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Q & A: moving universe?

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Most recent answer: 05/16/2013
Q:
Great to find a place where I can ask a question that has been on my mind for some time now. The question is simple, and I hope there is a real answer to my question :)

Does the observable universe move through space?

The reason I am asking is because it seems to me that if the observable universe as a whole moves through space, it should result in a slight difference in what we see in different directions.

The red shift that is used to determine distance should then also be slightly different in different directions, though perhaps we can measure this if red shifts are the only way to measure really long distances.

However, reasoning further, the average size of really far away galaxies should be slightly different in different directions, if the observable universe as a whole is moving through space.

My knowledge of these things is pretty limited, so the above could be a big bunch of uninformed nonsense,. :) But my main question remains: Does the observable universe move through space?

Thank you very much in advance for considering my question.

Sincerely,

Peter
- Peter (age 36)
São Paulo, SP, Brazil
A:
Not such a simple question!
We really don’t know what it would mean for the observable universe to move through space. The whole framework of Relativity says that there’s no meaning to that question, no physical sign to separate space from the things in it.

On the other hand it is meaningful to ask how we are moving with respect to most of the observable universe, and even with respect to the background radiation left from the Big Bang. We are moving significantly with respect to that, so the background looks a little hotter in one direction and a little colder in the other. According to a Wikipedia article, this effect is consistent with "the Earth moving at some 380 km/s towards the constellation ."

Mike W.

(published on 10/22/2007)

Follow-Up #1: everything moves?

Q:
is everything in the universe moves? cite a theory.
- julieta g. elano (age 16)
tago,surigao del sur, philippines
A:
We don't need much theory to see that things in the universe are moving relative to each other. Some things are getting closer to us, most are getting farther away, etc. We can tell that by looking at light coming from stars, since the detailed colors of the light depend on whether the star is getting closer to us or farther- or at least whether it was when the light headed our way. Other things can be seen directly to be getting closer to each other or farther apart, even if they stay about the same distance from us. As for who is moving- us or them or both- according Special Relativity (there's a theory!) it's absolutely meaningless to ask, since no observation depends on what answer you make up. The same is true in General Relativity.

Mike W.

Lee H


(published on 10/22/2007)

Follow-Up #2: big questions

Q:
It would seem that we don't indeed know all, wgen I was a kid I remember thinking once in a while, that we are nor smart enough or capable of understanding the big question why are we here at all, try to think of nothing,,,we can't, we see either light or dark and these are both something, I believe if we could see the answer we would go insane
- alexander sword (age 77)
vernonia ore 97064 158
A:
You could be right.

Mike W.

(published on 05/16/2013)

Follow-Up #3: Rate of expanding universe?

Q:
If the universe is expanding, what is the rate of its expansion? Is expansion uniform or uneven, i.e. more at some places and less in another?
- Indrajit
New Delhi, India
A:
The rate of expansion of the universe in our locality is measured by the Hubble Constant, H0,  which relates the receding velocity of a far away object with its distance from our observing point. Hubble's law often expressed by the equation v = H0D, with H0 the constant of proportionality  between the distance D to a distant galaxy and its velocity v.   Current observations do not detect significant deviations from isotropy. 
There is evidence that the current Hubble constant is larger than it was at much earlier times in the universe.  This is called  'accelerated expansion' and is a hot topic in present day astronomy and cosmology.  The main upshot is that the 'Hubble Constant' is not really a constant but changes as the universe evolves.   See:    and 

LeeH

(published on 07/01/2010)

Follow-Up #4: No cosmological questions

Q:
The big bang theory is incorrect. The universe is an infinite sphere that has no beginning and no end. The center of this sphere is where the observer is located- so man is at the center of the universe- and its spinning according to the laws of the universe- that’s the reason we observe some objects moving away and other moving toward us.
- Robert (age 45)
Chicago
A:
Robert- That's a collection of statements, but I guess the implicit question is why we would believe in the Big Bang description.

The Big Bang description is derived from General Relativity, a theory which has been confirmed to high accuracy via many types of experiments. From the BB theory, we then draw rather accurate predictions for:
1. The redshifts of the spectral lines of "standard candles".
2. The abundances of the light elements.
3. The spectral form of the cosmic microwave background (CMB)
4. The angular distribution of fluctuations in the CMB intensity, including a variety of details.
5. The lumpiness of matter in the current universe.

You give zero evidence for your alternate description. It's not really clear what it means or what sort of predictions you could draw from it.


Mike W.



(published on 08/05/2011)

Follow-Up #5: edgeless universe

Q:
Robert, this analogy will help you understand why the universe has no boundary and no center. Imagine yourself living in a 2 dimensional universe. You can move left-right, foward-back but you cannot move up-down. That means that in such a universe, height doesn't exist. You and everything else is perfectly flat. Now imagine that this 2D universe is curled up on itself in a 3rd dimension out of your reach. That universe could form a sphere or a donut but you cannot sense it. You and all of Nature is limited to the surface of such a sphere. Now, does the surface of a sphere have a center? I'm not talking about the sphere (you would say that the center is inside the sphere), I'm talking about the surface only. Take a pen and draw a line on an inflated balloon and keep drawing that line until you reach an edge or boundary. You never will since the surface a balloon has no boundary, no edge. And if something has no edge or boundary, then it has no center since a center always refer itself to the boundaries of an object. Now, increase all the dimensions in the story by 1, you will then have something that many cosmologists think may actually apply to us. Our universe is 3D but maybe it is curved into a 4th pysical dimension out of our reach. We would then be living on the hypersurface of a 4D sphere. Like the surface of an ordinary sphere has no center, the hypersurface of a 4D sphere has no center too. Theists linger to have mankind placed at the center of the universe. God wouldn't placed us anywhere else. But evidence shows us that we inhabit some lost place of the universe. It doesn't prove anything about God's existence. Thus you can accept the truth and still believe that there is a Creator. Now about the expansion of the universe. You may say: "if we don't live at the center of the universe, how come that distant galaxies are rushing away from us?" To help you understand why it is possible to have everything rushing away from us and still not being at the center, try the following experiment: Take an inflatable balloon (like the ones we use for parties) and a black ink permanent marker (you know, those which reek with chemicals). With the marker, draw dots all over the uninflated balloon and take notice of the distance between the dots. Now inflate the balloon all the way. Now, what happened to the distance between EVERY dot? It has increased! The same thing happens in our universe execpt that our galaxies don't grow larger like the dots did on the balloon. Why? Gravity! Here is a nice explanation by Carl Sagan about the geometry of our universe. http://www.youtube.com/watch?v=3WL_vtu4r1w
- Anonymous
A:
It's fun to serve as a sort of forum, just adding a few comments.

1. If you use little pieces of confetti instead of painted dots on your balloon, they keep the same size as the balloon expands, like galaxies.

2. Although the extra dimension is useful for making a picture in our Euclidean minds, it has no physical significance. All the geometrical properties of the curved space ae describable purely internally, by a set of distances between points, with no reference to some other coordinates.

3. The finite balloon-like picture may or may not capture the large-scale structure of or universe. An infinite space is also just as possible, and maybe compatible with a wider range of theories.

Mike W.

(published on 08/05/2011)

Follow-up on this answer.