Starship Asterisk*

Spif wrote:

Anthony Barreiro wrote:MOND is not "self-published ... clearly insane crack-pottery."

To be clear, I did not make that assertion. I started out conceding that I haven't read the paper ... that's my way of pointing out that I have no specific opinion about the work involved.

-s

I'm sorry I wasn't clearer. I was just trying to put MOND in context as an idea that is being proposed by respected astrophysicists in peer-reviewed journals. In the more popular press, the April 2014 Astronomy magazine has a cover story by Bob Berman about dark matter vs. MOND.

MOND is off the mainstream enough that I lock threads about it.

I think today's APOD was a very provocative subject that many could easily fall prey to APOD's own rules of sticking with non-speculation. It tempts one to comment with a "silly explanation" or half-serious questions because no one really knows what dark matter is physically. Though it can seeming be measured indirectly with a variety of tools, theories or hypotheses' are what I and probably many others find almost inescapably drawn to just for the sense of participating in discovery. People are intrinsically curious and the unknown will always draw us in. Today's subject was a fine example.

And last night's "Cosmos" was great for that too!!!

Chris Peterson wrote:I think you're confusing dark matter with dark energy. Dark matter doesn't demonstrate any unusual forces.

I didn't mean to suggest that dark matter demonstrates unusual forces, just unusual indetectibility. The nearest alternate, and more accurate, term is dark gravity. Dark because the matter that creates it is indetectible. From what I've read, dark energy is what is causing the accelerated expansion of the distance between everything in the universe. Dr Tyson's assertion that we're better off referring to dark matter and dark energy by the names "Fred and Wilma" seems prudent, because the identities of the culprits are not currently known, and we have assigned bias-inducing names. But I agree with your assertion of caution and not going too far too soon in wango "theories". That isn't science, and maybe not even prudent science fiction.

Chris Peterson wrote:

Spif wrote:Theories don't get very far unless you can back them up with experimental results based on their predictions.

That's a rather obsolete view of how science works. It would be much more accurate to say that theories are either bolstered or disproved by observational results (which may or may not be from experiments).

I think the majority of the experimental physics community would take some issue with that particular bit of semantic wordplay.

String Theories are a good example... People have been hunting desperately to find ways to validate many of the core and exotic assertions of these theories precisely because these theories suffer a lot of disrespect and disregard for being "unverifiable philosophy".

Spif wrote:

Chris Peterson wrote:

Spif wrote:Theories don't get very far unless you can back them up with experimental results based on their predictions.

That's a rather obsolete view of how science works. It would be much more accurate to say that theories are either bolstered or disproved by observational results (which may or may not be from experiments).

I think the majority of the experimental physics community would take some issue with that particular bit of semantic wordplay.

No, I think almost every experimental physicist would agree. Particularly as science moves away from the traditional concept of a theory and towards models of complex systems, ideas are increasingly tested against observation. And of course, the vast majority of astronomy is observational, not experimental. Experiments are just a subcategory of observation.

String Theories are a good example... People have been hunting desperately to find ways to validate many of the core and exotic assertions of these theories precisely because these theories suffer a lot of disrespect and disregard for being "unverifiable philosophy".

I'd say string theories are terrible examples. You're talking about poor quality theories due to the inability to verify. That has nothing to do with experiments. People would be perfectly happy with string theory given some observational predictions.

Chris Peterson wrote:

String Theories are a good example... People have been hunting desperately to find ways to validate many of the core and exotic assertions of these theories precisely because these theories suffer a lot of disrespect and disregard for being "unverifiable philosophy".

I'd say string theories are terrible examples. You're talking about poor quality theories due to the inability to verify. That has nothing to do with experiments. People would be perfectly happy with string theory given some observational predictions.

Ok, I see what you're hung up on ... I don't make a significant distinction between "experimental" or "observational" data, which, frankly is a bit pedantic given that the point I am making is about credibility through verifiability.

The point is that without real data that comes from, well, reality, theories have a hard time attaining respectability. As it should be.

The gamut of String Theories are, ironically, both an example and a counter example of this. There are so many physicists out there who have spent significant parts of their careers in this field because at some level the theory seemed so elegant and so "right" that people really really wanted them to be true. This field achieved a certain (inflated) respectability without real data. But sanity and increasing clamor for real data appears to be balancing out the over exuberance now.

From what some people here have been saying, apparently this is also a gap for the MOND theories.

Anyway, it seems to me that there is no actual argument here.

-s

Could there be another SOURCE for the Gamma Rays....beyond WIMPS....when all the other sources are accounted for, and taken out of the picture? If we eliminate WIMPS, just for the moment, is there a sporadic, low level, gas, or matter interaction, that can cause such a phenomena?

I have enjoyed all your conversations and input, as it was my original comment that started the direction of the discussion. I have gained allot from it.

Dark Matter, and maybe even Dark Energy, (may not be of THIS Universe), may not be other universes, BUT possibly, other Dimensions....as String theory required 11 dimensions just for the math to come together, to formulate M or Membrane Theory, where two undulating membranes of energy wave about and sometimes touch, and spark, and create a Universe. Dark Matter, and Dark Energy, do not have to be a part of this dimension.....but affect by influence from another place...as Gravity is sometimes supposed by some to be FILTERED by these other dimensions, and thus a weaker force than the other forces....thus making it harder to fit in.

Thank you for the Stimulation...

:---[===] *

Boomer12k wrote:Could there be another SOURCE for the Gamma Rays....beyond WIMPS....when all the other sources are accounted for, and taken out of the picture? If we eliminate WIMPS, just for the moment, is there a sporadic, low level, gas, or matter interaction, that can cause such a phenomena?

Have you tried reading the paper on this?

Boomer12k wrote:Could there be another SOURCE for the Gamma Rays....beyond WIMPS....when all the other sources are accounted for, and taken out of the picture? If we eliminate WIMPS, just for the moment, is there a sporadic, low level, gas, or matter interaction, that can cause such a phenomena?

Of course there are other possibilities. But science generally considers the best and simplest options to be the ones that deserve the most consideration. Why make things unnecessarily complex when we don't need to? Most physicists expect dark matter to simply be another particle. After all, its properties are not that different from particles already known, observational evidence continues to move in that direction, and not much new physics is required. Quite unlike extreme and entirely speculative quackery involving multiple universes!

chuckster wrote:Just asking you people who seem to have a better overall knowledge of the flow of current investigations: Is the idea of multiple universes still too far-out to be incorporated into serious theoretical work ? I have thought that it's possible that all the hoopla about the search for dark matter may turn out to be a snark hunt, and the dark gravity out there is originating from mass that is not of this universe. The search for dark matter is necessary, but it may turn out to be an elimination of it as an actual feature of nature and relegate it back to place-holder status . It has been suggested that gravity acting over multiple universes explains its supposed weakness relative to the other basic forces in physics, which would mean that gravity from 'elsewhere' could affect this universe, as well as the reverse situation.

Good old general relativity is still the established theory of gravity. In GR gravity is controlled by the mass content of a system. Several different experiments have confirmed that visible matter (stars, planets, gas clouds) is not sufficient to explain observations. By Occam's razor, including invisible matter (and dark energy in the cosmological context) is the simplest solution, even though we have no current understanding of what dark matter is.

Now, there are two roads that you can follow: either you accept GR and try to understand dark matter (through WIMPS, axions, or other type of "particles"), or you reject dark matter and look for another law for gravity (MOND, or gravity in higher dimensions belong to this class). Maybe even both parts need to be modified. But here you start to open Pandora's box, as the more "exotic" your theory becomes, the more free parameters and assumptions your theory needs, which makes it even more difficult to reject by observations. The most extreme point of view (shared by a tiny but vocal minority) is "the multiverse", which roughly boils down to saying that physics laws are random and we only happen to live in the part of the multiverse which allows for humans to live. Naturally, this is impossible to prove or disprove by observation, since we can only observe our universe. In my opinion, this disqualifies "the multiverse" from ever being "incorporated into serious theoretical work".

Altho my opinion counts very little, and altho I respect Chris's brains (and patience), I'm on Art's side.
Hard (for me) to respect a science that just creates out of the blue a whole class of 'Matter' to get their calculations to add up correctly. I would respect it more if they just consented to scratch their heads.
Matter is represented by the periodic chart, and its anti-matter correlates, if they exist anywhere. Matter as we know it MUST interact w EMR. I believe the Dark Matter will someday take a place on the shelves of Science next to Ether.

Chris Peterson wrote: Most physicists expect dark matter to simply be another particle.

(Our post crossed, didn't see this when was writing my first.)
Glad to hear this. And in your opinion is it impossible for interstellar hydrogen (elemental or molecular) to account for the missing mass????

tomatoherd wrote:Hard (for me) to respect a science that just creates out of the blue a whole class of 'Matter' to get their calculations to add up correctly.

You mean like electrons? Protons? Neutrons? Because these particles were "created out of the blue" to explain observations. And that allowed for a broader understanding of the wider range of particles, allowing others to be predicted before they were observed.

Dark matter is not being created to explain calculations, but rather to explain solid observations of several different kinds. If you feel something kicking you in the butt, it's reasonable to assume there's somebody behind you (most likely in our own universe!), even if you are prevented from turning around and looking.

Matter as we know it MUST interact w EMR.

Where are you getting this idea? There is no requirement in our standard model that all matter interact with the EM force.

In the webpage brought up through the "gamma-rays" link in the explanation to the APOD it has a link to information in which it states "Gamma-ray bursts are the most energetic and luminous electromagnetic events since the Big Bang and can release more energy in 10 seconds than our Sun will emit in its entire 10-billion-year expected lifetime!". Wow!!!

tomatoherd wrote:

Chris Peterson wrote: Most physicists expect dark matter to simply be another particle.

(Our post crossed, didn't see this when was writing my first.)
Glad to hear this. And in your opinion is it impossible for interstellar hydrogen (elemental or molecular) to account for the missing mass????

It is vanishingly unlikely. Hydrogen is detectable with our current tools. It would radiate heat. Show up in radio wavelengths. It would interact with other matter to produce ionized light and shock fronts. Because of its interaction, it would align in discs, not in spherical halos.

Chris:
good points. Like I said, I'm not qualified to have a contributing opinion.
But as far as "spherical halos", these scientists are postulating dark matter in "discs", actually, relatively razor-thin discs!
http://uk.news.yahoo.com/were-dinosaurs ... ml#N2TWOea
See why laymen like myself might think the whole "dark" theories are just the Emperor's new clothes???

tomatoherd wrote:Chris:
good points. Like I said, I'm not qualified to have a contributing opinion.
But as far as "spherical halos", these scientists are postulating dark matter in "discs", actually, relatively razor-thin discs!
http://uk.news.yahoo.com/were-dinosaurs ... ml#N2TWOea
See why laymen like myself might think the whole "dark" theories are just the Emperor's new clothes???

If you get your science education from the news media, then, yeah, you are going to think that scientists are all complete morons and have no idea what they are doing because the authors of news articles have a large chance of either presenting something factually wrong or, at the very least, making a sensational headline out of practically nothing. "Were Dinosaurs Killed by Disc of Dark Matter?" If it looks like a duck and it quacks like a duck then it's probably a duck.

tomatoherd wrote:Chris:
good points. Like I said, I'm not qualified to have a contributing opinion.
But as far as "spherical halos", these scientists are postulating dark matter in "discs", actually, relatively razor-thin discs!
http://uk.news.yahoo.com/were-dinosaurs ... ml#N2TWOea
See why laymen like myself might think the whole "dark" theories are just the Emperor's new clothes??? :)

You are making the mistake of treating all ideas as if they have equal merit. That's a huge fallacy. What is the single most valuable way to assess the quality of scientific ideas if you're not a specialist? Consensus. Both the degree of consensus and the focus of that consensus. There is an overwhelming consensus that we are observing something in spherical halos around galaxies and galaxy clusters that behaves like any ordinary matter with mass. There's also a consensus, although smaller, that massive particles that don't interact with the EM force offer the best explanation. So if you're not an expert, the wise thing to do is to believe the experts, and consider this the most likely truth. Of course, that doesn't mean you should accept it as absolute.

And alternate ideas? It's good to be aware of them, but don't treat each one as chipping away from the consensus view, since that's still likely to be closest to the truth.

This idea about the disc of dark matter and the dinosaurs? How does it change anything? It isn't an argument against spherical halos (which we actually observe). It only follows a line of theoretical analysis that suggests dark matter particles interact very weakly, and at a sufficiently high density (as you might create in a strong gravitational field) they will do what all interacting matter does, and form a disc. The article you link isn't at odds with current theories of dark matter at all.

Thank you, Chris, for a very thoughtful and patient reply. I accept all you say, and in the way it was meant. I will try to keep an open mind, knowing dark matter theory will neither be hindered nor advanced whether I concur or not.

geckzilla wrote:"Were Dinosaurs Killed by Disc of Dark Matter?" If it looks like a duck and it quacks like a duck then it's probably a duck.

http://www.slate.com/blogs/bad_astronom ... vents.html
Emphasis mine:

You could argue that this is a paper about an answer searching for a question. That case can be made, but I don’t have too big a problem with it. Basically, the paper is more of an exercise of extrapolation, an experiment to take some physics and see what you get, what’s possible, and perhaps make some predictions based on that. That’s fine! It’s a good idea to put that kind of edgy stuff out there so people see it; that way it can be poked at, prodded, and see what happens. Maybe it’ll fall apart (for example: If dark matter is nudging space rocks toward Earth, shouldn’t we see multiple impact events all around the same time?). Maybe someone will detect some observational evidence to support it. Either way, it’s always good to keep in mind this is speculation based on scanty (but not unscientific) evidence.

That of course has not stopped some media from running away with the idea. A search on “dark matter dinosaurs” will yield some sober analysis (the original article in Nature sums it up pretty well), as well as some breathless articles making it seem like this is fact (cough cough Daily Mail cough cough—a rag I wouldn’t wrap moldy fish in, because it would insult the fish—and in that article they only discuss the doubts about the research at the very end).

All assumptions introduce possibilities for error; if an assumption does not improve the accuracy of a theory, its only effect is to increase the probability that the overall theory is wrong.

Newton's idea of light particles seemed simpler than Christiaan Huygens's idea of waves, so many favored it; however in this case, as it turned out, neither the wave- nor the particle-explanation alone suffices, since light behaves like waves as well as like particles.