# Dark energy vs. modified gravity: Which one will prevail?

Einstein's theory of general relativity predicts the existence of dark energy—a mysterious form of energy that permeates space and accelerates the expansion of the Universe. But what if Einstein was wrong and there was no such thing as dark energy? The GalaxyDance project has been investigating this scenario.

As accurate as it has proven to be so far, general relativity is not the only theory that can account for gravitation. In fact, there are various alternative theories out there. Scientists are just not sure how these can resist observation and simulations.

To close this gap, the GalaxyDance project, undertaken with the support of the Marie Skłodowska-Curie program, has been using information encoded in peculiar velocity statistics of galaxies in the Local Universe as well as observed redshift space distortions (RSD) of distant galaxies.

Dr. Wojciech Hellwing, coordinator of the project and Research Fellow at the Centre for Theoretical Physics of the Polish Academy of Sciences, discusses the project's findings so far.

**What makes the expansion of the Universe so difficult to comprehend?**

As we go deeper and further in our observations of the Universe, we are still puzzled by some of its properties. One of these is the accelerated expansion of space-time, which is presently attributed to dark energy. But the truth is, we need to consider dark energy only if Einstein's theory of gravity is valid at all scales of the cosmos.

There are other possible explanations for the accelerated expansion that do not require dark energy. These theories go beyond general relativity and are commonly called "modified gravity." Testing general relativity and these alternatives at the intergalactic scale is a pressing and important issue for modern extragalactic astronomy, and it was the purpose of GalaxyDance.

**Can you tell us more about your approach?**

GalaxyDance introduces a novel approach that consists in using low-order statistics of galaxy velocities and clustering to test Einstein's theory of gravity and its counterparts. This test covers intergalactic scales, a regime in which the theory of gravity has not been rigorously tested so far. I have demonstrated that this approach has several unique advantages: it is gravity-model independent, free of significant galaxy bias and largely unaffected by baryonic physics.

I have used state-of-the-art computer simulations that recreate a virtual Universe in a supercomputer. By running and analyzing these simulations, we can test beyond-GR theories and outline promising results.

**What makes this approach particularly innovative?**

The use of large supercomputer simulations was previously impossible in beyond-GR models, due to their complexity and numerical expensiveness. To mitigate this problem, we have decided to use a speed-up algorithm which—at the expense of some accuracy—can model the evolution of the Universe much more efficiently.

I have successfully demonstrated that, in the case of cosmic velocities, such an approximated approach is sufficient to obtain robust results.

**What are the project's most important outcomes? **

Undoubtedly, the new set of large, state-of-the-art simulations of alternative theories which will allow for unprecedented studies of cosmic velocity fields.

We have already demonstrated that low order statistics of the galaxy velocity field should contain a strong signal of modified gravity. However, we have also shown that, to measure and extract this signal, dedicated and thorough modeling of the impact of our nearby cosmic structures, such as the Virgo galaxy cluster, will be of paramount importance for the success of our method.

**What do you still hope to achieve before the end of the project?**

We will implement additional modeling of the processes that determine galaxy colors, luminosity and shapes. This will enable the creation of artificial galaxy catalogs showing what would have been created in a Universe ruled by alternatives to Einstein's theory of gravity.

From thereon, we will compare our results with the existing and forthcoming astronomical observations to provide new stringent tests of gravity on the largest scales.

**What has been the feedback from the scientific community so far?**

Many colleagues expressed interest and even enthusiasm regarding our results when we presented them at international cosmological conferences. Furthermore, we have started new collaborations with colleagues who have complementary expertise in galaxy observations (from Lyon in France) and in the modeling of nearby cosmic structures (colleagues from Potsdam in Germany). We are very excited about these.

**What do you hope will be the long-term impact of the project? How does it prepare the scientific community for the era of big cosmological data?
**

GalaxyDance will provide a new way to make cosmological tests of gravitational theories a reality. The final results, no matter which theory (dark energy or modified gravity) they favor, will have far-reaching and ground-breaking consequences for our understanding of the Universe on the largest scales.

If our tests eventually provide a signature of new physics foreseen in beyond-GR theories, it will shake our current view and understanding of the large-scale evolution of the cosmos. If, on the other hand, our inquiry strengthens general relativity, it will mean that we need to look harder to explain the mystery of dark energy.

**More information:**Dance of galaxies: testing General Relativity and alternatives using galaxy velocity fields: cordis.europa.eu/project/rcn/209785/factsheet/en

**Citation**: Dark energy vs. modified gravity: Which one will prevail? (2019, August 2) retrieved 15 September 2019 from https://phys.org/news/2019-08-dark-energy-gravity-prevail.html

## User comments

Whydening GyreRobertKarlStonjekEinstein's conception was of an infinite universe with an unknown force that prevented gravitational collapse.

Einstein never accepted the expanding universe or the Big Bang model and even prepared a paper refuting the expansion model but when students found errors in his calculations he abandoned the paper and it was subsequently never published. But this indicates his mind set: like Hubble he did not think that the Universe is expanding but did not align himself with any other model of the history of the universe.

cantdrive85Neither, they are both incorrect based on misinterpretations of the plasma ignoramuses.

Anonym324154I may be tending to think about cyclic polynomials and physics together too much here, as more than a clumsy analogy, but the idea of gravity as a residue (syndrome) of the strong force makes some sense, and DE may independently, or dependently, enhance the residue. DE would have lower quantum energy and larger spatial wavelength compared to gravity.

But before I got to unifying DE this way it helped to see that DM ends up as constantly-radiated galactic wave-scale gravity ripple effects misunderstood by GR.

danRphysics.nyu.edu/sokal/transgress_v2_noafterword.pdf

Nov 28, 1994 - Towards a Transformative Hermeneutics of Quantum Gravity. Alan G. Sokal. Department of Physics. New York University

danRhttps://phys.org/...rse.html

"However, in an April 1931 report to the Prussian Academy of Sciences, Einstein finally adopted a model of an expanding universe. In 1932 he teamed up with the Dutch theoretical physicist and astronomer, Willem de Sitter, to propose an eternally expanding universe which became the cosmological model generally accepted until the middle of the 1990s."

Sounds to me like he most definitely accepted an expanding universe.

copernicusonE n e r g y

Da SchneibBenni"Einstein's theory of general relativity predicts the existence of dark energy—a mysterious form of energy that permeates space and accelerates the expansion of the Universe. But what if Einstein was wrong and there was no such thing as dark energy? "

Ok Prof, in what section of Einstein's GR do we read about this? Or are you just another grandstanding acolyte continuing rearranging the stage furniture for the next ludicrous Pop-Cosmology statement?

There is not a single word of this in General Relativity, anyone who does not believe that is free to do a word search in the actual document, I did it a few minutes ago, it came up empty, took 30 secs.

It's a different thing to discuss statements Einstein made SUBSEQUENT to writing GR, but to be guilty of claiming those words exist inside a document that is empty of ANY of those words is fraud.

CastrogiovanniYep, and you also did a word search for 'warped' and 'curved'. However, you forgot 'geodesic' and 'curvilinear'! Lol.

PhysicsIsDeepBut there is too much wrong with the Einstein model. Even with Lambda-CDM, which has been highly successful, there are now new discrepancies: inconsistent Hubble expansion constants, satellite galaxies that rotate in satellite planes, hydrogen atoms from the early universe that are half as energetic as they should be, etc...

Not to mention, the existence of dark matter and its making up of 85% of all matter seems a bit ridiculous. We don't even understand or know anything of its properties. Einstein said nothing of dark matter and knew nothing of galaxies; they were unknown at the time of GR.

Lambda-CDM is outdated.

Da SchneibPhysicsIsDeepEntropic Gravity by Verlinde reproduces Einstein's Field Equations exactly by considering the equivalence principle and thermodynamics. I understand it less than I do GR, and I don't understand the Field Equations well at all, but apparently entropic gravity is successful without dark matter and many criticisms it faces seem trivial.

Another reason GR fails, on top of recent findings, is that black holes are not well characterized. Gravity can't actually be infinite, nature hates infinities. I think once scientists figure out what exactly happens in a black hole the secrets of the universe will be laid bare.

Benni......and the reason gravity can never be infinite is because gravity is MASS DEPENDENT & there is no such thing as INFINITE MASS.

Da SchneibThe big one, which you didn't address, is that the light and the gravitational waves from GW170817 arrived at the same time, which rejects Verlinde's hypothesis.

Da Schneibvaleriy_polulyakhhttps://www.acade...k_Energy

PhysicsIsDeepGR predicts that stars of a sufficient mass and radius will form black holes when they die. So yes, black holes are a direct result of GR as we currently understand them.

When you pack a huge amount of mass into an infinitely small space, gravity is infinite according to GR. "A gravitational singularity, spacetime singularity or simply singularity is a location in spacetime where the gravitational field of a celestial body is predicted to become infinite by general relativity in a way that does not depend on the coordinate system." https://en.wikipe...gularity

Da SchneibProtoplasmixWith a little more mass (anything above 3.2 solar masses) all the particles are confined with extreme certainty, specifically to quantum states with relativistic energies, because the density is just that high, and the degenerate matter collapses completely -- forming a black hole.

Nature obviously accommodates and resolves infinities in the physics.

Benni.......do you know how to word search a document?

...it doesn't matter what Wiki says, a WORD SEARCH within the GR document is PROOF this isn't in GR.

PhysicsIsDeep"Keep in mind that most relativists don't believe that anything infinite happens in black holes."

Exactly, but GR alone is insufficient at explaining what goes on in a black hole. This is well known and incontestable.

BenniHave you ever downloaded & read actual General Relativity text?

Before you continue trying to quote for us all the things you've read as to what others write about the contents of Einstein's General Relativity, go read it for yourself. There is not one single thing you have written that is factually correct as to the CONTENTS of the actual document. I'm just trying to be fair to you, nothing snarky, I hope you take it that way.

......and of course GR alone is insufficient, but how would you like explaining how FINITE MASS can generate INFINITE GRAVITY on a stellar mass called a black hole?

Benni.....so what is so magical about going from 1.44 to 3.2 solar masses? That at 3.2 solar mass INFINITE GRAVITY rears it's head up & devours everything?

rrwillsjyou claim to understand the words?

yet you show no evidence that you understand the math

the "words" did not make possible nuclear bombs

but the "math" preceded the engineering

Da SchneibIf you're patient and smart, and ignore the trolls, we can tell you what real physicists say and back it up with references. If you don't have the math, I think you'll be surprised at how much of it we can show you and explain it so you'll understand it.

For example, in the last couple of days, @Proto did a very good explanation of the Einstein field equations that I found most evocative. @Proto, that thing with the LHS of the EFEs being how space curves, and the RHS being how matter and energy make it curve, was excellent. I wish I'd thought of it years ago.

PhysicsIsDeepThat sounds interesting. I come from a different academic background but, had I known what I know now, I would have studied physics right away. Where on the internet do you guys explain the math of GR?

Da SchneibRight here, with references to various dependable sources like Wikipedia, John Baez's various physics pages, academic papers that are in the public domain, and things like that.

I'm not going to explain @Proto's great idea, I don't want to steal his thunder.

PhysicsIsDeepI can do algebra and trig at the high school level. I have calculus and linear algebra as well, and will be retaking them soon. Explain anything as well as you can and I can Google things, I'm a quick learner.

Da SchneibHere's the first thing. Do you know the Lorentz transforms? You can get most or all of that with just algebra.

Look this over and see what you think: https://en.wikipe...ormation

Benni......"we"? Who are these "we" guys who "can show you & explain it"?

Einstein's words are public enough for everybody to read, but you think Einstein's GR requires an interpretation? And YOU can fill in for Einstein's inability to interpret text from his own documents? Well then this should be good, start by explaining what Einstein wrote in GR about the existence of INFINITE GRAVITY on a FINITE MASS? Start by telling us how many times INFINITE GRAVITY appears in General Relativity......I'll save you the trouble, a document word search reveals a big fat goose-egg zero, didn't know that did you?

PhysicsIsDeepI know about Lorentz transformations. I have taken basic classical mechanics, E&M (really dense), Optics and Modern Physics, and Thermodynamics. These were covered in Optics and Modern Physics.

I know up until Inverse boost

BenniI know about Lorentz transformations. I have taken basic classical mechanics, E&M (really dense), Optics and Modern Physics, and Thermodynamics. These were covered in Optics and Modern Physics. .......then you know about this? https://www.fourm...ntz.html

Da SchneibNote the similarities between the ordinary 3D rotation formulae and the 4D rotation formulae using hyp trig. Use the HYP key on your calculator (Windows calculator in scientific mode will show this key so it's already right on your computer).

PhysicsIsDeepDa SchneibI wanna make sure you understand SRT (special relativity theory) first, @Physics. It's fundamental to GRT (general relativity theory) because it uses the same postulates, plus one more. What I give you will depend on what you already know; so let's just walk through all this first. It shouldn't take you long judging by your understanding so far.

BenniAll this Lorentz Transformation is pointless unless you have a full comprehension of the INVERSE SQUARE LAW, it is the best explanation you'll ever need for the immutable law of physics that explains why gravity can never reach infinity on any kind of MASS.

Da SchneibDo you have the slightest idea how stupid you are making yourself look in front of someone who knows classical mechanics? ISL is present in Newton's Theory of Universal Gravitation from the 17th century.

PhysicsIsDeepI fully understand everything up until Baez writes "In any event, we can ask for still more symmetry than conformal symmetry. We can ask for symmetry under all smooth coordinate transformations!" Then it gets tricky. Still reading. But for the most part I understand SR, Lorentz transformations, etc...

CastrogiovanniNo more stupid than claiming carbon-14 decay is an example of gamma decay! Lumberjacks beware! Next time you cut down a tree, get the hell away from it ASAP!

Da SchneibDa SchneibPhysicsIsDeepWhen it gets to functors it becomes very technical. But I've learnt about symmetry groups, their relationship to conservation laws, what you mentioned (similarity of LT to rotation formulae), and the special case of massless

Da SchneibYou'll find that the standard algebraic LTs have the same problem if you try to do the same thing.

Da SchneibIn the case of the standard LTs, you will note that when you plug zeroes in, or c, either beta or gamma becomes undefined due to the presence of a zero in the denominator. As far as anyone can tell, either of these being undefined means the equation is not a representation of reality. For all real velocities, neither is undefined. The transition happens at the speed of light.

Mimath224PhysicsIsDeepcantdrive85Yep, when it is acknowledged that black holes are pseudoscientific maths claptrap and accept they are observing plasmoids at galactic centers then the Plasma Universe will be laid bare.

BenniYou're having a problem understanding Lorentz Equations because you are not yet well grounded in the most basic understanding of of gravity where all physics students must start.

You are starting from the premise of a theory (infinite gravity) & working your way backwards trying to prove why it exists in exclusion to the INVERSE SQUARE LAW, that's like trying to build a house starting at the roof first. If you don't have a foundation to build a theory on, how do you expect to reach the pinnacle? Instead YOU declare the pinnacle & imagine you can work from the top down.

PhysicsIsDeepCastrogiovanniOnly an idiot would claim that a black hole is a plasmoid! Lol. I'm still waiting for the calculations for the stellar orbits around this non-existent plasmoid woo.

Anonym324154I suggested polynomials and syndromes were a clumsy analogy. Other than that flight of innocence there is nothing even remotely close to Sokal-level social engineering involved in what I said.

Da SchneibAs for how time rotates into space, look at what both of the LTs give you (we could call the hyp trig version the "Poincare transform," if it will help you keep them straight). In both of them, space turns into time (turns, literally!) and time into space. If they can turn into each other in this manner, then they must be the same underlying thing; otherwise they wouldn't do that. The difference is only in their geometric relation to one another. This doesn't happen with the ordinary rotation transform because the space dimensions are related to one another circularly.

Da SchneibDa SchneibAnd this explains why both time and space are warped by gravity!

RealityCheck@Da Schneib.

Sure, the abstract maths/geometry approach is useful in a technical sense and up to a point regarding understanding bits of physical reality, but it obviously is not enough for that final step in understanding the whole physical reality...else we would have had the complete theory by now. Just as Newton and then Einstein came up with their initial insights and THEN 'did the maths/geometry' to model said insights, it remains that a further insight by some individual is needed to advance from the abstract/math/geom Einsteinian approach just as Einstein moved on from the Newtonian. The maths/theory is all well and good, but its obvious not enough..so just getting familiar with all the maths abstractions you bot have been discussing will not advance the science per se, it will only 'advance your own respective understandings of the current IN-complete abstract constructs for technical analysis/understanding of 'limited reality' domains. Good luck. :)

Anonym324154https://www.resea...ar_force

copernicusonBenniEven Minkowski couldn't explain this, just like your inability to explain it except to put up a lot of indecipherable psycho-babble that you Copied & Pasted from one of your favorite anonymous authors at WikiPedia.

CastrogiovanniWrong, idiot. It is only psychobabble to you because you are an unqualified janitor. You have been linked to the relevant text and equations from GRT. It is not our fault that you don't understand them.

PhysicsIsDeeprrwillsjis like me telling myself "okay, you have bought lotto tickets before, therefore this must finally be the winning ticket!"

yeah? i should be so lucky?

from the smarter than me set of this forum... they have speculated Quantum Gravity as the way forward.

Now we just have to find someone smart enough to help the rest of us comprehend such an advance

we don't give up simple arithmetic because calculus is available. it is still useful being competent at counting your change

quantum gravity would be a sea-change as disruptive to our personal view of reality as was Galileo & Einstein

this is one of the reasons so many people hate the Liberal Arts & especially the meme of "Modern Art"

as these force one's thinking to expand beyond the comfort of lineal blinkers

to discomfort the fakirs unable to create or invent or produce

rrwillsjyou will have to search under

J Baez, JC Baez, John Baez,

John C Baez, John Carlos Baez

& the longest list (i found)

at John C. Baez

http://math.ucr.e...pot.html

https://en.wikipe...ot_index

Da SchneibNoether's Theorem says that for every continuous symmetry there is a conservation law. This is not part of GRT; it is, however, partly drawn from it. If you're not familiar with it, certainly I'm not the one to tell it to you. Perhaps you can refer to the Wikipedia article on it and get more, but I think you're going to need a real teacher (which I am not) for that.

[contd]

PhysicsIsDeepI was just referring to your statements before, "This is the reason for the apparent differences in how time and space represent themselves to us, trapped as we are in classical mechanics, but it's not really how they are."

Thanks for these explanations, I have learnt a lot. I'm retaking calculus and linear algebra so math will come back to me.

Da SchneibIt doesn't; mass-energy equivalence is a result of the symmetries of spacetime. But this is aside from wanting to know about GRT. Like Noether's Theorem, mass-energy equivalence is a result from SRT, not an input to GRT. I put both of these in to give more compelling evidence of my statement that time and space can interchange under the Lorentz transform.

I'm glad Baez' page (one among many, actually- he's quite prolific) was useful for you.

The smooth coordinates are part of Riemann geometry, and the Ricci tensor is based on it. Notice that the transforms in SRT are all smooth too; there are no Lorentz boosts in reality, they are impossible because you can't change velocity without acceleration you can measure.

[contd]

Da SchneibEinstein's research into Riemann geometry led him partway to GRT; but I said before that there is an additional postulate in GRT that is not in SRT, and that postulate is the Einstein equivalence principle. This is not mass-energy equivalence; it is the equivalence of acceleration and gravity. From this and the implications of Riemann geometry, GRT was constructed.

Riemann geometry is present in SRT, but the manifold is static. What Einstein realized when he made the Einstein equivalence principle is that there are other shapes for the manifold than the static one in SRT; it is these other shapes (still smooth, but warped or twisted) that lead to gravity and acceleration. GRT is simply the description of how to write a transform from the static, simple, smooth manifold of SRT to these other twisted, stretched, and warped manifolds. And these manifolds apply when you encounter gravity or experience acceleration.

[contd]

Da SchneibNow I will respond to your interjected post's question: I didn't say trapped in space; I said trapped in classical mechanics. We can directly measure classical mechanics with simple tools like rulers and clocks; but we and these are made of matter, and subject to its limitations. We can see the *effects* of the shifts in the Riemann manifold, and we can even measure them by observing something under acceleration or gravity and noting the time dilation and other effects, but we cannot see these manifold changes directly. Just as we cannot see shifts in spacetime under SRT due to velocity. This is an important distinction, so ask many questions if you don't quite understand it.

Da SchneibCastrogiovanniWhat about Benni? Are you going to get back to him on the gamma decay of 14C? :)

Da SchneibThe basic idea is that the left hand side of the Newton gravity equation ("F") is analogous to the tensors in the left hand side of the EFE, and the right hand side ("GMm/r²") is equivalent to the factors and the stress-energy tensor in the right hand side of the EFE. As I said I found this most evocative.

Back to the salt mine.

Shootistdood just about everything thing you've written, it wrong.

RealityCheck@RobertKarlStonjek.

@Shootist, can you do him (and the forum) the courtesy of explaining exactly where/how what he wrote was wrong? Thanks. :)

ProtoplasmixGood material and sample problems, free sign up. The above chapter covers things like polarization, strain, radiated power, operation of Advanced LIGO, and mathematics of gravitational waves in general relativity.

Included is an incredible plot of data from the Hulse-Taylor binary system showing the change in the period of rotation over time, compared to the prediction of radiated power from the theory of gravitational waves. The agreement was remarkable enough to give scientists much confidence that LIGO would be successful at measuring the strain directly, and no one has been disappointed.

CastrogiovanniIIRC, the Crab Nebula pulsar was seen to be slowing down. As expected. The amount of energy it was losing matched very well the energy gained in the nebula.

Da SchneibIt's even been confirmed by astrophysical measurements; Hulse-Taylor which @Proto talks about is one of the best known of those, but there are others, notably the Bullet Cluster.

[contd]

Da SchneibAmong other triumphs, GPS was originally designed by stubborn engineers not taking gravitational and velocity redshift into account; luckily, the scientists on the project persuaded them to add a feature to the GPS satellites so their frequency could be modified, and after the first test, this feature was used to correct the frequencies for SRT and GRT time dilation. @Castro knows the story well and can tell it if he chooses.

Recently, a prediction of GRT called "frame dragging" was confirmed in Earth orbit by a satellite mission called "gravity probe B." And even more recently, LIGO confirmed the prediction of GRT of gravitational waves, most spectacularly with GW170817, where a pair of neutron stars collided, and were identified within a day with a flash that had been seen from their location by other satellites; thus, because of the timing, we know that gravity and light propagate at the same speed. More on that later in this response.

[contd]

Da SchneibThese are not beyond the possibility of systematic errors either in calculation or instrumentation. Until they are I am skeptical. @torbjorn and I both believe that this will be eliminated without other changes to ΛCDM and found to be systematic errors.

I don't know what you're referring to here. Could you clarify this point?

I'm not aware of a prediction by ΛCDM of the energy of hydrogen atoms from the early universe, nor the evidence of its supposed refutation. Again, could you clarify this point?

[contd]

Da SchneibThere are three good lines of evidence here. One is galaxy rotation; if we take the matter we see in galaxies as all there is, we cannot account for their rotation curves, and this is not a small discrepancy; it's huge. This is Rubin. The earliest discoverer was Fritz Zwicky, who found that the dynamics of galaxies in galaxy clusters had a similar huge discrepancy if we took the matter we could see as all there was. And the third is gravitational lensing by galaxies and galaxy clusters; the lensing gives the same results as Zwicky and Rubin's observations. This is pretty strong evidence there's something we can't see that's affecting the propagation of light through apparently empty space; we call that something "dark matter."

[contd]

Da SchneibSure we do; it makes gravity. We can directly see that. The mass we see cannot be all the mass there is. Neither near nor far field galactic cluster dynamics work without it; and near-field galactic rotation curves don't work without it either. And both of these indicate the same parameters, further confirmed by gravitational lensing which predicts the same parameters Rubin and Zwicky do.

Of course; but when we investigated them, we found yet more evidence GRT was correct, and the inclusion of Λ in the LHS of the EFE was justified, even after Einstein called it a mistake. It wasn't; he was right the first time. It's not the only mistake he ever made.

[contd]

Da SchneibNo, it's not; MOND has been refuted by the simultaneous detection of gravitational waves and light from GW170817. MOND theories (or anyway most of them, including Verlinde) have been seriously called into question, because most if not all of them require different propagation speeds for light and gravitation, and those are not the observed facts. GRT predicted they propagate at the same speed and that's what we saw. (Yet another triumph for GRT, incidentally.)

Now, do you have more evidence to present, and will you please clarify the two points I asked about above? I expect you will have to digest all this and will wait patiently.

Seeker2CastrogiovanniIt is the only opportunity we have so far had to test various theories for the speed of gravity. In the other GW detections, no EM signatures were seen. In the neutron star merger, three facilities (2 in the US & 1 in Italy) detected it. This allowed triangulation. And, lo and behold, there was an EM signature that hadn't been there before. Hence the death rattle of many, if not all, flavours of MOND. The more we keep testing relativity, the stronger it appears to get. It has to fail somewhere, because singularities can't exist. Scientists know this, and are always trying to see where observations might depart from predictions based on relativity. This was the case with the EHT observation of the event horizon in M 87. Relativity was just fine!

CastrogiovanniIndeed. Well summed up here;

http://www.leapse...vity.htm

PhysicsIsDeepIt is a lot of evidence in favor of GR, and I was trying to delete the quote "GR is outdated" since I felt that statement was too strong. But I do think another theory will supersede GR at some point simply to account for what black holes do, dark energy and dark matter, and to be consistent with quantum mechanics.

PhysicsIsDeepI think I read about this recently. A competing theory to GRT was an "asymptotically flat minkowski spacetime" containing a strange fluid for matter, postulated by Birkhoff and Graef.

BenniDa Schneib[contd]

Da SchneibAs for DM and DE, I am still holding out for particle dark matter, and I think Λ is most likely the explanation for dark energy. But we could argue over these for days and not get anywhere. All of this is opinion and you are welcome to yours as I am welcome to mine. But to call either one a defect in GRT is, so far, incorrect.

Da SchneibPhysicsIsDeephttps://physicsto...7a/full/

Da SchneibHmmm, I'll have to look for some more references, and see if a formal paper was ever submitted.

Da SchneibDa Schneibjoel in oaklandGravity relates to mass, right? Dark energy relates to the structure of space/time itself, no? One pulls toward, the other pushes away.

(I tried to go the comments to see if anyone had pointed out the typo or brain fart or whatever was behind the headline, but I'm not *that* masochistic).

Da SchneibSeeker2CastrogiovanniI can't remember where I saw the quote, but I'm sure I saw one scientist describe MOND as an exercise in curve fitting.

Castrogiovannihttps://www.quant...0180430/

BenniWhy don't you & a few others, like schneibo, in this chatroom sit down & spend some time reading the ACTUAL TEXT of GR instead of reading what others write about it's contents? Do this & your concept of the content of the document will take a sudden turn towards REAL SCIENCE instead of all this fantasy land of Pop-Cosmology that unscientifically fantasizes the existence of INFINITE GRAVITY on a FINITE STELLAR MASS labeled black holes, it certainly doesn't exist in GR & schneibo, castro, proto, etc, are unable to do a Copy & Paste to the appropriate section of GR.

BenniThe predicted fantasy "parameters" are that DM exists at a 5:1 ratio to ordinary matter, if this be the case why then does "Newton's universal gravitation theory (TUG)" work so well without the necessity to account for 5 times more gravity than there exists MASS to support such a theory that must be accounted for when navigating the solar system?

CastrogiovanniWhy don't you read it? And understand it? Geodesic? Curvilinear? Lol. The whole thing is a foreign language to you. And I'm not talking about the German original! Nobody believes there is infinite gravity. It is a fault with GR. We know that. It is the point at which it stops working.

CastrogiovanniOh Jesus! At those scales DM is insignificant. Why doesn't it work for galaxy rotation curves? Why do we see lensing from empty space? As in the Bullet Cluster. You really need to stick to cleaning toilets.

rrwillsjtell you what

let us amuse ourselves with a little thought experiment

'where you go up to the guy inserting the fuse into a thermo-nuclear bomb

& you explain to him that what he is doing is obviously a waste of time

that the bomb must fail as a dud since you know that Einstein was obviously wrong

because?

you claim to have found errors in Big Al's spelling & grammar

& your opinion is the only opinion that matters

the amusement in this thought experiment is in visualizing you running around the tarmac screaming with the Air Police dogs gamboling along, nipping at your ass!

yet you offer no criticism of the equations

benni, are you even competent to comment on potential mistakes in the math?

i find it telling that you do not apply the same critique to Newton's original Latin publication of the Principle's

that needed many corrections by Émilie du Châtelet plus adding in her work on energy

after all, fairs, fair, right?

Anonym324154Since his idea was such a famous media failure, it was decided the gravity-less circular dizziness of it should be officially re-cast as a modification of GR for the gape-jawed masses by the media gaslighting union. It has to be pointed out time and again to the dumbass who wants to keeps the tradition alive on this site merely because he is a low-watt propagandist.

Anonym324154Seeker2Anonym324154Another guy is apparently not buying it either: "MOND theory (MOdified Newtonian Dynamics), challenges the concept of dark matter and offers an explanation of the problem of flat rotation curve of spiral galaxies. MOND is based on a modification of Newton's second law at very low acceleration."

http://www.astron...ory.html

Protoplasmix"The theory, which emerged in the 1970s as a way to unify the fundamental forces of nature, has profoundly shaped the landscape of particle physics"

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