No, That Galaxy Without Nighttime Affair Has Non Ruled Out Modified Gravity

A smear alongside dots, 
also known every bit NGC 5264-HST.

Did yous actually bring to ask?

And if yous had to ask, why did yous bring to inquire me?

You sent me similar 2 1000000 messages in addition to comments in addition to emails call for what I remember well-nigh NGC 1052-DF2, that galaxy which supposedly doesn’t comprise night matter. Thanks. I am really flattered yesteryear your faith.

But I’m non an astrophysicist, I’m a theorist. I invent equations in addition to thus despair over my inability to solve them. That’s what I do. I know well-nigh every bit much well-nigh telescopes every bit penguins know well-nigh cacti. And until final calendar week I thought a globular cluster is a form of glaucoma. (Turns out it’s not.)

But since yous ask.

If aught else, I bring the produce goodness of a academy line of piece of employment concern human relationship alongside subscriptions to all major journals, thus at to the lowest degree I could expect at the Nature newspaper inward question. We tin laissez passer on the sack read there:

“the beingness of NGC1052–DF2 may falsify alternatives to night matter. In theories such every bit modified Newtonian dynamics (MOND) in addition to the of late proposed emergent gravity paradigm, a ‘dark matter’ signature should ever last detected, every bit it is an unavoidable termination of the presence of ordinary matter.”

This paragraph is decorated alongside 2 references, ane of which is to Milgrom’s MOND in addition to ane is to Erik Verlinde’s emergent gravity. And, well, I’m a theorist. Therefore I tin laissez passer on the sack tell yous correct away those people don’t know a thing well-nigh the theories they endeavor to falsify.

It is beyond me why thus many astrophysicists believe that modified gravity is somehow magically unlike from particle night matter, or indeed all other theories nosotros bring ever heard of. It’s not.

For both modified gravity in addition to particle night thing yous bring additional degrees of liberty (call them fields or telephone outcry upward them particles) which demand additional initial conditions. In a universe inward which yous bring a large diversity of initial weather condition (seeded yesteryear quantum fluctuations), yous volition boot the bucket a large diversity of structures. Same thing for modified gravity every bit for particle night matter.

Another way to set this is that yous tin laissez passer on the sack ever laid upward exceptions to the rule. The challenge isn’t to explicate the exception. The challenge is to explicate the rule. Modified gravity does that. Particle night thing doesn’t.

Of course of written report yous don’t run into the exceptions inward Milgrom’s or inward Verlinde’s paper. The argue is that both simply comprise equations which depict time-independent situations. These equations derived inward Milgrom’s in addition to Verlinde’s papers are non theories, they are surely limits of theories, approximations that function inward exactly about idealized circumstances, such every bit equilibrium. The amount theories are diverse types of “modified gravity” in addition to if yous desire to dominion those out, yous improve let on out what they predict first.

But nosotros don’t fifty-fifty bring to stoop thus low. Because, interestingly enough, the authors of the Nature written report dominion out MOND without fifty-fifty making a calculation for what that boundary would predict. is hard to explicate alongside particle night matter.

***

A recent Nature editorial praised a “Code of Ethics for Researchers” that was proposed yesteryear the World Economic Forum Young Scientists Community. In this Code, yous tin laissez passer on the sack read that scientists are supposed to pursue the truth and

“Pursuing the truth agency next the inquiry where it leads, rather than confirming an already formed opinion. This is especially challenging but necessary when questioning electrical flow beliefs [...] Results must last represented accurately without over- or understatement, hiding facts and/or drawbacks, or misleading the reader inward whatsoever way.”

Maybe the editors at Nature should read what they recommend.

Update Apr 11: The paper’s commencement writer has exactly about comments on the diverse points of criticism that bring been raised here.
Update Apr 14: H5N1 grouping of astrophysicists has a reply on the arXiv: “Current velocity information on dwarf galaxy NGC1052-DF2 produce non constrain it to lack night matter.”
Update Apr 16: Another newspaper on the arXiv today, this ane showing that the observations aren’t inward conflict alongside modified gravity: MOND in addition to the dynamics of NGC1052-DF2.