlap with the distance estimates for NGC 4993, you’d end up with a redshift consistent with that of the galaxy. For precise numbers you’d need to factor in the peculiar velocity of the binary.

Using this piece of advice and data from the PRL paper on GW170817 the redshifted chirp mass in the detector frame (CM(redshift)) was 1.1977 solar masses, while the chirp mass in the rest or source frame (CM(rest)) for typical neutron star binaries averages 1.188 solar masses.

Using the formula CM(redshift)=(1+z)CM(rest) and substituting in these mean values, the redshift for GW170817 is found to be z=0.008.
From the SIMBAD astronomical database NGC 4993 has a redshift z=0.009787.

This doesn’t factor in the peculiar velocity of GW170817 which is the velocity of the binary in space rather than due to the expansion of the Universe.
There is some promise even with this rough back of the envelope calculation…………….

[xelasnave]

Hi Steven
It is so good to have you input meaningful comment and give members a little better understanding of the research.

No doubt you are better placed than most to offer reasons why hunting gravity waves is worthwhile and so I ask could you take the time to share with us if there are any particular expectatuons that it is hoped that this branch of GR may produce.

Alex

[sjastro]

Thanks Alex.
While the technology is still very much in its infancy, the ultimate purpose is to develop gravitational wave astronomy over a wide range of frequencies much like conventional astronomy is done over the electromagnetic spectrum.

Astronomy in the electromagnetic spectrum is limited up to the Cosmic Radiation Background which is an opaque barrier.
Gravitational wave astronomy should allow this barrier to be penetrated and in theory take us back to the inflation era of the Universe which is a source for low frequency gravitational waves.
https://en.wikipedia.org/wiki/Gravitational-wave_astronomy#/media/File:Gravitational-wave_detector_sensitivities_and_ast rophysical_gravitational-wave_sources.png

[xelasnave]

Thanks for the link Steven I read it all but I think I read it a while back..no matter these days with a failing memory most things seem new☺
Is there any physical nature to a gravity wave and I ask perhaps because of my incomplete understanding of GR...but I see it as a coordinate system describing somewhat movement of space and objects in it with no explaination of the particles involved...I expected ct at some level there must be particles or at least a means of carrying information...I know the eather is not needed but do you see at some level there has to be some form of particle soup that makes up space...You know my passion for a push gravity mechanism☺ but I guess what I ask really is there any view from a quantum level as to what makes up a gravity wave.
I guess I am revisting the idea that a wave must travel in a medium...and I know light is said not to have a mediun so I guess I just cant get my head around how things can move with no medium.
Say take gravity waves essentially a expansion and contraction of space ... what is this medium that expands and contracts..it must be something as it can't be nothing.
I expect what I ask for can only be speculative but I would be happy with that.

Alex

[xelasnave]

Also given the incredibly short duration of inflation I do wonder about what they expect to be able to find...seems most ambitious.
Mind you as I have said many times I dont accept inflation and think it always was a patch that should have been replaced shortly after the fix☺...I cant understand why science disregards my concerns☺.

You may as well say inflation os synonymous for "instantaneous" for the time allocated to it...I can not accept that it all went from the size of a basket ball to greater than the observable universe in a zillionth of a zillionth of a zillionth of a second...to quote Neil de G.

Does the scientific community think inflation is reasonable or are there better ideas brewing?
Alex

[sjastro]

Alex,

Newton considered space to be nothing more than a coordinate system.
Einstein considered spacetime to be a gravitational ether which is analogous to the old luminiferous ether concept that was once considered the medium in which light propagated.
The gravitational ether allows the propagation of gravitational waves in the form of ripples in spacetime which causes the elongating of spacetime in one direction and contraction in the perpendicular direction.
This elongation and contraction is a very real physical effect and is detected at LIGO and VIRGO which are very sophisticated interferometers as a time delay between a laser beam that travels a slightly further distance in the stretched direction of spacetime than the beam that travels in the contracted direction.

As you are aware spacetime can bend in the presence of mass or expand as in the case of an expanding Universe.
Another property of spacetime if the geometry changes rapidly with time such as in black hole and neutron star mergers or even inflation, gravitational waves are generated.
Gravitational waves carry information in the form of energy.
For example when binary neutron stars merge their combined mass is not the sum of the individual masses but less.
The difference is the energy carried by the gravitational wave.

[sjastro]

The period of inflation lasted from about 10^-36 s to around 10^-32 s after the Big Bang.
As to how big the Universe expanded in this period causes some confusion.

The size of the Universe may in fact be infinitely large; we don’t know its size true but since the Universe expands we know its scale changes.
We can only express the size of the Universe in terms of the observable Universe.
The cosmic scale of the Universe as it is now, is arbitrarily set as equal to one; the cosmic scale factor is the cosmic scale as it was at some point in the past divided by the current cosmic scale.
Using the cosmic scale factor calculated for immediately before and after inflation we can roughly calculate the size of the observable Universe over this time frame.

At 10^-36 s the size of the observable Universe was around 8 X 10^-30 meters, immediately after inflation was completed at 10^-32 s it expanded to around the size of a grain of sand.

Inflation still provides the best explanation of why the Universe is flat and causally connected.
Most importantly it is a falsifiable theory as inflation predicts the existence of low frequency gravitational waves and a particular type of polarization in the Cosmic Radiation Background.
Unfortunately a few years ago there was a premature announcement that inflation was confirmed as the polarization in the Cosmic Radiation Background was detected but the discovery was withdrawn after the polarization was found to caused by magnetic dust particles in our galaxy.

[xelasnave]

Thanks for all of your input Steven.
And particularly re faulsibility of inflation which I was unaware of...I am sure some one wrote someplace that it wasnt but they may have ment in relation to capabilities at a particular time...

Thanks for contributing here I am sure your input will be of great interest to new members perhaps developing an interest in cosmology.

Alex

[xelasnave]

Steven re the first post reply.

I suppose what I have difficulty with is that presumably because of my background is I tend to think at some level there must be a physical thing, a very small thing, discrete, as opposed to thinking of energy as ...well the way its thought of☺.

Thanks again it is really great that you have popped it.
I hope all is well in your world.
Alex