The notion of dark energy is peculiar, even by cosmological standards.
Cosmologists have foisted the idea upon us to explain the apparent accelerating expansion of the Universe. They say that this acceleration is caused by energy that fills space at a density of 10-10 joules per cubic metre.
What’s strange about this idea is that as space expands, so too does the amount of energy. If you’ve spotted the flaw in this argument, you’re not alone. Forgetting the law of conservation of energy is no small oversight.
I like to think that, if I were not a professional cosmologist, I would still find it hard to believe that hundreds of cosmologists around the world have latched on to an idea that violates a bedrock principle of physics, simply because they “forgot” it. If the idea of dark energy were in conflict with some other much more fundamental principle, I suspect the theory would be a lot less popular.
But many people have just this reaction. It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity. (With caveats to be explained below.)
The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
It’s not that all hell has broken loose; it’s just that we’re considering a more general context than was necessary under Newtonian rules. There is still a single important equation, which is indeed often called “energy-momentum conservation.” It looks like this:
{refer to article}
The details aren’t important, but the meaning of this equation is straightforward enough: energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.
In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up.
This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity. And one that has been experimentally verified! The success of Big Bang Nucleosynthesis depends on the fact that we understand how fast the universe was expanding in the first three minutes, which in turn depends on how fast the energy density is changing. And that energy density is almost all radiation, so the fact that energy is not conserved in an expanding universe is absolutely central to getting the predictions of primordial nucleosynthesis correct. (Some of us have even explored the very tight constraints on other possibilities.)
Having said all that, it would be irresponsible of me not to mention that plenty of experts in cosmology or GR would not put it in these terms. We all agree on the science; there are just divergent views on what words to attach to the science. In particular, a lot of folks would want to say “energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.” Which seems pretty sensible at face value.
There’s nothing incorrect about that way of thinking about it; it’s a choice that one can make or not, as long as you’re clear on what your definitions are. I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved, for two reasons.
First, unlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space. So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields. The second reason is that the entire point of this exercise is to explain what’s going on in GR to people who aren’t familiar with the mathematical details of the theory. All of the experts agree on what’s happening; this is an issue of translation, not of physics. And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down. Whereas if you say “in general relativity spacetime can give energy to matter, or absorb it from matter, so that the total energy simply isn’t conserved,” they might be surprised but I think most people do actually gain some understanding thereby.
Energy isn’t conserved; it changes because spacetime does. See, that wasn’t so hard, was it?
From the site of cosmologist/theoretical physicist Sean Carroll
https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
He has some special formatting for equations and stuff that can’t be easily copied over, so check the site if you’re looking for that
It is not a law, it is hypothesis for building theories. Ufortunately, in modern science this was limited to only one theory that put a severe constraints and limitations on any development of other theories.
Hypothesis of enregy conservation is perfectly valid, and there is no any problems with it. The problem is with modern single theory, that does not have place for any unknown energy conversions, so nobody study them.
Dark matter / dark energy is a crutch for modern theory invented in attempt to somehow fit experimental observations into the moderm theory that declared only correct one. It is just a mathematical "unknown" that mathematicians put on the one or another side of equation to make their equations look corresponding to observations.
General relativity equation turned from a theory into dogma, that is why everything observed had to be squizeed into this theory math at any cost, to not allow any doubts in dogma. "Eisnstein always right" regardless of what we observe in experiments.
So, energy conservation hypothesis just state that energy/matter can't appear from nowhere and disappear into nowhere. Einstein dogmas put hard constraints on the ways energy/matter could convert between different forms, so the only way to fit math with reality is to push inconsistency onto some "dark" thing, that just exist.
Throwing out Einstein dogmas we could easily imagine that there are just other energies / form of matter we didn't discovered yet and there are other undiscovered ways of conversion from known energy/matter forms to unknown forms. But since all research is directed only by Einshtein dogmas, there is no chance this possible ways and forms will ever be studied.
There are also mutiple other ways of how things could be in universe for real, from fractional dimentionalities, to just that constants declared as constants in modern theory are not really constants at all.
Energy conservation hypothesis is very useful for practical applications and nearly everything humanity invented is in one way or another use this hypothesis. So, I don't see any reasons to abandon it. And if energy/matter disappear into nothing or appear from nothing, I'll more likely suggest that we have to look for unknown forms of energy/matter, especially if there is no place for them in Einstein dogmas, than to fall into a trap of discarding perfectly working and practically useful energy conservation hypothesis.
Great comment and I largely agree - I think these fields where normal people stand no chance of dealing with them hands on (“just build your own particle collider”) are full of navel gazing. I just think it would be better if you discussed more so the observations ( rate of redshift increasing with distance aka “spacetime expansion”) and less the weakness of the label and the system of obsessive labeling. While it’s an important point, I’d also like to hear your scientific mind’s thoughts on the scientific observations (which do appear to “disprove” the notion that the universe as a whole conserves energy - though of course with the acknowledgement that it’s “true” “often enough to be very useful knowledge” e.g. in basically any normal human endeavor)
This is not as hard, as you think, really. :) If you for whatever reason need one, you could build it in your garage at weekend. Search for "fusor" or "star in a jar" in internet. It will easily collide ions of whatever gas you pump into it for you.
This observations does not disprove anything about energy conservation, they disprove only exact modern official theory.
May be universe in whole conserve energy, may be not, but it is reasonable to use assumption that energy is always conserved in our practice. This is very helpful even for solving everyday problems.
We don't even know how antimatter interact with gravity, there was no single experiment set to study this question, we don't know if inertial mass is equal to gravitational mass, we don't know if a speed of light is really constant, but you want an answer to much bigger and further question about whole universe.
The problems you observe in modern science mostly are a result of abandoning a real scientific way, where every single theory statement should be proven in independent and replicateable way by real experiments. Today, mathematical masturbation almost replaced experimental research, so we hardly moved forward in studying world around us since 1970s.
This is brilliant! One issue is that quantum theory itself abandoned Einstein's later work in the 20s and 30s and became "Bohr-Heisenberg always right" so what's being defended is not so much Einstein anymore as a false structure built upon him. (Even when Heisenberg took a wrong turn in his mountaineering and couldn't build the bomb that Oppenheimer could.) But you've got the core dogmatism of the movement absolutely right. Thank you for reading and understanding all that is written here, and I appreciate your comments on other issues as well even when I don't say so.
This is still same dogmatism, quantum mechanic does not fit into general relativity - it is a problem of QM, and never GR. All that quantum field theory, quantum gravity and so on, are attempts to fit quantum world into general relativity, never vice versa. And ths is in situation when number of real, replicateable experiments that confirm quantum mechanics validity are orders of magnitude larger than very few observations (not even controlled experiments) that could be explained by general relativity. Fuck, we practically use quantum mechanics laws even when typing our messages on thins forum, but there is zero real practical applications of general relativity. But it is quantum mechanics should be changed, not general relativity.
Thinking about that, you also could notice that it is not quantum mechanics that put limitations on further technological progress. So, the barely proven theory dictates what things shouldn't be researched should be kept intact, while solid proven theory that doesn't limit our progress should be somehow changed to fit former one. Looks like it is limitations that relativity put on progress are very important for those who keep relativity as dogma.
Something like that.
Thank you for writing interesting things, that make this forum worth reading.
Thank you! I had to read your comment twice, first as if you were sincere and pointing out that even despite the inroads of QM there is still validity to relativity, and only second in the sarcastic sense in which you appear to actually have meant it.
Yeah, I'm still in the defiant Einstein camp. QM works because its math is accidentally right but its explanations of reality are lousy and this has been pointed out from within the mainstream a number of times. Someday we'll get the best of both worlds.
Dark energy is peculiar because it's a deceitful epicycle attached to a failed theory to attempt to patch a hole in the theory. Specifically, dark energy has no function except that it keeps cosmic structures together for as long as materialists say they existed because otherwise we'd have to admit they didn't exist that long. But they forget ....
I'll just get that out of the way before reading the article.
That’s dark matter you’re thinking of fyi - dark energy has nothing to do with the structures in the universe, but the energy density of “empty” space.
Dark energy is also held to slow down movement in the universe as well as dark matter, but I neglected that it had a second purpose, to support an accelerating expansion model with faulty calculations. The problem is that we know there's some kind of zero-point energy out there but then scientists just said let's make dark energy a category of it so we can get our math to work even though there's no experimental evidence of dark energy otherwise. Until all the math agrees, though, any theory can be entertained.
I don’t see why you want to drive an uncrossable gulf between “ZPE fields” and “expanding spacetime”, when it seems the obvious (observed) reality is an expanding spacetime with/comprising a ZPE field
We’ve seen the small scale effects (e.g. Casamir) and the large scale effects (e.g. cosmological redshift) and everything in between from Hawking radiation to Tibetan monks that work with this energy field, to whatever other X-files we’ve collected in our personal files.
But putting aside our preferred tangents and sticking to “the Science” as it stands today, where do you see the disconnect between the observations (redshift) and the explanation (cosmological constant)?
Well, since nobody has explained the disconnect I'll just make a guess. The redshift says that the universe expanded in the past, but Einstein thought the cosmological constant (which is now used to argue for accelerating expansion in the present) was his biggest blunder. So I'm not convinced of any value of (or for!) the cosmological constant. But to be able to lay out a preferred CDK math for the past and present rates that I could commit to would take more work. I usually cite Joao Magueijo but his math is not the only model out there; that would indicate that the actual power of the ZPE is 10^60 greater than what we observe and accounts for the disconnect at the executive level without going into the elbow grease. So that might be enough for your question for now.
It’s still not clear to me why you dont consider “spacetime expansion” as an explanation for the observation of cosmological redshift. Without needing to get into any math, how are you explaining a rate of redshift that increases with distance (as the cosmological constant model predicts, and as we observe)?
I do agree that expansion explains redshift. Coincidentally, God tells me that he stretched out the heavens, so that's in agreement with the observations. Then this expansion slowed down dramatically.
What's in question is whether it's expanding right now, how much, and whether the expansion is accelerating or decelerating, and that part isn't measured by redshift but by a longer chain of inferences.
Oh. Thats your issue…
How do you figure that you can still observe galaxies that are further away having higher rates of redshift, if expansion stopped at some point in the past? Surely that would be seen in observation of the furthest objects - if expansion stopped in the past, then the accelerating expansion would hold until some distance where it failed to hold. Yet we don’t observe that. We observe an accelerating expansion as far as we can see, a distance which increases as our tech improves.
I don’t think this is the case at all. I mean, assuming we’re talking about scientific theories and not feelings
Exactly. It does not even meant to be something real, it is just a dirty mathematical fix to make general relativity equations somehow correspond to real observations.
So I understand you may be looking for an article saying "energy is not conserved" but what you found was an article about how both can be true depending on definitions. His preferred language is:
but this is giving/absorbing spacetime identical to according a ZPE field to spacetime that receives energy (such as from redshift) and releases energy (such as to the background field). Which is conservation.
The problem he cites at the beginning is a biggie, across the field, not something that qualifies his view as better or another as worse. More simply it's the idea that some observation suggests there's a giant energy field holding everything together and other observation suggests this field is excessively generally uninterested in working with things, which seem to be contradictory behaviors for the same energy, which can be quantified as many orders of magnitude apart.
My basic solution, though I don't have all of it and am still studying, is that the variability of certain "constants" changes the timescale and removes the calculation errors that lead to the discrepancy. (This also removes the need for imagining dark energy out of nowhere.)
His proposal doesn't solve the problem either, though, it merely attempts to improve the description so that we can get around to solving the problem of why the zero-point energy appears massive.
Now, cutting to the chase, what everyone wants to know is how miracles get done. The answer is that they arise by tapping the hidden energy of the universe, not by breaking laws of conservation but by opening up yet-unexplained phenomena that access that energy. Scientists and theologians are scrambling over each other trying to get control of that phenomenon, but it's elusive for a reason and knowledge will proceed according to plan. Whether we define miracles as conservative (as I do) or as nonconservative (as OP does) won't matter as long as the definition accords with the data.
And my point has been that all scientific observations have problems that don't complete the explanation of the data, and that this proves the universe is not closed but instead contained. And for that purpose we'd conclude that there is something that doesn't follow conservation somewhere in the system until we define it better. For Big Bang Theory, that lack of following, that connection to the container, is found in the first Planck instant. Maybe Carroll is defining other connections to the container (which theologians would call "providence") but he still follows the general rule of leaving the universe open to a Creator.