from Hacker News

No, negative masses have not revolutionized cosmology

by benwr on 12/7/18, 2:48 PM with 82 comments

• by mbell on 12/7/18, 6:59 PM

  I'm not a physicist, just an interested bystander but some of these arguments don't seem to hold water to me:

  > There’s a more general point to be made here. The primary reason that we use dark matter and dark energy to explain cosmological observations is that they are simple.

  > A creation term is basically a magic fix by which you can explain everything and anything.

  Dark matter is an unknown 'substance' that interacts only through gravity (weakly) and must have a very specific and complex distribution in the universe to 'work'. That strikes me as neither 'simple' nor much different than tossing a constant into an equation to make it work. Similarly Dark Energy is an unknown form of energy that in uniformly distributed through the universe, which to me is just a fancy way of saying "we added a constant to make it work". In both cases I don't see how either are implicitly better than adding a 'creation term'.

• by benwr on 12/7/18, 2:51 PM

  This is a critical response to https://news.ycombinator.com/item?id=18609375 ; in the comments is a response by Jamie Farnes, the author of the paper, and a rebuttal by the blog's author.

• by duality on 12/7/18, 6:47 PM

  "[T]he gravitational interaction is exchanged by a spin-2 field, whereas the electromagnetic force is exchanged by a spin-1 field. Note that for this to be the case, you do not need to speak about the messenger particle that is associated with the force if you quantize it (gravitons or photons). It’s simply a statement about the type of interaction, not about the quantization. Again, you don’t get to choose this behavior. Once you work with General Relativity, you are stuck with the spin-2 field and you conclude: like charges attract and unlike charges repel."

  There was a bit of discussion about this on https://news.ycombinator.com/item?id=18609375 as well. Working through the exercise of how spin-2 mediated forces differ from spin-1 is a worthwhile exercise for those who are so inclined.

• by khawkins on 12/7/18, 6:56 PM

  Occam's razor is a heuristic used in the investigative process, not a principle. While it's fair to point out that a theory makes everything more complicated and thus might make it less likely to be sound, it's not fair to push back on the first bit of research into a theory because they haven't had the time to fully develop it.

  Indeed, a scientific revolution generally starts by treating as false an assumption previously held as true. Not to say that this is a revolution, but if you push back too hard it won't be, whether it's true or not.

• by apo on 12/7/18, 8:12 PM

  Can't help but think of phlogiston:

  Eventually, quantitative experiments revealed problems, including the fact that some metals gained mass when they burned, even though they were supposed to have lost phlogiston. Some[who?] phlogiston proponents explained this by concluding that phlogiston had negative weight;

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

  Eventually, the mass paradox was resolved by the realization that combustion is really something else altogether: the combination with a then-unknown element, oxygen:

  Phlogiston remained the dominant theory until the 1770s when Antoine-Laurent de Lavoisier showed that combustion requires a gas that has mass (specifically, oxygen) and could be measured by means of weighing closed vessels.

• by onhn on 12/7/18, 5:54 PM

  It is fun to read these things, and of course discussion is a good thing, but I do hope that blogs and comment sections do not end up serving any formal role in the scientific literature.

  There are several reasons for this: a blog's visibility is low compared to a preprint server (in the scientific community at least), the contents of the blog probably won't be as well-preserved, and there is a tendency to be more casual with the arguments.

• by diffeomorphism on 12/8/18, 3:26 AM

  > These equations tell you that like masses attract and unlike masses repel. We don’t normally talk about this because for all we know there are no negative gravitational masses, but you can see what happens in the Newtonian limit.

  I feel like I am misunderstanding what the author wants to say here. It seems to me that this would only be the case if you change the sign of the gravitational mass (F[-m_1,-m_2]=F[m_1,m_2]), but not of the inertial mass?

  In the Newtonian case you get that the force is proportional to m_1m_2, so ++=+, +-=- and --=+, but then F=ma flips the direction of the acceleration, right?

  ++ gives F>0 and a>0, so attraction.

  -- gives F>0, but negative inertial mass yield a<0 and hence repulsion.

  +*- gives F<0, so the positive inertial mass sees a<0 and is repelled, while the negative inertial mass sees a>0 and is attracted.

  What am I missing here?

• by eutropia on 12/7/18, 7:03 PM

  Tone of this blog post is extremely pedantic and comes across as if the author were personally insulted by the paper.

  But her argument is basically "You didn't understand the math, and you misunderstood the work that you cited".

  I feel like the burden is a little higher -- i.e. put in some effort to at least show the readers the math she's talking about and the counterfactual conclusions they arrive it if worked out.

  I would be much more convinced if she took the original paper's claims at their strongest and most convincing and formulating a simple proof or mathematical argument why the paper is wrong -- instead it feels like she's knocking down a straw man and saying "you're too stupid to be doing this kind of work"...

• by 8bitsrule on 12/8/18, 5:28 AM

  "highly problematic to introduce negative inertial masses .... This fits badly with our observations."

  Science news is not scarce. Click-bait titles aren't either. There's no shortage of catchy on-paper theories that 1)are not backed by evidence, 2) make no predictions.

  Cosmology has a big problem, and thrashing around in desperation is not becoming.

• by hirundo on 12/7/18, 6:28 PM

  Negative matter is created spontaneously everywhere, according the article in theconversation.com. Why then can't we collect it, isolate it, and poke and prod it? Because the particles are too small and interact too weakly?

• by btilly on 12/7/18, 7:49 PM

  Obligatory XKCD: https://xkcd.com/955/

  When you read breathless science journalism about the latest revolutionary paper, remember how it usually works out. Enjoy it as entertainment if you wish, but don't get your hopes up.

• by ykonstant on 12/8/18, 1:01 AM

  Well, the negative consensus is disappointing, but the criticisms are absolutely massive.