All galaxies are exploding, says scientist

I think the galaxy course killed my motivation to do any "comments on arXiv papers" for a while, but this one is bonkers enough to resurrect it. I wouldn't normally bother : alternatives to dark matter are ten a penny. But they usually come from retired engineers, not associate professors in New York claiming to have taught astronomy courses. This is an oh-so classic case of a lot of improperly taught knowledge being more dangerous than no knowledge at all. Fair warning : this person uses SI units where they're not appropriate. Yes, we're talking that level of crazy.

The basic claim is that instead of being essentially stable systems, galaxies are in a continual state of disintegration. Hence there's no need for dark matter or modifying gravity to hold galaxies together, because they're simply exploding.

Anyone who has played with firework spinners as a child (or an adult) must have noticed their resemblance to spiral galaxies. Anyone who has not can always search “firework spinner” on YouTube to see it. The trajectories of the glowing embers in a spinner look like the stars of the spiral arms.

But wait, it gets better.

Quite obviously, the actual motion of the stars cannot be observed directly.

I think you'll find that it can. And indeed already has been for very large numbers in the Milky Way. Of course, the leading project is the Gaia spacecraft, which has had plenty of press coverage. True, it's very difficult to do this for other galaxies, but it is possible. And it's not even remotely sensible to assume our Milky Way is stable while all other galaxies are not.

But the still picture that we see suggests non-circular trajectories (like the firework spinner) rather than the circular trajectories as assumed by most analyses.

No, it does not. Literally nothing about them suggests that.

In the first model, a spiral galaxy is considered to start as a compact spherical core surrounded by a functionally rigid spinning disk held together by gravity as well as electromagnetic scattering forces (see section IV).

Mercifully, EM forces are only mentioned as a hand-waving, "and there might be EM forces as well" token comment rather than in any detail.

Here, in the simplest version of this model, we will assume that the stars separate from the disk edge with initial velocities equal to that of the edge.

Well, then, disintegration would be extremely rapid. Look, here's a simulation I made earlier !

The explosion of the outer parts of a typical spiral galaxy would be extremely rapid indeed : < 100 Myr. Given that we see large numbers of spiral galaxies over most of the Universes ~13 Gyr history, and none at all looking like their exploded remnants, this idea is immediately falsified. But let's press on regardless.

As an individual star moves away from the core, its outward radial speed increases and could eventually become measurable. However, several mitigating factors are expected to make such measurement difficult. First, the density of stars decreases with increasing radial distance.

Well that bit's actually true. But it isn't going to make the measurements difficult if you can measure the velocities of individual stars - which is what you have to do to get 3D motions. So far as I know there's no way to measure bulk proper motions, unlike radial measurements where you can get the average velocity field. I suppose you could do it statistically to reduce the errors by measuring lots of stars in the same region, but you'll still be measuring the velocities of individual stars.

Second, the stars at greater radial distances are expected to be colder and dimmer.

A heck of an assumption given the complexities of star formation, and essentially wrong for individual stars. In the 100 Myr of the galaxy's disintegration, the very brightest stars will die off, but most will be unaffected.

For the second model, one may consider the early stage of a spiral galaxy to be a compact ball of matter with significant angular momentum. This compact object could explode due to maybe a thermonuclear event.

Eh what ? No, seriously, what ?

The explosion fragments are expected to be of a wide range of sizes. Granular particles or even particles of atomic size would be the primary fragments. Let us call this collection of small fragments the dust plume.

NO ! Let's not do that, because plumes are linear features and you haven't described why it should be linear or which orientation the feature should have. Consequently the rest of the model is rendered unintelligible. So far as I can tell, the bulk of the mass is ejected at relativistic speeds, leaving the stars exposed and expanding much more slowly (~100 km/s). He calculates that the plume speed is (of course) so great that it disappears almost instantly compared with the motions of the stars. But then :

Hence, Doppler shift is the only means of measuring their speed.

Not in the Milky Way it isn't. And you could predict what the disintegrating galaxies would look like. Guess what ? They don't look like that.

I freely confess to a perverse approval of lunatic papers on arXiv. Sometimes debunking is good for the soul.

https://arxiv.org/abs/1801.09304

Not everything needs to be a paper

Now, I am all for outreach, but this is singularly dreadful. Or rather, it feels like something that should be sent to a grant agency, not publically disseminated on arXiv, because that's just silly.

A better communicator is always a better scientist

That is the ludicrous claim of the title which is nowhere justified in the text.

Engaging in science communication improves the own understanding of the communicator. Indeed, concepts or ideas that look simple when used on a daily basis may reveal unexpected complexity if discussed with a non-expert audience. The contextualization of his/her own research also allows a better understanding of the implications and increases the self confidence. The visibility of the communicator among its community also benefits from its engagement in science communication. Finally, this engagement further helps to develop communication skills that will be useful to express ideas in any other professional situation.

Fair enough.

It is often thought that communication is at the expense of quality research.

Eh ? Who thinks that ? I've known people who fit into all parts of the science-communication quality map.

90degree South was a set of activities organized in the framework of the recent trip of G. de Wasseige, PhD student at the Interuniversity Institute for High Energies (ULB-VUB), to the South Pole. As a member of the IceCube collaboration, she has been selected to visit the IceCube neutrino telescope buried in the South Pole ice.

What she should therefore be doing is writing a bloody blog, not being third author on a "paper" about it.

This experiment contest was dedicated to primary and high school students. Open to science and non-science oriented students, the challenge was to design an experiment answering the question "Belgium-South Pole: what is the difference?". An international jury selected the 3 experiments that have been carried out at the South Pole.

That is not an experiment. That is an outreach activity. Sending people along to do outreach for the sake of it is fine, but that's not something that you write a paper about !
https://arxiv.org/abs/1801.08874

Shades of grey in the multiverse

Well, I agree with Sean Carrol about there being shades of grey as to what constitutes a scientific or unscientific theory. I also agree with him regarding some people taking falsification to extremes, even if the references he cites don't actually demonstrate this.

I agree with the other authors that the multiverse isn't business as usual, because you can't test - not falsify, but merely even evaluate it against other theories - its major prediction. I think the Nature article linked by Carrol says it best :

As we see it, theoretical physics risks becoming a no-man's-land between mathematics, physics and philosophy that does not truly meet the requirements of any.

Cosomology, someone once said, is always on the edge of mysticism. And regarding the Many Worlds interpretation - surely the philosophical next of kin to the inflationary multiverse - someome else once said, "surely it doesn't take the creation of an entire universe to kill one cat." And again from the Nature article :

In our view, cosmologists should heed mathematician David Hilbert's warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.

However, I take issue with a couple of points in the Nature article :

In our view, the issue boils down to clarifying one question: what potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory... Dawid argues that the veracity of string theory can be established through philosophical and probabilistic arguments about the research process... Instead of belief in a scientific theory increasing when observational evidence arises to support it, he suggests that theoretical discoveries bolster belief.

Well, this clearly does show that Carrol was not attacking a straw man when he said that some people take falsification and even testability too far. Yet while it's wrong to suggest that belief in a theory should increase because of theoretical arguments, that doesn't mean that theoretical arguments can't lend a preference for it. It's a very good thing, in my opinion, to prefer simple ideas that avoid infinities. You just shouldn't cling militantly to that mere preference in the face of the evidence.

I'll further muddy the waters by noting that "scientific" and "useful" are certainly not the same thing, nor is being useful even necessary for a scientific theory. The idea that the Universe may extend beyond the visible horizon is logical, rational, eminently scientific and perhaps even escapable given current knowledge. The idea that it extends to infinity and perhaps contains other spacetimes with different physical laws, well, I don't know if that's scientific or not - it's certainly not pseudoscience or mystical woo, so perhaps it's a new class of weird - but it's definitely useless (though see Hossenfelder's blog post).

Also :
http://astrorhysy.blogspot.cz/2017/05/i-told-you-he-was-tricksy.html
http://astrorhysy.blogspot.cz/2016/03/youll-have-your-eye-out-with-that.html

Originally shared by Abhijeet Borkar

Some really interesting discussions going on in the field of Philosophy of Science:

https://www.preposterousuniverse.com/blog/2018/01/17/beyond-falsifiability/

http://www.math.columbia.edu/~woit/wordpress/?p=9938

https://platofootnote.wordpress.com/2018/01/22/peter-woit-vs-sean-carroll-string-theory-the-multiverse-and-popperazism/

and

https://www.npr.org/sections/13.7/2018/01/22/579666359/scientific-theory-and-the-multiverse-madness
https://www.preposterousuniverse.com/blog/2018/01/17/beyond-falsifiability/

Homework assignments

I have a vague recollection that one or two crazy people were interested in trying the homework assignment for my galaxy lectures, so here it is.

Complete description (read at least the first page) :
https://astro.mff.cuni.cz/vyuka/AST021/2017-2018/Taylor-ukol.pdf

The assignment itself :
https://astro.mff.cuni.cz/vyuka/AST021/2017-2018/Answers-Table-template.pdf

The required data files (300 MB) :
https://astro.mff.cuni.cz/vyuka/AST021/2017-2018/FITSFiles.zip

Have fun...
https://astro.mff.cuni.cz/vyuka/AST021/2017-2018/Taylor-ukol.pdf

The scientific method gone badly wrong

Pretty much. Needs stuff about popularity and highly funded grants.

I need scarcely remind readers that I do not think this indicates anything whatsoever about how common this is in practise.

The multiverse is not a normal kind of theory

A very interesting essay, worth reading in its entirety if you have the time. Some selected highlights for those that don't.

In its strongest from, the objection argues that the very idea of an unobservable multiverse shouldn't count as science at all, often appealing to Karl Popper's dictum that a theory should be falsifiable to be considered scientific. At the same time, proponents of the multiverse (and its partner in crime, the anthropic principle) will sometimes argue that while multiverse cosmologies are definitely part of science, they represent a new kind of science, "a deep change of paradigm that revolutionizes our understanding of nature and opens new fields of possible scientific thought".

In this essay I will stake out a judicious middle position... The point is not that we are changing the nature of science by allowing unfalsifiable hypotheses into our purview. The point is that "falsifiability" was never the way that scientifictheories were judged (although scientists have often talked as if it were)... The best outcome of current controversies over the multiverse and related ideas (other than the hopeful prospect of finding the correct description of nature) is if working scientists are nudged toward accepting a somewhat more nuanced and accurate picture of scientific practice.

Science proceeds via an ongoing dialogue between theory and experiment, searching for the best possible understanding, rather than cleanly lopping off falsified theories one by one. (Popper himself thought Marxism had started out scientific, but had become unfalsifiable over time as its predictions failed to come true.) While philosophers of science have long since moved past falsifiability as a simple solution to the demarcation problem, many scientists have seized on it with gusto, going so far as to argue that falsifiability is manifestly a central part of the definition of science.

The multiverse, therefore, is a case of science as usual: we evaluate it on the basis of how likely it is to be true, given what we know on the basis of what we actually have observed. But it is not only examples of literal new data that can cause our credences in a theory to change. The multiverse hypothesis reminds us of how better understanding, as well as actual experimental or observational input, can serve as "data" for the purposes of Bayesian inference... A correct accounting for the multitude of influences that shape our credences concerning scientific hypotheses is in no sense a repudiation of empiricism; it is simply an acknowledgment of the way it works in the real world.

The best reason for classifying the multiverse as a straightforwardly scientific theory is that we don't have any choice. This is the case for any hypothesis that satisfies two criteria: 1) It might be true. 2)Whether or not it is true affects how we understand what we observe.

None of which is to say that there aren't special challenges posed by the multiverse. At a technical level, we have the measure problem: given an infinite multiverse, how do we calculate the relative probabilities of different local conditions? Skeptics will sometimes say that since everything happens somewhere in the multiverse, it is impossible to make even probabilistic predictions. Neither of these two clauses is necessarily correct; even if a multiverse is infinitely big, it does not follow that everything happens, and even if everything happens, it does not follow that there are no rules for the relative frequencies with which things happen... There still remains the question, even if there is a correct measure on the multiverse, how will we ever know? It seems hard to imagine doing experiments to provide an answer. That, in a nutshell, is the biggest challenge posed by the prospect of the multiverse. It is not that the theory is unscientific, or that it is impossible to evaluate it. It's that evaluating it is hard.

Well, I remain a skeptic. I don't see how you get a meaningful explanation of anything if you through an infinity in there - to me, that's a sign of a theoretical failure. Sure, the world might be like that, but that would basically reduce it to being fundamentally illogical. I can't conceive of how you can have meaningful probabilities in an infinite reality. Maybe you can, but it feels an awful lot like cheating to me.

IMHO, string theory, inflation, the multiverse and all that jazz are not straightforward, "business as usual" scientific theories. They're a far cry from being pseudoscientific bunk, but neither are they comparable to relativity or Maxwell's eqauations. They hardly represent some wonderful new advanced sort of science, rather, they are more in the fuzzy grey area between genuine pseudoscientific woo and hard physical reality. See, while I agree wholeheartedly that "falsification" can't be the whole definition of a scientific theory, I do hold that the prospect of falsifiability is always better. That doesn't lead to anything so binary as "non-falsifiable is bad, falsifiable is good", let alone scientific/unscientific. But it does suggest that there is something at least different about unfalsifiable ideas like the multiverse.

I maintain that a scientific idea should be at least testable, if not falsifiable. You have to be able to evaluate its success with respect to observational evidence and other competing theories. The multiverse might satisfy that criteria, but currently string theory does not. That doesn't preclude them from ever becoming testable, however. Perhaps we should think of them as proto-science.

See also : http://astrorhysy.blogspot.cz/2017/05/i-told-you-he-was-tricksy.html
https://arxiv.org/abs/1801.05016

Space Nazis ?

I'm giving a courtesy proof-read of a friend's paper on using simple breeding restrictions on multi-generational spaceships to ensure a healthy crew over a long duration.

Is it too much to suggest the title include the words SPACE NAZIS ?