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

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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

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

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.
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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

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

Hmm, itys a kind of placeholder then till we see what is really going on.
I wonder if these same forces are observable at the very small level, or
will be.
Brian

--
From the Bed of Brian Gaff.
The email is valid as
Blind user.
"David Spain" wrote in message
...
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

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

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 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--
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