Ceci n'est pas une pipe (APOD 2009 May 22)

[neufer]

http://apod.nasa.gov/apod/ap090522.html

<<The Dark Horse Nebula or Great Dark Horse is a large dark nebula, which as seen from Earth, obscures part of the upper central bulge of the Milky Way. The Dark Horse lies in the southern constellation Ophiuchus (the Serpent Bearer), near its borders with the more famous constellations Scorpius and Sagittarius. This region of dark nebulae is called Dark Horse because it resembles the side silhouette of a horse and appears dark as compared with the background glow of stars and star clouds. It is also known as "Great" because it is one of the largest (in apparent size) groups of dark nebulae in the sky.



The rear of The Great Dark Horse (its rump and hind legs), is also known as the Pipe Nebula, which itself carries the designation B77, B78, and B59. (The 'B' numbers named after the astronomer Edward Emerson Barnard, who catalogued dark nebulae.) The ability to see The Great Dark Horse with the naked eyes is an indication that the skies are very dark.>>

• Rev.6:5 I heard the third beast say, Come and see.
  And I beheld, and lo a black horse;
  and he that sat on him had a pair of balances in his hand.

[NoelC]

Translation: This is not a pipe

I'm getting spoiled by all these GREAT wide field images lately. Sadly, all I can see from my house is a bright orange sky glow everywhere.

Thank you for sharing your wonderful view from Chile, Yuri.

-Noel

[bystander]

Ceci n'est pas une cheval

The picture shows a pipe that looks as though it might come from a tobacco store advertisement. Magritte painted below the pipe: "Ceci n'est pas une pipe" (This is not a pipe), which seems false but is actually true. The painting is not a pipe, but rather an image of a pipe. As Magritte himself commented: "The famous pipe. How people reproached me for it! And yet, could you stuff my pipe? No, it's just a representation, is it not? So if I had written on my picture 'This is a pipe,' I'd have been lying!" (cited in Harry Torczyner, Magritte: Ideas and Images, p. 71.)

[neufer]

Ceci n'est pas une cheval

Cela est un cheval.

[bystander]

Cela est un cheval.

Non, ce n'est pas un cheval.
Il ressemble plus à un orignal,
mais ce n'est pas un orignal, soit.

http://en.wikipedia.org/wiki/File:Moose ... -750px.JPG
http://en.wikipedia.org/wiki/File:Moose_standing.jpg

[neufer]

Cela est un cheval.

Non, ce n'est pas un cheval.
Il ressemble plus à un orignal,
mais ce n'est pas un orignal, soit.

http://en.wikipedia.org/wiki/File:Moose ... -750px.JPG
http://en.wikipedia.org/wiki/File:Moose_standing.jpg

Cela est un original pamplemousse.

[Doum]

Et si cela était un zèbre. Nonnn c'est un cheval.

[DavidLeodis]

Yes NoelC, it is a wonderful view. It must be amazing to be able to see such a clear sky view.

I must be learning from APODs, as when I saw the image I thought that it shows the Pipe Nebula even before I read the explanation! Realising that the image seemed very famiIiar I've just done a search of the APOD archive and found the APOD of June 23 2006 http://antwrp.gsfc.nasa.gov/apod/ap060623.html. That the image in the two APODs is so very similar should not perhaps be a surprise, but I still think it's awesome that there is no really obvious change despite that the Universe is said to be expanding rapidly (I assume the APOD image of May 22 2009 was taken recently). It really is a mind boggling Universe out there. 8)

[neufer]

Yes NoelC, it is a wonderful view. It must be amazing to be able to see such a clear sky view.

Realising that the image seemed very famiIiar I've just done a search of the APOD archive and found the APOD of June 23 2006 http://antwrp.gsfc.nasa.gov/apod/ap060623.html. That the image in the two APODs is so very similar should not perhaps be a surprise, but I still think it's awesome that there is no really obvious change despite that the Universe is said to be expanding rapidly. 8)

The Galactic Center is located about .0076 Mpc away.

Hubble expansion constant = 74.2 ± 3.6 (km/s)/Mpc.

Galactic Center is retreating by 1261 miles per hour due to galactic expansion.

Retired Concorde aircraft cruising speed for optimum fuel consumption: 1400 miles per hour
(supersonic drag minimum, although turbojet engines are more efficient at high speed)

[Chris Peterson]

The Galactic Center is located about .0076 Mpc away.

Hubble expansion constant = 74.2 ± 3.6 (km/s)/Mpc.

Galactic Center is retreating by 1261 miles per hour due to galactic expansion.

I'm a little confused. Galactic expansion? What's that? I'm guessing (since the calculation works) that you mean Universal expansion. However, the Milky Way is gravitationally bound, and is not itself getting any larger due to the expansion of the Universe. We don't see the galactic center retreating.

However, we do see changes in many nebulas over a fairly short period- years or less- because they are typically very dynamic (and nearby) objects. Everthing to do with moving material, and nothing at all with the dynamics of the Universe.

[neufer]

The Galactic Center is located about .0076 Mpc away.

Hubble expansion constant = 74.2 ± 3.6 (km/s)/Mpc.

Galactic Center is retreating by 1261 miles per hour due to galactic expansion.

I'm a little confused. Galactic expansion? What's that? I'm guessing (since the calculation works) that you mean Universal expansion. However, the Milky Way is gravitationally bound, and is not itself getting any larger due to the expansion of the Universe. We don't see the galactic center retreating.

Well, if it really is universal expansion (i.e., the expansion of space time itself) then it ought to take place within galaxies as well, although not nearly enough (a few kilometers per second) that one would notice it compared to other galactic motions. However, if what we are talking about is simply the recoil of galaxies from an initial explosion (with slowing due to matter and expansion due to dark energy) then I agree that that is a somewhat different matter. But if that is the case, I don't understand why it has taken so long for photons from the cosmic microwave background to reach us. (But, then, there are a lot of things that I don't understand.)

[Chris Peterson]

Well, if it really is universal expansion (i.e., the expansion of space time itself) then it ought to take place within galaxies as well, although not nearly enough (a few kilometers per second) that one would notice it compared to other galactic motions.

What you calculated from the Hubble constant was the expansion of the Universe. But we don't see that expansion within the galaxy (and we are easily capable of measuring a few kilometers per second using Doppler shift) because the gravitational field of the galaxy is much too strong to allow the local space to expand.

However, if what we are talking about is simply the recoil of galaxies from an initial explosion (with slowing due to matter and expansion due to dark energy) then I agree that that is a somewhat different matter. But if that is the case, I don't understand why it has taken so long for photons from the cosmic microwave background to reach us. (But, then, there are a lot of things that I don't understand.)

The photons from the edge of the observable Universe have been reaching us for 13.7 billion years (or so). In the beginning, they were much more energetic. Over the billions of years, as space expanded, they have had their wavelength stretched more and more by expanding space. What we're seeing now was emitted 13.7 billion years ago, but is only now reaching us because the space between the emitting material and us has expanded so far (47+ billion light years). In another 13.7 billion years we'll still see the photon background, but it will be even colder.

[astrolabe]

Hello Chris,

So using the Hubble Constant how big will the visible universe be in another 13.7 billion yrs? This is of course if someone was still around to see it. If so, the instrumentation would have to good enough to see back to 600 million years after the Bang at least in order to actually see anything at distance "x". I wonder if if any one or any instrument would survive if the technology then could, when viewing through some apparatus, allow a view of the BB itself?

Could be Cosmologies version of the Tower of Babel in which the civilization at that time tried to build a tower up to heaven and therefore see God. The biblical story could have been an oral account finally written down of a previous civilization before this one that was highly advanced and destroyed itself somehow. I've always felt so even though it's far, far from probable.

[neufer]

Well, if it really is universal expansion (i.e., the expansion of space time itself) then it ought to take place within galaxies as well, although not nearly enough (a few kilometers per second) that one would notice it compared to other galactic motions.

What you calculated from the Hubble constant was the expansion of the Universe. But we don't see that expansion within the galaxy (and we are easily capable of measuring a few kilometers per second using Doppler shift) because the gravitational field of the galaxy is much too strong to allow the local space to expand.

Perhaps...but let us take the case of the Andromeda Galaxy whose Doppler shift
(for some bizarre reason) IS only capable of being measured to a few kilometers per second:

• The Andromeda Galaxy is observed to be advancing at 301 ± 1 km/s.
  
  The Andromeda Galaxy is located about 0.778 Mpc away.
  
  Hubble expansion constant ~ 74.2 (km/s)/Mpc.

Now I would argue that the Andromeda Galaxy is retreating by about 58 km/s (= 74.2 x 0.778) due to universal expansion but it is actually observed to be advancing at 301 ± 1 km/s thanks to a combination of a strong initial velocity and (to a much lesser extent) by its attraction to the Milky Way.

I'm assuming that you would argue that there IS no expansion within the Local (Galactic) Group because the gravitational field of the Local (Galactic) Group is too strong to allow the local space to expand. Is that your argument? (At what point is universal expansion finally allowed?).

However, if what we are talking about is simply the recoil of galaxies from an initial explosion (with slowing due to matter and expansion due to dark energy) then I agree that that is a somewhat different matter. But if that is the case, I don't understand why it has taken so long for photons from the cosmic microwave background to reach us. (But, then, there are a lot of things that I don't understand.)

The photons from the edge of the observable Universe have been reaching us for 13.7 billion years (or so). In the beginning, they were much more energetic. Over the billions of years, as space expanded, they have had their wavelength stretched more and more by expanding space. What we're seeing now was emitted 13.7 billion years ago, but is only now reaching us because the space between the emitting material and us has expanded so far (47+ billion light years). In another 13.7 billion years we'll still see the photon background, but it will be even colder.

So... space expands (and photon wavelengths are stretched) only between Local (Galactic) Groups and never within a Local (Galactic) Group?

[astrolabe]

Hello neufer,

A while back an image was posted that showed the red and blue shifting in the CMB indicating to me our movement in the Universe relative to it. The question that follows is this: Are we advancing toward Andromeda in relation to the CMB or is it the other way around? Now, I know it could be mutual unless one was chasing the other because a third party (or more) may have some dynamic influence. I am also thinking that the expansion of space in between (if it exists) is still happening and that it probably expands everywhere, even within or through galaxies, but inter/intra galactic processes overpower it's properties. What can I say I'm like the village idiot of sorts and constantly strive to oversimplify things so I can grasp ideas until called wrong.

[Chris Peterson]

Perhaps...but let us take the case of the Andromeda Galaxy whose Doppler shift
(for some bizarre reason) IS only capable of being measured to a few kilometers per second:

• The Andromeda Galaxy is observed to be advancing at 301 ± 1 km/s.
  
  The Andromeda Galaxy is located about 0.778 Mpc away.
  
  Hubble expansion constant ~ 74.2 (km/s)/Mpc.

Now I would argue that the Andromeda Galaxy is retreating by about 58 km/s (= 74.2 x 0.778) due to universal expansion but it is actually observed to be advancing at 301 ± 1 km/s thanks to a combination of a strong initial velocity and (to a much lesser extent) by its attraction to the Milky Way.

I'm assuming that you would argue that there IS no expansion within the Local (Galactic) Group because the gravitational field of the Local (Galactic) Group is too strong to allow the local space to expand. Is that your argument? (At what point is universal expansion finally allowed?).

No, I think your assessment is correct, or nearly so. The fields found between the bound members of galaxy clusters aren't strong enough to completely counter expansion. Eventually most galaxy clusters will come apart (except where some of their components first merge).

[neufer]

I think your assessment is correct, or nearly so. The fields found between the bound members of galaxy clusters aren't strong enough to completely counter expansion. Eventually most galaxy clusters will come apart (except where some of their components first merge).

Thanks, Chris. There is a lot of stuff I don't understand very well...and even the stuff I sort of understand I don't necessarily explain it well.

[neufer]

Hello neufer,

A while back an image was posted that showed the red and blue shifting in the CMB indicating to me our movement in the Universe relative to it. The question that follows is this: Are we advancing toward Andromeda in relation to the CMB or is it the other way around?

Our whole local group of galaxies is moving at ~627 km/s in the direction
of galactic longitude l = 276°, b = 30° (vis-a-vis the CMB).

Now relative to our local group of galaxies the Andromeda Galaxy
is moving at ~150 km/s in more or less the same direction:
galactic longitude l = 301°, b = 22°.

So the Andromeda Galaxy is the faster [627+150 km/s] dog
chasing us (the slower [627-150 km/s] Milky Way cat)
as we all move in more or less the same direction vis-a-vis the CMB.

(It's late at night so someone might want to check my back of the envelope calculations.)

[DavidLeodis]

This is a fascinating discussion, which I've read with interest even though most of it is beyond me! As to an expanding Universe I can't help but wonder, if it is expanding just what is it expanding into .

I stll think the image is awesome.

[astrolabe]

Hello DavidLeodis,

As has been said in other threads (not by me 'cause, like you, I'm a relative novice) that the Universe creates space as it goes. Approximately 46 billion ly. across now by some estimates and which has taken about 13.7 billion lyrs. for it to get to that diameter. Mind boggling to be sure! Some have said that beyond the visible parameter the Universe could be much larger -even infinite- but without the instruments there is no way of knowing and most if not all arguments concerning the nature of the great beyond are mental exercises only and rather futile. No one can tell yet if in fact there are influences at all beyond what humans can currently see. IMHO we have quite enough to keep us busy as it is! But this is as you say a good thread- very interesting indeed.

Ya think?

[Chris Peterson]

Approximately 46 billion ly. across now by some estimates and which has taken about 13.7 billion lyrs. for it to get to that diameter.

Radius. The diameter is 93 billion ly. And to be clear, that's the observable universe. The entire thing is almost certainly larger- probably much larger.

[astrolabe]

Hello Chris,

Thank you for the correction. Just goes to show that good intent doesn't necessarily get followed by fact.
93 billion ly diameter it is.

[NoelC]

What if the universe is not expanding at all?

What if the passage of time isn't constant?

Maybe it's still the size of a pea.

From an observer inside if the passage of time changed it might seem that things are getting farther apart as photons would take longer to get from one place to another.

Very few folks (certainly not I) can get their heads around this kind of relativity.

-Noel

[Chris Peterson]

What if the universe is not expanding at all?

What if the passage of time isn't constant?

Maybe it's still the size of a pea.

From an observer inside if the passage of time changed it might seem that things are getting farther apart as photons would take longer to get from one place to another.

Very few folks (certainly not I) can get their heads around this kind of relativity.

Well, you can play "what if" games all you like, but what's the real point? We have a working theory, it describes what we see, and has been useful in predicting observations and guiding experiment design. That's all that science asks.

For your questions to make sense, you'd need to find a way to express them scientifically. For instance, what does it mean that "time isn't constant"? Constant compared to what? What does it mean to be "the size of a pea"? In what fundamental units? If the Universe is the size of a pea, how big is an actual pea?

How can you express the questions so they could be tested? Otherwise, it's just philosophy (and frankly, not very good philosophy).

[NoelC]

Aw c'mon. There's no rule here that says everything written has to be hard science. Philosophy helps people reach for science; I'm just throwing things out there to help the less technical among us expand their thought processes. To make them wonder. To get them thinking.

Frankly I don't care to think on this particular subject hard enough to even try to understand current theory. It's not what lights my fire. As I noted quite clearly, I certainly don't have my head around it.

frankly, not very good philosophy

Let me toss this snide comment right back at you - your "working theory" doesn't model reality particularly well. Look at all the invisible crap that has had to be invented (dark this and that) to make it work. And from what I can see not everyone agrees on ONE working theory either, so there is no "we" as you'd like to imply. Try not to be so uppity. There is room for more than just your opinion here.

-Noel