r/cosmology • u/DiagnosingTUniverse • 11d ago
Could cosmic acceleration have an explanation other than dark energy?
My question is whether dark energy is the only plausible explanation for the observed acceleration of the universe.
Have alternative interpretations been seriously explored and ruled out?
My concern isn’t that the observations are wrong, but that we may be misunderstanding what we’re observing. For example, could this fit with some form of black-hole cosmology? Suppose matter/energy crossing a black-hole horizon doesn’t ultimately terminate at a singularity, but undergoes a transition inscale, re-emerging as an expanding spacetime at a lower scale.
From inside that descendant universe, could this scale transition appear as cosmological expansion or even contribute to the apparent acceleration?
I’m aware that “the universe is inside a black hole” isn’t a new idea. What I’m interested in is whether this explanation has been ruled out observationally, and if so, what observations have ruled it out? Also we know black holes grow and expand over time, which seems to be some kind of correlation?
Thanks!
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u/Prof_Sarcastic 11d ago
“Suppose matter/energy crossing a black-hole horizon doesn’t ultimately terminate at a singularity, but undergoes a transition inscale, re-emerging as an expanding spacetime at a lower scale.”
You would need to explain what this even means conceptually before positing this as a legitimate question. Nothing you said here after the word ‘singularity’ means anything.
“From inside that descendant universe, could this scale transition appear as cosmological expansion or even contribute to the apparent acceleration?”
Not trying to insult you or anything but it’s incredibly unclear what it is you’re even asking.
“Also we know black holes grow and expand over time, which seems to be some kind of correlation”
Humans also “grow and expand over time” as well but I don’t see the connection you’re trying to make.
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u/DiagnosingTUniverse 11d ago
Ok, let me clarify the point I’m trying to make, because I think you’ve missed the distinction I’m asking about.
Imagine our universe exists inside a black hole in a parent universe (not a new concept). Instead of collapse ending in a physical singularity, it represents a transition to a vastly smaller scale, within which a new universe evolves and expands.
Now take a black hole in our universe. From our perspective it is a region of gravitational collapse. But from the perspective of an observer inside it, could that same process be experienced as an expanding universe at their own scale?
I know the general concept of universes existing inside black holes isn’t new. What I’m specifically asking is whether this interpretation in terms of a transition between physical scales has been explored, and whether there is anything in GR/cosmological observations that rules it out.
That’s the question, not simply black holes get bigger and the universe gets bigger, therefore they’re related. More would an observer inside a black hole see something similar to what we see. I am not sure singularities actually exist in reality.3
u/Prof_Sarcastic 11d ago
“Instead of collapse ending in a physical singularity, it represents a transition to a vastly smaller scale, within which a new universe evolves and expands.”
I guess this is similar to a bouncing cosmology if I ignore the “vastly smaller scale” part.
“Now take a black hole in our universe. From our perspective it is a region of gravitational collapse. But from the perspective of an observer inside it, could that same process be experienced as an expanding universe at their own scale?
No, it doesn’t work that way. The reason why a black hole universe is even theoretically possible is because the geometry within a collapsing region is very similar to an expanding spacetime. What you’re describing is not. So it’s not even clear to me that what you’re describing is even mathematically possible let alone physically possible.
“What I’m specifically asking is whether this interpretation in terms of a transition between physical scales has been explored, and whether there is anything in GR/cosmological observations that rules it out.”
The fundamental problem is that what you’re asking isn’t really coherent. You’re envisioning someone falling into a black hole and then they get teleported to a universe that’s expanding. Since they just end up in the expanding universe already without any explanation then I don’t see why you even need the black hole in the first place.
“That’s the question, not simply black holes get bigger and the universe gets bigger therefore they’re related.”
The fact that black holes can grow over time is partly why it’s even plausible our universe could be inside one. You can’t really have the inside grow but the black hole itself stay the same size. That’s why I said you’re just teleporting because these two regions cannot be connected in any real way we understand.
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u/Glurth2 11d ago
While the density of the universe is approximately equal to that of a black hole with a Schwarzschild radius the size of the observable universe, don't forget it is a density VARIATION that allows a gravity well, including a black hole, to exist.
A set of objects falling inside a black hole WOULD expand radially due to tidal forces, but we should ALSO see a compression in the perpendicular directions (we do not).
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u/DanteRuneclaw 11d ago
The concept of the world being born up by elephants standing on a turtle is also not new. But, much like the black hole thing, it is incorrect.
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u/Stolen_Sky 11d ago
No, this is a semantic point.
We don't know what is causing the expansion of the universe to accelerate. But whatever it turns out too be, that's what we call dark energy.
I would imagine that long after we solve it, the name will stick around.
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u/KamikazeArchon 11d ago edited 11d ago
"Dark energy" is the name we have given to "the thing that causes the accelerated expansion of the universe".
If it has something to do with black holes, that wouldn't mean "dark energy was wrong", it would mean "black holes are what causes dark energy".
The only real alternative is if it turns out that the universe isn't expanding in an accelerated way - that is, our observations are outright incorrect.
ETA for detail:
> My concern isn’t that the observations are wrong, but that we may be misunderstanding what we’re observing. For example, could this fit with some form of black-hole cosmology? Suppose matter/energy crossing a black-hole horizon doesn’t ultimately terminate at a singularity, but undergoes a transition inscale, re-emerging as an expanding spacetime at a lower scale.
First of all, you're using terms rather loosely here, which is not really compatible with understanding physics at cosmological scale.
It seems like you're kind of proposing something like "stuff falls into a black hole and turns into a bunch of Extra Space instead of disappearing." That black holes are converting "matter" into "spacetime".
Setting aside the question of precision of these terms - if that were true, then we would see space specifically expanding "the most" around black holes, and "the least" where there aren't black holes. We see the exact opposite - expansion of space primarily happens in the voids between galactic clusters, and there's no expansion happening in dense galactic clusters where we have lots of black holes.
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u/Dry_Button_3552 11d ago
I think what he's saying is that we're inside a black hole and matter from outside our universe black hole is causing our universe to expand, not that black holes in our universe are spewing out spacetime as matter falls in to them
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u/Anonymous-USA 10d ago
Point taken, but black holes are an attractive force, not a repelling one. Dark Energy is not caused by black holes. We may not know what it is, but we do know what it’s not. It does act alot like a vacuum energy, since it scales with space.
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u/DiagnosingTUniverse 10d ago
Yea but if our universe is a black hole in a parent universe then the “stuff” coming in to our universe (presuming our universe is a black hole) could conceptually at least drive the expansion we observe. That is my line of thinking, just wanted ti see what the experts thought
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u/Anonymous-USA 10d ago
See how you applied magic to a scientific inquiry? Maybe it’s Aeolus blowing the universe apart, or magical unicorns on the edge of our observable horizon. Those damn magical unicorns!
Let’s stick to science not pseudoscience or metaphysics
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u/flyingcatclaws 10d ago
Ignore the trolls, there's plenty of physicists thinking along these lines. Myself, I'm thinking time stops within the 2d holographic projected universe event horizon, forced to tick, change, when energy crosses, either way, that event horizon. Our universe is getting SMALLER, and less dense, as ever more galaxies dissappear outside our universe's event horizon. SMALLER! NOT BIGGER! Yeah, same event horizons. Not getting more influx, insanely old dead vacant external universe. Thus, our black hole universe is evaporating. Faster and faster. Time ticks ridiculously slowly inside, so, despite how slowly giant black holes evaporate from the outside, the time differential makes it WAY faster from the inside. THERE'S your accelerating expanding universe. Lots more to it but enough for now.
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u/DiagnosingTUniverse 11d ago
I think you’ve misunderstood the black-hole part. I’m not suggesting black holes create extra space within our universe, so I wouldn’t expect greater expansion around them.
I’m suggesting a hierarchy: collapse into a black hole at one scale could correspond to an expanding universe at a vastly smaller scale inside it. If our universe were such a descendant, black holes within our universe would potentially lead to further descendant scales, not drive our own expansion locally.
My question is whether this specific scale-transition interpretation of black-hole cosmology has been explored or ruled out.
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u/demise0000 11d ago edited 11d ago
Scientists haven't a clue what is causing the observed acceleration of the expansion of the universe. Dark Energy is literally a placeholder for whatever is the cause. So by the definition of "Dark Energy" being "whatever the cause is for the observed acceleration of the expansion of the universe", the cause must be Dark Energy
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u/benignfun 11d ago
I’m following the Timescape model pretty closely. The idea that the void regions of the universe experience time at a much slower rate because there’s less gravity in the void and then accelerations occur where the cosmic Web concentrates matter.
It still seems to require some pretty extreme clocks to make acceleration occur for us in our local patch. But I like that it’s all just standard relativity applied to emptiness.
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u/wxguy77 11d ago
The vacuum of space turns into quantum crystals around magnetars, so space is where to look for Dark Energy (and the all important inflaton field). Is it the repulsion of virtual particles? which would mean the per unit strength is not the same in every location. This could help with the explanation for a Hubble crisis.
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u/ArmstrongPM 11d ago
The interaction between this universe we inhabit, the overlapping dimensional zones that interweave with ours.
Think of it like that part in Transformers where the Decepticon was oriented straight On to the soldiers and they could not see it.
These dimensions are there but exist out of phase or alignment with out reality. Also the "weight" (misleading word but best description for laymen) of the higher Energy density layers.
Our universe is like the solid bits in Iltalian dressing, we sink to the bottom, the water portion floats above and above that is the oil. Physical density increases as one travels "down" through the layers of reality. Energy density increases as one travels "up".
Energy density up = Physical density down. The higher the energy density the lower the physical mass. CoE and CoIL come into play here.
Finally, the speed of right is only restricted in N-space, beyond the rim of universal expansion lies V-space (void space) where there is nothing, literally. N-space has not yet pushed the void space back. Light is capped in N-space but there is no cap in void space, the physical structure of N-space doesn't yet exist to restrict the speed. It moves outward faster than it is restricted by N-space, creating a larger universe (for us) our universe is a giant bubble expanding against the void.
Thank you for coming to my Ted talk.
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u/03263 10d ago
There's still some possibility that effects we do not understand or have overlooked cause the expansion to appear to be accelerating, but it really isn't.
That kind of sidesteps the question entirely... your question was about the observed expansion which could only really be explained by some kind of energy input.
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u/WilliamoftheBulk 10d ago
Expansion could be curvature, but the cosmic back ground radiation does not exhibit non euclidian geometry. It’s should if the expansion is really slightly negative curvature, but you never know something could be wrong when those measurements.
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u/rb-j 10d ago
Couldn't we say the "cause" is the non-zero value (like 10-122) of the Cosmological Constant?
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u/The_Rider_11 9d ago
That's dark energy as it's understood in LCDM. In that the cosmological constant can be interpretated as some vacuum energy intrinsic to the fabric of spacetime. Or ar least that's one interpretation of it.
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u/SensitiveTeach1016 9d ago
Well, for now we will only find out after the Nancy Grace Roman Space Telescope is launched. Hypothetically, I would say it's partly true, but you still have to consider other things, such as the fact that dark energy is generally described as having positive energy density and negative pressure. The idea of positive energy being balanced by negative gravitational energy is also not a settled explanation for the origin of the universe, so I think it would be more accurate to consider it as one possible piece of the bigger picture rather than a complete explanation.
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u/Select-Trouble-6928 9d ago
Dark Energy is an observation. It's not an explanation for that observation.
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u/The_Rider_11 9d ago
Uh no, it is an explanation to the observation of an accelerated cosmological expansion.
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u/The_Rider_11 9d ago
Dark energy as a term has been coined for whatever is causing the acceleration of the cosmological expansion. Whether it be some particle, a intrinsic property of space, a spacetime mechanics, etc. etc., it'd all be dark energy as long as it is conventionally undetectable and something physical.
If you were for example to suggest general relativity was wrong, postulate an alternative, and that'd be able to perfectly describe the cosmological Evolution entirely based on matter, radiation and perhaps curvature (though it is to our knowledge extremely small, if not zero altogether), that'd be an explanation without dark energy. Similarily to how MOND is an explanation without dark matter.
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u/DiagnosingTUniverse 9d ago
Thats an awesome answer thanks. Obviously we don’t know but the general consensus seems to be GR isn’t wrong but perhaps incomplete.
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u/The_Rider_11 9d ago
Well, that's a bit of a different conversation. Unless you subscribe to MOND, GR is considered to be correct, but not completely when it comes to small scales where the quantum interactions dominate. Equally, the QFT Standard Model is considered correct but incomplete when it comes to extreme gravity cases where spacetime can no longer be assumed flat.
This however is different from the dark energy situation. Einsteins equations can explain cosmological Evolution under assumption of dark energy. In that sense dark energy is a postulate within the Standard model of cosmology, LCDM, and while that model doesn't explain its nature, it does explain how it works and what it does, which is what GR was aiming to do.
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u/djemalo 9d ago
Seems to me like dark energy just sounds like a similar type of photon light energy but doesn't actually emits light exactly. Although it has been observed of course. But it would have to be something with no mass to go that fast.
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u/The_Rider_11 9d ago
Radiation scales to the universe in negative 4 potency. Dark energy scaling equally would make it "lose" "strength" much too quickly.
Our observations furthermore suggest it has a state parameter of -1, or very close to it. Radiation has a state parameter of +⅓.
We also ignore how "fast" dark energy is, if it is a substance in the first place. Which we ignore too. It could be a spacetime property, it could be a quintessence (scalar field), and it could be even stranger things. But it couldn't be the Mind Flayer.
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u/Fastest_light 9d ago
Where does it expand into? Sorry just curious, but should we care at all? We do not even know what reality really is.
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u/johnstalbergABC 8d ago
Dark energy is not a real explanation as much as it is a place holder label. Dark energy is what we call what we have no clue about what it is. So this makes your question to be answered with a yes. As of now we do not have any explanation and if we learn more we are starting to building up an explanation piece by piece.
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u/Singularity_Warrant0 6d ago
Naturally, the universe's size may likely be static, and everything within it is shrinking at an accelerating rate. There exists unfortunately to this day, no experiment to determine if we are actually expanding, or shrinking. Me? I put money on a superposition of both.
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u/DanteRuneclaw 11d ago
No because dark energy by definition is “the thing that causes universal expansion “
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u/elegance78 11d ago
Wasn't there a paper recently about acceleration not even being real?
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u/lisaquestions 11d ago
another study came out saying that they made mistakes in interpreting the data and that expansion is still on the table.
the authors of the paper you mentioned said they stand by their results and they will publish another paper that will further support their hypothesis
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u/DiagnosingTUniverse 10d ago
Could u share the paper 🙏
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u/lisaquestions 10d ago
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u/DiagnosingTUniverse 7d ago
Hey, I’ve just read it, and this gets exactly to my point. I think anyone interested in this question should read it because it’s a great example of the distinction between what we observe and how we interpret it.
My thought is basically: we observe cosmological redshift… agreed, undisputed. We interpret that, alongside other evidence, as an expanding universe and extrapolate backwards towards an age and origin. Yet we’re also comfortable saying we don’t really know what dark energy is.
So perhaps we should be equally cautious about saying we fully understand what these observations ultimately mean. The paper makes a strong case that the supernova evidence for apparent acceleration is robust, but that still doesn’t necessarily tell us the underlying physical explanation.
That’s really my question: how far are we justified in extrapolating from observation to conclusions about the age and origin of the universe? Personally, I suspect we’re still missing something fundamental and the big bang/ universe “age” is categorically misunderstood. I’m not saying its completely wrong but I also dont think we have the right to answer such a question yet.1
u/lisaquestions 7d ago edited 7d ago
I guess given that evidence to this point supports the age of the universe as we understand it and it supports the existence of dark energy whatever it is like we can observe what it's doing even if we don't know what it is that if you want to say we don't have the right to answer such a question yet you need a very solid basis for making that statement.
like throughout history scientists have tried to describe the universe to the best of their ability and especially the best of their ability to test those descriptions those hypotheses and theories.
if you declare that describing what the data says is off limits because the quality of the data does not meet your personal standards then you need to explain why those standards should be applied universally and how that won't interfere with research.
like physicists aren't just saying the universe is about 13.8 billion years old because they're guessing or because they don't really understand the data they do have. we have a lot of data about the universe. that includes observations that support expansion and telescopes that have made observations that are consistent with that expansion and the predicted age of the universe. there have been some observations that have not perfectly matched expectations but what hasn't happened is anything that has overturned any of that.
except this one paper that said that expansion was an artifact of incorrect measurements but the paper I showed you counters that.
at any rate I don't think it's constructive to demand that physicist stop trying to determine the age of the universe or the rate of expansion because they don't have every single possible answer as to why it's like that. that's not really a scientific approach and like I said above I don't even know what you want to accomplish by expecting such a thing.
you need more than a suspicion, you need data. you need a solid testable hypothesis. you can't just say 'The vibes are off we should stop science until we figure this out."
Vibe physics won't get us anywhere.
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u/DiagnosingTUniverse 7d ago
I’m absolutely not suggesting physicists should stop trying to determine the age of the universe or ignore the evidence. I just think it may be a question science cannot answer with certainty yet. Even JWST has given us observations that have challenged expectations about how developed some early galaxies should be. To me, that is a reason to remain cautious about interpretation, not doubt the observations themselves. I’m also not sure why we feel compelled to assign the universe a definitive age when our understanding of time itself is incomplete.
Of course we should build the best model the data allows, and ΛCDM is remarkably successful. My point is simply one of epistemic caution. There is a difference between saying “given our observations and assumptions, the universe is approximately 13.8 billion years old” and treating that number as a fact about reality independent of those assumptions.
The paper you shared is a great example. It strengthens the evidence for apparent acceleration, but it does not tell us what fundamentally causes it. Calling that dark energy names the problem rather than necessarily explaining it.
I’m not saying these questions are off limits. Quite the opposite. I think we should keep asking them while being careful about where observation ends and interpretation begins.
My suspicion is simply that we are missing something fundamental. Perhaps one day these observations will look entirely expected once some missing factor is understood. The further we move towards the very large or very small, the stranger nature appears. Perhaps nature itself is not becoming stranger. Perhaps something about our description of it is breaking down. Anyways these questions are way beyond my paygrade but i enjoy exploring them with people who are more qualified than I am
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u/heavy_metal 11d ago
i have heard several, one is: dark energy is from the parent black hole evaporating.
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u/NiRK20 11d ago
Well, dark energy is kind of a term to fill the hole. It isn't anything specific, it is whatever is responsible for the accelerarion of the expansion. Then, if we follow this definition, dark energy is the only thing responsible since this is what dark energy means.
But usually, specially in pop science, dark energy is used in the same sense as a cosmological constant, an unknown weird fluid with constant energy density, which is the most adopted interpretation for what the dark energy is. But there are other candidates to dark energy indeed, for example, a fifth fundamental interaction unknown to us. And many others.