Dark Energy Dark matter

On 5/2/2013 8:48 PM, wrote:
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 [phenomena] have the same cause?

I haven't read or seen anything addressing this specifically.
It would be fascinating to discover that this were true. But it would
have to be some type of meta-theory, something akin to string theory,
that would try to explain them as different aspects of some other
fundamental process.

But for now, the only commonality between the two are the use of the
word "dark" as a substitute for the phrases "not well understood" & "not
easily observed".

As you may be aware, the two describe very different phenomena.

Dark Matter is an attempt to explain within conventional Gravitational
theory why Galaxy's hold together when there isn't enough "visible"
matter present to gravitationally bind the stars within them together.
Without the "Dark Matter" postulate galaxies should be unstable and
should spin apart.

Dark Energy is an attempt to explain why the Universe is expanding and
doing so at an increasing rate.

Another *very* simplistic way to look at it:

Dark Matter: pro-Gravity
Dark Energy: anti-Gravity

Personally I have grave reservations about the Dark Matter hypothesis.
There are some very peculiar properties about having a Universe full of
(25% thereof give or take) non-baryonic matter. Having it available as a
crutch to aid conventional theories of Gravitation holds our model of
Gravitation together (there's a pun in there somewhere) but it's a weak
crutch for a crumbling theory that hasn't been given much serious
conceptual consideration since the days of Newton. That's starting to
change. Google Roger Babson.

Dark Energy I don't have a problem with. I think it's fundamental to why
the 2nd Law of Thermodynamics is the way it is.

Dave

In article ,
David Spain writes:
But for now, the only commonality between the two are the use of the
word "dark" as a substitute for the phrases "not well understood" & "not
easily observed".

As you may be aware, the two describe very different phenomena.

Looks right to me.

Without the "Dark Matter" postulate galaxies should be unstable and
should spin apart.

Also galaxy clusters. And the power spectrum of microwave background
fluctuations would be different from what's observed. And there's
direct evidence of dark matter from gravitational lensing.

Dark Energy is an attempt to explain why the Universe is expanding and
doing so at an increasing rate.

Right: primarily the supernova distances but also CMB fluctuations
and baryon acoustic oscillations.

... a weak crutch for a crumbling theory that hasn't been given
much serious conceptual consideration since the days of Newton.

General relativity? I think you will find ample experimental
attention if you look for it. There has been no lack of alternative
theories, by the way, but so far nothing but GR fits the data.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On Mon, 6 May 2013 11:57:17 EDT, David Spain wrote:

On 5/2/2013 8:48 PM, wrote:
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 [phenomena] have the same cause?

I haven't read or seen anything addressing this specifically.
It would be fascinating to discover that this were true. But it would
have to be some type of meta-theory, something akin to string theory,
that would try to explain them as different aspects of some other
fundamental process.

But for now, the only commonality between the two are the use of the
word "dark" as a substitute for the phrases "not well understood" & "not
easily observed".

As you may be aware, the two describe very different phenomena.

Dark Matter is an attempt to explain within conventional Gravitational
theory why Galaxy's hold together when there isn't enough "visible"
matter present to gravitationally bind the stars within them together.
Without the "Dark Matter" postulate galaxies should be unstable and
should spin apart.

Dark Energy is an attempt to explain why the Universe is expanding and
doing so at an increasing rate.

Another *very* simplistic way to look at it:

Dark Matter: pro-Gravity
Dark Energy: anti-Gravity

Personally I have grave reservations about the Dark Matter hypothesis.
There are some very peculiar properties about having a Universe full of
(25% thereof give or take) non-baryonic matter. Having it available as a
crutch to aid conventional theories of Gravitation holds our model of
Gravitation together (there's a pun in there somewhere) but it's a weak
crutch for a crumbling theory that hasn't been given much serious
conceptual consideration since the days of Newton. That's starting to
change. Google Roger Babson.

I think Einstein did some serious conceptual considerattion of gravity
post-Newton.

Dark Energy I don't have a problem with. I think it's fundamental to why
the 2nd Law of Thermodynamics is the way it is.

Dave

On 5/7/2013 5:35 AM, Steve Willner wrote:
... a weak crutch for a crumbling theory that hasn't been given
much serious conceptual consideration since the days of Newton.

General relativity? I think you will find ample experimental
attention if you look for it. There has been no lack of alternative
theories, by the way, but so far nothing but GR fits the data.


Sorry for the long delay in response. The day job has kept me pretty busy lately.

I figured my posting would bring in a comment or two about Einstein.

I have no qualms with GR, but I prefer to think of it as more a theory dealing with effect rather than cause. It's of course the
accepted theory for the effects of gravity at the macroscopic scale. But has little to nothing to say about gravitation at the
microscopic (quantum) scale. Which is where we get to causation. Right now we have even a struggle to bring gravitation into the
Standard Model, which could do almost by itself w/o gravitation. But of course not a situation anyone really wants to accept. We
have a notion of "exchange" of "gravitons" from what I have read. But where are the "Gravity Waves" we should have discovered by now?

The need for CDM theory to explain why galaxy's hold together should be cause for concern. I think we have a whole lot of learning
ahead of us. We have the same reasons not to get complacent about our knowledge of Physics today as we did at the end of the
nineteenth century, when, after the discovery of Maxwell's equations (which I read recently are actually Oliver Heavisides'
restatement of Maxwell's work) physicist generally assumed that between Newton and Maxwell we pretty much understood all the
phenomenon of nature with just a little janitorial work remaining. Some clean-up effort since...

Dave

In article ,
David Spain writes:
I have no qualms with GR, but I prefer to think of it as more a
theory dealing with effect rather than cause.

How does that differ from any other theory? The questions scientists
ask are whether the theory fits the data (and how much data and how
well) and how many free parameters there are.

[GR] has little to nothing to say about gravitation at the
microscopic (quantum) scale.

Yes, there is no quantum theory of gravity, and GR is incorrect in
that sense. I think that's in the relativity FAQ; anyway it's no
surprise. But that's not relevant at cosmological scales.

But where are the "Gravity Waves" we should have discovered by now?

Did you mean "gravitational waves?" Why do you say "should have
discovered by now?" What amplitude waves do you expect from what
sources, and how does that compare to detection sensitivity?

Gravitational waves have been detected indirectly via binary pulsar
timing, but you probably knew that.

The need for CDM theory to explain why galaxy's hold together
should be cause for concern.

I'm not sure what "cause for concern" means. People are working on
alternative theories, but so far none fits the data (at least not
without a lot of free parameters). Remember, galaxy rotation curves
are not the only phenomenon explained by dark matter. Either one
needs separate theories for all these, or one needs a theory that
explains them all in some way other than dark matter. So far, no
success.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA