"It is only through labor and painful effort, by grim energy and resolute courage, that we move on to better things." -Theodore Roosevelt
Energy is a fundamental property of nature, and yet it’s also one of the most purely understood phenomena from a conceptual point of view. Some objects have energy inherently, such as in the form of rest mass. Other types of energy include binding energy, which is negative, and kinetic energy, which is the energy of motion. Regardless of the form it appears in, energy cannot exist without being attached to some other physical phenomenon.
As two neutron stars orbit each other, Einstein's theory of general relativity predicts orbital decay, and the emission of gravitational radiation. Image credit: NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer.
We thought there might be a way to push energy into the fabric of space itself, as the inspiral and merger of massive objects appeared to lose energy. However, this gravitational radiation is itself a form of radiation, and carries energy at the speed of light, no different from photons. There’s only one hope left for pure energy at this point in time: dark energy, responsible for the expansion of the Universe.
Without dark energy, the Universe wouldn't be accelerating. But there's no way to access that energy via any other particles in the Universe. Image credit: NASA & ESA.
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This distinction between Dark Energy and the other forms energy assumes is intriguing.
Oh dear.
Some other time perhaps ...
Only perhaps? Interesting....
A hint for Dark Matter?
Creating energy independently of the usual wave-particle transfer? That seems to be the case, indeed, with Dark Energy. It’s the exact description of what seems to be happening, as the universe’s expansion accelerate.
But then the obverse proposition naturally arises. If energy can be created ex-nihilo, independently of wave-particle transfers, as apparently observed, why couldn’t energy be DESTROYED during, because of, and AS the usual wave-particle transfer?
Yet, why couldn’t we nevertheless insist upon conservation of energy, the conservation of pure energy, independently of wave-particle transfer violation? Why couldn’t that be? The idea of conservation of pure energy is, conceptually, independent of the idea of transfer of said energy by known processes (namely wave-particle phenomena).
And how would the apparition of pure energy from losses during wave-particle show up? As Dark Matter! If that idea is true, no wonder why searching for Dark matter as wave-particle fails!
Therein Dark Energy, the hint for Dark Matter?
So where did you learn that? What education did you take to understand the source that you interpreted that way?
It is silly to speculate that actual particles of our universe can not access/interact with imagined dark energy, while at the same time proposing that the dark energy is having an affect on those same said particles by accelerating them. Paradox may work as a suitable plot device on Star Trek, but it makes for very poor science theory.
Why is it silly to do that? And where is this being done, so we may investigate your claims' accuracy.
@ CFT & Patrice Ayme,
The more things change, the more they stay the same.
Apparently you say so.
Energy untethered from matter has to exist or there'd be no such thing as a frozen neutrino. Modern frozen neutrinos have a fraction of the aggregate energy relative to the CMB rest frame compared to what they had at creation. They haven't interacted with anything. They haven't generated any photons. The energy is simply less. It went somewhere, perhaps into space itself, but it went somewhere that has nothing to do with being tethered to matter.
Why?F they don't interact with anything, then they don't mean energy is untethered from matter, since those neutrinos have energy.
They just don't pass it on or get it passed to them much.
Your requirement would have to have the neutrinos CANNOT interact, not interact rarely.
@ #7 CFT
Keep in mind that the terms “Dark Matter” and “Dark Energy” are euphemisms used because current Physics doesn’t know what they are. While there is some description, there is no explanation.
In the instance of Dark Energy, rather than thinking of this phenomenon as “energy that pushes things apart”, consider it instead as “more space being created”.
As Ethan pointed out, energy can transform into and out of matter, while Dark Energy has not been observed doing so. If you think of Dark Energy as more space (universe) being created, then the matter/energy interactions associated with the matter and energy of the Standard Model need not be expected.
Wow wrote:
No. Not neutrinos. FROZEN neutrinos. I'm talking specifically about frozen neutrinos. Frozen neutrinos in our universe have a specific history and part of that history includes no interactions with matter. It is not that they can't interact. It is that if they had interacted they wouldn't be frozen neutrinos.
"No. Not neutrinos. FROZEN neutrinos"
Ah, so neutrinos in a Disney movie.
Frozen neutrinos have been explained to you before.
http://scienceblogs.com/startswithabang/2016/07/13/could-dark-energy-be…
What happened in the meantime?
Expansion of the universe could reduce neutrino energies just like they change photon energies (from massive incandescence of the big bang afterglow and the microwave energies we see today.
As long as nothing comes along to impart energy to it, how will it gain more energy?
@ John
" rather than thinking of this phenomenon as “energy that pushes things apart”, consider it instead as “more space being created”."
I would disagree on both accounts, here's why. First, it's not energy that pushes things apart, because it acts on space and not on bodies directly (at least in general scenario where's it's lambda). The second part is IMO more important. If you go with "it creates more space", then a follow up is where is it creating this space from? And you would be hard pressed to come up with an explanation of where that space comes from into our universe. Instead IMO it's much more useful to think of it as pressure of vacuum (after all, it has ro-vacum in formula), that "stretches" space, because it's the metric that we are talking about in the end. And changes in metric are not changes in more or less space, rather they are about energy density of that space. We are not quanitifying space and saying there's more of it being made. Not yet at least.
@ #16 Sinisa Lazarek
“… it’s not energy that pushes things apart …”
We agree about that.
“… IMO it’s much more useful to think of it as pressure of vacuum (after all, it has ro-vacum in formula), that “stretches” space …”
If you prefer to think of it as the same amount of space, merely “stretched” rather than as "more" space, go for it! As I understand it, the amount of Dark Energy per unit volume of space remains constant, which would mitigate against the "stretched" interpretation.
vacuum energy (or dark energy) density is constant regardless of volume, yes. And it's part of the friedman equations... and what do they deal with.. expansion of universe... or more precisely the scale factor. Since the hubble constant is just square root of lambda in dark energy only universe. But that aside, friedman equations, or einstein field equations in general don't talk about creation of space, instead they show expansion and contraction of the metric and thus in effect the expansion and contraction of spacetime. When the metric changes due to the different curvature of spacetime, there is no more or less space being created and destroyed there. That's not what GR says.
If you think the universe is expanding "into" something, and "creating more" space in the process, then that's not the picture GR cosmology with FRW metric says happens. Just like inflation didn't create more space, that wouldn't fix anything. No, it expanded or stretched the existing spacetime so it became uniform and flat. It might not sound that there is a difference, but there is. All of our theories take spacetime as being there always. In the past it was static, nowdays is turbulent and changing depending on the content of energy and matter in it, but no theory is creating it out of thin air :)
p.s.
"but no theory is creating it out of thin air."
ok.. LQG might be doing just that, since there spacetime becomes an emergent phenomenon out of causal loops.. but that's a different thing altogether
@ #18 Sinisa Lazarek
“… If you think the universe is expanding “into” something, and “creating more” space in the process, then that’s not the picture GR cosmology with FRW metric says happens …”
That is not what I was attempting to present.
I presented to CFT is a representation of Dark Energy that did not have it as an active actor pushing matter – SM or Dark – apart, or even interacting with them, while nevertheless being that which increases their separation when not overridden by more energetic phenomena, as when matter is gravitationally bound.
For many discussions using only natural language, the effect, as in, “… they show expansion and contraction of the metric and thus in effect the expansion and contraction of spacetime …” while lacking technical accuracy, is sufficient to convey ideas.
This is, in my opinion, a central tension in Science; is its purpose to describe, or explain?
@ John
you wrote: "consider it instead as “more space being created”.
and
" If you think of Dark Energy as more space (universe) being created, then the matter/energy interactions associated with the matter and energy of the Standard Model need not be expected."
then I wrote and gave an example why that view is not correct and might lead to more issues then answers. then you wrote: "If you prefer to think of it as the same amount of space, merely “stretched” rather than as “more” space, go for it! As I understand it, the amount of Dark Energy per unit volume of space remains constant, which would mitigate against the “stretched” interpretation."
then I wrote again and gave a detail explanation why it's not a matter of preference or semantics, but what the actual physics says about it. There is no more space being created... just like gravity isn't destroying space between two bodies, so is lambda not creating more space between bodies.
then you say: "That is not what I was attempting to present." yet your previous comments are presenting exactly that... repeatedly.
I am not saying you are giving bad analogies on purpose. All I noted is that you shouldn't really tell people that DE is creating more space because while some might feel that way, it's not correct and cosmology isn't saying that.
@ #19 Sinisa Lazarek,
CFT described (#7) as paradoxical the non-interaction of Dark Energy on matter (SM & Dark), and the apparent effect DE has on it by accelerating them.
In responding to CFT’s comment, I offered an alternative to that paradox in which DE produced the effect (increasing distance), while avoiding the affect (accelerating the matter). Many people think that if, at the end of some period of time, two objects are separated by a distance greater than they were at the beginning of that period, there is more, or additional space between them.
It was certainly not my intent to ruffle any technical feathers, but rather to present the observations in a fashion that CFT would find less paradoxical. If you think that a technical treatment of the subject is more likely to resolve CFT’s perceived paradox, then go for it.
Sorry, that should read @ #21, not @ #19.
@ John
the answer to CFT's question could've been that there is no paradox in the first place. The reason we don't see it's effects every day is because it's value is so incredibly small, not because it's creating space and not caring about rest of us. If it's energy density was higher, we wouldn't be here to ponder about it.
And I don't mind at all that your posts aren't technical, far from it, and I fully welcome and appreciate that you're trying to explain difficult concepts to other posters. And hope you continue to do that. What I did mind is that when you were corrected on the "creating more space" part, you kept deflecting and insisting that it's purely interpretation. It's only now in your last post that you correctly used "distance" instead. So, all good. The important part is to understand that lambda is not creating the universe or creating spacetime out of nothing. :)
Wow wrote:
In an open universe it can't, however in a closed universe such as in the following link the process is entirely reversible. The frozen neutrino would gain energy from the universe without interacting with any particle.
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.101302
"In an open universe it can’t, "
Why does the openness matter? Or are you talking about entropy "closed system" open? In which case, why would it being closed be changed? It's only been 14 billion years.
And barely interacting systems can do precisely what I said reversibly. No go in, no goes out.
The energy loss is not lost to something, it's just lost like the high energy photons leaving the very hot big bang glow lost energy in the intervening expansion of the universe.
Yet again, this was all explained to you earlier. Apparently you were not listening or just not comprehending.
Energy is not taken from neutrinos by something, therefore reciprocity means it could be given back, energy is just lost. Again, if the source of the neutrino is going away at Z=5+ then it will lose energy because it has been redshifted in energy.
What do you "think" happened to the photon energy from the very distant stars? Were they absorbed to be reemitted by some colder interstellar gas by your opinion?
@ #24 Sinisa Lazarek,
Very few of my posts cannot be improved. Feel free to suggest enhancements to them, or better still, post better explanations than mine. We'll all benefit from that.
But at least recently you've actually put some content in them and actually admitted to making claims. So there's some improvement.