First test of rival to Einstein’s gravity kills off dark matter (opens in new tab)

Seems like it's pretty easy to make dark matter a good fit, because you can just adjust the presumed distribution of dark matter to fit the data.

Well, I wouldn't focus on the MOND part of Verlinde's recent work; the crucial things are that it's emergent gravity, that it's strings underneath, and that he proposes a long range entanglement between strings from which he argues the CDM-like generator of the metric emerges (or, if you like, from which the MOND-like kinematics emerge).

From a couple of days ago :

https://news.ycombinator.com/item?id=13176483

I like Ethan Siegel's explanation of the Verlinde's paper much more than the article with the "kills off" in the title:

http://www.forbes.com/sites/startswithabang/2016/11/12/ask-e...

"The hope is, with the right assumptions, a full theory of gravity, That's the big hope, and what Verlinde is working towards. (Others are also working towards it independently.) This paper is an update on how it's going. So, how's it going?

"There are some successes given very specific assumptions, but there are a lot of problems. The largest problem, quite simply, is that one needs to make a multitude of seemingly arbitrary "interpretation" decisions to wind up with something other than nonsense. For example: the full motivation for this approach is based in anti-de Sitter space (or space with a negative cosmological constant), but our Universe is observed to have a positive cosmological constant (i.e., de Sitter space), and the mathematics of the two spaces have very different properties. For another, you need the entropy to obey a strict area-based law to get the Einstein equations out, but you don't get a cosmological horizon out if you do. (And our Universe has one.) And finally, if you make all the assumptions you need to in order to get the gravitational acceleration for galaxies out, you destroy all of General Relativity's successes on larger-than-galaxy scales. (Verlinde, on pp. 39-40, makes the argument that it could succeed, but the observations of colliding galaxy clusters completely undermine his line of thought.)"

There's even more discussion in the Ethan's article, which is much more balanced.

And another take on Verlinde's paper by Sabine Hossenfelder:

http://backreaction.blogspot.co.at/2016/12/can-dark-energy-a...

"General Relativity is a rigorously tested theory with many achievements. To do any better than general relativity is hard, and thus for any new theory of gravity the most important thing is to have a controlled limit in which General Relativity is reproduced to good precision. How this might work in Verlinde’s approach isn’t clear to me because he doesn’t even attempt to deal with the general case. He starts right away with cosmology."

"I'd say he takes inspiration from models that are best understood in AdS." but "he starts with de-Sitter space which means he assumes dark energy. It doesn't make sense to say that this is a source of dark energy, it's the same thing, period."

Motl is notorious for this sort of thing. He once called me a "category 5 loon" because something I said in a talk was wrong. But the reason it was wrong is because I was advancing it as a straw-man precisely to show it was wrong.

http://motls.blogspot.com/2012/10/evading-quantum-mechanics-...

Lubos Motl hasn't been in academia for almost a decade. Almost everyone inside and outside it finds him obnoxious.

> I find this rudeness and pedantry in academia infuriating.

So you'd rather people quietly knife you in review? Because that's what happens if you penalize people for public rudeness. Personally, I'd rather have a loud critique to my face than a polite one behind my back or, even worse, no engagement at all.

I don't need your politeness or friendship when I'm putting forth some new theory. I need accurate, engaged criticism and the number of people who will do that is vanishingly small. And a lot of the ones who will do that have social issues almost by definition.

That's pretty much what academia told Motl.

He hasn't been a working physicist for a long time precisely because of how unnecessarily and uncharacteristically nasty he is.

Characterizing him as an example of any sort of trend in academia is both uninformed and deeply insulting.

As others have mentioned, Lubos Motl is no longer in academia. He seemed to have spent more time criticizing others (and not just their works) than on actual physics. His appointment at Harvard was not reviewed.

I'm frankly surprised New Scientist bothered to quote him.

> I find this rudeness and pedantry in academia infuriating.

vs all those "I just don't believe in being fake and sugar coating things" folks in every other industry? Not much unique to academia on that front.

He's engaging in a power fantasy that has a fellow scientist as a student. I'll bet this guy is a lot of fun to have as a professor.

For me, more interesting "gossip-like" detail that Motl enviously mentions is the "money" Verlinde received. Wikipedia has the details:

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

"In June 2011, the Netherlands Organisation for Scientific Research (NWO) awarded Verlinde the Spinoza Prize, the highest award available to Dutch scientists including a 2.5 million euro grant for future research.[14] The committee cited his work on the Verlinde formula, the Witten–Dijkgraaf–Verlinde–Verlinde equations, the Cardy-Verlinde formula and entropic gravity as the major achievements leading to the award."

By the way, my impression is that reading Motl is not a pleasant experience for anybody but himself.

He's not exactly a crank, but he's not a working physicist either, afaik.

I'm being pedantic, but I downvoted you because you started with the obvious observation "Motl is really really rude" (yeah, he's a real piece of work, check out the rest of his blog for stuff much worse), and then wrote "I find this rudeness and pedantry in academia infuriating.", which isn't supported by the observation that that one guy is rude. (But the rest of your comment is fine.) Individual people can be really rude with or without it being a cultural problem. There's no need to bring academia up like that—that's a lot of people, decent people, and most of them are really quite nice people and good scientists.

You can also have the idea that there are one-way interactions between the normal-matter universe and the dark-matter universe.

It isn't too difficult to formulate a mathematical system where two subsets are completely identical when considered in isolation, but when interacting, one subset operates as if the other doesn't exist, while the other is easily perturbed by any values in the mirror subset. I'm not sure if you can do it without at least one dimensional basis unit that squares to zero, though.

Imagine, if you will, that there are dark-matter people. We have no evidence whatsoever that they exist, any they are constantly annoyed by all the real-matter people that wander between their dark-couches and dark-televisions, and the real-matter bicyclists that pedal through their dark-bedrooms at the worst possible times.

IANAP, but I think the most widely accepted view on dark matter is that it is made of "dark" particles that cannot lose energy by radiation. In other words, it cannot condense and form dark stars or planets. When two lumps of dark matter collide they just pass through each other.

Sorry for ruining your dream. :/

I wouldn't be so worried yet. Verlinde's theory is quite fresh and it will take time to conclusively rule out Standard Cosmological model. As of yet, no one has properly worked out entropic gravity equivalent of various gravitational effects that arise in General Relativity such as gravitational lensing, a part of which was used in the paper discussed in the article.

Never the less, Verlinde's ideas are more interesting and reasonable than other proposed modification of gravity, but that's just my opinion.

I had this thought as well. Time to start subscribing more heavily to a viable multiverse theory, at least to support my tastes in science fiction novels anyway.

Sounds like Stranger Things to me.

Typical New Scientist really. I went to a lecture and Q&A with Alain Aspect when he visited my department in 2007 and he had a bit of a rant about how they had fundamentally misunderstood his work. They published an article claiming his Bell experiment could be used to send messages back in time.

Moreover, it's not even a complete "theory" in the sense that it's still not known if it can even repeat the results of the General Relativity.

https://news.ycombinator.com/item?id=13197595

What about the Bullet Cluster[0]? How does his idea address that?

His idea deserves some study but a title will "Kills off dark matter" is very infuriating

[0] https://en.wikipedia.org/wiki/Bullet_Cluster

I remember reading about this as an undergraduate and thinking how attractive his ideas were -- I think Verlinde's ideas have been around for some time. Back then it seemed like few people were giving these ideas thought.

I hope more people decide to explore this avenue. It really is a fascinating take on gravity.

That says MOND is a non-theory, so now I'm even more confused since this theory "builds on" MOND.

So basically there are four forces: weak and strong nuclear forces; gravity and EM.

EM is mediated by photons and visible matter is constantly absorbing and emitting photons.

Some particles don't though. Neutrinos for instance. They're dark, they don't interact with light.

So when observation showed that there needs to be more matter laying around than we could see some enterprising young turks said "hey, maybe there's a shit ton of dark matter" and that makes the math come out right.

the obsession is mostly because people who aren't astronomers seem to think "dark" is a metaphor and go "aha now that no one cares about the oxford comma this will be my new opinion"

Up for debate is what kind of particles make up the dark matter and how much mass is dark vs just poor measurements and/or some tweaks to gravity, but unless some one manages to disprove neutrinos: dark matter exists.

"Dark Matter" is a phrase we use to describe a hole in our understanding of the universe. To put it simply, when we look out into space, at very large scales like galaxies, everything is just too heavy. It appears as if there is a LOT more matter out there than we can see. Things are orbiting faster than they should be, like galaxies are heavier than makes good sense..

Maybe there is some matter out there that is "dark", so we just can't see it. That would be a solution. Or maybe the laws of gravity we wrote down are bad at large scales. No one knows. Trust no one who tells you they know the answer: if they did they would have a Nobel Prize.

The "next test" would be to look at more galaxies. They did not actually try to apply their theory too many real world observations. The goal of this paper is to get funding to try and apply their new theory to a huge number of galactic measurements. Until they do THAT, no one in the physics community is going to listen to them.

From the discussion section of Verlinde's paper[1]:

> We have shown that the emergent laws of gravity, when one takes into account the volume law contribution to the entropy, start to deviate from the familiar gravitational laws precisely in those situations where the observations tell us they do. We have only made use of the natural constants of nature, and provided reasonably straightforward arguments and calculations to derive the scales and the behavior of the observed phenomena. [..]

> In our view this undercuts the common assumption that the laws of gravity should stay as they are, and hence it removes the rationale of the dark matter hypothesis. Once there is a conceptual reason for a new phase of the gravitational force, which is governed by different laws, and this is combined with a confirmation of its quantitative behavior, the weight of the evidence tips in the other direction.

[1]: https://arxiv.org/abs/1611.02269

Say that you want to estimate what is the chance that observation 1 fits theory A just by accident (the lower this chance is the higher your confidence can be that theory A is "real").

If theory A has parameters you can adjust, it becomes easier for an observation to fit the theory just by accident (because you can adjust the free parameter).

This is a fairly flawed description, but it should be a good enough ELI5.

When you have free parameters, you are actually opening the door to a whole family of predictions. You're saying that of this entire family of models, you'll choose the one that best fits the data. Without free parameters, you have to come in with a fully specified model to begin with.

Loosely speaking, with an incorrect family of models, there's a lot of wiggle room to find one that still looks quite a lot like your data, while that freedom is not there when making a single specific prediction. There are semi-rigorous ways to take that into account while comparing models https://methodology.psu.edu/node/504

principle of parsimony

This is different because it's an experiment for this theory.