What is dark energy?

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Bok Globules are opaque not due to hydrogen but due to dust.
Yes, that might explain it, even though dust is only about 1% of GMCs or Bok globules.

Since the ISM seems to be transparent, and I assume comprised mainly of H2, then your view seems correct.

I need to look at some books I have at home that may help me. There seems to be very little I find helpful in my search for answers via Google.
 
I think that Bill has explained it correctly - and some of the articles do seem to have incorrect statements in them, causing confusion.

One other point is that once a lot of stars formed, the diatomic hydrogen molecules seem to have split into monatomic hydrogen atoms and then lost electrons and become ions (really just protons) plus free electrons. But, by then, a lot of the hydrogen had condensed into stars, so the ionized hydrogen concentration in the universe was much lower than when everything was ionized and evenly distributed. So, today, we can still see through space, even though it does contain ionized hydrogen (plus other stuff made by those stars).
 
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Helio
I too am exasperated by failed attempts on google to find information. It is very hard to discern "bravo sierra" from legitimate information. I read that 97% of information on the internet is behind paywalls. The best info is peer reviewed papers but most of them are expensive to download.
Probably the best source is arXive. The stuff is not peer reviewed but the next best thing, and its free.

Unclear Engineer
Hydrogen atoms per cubic meter in interstellar space about 10^6. If you swept out one square meter from here to Proxima Centauri you would not gather but .07 gram of hydrogen.
Interstellar space is even less dense with but one atom per cubic meter. Sweep a square meter from here to the Andromeda galaxy and collect but .04 gram hydrogen.
Ionized or not, it wouldn't stop much light.
 
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Basically, I think, dark energy is a name we give to something we believe must exist because of the behaviour of the Universe, but that we do not yet understand nor have we proved its existence.
 
Bo Reipurth’s book on star birth notes that H2 (forming at low temperatures) doesn’t react with light, implying it is transparent. Monoatomic hydrogen is, however.

That helps, but it’s monoatomic hydrogen that formed at Recombination, so its as if the light was freed from electron scattering but immediately was mangled by mono hydrogen. Or, at those higher temps., perhaps it was transparent. I’m still confused since how can we see such a near-perfect BB distribution from the CMBR if that light was mangled by mono h?
 
Helio, I am no expert on the underlying calculations for the BBT, but, as I understand it, the ionized hydrogen that formed from subatomic particles during "inflation" was effectively cooled by adiabatic expansion during the ongoing "inflation" so that the energy of the particles was low enough for neutral atoms to form, and then for those atoms to make molecules of H2. At the point where the hydrogen makes diatomic molecules, it seems that space becomes transparent.

But, where my understanding lapses is how the photons that were created in the first step, when the free electrons are captured by the free protons, could have created a sea of photons that somehow survived until the next step of hydrogen forming molecules was completed, so that it could shine forever through space.

I thought the CMBR is supposed to be black body radiation at something like 3,000K temperature, stretched by a factor of 1080 by ongoing expansion of the universe since its emission at the point where hydrogen became diatomic molecules. So, that does not sound like a "signal" for the deionizing process where free electrons are captured by protons to make monatomic hydrogen.

So, I am probably misunderstanding something - maybe because the people writing these articles don't understand it themselves and are not communicating it clearly to us readers.
 
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Helio, I am no expert on the underlying calculations for the BBT, but, as I understand it, the ionized hydrogen that formed from subatomic particles during "inflation" …
There are numerous views on inflation, but the common view is of a time before protons formed, IIRC.

…was effectively cooled by adiabatic expansion…
Yes, like an Ideal gas.

… so that the energy of the particles was low enough for neutral atoms to form, and then for those atoms to make molecules of H2.
Ok, the formation from H to H2 at or below 3000K makes some sense. This is left out of the explanation in articles, but it’s logical to allow the needed transparency.

This temp is at the point where the hydrogen makes diatomic molecules, it seems that space becomes transparent.

With continued expansion, the visible light redshifted into IR and longer wavelengths, hence darkness (visible band) abounded.

But, the story is that it took stars to form in enough numbers to ionize the gas, allowing light to propagate. So WAIM here?

I thought the CMBR is supposed to be black body radiation at something like 3,000K temperature, stretched by a factor of 1080 by ongoing expansion of the universe since its emission at the point where hydrogen became diatomic molecules. So, that does not sound like a "signal" for the deionizing process where free electrons are captured by protons to make monatomic hydrogen.
Yeah, but it could have been shortly thereafter as 3000K allows H2 formation.

Regardless, if it took a little more expansion to allow enough H2 to give us transparency, then the BB (black body) distribution would still not have been disturbed, IMO.

So, I am probably misunderstanding something - maybe because the people writing these articles don't understand it themselves and are not communicating it clearly to us readers.
I suspect they do understand but are struggling trying not to get too deep in the weeds for most readers.

But you’d think there would be articles that would exist to address the ambiguity we are seeing.
 
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Is this a typo? There are ~ 1E25 cu. cm in a 1 meter sq. pipe extended to Andromeda, if my iPad use is right.
The density of hydrogen atoms in intergalactic space is cited as being 1 atom per cubic meter.
The distance to Andromeda galaxy is 2.5 million light years.
A light year is 9e15 meters.
Number of cubic meters swept out by a one square meter collector is thus 2.3e22. That is the number of hydrogen atoms.
There are 6e23 hydrogen atoms in a mole, which is 1 gram.
2.3e22 divided by 6e23 is 0.04.
 
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The density of hydrogen atoms in intergalactic space is cited as being 1 atom per cubic meter.
The distance to Andromeda galaxy is 2.5 million light years.
A light year is 9e15 meters.
Number of cubic meters swept out by a one square meter collector is thus 2.3e22. That is the number of hydrogen atoms.
There are 6e23 hydrogen atoms in a mole, which is 1 gram.
2.3e22 divided by 6e23 is 0.04.
Thanks, Bill. I thought it was much greater.
 
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I was quite surprised when I ran the numbers. I had been looking at an article on the Broussard Drive and wondering just how much hydrogen it might collect. Such a vehicle would need to collect hydrogen from a very, very large swath of space.
 
I was quite surprised when I ran the numbers. I had been looking at an article on the Broussard Drive and wondering just how much hydrogen it might collect. Such a vehicle would need to collect hydrogen from a very, very large swath of space.
Apparently so!

Perhaps many routes have nearby clouds for “drive-through” refueling. :)

(in dentist chair)
 
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Yes, must be careful of the clouds. If your spaceship is travelling at 0.1 c and it sweeps up a million hydrogen atoms per cubic meter the kinetic energy of those atoms hitting the collector is about 22 kilowatts. If the collector is "many square kilometers" such as proposed by Brussard, that is a bunch of force acting in the wrong direction.
 
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Yes, must be careful of the clouds. If your spaceship is travelling at 0.1 c and it sweeps up a million hydrogen atoms per cubic meter the kinetic energy of those atoms hitting the collector is about 22 kilowatts. If the collector is "many square kilometers" such as proposed by Brussard, that is a bunch of force acting in the wrong direction.
I wonder if something similar to a “ram jet” could be developed, where it would go in at the scoop, then accelerated without encountering any parts, except at tube walls?

[This propulsion fascinated me in Thermo class.]
 
But, the story is that it took stars to form in enough numbers to ionize the gas, allowing light to propagate. So WAIM here?
We’ll, some of the answer seems to be that the low density of the Cosmic Dawn prevented much scattering by the newly re-ionized hydrogen. [Wiki]

But given that UV light (for reionization) comes packaged with visible light, then why do we need hydrogen to be ionized to see stars? WAIM?
 
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billslug and Helio

I never meant to argue, and admire what I am learning from your exchange.

Among the physical processes we know, how do you think energetic gamma rays, as those responsible for photodisintegration of deuteron or other forms of hydrogen would express themselves as part of CMBR?

Similarly as per Ergodic hypothesis or theorem, CMBR could result from several samples of the universe.

Are we to close our mind to alternate possibilities.

BSM, Quantum Gravity, this year's Nobel, all question SM etc.!

So last two Qs

1. How we think DM and DE are related other than the fact that both are not able to be measured except DM is related to gravity?
2. Is the theory proposed by me that DE is result of disappearance of Matter-Energy back to DM not acceptable?

Regards,
Ravi
(Dr. Ravi Sharma, Ph.D. USA)
NASA Apollo Achievement Award
Chair, Ontology Summit 2022
Senior Enterprise Architect
Particle and Space Physicist
 
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"I wonder if something similar to a “ram jet” could be developed, where it would go in at the scoop, then accelerated without encountering any parts, except at tube walls?" - Helio

Yes, I am sure that would be the essence of such a drive.
First you make a coil of wire with electricity flowing through it. The axis of the coil points in the direction of travel. The field lines extend far ahead of the craft, diverging as they do so. Impinging charged particles will spiral down the field lines, compressing as they go since the field lines move closer and closer together. At the throat there would be considerable pressure. Energy would be injected into the gas, it would fuse and exit out the back.
 
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Among the physical processes we know, how do you think energetic gamma rays, as those responsible for photodisintegration of deuteron or other forms of hydrogen would express themselves as part of CMBR?
This energy range was reduced with expansion, which took trillions of kelvins down to the CMBR creating event of 3000 kelvins. The result was one of the most perfect black body energy distributions ever discovered, which was a BBT prediction. There were no gamma rays to speak of at 3000K.

Are we to close our mind to alternate possibilities.
I’m no physicist, but it’s clear that mainstream is very much a BBT explanation.

There are many elements found in the CMBR discovery that you may wish to study, so not just the black body distribution. The isotropy and anisotropy levels, it’s power spectrum, it’s wavelength temperature, etc. all point to the BBT explanation. Hawking callits discovery as the greatest for mankind. It gave cement to the theory that was rejected, initially, by Einstein.

1. How we think DM and DE are related other than the fact that both are not able to be measured except DM is related to gravity?
DM is not just a label, unlike DE, as its distribution in and around galaxies is detectable, indirectly.

DE is too much an unknown to offer mych real science to explain it…yet. There are dozensof theories (with names for each) that do make predictions, but tests for these will be difficult.

Such theories require GR knowledge far beyond what little I know.

2. Is the theory proposed by me that DE is result of disappearance of Matter-Energy back to DM not acceptable?

Regards,
Ravi
(Dr. Ravi Sharma, Ph.D. USA)
NASA Apollo Achievement Award
Chair, Ontology Summit 2022
Senior Enterprise Architect
Particle and Space Physicist
You might try the physics forums with this, given your excellent background.

iPhone
 
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"I wonder if something similar to a “ram jet” could be developed, where it would go in at the scoop, then accelerated without encountering any parts, except at tube walls?" - Helio

Yes, I am sure that would be the essence of such a drive.
First you make a coil of wire with electricity flowing through it. The axis of the coil points in the direction of travel. The field lines extend far ahead of the craft, diverging as they do so. Impinging charged particles will spiral down the field lines, compressing as they go since the field lines move closer and closer together. At the throat there would be considerable pressure. Energy would be injected into the gas, it would fuse and exit out the back.
Yep, perfect. Problem solved. *wink*.

Getting fusion to work with a 0.1c, or greater, flow rate would be no small challenge, no doubt. But this design makes so much sense even if far in the future.

An optimal design like this needs to be found and made a goal. Any travelers with less will too likely have to just wave at the more advanced propulsion as it passes, at an incredible speed (relative to them), knowing that these folks would, likely, beat them by years to any stellar destination.
 
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It would be reasonable to assume fusion would pretty much be limited to that of hydrogen into helium. Temperatures and pressures going any higher are ridiculous for anywhere but inside a star. The fusion we might use will convert about 0.7% of the mass of the propellant into energy. Going all the way up to iron only adds another 0.3% and is unreasonably difficult.
 
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It would be reasonable to assume fusion would pretty much be limited to that of hydrogen into helium. Temperatures and pressures going any higher are ridiculous for anywhere but inside a star. The fusion we might use will convert about 0.7% of the mass of the propellant into energy. Going all the way up to iron only adds another 0.3% and is unreasonably difficult.
Yes. There are about 9 hydrogen atoms to every helium atom. H fuses at a much lower temp, too.
 
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I’d like to posit, chronologically, what I think is the answer to the ambiguities….

1) Expansion lowered plasma temp. When it dropped to 3000K, electrons bonded to protons to produce first atoms. [He atoms formed slightly earlier.]

2) But atomic h is opaque. Shortly after the above, H2 formed. This is when the cosmos became transparent, allowing us to now see this glow in the form of the famous CMBR.

3) With continued expansion, nothing existed that glowed, hence came the Dark Ages.

4) The slight amount of anisotropy (huge clumps) , after perhaps150 million years or so, allowed the first protostars to form. Their release of light from gravitation energy (collapse energy) caused their surrounding envelopes to become ionized. These local regions became opaque as a result, so the Dark Ages continued.

4) As these massive stars multiplied, exploded to produce dust, they eventually formed galaxies. This dust contributed to the opacity.

5) But the galaxies were powerful radiation emitters, which eventually pushed the dust, and enough ionized gas, aside to allow their light to travel through the vast molecular (transparent H2) clouds that were envelops around the stars and galaxy. The Cosmic Dawn was born.

Is this close?

iPhone at Snooze. 😀
 
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Sounds right to me. Note that the point at which more hydrogen was recombining that was ionizing happened at 378,000 years after the Big Bang. The first stars appeared at 250-300 million years.
 
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Again I learned from your excellent comments and observations. I will try to locate some physics forums for my DE hypothesis.

Now to basic Q, how was hydrogen formed? For that we need to understand how nucleus was formed.

That is the power of DM in front of us for millennia. Describing details of how DM manifested and transformed itself from being ground state of matter to energetic quantum states and through a multidimensional geometry model, created quanta, energetic quanta and eventually stable particles with mass such as p n e.

once we know how h nucleus was formed (in a paper to be shortly published) it takes electron orbits, nuclear atomic mass enrichment to get matter as we observe it.
This description describes local "big bang" but does not need the single BB!

Thanks.
Ravi
(Dr. Ravi Sharma, Ph.D. USA)
NASA Apollo Achievement Award
Chair, Ontology Summit 2022
Senior Enterprise Architect
Particle and Space Physicist
 
Sounds right to me. Note that the point at which more hydrogen was recombining that was ionizing happened at 378,000 years after the Big Bang. The first stars appeared at 250-300 million years.
Yes, though the very first stars may have come on or before ~ 200 million years.

I mainly was trying to understand the Dark Ages and Cosmic Dawn, especially the transparency explanations. It’s still puzzling why so many authors seem to associate “Reionization” with our first ability to see the first galaxies, especially when ionized hydrogen is opaque to visible light. Perhaps it’s a reference to H2+?? If so, they should say so. [Is ionized H2 transparent?]
 

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