Galaxy survey to probe why the universe is accelerating

June 30, 2015 by Carlton Baugh, The Conversation
Understanding how galaxies are arranged could be the key to figuring what causes the expansion of the universe. Credit: ESA/Hubble, NASA and S. Smartt (Queen's University Belfast), CC BY

We know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. The most likely explanation is that a strange force dubbed "dark energy" is driving it. Now a new astronomical instrument, called the Physics of the Accelerating Universe Camera (PAUCam), will look for answers by mapping the universe in an innovative way.

The camera, which will record the positions of around 50,000 galaxies at once, could also shed light on what dark matter is and how the cosmos evolved.

In the 1990s, astronomers studying exploding stars – supernovae – in galaxies far away discovered that the universe's expansion was accelerating. This came as surprise, as scientists at the time thought it was slowing down. With no obvious solution at hand, scientists argued that there must be some sort of mysterious force – dark energy – pulling the apart.

Fast forward about two decades and we still don't know what dark energy is, thought to make up 71% of all the energy in the universe. One theory says it can be explained by an abandoned version of Einstein's theory of gravity – known as the "cosmological constant" – which is a measure of the energy density of the vacuum of space. Another argues that it is caused by enigmatic scalar fields, which can vary in time and space. Some scientists even believe that a weird "energy fluid" that fills space could be driving the expansion.

Mapping the sky

Of course, the only way to find out is through observation. After spending six years under design and construction by a consortium of Spanish research institutions, PAUCam was successfully tested out for the first time this month – seeing "first light" on the 4.2 metre William Herschel Telescope on La Palma in the Canary Islands.

Using the information captured by PAUCam, an international team, including researchers from Durham University's Institute for Computational Cosmology, is being set up to build a unique map of how galaxies are arranged in the universe.

Galaxy survey to probe why the universe is accelerating
Timeline of the universe, assuming a cosmological constant. Credit: Coldcreation/wikimedia, CC BY-SA

Such a map will contain detailed new information about the basic numbers which govern the fate of the universe; its expansion and about how the galaxies themselves were made. The map will reveal the extent of structures in the distribution of galaxies. These structures grow due to gravity – if the expansion of the universe is speeding up, then it is harder for gravity to pull matter together in order build these structures. Knowing the strength of gravity and measuring the size of structures in the galaxy distribution can therefore help us deduce the expansion history of the universe.

Astronomers can map the positions of galaxies on the sky by taking images or photographs. These are projected positions and so do not tell us the distance to a galaxy from the Earth. A galaxy could appear to be very faint because it is at a large distance from us or simply because it is nearby, but is intrinsically faint with few bright stars.

Traditionally, astronomers have used spectroscopy to measure the distance to a galaxy. This technique works by capturing the light from the galaxy and spreading it out into a spectrum according to its wavelengths. In this way, they can investigate the pattern of lines emitted by the different elements in the stars that make up the galaxy. The further away the galaxy is, the more the expansion of the universe shifts these lines to appear at longer wavelengths and lower frequencies than they would appear in a laboratory here on Earth. The size of this so-called "redshift" therefore gives the distance to the galaxy.

Early surveys of galaxy positions painstakingly measured such spectra one galaxy at a time, pointing the telescope at each galaxy in turn. Modern surveys can now record up to a few thousand galaxy spectra in a single exposure.

PAUcam will revolutionise survey astronomy by measuring the distances to tens of thousands of galaxies it can see each time it looks at the sky. It does this by taking 40 photographs or images using special filters that isolate a portion of the light emitted by a galaxy. This allows a quick spectrum to be built up for each galaxy at a fraction of the traditional cost. This spectrum also acts like a DNA for each galaxy, encoding information about how many stars it contains and how quickly new stars are being added.

The camera has been tested using the William Herschel Telescope. Credit: wikimedia commons, CC BY-SA

Looking for answers

My team here at Durham will build computer models of the evolution of the universe, which aim to describe how structures like galaxies have developed over 13.7 billion years of cosmic history. The cosmologist's universe is mostly made up of an unknown substance called dark matter, with a small amount of "normal matter".

PAUCam will allow cosmologists to test their models for building galaxies by measuring the lumpiness of the galaxy distribution in the new map. This is important because it tells us about the distribution of the dark matter, which we cannot see directly.

We know from previous observations that galaxy clusters contain dark matter. By counting the number of galaxies in a cluster, can estimate the total amount of (visible) matter in the cluster. By also measuring the velocities of the galaxies, they find that some are moving so fast that they should escape the gravitational pull of the cluster. The reason they don't is because huge amounts of invisible dark matter is increasing the gravitational pull. If the galaxies are very clustered – or their distribution is lumpy – then the computer simulations show that this means the galaxies live inside more massive dark matter structures.

PAUCam will allow us to learn more about an effect called gravitational lensing, in which the mass in the universe bends the light from distant galaxies, causing their images to appear distorted. Scientists can study the distortions to calculate how massive the patch of the universe really is – including the dark matter. This is one of the key probes of that is planned for the European Space Agency's Euclid mission, which is scheduled for launch in 2020.

The lensing distortion depends on the lumpiness of the , which is turn is determined by how fast the universe is expanding. If the universe expands at a fast rate, then it is harder for gravity to pull structures together to make bigger ones. PAUCam will help us to disentangle the signal from gravitational lensing from simple alignments between the orientations of galaxies which develop as they form.

A galaxy survey like PAUCam has never been attempted on this scale before. The resulting map will be a unique resource to help us learn more about how are made and why the expansion of the universe seems to be speeding up. We hope to have the answer once the PAUCam survey is finished by around 2020.

Explore further: Astronomers discover more than 800 dark galaxies in the famous Coma Cluster

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Tuxford
1.5 / 5 (8) Jun 30, 2015
By also measuring the velocities of the galaxies, they find that some are moving so fast that they should escape the gravitational pull of the cluster. The reason they don't is because huge amounts of invisible dark matter is increasing the gravitational pull.


Just can't let these stated assumptive facts go unchallenged. Otherwise, there is no exit to the confused state of modern cosmology, built on endless assumptions.

Yes, some galaxies are moving so fast to exit the cluster, since they were formed and ejected therefrom. Why the assumption that they must be held thereto by mysterious forces? And why the assumption that gravity has influence over infinite distances? Just because if fits a math model over shorter distances? Really? That's enough justification?

a weird "energy fluid" that fills space...
Well that's a start. Everything detectable is simply the salt in the ocean.
docile
Jun 30, 2015
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docile
Jun 30, 2015
This comment has been removed by a moderator.
denglish
3.9 / 5 (7) Jun 30, 2015
Why the assumption that they must be held thereto by mysterious forces?

Not an assumption. An educated guess based on observation. There is unseen sources of gravity. These sources have been called dark matter.

Just because if fits a math model over shorter distances? Really? That's enough justification?

That's better than wild speculation.

JustAnotherGuy
3 / 5 (1) Jul 01, 2015
Hello.. just a common dude passing by here. Wanted to point something about these "assumptions" made in this article.
It seems to be that a more powerful instrument is being developed to obtain more accurate data from properties and behavior of galaxies for further use in hypothetical topics like "dark matter" and "dark energy".
Is there need for new instrument if the assumptions are made already? That must mean something..

But don't mind about my words, I'm no expert.
Just watching the pics: that's a good one with telescope over the clouds!
EnsignFlandry
not rated yet Jul 01, 2015
Dark matter is formed with (magnetic) turbulences and density fluctuations of vacuum, which forms the space. It's closely related to B-field of inductors and scalar waves of Nicola Tesla - so it can be generated and manipulated in the lab. It represents the longitudinal component of CMBR noise, whereas the photons represent the transverse component of it. The dark matter is not so transparent and inert as it looks at the first sight - but the materials or arrangements which are capable to manipulate it don't occur naturally - charged capacitors, superconductors, ferromagnetic domains in monopole state. Actually the more the material is transparent for photons (graphene), the less it gets transparent for scalar waves.


Well, yes, all that is well known by all physicists. You just have expressed it in a rather unique way.
JeanTate
4.2 / 5 (5) Jul 01, 2015
@Tuxford:
Yes, some galaxies are moving so fast to exit the cluster, since they were formed and ejected therefrom. Why the assumption that they must be held thereto by mysterious forces?
Because they are still 'in' the cluster?
And why the assumption that gravity has influence over infinite distances? Just because if fits a math model over shorter distances? Really? That's enough justification?
Of course not. Better is that the physics theory which 'describes' gravity - General Relativity - has passed all experimental and observational tests with flying colors (so far) ...
JeanTate
4.4 / 5 (7) Jul 01, 2015
@JustAnotherGuy:
Hello.. just a common dude passing by here. Wanted to point something about these "assumptions" made in this article.
It seems to be that a more powerful instrument is being developed to obtain more accurate data from properties and behavior of galaxies for further use in hypothetical topics like "dark matter" and "dark energy".
Is there need for new instrument if the assumptions are made already?
I think you're being tripped up by the langauge of popsci, and its conflict with what scientists actually write ... "dark matter" and "dark energy" are, at one level, just hypotheses, and a key goal of astronomy (as a branch of science) is to test hypotheses. These are different from the "postulates" (a.k.a. "assumptions") at the heart of a theory of physics, such as General Relativity (e.g. The laws of physics are the same in all inertial frames of reference) ...
JeanTate
4.3 / 5 (6) Jul 01, 2015
@docile:
But the mainstream physicists elevated their ignorance to a whole new level: they're denying whole century the phenomena and artifacts, which they're trying to find at least last forty years - just under another names
But at least they still insist on testing their hypotheses, models, assumptions, theories etc via experiments and observations.

It seems to me that you are advocating abandoning this key part of the doing of science, are you?
JustAnotherGuy
not rated yet Jul 01, 2015
I think you're being tripped up by the langauge of popsci, and its conflict with what scientists actually write ... "dark matter" and "dark energy" are, at one level, just hypotheses, and a key goal of astronomy (as a branch of science) is to test hypotheses.

Not really such a confusion. That is how I already suppose science works.
Just pointing out about the called "assumptions" in comments above.
I should have quoted the comments, the more clear my comment should be.

By the way, article starts stating something that IS:
"We know that our universe is expanding at an accelerating rate"
And finish it with something that SEEMS TO BE:
"and why the expansion of the universe seems to be speeding up"
It's clearly not to be taken so "strictly" about definitions..
TechnoCreed
4.5 / 5 (8) Jul 01, 2015
@JustAnotherGuy
Wanted to point something about these "assumptions" made in this article.
First thing; an article is not a scientific paper. Second, before you post any dismissive comments make sure that you understand what has been observed. About dark energy, you can question the validity of the postulates, but you cannot deny the observations. http://cordis.eur..._en.html
EnsignFlandry
5 / 5 (2) Jul 01, 2015
@Tuxford Just can't let these stated assumptive facts go unchallenged. Otherwise, there is no exit to the confused state of modern cosmology, built on endless assumptions.

Yes, some galaxies are moving so fast to exit the cluster, since they were formed and ejected therefrom. Why the assumption that they must be held thereto by mysterious forces? And why the assumption that gravity has influence over infinite distances? Just because if fits a math model over shorter distances? Really? That's enough justification?


Gravity has an infinite range according to the equations. This has been verified out to billions of parsecs, not exactly a short range. Gravity is not an assumption. There is no assumption about mysterious forces. They are curious about some things and want to find answers.
EnsignFlandry
5 / 5 (6) Jul 01, 2015
The medieval Church was indeed ignorant and it denied the experimental observations. But the mainstream physicists elevated their ignorance to a whole new level: they're denying whole century the phenomena and artifacts, which they're trying to find at least last forty years - just under another names. It would be rather entertaining to watch, if this ignorance wouldn't also lead into environmental, energetic, financial and geopolitical crisis. This is the result of belief into power of reductionist theories and formal math - and also the result of occupational driven attitude, which pervades whole scientific community.


Hmmm, let me be polite and say that what little of that makes any sense is utterly wrong. I'll go out on a limb and guess that you are not a professional scientist, or have a degree in a natural science.
TechnoCreed
5 / 5 (3) Jul 01, 2015
@EnsignFlandry
Gravity has an infinite range according to the equations.
Two massive objects are in interraction within the Hubble radius only; gravity travels at the speed of light.
JustAnotherGuy
not rated yet Jul 02, 2015
First thing; an article is not a scientific paper.

Kind of old news. But that's very coherent with the fact that I referred on an article's content, not on a scientific paper's content.

Second, before you post any dismissive comments make sure that you understand what has been observed.

Seems to be something in my comments makes you suspect of dismissive purposes. Not pretty sure what was it. Hope next time i do better, to avoid susceptibilities....

About dark energy, you can question the validity of the postulates, but you cannot deny the observations. http://cordis.eur..._en.html

I can question this 'postulate' of me denying something. That's for sure!

rossim22
1.7 / 5 (6) Jul 04, 2015
The entire foundation of this concept rests on the assumption that redshift can ONLY be caused by recessional velocity. If any other mechanism exists, then every theory produced with the expansion of 'space-time' in mind will be erroneous.
Bookbinder
1 / 5 (2) Jul 04, 2015
Dark Energy: the new, new, NEW and improved version of the cosmological constant. So, let me throw this out there: The universe is accelerating because we are still in the throws of the Big Bang. It is early days yet. Creation is still taking place and the shock wave is still radiating out, space time continues expanding, while the increased distances reduce the force of gravity slowing it down. Using the bullet analogy, when the gun is fired the bullet accelerates from zero before it slows due to gravity. We are still in that acceleration phase but the force of gravity has lessened since the gun was fired. OK? So commence firing.
docile
Jul 04, 2015
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TechnoCreed
5 / 5 (5) Jul 05, 2015
@JustAnotherGuy
I can question this 'postulate' of me denying something. That's for sure!
Alright, maybe I misunderstood your first comment... Let's see.
It seems to be that a more powerful instrument is being developed to obtain more accurate data from properties and behavior of galaxies for further use in hypothetical topics like "dark matter" and "dark energy".
Dark matter and dark energy are not hypothetical; they are real observed phenomenons. DM and DE are not the only thing being investigated by these ever powerful instruments but they are part of the Universe and as such deserve their share of considerations. Explain why you are questioning the value of these observations?

Just in case you do not know this, the current cosmological model is called ΛCDM read Lambda-CDM. The lambda refers to Einstein's cosmological constant and to the accelerating expansion of the Universe and the CDM to cold dark matter. https://en.wikipe...DM_model
JeanTate
5 / 5 (5) Jul 05, 2015
The entire foundation of this concept rests on the assumption that redshift can ONLY be caused by recessional velocity.
a) it's not an assumption
b) this is not the only foundation (primordial abundance of light nuclides, angular power spectrum of the CBM, ...)
c) it's not even 'recessional velocity'!
If any other mechanism exists, then every theory produced with the expansion of 'space-time' in mind will be erroneous
And if wishes were horses, beggars would ride.

Wishful thinking is not astrophysics or cosmology; both require very hard work and many years of intense study ... may I ask how much of that have you done?
JeanTate
5 / 5 (4) Jul 05, 2015
@Ren82:
Expansion of fictional space-time was never observed yet
Of course it has been ... please, don't further damage your (rather limited) credibility with such nonsense
So this theory is based only on faith and can no be called science
Apart from the fact that the premise is false, your logic is faulty too ... every theory in physics rests on postulates, and physics is the 'hardest' of sciences; further, the key to science is the *testing* of conclusions derived from models, built on theories. In this case, the conclusions are consistent with all relevant observational and experimental results.

Questioning conclusions and experimental data is fine; doing so on the basis of a ridiculous strawman is not. Please stop it.
brodix
1 / 5 (2) Jul 05, 2015
If redshift is an optical effect that compounds on itself, it would far more effectively explain why the rate increases proportional to distance, rather than having to add the fudge factor of dark energy.
We appear to be at the center of this expansion and so the argument is that space itself expands, based on the premise of the "fabric of spacetime," but if General Relativity is to be invoked, presumably the speed of light needs to increase proportionally, in order to remain Constant, but if that were so, there would be no redshift, as the light would still arrive at the same rate.
Which gets back to redshift as optical, as we are at the center of our view of the universe.
In which case, the CMBR would be the solution to Olber's paradox. The light of ever more distant sources, shifted entirely off the visible spectrum.
JeanTate
5 / 5 (4) Jul 05, 2015
@brodix:
We appear to be at the center of this expansion [...] as we are at the center of our view of the universe
There is a class of cosmological models which looked at something like this ('void cosmology'), but it turns out it isn't consistent with the data
the CMBR would be the solution to Olber's paradox. The light of ever more distant sources, shifted entirely off the visible spectrum
Nice idea, but strongly incompatible with the astronomical data; for example, its spectrum is completely unlike that of 'redshifted ever more distance sources'
If redshift is an optical effect that compounds on itself
Trouble is, no one has come up with any remotely plausible such effect, not even by 'reverse engineering' it. If wishes were horses, beggars would ride ...
Returners
1 / 5 (3) Jul 05, 2015
General Relativity actually predicts an accelerating universe. Here's why.

Recall basic concepts:
In the presence of a strong gravitational field, time passes more slowly. Far away from a strong gravitational field time passes more quickly.

Therefore when two galaxies are close to one another, each galaxy experiences time passing more slowly. As the two galaxies move away from one another, each galaxy experiences time accelerating because the net curvature of space-time is less the farther the two galaxies are from one another.

Now where's my second Nobel? They haven't even given me the first one yet for disproving Dark Matter theory.
Returners
1 / 5 (3) Jul 05, 2015
Also, each second within the gravitational field of a star passes slightly faster than the previous second, because the star has burned off a tiny amount of its mass, which has escaped as energy in the form of photons, and in the form of particle ejecta, thereby weakening it's gravitational field. Weaker gravitational field means time moves faster.

So for example, every second on Earth is very, very, very slightly shorter than the previous second, because the Sun is always losing mass, and the gravitational field is always slightly smaller than it was during the previous second. Thus when you look at a distant galaxy today, time is passing faster for us than say a billion years ago, but it is also passing faster for that galaxy than it was a billion years ago, because that galaxy is farther away, and that galaxy has burned off some of it's mass during that time.

General Relativity predicts an accelerating universe, for at least two reasons as I've outlined here.
Returners
1 / 5 (2) Jul 05, 2015
Now, if time is passing faster for that galaxy, because it is farther away and in a region of space-time which is relatively "flatter" than say in the previous billion years, then we have a self-reinforcing acceleration. If the galaxy is moving say 10,000km/s through "local" space-time, but the length of it's "second" is constantly decreasing as it moves into flatter and flatter space-time, and as its constituent stars burn of some of its mass, which escapes into inter-galactic space as degenerate photons, then to a distant observer, that galaxy would appear to be "accelerating" in velocity.

Distance/Time...

10,000km/s

If the length of a second got 1% smaller over a billion years, then to a distant observer the galaxy would appear to be moving 10,101km/s through local spacetime...thus "accelerating".

This is actually relatively simple to grasp.
brodix
not rated yet Jul 05, 2015
JeanTate,
Here is an interesting proposal;
http://fqxi.org/d...kets.pdf
Keep in mind that it is impossible to falsify a theory if every time observations don't match it, you are allowed to invent an enormous new force of nature, as with both Inflation and Dark Energy.
If you followed the early history of this cosmology, it was assumed it was an expansion in space and the problem arose that there is no apparent lateral action to match the redshift, so it appears that we are the center of the universe. So then it was argued that space itself expands, which makes every point appear as the center.
Yet that means there is a constant measure of space determined by the speed of intergalactic light, since it presumably takes light longer to cross this distance. Than an expanding measure based on the spectrum of the very same light. So which is space, that defined by the speed of light, or that defined by redshift?
brodix
not rated yet Jul 05, 2015
Returners,
Wouldn't these two effects balance each other?
That what is expanding between galaxies is balanced against what is contracting into them.
Wouldn't that be Einstein's Cosmological Constant, which was originally proposed as a balance to keep gravity from collapsing the universe to a point.
JeanTate
5 / 5 (4) Jul 05, 2015
@brodix:
Here is an interesting proposal
Would you mind explaining, please, why this is interesting, in the context of cosmology? My read of it is that it has nothing to do with cosmology
Yet that means there is a constant measure of space determined by the speed of intergalactic light, since it presumably takes light longer to cross this distance. Than an expanding measure based on the spectrum of the very same light. So which is space, that defined by the speed of light, or that defined by redshift?
This might seem confusing, when you try to explain it with just words; however, when you look at this within the framework of GR, it's a whole lot less confusing.

And it's consistent ... models built using GR are consistent with all relevant experimental and observational results, including the 'Hubble law'.

I can give you some references to introductory material on this, if you are interested ...
JeanTate
5 / 5 (4) Jul 05, 2015
@Returners:
General Relativity predicts an accelerating universe, for at least two reasons as I've outlined here.
Perhaps you could put numbers to your words, based on GR, the estimated masses of the various objects, and the relevant distances?

My guess is that when you 'do the numbers' you'll find they do not 'add up' (the observed relationships, e.g. the 'Hubble law', are strongly inconsistent with your numbers)
RealityCheck
1.7 / 5 (6) Jul 05, 2015
Hi TechnoCreed, JeanTate. :)

@Techno: the DM/DE hypotheses are just that, hypotheses based on light-observations being interpreted via a model of GR-based assumptions about what causes 'spacetime curvature' and hence 'lensing' etc. It may be DM is not cause of gravitational anomalies observed via affected light signals at this distance.

@JeanTate: Big Bang, Inflation etc not only way to get "primordial abundance of light nuclides, angular power spectrum of the CMB etc". They can occur via common processes.

It is encumbent upon scientists to beware forming 'religious beliefs' too. The 'certainties/statements' re expansion, CMB, DM etc lead to over-reach of actual dataset, putting overlays/extrapolations on it which become just as 'religious' beliefs as Ren82's!

The Planck-Bicep findings indicate universe a mixmaster for light signals, replete with processes being missed when 'interpreting' what we 'see'.

Avoid unwarranted beliefs/assertions/certainties for time being. :)
Uncle Ira
3.4 / 5 (5) Jul 05, 2015
@Returners:
General Relativity predicts an accelerating universe, for at least two reasons as I've outlined here.
Perhaps you could put numbers to your words, based on GR, the estimated masses of the various objects, and the relevant distances?

My guess is that when you 'do the numbers' you'll find they do not 'add up' (the observed relationships, e.g. the 'Hubble law', are strongly inconsistent with your numbers)


@ Jean-Skippette. How you are Cher? I am just tickled as can be. I had a great 4th week and did good in the radio 13 Colonies Special Event.

You must have missed Returning-Skippy's video where he put the numbers in little rows that proved dark matter is not real. His rows of number were very neat and orderly, but they really didn't prove much other than Returnering-Skippy needs a real hobby. Ask him for the link, or ask Viet-Vet-Skippy, I think he saw it too.
brodix
1 / 5 (1) Jul 05, 2015
JeanTate,

Both as a way for redshift to occur that is not explicitly due to recession and as an example of how seemingly minor, but important factors can be overlooked. In this case, that multi spectrum quanta will be affected differently than single spectrum.

As you seem to understand the problem, then I will frame it as a simple question; As Einstein said, space is what you measure with a ruler, so is the ruler the speed of light, or the shifting spectrum of that light?

So far, the only answer anyone has tried to give is that the light is just being "carried along" by this expansion, which makes no sense at all, since the redshift would necessarily be due to the light taking longer to cross this distance.

Also, if the ruler is the shifting spectrum, then why wouldn't the issue be that the light is taking longer to cross the distance defined by this ruler and so it would seem to be a question of slowing light, not increasing distance/space
JeanTate
5 / 5 (5) Jul 06, 2015
@brodix:
As Einstein said, space is what you measure with a ruler, so is the ruler the speed of light, or the shifting spectrum of that light?
Neither, in GR; 'distance' or 'size' no longer has a single meaning ... it depends on how you measure it. For example, there's one distance that relates to observed luminosity ('standard candle' sorta thing), another related to the observed 'size' of a distant object, and a third is like a 'radar distance' (time for a 'pulse' to 'bounce off' the distant object).

Counter-intuitive? Yep.
JeanTate
5 / 5 (4) Jul 06, 2015
@Uncle Ira: It's 'up and down' for me, thank you for asking (and glad to hear you are well)
You must have missed Returning-Skippy's video where he put the numbers in little rows that proved dark matter is not real
I have not seen that.
Uncle Ira
3.7 / 5 (6) Jul 06, 2015
@Uncle Ira: It's 'up and down' for me, thank you for asking (and glad to hear you are well)
You must have missed Returning-Skippy's video where he put the numbers in little rows that proved dark matter is not real
I have not seen that.


@ Jean-Skippette. I will see if I can find him Chere, but it might be tough. He was a good silly your tube video but not so good that I put a bookmark on him. Maybe Viet-Vet-Skippy might remember where it was but I will look around today while I am busy not doing anything.

It's about 8 or 7 minutes long and shows Returning-Skippy pointing to his rows of numbers and letters while he is explaining that they prove there is no dark matter. Hooyeei, I am glad me that it does not show his face because that might give the little Skippys the nightmares.
Uncle Ira
3.7 / 5 (6) Jul 06, 2015
Hooyeei Jean-Skippette you got lucky today you. Chere that was too easy for me to find in two minutes, eh? Here is Returnering-Skippy on the your tube channel proving there is not any dark matter.

https://www.youtu...uOqChEl8
brodix
1 / 5 (2) Jul 06, 2015
JeanTate,
No they are not counter intuitive. They are geometry, perspective, the various tools we use to calculate distance and nothing to do with my question, so let me rephrase it;
As the universe expands, galaxies move apart and the consequence is that the light from one is redshifted when it enters the other. This is due to classic doppler shift. That because the source is receding, each wave is taking longer than the previous. Do we agree so far?
Now my problem is this still assumes a stable speed of light, or at least one not defined in terms of the expansion, because there are more lightyears between these points, not stretched lightyears.
Now in GR, in a moving/accelerating/gravitational frame, both the distance traversed by the light and the rate it does so are affected equally and so it remains CONSTANT!
Yet that is not what happens with cosmic redshift, which requires the light to take longer to cross this distance, in order to be redshifted.
JeanTate
5 / 5 (4) Jul 06, 2015
@Uncle Ira: thanks!

@brodix:
As the universe expands, galaxies move apart and the consequence is that the light from one is redshifted when it enters the other. This is due to classic doppler shift. That because the source is receding, each wave is taking longer than the previous. Do we agree so far?
Nope. It is the same, observationally, but in terms of an explanation 'due to physics', not at all 'due to classic doppler shift'!
Now my problem is this still assumes a stable speed of light, or at least one not defined in terms of the expansion, because there are more lightyears between these points, not stretched lightyears
Also nope; in GR geometry isn't so simple
Now in GR, in a moving/accelerating/gravitational frame, both the distance traversed by the light and the rate it does so are affected equally and so it remains CONSTANT!
False premises, so false (or indeterminate) conclusion ...
brodix
1 / 5 (2) Jul 06, 2015
So the reason for the redshift from an expanding universe, is "physics," not doppler effect? Is that like "God does it."

It may not be simple, but the speed of light doesn't remain constant to this expanded universe, otherwise we would not have any scale to judge the expansion against.

So the premise that in GR the measure of the speed of light remains constant is false?
brodix
1 / 5 (3) Jul 06, 2015
JeanTate,

Maybe you really just don't see the contradiction between saying space expands, based on the redshift of light, yet judge it against the otherwise stable speed of the very same light, but in my world, that's just not the kind of math I'm willing to sign off on.
JeanTate
5 / 5 (5) Jul 07, 2015
@brodix:
So the reason for the redshift from an expanding universe, is "physics," not doppler effect?
Correct
the speed of light doesn't remain constant to this expanded universe
c is constant 'locally' for all observers (i.e. it's constant within your 'lab')
otherwise we would not have any scale to judge the expansion against
Nope; the observed redshift - along with things like the Tolman surface brightness test - gives estimates of a (the scale factor)
Maybe you really just don't see the contradiction between saying space expands, based on the redshift of light, yet judge it against the otherwise stable speed of the very same light, but in my world, that's just not the kind of math I'm willing to sign off on
Maybe the problem is that you have, unconsciously, got a model of the universe which has some form of absolute space/time? Check out Davis&Lineweaver for an exploration of this issue: http://arxiv.org/.../0310808
JeanTate
5 / 5 (4) Jul 07, 2015
(continued) One way to grock that the 'cosmological redshift' is not the same as the 'Doppler effect redshift' is to consider that, for objects with a redshift > (some value; the value is dependent on the parameter values in the cosmological model you're using), the 'recession speed' is greater than c! This then cannot be due to the Doppler effect ...
brodix
1 / 5 (2) Jul 07, 2015
JeanTate,
I am not using an absolute spacetime. The problem is that the speed of light is being used as the denominator and the redshift is the numerator.
In other words, it is being argued that these galaxies are receding and that eventually they will disappear, so that means this recession is being calibrated in units based on the speed of light, since over time, it takes light longer to cross this distance.
For example, if the universe expands sufficiently that two galaxies x lightyears apart grow to be 2x lightyears apart, that means there are more of these units, not that these units were stretched. So the argument is that space is stretching, but we have this other dimension of space against which to calibrate this expansion. That makes the one used for calibration the denominator and the one that is changing the numerator. There are no absolutes here, just relating one measure to another. So which is the real measure of space?
JeanTate
5 / 5 (2) Jul 07, 2015
@brodix: Did you read the Davis&Lineweaver document?
The problem is that the speed of light is being used as the denominator and the redshift is the numerator
Hmm ... I don't think so ... the redshift is simply a ratio of the observed frequency (or wavelength) to the 'rest frame' one (i.e. locally, where the light is/was emitted); there's no assumption re c (not directly anyway).

Crunching GR gives you a way to relate the observed redshift to the 'scale factor' in the cosmological model you're using. The 'calibration' you seem to be using is not what is used ...
docile
Jul 07, 2015
This comment has been removed by a moderator.
brodix
1 / 5 (1) Jul 07, 2015
JeanTate,
I didn't because according to your suggestion, it doesn't address the issue I'm raising.

There is the assumption that this redshift is due to the "expansion" of the universe.

Presumably the same effect would result if the light were to slow over time, but this "tired light" theory was rejected because the only method would require some form of interference, which would result in diffusion that is not observed.

So what is it expanding relative to, if not the speed of light?
brodix
1 / 5 (1) Jul 07, 2015
docile,
And as I'm trying to point out to JeanTate, it is only space which is being presumed to expand, because the speed of light and thus the clock rate, is assumed to be stable. If time were to "expand" proportionally, then the light would speed up as well, in order to remain constant and arrive at the same rate, which would negate causing a redshift.
docile
Jul 07, 2015
This comment has been removed by a moderator.
docile
Jul 07, 2015
This comment has been removed by a moderator.
antialias_physorg
5 / 5 (2) Jul 07, 2015
Check out Davis&Lineweaver for an exploration of this issue: http://arxiv.org/.../0310808

That is one nice paper. Thanks for sharing.
JustAnotherGuy
1 / 5 (1) Jul 07, 2015
@TechnoCreed
Dark matter and dark energy are not hypothetical; they are real observed phenomenons.

Ohh, I see.. "hypothetical"
My apologies. In honor to truth, I didn't noticed that by adding such adjective a denial attempt could have been inferred. Rest assured, I DO NOT question (nor confirm) the observations.... nor DE, nor DM, nor ΛCDM, nor Einstein's CC, nor... for Copernicus's sake! I'm NOT questioning Heliocentrism! (ok, old-fashioned)
Perhaps I should have avoided unnecessary adjective.

NOW if you're REALLY SO CONCERNED about the use of specific terms, and considering that YOU SEEMS TO TRUST the next sources, you may want to 'take action on the matter'. Since words such as "hypothetical" seem to be used A LOT!:
DE: https://en.wikipe...k_energy
DM: https://en.wikipe...k_matter
CDM: https://en.wikipe...k_matter
By the way, no need to tell me how these 'homework' are going. I couldn't care less..
Thank you anyway.
JustAnotherGuy
not rated yet Jul 07, 2015
@TechnoCreed:
Alright, maybe I misunderstood your first comment...

Maybe..
Or maybe you have understood, but wants some "you-can't-prove-me-wrong" comments contest, or something like that...
In which case, I can suggest you to look for another user. This isn't of my interest.
For eg, user JeanTate which commented:
.."dark matter" and "dark energy" are, at one level, just hypotheses..

Well, you may get a nice confrontation.. "at one level' at least.
Uh.. sorry about that. Bad manners. I shouldn't involve more people in this "matter". Forget about it..
Best regards
docile
Jul 07, 2015
This comment has been removed by a moderator.
brodix
1 / 5 (1) Jul 07, 2015
docile,

I suspect there are a large number of possibilities that haven't been fully explored and considered, but this doesn't seem to be a particularly neutral audience to examine many of them. I am simply trying to make the very basic point that trying to use the premise of spacetime to explain how space alone can expand overlooks a major factor. When the response seems to be to sidetrack the debate, it would be counter productive for me to delve into tangental factors.

As for the Tolman brightness test falsifying BB, here is an old link, if you haven't seen it;
http://www.americ...folktale
JeanTate
5 / 5 (2) Jul 07, 2015
@brodix:
There is the assumption that this redshift is due to the "expansion" of the universe
It's not an assumption
Presumably the same effect would result if the light were to slow over time
Not really
but this "tired light" theory was rejected because the only method would require some form of interference, which would result in diffusion that is not observed
Tired light ideas have a great many failures
So what is it expanding relative to, if not the speed of light?
There are quite a few (apparent) misconceptions/misunderstandings in your comments.

I doubt that I could satisfactorily deal with them, within the 1k char limit here, so I recommend that, if you are really interested in nailing this down, you post to Physics Forums, CosmoQuest, or the ISF. All have helpful and knowledgable members, more than willing to devote a lot of time to explaining GR and the cosmological models based on it.
JeanTate
5 / 5 (2) Jul 07, 2015
@docile:
The galaxy survey was originally used for justification of alleged space-time expansion (Hubble 1929)
Astronomical obsevations have grown in size, depth, quality, etc a great deal since then. And many new tests of GR-based cosmological models developed; some well after Hubble died
so it can hardly serve for explanation of it - or we would face a circular reasoning
False premises, moot conclusion
Hubble himself opposed the interpretation of his red shift observed with expanding Universe model. Maybe it would be useful to reconsider his classical arguments again
AFAIK, this is an exercise often given to astronomy grad students ...
JeanTate
5 / 5 (2) Jul 07, 2015
@docile:
But it ["the tired light model"] can work, if we would consider the scattering of light at the density fluctuations of vacuum which are each larger but less temporal than the light wave itself. These density fluctuations may also lead to some lensing collectively, but without presence of actual material particles
Perhaps it can, perhaps it can't. But it certainly cannot 'work' if is not published, in an objective form, one that can be independently verified.

How about we hold any comments on "the tired light model" until you publish it?
JeanTate
5 / 5 (2) Jul 07, 2015
Tolman surface brightness test - gives estimates of a (the scale factor)
Are you sure?
Yes, quite.
Tolman brightness test http://wattsupwit...nding...
You might have chosen to cite the primary source; it's arXiv:1405.0275 (preprint version anyway). It's an interesting paper, but how well it stands up to detailed scrutiny we'll likely have to wait a few years to tell (no doubt you have your own critiques of it, right?)
JeanTate
5 / 5 (2) Jul 07, 2015
@brodix:
As for the Tolman brightness test falsifying BB, here is an old link, if you haven't seen it;
Ah Mike Disney ... you spotted a good dozen or so non-sequiturs, logical fallacies, etc in his presentation, just on the first reading, right?
docile
Jul 07, 2015
This comment has been removed by a moderator.
Captain Stumpy
5 / 5 (2) Jul 07, 2015
How about we hold any comments
Censorship in science, huh?
@Zephir
no, it is about the ability to validate a claim... or to show methodology behind the claim that may or may not be flawed...

it also weeds out the pseudoscience, like AW/DAW and electric universe, so that legitimate science and claims can be addressed because the others don't meet the strict requirements of the scientific method

this should be obvious to you after you linked that retracted study supporting your aether/cold fusion argument
RealityCheck
1 / 5 (3) Jul 07, 2015
Hi JeanTate. :)

Just a note to say still trying to find time in my busy schedule to compile that links list we discussed, re the research culture/system and biases/flaws in literature and in observations/interpretations etc.

While I'm in today, I would like to caution you about your 'certainties' again when replying to others' observations; eg:
@docile:
Hubble himself opposed the interpretation of his red shift observed with expanding Universe model. Maybe it would be useful to reconsider his classical arguments again
AFAIK, this is an exercise often given to astronomy grad students
As you just acknowledged, things have changed since all these hypotheses/observations/interpretations were put into 'theory' using assumptions from those times. Try to curb your certainty 'attitude' and realize that your "astronomy grad students" is a self-selecting group inculcated before given the 'exercise'. Much like initial Bicep2 'team'. The biased 'exercise/results'=GIGO.

Cheers.
brodix
1 / 5 (2) Jul 07, 2015
JeanTate,
""So what is it expanding relative to, if not the speed of light?"
There are quite a few (apparent) misconceptions/misunderstandings in your comments."

So you have no idea what it is expanding relative too?
Or you are just not saying?
MandoZink
5 / 5 (4) Jul 08, 2015
Maybe the problem is that you have, unconsciously, got a model of the universe which has some form of absolute space/time? Check out Davis&Lineweaver for an exploration of this issue: http://arxiv.org/.../0310808


--- "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe" - Tamara M. Davis and Charles H. Lineweaver ---

Jean Tate, I am delighted to see someone else has read that. I discovered it several years ago and printed up a few copies. One copy is actually on the table at which I currently sit.

It took me a while to fully absorb the complete picture of velocities, horizons, limits and various observational perspectives. It was rewarding indeed. I've recommend the paper in a few astronomy discussions.

The other day I was on the "Observable universe" Wikipedia page and noticed the entry was quite well written. Sure enough, one of the references was the Davis/Lineweaver paper.
JeanTate
5 / 5 (3) Jul 08, 2015
@brodix:
JeanTate,
""So what is it expanding relative to, if not the speed of light?"
There are quite a few (apparent) misconceptions/misunderstandings in your comments."

So you have no idea what it is expanding relative too?
Or you are just not saying?
I'm saying that the question ("So what is it expanding relative to, if not the speed of light?") is ill-posed, and attempting to answer it - in that form - would, almost certainly, propogate misconceptions and make understanding what GR-based cosmological models actually are much harder.

For example, the Wikipedia entry on the Friedmann–Lemaître–Robertson–Walker metric may be accurate, but it is almost impossible to get an answer to your question (as posed) from what's in it.

Is it unsettling to not be able to get a robust answer to your question? Sure. Does this mean that cosmological models (based on GR) are unreliable/flawed? No
antialias_physorg
5 / 5 (4) Jul 08, 2015
Hooyeei Jean-Skippette you got lucky today you. Chere that was too easy for me to find in two minutes, eh? Here is Returnering-Skippy on the your tube channel proving there is not any dark matter.

https://www.youtu...uOqChEl8

Ahahaha...how did I miss this? This is pure gold.
brodix
not rated yet Jul 08, 2015
JeanTate,
When I get around to it, I will go back and read the Davis Lineweaver paper, but, yes, it is disconcerting to think, as you say, that redshift is due to the expansion of the universe, but it isn't because it consequently takes light longer to cross this increasing distance.
It seems to me one of those situations where you have to believe five impossible things before breakfast to be a member of the Mad Hatters Club.
JeanTate
5 / 5 (3) Jul 08, 2015
@brodix:
When I get around to it, I will go back and read the Davis Lineweaver paper
And if you have questions, please ask them. However, to repeat, this is not a good place to have this kind of discussion, the 1k char and formatting limits are too severe
but, yes, it is disconcerting to think, as you say, that redshift is due to the expansion of the universe, but it isn't because it consequently takes light longer to cross this increasing distance
Special Relativity is bad enough, with its counter-intuitives, but GR applied to the universe can be a lot worse; 'expanding space' is a nice shorthand, but IMHO it creates too much confusion when you try to work out, intuitively, 'what is happening, physically'

It seems to me one of those situations where you have to believe five impossible things before breakfast to be a member of the Mad Hatters Club
Quantum mechanics is far, far 'worse' in this regard, and yet it really does work!
TechnoCreed
5 / 5 (2) Jul 08, 2015
@JustAnotherGuy
Or maybe you have understood, but wants some "you-can't-prove-me-wrong" comments contest, or something like that...
Nothing like that. I am just curious about your first comment. Do you care to clarify and justify it? My comments and questions are in this sense. FYI, I do not have any habits to go into extensively long discussions and is usually the first one to give up on pointless argumentations; I do not have any needs to change your convictions or to have the last word. I weed-out pseudo-science and what I call 'bondieuserie' (a word from my native French-Canadian language that put religiousness and religious knick-knacks in a single package); under this article for example, the comments of Tuxford, docile and Ren82 are on 'ignore'. I hope this clarification satisfies you.

Shall we continue our discussion?
docile
Jul 08, 2015
This comment has been removed by a moderator.
brodix
not rated yet Jul 08, 2015
JeanTate,
Jeez. Delving into this does impress on me my limits.
I still have the same issue though. By recession, they really do seem to mean recession. There are more lightyears between points.
So go to my issue; Length contraction and time dilation as the conceptual basis of spacetime;
https://en.wikipe...traction
In that in an accelerated frame, length shrinks and time slows, so the measured speed of light remains constant.
So if space expands, why doesn't the clock speed up as well?
Obviously there is much I'm missing here and this isn't high enough on my priorities to give it the time it requires(life,work....), but it does seem the speed of light as a measure of space seems fairly rational and if it's taking more lightyears to cross this space, that's not constant to that dimension of space.
brodix
not rated yet Jul 08, 2015
And by local, they mean in the specified frame and in this instance, that frame is light arriving from other galaxies.
brodix
not rated yet Jul 08, 2015
For example;
"recession velocities can exceed the speed of light,"
What is the basis of the "speed of light," if space itself is expanding?
JustAnotherGuy
not rated yet Jul 09, 2015
@TechnoCreed:
Our ... "discussion"? a generous appreciation I must say.
Welcome to the pointless and extensive discussion, dude. My first. Hope be the last..
By the way, nice small 'bio' you just posted, look! some people already liked it! ..Guess what? I'm not neither on pseudo-science nor religion! ..but, I don't ignore, I read , and may comment about it. So, may be suitable for you ignore mine. Don't worry..

About the first comment... already clarified that. It's embarrassing. I didn't quoted the user's comment I was pointing out. Casually one of your 'ignored' friends. I gave up anyway, people here likely not open to 'arguments'.
Have nice day.
TechnoCreed
5 / 5 (1) Jul 09, 2015
@JustAnotherGuy
Our ... "discussion"? a generous appreciation I must say.
Welcome to the pointless and extensive discussion, dude. My first. Hope be the last..
By the way, nice small 'bio' you just posted, look! some people already liked it! ..Guess what? I'm not neither on pseudo-science nor religion! ..but, I don't ignore, I read , and may comment about it. So, may be suitable for you ignore mine. Don't worry..
Isschh! Dry humour, are you exasperated?
About the first comment... already clarified that. It's embarrassing. I didn't quoted the user's comment I was pointing out. Casually one of your 'ignored' friends. I gave up anyway, people here likely not open to 'arguments'.
Have nice day.
Thanks! Now I understand.

Cont.
TechnoCreed
5 / 5 (2) Jul 09, 2015

I will bring to your attention that in the second comment you made, the one where you tried to clarify your position, you went from one subject to another adding to the confusion. Look at your karma points; nobody knew what to make of your comments.

Nice day to you too.
JustAnotherGuy
5 / 5 (1) Jul 10, 2015
@TechnoCreed:
"Isschh! Dry humour, are you exasperated?" Nope..heh!.. Just some sarcasm ;) Don't mind about it.
"Thanks! Now I understand." You're welcome.
"I will bring to your attention that......"
Indeed. And a good reason to ask before to attempt any arguments exchange. Well, nobody's perfect... right? Bad mine don't worry.
bye

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