Accelerated expanding Universe.. or not?

[bojan]

There was a doubt cast on widely accepted theory of accelerated expansion of the Universe, see below:
http://physicsworld.com/cws/article/news/2016/oct/21/supernovae-analysis-finds-scant-evidence-for-dark-energy
http://www.nature.com/articles/srep35596

[julianh72]

I'll be following this one with interest.

The problem for me is that I don't really understand the concept of "dark energy" (does anyone?), and the statistical analysis presented is WAY beyond my level of comprehension, so I'm totally reliant on the popular scientific press to get an interpretation that I can comprehend. (And I'm by no means certain that the modern popular scientific press is up to the job of understanding this sort of material!)

From what I have read, the analysis presented in this paper downgrades the likelihood of an accelerating expansion of the universe (based on analysis of Type 1a supernovae) from 5-sigma to about 3-sigma. E.g. see http://www.ox.ac.uk/news/science-blog/universe-expanding-accelerating-rate-%E2%80%93-or-it

As I understand it, 5-sigma is the "rock solid gold standard" for statistical correlation (one in 3.5 million chance that the observation is a "fluke"), while 3-sigma is still "pretty darn certain" (99.73% probability of a meaningful statistical correlation.
http://www.physics.org/article-questions.asp?id=103
https://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule

I think it's probably too early to dismiss the current "standard model" of an accelerating expansion of the universe driven by "dark energy" - even though that very concept is mind-boggling to me!

[bojan]

By looking at those graphs... I am not sure how they claimed even 3-sigma.
There is a lot of noise in data...

[OICURMT]

The simplest explanation...

https://www.youtube.com/watch?v=dqij-0gf6xY

[julianh72]

Thanks - that helps a lot!

:confused2:

[xelasnave]

Is the Universe expanding at all ?
Well of course it is according to the current model however I followed a thread elsewhere where, I will call it, a "shrinking ruler model" was discussed.
So in that model everything is shrinking.
Now at first that sounds crazy but the only scientists in the discussion pointed out how such a model could fit the observations and in that the math worked better.
The difficulty with all of this stuff is you need to specialise in a field to understand what the current model really is saying. We can read papers but for anyone outside the field, any field really, one can ask are they educated enough to comment.
Personally I believe the current model is probably does not reflect reality only because of the way it is presented by journalists.
I do not understand inflation, without which the big bang fails, but there are folk who rightfully can say your education is insufficient for you to really grasp the concept.
All I can use is my "common sence" whatever that is to analyse the proposition of the big bang model that the Universe evolved from a very small hot dense region, some suggesting this region to be smaller than an atom, and that such region expanded or grew to a size equivalent to or greater than the observable universe in a split second.
I seem to recall Degrasse saying "in under a zillionth of a zillionth of a zillionth of a second...
Well I don't buy that but of course I am uneducated and don't understand things the way a professional does.
It smacks of creation and given a priest had a hand in developing the model I suspect observations fit a satisfactory philosophical model of cosmology.
And if you had spent your life studying the current big bang model it would be difficult to consider that any competing model could be valid...and if you did you would not say zip if you wanted to keep your name and career in tact.
The current model needs dark matter and dark energy such that we must accept a major part of the universe can not be observed or explained.
I wonder what models other intelligent species have come up with...
Now I am not being critical or cynical I don't know enough to enjoy either but I hope before I die they come up with a more " common sence" model.
I do like the steady state style model as it does not need expansion, or contraction dark energy or dark matter...or a creation point.
Alex

[xelasnave]

:DMy point or rather the point of a shrinking ruler model is ...if shrinking our observations would suggest expansion and probably an accelerating expansion.
Our universe may be like a piece of fruit drying up in the Sun.
Discuss... marks will be awarded for neatness.
All hearsay evidence considered.:rolleyes:

[markbakovic]

"For simplicity we adopt global, independent gaussian distributions for all parameters, M, x1 and c"

if there was a compelling explanation in the article of why they chose to use a normal curve for x1-hat instead of the skewed distribution suggested by the JLA data (other than "because we don't trust it") it's obviously beyond me to find it.

They also "fix h to 0.7, which is consistent with independent measurements": my question is "how?" as a) they don't reference them and b) there is generally problematic clarity on h values anyway (see https://arxiv.org/abs/1308.4150 for a very detailed discussion, or just refer to the handy graph on page 4 for the highlights).

While i generally applaud efforts to apply some of the advances of the past 120 odd years in statistics and hypothesis testing to physics (which seems otherwise mired in almost victorian ideas of macroscopic certainty as yardsticks by which to measure highly probabilistic phenomena), which the authors attempt quite convincingly, they then go and shove all that in the bath with the baby by summarising with their assumption-laden contour plot "look, only the 3 sigma oval is above the "not accelerating" line!!!" when blind freddy can see that a "7 sigma" oval on the same plot would still encapsulate far more "acceleration" likelihood estimates than "deceleration": ie acceleration is statistically more likely. Considering the number and magnitude of the assumptions they've made and the number of times they've cranked the analysis handle... hmmm...

Of course I'm no expert and I could be completely wrong, but there's my opinion, worth the infinite sum of 1/2^n cents.

[markbakovic]

are you suggesting that some analogue to water is evaporating from inside our universe to outside it, leaving cells unable to support an outer rind of less saturated material with comparitively unchanged dimension unsupported by internal pressure causing it to fold that extra extent into a smaller volume? Does spacetime occupy the surface of the fruit or the powdery flesh inside?

Because if we're talking about observable topologies of space of lower dimension than the universe actually possesses it's worth remembering that expansion scales as an extra exponent for each higher dimension, think of a sphere with increasing radius r whose surface thus increases as r^2 (and volume as r^3) etc. But in your example the opposite is true for 2 but not three dimensions: small r decrease, smaller r^2 decrease (due to folding) but much greater r^3 decrease... this seems like the system has less symmetry than we'd expect...

:P where's the emoji that stirs a pot?

[xelasnave]

Hi Mark,
Having only recently heard of the shrinking ruler model, and I use the term loosely as I doubt there has been a paper, I grabbed the first anology that poped into my head.
I think using anologies is dangerous because we can seek to question the validity of the anology rather than the theory upon which the anology is based.
I think in the hypothesis I followed the suggestion was that atoms get smaller.
My interest was aroused simply because of the face of it observations could support the shrinking rulers model.
And so I found that interesting.
Its a pity I really don't care about the model such that I could defend it and point out that you are right but...you know a great discussion on how the universe works is always a stimulating pursuit.
But no I can't defend the idea.
Now why should I use a pot stirring emo when all here even new members can see clearly what I am up to...but I do it in the hope interesting discussion follows.
But as it is late I will mark your paper tomorrow and complement you on doing home work on a week end.
Alex:D

[xelasnave]

I am starting to think I dreamed the shrinking ruler model I can't find what I was following.
I wanted to check the mechanism.
I may google but I have enough to do other than looking at non mainstream stuff.
Alex

[xelasnave]

Here is something at cosmoquest but that was not it...but its out there

https://forum.cosmoquest.org/archive/index.php/t-124881.html

Alex

[Eratosthenes]

....a common misconception about the expanding universe is that everything "in" the Universe must also be expanding at the same rate. The Universe may be expanding but your Computer or car isnt

[julianh72]

If you want to understand why we believe the universe is expanding at an accelerating rate, and how this is corroborated through several independent lines of study, a great start would be to take a look at "Universal" by Brian Cox and Jeff Forshaw, which I reviewed in another post: http://www.iceinspace.com.au/forum/showthread.php?t=150183 I

This book is a very accessible account of modern cosmology, and a lot more compelling than popular press reviews of the abstracts of scientific papers, which I genuinely doubt the journalists have actually read, let alone understood!

[madbadgalaxyman]

[QUOTE=julianh72;1277602]I'll be following this one with interest.

The problem for me is that I don't really understand the concept of "dark energy" (does anyone?), and the statistical analysis presented is WAY beyond my level of comprehension, so I'm totally reliant on the popular scientific press to get an interpretation that I can comprehend. (And I'm by no means certain that the modern popular scientific press is up to the job of understanding this sort of material!)

[QUOTE]

Here is a goodish collection of reasonably informative popular-level articles on 'dark energy' that are at least written by people with demonstrated knowledge of cosmology. Not vastly good explanations here, but some thought-provoking ideas::

https://theconversation.com/au/topics/dark-energy-328

[xelasnave]

A common misconception is that there are no two snow flakes the same.
This sounds plausible as do so many things but no one has ever checked all the snow flakes to see if that statement is true.
So many things we accept as fact without question.
Alex

[sjastro]

Robert,

No one fully understands what dark energy is, only an inkling of what it might be.
As you know in quantum mechanics particles such as electrons exist in discrete (quantum) energy levels in an atom.

This idea can be extended further by applying special relativity to quantum mechanics.
Like the electron, the surrounding electric field can also exist in discrete energy levels.
From a classical physics perspective the field is a product of the presence of the electron, in quantum field theory it's the other way around.
In fact if you remove the electron the field is still there.

This leads to the subject of vacuum energy which frequently crops up in discussions in what dark energy might be.
Since a field can exist in quantum states, the lowest energy state associated with a field is a vacuum.
So once again we have a deviation from the classical physics definition where a vacuum is associated with "nothingness" to a field with the lowest energy state.
It has been shown in laboratory conditions that vacuums can exert pressure by the Casimir effect (https://en.wikipedia.org/wiki/Casimir_effect) which is a vindication of the quantum field definition of a vacuum.

This is where things get interesting. There are vacuums and then there are false vacuums (https://en.wikipedia.org/wiki/False_vacuum).
A false vacuum has an energy state higher than a true vacuum state and is not necessarily stable.
The instability of a false vacuum in analogous to the old physics party trick of trying to balance a chair on one leg. While it is difficult it is possible.
A chair balanced on one leg is said to be in an unstable equilibrium. The slightest disturbance rebalances the chair on all four legs. In the process of rebalancing energy is released in the process.

It is theorized a false vacuum existed in the early history of the Universe. Like the chair balanced on one leg it was unstable and when subjected to some disturbance went to the lower vacuum energy level releasing dark energy in process.

While this non mathematical description might sound plausible, the cold hard facts are when the maths is done the amount of dark energy predicted by the transition from a false vacuum to vacuum state is out by a whopping factor of 10^120 to the amount of dark energy "observed".

There is alot of work to be done to understand what the hell is going on.

Steven

[alpal]

Can Nobel Prizes be retracted?

http://physicsworld.com/cws/article/news/2011/oct/04/dark-energy-pioneers-scoop-nobel-prize

[rustigsmed]

a good vid

https://www.youtube.com/watch?v=7UNLgPIiWAg

[sil]

Try comparing the expansion rate to the global warming rate (energy increase into the atmospheric system). See if there is a regional "global warming" observation that matches.

Then go looking in that region for pieces of fruit drying in the sun.

With accurate measurements we should be able to find the piece of fruit our universe exists in and rehydrate it.

Am now accepting donations for a fact finding mission to the dried goods markets around the meditteranean :)

[sil]

On a serious note I've always doubted the accelerated expansion model. I don't have the skills to unstand the papers or investigate my ideas, but in the end I expect it to be a misunderstanding of the data. From the observations I've heard described an apparent accelerated expansion makes perfect sense since they havent accounted for time it seems.

[Eratosthenes]

There are physicists who think that the speed of light may not be a constant, and in fact was faster during the early stages after the Big Bang event. The horizon problem was always a challenge to the evolution of the cosmos post big bang. Inflation theory was introduced to the early periods of the Big Bang in order to tackle the Horizon problem. (this has fundamental problems in its self even though it works and is a beautiful solution to a very difficult problem)

Magueijo and others, suggest a way to test the Variable Speed of Light theory - the measurement of the spectral index. They propose a fairly accurate estimate to the spectral index = 0.96478. Current estimates from Cosmic Background radiation measurements are 0.968 - close but the small difference is critical according to Magueijo.

Lots to play out in the Big Bang theory yet as well as in Relativistic Physics - it may turn out that dc/dt is not equal to zero.

:D

[raymo]

I have often wondered if the theorised current age of the universe is
analogous to the nano second or whatever amount of time elapses between
an explosion occurring, and the blast accelerating to its its maximum outward velocity, before beginning to slow down.
raymo

[xelasnave]

An explosion is hideously slow compared to inflation.
From zip to at least the size of the observable universe in a trillionth of a trillionth of a trillionth of a second...as the story is told.
But I don't know I was not around to see what happened.
But if we take the time as it seems to be presented I find it hard to accept.
Alex

[sjastro]

Inflation and dark energy should not be confused for being equivalent mechanisms.
Inflation occurred in a radiation dominated Universe, lasted in the period from 10^-36 sec to 10^-32 after the Big Bang, dark energy about 6 billion years later in a matter dominated Universe and has existed ever since.

In a radiation dominated Universe the expansion characteristic of the Universe is defined as a time dependant scale factor (https://en.wikipedia.org/wiki/Scale_factor_(cosmology)) which is different from the matter dominated Universe.
Taking this into consideration plus how the Universe eventually turned out one can calculate the duration for Inflation.
If the Inflation period was too short, the horizon problem would not be solved and the Universe would not be observed to be isotropic.
Conversely if it was too long, the Universe would take on an open or hyperbolic geometry where complex structures could not form including life itself.

As far as scientists misunderstanding the data there are two different and independent observations both of which point to dark energy.

First is the time dilation of type IA supernova light curves in distant galaxies. This a standard ruler for measuring distance.
The larger than predicted distances indicates acceleration.

Second is the flatness of the Universe itself which can only be explained by dark energy.
The evidence is provided through Baryon acoustic oscillations (https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) in the CMB (cosmic radiation background).
In the CMB plasma wants to collapse under its own gravity but is prevented by radiation pressure exerted by colliding photons.
These opposing forces create an oscillation in the plasma much like a sound wave travelling through air, and create hot and cold spot structures in the CMB.
The true size of these structures can be calculated and compared to their apparent size as measured by the observer.
Comparison of the two reveals the geometry of the Universe is flat.
https://map.gsfc.nasa.gov/mission/sgoals_parameters_geom.html

Steven