Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Breakthrough Announced in Dark Matter Detection Technology

washington.edu

Post reply on HN
Print view View original

51–52 of 52 posts

Re: Breakthrough Announced in Dark Matter Detection Technology

#51

Post by truantbuick »

raattgift wrote: post #38
truantbuick wrote: post #20

Earlier quoted context omitted.

Some would disagree: http://backreaction.blogspot.com/2018/04/no-that-galaxy-with... As a non-scientist, it seems like dark matter has been relentlessly adjusted and overfitted and still appears very inadequate to fit all the evidence.

> As a non-scientist Unfortunately you're missing the thrust of Hossenfelder's developing argument: in upgrading MOND to a full relativistic theory, you necessarily seriously blur the difference between "modified gravity" and "particle dark matter". There's some meat on this in the comments on that blog page, notably the point raised (and her subsequent reference to it) by "M_Malenfant". Essentially her point is that…

I was specifically responding to the commonly held belief that modified gravities and observations of the bullet cluster are absolutely irreconcilable. I'm not necessarily drawing any line in the sand about whether I believe in modified gravities over particle dark matter, or whether that distinction is even important.

In general, I'm suspicious of dark matter. It would make an interesting development if it ended up being the planet Vulcan of our time, where we doggedly postulate its existence despite mounting counter-evidence because it's unpleasant to question baser theories.

https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)

Re: Breakthrough Announced in Dark Matter Detection Technology

#52

Post by raattgift »

truantbuick wrote: post #51
raattgift wrote: post #38

Earlier quoted context omitted.

> As a non-scientist Unfortunately you're missing the thrust of Hossenfelder's developing argument: in upgrading MOND to a full relativistic theory, you necessarily seriously blur the difference between "modified gravity" and "particle dark matter". There's some meat on this in the comments on that blog page, notably the point raised (and her subsequent reference to it) by "M_Malenfant". Essentially her point is that…

I was specifically responding to the commonly held belief that modified gravities and observations of the bullet cluster are absolutely irreconcilable. I'm not necessarily drawing any line in the sand about whether I believe in modified gravities over particle dark matter, or whether that distinction is even important. In general, I'm suspicious of dark matter. It would make an interesting development if it ended up…

> commonly held belief

Chandra data for the Bullet Cluster is from 2004; it was a crisis for then non-relativistic MOND, precisely because the Bullet Cluster is manifestly a relativistic, dynamical system. It is not now a crisis for appropriate relativistic theories of "modified gravity" where an additional field is added to General Relativity (again, see Famaey & McGauch 2011 -- section 8.3 is directly relevant) where in the non-relativistic and static limit (with some additional symmetries) the MOND interpolating function is recovered. This was tremendous progress, but leads ineluctably to the question: what is really the difference between adding a vector or scalar field on one side or the other of the EFEs?

The result: convergence on the idea that there is some field content that drags on luminous matter. We already had that with particle dark matter, with the main disagreements being the nature of the field (WIMPs vs axions etc.). Now it's more a question of how to do an initial values formulation that concords with available evidence. For straightforward particle dark matter, that's really easy once a candidate is found in a lab experiment. For less straightforward particle dark matter -- and for "modified gravity" fields on curved spacetime -- it's not so obviously easy, but almost certainly easier than was believed in 2004!

In all cases, structure evolution simulations are possible today that were undreamed of in the 1980s when MOND and CDM were first proposed.

> suspicious of dark matter

There can't be many people whose job -- or even calling -- it is to convince you personally of anything rather than, say, look for evidence to further constrain the CDM parameter space. However, I'm sure you could arrange something. You seem to like Bee, so perhaps http://backreaction.blogspot.com/p/talk-to-physicist_27.html is worth a shot.

Post reply on HN