What is dark energy?

Glad to see this plainly stated in the article, "Unfortunately, the cosmological constant λ is as much of a headache for cosmologists now as it was for Einstein, maybe more. The prime suspect accounting for λ currently is the vacuum energy of space itself actually exerting negative pressure on cosmic objects. This would imply that dark energy is the same everywhere, but there is a major problem with this explanation. There exists a huge disparity between the large value of vacuum energy suggested by quantum theory and the value of λ given by observation. The theoretical estimate for this energy of empty space from quantum field theory is somewhere in the order of 1 X 10^120 (1 followed by 120 zeroes) larger than the value of λ astronomers observe out in the cosmos by looking at the redshift of supernovas."

There is plenty of discussion on dark energy and the cosmological constant and expanding space.

Something is wrong with Einstein's theory of gravity, https://forums.space.com/threads/something-is-wrong-with-einsteins-theory-of-gravity.58751/

It remains to be shown how and when in the BB model, dark energy is created and when it appears, like from the Planck time and Planck length until the CMBR appears as light. Simply citing Type 1a SN shows when dark energy is said to be seen, but not its origin or when relative to the overall BB model. For example, during the quark-gluon plasma phase of the universe, did dark energy appear then or before?

Quarks: What are they?, https://forums.space.com/threads/quarks-what-are-they.58460/

Who, what, when, where, how, and why investigative reporting is needed I feel in cosmology to break it all down now and show how all these pieces (dark energy, dark matter, origin of normal matter in standard model) the BB cosmology predicted, or just works up patches to accommodate so the model continues :)
 
This article seems to have some problems with its numbers. For instance
"13,360 miles per second (500 km/s) ,
and
" one of the oldest galaxies ever discovered which we see as it was when the universe was just 400 million years old. An estimated 32 billion light-years away, dark energy is expanding the fabric of space at such a rate that GN-z11 is moving away from us at an estimated speed of 426,882 miles per second (687,000 km/s) — over twice the speed of light. "

My math says 13,360 mi.es per second is 21,500.8 kilometers/second - so maybe just a typo?

But, what about the second item? If GN-z11 has a redshift of 11, and that is assumed to mean that it is being seen by us now by light that it emitted (13.8 billion minus 0.4 billion =) 13.4 billion years ago, this distance must be calculated on where and at what speed it is theorized to be now, not when it emitted that light. That is really misleading, the way it was written. As written, it seems to mean that we are seeing now light that was emitted by something that is 32 billion light years away and moving away at twice the speed of light, in a universe that is only 13.8 billion years old.
 
  • Like
Reactions: rod
My observation. All redshifts 1.4 or larger in BB model today, are considered to be in 4D space expanding faster than c velocity, this is the comoving radial distances shown in cosmology calculators and the 32 billion light-years distance used in the space.com article. The other distance is more common to see, light-time or look back distance thus according to BB model, we should not see light in the universe farther away than 13.8 billion light-year distance today in our telescopes. However, that light-time distance is where the CMBR is at with postulated redshift z~1100. The comoving radial distance is out some 46 billion light years as measured from Earth, thus 4D expanding faster than c velocity - again. If you convert the H0 from 67 km/s/Mpc or 75 km/s/Mpc, into c.g.s. units, I find space expands in the range of 10^-18 cm/s/cm, much slower than c velocity. Things get interesting in expanding space explanations for large redshifts especially comparing to areas of the universe that must be expanding faster than c velocity for the cosmological redshift interpretation to work, a critical concept necessary for the BB model.
 
Yes, "interesting" is about the only word for it. I keep seeing posts that claim that light from objects moving away from us at more than the speed of light will still have light that eventually gets to us. Intuitively, that does not seem possible. Those posts talk about light travelling "over the hump" to space that is not moving faster than light away from us, but I have not been able to mathematically construct an algorithm that would do that.

Thinking about it as a physical analog: if space is considered to be an infinitely stretchable string, with a photon considered to be a particle traveling at a fixed velocity along the string at whatever location it occupies at the moment. then it seems to me to be quite obvious that the space between that photon and some other location on that string that is moving away at more than light speed from the position occupied by the photon will always stay ahead of the photon on that string. Yes, the photon will move toward the other location, but the distance to the other location will be increasing faster than the photon can close it.

Am I missing something?
 
  • Like
Reactions: rod
Yes, "interesting" is about the only word for it. I keep seeing posts that claim that light from objects moving away from us at more than the speed of light will still have light that eventually gets to us. Intuitively, that does not seem possible. Those posts talk about light travelling "over the hump" to space that is not moving faster than light away from us, but I have not been able to mathematically construct an algorithm that would do that.

Thinking about it as a physical analog: if space is considered to be an infinitely stretchable string, with a photon considered to be a particle traveling at a fixed velocity along the string at whatever location it occupies at the moment. then it seems to me to be quite obvious that the space between that photon and some other location on that string that is moving away at more than light speed from the position occupied by the photon will always stay ahead of the photon on that string. Yes, the photon will move toward the other location, but the distance to the other location will be increasing faster than the photon can close it.

Am I missing something?
Unclear Engineer, very intriguing :) My answer, I do not know if something is missed :) From what I understand about General Relativity and the expansion of space, not only is 3D space involved in the geometry but 4D space too because a hyperspace coordinate in the math for expansion of space is used. You said, "I keep seeing posts that claim that light from objects moving away from us at more than the speed of light will still have light that eventually gets to us."

I agree, this seems to be a common approach to explaining the comoving radial distances found for large redshifts like the 32 billion light years in the space.com report for GN-z11 is presented to the public. However, answers like this just assume GN-z11 still exists some 32 billion light years away without the ability to test and verify, as well as space expanding at least 2x c velocity that the article disclosed. I am glad that space.com did report this to the public though. People like you can ask good questions here.

Using Special Relativity, perhaps, someday, billions of years into the future on Earth, this postulated light (32 billion light years away now) from GN-z11 could be seen compared to what telescopes see today. Verifying and testing the expanding universe answers like this, including 4D space moving faster than c velocity, seems dubious in my opinion. In my thinking, it seems redshifts of 1.4 or larger must have the comoving radial distances from Earth where 4D space expands faster than c velocity, thus a tweak to avoid another problem. Otherwise, such large redshifts would indicate matter and mass are moving away from Earth faster than c velocity, something that will be rejected in cosmology. Looks like there is more than one tweak now to keep the BB model looking good :)
 
I am not (at this point) arguing that space cannot expand and carry matter with it such that two pieces of matter can be moving apart at more than the speed of light. What I am questioning is how the light emitted now is still supposed to eventually get from one to the other, assuming that space keeps expanding at the same rate (or faster).
 
I’ll offer some historical tweaks....

“The discovery of the red shift of light from distant sources and thus the expansion of the universe by famous astronomer Edwin Hubble...”.

And, “Hubble's revelation that the universe was expanding may have shocked the scientific community,...”.

The non-static (expanding or contracting) universe idea was introduced first in math form by Friedmann. Then independently in both math and physics form (objective-based evidence) by Lemaitre (1927). It took Eddington and DeSitter to get Einstein off the dogmatic Static model, by the early 1930’s.

Hubble is often erroneously credited for the expansion discovery. No one has yet to produce, AFAIK, any statement showing Hubble argued for expansion. He did state he was leaving this to the theorists.

It was Hubble’s distances, however, that allowed Lemaitre to first estimate the expansion rate (using Slipher’s redshifts), but there was a large error in Hubble’s use of Cepheid data, though not Hubble’s fault. [Cepheids, it turns out, come in more than one flavor.]. Hence Lemaitre’s expansion rate estimate was about 7x too high.

Hubble and Humason soon dominated the stage in giving the best data for both distances and redshifts. So they certainly deserve great credit as astronomers, just not as theorists.

iPad
 
Just to be clear, the space.com report does say 32 billion light years for GN-z11. "The rate of expansion has been measured for the galaxy Galaxy GN-z11, one of the oldest galaxies ever discovered which we see as it was when the universe was just 400 million years old. An estimated 32 billion light-years away, dark energy is expanding the fabric of space at such a rate that GN-z11 is moving away from us at an estimated speed of 426,882 miles per second (687,000 km/s) — over twice the speed of light. While it's true that nothing can travel through space faster than the speed of light in a vacuum, 186,282 miles per second (299,792 km/s), dark energy demonstrates that the fabric space itself is not bound by such speed limits."

Comments like this do not show that GN-z11 is presently sitting in 4D space expanding faster than c velocity, this is an interpretation, not an independent measurement observing 4D space expanding at some 6.77 x 10^10 cm/s. We could see GNz-11 32 billion light years away, If the universe is 32 billion years old since the BB event, in theory. According to that view, perhaps you could see GN-z11 at that distance from Earth but only if the universe is 32 billion years old. Space.com did not point this out to the public. However, what we see is look back time distance so GN-z11 light is still coming to us from 4D space expanding slower than c velocity. I do not see this pointed out to the public - clearly. Thus, dark energy, does not verify that GN-z11 presently is moving away in 4D space expanding at least 2x c velocity.
 
Unclear Engineer and post #5 said, "I keep seeing posts that claim that light from objects moving away from us at more than the speed of light will still have light that eventually gets to us."

My post #9 shows what is wrong with thinking like this found on the forums that promote the BBT. Yes, light from a remote object using the comoving radial distances in BB cosmology to explain the large redshifts we do see today, this light could eventually reach Earth. However, only when the universe is potentially, billions of years older than the current accepted 13.8-billion-year age. Testing this concept in BB cosmology appears difficult :)
 
Jan 4, 2020
219
96
1,660
Despite the barrage of unnecessary article detail, it suffices to say that the vacuum energy density is the leading physics, that "recession velocity" is a pre-relativistic idea of the Hubble scale expansion rate (using scale factor of cosmological models) and that the expansion is adiabatic in a flat universe.

In relativistic models it is the inner energy state that constrains the form of the summed expansion, but there is no energy driving the expansion in the adiabatic, free expansion case. The swing analogy doesn't apply here.

https://en.wikipedia.org/wiki/Scale_factor_(cosmology)
 
Jan 4, 2020
219
96
1,660
I am not (at this point) arguing that space cannot expand and carry matter with it such that two pieces of matter can be moving apart at more than the speed of light. What I am questioning is how the light emitted now is still supposed to eventually get from one to the other, assuming that space keeps expanding at the same rate (or faster).
The article is poorly written and contains errors as well, so it is good to be critical. But that space expands in scale is not typically taken to mean either the article "recessional velocity" or "carry matter with it" since those are pre-relativistic notions.

In general relativity there are some additional non-intuitive effects to special relativity such as gravitational time dilation and space expansion with its redshift of photon wavepackets that are expanded in wavelength as they travel through expanding space. From a relativity perspective of observers you are not expanded (since you are a cohesive object) nor "carried away" (since you are defining your reference frame).

The question is partly semantical if you want to use any other reference frame than the astronomer "here and now" describing what is observed here on Earth happens in objects with emissions redshifted to z=11 as happening "now". But it is also a matter of science if you want to use the redshift expansion value to estimate the age of emission, or if you want to be skeptical of the accepted cosmology that this is what happened and that the galaxy (bar aging, mergers et cetera) still exist at a certain redshift distance. And specifically it becomes a matter of many distance measures (see links below) if you want to disentangle all these ways of valid descriptions.

I'm not sure what you are asking here. But when cosmologists model the photon travel in a universe those expansion sum to different expansion scale changes depending on the dominant energy state (inflation, radiation, matter and now dark energy - see the link to scale factor in another comment) they see that photons emitted very early at some part of their journey actually lost ground to the expansion radius. And yes, early galaxies that we can observe has disappeared behind the far future cosmological horizon. (And in fact all galaxies apart from the gravitationally bound Local Group will eventually do so.)

You can say that the horizon says these 'disappeared' galaxies are now at a spatial distance that grows faster than the radius of the observable universe will ever do. But I think the important theoretical physics here is that free traveling photons would be diluted and redshifted by factors r^-3 respectively r^-1 (with r the observable universe radius) so becomes undetectable among detector noise. In real physics we can only see as far back as the cosmic background radiation since the early plasma caught all the photons until it was diluted and cool enough to (re)combine to neutral gas.

Cosmology calculators for redshifts et cetera
The many distances of cosmology - tutorial
 
Last edited:
  • Like
Reactions: Unclear Engineer
I did not say GR is wrong. In my post #2, I quoted a title and report by space.com on the subject. Something is wrong with Einstein's theory of gravity, https://forums.space.com/threads/something-is-wrong-with-einsteins-theory-of-gravity.58751/

It remains to be shown how and when in the BB model, dark energy is created and when it appears, like from the Planck time and Planck length until the CMBR appears as light. Simply citing Type 1a SN shows when dark energy is said to be seen, but not its origin or when relative to the overall BB model. For example, during the quark-gluon plasma phase of the universe, did dark energy appear then or before?

Quarks: What are they?, https://forums.space.com/threads/quarks-what-are-they.58460/

Who, what, when, where, how, and why investigative reporting is needed I feel in cosmology to break it all down now and show how all these pieces (dark energy, dark matter, origin of normal matter in standard model) the BB cosmology predicted, or just works up patches to accommodate so the model continues :)

I am glad you use some of the cosmology calculators available now. Some that I use:

LAMBDA - Links to Calculators (nasa.gov)

Cosmology calculator | kempner.net

Cosmology Calculators (caltech.edu)
 
Last edited by a moderator:
Torbjorn Larsson - Good to read that you are seeing the physics the same as I do, with respect to light being emitted by some things far enough away actually "losing ground" to the continuing expansion, and thus being beyond the dimension of the "observable universe".

As for the noise and the CMBR hiding much of the early star emissions , have you seen https://pib.gov.in/PressReleasePage.aspx?PRID=1802645 ?
Unclear Engineer, very intriguing comment about light and expansion. The CMBR is postulated to have a redshift about 1100 but as far as I understand, no spectroscopic measurement supports this redshift or Lyman break method. What you said, *beyond the dimension of the "observable universe" should be a concern in the BB model I would think. Concerning your press release reference, SARAS 3 radio telescope refutes recent claim of the discovery of a radio wave signal from cosmic dawn. I note here some more references.


"This non-detection allowed the researchers to make other determinations about the cosmic dawn, placing restraints on the first galaxies, enabling them to rule out scenarios including galaxies which were inefficient heaters of cosmic gas and efficient producers of radio emissions."

"It's amazing to be able to look so far back in time—to just 200 million years after the Big Bang—and be able to learn about the early universe," said Bevins."

I note using H0 = 67 km/s/Mpc and a look back time distance of 13.6 billion light-years from Earth, 4D space is expanding 2.7937316E+05 km/s or slightly more than 93% c velocity. Using H0=73 km/s/Mpc, 4D space expands 3.0439165E+05 km/s or 1.015 c velocity at 13.6 billion light years radius from Earth.

Ref - Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal, https://www.nature.com/articles/s41550-022-01825-6, 28-Nov-2022.

"Abstract Observations of the redshifted 21-cm line of atomic hydrogen have provided several upper limits on the 21-cm power spectrum and a tentative detection of the sky-averaged signal at redshift z ≈ 17. Made with the Experiment to Detect the Global EoR Signature (EDGES) low-band antenna, this claim was recently disputed by the SARAS 3 experiment, which reported a non-detection and is the only available upper limit strong enough to constrain cosmic dawn astrophysics. We use these data to constrain a population of radio-luminous galaxies ~200 million years after the Big Bang (z ≈ 20)..."
 
As for the noise and the CMBR hiding much of the early star emissions , have you seen https://pib.gov.in/PressReleasePage.aspx?PRID=1802645 ?
This claimed reception comes after the CMBR. When atoms first formed (Recombination), producing today's CMBR, then the universe quickly entered the Dark Ages since neutral hydrogen is essentially opaque to visible light. But the 21 cm line would be emitted without much obstruction, and we would see it today at roughly 100 Mhz, or so.

It would be a very weak signal, especially with ground reception. The far side of the Moon would be better. :)
 
Ref - Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal, https://www.nature.com/articles/s41550-022-01825-6, 28-Nov-2022.

"Abstract Observations of the redshifted 21-cm line of atomic hydrogen have provided several upper limits on the 21-cm power spectrum and a tentative detection of the sky-averaged signal at redshift z ≈ 17. Made with the Experiment to Detect the Global EoR Signature (EDGES) low-band antenna, this claim was recently disputed by the SARAS 3 experiment, which reported a non-detection and is the only available upper limit strong enough to constrain cosmic dawn astrophysics. We use these data to constrain a population of radio-luminous galaxies ~200 million years after the Big Bang (z ≈ 20)..."
Nice link, Rod.

The strongest spots in the sky for the redshifted 21-cm would come from the eventual concentration of gas in the cosmos, which formed the first galaxies.... ~ t = 200 million years.

This is another weak area for me since I don't quite get how the sudden flash from the Recombination could cut through the opaque neutral hydrogen to give us our CMBR. So, WAIM? (might as well finally abbreviate - What Am I Missing? :) ).
 
Neutral hydrogen is transparent, it is ionized hydrogen that is opaque. When the ionized hydrogen recombined to become neutral is when the CMBR escaped.
Yes, but notice how the Dark Ages story contradicts this.

In searching under "Dark Ages cosmology", you will find the basics to light at this time from the CMBR to the Dark Ages to the Cosmic Dawn.

The DA (Dark Ages) claim is that once neutral hydrogen formed, it blocked light's propagation until the birth of stars would ionize (Reionization) the hydrogen, which allows propagation.

So the nutshell version (to emphasize how the lack of details greatly distorts the story) is that once the early ionization ended (atoms first formed) then light propagated freely, but only when those atoms reionized could we see it. Hence, ionized atoms prevent propagation, and ionized atoms allow propagation. How can they do both? Ug!

This isn't explained in the few sites I searched, but I did find a hint in one, which simply mentioned transitory states, without explanation. So my take is that at the time of the CMBR (~ 3000K), the temperature was high enough so that the transitory states of hydrogen did allow light's propagation (little to no absorption). But it soon cooled enough to block propagation of visible light. With expansion (lower densities), the ionized hydrogen (~ 200 million years later) was cooler as well and allowed propagation (Cosmic Dawn).

It's worth noting the molecular hydrogen (H2) blocks light, which gives us the Bok globules. The outer regions of these nebulae become translucent with lower density and ionization. I see nothing in the text about H2 being the culprit for the DA, however. [I wouldn't expect it to be an issue given the hotter universe conditions.]

Do you think I have it correct?
 
Last edited:
Feb 14, 2020
80
23
1,535
Dark Energy is a mystery, but why do we need a Big Bang?
There are known local and small regional explosions in astrophysics.
At least DM is cause of 5% or so of measured / observed matter-energy.
As LHC and Astrophysical observations increase, we will likely see early regions of where DM makes Matter-energy, by using mostly QFT, QCD and QED tools!
DM DE existed and only known Matter-Energy is causing CMBR!
 
Nov 19, 2021
584
267
1,260
Helio - Which of these do I have wrong?

In the case of a neutral monoatomic gas, there is an electric dipole that can be rotated thus scattering light and becoming opaque.

An ionized monoatomic gas also has an electric dipole thus also scatters light.

In molecular (diatomic) gases, the electric dipoles cancel out and the gas is transparent to visible light.

From the Big Bang until recombination ca 300,000 years there was ionized monoatomic hydrogen and free electrons and it was opaque.

At the point of recombination, hydrogen alpha photons were released creating a flash of light now seen as CMBR.

The universe was transparent after recombination and prior to the first stars but it was dark, not because it was opaque but because there were no sources of light (other than CMBR).
 
  • Like
Reactions: Unclear Engineer
Feb 14, 2020
80
23
1,535
Can we think of how the matter-energy dispersion products that you describe as gases etc. visible in ordinary light or in any part of EM spectrum can be there to give CMBR even when there was no big bang?
 
Nov 19, 2021
584
267
1,260
No, because I believe there was a Big Bang, which created mostly hydrogen, which recombined around 300,000 years later, forming a bright flash in hydrogen alpha wavelenth seen now as the red shifted CMBR.


The Big Bang is the mainstream theory for formation of the Universe and there are many lines of evidence supporting it. These lines of evidence are barely within my ability to understand them and working on that understanding is my current priority. I have no interest in evaluating, arguing or trying to understand non-mainstream alternatives. If you want to argue, you have the wrong guy. Try someone else.
 
Helio - Which of these do I have wrong?

In the case of a neutral monoatomic gas, there is an electric dipole that can be rotated thus scattering light and becoming opaque.
But you stated earlier, "Neutral hydrogen is transparent, it is ionized hydrogen that is opaque ." So, once again, you are agreeing with the articles that neutral hydrogen is both transparent and opaque. WAIM??

But you are stating mainstream view of how light is handled by neutral hydrogen, but without the proper explanation, which I seek.

An ionized monoatomic gas also has an electric dipole thus also scatters light.
Well, that was prior to Recombination. But note that the Cosmic Dawn is the time period when H became ionized by the UV of the first stars, which allowed visible light's propagation. WAIM?? :)

In molecular (diatomic) gases, the electric dipoles cancel out and the gas is transparent to visible light.
Are Bok globules transparent?

From the Big Bang until recombination ca 300,000 years there was ionized monoatomic hydrogen and free electrons and it was opaque.
Yes, the free electrons were busy scattering every photon they could get their little hands on. ;)

At the point of recombination, hydrogen alpha photons were released creating a flash of light now seen as CMBR.
Yes, that is the highly respected mainstream view.

The universe was transparent after recombination and prior to the first stars but it was dark, not because it was opaque but because there were no sources of light (other than CMBR).
That is a fair point, but this doesn't seem to be the key to the darkness.

The Cosmic Dawn, when light finally broke through the clouds ("fog") was when enough hydrogen (neutral) became ionized, according to the articles I've read. It's possible they mean diatomic, which is opaque, but that's not the impression I have.
 
Nov 19, 2021
584
267
1,260
"But you stated earlier, "Neutral hydrogen is transparent, it is ionized hydrogen that is opaque ." So, once again, you are agreeing with the articles that neutral hydrogen is both transparent and opaque. WAIM??"

I failed to specify "neutral diatomic hydrogen". This is the gas we know as every day hydrogen. Completely transparent to visible light.

Neutral monoatomic hydrogen has a dipole moment thus can scatter light.

The Cosmic Dawn was when the first stars appeared. The universe had been transparent but dark for the 250 million years since recombination.

Again, diatomic gases are transparent to visible light, not opaque.

Bok Globules are opaque not due to hydrogen but due to dust.
 

ASK THE COMMUNITY