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Q about earth's movement and universe expansion
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Mark Buchanan
Nov 11, 2012, 12:59:10 PM11/11/12
to
I was listening to a talk about the size, age, and expansion of the
universe recently and the topic of dark energy and accelerating
expansion came up.
So the question is this: If dark energy is accelerating the expansion of
the universe then that should apply to earth - withing our local group
of galaxies. So why don't we feel that acceleration?
It's possible that the acceleration is to small to detect. Even trying
to find out how fast we are moving relative to the CMBR isn't easy. This
NASA site:
http://apod.nasa.gov/apod/ap030209.html
says it's 600 k/s but this Wiki article
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
says it's 371 k/s towards Leo - no reference given though.
Is there someone who knows in the NG?
Mark
TomS
Nov 11, 2012, 1:17:29 PM11/11/12
to
"On Sun, 11 Nov 2012 12:59:10 -0500, in article <k7op1f$qpg$1...@dont-email.me>,
Mark Buchanan stated..."
enlightenment rather than a response:
My understanding is that within the Local Group of galaxies (including
the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
so on), cosmological effects are not significant - gravity is more
important. Dark Energy has an effect only on a scale of billions of
light years, rather than mere (!) millions.
>
>It's possible that the acceleration is to small to detect. Even trying
>to find out how fast we are moving relative to the CMBR isn't easy. This
>NASA site:
>
>http://apod.nasa.gov/apod/ap030209.html
>
>says it's 600 k/s but this Wiki article
>
>http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
>
>says it's 371 k/s towards Leo - no reference given though.
>
>Is there someone who knows in the NG?
>
>Mark
>
--
---Tom S.
Mark Buchanan stated..."
>
>
>I was listening to a talk about the size, age, and expansion of the
>universe recently and the topic of dark energy and accelerating
>expansion came up.
>
>So the question is this: If dark energy is accelerating the expansion of
>the universe then that should apply to earth - withing our local group
>of galaxies. So why don't we feel that acceleration?
I am not an astronomer or physicist, so take this as a request for
>
>I was listening to a talk about the size, age, and expansion of the
>universe recently and the topic of dark energy and accelerating
>expansion came up.
>
>So the question is this: If dark energy is accelerating the expansion of
>the universe then that should apply to earth - withing our local group
>of galaxies. So why don't we feel that acceleration?
enlightenment rather than a response:
My understanding is that within the Local Group of galaxies (including
the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
so on), cosmological effects are not significant - gravity is more
important. Dark Energy has an effect only on a scale of billions of
light years, rather than mere (!) millions.
>
>It's possible that the acceleration is to small to detect. Even trying
>to find out how fast we are moving relative to the CMBR isn't easy. This
>NASA site:
>
>http://apod.nasa.gov/apod/ap030209.html
>
>says it's 600 k/s but this Wiki article
>
>http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
>
>says it's 371 k/s towards Leo - no reference given though.
>
>Is there someone who knows in the NG?
>
>Mark
>
---Tom S.
Paul J Gans
Nov 11, 2012, 1:36:15 PM11/11/12
to
of space that is expanding.
To use the old balloon analogy, imagine a two-dimensional universe
on the surface of a balloon. Mark stars with bits of sticky paper.
Now make the balloon bigger. The sticky bits of paper get further
away from each other. But the sticky bits of paper don't expand.
Gravity holds them together.
Same in our three-D universe. Gravity keeps everything that
was close together together.
--
--- Paul J. Gans
Mark Buchanan
Nov 11, 2012, 2:17:43 PM11/11/12
to
On 11/11/2012 1:17 PM, TomS wrote:
> "On Sun, 11 Nov 2012 12:59:10 -0500, in article<k7op1f$qpg$1...@dont-email.me>,
> Mark Buchanan stated..."
>>
>>
>> I was listening to a talk about the size, age, and expansion of the
>> universe recently and the topic of dark energy and accelerating
>> expansion came up.
>>
>> So the question is this: If dark energy is accelerating the expansion of
>> the universe then that should apply to earth - withing our local group
>> of galaxies. So why don't we feel that acceleration?
>
> I am not an astronomer or physicist, so take this as a request for
> enlightenment rather than a response:
I'm not either.
> "On Sun, 11 Nov 2012 12:59:10 -0500, in article<k7op1f$qpg$1...@dont-email.me>,
> Mark Buchanan stated..."
>>
>>
>> I was listening to a talk about the size, age, and expansion of the
>> universe recently and the topic of dark energy and accelerating
>> expansion came up.
>>
>> So the question is this: If dark energy is accelerating the expansion of
>> the universe then that should apply to earth - withing our local group
>> of galaxies. So why don't we feel that acceleration?
>
> I am not an astronomer or physicist, so take this as a request for
> enlightenment rather than a response:
>
> My understanding is that within the Local Group of galaxies (including
> the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> so on), cosmological effects are not significant - gravity is more
> important. Dark Energy has an effect only on a scale of billions of
> light years, rather than mere (!) millions.
>
Understood but supposedly anything happening on the scale of billions of
> My understanding is that within the Local Group of galaxies (including
> the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> so on), cosmological effects are not significant - gravity is more
> important. Dark Energy has an effect only on a scale of billions of
> light years, rather than mere (!) millions.
>
light years away from us is also happening to us - since we are no more
at the center of the universe than anything else.
Mark Buchanan
Nov 11, 2012, 2:26:04 PM11/11/12
to
- at least in principle. What I don't get is this: distant galaxies are
moving away from each other at speeds relative to their distances from
each other but all speeds should be slowing down, not speeding up. So if
everything is speeding up away from each other shouldn't we as well
experience that acceleration?
The person giving the talk is a physicist himself. When I asked the
question he didn't know the answer.
This paper discusses this in more details but seems to be older (no date
given):
http://muller.lbl.gov/COBE-early_history/SciAm.pdf
Mark
jillery
Nov 11, 2012, 3:46:07 PM11/11/12
to
Gravity?
ISTM Paul's explanation was pretty good, with a small minor nit: the
fabric of space also permeates the sticky papers, but there just isn't
enough space within them to overcome their internal gravity, as Paul
said.
OTOH and AIUI as the Universe expands, so the amount of space between
any two points in the Universe increases. IOW the more the Universe
expands, the faster it expands.
I found this article helpful:
<http://scienceblogs.com/startswithabang/2012/07/26/empty-space-has-more-energy-than-everything-in-the-universe-combined/>
Mike Dworetsky
Nov 11, 2012, 5:31:44 PM11/11/12
to
mean the Sun, because the Earth would produce an orbital variation through
the year) relative to the CMBR is 371 km/s, but that the Local Group of
Galaxies (presumably its centre of mass) is moving at 627 km/sec relative to
the CMBR. The latter figure is found from the Sun's orbital speed and
direction around the galactic centre and the best estimate of the Galaxy's
velocity relative to the Local Group centre of mass.
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply)
J. J. Lodder
Nov 11, 2012, 5:56:11 PM11/11/12
to
Mark Buchanan <marklynn...@gmail.com> wrote:
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
>
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
>
> It's possible that the acceleration is to small to detect. Even trying
> to find out how fast we are moving relative to the CMBR isn't easy.
Nonsense. The speed is accurately known.
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
>
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
>
> It's possible that the acceleration is to small to detect. Even trying
> to find out how fast we are moving relative to the CMBR isn't easy.
Even the yearly variations due to the earth orbiting the sun
are easily measurable.
> This NASA site:
>
> http://apod.nasa.gov/apod/ap030209.html
>
> says it's 600 k/s but this Wiki article
>
> http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
>
> says it's 371 k/s towards Leo - no reference given though.
The speed depends on which of the known local speeds
you add or subtract.
The 600 km/s is the speed of the whole local group (of galaxies)
wrt the cmb.
IIRC the 371 km/s is the speed of the solar system.
Jan
Mark Buchanan
Nov 11, 2012, 8:52:35 PM11/11/12
to
unanswered. Is the 627 k/s changing over time?
My understanding is that no one knows why we are moving 627 k/s towards
Leo in the first place.
Mark
Mark Buchanan
Nov 11, 2012, 9:24:57 PM11/11/12
to
the expansion of the universe is accelerating was a surprise to
cosmologists.
>
> ISTM Paul's explanation was pretty good, with a small minor nit: the
> fabric of space also permeates the sticky papers, but there just isn't
> enough space within them to overcome their internal gravity, as Paul
> said.
>
'fabric of space'.
> OTOH and AIUI as the Universe expands, so the amount of space between
> any two points in the Universe increases. IOW the more the Universe
> expands, the faster it expands.
jillery
Nov 11, 2012, 10:37:42 PM11/11/12
to
On Sun, 11 Nov 2012 21:24:57 -0500, Mark Buchanan
Why of course gravity? Astronomers have known for some time there
isn't enough normal matter to slow down the Universe's expansion.
Astronomers have also known for some time that something is wrong
about their understanding of gravity at the galactic scale. They
calculated that all the matter they can see within galaxies isn't
enough to explain the motions of stars within them. And they see
gravitational lensing that can't be explained by the matter they can
see. So they invented dark matter, some mysterious substance that
doesn't emit or absorb photons but still has gravitational effects.
The acceleration of expansion is an entirely different thing. Before
they looked at those distant supernovae, there was no reason to
suppose that the rate was accelerating. Now astronomy has another
great mystery, that it has an effect but no idea what is the cause.
>> ISTM Paul's explanation was pretty good, with a small minor nit: the
>> fabric of space also permeates the sticky papers, but there just isn't
>> enough space within them to overcome their internal gravity, as Paul
>> said.
>>
>I understand the balloon thing well enough - I don't 'get' the concept
>'fabric of space'.
It is a metaphor, and that might be what is confusing you. Perhaps
you could elaborate more fully on what you don't get, taking into
account what has already been said.
>> OTOH and AIUI as the Universe expands, so the amount of space between
>> any two points in the Universe increases. IOW the more the Universe
>> expands, the faster it expands.
>
>Without 'dark energy' this wouldn't be true.
Again, no. AIUI the 'effect' of accelerated expansion is more-or-less
established. It's not clear at all what is the actual 'cause'. The
phrase "dark energy" is purely a placeholder label.
>> I found this article helpful:
>>
>> <http://scienceblogs.com/startswithabang/2012/07/26/empty-space-has-more-energy-than-everything-in-the-universe-combined/>
What do you think of this article?
isn't enough normal matter to slow down the Universe's expansion.
Astronomers have also known for some time that something is wrong
about their understanding of gravity at the galactic scale. They
calculated that all the matter they can see within galaxies isn't
enough to explain the motions of stars within them. And they see
gravitational lensing that can't be explained by the matter they can
see. So they invented dark matter, some mysterious substance that
doesn't emit or absorb photons but still has gravitational effects.
The acceleration of expansion is an entirely different thing. Before
they looked at those distant supernovae, there was no reason to
suppose that the rate was accelerating. Now astronomy has another
great mystery, that it has an effect but no idea what is the cause.
>> ISTM Paul's explanation was pretty good, with a small minor nit: the
>> fabric of space also permeates the sticky papers, but there just isn't
>> enough space within them to overcome their internal gravity, as Paul
>> said.
>>
>I understand the balloon thing well enough - I don't 'get' the concept
>'fabric of space'.
you could elaborate more fully on what you don't get, taking into
account what has already been said.
>> OTOH and AIUI as the Universe expands, so the amount of space between
>> any two points in the Universe increases. IOW the more the Universe
>> expands, the faster it expands.
>
>Without 'dark energy' this wouldn't be true.
established. It's not clear at all what is the actual 'cause'. The
phrase "dark energy" is purely a placeholder label.
>> I found this article helpful:
>>
>> <http://scienceblogs.com/startswithabang/2012/07/26/empty-space-has-more-energy-than-everything-in-the-universe-combined/>
Mike Dworetsky
Nov 12, 2012, 3:19:46 AM11/12/12
to
can reach speeds of order 500-1000 km/sec. This can be seen on plots of
redshift vs distance as scatter. Further scatter comes from uncertain
measurements of distance.
So the answer to "why" is "random motions". There is absolutely no reason
why any particular collection of galaxies such as the Local Group should be
at rest with respect to the CMBR.
The 627 km/sec is not changing with time except possibly on a timescale of
billions of years, due to the Local Group orbiting around larger clusters
such as Virgo, or acceleration towards the Great Attractor (a very large
giant cluster or supercluster towards which there seems to be a
gravitational flow of galaxy clusters in our vicinity).
Steven Carlip
Nov 12, 2012, 2:02:53 PM11/12/12
to
In article <k7op1f$qpg$1...@dont-email.me>,
still some debate about the exact amount -- it's a complicated
question in general relativity, and a solution of the relevant
equations requires a number of approximations. But the answer
is certainly tiny: for the Solar System, by one reasonable
calculation, it's 44 orders of magnitude smaller than the
acceleration of the Earth due to the Sun's gravity (see
http://arxiv.org/abs/astro-ph/9803097). At the galaxy cluster
scale, the expansion induced by cosmological expansion is larger,
but still about seven orders of magnitude smaller than the local
gravitational accelerations.
Price has argued (see http://arxiv.org/abs/gr-qc/0508052) that
for an exponentially expanding Universe, there's actually no
local effect, but this seems to be a special case.
If the rate of acceleration of the Universe is itself increasing
-- a so-called "big rip" scenario -- it will *eventually* be
important at local scales, but we'll have a very long wait.
Steve Carlip
Mark Buchanan <marklynn...@gmail.com> wrote:
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
> It's possible that the acceleration is to small to detect.
That's right -- too small by a very large margin. There is
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
> It's possible that the acceleration is to small to detect.
still some debate about the exact amount -- it's a complicated
question in general relativity, and a solution of the relevant
equations requires a number of approximations. But the answer
is certainly tiny: for the Solar System, by one reasonable
calculation, it's 44 orders of magnitude smaller than the
acceleration of the Earth due to the Sun's gravity (see
http://arxiv.org/abs/astro-ph/9803097). At the galaxy cluster
scale, the expansion induced by cosmological expansion is larger,
but still about seven orders of magnitude smaller than the local
gravitational accelerations.
Price has argued (see http://arxiv.org/abs/gr-qc/0508052) that
for an exponentially expanding Universe, there's actually no
local effect, but this seems to be a special case.
If the rate of acceleration of the Universe is itself increasing
-- a so-called "big rip" scenario -- it will *eventually* be
important at local scales, but we'll have a very long wait.
Steve Carlip
John S. Wilkins
Nov 12, 2012, 4:03:43 PM11/12/12
to
--
John S. Wilkins, Associate, Philosophy, University of Sydney
http://evolvingthoughts.net
But al be that he was a philosophre,
Yet hadde he but litel gold in cofre
Mark Buchanan
Nov 12, 2012, 5:56:35 PM11/12/12
to
Mark
Steven L.
Nov 12, 2012, 6:52:54 PM11/12/12
to
On 11/11/2012 1:17 PM, TomS wrote:
> "On Sun, 11 Nov 2012 12:59:10 -0500, in article <k7op1f$qpg$1...@dont-email.me>,
> Mark Buchanan stated..."
>>
>>
>> I was listening to a talk about the size, age, and expansion of the
>> universe recently and the topic of dark energy and accelerating
>> expansion came up.
>>
>> So the question is this: If dark energy is accelerating the expansion of
>> the universe then that should apply to earth - withing our local group
>> of galaxies. So why don't we feel that acceleration?
>
> I am not an astronomer or physicist, so take this as a request for
> enlightenment rather than a response:
>
> My understanding is that within the Local Group of galaxies (including
> the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> so on), cosmological effects are not significant - gravity is more
> important. Dark Energy has an effect only on a scale of billions of
> light years, rather than mere (!) millions.
In fact, the Milky Way Galaxy and the Andromeda Galaxy are moving
> Mark Buchanan stated..."
>>
>>
>> I was listening to a talk about the size, age, and expansion of the
>> universe recently and the topic of dark energy and accelerating
>> expansion came up.
>>
>> So the question is this: If dark energy is accelerating the expansion of
>> the universe then that should apply to earth - withing our local group
>> of galaxies. So why don't we feel that acceleration?
>
> I am not an astronomer or physicist, so take this as a request for
> enlightenment rather than a response:
>
> My understanding is that within the Local Group of galaxies (including
> the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> so on), cosmological effects are not significant - gravity is more
> important. Dark Energy has an effect only on a scale of billions of
> light years, rather than mere (!) millions.
closer. May collide in another 4 billion years or so.
--
Steven L.
Burkhard
Nov 12, 2012, 7:04:55 PM11/12/12
to
On Nov 12, 11:57 pm, "Steven L." <sdlit...@earthlink.net> wrote:
> On 11/11/2012 1:17 PM, TomS wrote:
>
>
>
>
>
>
>
>
>
> > "On Sun, 11 Nov 2012 12:59:10 -0500, in article <k7op1f$qp...@dont-email.me>,
> On 11/11/2012 1:17 PM, TomS wrote:
>
>
>
>
>
>
>
>
>
> > Mark Buchanan stated..."
>
> >> I was listening to a talk about the size, age, and expansion of the
> >> universe recently and the topic of dark energy and accelerating
> >> expansion came up.
>
> >> So the question is this: If dark energy is accelerating the expansion of
> >> the universe then that should apply to earth - withing our local group
> >> of galaxies. So why don't we feel that acceleration?
>
> > I am not an astronomer or physicist, so take this as a request for
> > enlightenment rather than a response:
>
> > My understanding is that within the Local Group of galaxies (including
> > the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> > so on), cosmological effects are not significant - gravity is more
> > important. Dark Energy has an effect only on a scale of billions of
> > light years, rather than mere (!) millions.
>
> In fact, the Milky Way Galaxy and the Andromeda Galaxy are moving
> closer. May collide in another 4 billion years or so.
>
Darn, what will that do to house prices?
>
> >> I was listening to a talk about the size, age, and expansion of the
> >> universe recently and the topic of dark energy and accelerating
> >> expansion came up.
>
> >> So the question is this: If dark energy is accelerating the expansion of
> >> the universe then that should apply to earth - withing our local group
> >> of galaxies. So why don't we feel that acceleration?
>
> > I am not an astronomer or physicist, so take this as a request for
> > enlightenment rather than a response:
>
> > My understanding is that within the Local Group of galaxies (including
> > the Milky Way Galaxy, the Magellanic Clouds, the Andromeda Galaxy and
> > so on), cosmological effects are not significant - gravity is more
> > important. Dark Energy has an effect only on a scale of billions of
> > light years, rather than mere (!) millions.
>
> In fact, the Milky Way Galaxy and the Andromeda Galaxy are moving
> closer. May collide in another 4 billion years or so.
>
.
jillery
Nov 12, 2012, 7:30:37 PM11/12/12
to
tremendous respect for the time you take to provide quality replies.
I am not an expert in these things, so it's no surprise to me that
your answer leaves me with some questions. I hope I can phrase them
well enough that you can understand them.
First, I remain unclear how an accelerating expansion of space applies
to Earth. I don't expect any object, Earth included, to be at rest
relative to the CMB, but I missed how that relative motion is a
consequence of the accelerating expansion.
Second, I remain unclear how the Big Rip becomes important at local
scales. Am I correct in my understanding that the accelerating
expansion of space is a consequence of the increasing amount of space?
If so, then if gravitationally-bound objects remain so even as space
expands around them, why wouldn't gravitationally-bound objects remain
so even as the expansion accelerates?
Thank you in advance for helping me clear up my confusion.
Mark Buchanan
Nov 12, 2012, 9:48:37 PM11/12/12
to
If the expansion of the sun doesn't finish us off first we might be
ejected right out of the galaxy.
Mark
Mark Buchanan
Nov 12, 2012, 9:51:48 PM11/12/12
to
Too many random pictures of seemingly unrelated things.
Mark
jillery
Nov 12, 2012, 11:14:03 PM11/12/12
to
On Mon, 12 Nov 2012 21:51:48 -0500, Mark Buchanan
I apologize. It appears I totally misunderstood your original
question.
question.
Walter Bushell
Nov 13, 2012, 7:10:13 PM11/13/12
to
In article <1kthno9.1cxegz613icg1uN%jo...@wilkins.id.au>,
Don't worry, you'll be dead long before you have to worry about local
effects of the rip tide.
--
This space unintentionally left blank.
effects of the rip tide.
--
This space unintentionally left blank.
Earle Jones
Nov 17, 2012, 2:07:36 AM11/17/12
to
Yes.
The Bible (in several different places) says the earth is immovable.
Why would you ask?
earle
*
Craig Franck
Nov 17, 2012, 9:32:29 PM11/17/12
to
On 11/11/2012 12:59 PM, Mark Buchanan wrote:
>
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
>
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
http://www.youtube.com/watch?v=3Pa34orcwwA
>
> I was listening to a talk about the size, age, and expansion of the
> universe recently and the topic of dark energy and accelerating
> expansion came up.
>
> So the question is this: If dark energy is accelerating the expansion of
> the universe then that should apply to earth - withing our local group
> of galaxies. So why don't we feel that acceleration?
> It's possible that the acceleration is to small to detect.
in such a way that there is no local expansion.
A less optimistic scenario:
http://en.wikipedia.org/wiki/Big_Rip
Craig
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