Colliding neutron stars falsify some theories of gravity | Hacker News Reader

Colliding neutron stars falsify some theories of gravity

arstechnica.com

132 pointsBerislavLopac75 comments

There were indirect proofs that the speed of gravity is close to the speed of light since at least 1980-es, based on the 1974 discovery of a pulsar in the binary system (1993 Nobel Prize in Physics for Hulse and Taylor) and the measurements and analysis of that data:

https://www.forbes.com/sites/startswithabang/2016/04/28/why-...

"we have constrained the speed of gravity to be equal to the speed of light with a measurement error of only 0.2%!"

But this one now is the first direct and so precise measurement that there is no more wiggle room for those who needed it for their hypotheses.

Written in 2016 in the article I've linked:

"The best results, at the present time, tell us that the speed of gravity is between 2.993 × 10^8 and 3.003 × 10^8 meters per second, which is an amazing confirmation of General Relativity and a terrible difficulty for alternative theories of gravity that don’t reduce to General Relativity!"

Now in 2017 also confirmed by the direct observation. The Einstein's General Relativity (1915) is more than 100 years old.

Those who designed all the detectors for the gravitational waves were sure decades ago. There were already enough consensus even then that allowed that long work, after all, it's all based on the 1915 theory confirmed in many different ways since. But it's so nice that now we have the real direct measurements of the gravitational waves and the EM signals together. It's really something comparable to the first use of the telescope 400 years ago.

As as result of the recent detection gravity is now known to update at the speed of light to within ~0.0000000000000001%, if I'm not mistaken.

I found the writing in this article cutesy and incomprehensible, but the subject matter sounds very interesting. Are there any more lucidly written descriptions of this work? The actual paper is hard to understand.

Yup. http://backreaction.blogspot.in/2017/10/new-gravitational-wa...

This is why I love HN.

There is also a recent hypothesis that doesn't require anything 'dark'

> It is shown that reduction of the gravitational mass of the system due to emitting gravitational waves leads to a repulsive gravitational force that diminishes with time but never disappears. This repulsive force may be related to the observed expansion of the Universe.

https://arxiv.org/abs/1608.01541

Published in MNRAS https://doi.org/10.1093/mnras/stw1517

In their other work they try to explain the EM-drive as a crude detector of high-frequency (GHz range) gravitational wave background.

Even if you wrote in your later replies here that (your words follow) "the math in the original article is more or less solid, no errors were found since publication in 2016" that statement seems quite dishonest, as you also wrote later, as you communicated with me, that you are aware of the direct rebuttal, which was published shortly after the article appeared, which I link here and quote the abstract if full:

https://arxiv.org/abs/1608.02882

"We show that a recent assertion [arXiv:1608.01541] that gravitational wave emission can lead to a repulsive force explaining the accelerated expansion of the Universe is totally unfounded."

I think it can't be shorter and more precise. I also thank you here for the information about that rebuttal article, as well as about another article which mentions how wrong the Gorkavyi's article is

https://arxiv.org/abs/1608.07136

both of which I haven't been aware of before the communication with you.

Sounds kooky. But... the Royal Astronomical Society is publishing it?

One relevant reaction to this paper (especially because there was no direct agreement with the article by any scientist) is here:

https://arxiv.org/abs/1608.07136

"Every now and then some confused authors use wrong, non-covariant, definitions of velocity, acceleration and gravity, based on their vague Newtonian intuitions and hidden in a superficial, often purely semantic, relativistic disguise. A recent example of such a confusion (Gorkavyi & Vasilkov, 2016) is discussed at the end of this Note."

It concludes:

"The paper by Gorkavyi & Vasilkov (2016) is not even wrong, it is simply a nonsense. The only question that may be of interest here is — how such a paper could possibly slip into the Monthly Notices of the Royal astronomical Society? I may offer just one explanation. I was told a story, perhaps apocryphal, about a famous referee report (many years ago) by Jim Pringle: “The paper is so obviously wrong that it should be published as it stands”."

Regarding Gorkavyi's linking of EM drive and his hypotheses, he tried the same with the Pioneer anomaly, but the anomaly was eventually explained completely without that, so it really seems that he looks for anything "unexplained" at the moment to popularize himself, knowing enough formulas to casually appear as he knows what he talks about, but inventing his new semantic out of thin air.

The math in the original article is more or less solid, no errors were found since publication in 2016.

The EM-drive idea is an attempt at an experiment to prove/disprove that the math has any relation to the reality.

edit: inventing undetectable dark this or dark that sounds way more kookier than this.

From the 1608.01541 (2016) paper you linked:

"We hope that our theoretical prediction about decreasing acceleration of the Universe can be verified by observations."

But the observations actually see the opposite, the increasing acceleration, verified enough that five years before that paper, the 2011 Nobel Prize in Physics was for that discovery of the increasing acceleration, based on the measurements of Ia supernovae:

https://www.nobelprize.org/nobel_prizes/physics/laureates/20...

"What will be the final destiny of the Universe? Probably it will end in ice, if we are to believe this year's Nobel Laureates in Physics. They have studied several dozen exploding stars, called supernovae, and discovered that the Universe is expanding at an ever-accelerating rate. The discovery came as a complete surprise even to the Laureates themselves."

I'm not a scientist. I can only post links and say "let's see, this might have some merit".

The authors (or at least N. Gorkavyi) recently (12th Sep) announced a new paper (literally "it's in print" whatever that means) that as far as I understand tackles the question.

A crude translation of the announcement:

> In the second article, (in print) we show that the reverse process - growth of the black holes by consumption of high-frequency gravitational waves - is the cause of the currently observed increasing acceleration of the expansion of the Universe. We have even got the correct value of the cosmological constant, solving the problem which is about a hundred years old.

Might be the hope that you quoted was about surviving long enough to witness the acceleration to cease increasing.

edit: spelling

Looking at who cited the paper you gave, I've found only one, and there is actually one rebuttal of the paper that cited the former:

https://arxiv.org/abs/1708.00799

The authors of the rebuttal of that paper write:

"Since those early years, a discussion took place on the different geodesics that can be written using local or non-local coordinates. Large accounts were published on this debate [10, 12–14].

Two sort of claims are recurring. Ignoring previous literature, there is a long list of scholars who pretend having discovered repulsion. They are listed in [10, 12–14]. The other concerns the attribution of physical consequences in the local environment of the falling body. For dismantling the latter claim, we follow the analysis by Cavalleri and Spinelli [15, 16]."

"It is a coordinate effect appearing to an observer at a remote distance from the black hole and when coordinate time is employed. Repulsion has no bearing and relation to the local physics of the black hole, and moreover it cannot be held responsible for accelerating outgoing particles. Thereby, the energy boost of cosmic rays cannot be produced by repulsion."

The rebutted paper doesn't have the same topic as the one you cite, so it doesn't have to mean too much or anything. But it hints about the way the "repulsion" claims can be problematic:

"The main shortcoming of [17] is the assumption that repulsion, type i), is a physical effect and not just a coordinate effect. In other words, repulsion is only present when coordinate time is adopted and cannot explain phenomena local to the source, and ruled by proper time."

However the lack of other responses to the paper you cite is so big at the moment that I don't expect much of it. Is there any response to the paper you cite, by any scientist, that you are aware of?

But I see that the guy is productive, and produced dubious papers before, so much that he doesn't list them himself but that could be found:

http://adsabs.harvard.edu/abs/2005AAS...206.4904G

The Pioneer anomaly is currently considered solved,

https://en.wikipedia.org/wiki/Pioneer_anomaly

and definitely not the way he attempted to do, just like now he mentions then "a total energy of relic high-frequency gravitational radiation in our Universe" etc.

So I'm not holding my breath for his next paper.

Edit: thanks for the link to his Russian blog. It seems even weirder than I could imagine, I haven't tried Google translate, but just looking, it appears that in one post he first writes about the EM drive stuff and only then he mentions that he apparently solved all the cosmological problems? Wow, he has his priorities. A typical troll, the way I see him.

NASA ADS (link is ugly and is at the arxiv page) lists three citations.

Of those, 1608.02882 (and also 1608.07136v1 which is not listed there) are a straight attempt at rebuttal, by the same author, the other two I didn't read yet.

As far as I understand, which is not much, that attempt was found not well founded.

At this point I can only suggest somehow searching for discussions that appeared back then in 2016. I don't think there was any formal (as in a published article) rebuttal of this rebuttal, only a summary in Gorkavyi's blog, which is in Russian and too complex for me to translate[1]

I'd wait for more papers from the original authors, in the hope that they would generate more discussion. One has to take the academia's inertia into account - someone who wrote a couple of dozen papers on dark stuff is understandably reluctant to even mention and thus acknowledge a competing hypothesis.

1. https://don-beaver.livejournal.com/176937.html

> But the observations actually see the opposite, the increasing acceleration

No, the observations are consistent with an increasing expansion rate, i.e. with a positive first derivative of the expansion rate, a.k.a. acceleration. How does that derivative change over time? If the second derivative is negative, you have a decreasing acceleration: the expansion rate is accelerating, but less at time T+1 than at time T.

In other words, you are getting your derivatives mixed up.

> inventing undetectable dark this or dark that sounds way more kookier than this

It's not really "invented". People get stuck on names way too much, forgetting these are simply placeholders, stopgap measures for a still incomplete, but evolving, understanding of nature.

I'm pretty sure the two names of 'dark matter' and 'dark energy' have caused more confusion than anything else in modern science. They were horrible choices that were worse than even the 'god particle.'

Horrible. Explaining they are placeholders has actually eaten up a fair amount of my time. I'm betting I've probably spent days, if we total the hours up, explaining just that. (I like to go make science simple for people. Having to explain that it is a placeholder doesn't make it easy. So much wasted time.)

I agree that the name choices were unfortunate.

You are right, 'inventing' the wrong word, and the same can be said about 'kooky'.

Still, gravitation waves were detected, while darks were not.

I dropped out of my physics phd program so take it with a grain of salt but I have never been a fan of dark matter or really any of the new theories that attempt to explain the expansion of the universe or propose things far outside the standard model (like string theory). These measurements are super interesting as they can falsify so many crazy ideas.

I'm a fan of Penrose's idea that inflation is actually the image of the infinite time boundary of a previous universe, and that there was no big bang at all, just a sequence of nested time domains.

[0]: https://www.youtube.com/watch?v=npmDbbGbSoE

As an outside observer the mystery of dark matter is interesting, but I can agree that the theories are not always so fun.

My entirely uneducates idea is that dark matter probably is some by-product of what's going on in that place of the universe we know nothing about: inside black holes--maybe spacetime curvature can only be so deep and hits a floor, spreading out in a halo around galaxies? This would be consistent with dark matter hanging out around galaxies, but not interstellar dust clouds, and also being proportional to the size of the galaxies, which is proportional to their central supermassive blackholes. Anyways this is just a wildly uneducated "arm-chair" hypothesis, but it just possibly seems when comparing this to some of the wild theoties out there, that it would be more likely a product of a known-unknown (interior of black holes), and not an unknown-unknown (new particles, new laws of physics). In that sense, if it's not ruled out already (it probably is, someone else must have thought of it), it's less crazy than modified gravity apparently was.

Dark matter may not have been detected yet, but we don't need to detect things directly to prove their existence. Sometimes, enough circumstantial evidence is sufficient.

For example, if you see a human-shaped shadow around the corner, you can safely assume that it's probably a human, even if you can't see them directly. It may of course turn out to be something else (maybe a scarecrow!) but that's okay.

Black holes are similar: we can't observe them directly but we can detect their gravitational effects, such as the way they bend light around them.

> inventing undetectable dark this or dark that sounds way more kookier than this

Just because something doesn't interact with light doesn't mean it's undetectable. The reason we posit it's there is because we detect it.

Agree with Florin_Andrei. If they had just named it skotonic matter or something, no one would have these objections. It's a working model with growing evidence to support it. That's it.

And if weird types and states of matter that we haven't been able to detect directly is really an issue, I have bad news about virtually all our knowledge of particle and stellar physics...

depends how you calibrate kooky. how do you feel about plasma cosmology?

"If the Universe were your local neighborhood, dark matter is the family that communicates with everyone, even other family members, only by changing the name of their WiFi network."

Ha! There are a couple of other gems in the article. Entertaining and educational.

That's actually pretty horrible. Gotta be honest.

HN has enough people who could design a protocol and hardware to do exactly that with wifi. HN can't adequately explain dark matter, except to say it is a placeholder and to define how we observe the effect. Anything more than that is conjecture and anyone who says otherwise is a dirty rotten liar.

Really.

I hate the name Dark Matter. It's a horrible name.

But, someone here understands electromagnetism well enough, pulse signaling, electronics, binary, spectrums, radio, whatever. They could build some sort of mesh network to do exactly that. They could probably build it with COTS and do it for pretty cheap - and write you a damned good paper.

Don't have a damned clue what Dark Matter really is. Nope.

Edit: Hell, now that I think about it, someone here would probably set that up on like their ham radio stuff at 600 baud just for fun and make it all operate out of terminal.

That's a compliment, really. There'd be a Show HN and someone would tell them it had an Emacs shortcut.

It's a fun way to describe the difference, if possibly not entirely clear to someone who knew nothing.

But the description of the actual result is very clear and very well done.

TIL that SSIDs exhibit weak force coupling

>The light and the gravitational waves travel along the direct line of sight to us, curling around the gravity wells of intervening galaxies along the way. As a result, the initial burst of light and gravitational waves hid a little gem: the time difference between the arrival of the gravitational waves and the light. All 1.7 seconds of it.

I'm not clear on this part. Was the light slower by 1.7 seconds because it interacted with intervening matter?

At the moment, the researches don't believe that the light was slower, but that it took that much time for the electromagnetic "flash" to be produced, compared to some specific point in the signal observed by the gravitational waves detectors. The later signal is not a point-like but a long signal which gets stronger as the stars get closer and closer to one another and then it disappears once there are no two stars anymore.

https://www.forbes.com/sites/startswithabang/2017/10/17/why-...

"It's anticipated that these two speeds are exactly equal, and the delay of the light signal comes from the fact that the light-producing reactions in the neutron star take a second or two to reach the surface."

A lot about this event was modeled even before this observation, and there will now be more attempts to make more precise models that better match what was measured. And the best is, these models will be evaluated by the next, planned observations.

The same process, but in a different scenario, was observed in supernova 1987a:

"Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to neutrino emission, which occurs simultaneously with core collapse, but preceding the emission of visible light. Transmission of visible light is a slower process that occurs only after the shock wave reaches the stellar surface."

This result set a pretty strong upper bound on the neutrino mass because it must be small enough that, across the 168,000 light year distance from the LMC to us, the neutrinos kept their lead on the photons emitted a few hours later.

A neutron star is much smaller, the process is much faster, and the event happened much further away, so the constraints on the difference in speed between the gravitational waves and photons should be even more tightly constrained in this event.

There are two parts to this:

* For the theories to be correct, the difference in arrival time between the gravity waves and the light waves would need to be more like 3 years. 1.7 seconds from 130 million LY is a very small difference.

* The gravity waves peak as the stars are just approaching each other, the gamma pulse happens when they collide.

"These two seemingly independent metrics [for light and gravity] can explain the structures of galaxies and of collisions between galaxy clusters, but the idea has consequences. For instance, if a something should emit both gravitational waves and light, the two waves will travel by different paths depending on the masses they encounter. So, light and gravitational waves won't arrive at a distant observation point at the same time."

However,

"The measured delay was so much shorter than the difference predicted by double metric theories that the researchers didn't even bother performing more detailed calculations. There is, in their view, simply no way to include the intervening galaxies and exclude dark matter. This is a dead MOND theory."

Disclaimer: not an expert.

Photons have an anomalous magnetic moment. Not going to pretend to be qualified to explain it, but if the photons and gravitons are originating from a region with electromagnetic fields, the photons will be slightly retarded compared to the gravitons which as far as we know do not interact.

https://en.m.wikipedia.org/wiki/Anomalous_magnetic_dipole_mo...

Disclaimer: Also not an expert.

Photons have no magnetic moment. You know this because the propagation of light is unaffected by the presence of the strongest magnetic fields we generate here on earth (which is several tesla.)

The article you're linking is not discussing the anomalous magnetic moment of the photon, but the electron. (Also muon and tau, but didactic QED texts usually focus on the electron.) You would expect the electron magnetic moment to be 2 \mu_B, where \mu_B is the Bohr magneton, if you calculated the magnetic moment purely from Dirac's Equation. However, due to coupling with particles winking in and out from vacuum fluctuations, the magnetic moment is slightly different than 2 \mu_B.

Odd that the title here has been edited to not match the source when usually titles are edited to match the source. If ars uses a click bait title why should HN fix it?

Ars Technica articles get two headlines. After A/B testing for a bit it settles on the more popular one. It's possible that was the other title that showed up on this article.

For something like an article title one could even try A/B/C/D/E testing.

But how do we know that light and gravitational wave were emitted exactly at one moment? It is not obvious for me.

What is your resolution on "one moment"? At the second-or-so level, we'd think that they weren't emitted at the same moment, as the gravity waves come from the orbiting stars before they collide with each other, i.e., mostly prior to the collision.

However, relative to a prediction that they should be separated by over a year, they arrived simultaneously.

You might wonder whether perhaps we correlated the gravity waves from one event with the light from another; this is counterindicated by the fact that the gravity waves match theoretical predictions about colliding neutron stars, and the resulting light data we gather matched theories about what colliding neutron stars might look like, an event never before witnessed. The coincidence of these two factors makes it rather likely these events are connected, in another spectacular triumph of theory predicting events that we've never seen before. I don't know that the popular press articles captured or explained this aspect very well, but I think it is part of why the astronomy community got so excited about this. Only part; there's plenty to be excited about in this event! It may well be the most exciting single astronomical event in my lifetime, because there were just so many bits that came together all at once for the first time.

Yes, I know that coincidence of two such events is highly unlikely, but to "compare" paths of gravitons and photons we need to imagine how much time divides 2 emission events. Seconds? Minutes? Hours? Perhaps it isn't very important but it's still interesting.

It was one event, a neutron star merger. The gravitational waves were emitted during the inspiral, the light was emitted as the neutron stars smashed into one another and then blew apart in a "kilonova". The two weren't emitted simultaneously, there was a slight delay between the production of gravitational waves and the peak brightness. However, the important aspect is that MOND theories predict not just a slight difference in travel times but literally months or years worth of delay.

Good. Space Time Quantification (STQ) theory predicts and justify the existence of dark matter particles. It can also predict and justify how all elementary particles react with each other. It provides the equivalent of a mendlejev table for elementary particles. These are conclusion based on the single premice that space measurement is quantified by a unit a. See http://www.scirp.org/journal/Articles.aspx?searchCode=August...

It sounds more like a confirmation of GR. Mass-energy tells spacetime how to curve through gravity, and spacetime tells light where to travel.

Yes, the article even has a section where they straight up say "Einstein was right".

The title of the article "Colliding neutron stars falsify some theories of gravity" is accurate, but the theories of gravity that it falsifies isn't the popular mainstream one (Einstein's) that, let's face it, we've all been secretly hoping to take down. Instead, it falsifies some of the new challenger (MOND) theories.

I, for one, welcome our continuing Einsteinian Relativistic overlord theories of gravity (at least when it comes to dark matter)

> ...the popular mainstream one (Einstein's) that, let's face it, we've all been secretly hoping to take down.

Please ELI5 what benefits follow from taking down the GR-based gravity theory?

Well I for one hope there’s a loop hole for FTL. Absolutely all evidence currently points to c as a hard limit.

Not a loop hole, but possibly a worm hole.

Fame, money, Nobel prize, etc...

Well, in practice we can't really confirm a theory so much as "fail to reject" it. There's a zoo of gravitation theories out there and this new data weeds out some of them.

The problem I see with the "confirms GR" language is that the new data also fails to reflect some of the MOND models, but are we going up say that it "confirms MOND" as well? That sounds really misleading to me.

You’re absolutely correct. I’m still really skeptical of dark matter. It just feels more like a massive black box of not understanding what’s going on than non-visible matter.

I'm not sure how most of the alternatives are any better. MOND is a massive black box of not understanding what's going on with gravity.

Dark matter: Some sort (or sorts) of particle that interacts gravitationally. It can't interact via the strong or electromagnetic forces. If we're very lucky it interacts via the weak force as well and we'll be able to directly detect some, but there's a good chance that it doesn't and we'll only ever have the indirect detections. And there are a lot of indirect detections that the current theory (Lambda-CDM, henceforth ΛCDM) predicts: the anisotropies in the cosmic microwave background, the large scale structure of the universe, galaxy rotation curves, gravitational lensing where no visible matter exists to create the lens, velocity dispersions of elliptical galaxies, galaxy cluster radial velocity distributions, galaxy cluster x-ray spectra, baryon acoustic oscillations, redshift survey distortions, Type Ia supernova distance measurements, Lyman-alpha forest measurements, and now the measured speed of gravitatonal waves.

Any alternative to cold dark matter + dark energy needs to agree with all the observations. Not just some, ALL. ΛCDM does. Some alternatives agree with parts and make no predictions about the rest, so they can't be eliminated (eg entropic gravity). But ΛCDM is currently the best fit for the observations.

I am not a physicist. I acknowledge that we need a way to unify QM and General Relativity, so one or both of those two must be incorrect. I just don't think that Dark Matter is an hypothesis thing to discard, given the evidence.

Dark matter disproven, wow this is amazing. This is literally one of the most important shake ups in modern astrophysics.

You seem to have read the article backwards. It's saying that it falsifies certain modified gravity theories (including TeVeS and STVG), not that it falsifies dark matter.

Clickbait title, but interesting article.

I Am Not a Physicist, so I need a real one to explain why I'm wrong, but I've thought for a while the cleanest explanation for dark matter is

1. The universe is inside a black hole.

2. Dark matter is matter which is outside the black hole, which explains why it has mass but no other observable properties.

> The universe is inside a black hole.

This is trivially true, btw. The Schwarzschild radius of the observable universe is less than the presumed plausible size of the universe as a whole. Or alternatively, a "black hole" is a region of space that nothing can escape, not even light, and ongoing and accelerating spatial inflation causes that to be true on an even smaller scale -- most of the universe is unreachable by light emitted today.

> Dark matter is matter which is outside the black hole, which explains why it has mass but no other observable properties

Except that it interacts as if it was superimposed over objects in this universe, not from outside of it.

If the universe is inside a black hole what's outside the black hole?

observable universe. The rest of the universe is outside of it.

another universe. and inside black holes in our universe are different universes. goes both directions, who knows how deep. black holes all the way down and up.

Our part of the universe*... The presumption is that neutron stars are the results of gravity overcoming nuclear forces, and black holes are the results of some other force being overcome, and therefore our visible universe is the inside of a greater collapse... Or the explosive eventual death of a black holes...

It's a novel idea, but it's just turtles all the way down

No, that's not really what I'm saying. A black hole is a just a region that light can't escape from. It is entirely possible for the inside of the black hole to be composed of normal, everyday matter, non-singularity matter. The Schwartzchild radius scales linearly with mass, an unusual relationship that means that for any density the O(r^3) volume will eventually be overtaken by the O(r) Schwartzchild radius.

I think you mean the O(r^3) Schwartzchild radius will eventually overtake the radius r?

Yes, thank you.

You confuse dark matter and dark energy. The later is the name for the energy that accelerates the expansion of the universe.

The rest of your hypothesis also has no sense, given what we know today. The big "black hole" can't be "outside" of our universe as our universe is all that is, including the space in which it is.

The universe doesn't expand inside of its own space, there is actually more space between the galaxies appearing, that is, the new space is appearing, according to what we observe. So the mechanism can't be easily explained by imagining some mass "outside" as the mass must be in the very space we talk about.

What we see we call the "observable universe" and because of the finite speed of light, observing the stuff in the distance we see the past! What we see in the farthest distance is actually just a glow of the so-called "big bang," a phase of the universe when there were no stars, no galaxies, just the elementary particles, specifically, we see the moment in which that state became "visible", that is, allowed the photons to travel long enough.

So the farthest everywhere we look is just the glow. It is all around because around the point where we are now, just like any other point, there was much less space early enough. The glow is called the CMB:

https://en.wikipedia.org/wiki/Cosmic_microwave_background

It was first time measured in 1964, and the scientists received 1978 Nobel Prize in Physics for that.

We see the big bang in the distance, even if the big bang ended around 14 billion years ago.

I hope you see why we can't explain what we actually observe by imagining the "black hole outside."

Leonard Susskind said in his book that "the universe is the inside of a black hole" is the #1 theory of cranks that reach out to contact him. The stuff written to popularize physics really has almost no correlation to the real thing, it's all analogies and stuff, so I would be careful.

> You may have noticed that the universe is actually expanding, rather than contracting as you might expect the interior of a black hole to be. That’s because, if anything, our universe bears a passing resemblance to a white hole. Our universe (according to conventional general relativity) has a singularity in the past, out of which everything emerged, not a singularity in the future into which everything is crashing. We call that singularity the Big Bang, but it’s very similar to what we would expect from a white hole, which is just a time-reversed version of a black hole.

> That insight, plus four dollars or so, will get you a grande latte at Starbucks.

Why would we then detect dark matter inside our universe?

We're at the very edge of the event horizon and so is dark matter, just on the other side.

No, we see evidence of dark matter everywhere inside the universe, around galaxies; you may be confusing dark matter with dark energy.

I am almost certainly just talking nonsense, but it seems to me if the light-emitting universe is on one side of a flat plane and dark matter is on the other, the physical distance between the light-emitting universe and dark matter could be 0.

You are indeed talking nonsense.

Yea, total nonsense, the universe isn't 2d, and like I said, see the bullet cluster. Dark matter is here, in our 3d universe, mixed with normal matter.

> The universe is inside a black hole.

More like it is itself an inside out black hole, or acts like one. I suggest Leonard Susskind's talks/lectures on Youtube for a clear explanation.

See the bullet cluster; you misunderstand the evidence for dark matter.

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