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Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly Send a noteboard - 31/05/2011 09:16:22 AM
OK, done, but I'm expanding the quote because I think it has additional relevance:
The point is that, independently of any specific model of modified gravity, we now know that there definitely is dark matter out there. It will always be possible that some sort of modification of gravity lurks just below our threshold of detection; but now we have established beyond reasonable doubt that we need a substantial amount of dark matter to explain cosmological dynamics.

That’s huge news for physicists. Theorists now know what to think about (particle-physics models of dark matter) and experimentalists know what to look for (direct and indirect detection of dark matter particles, production of dark matter candidates at accelerators). The dark matter isn’t just ordinary matter that’s not shining; limits from primordial nucleosynthesis and the cosmic microwave background imply a strict upper bound on the amount of ordinary matter, and it’s not nearly enough to account for all the matter we need. This new result doesn’t tell us which particle the new dark matter is, but it confirms that there is such a particle. We’re definitely making progress on the crucial project of understanding the inventory of the universe.

I see nothing in there that, in itself, rules out MACHOs causing the observed gravitational lensing of the Bullet Cluster; the limits he references only rule them out in because MACHOs are expected to be homogeneously distributed at large scales, which he treats as implicit, without stating. Now we can pinpoint the other 75% of the universe, the dark energy that should be homogeneously distributed at large scales. It's necessary for observed expansion acceleration at great distances because large masses can't be causing it since the universe should be homogeneously distributed at large scales. Can you spot the established principle all of that logic deliberately avoids re-evaluating? ;) Again, I'm not saying that principle is invalid, just that there might be cause to re-examine it. That's not my main point here (though it's a consequence of my overarching one in this thread).


The universe being homogeneously distributed at large scales and MACHOs being homogeneously distributed at large scales sound like similar concepts, but they come from different principles (and the "large scales" in each case are quantitatively different). The distribution of the universe is due to the early inflation period, and MACHOs would not have existed at that point. MACHOs would be homogeneous within galaxies, and it's galactic clusters that are homogeneous within the universe. This is orders and orders of magnitude in difference.

That the article doesn't tackle MACHOs directly isn't my main point here either, but what it DOES tackle instead. The sections I bolded above, as the others I bolded below, unequivocally state exotic dark matters existence as a fact observations of the Bullet Cluster prove. Dr. Carroll takes pains to make clear he's saying that; he explicitly says some form of MOND might still be valid, but that exotic dark matter is a fact and reality regardless. His use of words like "definitely" and "confirms" isn't figurative and doesn't come with attached qualifiers; when he says, "we have established beyond reasonable doubt that we need a substantial amount of dark matter to explain cosmological dynamics" that's just what he means. In my very humble opinion, I don't think the case has been proven beyond a reasonable doubt, only by a preponderance of evidence. MACHOs may have to sell their Heisman and give exotic dark matter the profit, but no death penalty. :P


Exotic dark matter has been established beyond a reasonable doubt. That doesn't mean that many people don't still have doubts about it, obviously, but a full consideration of the evidence and theoretical concerns shows those doubts to be unreasonable.

I wish I were as confident that's all he's saying, but his language reads more like those hypersensational publicists you (rightly) disparage than a cautious methodical researcher. In fact, it reads like the very thing about which I remain concerned despite your assurances that it's now rare to the point of being negligible: Someone who, rather than diligently collecting and analyzing all the data to determine what it says, has relentless sought out the specific data that "confirms... beyond reasonable doubt that we need a substantial amount of dark matter to explain cosmological dynamics". That sounds like fitting data, or in this case datum, to ones curve; a single point makes a lousy curve. He doesn't say there remain things we don't know, explicitly says the opposite, but he DOES say exotic dark matter is something we DO "know" as certainly as anything can be known. I simply can't agree with that; exotic dark matter is not, in my admittedly non-professional opinion, established on the same level as, say, the Laws of Thermodynamics, or wave/particle duality. It's probably valid, and you HAVE convinced me that's the way I'd bet if pressed, but I don't consider it the fact that he does.


You have no evidence that he has "relentless (sic) sought out the specific data that 'confirms...'". The Bullet Cluster is far from the only data point on which that conclusion is based; there are other cluster collisions that have been observed (link below), and other forms of evidence beside that.

He explicitly says "The challenge for early-twenty-first-century cosmology will actually be to understand the nature of these mysterious dark components." That is admitting there are things we don't know.

That is indeed the rub; I don't think the probability is near enough to 100% yet for me to treat it as equal. If you (or Dr. Carroll) want to say exotic dark matter is 95±5% certain, I won't argue with that, but 100% is too much for me at present.


100% is not really a probability, in the same way that infinity is not really a number; that's why I said "nearing 100%." I would estimate the probability of exotic dark matter being the correct class of hypotheses to be at least 99.9%, i.e. I feel that I could make 1000 such statements and only 1 of them would be wrong. (No, I am not going to make 1000 such statements in a reply in this thread.)
When Clusters Collide!
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Exciting video about the universe Camilla - 28/04/2011 10:14:55 AM 1092 Views
Cool, and true *NM* Stephen - 28/04/2011 11:46:29 AM 332 Views
I still think dark matter's just non-luminous matter without a convenient light source to reflect. Joel - 28/04/2011 10:34:21 PM 817 Views
We've just about ruled out the idea that dark matter is just non-luminous "ordinary" matter. Dreaded Anomaly - 28/04/2011 11:44:34 PM 750 Views
I'm aware of the Bullet Cluster, though admittedly not much more than that. Joel - 29/04/2011 01:52:49 AM 682 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. Dreaded Anomaly - 29/04/2011 02:56:32 AM 793 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. Joel - 30/04/2011 05:02:49 PM 750 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. Dreaded Anomaly - 30/04/2011 08:56:35 PM 621 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. Joel - 02/05/2011 01:28:30 AM 654 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. Dreaded Anomaly - 04/05/2011 04:18:18 AM 760 Views
There's such a thing as knowing when you're licked, and I believe I am. Joel - 07/05/2011 02:04:53 AM 831 Views
Re: There's such a thing as knowing when you're licked, and I believe I am. Dreaded Anomaly - 09/05/2011 11:28:48 PM 674 Views
Re: There's such a thing as knowing when you're licked, and I believe I am. Joel - 14/05/2011 05:36:45 AM 620 Views
Re: There's such a thing as knowing when you're licked, and I believe I am. Dreaded Anomaly - 17/05/2011 02:09:40 AM 708 Views
Re: There's such a thing as knowing when you're licked, and I believe I am. Joel - 19/05/2011 04:55:21 AM 629 Views
Re: There's such a thing as knowing when you're licked, and I believe I am. Dreaded Anomaly - 24/05/2011 09:32:27 PM 706 Views
The Pati-Salam model was the one I had in mind. Joel - 24/05/2011 10:34:04 PM 648 Views
Re: The Pati-Salam model was the one I had in mind. Dreaded Anomaly - 24/05/2011 11:08:01 PM 857 Views
Re: The Pati-Salam model was the one I had in mind. Joel - 25/05/2011 01:27:10 AM 669 Views
Re: The Pati-Salam model was the one I had in mind. Dreaded Anomaly - 31/05/2011 09:16:18 AM 738 Views
Apologies for the delay; internet's been spotty and I've been busy lately. Joel - 10/06/2011 12:09:04 AM 989 Views
Re: Apologies for the delay; internet's been spotty and I've been busy lately. Dreaded Anomaly - 14/06/2011 03:38:18 AM 991 Views
Also, re: lensing from ordinary matter: Dreaded Anomaly - 29/04/2011 05:18:47 AM 681 Views
This seems like another example of what confuses the issue. Joel - 30/04/2011 05:25:04 PM 800 Views
Re: This seems like another example of what confuses the issue. Dreaded Anomaly - 30/04/2011 08:56:40 PM 773 Views
That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 02/05/2011 01:29:03 AM 764 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 04/05/2011 04:18:24 AM 726 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 07/05/2011 02:05:02 AM 902 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 09/05/2011 11:29:36 PM 668 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 14/05/2011 05:35:56 AM 950 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 17/05/2011 02:09:55 AM 576 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 19/05/2011 02:47:25 AM 916 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 24/05/2011 09:46:30 PM 701 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 25/05/2011 12:20:10 AM 982 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 31/05/2011 09:16:22 AM 801 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Joel - 10/06/2011 12:04:06 AM 1040 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible". Dreaded Anomaly - 14/06/2011 03:38:12 AM 805 Views
Re: I still think... (apparently, there is a 100 character limit on subjects, and yours was 99) Tor - 28/04/2011 11:57:15 PM 999 Views
Seems to happen to me a lot; sorry. Joel - 29/04/2011 12:56:14 AM 699 Views
None of this reflects on the actual facts of dark matter. Dreaded Anomaly - 29/04/2011 01:32:52 AM 664 Views
I concede my grasp (or grope) is a somewhat superficial laymans, yes. Joel - 30/04/2011 04:30:28 PM 781 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. Dreaded Anomaly - 30/04/2011 08:56:44 PM 614 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. Joel - 02/05/2011 01:28:58 AM 1132 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. Dreaded Anomaly - 04/05/2011 04:18:27 AM 658 Views
I don't object to changing my mind, but can take more convincing than I really should. Joel - 07/05/2011 02:05:09 AM 850 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 09/05/2011 11:32:17 PM 777 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Joel - 14/05/2011 05:36:24 AM 929 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 17/05/2011 02:10:03 AM 686 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Joel - 19/05/2011 04:33:06 AM 930 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 24/05/2011 09:59:38 PM 680 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Joel - 24/05/2011 11:19:43 PM 650 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 24/05/2011 11:33:58 PM 603 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Joel - 25/05/2011 12:55:36 AM 732 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 31/05/2011 09:16:24 AM 643 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Joel - 10/06/2011 12:09:13 AM 825 Views
Re: I don't object to changing my mind, but can take more convincing than I really should. Dreaded Anomaly - 14/06/2011 03:38:05 AM 803 Views
Might help if you clarified where your skepticism is at Isaac - 29/04/2011 02:32:07 AM 636 Views
Potentially either, or a combination of the two. Joel - 30/04/2011 02:36:50 PM 701 Views
It's hard to discuss without knowing your objections a bit more clearly Isaac - 30/04/2011 04:58:03 PM 615 Views
My primary objection is that alternatives to dark matter seem to have been ruled out prematurely. Joel - 02/05/2011 01:29:14 AM 754 Views
Well, they weren't, not really sure how else to put that Isaac - 10/05/2011 03:19:57 AM 789 Views
Alright then, objection withdrawn (cautious skepticism intact). Joel - 14/05/2011 05:34:17 AM 907 Views
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