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Dark Energy Dark matter
Now if this stuff actually exists in such abundance how does it not muck up
all the calculations of trajectories of the many spacecraft sent out into the suburbs of our solar system. One would have thought that if it was there, it would in effect change the laws of gravity to some extent even relatively locally. So maybe these are artefacts of what other forces are out there, or maybe part of gravity that only shows up when you are in a relatively weak field. Brian -- From the Bed of Brian Gaff. The email is valid as Blind user. |
#2
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Dark Energy Dark matter
On 2/13/2013 10:32 AM, Brian Gaff wrote:
Now if this stuff actually exists in such abundance how does it not muck up all the calculations of trajectories of the many spacecraft sent out into the suburbs of our solar system. One would have thought that if it was there, it would in effect change the laws of gravity to some extent even relatively locally. So maybe these are artefacts of what other forces are out there, or maybe part of gravity that only shows up when you are in a relatively weak field. Brian Well simple. Because 'Dark Matter' doesn't exist! :-) IMHO. Dark Matter is like the 'Luminiferous Aether' of two centuries back. A crutch we are currently leaning on because we don't really understand Gravity. Much like Classical Newtonian theory had issues explaining phenom. being discovered by the late 19th century: http://en.wikipedia.org/wiki/Luminiferous_aether 'Dark Energy' IMHO ought to by synonymous with non-zero ground state vacuum energy. Just we can't prove it yet nor do we know how. But we do know the Universe is expanding at an accelerating rate. Something has to be driving that expansion. In lieu of a quantum explanation we slap the label 'Dark Energy' on it. But to your point, both of these phenomena at local distances are extremely weak forces. Much much much weaker than even the weakest 'practical' force, gravity. They will not be seen 'relatively locally' and can be safely ignored when calculating things like spacecraft trajectories, as we have seen now for over 5 decades. Dave |
#3
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Dark Energy Dark matter
On 2/13/2013 7:23 PM, David Spain wrote:
On 2/13/2013 10:32 AM, Brian Gaff wrote: Now if this stuff actually exists in such abundance how does it not muck up all the calculations of trajectories of the many spacecraft sent out into the suburbs of our solar system. One would have thought that if it was there, it would in effect change the laws of gravity to some extent even relatively locally. [snip] Well simple. Because 'Dark Matter' doesn't exist! :-) IMHO. Dark Matter is like the 'Luminiferous Aether' of two centuries back. A crutch we are currently leaning on because we don't really understand Gravity. Much like Classical Newtonian theory had issues explaining phenom. being discovered by the late 19th century: http://en.wikipedia.org/wiki/Luminiferous_aether And now, just today, the similarities have becoming blatant and ludicrously striking! C'mon folks am I the only one that sees the irony of it all? http://www.sciencenews.org/view/feat...ht_in_the_Dark Put these two article links up in two windows of your browser, side-by-side, to maximize hilarity... Dave |
#4
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Dark Energy Dark matter
In article ,
David Spain writes: Dark Matter is like the 'Luminiferous Aether' of two centuries back. Are you confusing Dark Matter with Dark Energy? Evidence for dark matter, in chronological order, is 1) galaxy cluster velocity dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave background fluctuations, and 4) gravitational lensing. I won't swear this list is complete. Of course it's conceivable that there's something wholly different going on that explains all of these, but if so, no one has thought of it yet. But we do know the Universe is expanding at an accelerating rate. Something has to be driving that expansion. In lieu of a quantum explanation we slap the label 'Dark Energy' on it. Exactly right except that "know" ought to be qualified by the standard disclaimer that everything in science is tentative and can change if new evidence is found. Also 'quantum' should deleted. There's no reason dark energy can't have a quantum explanation. 'Dark Energy' IMHO ought to by synonymous with non-zero ground state vacuum energy. That's perhaps the leading explanation for a cosmological constant, which is perhaps the leading candidate for dark energy. The trouble is that a simple estimate for how big this effect should be gives a value that is 100 orders of magnitude (!) too large. One view is that there is some cancellation that is almost but not quite complete, and the cosmological constant is the tiny leftover bit. Another view is that the whole idea of cosmological constant being vacuum energy is wrong. The only thing clear at the moment is that there is not enough evidence. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#5
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Dark Energy Dark matter
On 2/15/2013 4:31 PM, Steve Willner wrote:
In article , David Spain writes: Dark Matter is like the 'Luminiferous Aether' of two centuries back. Are you confusing Dark Matter with Dark Energy? No I believe the theoretical underpinning for Dark Energy is much stronger than that for Dark Matter. The two are combined here because that was the topic of the OP. In fact in much of the media the two are often discussed interchangeably, as if somehow the concept of 'dark' unites the two. But in fact, 'dark' only implies our lack of understanding. The two are describing very different phenomena. Evidence for dark matter, in chronological order, is 1) galaxy cluster velocity dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave background fluctuations, and 4) gravitational lensing. I won't swear this list is complete. I contend that this is evidence of our incomplete understanding of Gravitation, not necessarily evidence for the existence of "Dark Matter" at least as currently envisioned through WIMPs. My biggest problem with WIMPs is how does this theory jibe with Black Hole formation? Or the theory that determines the size of an Event Horizon? When Black Hole theory was devised there was no concept of Dark Matter (I'll abbrev. as DM from here on). Hence it is not taken into account in the theory. But if something like 23-24% of all mass in the universe is DM why hasn't this led to Black Hole inflation? Why doesn't the current theory have to be revised to take WIMPs into account? Surely WIMPs don't escape the notice of a Black Hole? Of course it's conceivable that there's something wholly different going on that explains all of these, but if so, no one has thought of it yet. But there is working on-going in these areas. I will contend/predict this work will gain momentum as the newer round of experiments trying to pull DM out into the open... fail.... Steve, how's that for risk taking? I'm trying to figure out a criteria for establishing a bet with you that involves Dim Sum at Mary Chung's... But we do know the Universe is expanding at an accelerating rate. Something has to be driving that expansion. In lieu of a quantum explanation we slap the label 'Dark Energy' on it. Exactly right except that "know" ought to be qualified by the standard disclaimer that everything in science is tentative and can change if new evidence is found. Also 'quantum' should deleted. There's no reason dark energy can't have a quantum explanation. True. But at least we have some reason to believe there could be a quantum explanation... 'Dark Energy' IMHO ought to by synonymous with non-zero ground state vacuum energy. That's perhaps the leading explanation for a cosmological constant, which is perhaps the leading candidate for dark energy. The trouble is that a simple estimate for how big this effect should be gives a value that is 100 orders of magnitude (!) too large. One view is that there is some cancellation that is almost but not quite complete, and the cosmological constant is the tiny leftover bit. Another view is that the whole idea of cosmological constant being vacuum energy is wrong. The only thing clear at the moment is that there is not enough evidence. Agreed. But at least it's work in a promising direction... And now, naturally, I discover the AAAS just finished up their annual meeting in Boston this weekend, which I totally missed. Steve were you able to attend any of the sessions? And if you did, did you note anything remarkable in this area? For example, I just read this today: http://www.bbc.co.uk/news/science-environment-21499765 Dave |
#6
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Dark Energy Dark matter
SW Evidence for dark matter
In article , David Spain writes: I contend that this is evidence of our incomplete understanding of Gravitation, not necessarily evidence for the existence of "Dark Matter" Possibly. People work on "Modifications of Newtonian Dynamics" (MOND) alternatives to GR. The idea seems to be to insert a scale length and have gravity behave differently above and below that length. Aside from having no theoretical motivation, the problem seems to be that no single scale length explains all the phenomena attributed to dark matter. That is to say, the idea is in principle workable, but so far no specific formulation that fits the data in one regime even comes close in other regimes. I think there's likely to be the most severe problem with gravitational lensing; see the Bullet Cluster for a dramatic example. at least as currently envisioned through WIMPs. No one says dark matter has to be WIMPs. Those (at least in the sense that the W refers to the weak interaction) are largely motivated by particle physics. Specific examples can be searched for (as is being done), but particles that interact _only_ by gravity satisfy all the astronomical constraints. My biggest problem with WIMPs is how does this theory jibe with Black Hole formation? What's the problem? The dark matter density is low, and the accretion rate of dark matter onto black holes is tiny. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#8
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Dark Energy Dark matter
Hmm, well, in a way we are inside the experiment and attempting to find out
if there is anything outside it that is affecting what goes on. Brian -- From the Bed of Brian Gaff. The email is valid as Blind user. "Steve Willner" wrote in message ... In article , David Spain writes: Dark Matter is like the 'Luminiferous Aether' of two centuries back. Are you confusing Dark Matter with Dark Energy? Evidence for dark matter, in chronological order, is 1) galaxy cluster velocity dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave background fluctuations, and 4) gravitational lensing. I won't swear this list is complete. Of course it's conceivable that there's something wholly different going on that explains all of these, but if so, no one has thought of it yet. But we do know the Universe is expanding at an accelerating rate. Something has to be driving that expansion. In lieu of a quantum explanation we slap the label 'Dark Energy' on it. Exactly right except that "know" ought to be qualified by the standard disclaimer that everything in science is tentative and can change if new evidence is found. Also 'quantum' should deleted. There's no reason dark energy can't have a quantum explanation. 'Dark Energy' IMHO ought to by synonymous with non-zero ground state vacuum energy. That's perhaps the leading explanation for a cosmological constant, which is perhaps the leading candidate for dark energy. The trouble is that a simple estimate for how big this effect should be gives a value that is 100 orders of magnitude (!) too large. One view is that there is some cancellation that is almost but not quite complete, and the cosmological constant is the tiny leftover bit. Another view is that the whole idea of cosmological constant being vacuum energy is wrong. The only thing clear at the moment is that there is not enough evidence. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#9
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Dark Energy Dark matter
I haven't heard of Anyone addressing this: Is it possible that 'Dark Matter' and 'Dark Energy' are the same thing? In other words, both phenomenia have the same cause?
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#10
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Dark Energy Dark matter
" I haven't heard of Anyone addressing this: Is it possible that 'Dark
" Matter' and 'Dark Energy' are the same thing? In other words, both " phenomenia have the same cause? I would not think so. Take a look at what we do know about matter. as an example wood is matter it contains energy but to release that energy a chemical reaction has to take place. If we burn wood it releases heat energy and in doing so changes in to othe-- | Remove .my.foot for email | via Waldo's Place USA Fidonet-Internet Gateway Site | Standard disclaimer: The views of this user are strictly his own. |
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