Rate of change in expansion?

[Daecon]

From what I understand, the expansion of the Universe appears to be increasing?

Is it possible to determine the rate of the increase, for example - exponential, linear, cubic, or some other type of growth?

Or is such a thing impossible to work out from only a few decade's worth of measurement?

 

[paddoboy]

The last figure I have heard was 72Kms per sec per megaparsec.
But fairly recent news with regards to the type 1a standard candles could see that figure revised somewhat.
The rate of the accelerated increase I'm not able to give you

 

[Q-reeus]

From what I understand, the expansion of the Universe appears to be increasing?

Is it possible to determine the rate of the increase, for example - exponential, linear, cubic, or some other type of growth?

Or is such a thing impossible to work out from only a few decade's worth of measurement?

For currently understood best estimate, see here: https://en.wikipedia.org/wiki/Accelerating_universe
At present epoch expansion is mathematically somewhat complex, but long term is expected to be exponential - owing to the dominant last term inside that sqrt expression.
Remember there are plenty of knowledgeable theorists out there with models predicting a variety of different outcomes. Who knows how long before an accurate consensus finally emerges.

 

[paddoboy]

Or is such a thing impossible to work out from only a few decade's worth of measurement?

Refinement comes with time Daecon, and better more advanced instrumental probes such as WMAP.
All in all though the BB model remains the overwhelming accepted model of the evolution of space, time and the Universe.
The following article from 2012, gives the expansion at 74KMS/sec/Mparsec.
http://www.space.com/17884-universe-expansion-speed-hubble-constant.html

 

[Daecon]

Oh don't get me wrong, I'm in no way implying that I doubt the Big Bang model of the Universe.

 

[tashja]

Hi, Daecon. Some answers for you:

Is he related to Siméon Denis Poisson, or just a coincidence?

No relation. But it is possible we may have a common
ancestor.

Cheers!

Eric
_________________________________
Eric Poisson
Professor of Physics
University of Guelph

From what I understand, the expansion of the Universe appears to be increasing?

Is it possible to determine the rate of the increase, for example - exponential, linear, cubic, or some other type of growth?

Or is such a thing impossible to work out from only a few decade's worth of measurement?

Dear Tashja,

The expansion history is pretty well known (but it did take decades of
work!). We don't measure it as a continuous function of time, but we
measure at enough epochs to know that the model of a geometrically
flat Universe with a cosmological constant is a very good match to the
data.

That model says that the expansion goes as t^{1/2} for the first
100,000 years, then switches to t^{2/3} until about 5 billion years
ago. Now we're transitioning to an exponential in time.

Much work is now aimed at improving these measurements, driven by the
interest in testing finer points of the cosmology, such as whether the
dark energy is precisely the cosmological constant or itself evolves
in time.

I hope this helps,
Daniel Eisenstein

 

[Daecon]

Thank you tashja, much appreciated.

 

[Ned Wright]

From what I understand, the expansion of the Universe appears to be increasing?

Is it possible to determine the rate of the increase, for example - exponential, linear, cubic, or some other type of growth?

Or is such a thing impossible to work out from only a few decade's worth of measurement?

The expansion rate change is not measured by waiting a few decades, but by measuring distance and velocity of distant galaxies which we see as they were several billion years ago. Thus studies of distant supernovae show that the expansion is accelerating. See
http://www.astro.ucla.edu/~wright/cosmology_faq.html#CC

 

[tashja]

Welcome to Sciforums, Prof. Wright!

 

[Schmelzer]

About the actual acceleration, there is some reason to doubt. First, there it Wiltshire's proposal. He explains the "acceleration" as an effect of the inhomogenity, where time goes differently in the big voids and at the borders. This leads to an effect which, on the borders, looks like acceleration and starts at the time when the inhomogeneities become sufficiently big.

Another doubt is a recent one, I have seen the paper but, unfortunately, lost the link and cannot recover the source. It was a claim that it appears that there are two different types of SN 1a, with slighly different properties, and, unfortunately, the part of the SNs of these subtypes changes in time. If one ignores the difference, this leads to a systematic error, toward more acceleration AFAIR.

 

[OnlyMe]

About the actual acceleration, there is some reason to doubt. First, there it Wiltshire's proposal. He explains the "acceleration" as an effect of the inhomogenity, where time goes differently in the big voids and at the borders. This leads to an effect which, on the borders, looks like acceleration and starts at the time when the inhomogeneities become sufficiently big.

Another doubt is a recent one, I have seen the paper but, unfortunately, lost the link and cannot recover the source. It was a claim that it appears that there are two different types of SN 1a, with slighly different properties, and, unfortunately, the part of the SNs of these subtypes changes in time. If one ignores the difference, this leads to a systematic error, toward more acceleration AFAIR.

No idea what your original source was.., there was this 2014 paper, http://arxiv.org/abs/1408.1706, however, I am unsure just how this would affect expansion estimates.., or if it has been independently confirmed.

 

[danshawen]

Oh don't get me wrong, I'm in no way implying that I doubt the Big Bang model of the Universe.

Thank goodness you have no doubt, because if you did, certain people here would be certain to tell you why that idea is outright blasphemy, or tantamount to it.

By "Big Bang", we assume you meant "inflation followed by the Big Bang" of course. I'm not certain how or if the theory of inflation handles any discontinuity or dissociation of forces. Alan Guth is brilliant. He won the 1999 'messiest desk ever' contest AND the Nobel for his theory of inflation, and really, it's not bad. I admire both achievements. His inflation theory and definition of the cosmic superforce is both precise and specific, and explains the rate of expansion we see today, even if that figure is currently in doubt over a flap over misidentification of certain populations of type 1A supernovae.

I'd give a lot to see whatever happened to Alan's desk. No idea what happened to that contest. What do the rest of us have to strive for now? A dark messy desk in a cold, dead universe, perhaps. A fitting and final end to cosmological blasphemers of all stripes. May the dark force be with you always.

The Common Core science curriculum may even need a few tweaks on the topic of the BB eventually, which was still based on 1940s astronomy when I looked at it only a few years ago when I was a teaching intern. I told them, the 1940s were probably not the final word on the subject. Neither is Alan Guth's I suspect.

John Dewey's determination to teach whatever is currently in textbooks seems a bit out of place in the information enriched 21st century, doesn't it? You teach students whatever your job description and standardized curriculum tells you to, if you have any expectations of being paid for doing so. So much for my very brief teaching internship and any ideals about teaching students anything they may eventually find remotely useful in the years before the universe becomes so bitterly cold and dead. Perhaps some sort of contest would help motivate them to achieve better, attainable goals.

 

[Schmelzer]

No idea what your original source was.., there was this 2014 paper, http://arxiv.org/abs/1408.1706, however, I am unsure just how this would affect expansion estimates.., or if it has been independently confirmed.

Yes, this was it, thanks.

The abstract mentions that such a possibility exists:

This, in turn, leads to under-estimation of the optical luminosity of the NUV-blue SNe~Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.

But, if I correctly understand the text, this bias may not be really important, they say that, given the current uncertainties, "the first simulation is consistent with zero bias for all redshifts". Thus, all one has to expect is that, if they avoid this bias, this will give only a minor modification and higher accuracy.

About the error direction:

NUV-red SNe, which should have their extinction overestimated and their distance moduli underestimated, are more prevalent in the local universe.

That means, for small z the distance is underestimated, means the redshift in dependence of the distance overestimated, thus, the expansion velocity overestimated. This would be an error which would look like an acceleration.

 

[paddoboy]

About the actual acceleration, there is some reason to doubt. First, there it Wiltshire's proposal. He explains the "acceleration" as an effect of the inhomogenity, where time goes differently in the big voids and at the borders. This leads to an effect which, on the borders, looks like acceleration and starts at the time when the inhomogeneities become sufficiently big.

The inhomogenty as you mention is not what we generally observe.
In fact from observations it has been assumed that the Universe over larger scales is homogeneous and isotropic.

Another doubt is a recent one, I have seen the paper but, unfortunately, lost the link and cannot recover the source. It was a claim that it appears that there are two different types of SN 1a, with slighly different properties, and, unfortunately, the part of the SNs of these subtypes changes in time. If one ignores the difference, this leads to a systematic error, toward more acceleration AFAIR.

That in no way invalidated the concept of expansion, nor of any accelerated component in that expansion. At best it would just be a means of refinement of measuring and data.
Plus I was the person who raised the article as a point of interest.
http://phys.org/news/2015-04-universe-fast.html

and......

http://iopscience.iop.org/0004-637X/803/1/20/
THE CHANGING FRACTIONS OF TYPE IA SUPERNOVA NUV–OPTICAL SUBCLASSES WITH REDSHIFT
ABSTRACT:
Ultraviolet (UV) and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have revealed the existence of two distinct color groups, composed of NUV-red and NUV-blue events. The color curves differ primarily by an offset, with the NUV-blue

color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-redshift SNe Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We compare rest-frame UV/optical spectrophotometry of intermediate- and high-redshift SNe Ia with UVOT photometry and Hubble Space Telescope spectrophotometry of low-redshift SNe Ia, finding that the same two color groups exist at higher redshift, but with the NUV-blue events as the dominant group. Within each red/blue group, we do not detect any offset in color for different redshifts, providing insight into how SN Ia UV emission evolves with redshift. Through spectral comparisons of SNe Ia with similar peak width and phase, we explore the wavelength range that produces the UV/optical color differences. We show that the ejecta velocity of NUV-red supernovae (SNe) is larger than that of NUV-blue objects by roughly 12% on average. This velocity difference can explain some of the UV/optical color difference, but differences in the strengths of spectral features seen in mean spectra require additional explanation. Because of the slightly different

colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to underestimation of the optical luminosity of the NUV-blue SNe Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.

 

[brucep]

The expansion rate change is not measured by waiting a few decades, but by measuring distance and velocity of distant galaxies which we see as they were several billion years ago. Thus studies of distant supernovae show that the expansion is accelerating. See
http://www.astro.ucla.edu/~wright/cosmology_faq.html#CC

Thanks for the post. You're generally beloved by folks seriously interested in cosmology. Thanks for the faq and your maintenance of the content. And thanks to everybody involved in the great WMAP experiment.

 

[paddoboy]

Thanks for the post. You're generally beloved by folks seriously interested in cosmology. Thanks for the faq and your maintenance of the content. And thanks to everybody involved in the great WMAP experiment.

Wilkinson Microwave Anisotropy Probe
The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA Explorer mission that launched June 2001 to make fundamental measurements of cosmology -- the study of the properties of our universe as a whole. WMAP has been stunningly successful, producing our new Standard Model of Cosmology. WMAP's data stream has ended. Full analysis of the data is now complete.Publications have been submitted as of 12/20/2012.

WMAP TEAM RECEIVES THE 2012 GRUBER COSMOLOGY PRIZE

"The Gruber Foundation proudly presents the 2012 Cosmology Prize to Charles Bennett and the Wilkinson Microwave Anisotropy Probe team for their exquisite measurements of anisotropies in the relic radiation from the Big Bang---the Cosmic Microwave Background. These measurements have helped to secure rigorous constraints on the origin, content, age, and geometry of the Universe, transforming our current paradigm of structure formation from appealing scenario into precise science."

Other Members of the WMAP team are:
Chris Barnes, Rachel Bean, Olivier Doré, Joanna Dunkley, Benjamin M. Gold, Michael Greason, Mark Halpern, Robert Hill, Gary F. Hinshaw, Norman Jarosik, Alan Kogut, Eiichiro Komatsu, David Larson, Michele Limon, Stephan S. Meyer, Michael R. Nolta, Nils Odegard, Lyman Page, Hiranya V. Peiris, Kendrick Smith, David N. Spergel, Greg S. Tucker, Licia Verde, Janet L. Weiland, Edward Wollack, and Edward L. (Ned) Wright.

For more information about the prize visit: 2012 Gruber Cosmology Prize Press Release

WMAP's Top Ten

The WMAP science team has…

1. ... has put the "precision" in "precision cosmology" by reducing the allowed volume of cosmological parameters by a factor in excess of 68,000. The three most highly cited physics and astronomy papers published in the new millennium are WMAP scientific papers--- reflecting WMAP's enormous impact.
   
   
2. …mapped the pattern of tiny fluctuations in the Cosmic Microwave Background (CMB) radiation (the oldest light in the universe) and produced the first fine-resolution (0.2 degree) full-sky map of the microwave sky.
   
   
3. …determined the universe to be 13.77 billion years old to within a half percent.
   
   
4. …nailed down the curvature of space to within 0.4% of "flat" Euclidean.
   
   
5. …determined that ordinary atoms (also called baryons) make up only 4.6% of the universe.
   
   
6. …completed a census of the universe and finds that dark matter (matter not made up of atoms) is 24.0%
   
   
7. …determined that dark energy, in the form of a cosmological constant, makes up 71.4% of the universe, causing the expansion rate of the universe to speed up. - "Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background (CMB)." -Science Magazine 2003, "Breakthrough of the Year" article
8. … mapped the polarization of the microwave radiation over the full sky and discovered that the universe was reionized earlier than previously believed. - "WMAP scores on large-scale structure. By measuring the polarization in the CMB it is possible to look at the amplitude of the fluctuations of density in the universe that produced the first galaxies. That is a real breakthrough in our understanding of the origin of structure." - ScienceWatch: "What's Hot in Physics", Simon Mitton, Mar./Apr. 2008.
9. …detected that the amplitude of the variations in the density of the universe on big scales is slightly larger than smaller scales. This, along with other results, supports "inflation", the idea is that the universe underwent a dramatic period of expansion, growing by more than a trillion trillion fold in less than a trillionth of a trillionth of a second. Tiny fluctuations were generated during this expansion that eventually grew to form galaxies.
   
   
10. … determined that the distribution of these fluctuations follows a bell curve with the same properties across the sky, and that there are equal numbers of hot and cold spots in the map. The simplest version of the inflation idea predicted these properties and remarkably, WMAP’s precision measurement of the properties of the fluctuations has confirmed these predictions, in detail.
    http://map.gsfc.nasa.gov/

 

[brucep]

Wilkinson Microwave Anisotropy Probe
The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA Explorer mission that launched June 2001 to make fundamental measurements of cosmology -- the study of the properties of our universe as a whole. WMAP has been stunningly successful, producing our new Standard Model of Cosmology. WMAP's data stream has ended. Full analysis of the data is now complete.Publications have been submitted as of 12/20/2012.

WMAP TEAM RECEIVES THE 2012 GRUBER COSMOLOGY PRIZE

"The Gruber Foundation proudly presents the 2012 Cosmology Prize to Charles Bennett and the Wilkinson Microwave Anisotropy Probe team for their exquisite measurements of anisotropies in the relic radiation from the Big Bang---the Cosmic Microwave Background. These measurements have helped to secure rigorous constraints on the origin, content, age, and geometry of the Universe, transforming our current paradigm of structure formation from appealing scenario into precise science."

Other Members of the WMAP team are:
Chris Barnes, Rachel Bean, Olivier Doré, Joanna Dunkley, Benjamin M. Gold, Michael Greason, Mark Halpern, Robert Hill, Gary F. Hinshaw, Norman Jarosik, Alan Kogut, Eiichiro Komatsu, David Larson, Michele Limon, Stephan S. Meyer, Michael R. Nolta, Nils Odegard, Lyman Page, Hiranya V. Peiris, Kendrick Smith, David N. Spergel, Greg S. Tucker, Licia Verde, Janet L. Weiland, Edward Wollack, and Edward L. (Ned) Wright.

For more information about the prize visit: 2012 Gruber Cosmology Prize Press Release

WMAP's Top Ten

The WMAP science team has…

1. ... has put the "precision" in "precision cosmology" by reducing the allowed volume of cosmological parameters by a factor in excess of 68,000. The three most highly cited physics and astronomy papers published in the new millennium are WMAP scientific papers--- reflecting WMAP's enormous impact.
   
   
2. …mapped the pattern of tiny fluctuations in the Cosmic Microwave Background (CMB) radiation (the oldest light in the universe) and produced the first fine-resolution (0.2 degree) full-sky map of the microwave sky.
   
   
3. …determined the universe to be 13.77 billion years old to within a half percent.
   
   
4. …nailed down the curvature of space to within 0.4% of "flat" Euclidean.
   
   
5. …determined that ordinary atoms (also called baryons) make up only 4.6% of the universe.
   
   
6. …completed a census of the universe and finds that dark matter (matter not made up of atoms) is 24.0%
   
   
7. …determined that dark energy, in the form of a cosmological constant, makes up 71.4% of the universe, causing the expansion rate of the universe to speed up. - "Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background (CMB)." -Science Magazine 2003, "Breakthrough of the Year" article
8. … mapped the polarization of the microwave radiation over the full sky and discovered that the universe was reionized earlier than previously believed. - "WMAP scores on large-scale structure. By measuring the polarization in the CMB it is possible to look at the amplitude of the fluctuations of density in the universe that produced the first galaxies. That is a real breakthrough in our understanding of the origin of structure." - ScienceWatch: "What's Hot in Physics", Simon Mitton, Mar./Apr. 2008.
9. …detected that the amplitude of the variations in the density of the universe on big scales is slightly larger than smaller scales. This, along with other results, supports "inflation", the idea is that the universe underwent a dramatic period of expansion, growing by more than a trillion trillion fold in less than a trillionth of a trillionth of a second. Tiny fluctuations were generated during this expansion that eventually grew to form galaxies.
   
   
10. … determined that the distribution of these fluctuations follows a bell curve with the same properties across the sky, and that there are equal numbers of hot and cold spots in the map. The simplest version of the inflation idea predicted these properties and remarkably, WMAP’s precision measurement of the properties of the fluctuations has confirmed these predictions, in detail.
    http://map.gsfc.nasa.gov/

On the announcement page Professor Hawking congratulates the "The simplest version of inflation ....." As being confirmed by WMAP. He put lots of work into his "No Boundary Proposal" and it was ruled out based on it's prediction for the power spectrum. The simplest version is essentially Guths version which predicts Omega goes to 1 regardless what it might have been initially. This means the universe is infinite in extent. Flat. Anyway I just really think Hawking is amazingly cool. His No Boundary Proposal was the first initial state cosmology I ever came across.

 

[Daecon]

Does Dark energy have any connection to Vacuum energy?

As space expands, is the dark energy or the vacuum energy becoming more dissipated throughout the new regions of space? It seems counter-intuitive to think of it as remaining constant, because would that not seem to imply that new energy is being created to fill in the newly expanded regions of space? Which of course is silly, so I'm obviously misunderstanding something somewhere.

 

[Schmelzer]

The inhomogenty as you mention is not what we generally observe.
In fact from observations it has been assumed that the Universe over larger scales is homogeneous and isotropic.

Hm, where I have said something different? A, it seems you have misunderstood the "sufficiently big". This was indeed a misleading choice.

If the question is how "big" an inhomogeneity is, there are two meanings: "Big" in size (there are fluctuation of the background radiation which have a size comparable with the whole visible universe) and "big" in amplitude. I have in mind the last one. Initially, the size of the inhomogenities was extremely small, 1:10000 or so. Today, there are voids, quite large in comparison with our galaxy and local galaxy clusters, but small in comparison with the whole universe, and these "voids" contain almost no galaxies or so. I don't know exact numbers, but the point is that the differences are already much greater in their amplitude that the 1:10000 of the CMBR times, and, following Wiltshire, they already matter.

That in no way invalidated the concept of expansion, nor of any accelerated component in that expansion. At best it would just be a means of refinement of measuring and data.

I have never said that it somehow invalidates expansion. But it is, AFAIU, a systematic error which makes acceleration look greater than it really is. Having read now the paper I also agree that the correction of this bias will not make acceleration go away completely - but this is, of course, the "acceleration" based on an exactly homogeneous FLRW model.

Plus I was the person who raised the article as a point of interest.

Thanks. As you see, even reading your posts sometimes gives me interesting information. I'm actually even writing an article I would not have written without having read this forum. So, to look into such forums is useful for me - and I don't think the communication with a few scientists at some single institution would give me more.

 

[paddoboy]

Does Dark energy have any connection to Vacuum energy?

Vacuum energy density could be anything including the CC.
We know it exists but do not as yet know the nature of it.

As space expands, is the dark energy or the vacuum energy becoming more dissipated throughout the new regions of space? It seems counter-intuitive to think of it as remaining constant, because would that not seem to imply that new energy is being created to fill in the newly expanded regions of space? Which of course is silly, so I'm obviously misunderstanding something somewhere.

Not really. This explains the acceleration in the expansion we have observed.
The vacuum energy density remains constant throughout all of spacetime, acting over every square metre of space.
While at the same time, the same amount of mass/energy in the Universe, means that density is growing less...less density due to more spacetime, means faster acceleration.