Missing mass found?
jleonard
significance this purported discovery has:
http://www.sciencedaily.com/releases/2011/05/110524094515.htm
[Moderator's note: Not much. There is much discussion on the web,
almost all of it criticising the sensationalism and hype. See, for
example, https://telescoper.wordpress.com/tag/monash-university/ -P.H.]
Regards,
J Leonard
Nicolaas Vroom
news:1brz8wmlmzjkw.1...@40tude.net...
In a different article of the same magazine
http://www.sciencedaily.com/releases/2008/05/080506194033.htm
I read:
"Only about 5% of our universe is made of normal matter as we know it,
consisting of protons and neutrons, or baryons, which along with
electrons, form the building blocks of ordinary matter. The rest of our
universe is composed of elusive dark matter (23%) and dark energy (72%)."
Is there someone who can explain me in simple language what it means:
"composed of dark energy" ?
Normally energy is the "state" of something/mass, is closely
related to impulse and is described by the following two laws:
E = 0.5*m*v^2 and E = m*c^2
I expect dark energy describes something completely different.
Nicolaas Vroom
http://users.telenet.be/nicvroom/dark_mat.htm
Phillip Helbig---undress to reply
<nicolaa...@telenet.be> writes:
> In a different article of the same magazine
> http://www.sciencedaily.com/releases/2008/05/080506194033.htm
> I read:
>
> "Only about 5% of our universe is made of normal matter as we know it,
> consisting of protons and neutrons, or baryons, which along with
> electrons, form the building blocks of ordinary matter. The rest of our
> universe is composed of elusive dark matter (23%) and dark energy (72%)."
>
> Is there someone who can explain me in simple language what it means:
> "composed of dark energy" ?
The term "dark energy" is a term someone made up to sound cool. Its
content is essentially zero. As Sean Carroll pointed out, essentially
everything has energy and many things are dark. It's a stupid name,
which unfortunately has caught on. The name implies to some that there
might be a connection to dark matter, but this is at best pure
speculation.
It is simply what is otherwise known as the cosmological constant.
The cosmological constant can be thought of as negative pressure. It is
a force, distributed uniformly in the universe, which pushes things
apart, in contrast to gravity, which pulls things together (and the
source of gravity---mass---can be and is clumped, whereas the
cosmological constant is smooth; this led Sean Carroll to suggest
"smooth tension" as a better name (tension corresponding to negative
pressure), but this never caught on).
> Normally energy is the "state" of something/mass, is closely
> related to impulse and is described by the following two laws:
> E = 0.5*m*v^2 and E = m*c^2
> I expect dark energy describes something completely different.
Yes. Think of it---very roughly---as negative pressure.
Einstein originally introduced the cosmological constant since he
believed that the universe is static (i.e. not expanding), which is
possible with a special value of the cosmological constant. Friedmann
showed that other values can lead to expanding or contracting universes
and observations showed that the universe is expanding. As a result,
Einstein and de Sitter suggested to set the cosmological constant to 0
until there is enough observational evidence to suggest otherwise
(similarly for spatial curvature; this is known as the Einstein-de
Sitter cosmological model). Probably since calculations are more
complicated with the cosmological constant (especially before computers
were used), many people just assumed it was zero. A few decades ago,
this was compatible with the observations---but so was a non-zero value.
As observations became better, it became clear that the cosmological
constant is not zero.
Nicolaas Vroom
"Phillip Helbig---undress to reply" <hel...@astro.multiCLOTHESvax.de>
schreef in bericht news:j08rr3$4aj$1...@online.de...
> In article <krRVp.32174$29.1...@newsfe08.ams2>, "Nicolaas Vroom"
> <nicolaa...@telenet.be> writes:
>
>> In a different article of the same magazine
>> http://www.sciencedaily.com/releases/2008/05/080506194033.htm
>> I read:
>>
>> "Only about 5% of our universe is made of normal matter as we know it,
>> consisting of protons and neutrons, or baryons, which along with
>> electrons, form the building blocks of ordinary matter. The rest of our
>> universe is composed of elusive dark matter (23%) and dark energy (72%)."
>>
>> Is there someone who can explain me in simple language what it means:
>> "composed of dark energy" ?
>
>
>> related to impulse and is described by the following two laws:
>> E = 0.5*m*v^2 and E = m*c^2
>> I expect dark energy describes something completely different.
>
> Yes. Think of it---very roughly---as negative pressure.
>
Reading about the cosmological constant I found the following
text: See http://map.gsfc.nasa.gov/universe/uni_shape.html
" The WMAP spacecraft can measure the basic parameters
of the Big Bang theory including the geometry of the universe.
If the universe were flat, the brightest microwave background fluctuations
(or "spots") would be ABOUT one degree across.
If the universe were open, the spots would be LESS than one
degree across.
If the universe were closed, the brightest spots would be
GREATER than one degree across. "
What is the ratinale behind this subdivision ?
How do we know that 1 degree is such an important
deciding factor about the evolution of the Universe ?
Nicolaas Vroom
http://users.telenet.be/nicvroom/dark_mat.htm
Phillip Helbig---undress to reply
<nicolaa...@telenet.be> writes:
> Reading about the cosmological constant I found the following
> text: See http://map.gsfc.nasa.gov/universe/uni_shape.html
> " The WMAP spacecraft can measure the basic parameters
> of the Big Bang theory including the geometry of the universe.
> If the universe were flat, the brightest microwave background fluctuations
> (or "spots") would be ABOUT one degree across.
> If the universe were open, the spots would be LESS than one
> degree across.
> If the universe were closed, the brightest spots would be
> GREATER than one degree across. "
> What is the ratinale behind this subdivision ?
> How do we know that 1 degree is such an important
> deciding factor about the evolution of the Universe ?
That the relevant angular size is approximately a degree is just
coincidence. The reasoning is quite simple: early-universe physics
gives us a PHYSICAL size for density fluctuations, and the ANGULAR size
depends on the geometry and expansion history of the universe, just as
is the case with classical cosmological tests where one observes the
dependence of some distance (ultimately defined via an angle) with
redshift and compares this to theoretical predictions for different
values of Omega (density parameter) and lambda (cosmological constant).
Of course, the classical tests are at much lower redshift. For very low
redshift, one measures essentially q, which is Omega/2 - lambda. At
somewhat larger redshifts, such as the recent supernova data, it is
approximately Omega - lambda. At the redshift of the CMB, it is
approximately Omega + lambda. Omega + lambda determines the geometry of
the universe (1 is flat, less than one negatively curved (both of these
are infinite) and more than 1 is positively curved (finite (for experts:
assuming a simple topology)).
eric gisse
news:uq%Wp.44123$29.1...@newsfe08.ams2:
Both distance and angular scales (the latter being the relevant once
here) are wholly dependent on the large scale geometry of the universe.
> How do we know that 1 degree is such an important
> deciding factor about the evolution of the Universe ?
It isn't, but there is a tipping point in ye olde parameter space that
discerns between these scenarios:
1) Universe is too massive. Will collapse back in on itself.
2) Universe is not massive enough. Will expand forever.
3) Universe is just right. The pencil is balanced on its' tip.
This relates to the density of the universe, which we can discern by the
relative sizes of spots in the CMB which is what WMAP measured. That in
turn tells us the density, which we can feed back into the mathematics
and decide whether we have a future or not. Currently the answer is
sitting at #3.
And since you probably need it, read what this guy has to say about
cosmology:
http://www.astro.ucla.edu/~wright/cosmolog.htm
>
> Nicolaas Vroom
> http://users.telenet.be/nicvroom/dark_mat.htm
>
>
Phillip Helbig---undress to reply
gisse <jowr.pi...@gmail.com> writes:
> 1) Universe is too massive. Will collapse back in on itself.
> 2) Universe is not massive enough. Will expand forever.
> 3) Universe is just right. The pencil is balanced on its' tip.
Actually, it is the density (or, rather, the density parameter, which
is, up to a constant, the physical density divided by the square of the
Hubble constant); if the universe is infinite, then the mass is infinite
(or, in the empty case, zero).
With this change, the above is true (and 1), 3) and 2) correspond to
positive, zero and negative spatial curvature, with 1) being finite and
2) and 3) infinite)) if one assumes that the cosmological constant is
zero. However, we are pretty sure that that is not the case. The CMB
measures primarily Omega + lambda, and this tells us the spatial
curvature (see my other post in this thread). (If one assumes zero
spatial curvature, the quoted statements above also hold, though one
could argue that it is more the sign of the cosmological constant,
rather than the value of the density parameter, which determines whether
or not the universe will recollapse. If the cosmological constant is
negative, the universe will always recollapse, whatever the value of
Omega. If it is positive, for almost all parameter combinations, the
universe will expand forever.)
> This relates to the density of the universe, which we can discern by the
> relative sizes of spots in the CMB which is what WMAP measured. That in
> turn tells us the density, which we can feed back into the mathematics
> and decide whether we have a future or not. Currently the answer is
> sitting at #3.
In the sense that the spatial curvature is (nearly) zero. However, the
universe will definitely expand forever, unless observations are grossly
wrong.
Nicolaas Vroom
> In article <uq%Wp.44123$29.1...@newsfe08.ams2>, "Nicolaas Vroom"
> <nicolaa...@telenet.be> writes:
>
>> Reading about the cosmological constant I found the following
>> text: See http://map.gsfc.nasa.gov/universe/uni_shape.html
>> " The WMAP spacecraft can measure the basic parameters
>> of the Big Bang theory including the geometry of the universe.
>> If the universe were flat, the brightest microwave background
>> fluctuations
>> (or "spots") would be ABOUT one degree across.
>> If the universe were open, the spots would be LESS than one
>> degree across.
>> If the universe were closed, the brightest spots would be
>> GREATER than one degree across. "
>> What is the ratinale behind this subdivision ?
>> How do we know that 1 degree is such an important
>> deciding factor about the evolution of the Universe ?
>
> That the relevant angular size is approximately a degree is just
> coincidence.
the MWB fluctuations as a measurement to decide if the universe
is open, flat or closed.
See here:
http://www.astro.virginia.edu/~jh8h/Foundations/chapter11/chapter11.html
Look to Standard Model Summary Table:
Open means k=-1, Flat means k=0 and Closed means k=+1
Those same numbers are also used in the book:
The Big Bang by Josph Silk.
"We call k the curvature of space"
The following picture shows the MWB radiation:
http://en.wikipedia.org/wiki/File:WMAP_2010.png
The Nasa document claims that you can decide that the Universe is flat
and not open or closed based on the fluctuations.
I have difficulties to accept.
> The reasoning is quite simple: early-universe physics
> gives us a PHYSICAL size for density fluctuations, and the ANGULAR size
> depends on the geometry and expansion history of the universe,
That maybe all correct but the issue is how are those early fluctuations
captured in the MWBR that we observe today.
And how can be we be sure that those imprints are clearly an indication
that the Universe is not open or closed (but flat)
> just as
> is the case with classical cosmological tests where one observes the
> dependence of some distance (ultimately defined via an angle) with
> redshift and compares this to theoretical predictions for different
> values of Omega (density parameter) and lambda (cosmological constant).
> Of course, the classical tests are at much lower redshift. For very low
> redshift, one measures essentially q, which is Omega/2 - lambda. At
> somewhat larger redshifts, such as the recent supernova data, it is
> approximately Omega - lambda. At the redshift of the CMB, it is
> approximately Omega + lambda. Omega + lambda determines the geometry of
> the universe (1 is flat, less than one negatively curved (both of these
> are infinite) and more than 1 is positively curved (finite (for experts:
> assuming a simple topology)).
This whole discussion becomes more tricky if you study the following
document:
http://arxiv.org/ftp/arxiv/papers/1011/1011.3706.pdf
The message is here that the WMAP data not only tells us
dat "our" Universe is not open or closed, but also
what happened before the Big Bang.
Maybe the following page contains the answer:
http://cmb.phys.cwru.edu/boomerang/papers.html
Nicolaas Vroom
http://users.telenet.be/nicvroom/dark_mat.htm
Nicolaas Vroom
"eric gisse" <jowr.pi...@gmail.com> schreef in bericht
news:Xns9F2D73A8AFB8Ejo...@88.198.244.100...
>> text: See http://map.gsfc.nasa.gov/universe/uni_shape.html
>> " The WMAP spacecraft can measure the basic parameters
>> of the Big Bang theory including the geometry of the universe.
>> If the universe were flat, the brightest microwave background
>> fluctuations (or "spots") would be ABOUT one degree across.
>> If the universe were open, the spots would be LESS than one
>> degree across.
>> If the universe were closed, the brightest spots would be
>> GREATER than one degree across. "
>> What is the ratinale behind this subdivision ?
>
>
>> deciding factor about the evolution of the Universe ?
>
> It isn't, but there is a tipping point in ye olde parameter space that
> discerns between these scenarios:
>
> 1) Universe is too massive. Will collapse back in on itself.
> 2) Universe is not massive enough. Will expand forever.
> 3) Universe is just right. The pencil is balanced on its' tip.
>
> This relates to the density of the universe, which we can discern by the
> relative sizes of spots in the CMB which is what WMAP measured.
The issue is how do we know for sure that the relative sizes of the spots
(fluctuations) allow us to claim that it is not #1 or #2.
http://en.wikipedia.org/wiki/File:WMAP_2010.png
A better name for #3 is flat (curvature = 0, k=0)
>>
>> Nicolaas Vroom
>> http://users.telenet.be/nicvroom/dark_mat.htm
>>
>>
Phillip Helbig---undress to reply
<nicolaa...@telenet.be> writes:
> > That the relevant angular size is approximately a degree is just
> > coincidence.
> The issue is not so much the one degree but that you can use
> the MWB fluctuations as a measurement to decide if the universe
> is open, flat or closed.
This is a HUGE field, with thousands of papers having been written in
the last 20 years. It is extremely well understood and as far as I know
there are no uncertainties in the theory. (There might be some dispute
about systematic effects with certain experiments etc.)
> The Nasa document claims that you can decide that the Universe is flat
> and not open or closed based on the fluctuations.
> I have difficulties to accept.
You realise, of course, that you are questioning something which is not
even disputed within the mainstream community.
> > The reasoning is quite simple: early-universe physics
> > gives us a PHYSICAL size for density fluctuations, and the ANGULAR size
> > depends on the geometry and expansion history of the universe,
> That maybe all correct but the issue is how are those early fluctuations
> captured in the MWBR that we observe today.
> And how can be we be sure that those imprints are clearly an indication
> that the Universe is not open or closed (but flat)
I suggest reading up on CMB theory and observations. A usenet post
doesn't provide enough space, and the information is readily available
elsewhere.
eric gisse
$Dk2....@newsfe04.ams2:
The WMAP people explain all this better than I can, and in _far_ better
detail.
http://lambda.gsfc.nasa.gov/product/map/dr4/pub_papers/sevenyear/cosmolo
gy/wmap_7yr_cosmology.pdf
This will probably answer some questions you don't even realize you had.
>
>>>
>>> Nicolaas Vroom
>>> http://users.telenet.be/nicvroom/dark_mat.htm
>>>
>>>
>
>