The surprising quantum reason why the Sun shines

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And may the sun shine brightly on you all in this new year.

Happy New Year to you all.

Article by Ethan.

https://bigthink.com/starts-with-a-bang ... un-shines/

[Lady Fraktor]

An interesting article Arry.

[chasmanian]

thank you for this article.
and Happy New Year's everyone!!

and wondering about this. I thought Dark Energy is the greatest source of energy.
welcome any comments.
miss you and wishing happiness and peace, nFA. and comfort to all your family and friends.

"Starlight is the single greatest source of energy in the Universe throughout its entire 13.8 billion year history, subsequent to the hot Big Bang."

[helicon]

Nice article Arry and Happy New Year!

[Lady Fraktor]

When I was reading the article it brought to mind the old question, why is it dark at night?

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An interesting article Arry.

I thought so too, thanks

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Nice article Arry and Happy New Year!

And a happy and prosperous new year to you too, Michael.

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When I was reading the article it brought to mind the old question, why is it dark at night?

He he, Olber’s paradox. Luckily, we don’t live in an eternally static universe populated by an infinite number of stars or I wouldn’t be able to do astrophotography.

https://en.m.wikipedia.org/wiki/Olbers%27_paradox

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thank you for this article.
and Happy New Year's everyone!!

and wondering about this. I thought Dark Energy is the greatest source of energy.
welcome any comments.
miss you and wishing happiness and peace, nFA. and comfort to all your family and friends.

"Starlight is the single greatest source of energy in the Universe throughout its entire 13.8 billion year history, subsequent to the hot Big Bang."

My pleasure, Chas. And a happy new year to you too.

An interesting point about Dark Energy being a source of energy. I think the word "source" might be the problem. Dark Energy might be the source for the expansion of the universe but according to Ethan is the product of expanding space itself, and I quote "Dark energy is caused by energy inherent to the fabric of space itself, and as the Universe expands, it's the energy density — the energy-per-unit-volume — that remains constant. As a result, a Universe filled with dark energy will see its expansion rate remain constant, rather than drop at all." https://www.forbes.com/sites/startswith ... 6f66841268

Even though the energy density is very low at a mere 6×10−10 J/m3 (~7×10−30 g/cm3) its uniformity across space means it dominates the universe's mass-energy content and thus, in terms of scale, makes up a large percentage of the universe. But, because it has density, it also has pressure, negative pressure, which means that we get more as space expands because of the work that is done during expansion. see here https://en.wikipedia.org/wiki/Dark_energy

That's how I see it anyway.

[Ylem]

Very nice read Arry, thanks for sharing.

[chasmanian]

thank you for your excellent reply Arry.
I'll think about it for a bit, and reply more.
I remember with fondness,
threads with nFA, and him saying that figuring out the expanding Universe,
but energy density remaining constant phenomena,
would lead to an all expenses trip to Stockholm.

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Very nice read Arry, thanks for sharing.

Glad you enjoyed

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thank you for your excellent reply Arry.
I'll think about it for a bit, and reply more.
I remember with fondness,
threads with nFA, and him saying that figuring out the expanding Universe,
but energy density remaining constant phenomena,
would lead to an all expenses trip to Stockholm.

Thanks, Chas. I don't think we'll be taking any trips to Stockholm anytime soon, like...never lol...Well, unless it's for a well deserved holiday

[chasmanian]

I hear you, Arry.

and I can't think of anything more to add to your excellent reply.

I do notice the word source though, in this DE wiki entry about its history and Einstein's CC.

"The "cosmological constant" is a constant term that can be added to Einstein field equations of general relativity. If considered as a "source term" in the field equation, it can be viewed as equivalent to the mass of empty space (which conceptually could be either positive or negative), or "vacuum energy"."

https://en.wikipedia.org/wiki/Dark_ener ... peculation

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I hear you, Arry.

and I can't think of anything more to add to your excellent reply.

I do notice the word source though, in this DE wiki entry about its history and Einstein's CC.

"The "cosmological constant" is a constant term that can be added to Einstein field equations of general relativity. If considered as a "source term" in the field equation, it can be viewed as equivalent to the mass of empty space (which conceptually could be either positive or negative), or "vacuum energy"."

https://en.wikipedia.org/wiki/Dark_ener ... peculation

Excellent Chas and thanks for your most bodacious reply. Care to expand on it a little for me? Ha ha, pardon the pun.

Yeah, it's a good point. So, as you well know, during the formulation of his famous equations, Einstein postulated that the universe, despite being filled with matter, was static. And as we know, this was a huge problem for his theory. By postulating a static universe, zero expansion, he forced one side of his equations to zero while the other side wasn't because of the contribution from matter. To balance the idea of a static universe with one filled with gravity, he had to add a repulsive constant to his field equations. Meaning he had to give up one of his assumptions, but which? He couldn't sacrifice linearity and dropping the conservation of energy-momentum would've been too heavy. So adding a small constant "lambda" to the gravitational metric thus balancing the stress-energy tensor resulted in a static universe, and lambda being a constant, meant that the source term is automatically conserved. The cosmological constant, although small, is repulsive, and by nature, it has to be to balance his equation for a static universe, Just like negative matter-density, or, viewed as the mass of empty space. see here http://www.tapir.caltech.edu/~chirata/p ... /lec09.pdf

This is also stated in the link that you posted, "The cosmological constant was first proposed by Einstein as a mechanism to obtain a solution to the gravitational field equation that would lead to a static universe, effectively using dark energy to balance gravity.[17] Einstein gave the cosmological constant the symbol Λ (capital lambda). Einstein stated that the cosmological constant required that 'empty space takes the role of gravitating negative masses which are distributed all over the interstellar space'.[18][19]" When it says "effectively using dark energy" of course Einstein didn't know that at the time.

Now we have good evidence to suggest that the universe is expanding, dark energy is the source of that expansion and is described by the cosmological constant and that the universe is not static, but...what is the source of dark energy? No idea, but the negative pressure of dark energy that drives expansions comes directly from the fact that the energy density is constant. Whether that's from the zero point energy of space or, quintessence, or, whatever it is. Dark Energy is just a blanket term for what we don't, as of yet, fully understand...but Chas, what do you think about this question...Is the cosmological constant the same as dark energy? What do you think?

I don't know because I'm not an expert, but see below for what Ethan and Sabine think, who of course, are experts

https://bigthink.com/starts-with-a-bang ... rk-energy/

https://www.forbes.com/sites/startswith ... k%20energy.

[chasmanian]

thank you Arry.
bodacious, love it!!
and I have no clue.
I understand very little about all of this.
and yet am very fascinated by all of it.

here is a link to an Ethan article about zero point energy.

https://www.forbes.com/sites/startswith ... ca17b97ecb

I will let you know if I think of any more bright ideas about Dark Energy.
Charlie

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thank you Arry.
bodacious, love it!!
and I have no clue.
I understand very little about all of this.
and yet am very fascinated by all of it.

here is a link to an Ethan article about zero point energy.

https://www.forbes.com/sites/startswith ... ca17b97ecb

I will let you know if I think of any more bright ideas about Dark Energy.
Charlie

Most excellent and thanks for the link. I think we’re all in the dark when it comes to dark energy and dark matter You are right though, it really is fascinating!

[SkyHiker]

The article does not mention the model that is used to decide that two nuclei can never overcome the electrostatic force. Quantum physics models any phenomena that we cannot observe and/or model deterministically as a stochastic process because that's the best we can do. That works very well, and it allows for the existence of the tunnel effect on stochastic basis. But who knows what really happens at that scale? Maybe it is all deterministic and quite different than we imagine if we could observe it. So, it is odd to say that fusion could not occur deterministically if we have no clue what that deterministic world would look like. If you present it as two charged billiard balls that need to overcome the electrostatic force sure, I could believe that that is impossible and maybe that's what the author had in mind but that's an over-simplification. So, the article says that stochastic models work as they should, which is not a surprise.

[SkyHiker]

Wasn't the cosmological constant originally motivated as a way to explain the expanding universe? Einstein, Feynman and Weinberg seem to think it should be zero. That implies that they believe there might be alternatives that we don't know about. GR and cosmology are based on the simplest possible model, and it has some loose ends. Having to add dark energy and dark matter to explain our observations is not great. What if the gravitational constant is not a constant, and/or if inertia depends on the surrounding universe? What if ECSK gravity is real and there was never a big bang but a big bounce? There are lots of options that have not been fully explored so I take it with a grain of salt but that's just me, maybe not even worth 2 cents.

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Wasn't the cosmological constant originally motivated as a way to explain the expanding universe?

Well, it's an interesting way to look at it. And to be sure I've had a flick through the cosmology books I used at university and other reading material to see if there is anything that states that the cosmological constant was motivated as a way to explain the expanding universe. But that's not what I see or read.

Einstein first introduced his field equations in 1916, but at that time, they didn't have the cosmological constant. He did use these equations to investigate planetary motion in the solar system and to predict the non-Newtonian deflection of light by the sun. However, during the year between this set of equations and the publication of his paper "Cosmological Considerations in the General Theory of Relativity" (Einstein 1917) in which he tried to use general relativity to describe the space-time geometry of the whole universe, he realised that his assumptions in the 1916 equations were inappropriate in the broader context of cosmology.

In 1917 observations and evidence pertaining to cosmology were primarily limited to stars in our galaxy and there was no specific evidence to indicate that the universe was either expanding or contracting. From an observational standpoint, the universe at the time appeared static. Thus, he sought to modify his first set of equations in which the universe wouldn't have been static due to the nature of gravity, to one that would both satisfy Mach's principle for the relativity of inertia and be stable against the collapse from gravity. and I quote "The term is necessary only for the purpose of making possible a quasi-static distribution of matter, as required by the fact of the small velocities of the stars" (Einstein 1917)." http://www.scholarpedia.org/article/Cos ... l_constant

Einstein sought a value for the cosmological constant that would ensure that nothing would change with time. Given that universal expansion was unheard of at the time and his theory predicted the gravitational collapse of the universe, which he wanted to stabilise to conform to a static universe, it seems unlikely to have been motivated by expansion.

At the time the cosmological constant led to the relation Λ=4πGρ /C^2 which indicates a static universe. This is known as the "Einstein model" which doesn't represent the universe as we now know it. The Einstein model is static, neither expanding nor contracting, space is finite having a total volume that is proportional to Λ^-3/2. However, it is unbound meaning that you could travel as far as you like without encountering a boundary or an edge of space, so to speak. However, if you were to travel far enough in space you would arrive back at your starting point. As we know now this doesn't describe our universe.

Within a year of Einstein's 1917 publication, Willem De Sitter proposed a different empty space solution and then shortly after that Friedmann-Robertson-Walker showed that Einstein and De Sitter were special cases of a much wider class of expanding or contracting models. All of which were consistent with the field equations of general relativity and the cosmological principle. However, it was Hubble who put the final nail in the coffin for the Einstein model with observational data that proved an expanding universe and then Einstein abandoned the Cosmological constant.