Modified Gravity Strikes Back 

You mean Reese-Mogged?

Brutally mogged

she's even mewing in the thumbnail

Was abt to say this lol

Is it some weird furry thing you're into?

Yes, and I'd also want to understand which ones are more and less easy to fit to data by cherrypicking free parameters.

That's an interesting suggestion, thanks! I'll keep that in mind.

Gotta at least mention Electric Universe :)

​@@SubparFiddlegotta walk down to electric gravi-U

Hey how is this comment 23 hrs old? The video was uploaded just 29 min ago!!

John Candy was everyone's best friend.

Aren't we all . . .

"Ahhhh, when you're right, you're right, and you, you're always right!"

In the Final Fantasy series, Mog is a famous moogle, generally with a gold pom pom

@@scotthammond3230 Him and Chris Farley.

Mewbine Moggenfelder

@@thrwwccnt5845 🗿

fr

I can't help but understand / believe MOND. It seems like space is kinda like a waffle-pattern robe that also acts like broken ice on a pond. It just is

​@@lupin8876shoe fits - wear the mf

"they're doing WHAT to gravity? oh, we're not going anywhere near those lunatics!"

😂😂😂😂😂😂

IF there were aliens they would look at our technology and wars and laugh at us primitives

lol that's funny thanks for the laugh i needed it

@@user-om1pp5qe5z Or even conclude there is no intelligent life on Earth..

I TA'd his 1st-year physics course at UofT, many years ago, and so was always interested when I saw occasional news articles about his theories about a possible "fifth force." Later I invited him to come give a talk at our local Space Society, which he graciously did, on the topic of MOG. Which he explained so well that a room full of non-physicists came away with a reasonable understanding of its main elements (though I think I was the only one in the room to go on to read his papers on the topic, and try to decipher his extensions to GR!). He's a novel thinker, and a great explainer.

Probably. They already do it for the other fundamental forces :D

MOGwai, perhaps?

Or she has the Noble then for hear own theory

Mewbine Moggenfelder

@@thrwwccnt5845 i hereby revoke your youtube comment privileges

@@thrwwccnt5845 I think I'd be willing to watch a Vtuber that had that as their character name.

@@thrwwccnt5845one of the finest rizzicists of our time

All of us zoomers came out of their mother's basement to comment just this once for this moment

hairstyle?

The main problem I have with gravity is the idea that it's a field. Show me the grass. Show me the hedges. They can't.

> at which point is not different to dark matter Ehh there is a small difference, though it may be (perhaps likely is) entirely conceptual. A field without a particle meshes with the ideas of QFT (and thus the standard model) a lot nicer than a particle without a field would. That doesn't necessarily make it more "correct" (and it still wouldn't be a theory of quantum gravity... probably) but it might make it more palatable to some scientists and researchers. 80% being confident in some form of dark matter is still leaves a whole lot of very smart people looking for alternatives. And there's always the possibility of something like an M-theory breakthrough where someone discovers that the particles of dark matter theories are actually excitations of the MOG fields and that the theories are fundamentally equivalent. Still doesn't make it "correct" (string theory hasn't displaced anything yet and is not even really considered a TOE candidate anymore) but it could lead to some interesting and useful mathematical insights that can be applied elsewhere.

@@altrag "A field without a particle meshes with the ideas of QFT (and thus the standard model) a lot nicer than a particle without a field would. " Huh? According to everything I know, both possibilities don't work in QFT. When you have a field, you automatically have particles, and vice versa.

Sabine did mention at 6:30 that the difference between MOG and Dark Matter is that the former doesn't consist of particles, but that seems like an irrelevant detail to me: if you've accepted the existence of *some substance* that's distributed independently from normal matter, you've thereby accepted Dark Matter.

MOG doesn't involve any substance, it just changes the math for the gravitational field produced by ordinary matter.

It's funny you mention this, as this is exactly what Newtons description of gravity was, and he knew it. He said: " to derive two or three general principles of motion from phenomena, and afterwards to tell us how the properties and actions of all corporeal things follow from those manifest principles, would be a very great step in Philosophy, though the causes of those principles were not yet discovered." The causes of those principles were not explained by newton, the implication of his mathematics of "action-at-a-distance" was "so great an Absurdity, that I believe no Man who has in philosophical matter a competent Faculty of thinking can ever fall into it." according to him. When newton came along, there were already very good descriptions of the motion of planets and objects on earth. What he did was to unify them, (though his mathematics struggled to find many testable applications), with a new formalism, that did not even attempt to explain the the causes of what was observed. This new mathematical paradigm was then just internalised, and it itself now is considered the explanation. Or, another way to put it, those going into modern physics looking for physical interpretations of the maths are going to be disappointed. At best, your lecturer will tell you there isn't any physical interpretation to the math, at worst, they will give you a misleading analogy.

Indeed. It seemed like that should have been the principle point of the video, and yet was lacking.

The best answer I have found is in Ray Fleming’s book “The zero point universe”. He also does podcasts.

@@MassDefibrillator I understand where you are coming from but I don't feel like that is a fair comparison. The difference is that newtons new formula is far simpler and easier to work with. It simplifies the problem into a universal relationship between parameters. But Mog seems to be different. It's more like newton but imagine he had added a nonlinear smoothing function that regulated gravity based on speed to get the terminal velocity and to explain why an object stops speeding up but only for falling things on earth. To be fair its fairly obvious that this is due to friction with the air but I am just trying to create a (unfortunately tortured) analogy here. Like instead of explaining anything you just take the part you don't understand and push it somewhere else to quote the famous philosopher patrick star.

For physicists the math is all that really matters. 🤷‍♂️ For example, there are like 20 different interpretations of what quantum mechanics "means", but all of them agree on the math, so it doesn't matter that much. Sabine admittedly didn't even explain the math here, but it sounds like "there is a scalar and vector field and those cause gravity". For comparison, electricity and magnetism can also be explained in terms of a scalar and vector field. If you work with those fields enough you can develop intuition for how they work just as much as you can with other ways of expressing the math.

You said "Maybe when objects are closer together dark energy is repelling them more strongly but when they’re more isolated the repulsion is less" Then my question to you is why do we see galaxies drifting apart then? There are just a few atoms per square meter between galaxies, way less even then any isolated star? And why we don't see any stronger repulsive force from for example Sgr A* and surroundings?

That's exactly what dark matter does. The whirlpool idea with only visible matter doesn't match observations (look up "galaxy rotation curves" for more info). Dark matter was added to be more "water" in the whirlpool and that fixes the rotation rates to match observations. Modified gravity is also the whirlpool idea in a sense, but it says that very large whirlpools (galaxy-sized) whirl faster than more moderate whirlpools (solar system-sized). Neither theory produces any explanation for the "invisible hand". That's more of a philosophical question that science almost certainly won't be able to answer until we have a confirmed theory of quantum gravity, and possibly not even then (can't really be predicted as we currently have absolutely no idea what the true theory of quantum gravity will look like never mind analyzing any limitations it may have). Of course the "invisible hand" for real water-based whirlpools is gravity, but we can't say gravity is causing gravity as that would be a bit too self-referential :D.

@@altrag Thanks for sending my comment in a more educated direction.

@@JZsBFF One more thing to keep in mind is that the whirlpool (and the rubber sheet and whatever else people use to try and explain this stuff) are all 3-dimensional analogies to a fundamentally 4-dimensional phenomena (complex dimensions to boot). Experiments at both the very large (telescope observations of space) and the very small (particle physics) have confirmed the idea that space and time are connected, and that the 4-dimensional concept of spacetime is correct (or rather, we can't have less than 4 dimensions - more than 4 is still on the table, but that only makes the problem worse!) Unfortunately that means no analogy we can make or arguably even imagine with our 3D-expecting brains can even in principle be 100% accurate. The math can handle it just fine but our intuition often has trouble keeping up.

Except this has been around for 20 plus years

Much like the veritable zoo of particles posited as dark matter candidates. Both approaches have the problem that they can be adapted to fit data as needed - at least until we hit one that is accurate enough that it no longer needs to be adapted because it finally fits all of our available high quality data, or until we actually detect and confirm the existence of one of the dark matter candidates - unlikely given that in order to function as described they have to be essentially undetectable.

The Modern Physics Emperor has no explanatory cloths in the huge gravity/matter field: groping in the dark. Thanks for enlightening us on that Sabine!

That's kind of what GR does too. GR is a very, very loose framework and the simplest solutions certainly don't apply to every situation. There is certainly _some_ nicety in that you have a framework at all (so you just need to come up with new solutions to the equations rather than new equations) but at some level its still just plugging holes whenever something new shows up. And that's not really a bad thing. Every theory needs to be tweaked whenever something new shows up - that's how science progresses. When things work very well, somebody will notice a pattern to the tweaks and be able to derive a more universal theory from them, but that's not strictly necessary and is definitely not strictly necessary within any given period of time. It took 400 years for Newton to be displaced by Einstein. There's no reason to believe that displacing Einstein will happen within our lifetimes.

Playing the algorithm

AIUI it's more complicated than that. When the gravity of a star reaches you it pulls you more towards where the star is than where you see it in the sky. Like it has a sort of lateral movement based on the speed the star is moving at. So the speed of light limit of gravity doesn't really work the obvious way.

The distance might be thousands of lightyears but the objects need millions of years to travel that distance so the effect is negligible.

If I understood the results correctly, LIGO showed that gravity follows speed of light rules when we saw the two neutron stars merger with LIGO and telescopes, the signal arrived at almost the same time over very long range.I seem to remember something about neutrinos also being detected, but i may be wrong. MOND doesn't have speed of light limit because Newtonian physics doesn't, it was never going to be the final equations because of that, just a model to start looking in the right direction, unless you decide to replace General Relativity all together.

Gravity over thousands of lightyears of distance isn't exactly strong. Also, as heavy objects move with much much less than lightspeed, the direction of pull changes only marginally within a couple of years. Such gravity variations are likely hard to measure/observe at all, so having it in the equitation or not makes no measurable distinction.

The human race is still yet to prove that gravity even exists, so it could just be a specious discussion.

They rather support "their people", a "crony science" if you want, and Moffat was in the business of his MOG in Waterloo long before the PI was even opened 25 years ago or so.

What is brilliant in modifying general relativity in just one of zillions possible ways...

I've heard lots of physicists claim that a theory should be simple, elegant and beautiful, hence the low complexity mathematics.

@@jakeaurod I don't do physics, but as a computer scientist "Keep it simple" is always the go to approach. But at any point you should be ready to leave the simple solution behind if it doesn't solve your problem. You can write the most elegant and beautiful theories, but in the end if they aren't correct they are worthless.

@@jakeaurod -- a theory should be as simple as possible, and no simpler. Having simple theories is not useful if they are wrong. e.g. "gee, it sure seems like the ground is flat, so I theorize that the whole of the Earth is flat".

We also know that Newtonian gravity is wrong but we still use it because, well, quantum gravity is still not a thing. Cosmologists are just support to wait around until those quantum people get their act together? Edit to maybe clarify. Yes GR comes into play for high gravity. My understanding is that Mong deals with low gravity hence there is no real need to assume that GR plays a role and thus it would make sense mathematically to start with Newtonian gravity. Long live the Mongs.

@@cerad7304 erm, no we use Newtonian gravity for everything where the gravitational field is weak. however the orbit of mercury shows behaviour that deviates from newtonian gravity because mercury is quite close to the sun and there we use general relativity and it works perfectly. We don't need quantum anything for that. Even all our data on black holes is (so far) consistent with general relativity.

This also, In my opinion, applies to dark matter though. Like, they looked at an instance where the current math isn’t working and said “okay, so there’s some completely invisible answer undetectable substance here, that must be why the current math is failing” which is really frustrating honestly because it’s not even something that can ever really be disproven unless someone proves another explanation. I’d be happy just to know the answer, in all honesty, but as of now I think people are putting WAAAY too much emphasis on dark matter. We should be exploring (and funding) a myriad of different theories and approaches, that way we can at least narrow it down

@@sydneyvogel8121 I think the big issue with dark matter is, despite insisting it's just a historic name for an unknown, the term really has bottled people into thinking it must be a particle of some sort - with the corollary that, if there's no particle, then there must be an issue with gravitational theory. There being an alternative source of gravitational attraction(such as the mass of a galactic-scale electromagnetic field, to pick an amusing example) seems to be almost entirely unexplored.

If something becomes a singularity then something else must go to infinte

Yes, actually, the bullet cluster, though MOND proponents & those who build off it like those that work on Entropic Gravity respond that space time isn't immediately elastic. (Paraphrasing a quote I can't find currently unfortunately) The rare anti-dark matter observer will also point to Abell 520 the "Train Wreck Cluster" which goes against the implications of the bullet cluster/dark matter, & is much lesser known.

"Why should Dark matter be thinly distributed?" The distribution can be actually determined from the rotation curves of galaxies etc. "Suppose Dark matter has immense density but rather it's gravity coupling is weak." That doesn't make sense. The mass of a particle is essentially identical to its gravity coupling.

"Stretching" is exactly what happens (at least according to general relativity). That stretching _is_ gravity. Anti-gravity would be spacetime "bunching up", and as far as we know that doesn't happen in the real universe (though its not technically forbidden by GR, and those "warp drive" designs you see mentioned occasionally - including on this channel - attempt to utilize that feature. Of course they also require things like negative-mass matter which as far as we know doesn't exist so that's not helpful in the real world no matter how interesting the math behind it is).

@@altrag Not to offend anyone, but maybe it is possible Einstein did not model the fabric quite the way it functions. Like he made an assumptions things would always take the shortest path. Thanks though

@@MatthewSuffidy > maybe it is possible Einstein did not model the fabric quite the way it functions Not only is that possible, its almost a certainty. General relativity does not work with quantum mechanics, so we know they're bot not "quite the way it functions". That is not the same as being wrong though. Whatever replaces GR will necessarily be a "better" version GR in the same way that GR itself is a "better" version of Newton's F=ma. That must be the case because GR matches observations very, very well and the new theory also much match those same observations in addition to explaining new things that GR can't. If there is any sort of anti-gravitational "bunching up" or however you want to visualize it, it would necessarily be at an incredibly tiny scale for the simple reason that we would have seen it if it was at a scale we could see using current theories and equipment. The biggest hurdle we have to coming up with a better theory - whatever form that theory takes - is that neither GR nor the SM are expected to break down until we reach energy levels a million or more times higher than what the LHC can produce. To give you a sense of comparison, the new FCC collider that scientists currently want to build would be around 7 times higher than the LHC's energy levels. That is a very, very long way from the factor of a million we really need. I've seen estimates that a collider large enough to hit those energies would have to be somewhere in the ballpark of the Earth's orbit around the sun. Just a tad beyond our current engineering capabilities. That leaves us with astronomical observations and just crossing our fingers that we're looking in the right spot in the sky with the right telescopes when something happens that breaks our theories in a way that a new GR solution can't fix. It's part of why black hole physics has been such a big deal over the past couple of decades - they're one of the few objects in the entire known universe we have any hope of studying that can potentially do something extreme enough to make us reevaluate our current ideas. > Like he made an assumptions things would always take the shortest path That's not really an assumption. Or at least not Einstein's assumption. Its actually the principle of least action which predates Einstein by a couple hundred years. All Einstein did was reformulate it. In his theory the "least action" is achieved by following the shortest path through an appropriately curved spacetime. But the "least action" requirement itself comes from elsewhere. At the end of the day though, none of that matters. What matters is whether or not it matches observations and so far, GR passes that test with flying colors (mostly - adding an entirely unobserved mass is kind of a hack until and unless we actually find a dark matter particle - that's why a lot of scientists don't like the idea and are trying to find alternatives to GR). If you want to have a useful theory, you need to start with matching existing observations. If you want to posit a form of anti-gravity, you have to explain why we haven't seen such a thing yet - in addition to your normal-gravity side of the theory matching the stuff we have seen. Because if your theory doesn't match existing observations, then its immediately wrong - not just the "we know its only an approximation" kind of wrong that GR is, but flat out 100% incorrect. And unfortunately that almost always means doing the math. Nobody's going to take a 3-sentence "what if" seriously. Even if you're somehow right in some way, nobody will pay attention if you haven't done the work to prove that your idea at the very least works as well as GR or any other idea, nor is anyone else likely to bother trying to do the math for you.

There is only mention by a blog post by Ethan Siegel, he didn't actually publish this in the scientific literature. So I would take his argument with a heap of salt. :/

John Moffat and Norman Israel discusses The Bullet Cluster and MOG in this paper (from 2018): arxiv.org/pdf/1606.09128.pdf

Yup. Same here. I'm about 30 years ahead of you.

Gravitational lensing generally isn't particularly good at telling apart modified gravity from dark matter, and I don't expect it to be good at telling different modified gravities from each other. The issue is, in a nutshell, that the best-fit parameters to gravitational lensing images have very large uncertainties. You can almost always find something that fits somehow.

The fact that Lambda CDM needs inflation, dark matter AND dark energy is a huge red flag. Three different effects that we have no evidence for.

That "therefore" is not logically sound. In fact, most physicists believe dark energy *isnt* made of anything *and* composes 70% of the universes' energy. Energy can be intrinsic to spacetime itself.

THIS is the kind of scalding tea i want, tysm❤

Thinking and belief don’t factor in at all. It’s observation and how the math of accepted theory works. The effects are measurable and real, you might as well try disbelieving in gravity to fly.

@@hugegamer5988 they do matter, because physicists tend to believe what there is observational evidence for. In fact, when it comes to models, you can only have belief. The facts are black and white but you can't observe an interpretation for those fact. A theory is a model which must be constructed *from* observed evidence but can never itself be observed. Theories are abstract constructs that only exist in the minds of humans that are a only a reflection of reality. Therefore, thoughts and believes absolutely do matter when it comes to interpretations that have equal evidence (or lack thereof) behind them.

That's exactly what this is!

​@@Nomen_Latinummine is more accurate 😜 Then MOG sounds like a cat.

@@seriousmaran9414 I suppose, but when theoretical physicists talk about "gravity" they are almost always referring to General Relativity unless otherwise specified.

Never began

entanglement!

I guess you mean stretching the wavelength. The Doppler effect applies to all waves it means also to Gravitationlal waves. The interpretation of rhe LIGO data need the Doppler effect to be implied.

Yes, the stretching of electromagnetic waves due to cosmological expansion would apply to gravitational waves as well.

In modified gravity, the fields are normally assumed to be classical, ie they don't come with particles. It's because they're assumed to be part of the geometry, and if they had quanta that would be a sort of quantum gravity. One can ask whether it makes sense to assume they're classical, and I have wondered about that, too, but that's how the theory currently works. As to Turok -- there are so many particles that dark matter could be made of, I could talk about a different one each day and after a year I'd still be talking... Yes, right-handed neutrinos are good in the sense that we can need them for other things, too.

@@SabineHossenfelder I think part of his argument is that no more particles need to be "invented" for dark matter to be explained, if that one right-handed neutrino has the properties they hypothesize. Wouldn't other possible dark matter particles be outside of the current Standard Model? I think the assumption is that the right-handed neutrinos are implicitly inside the Standard Model, even though no accelerator has observed them. I didn't really follow his explanation about why the abundance of them would be so large; it was over my head.

It´s predicited that they have a huge mass, so they perhaps don´t need to be that common, to explain DM. But are they part of the standard model? Just like susy particles, that were invented to make the standard model more beauty, but also never were found?

@@Thomas-gk42 True, but the idea of having observed "handed" particles with no observed opposite-handed particles is disturbing and hints at what probably exists, even if they haven't been observed yet. Much like antimatter at the beginning of the 20th century.

That´s fairly true.

Yes, that's correct.

​@@SabineHossenfelder Sabine what happens if a complex vector is multiplied by a complex numbered scalar,does this situation show up at all in any interesting physical way? Sorry to pester you Thank you for being so honest,and self critical,its really refreshing

I don't know what that means either. So far, I've got "to move away : depart-usually used with off or on." and "Myelin Oligodendrocyte Glycoprotein (MOG) is a glycoprotein which is part of normal myelin and is found on the surface of the myelin sheath of nerve cells".

@@TooSlowTube It originates in the incel community. When the "Alpha Male Of the Group", the AMOG does something, it mogs those around him. Mogging someone else is the act of doing something supposedly better than someone else. When the guy at the gym heightmogs you by being taller, you can liftmog him by lifting heavier weights. To an incel, every social interaction, however slight, can be seen as a series of back and forth moggings. Sabine knowledgemogs us every time she uploads a video.

She's even mewing in the thumbnail 💀

A large enough asteroid can do pretty much everything, including killing all of us. So I think the answer is "yes"

The Universe is Electric.

​@@SabineHossenfelderbarry I can feel the magnitic forces here. 😂😂😂🌠🌠🌠

​@SabineHossenfelder barry reformat I know, the nature of your game.🤠

Our observable universe is some alien high school kid's science fair project. Cut it some slack. It doesn't have the best equipment and galactic rotational rates are hard. Sheesh.

Lol. Wtf. Absolutely not. We have observed dark matter halos

@@EnlightenedMinarchist: ========> Joke:You:Joke

It is falsifiable, but so far it fits the existing data. But that doesn't mean it's the best answer either, just as "epicycles" fit the planetary movement observations centuries ago. Epicycles fit well, but didn't really represent the real nature of the mechanics. It might be one of the tools to help us make better predictions until we have a better theory for the underlying reason why it seems to behave like MOG.

@@yeroca Well, MOND seems dead so now we have another modified gravity version. This is simikar to the way the Steady State Universe was dying.

MOG is not a modification of MOND. They're two entirely different theories. MOND doesn't have any additional fields. The two actually have very little in common (besides the similar sounding name).

@SabineHossenfelder Steady State versions were also very different but all had the same aim: to debunk Big Bang. It's the same story with modified gravity versions. Their sole purpose is to debunk dark matter, and they are becoming more and more complicated. The typical traits of a dying paradigm.

@@arctic_haze Steady State versions were kinda standard model BEFORE BigBang was, no? It changed with the discovery of CMB.

I saw that but couldn't find much to say about it. I'll have another look. The QCD potential has the wrong asymptotic behavior to work for rotation curves.

@@SabineHossenfelder Somehow I think that just saying the "strong force" at "galactic scales" might actually cause a linguistic singularity that collapses the internet.

​@@SabineHossenfelderbarry when are we coming home.

​@SabineHossenfelder barry. Just stop your crying. It's a sign of the times.. welcome to the final show. Hope you're wearing your best clothes. You can't bribe the door on your way to the sky. You look pretty good down here, but you aren't really good. We never learn. We've 🤠been here before. Why are we always stuck and running from the bullets.?. THE BULLETS.?. We never learn, we been here before, Why are we always struck and running from the Bullets.? Cool song barry. 🎵

Trouble is that's even less testable than dark matter and has the "benefit" of introducing some pretty big complications to the standard model. We certainly shouldn't rule anything out if the math appears to work, but it behooves us for purely practical reasons to try the things we have some hope of confirming or denying before putting too much effort into the more esoteric ideas. Occam's razor and all that.