Center of our galaxy and the universe

[Bell]

If I want to look at the center of our galaxy and the center of the universe, where do I have to look? In which or near which constellation would they be situated?

 

[~enigma~]

If I want to look at the center of our galaxy and the center of the universe, where do I have to look? In which or near which constellation would they be situated?

The proper answer is to look at me since I am the center of the universe. Then I would ask why you are staring at me since it is making me uncomfortable

 

[godless dave]

For the center of our galaxy, it's in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest (source: http://en.wikipedia.org/wiki/Galactic_center).

There is no center of the universe, as far as we know.

 

[AntiTelharsic]

Edit: scooped.

 

[roger]

Where's the center of the surface of a ball?

 

[Bell]

The proper answer is to look at me since I am the center of the universe. Then I would ask why you are staring at me since it is making me uncomfortable

That's because we haven't been properly introduced.
Say, haven't I seen you before? Can I buy you a drink?

For the center of our galaxy, it's in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest (source: http://en.wikipedia.org/wiki/Galactic_center).

Thanks for that!

There is no center of the universe, as far as we know.

Where's the center of the surface of a ball?

There's where I get lost. I assume the big bang, or whatever is left of it, is the center of the universe. Assuming the ever expanding (?) universe is like a balloon getting bigger and bigger.

Eta: with the balloon example, I mean that the universe is inside the balloon. So the bigger the balloon gets, the more distance there is between the stars.

 

[~enigma~]

on the one hand there is no center yet on the other hand the center is everywhere so on the other hand, the second post is true

 

[DC]

the center is everywhere

according to the big bang theory, yes

 

[roger]

There's where I get lost. I assume the big bang, or whatever is left of it, is the center of the universe. Assuming the ever expanding (?) universe is like a balloon getting bigger and bigger.

Eta: with the balloon example, I mean that the universe is inside the balloon. So the bigger the balloon gets, the more distance there is between the stars.

I didn't say a balloon. I said the surface of the ball (balloon). The balloon analogy is just that, an analogy. The 2D surface is an analogy for the 3 dimensions of space. However, the 3rd dimension of the balloon is analogous to nothing. If you lived on the surface of the balloon as a 2D creature you would have no access to the 3rd dimension, even though the surface curves. Now, as it happens, it's a 3D world, and space is curved, but don't mistake that for the implication that it is curved in 4D and there is a center there. Within our 3D space there is no center.

 

[DC]

Within our 3D space there is no center.

eehm, isnt it the case that we cannot see that center, or know where it is, but actually there must be a center.

 

[roger]

eehm, isnt it the case that we cannot see that center, or know where it is, but actually there must be a center.

I'll answer that when you tell me where the center of the surface of a ball is.

 

[The Man]

I didn't say a balloon. I said the surface of the ball (balloon). The balloon analogy is just that, an analogy. The 2D surface is an analogy for the 3 dimensions of space. However, the 3rd dimension of the balloon is analogous to nothing. If you lived on the surface of the balloon as a 2D creature you would have no access to the 3rd dimension, even though the surface curves. Now, as it happens, it's a 3D world, and space is curved, but don't mistake that for the implication that it is curved in 4D and there is a center there. Within our 3D space there is no center.

Technical it is curved in 4D space-time, but as you infer that doses not imply that curvature is into some additional 5th dimension, the 3 dimensions of space and one of time are sufficient for that curvature.

 

[MG1962]

Just at the momment. Jupiter is pretty much in the right direction....In the sky so to speak

Here is a diagram to help

http://www.earthsky.org/skywatching/

 

[wollery]

eehm, isnt it the case that we cannot see that center, or know where it is, but actually there must be a center.

Sorry, but no. Hard as it may be to wrap your head around that fact.

The Universe is an infinite 4D curved space-time, but we only perceive it in 3D. The balloon analogy is perfect to try to understand this. The surface of the balloon has no centre, and no preferred vantage point - all points on the surface are the same.

 

[The Man]

Circles and other spherical shapes have centers (generally defined as equally distant from all points on the circumference or surface). An ellipse has two foci and a center as it can be considered a circle viewed at an oblique but the foci are more related to the defined center of a circle where the sum of the distances from a point on the ellipse to each focus remains constant. Even oddly shaped masses have centers of gravity, curves do not necessarily have a center unless of course they are part of a circle or sphere (as far as I can recall).

 

[Bell]

Sorry, but no. Hard as it may be to wrap your head around that fact.

The Universe is an infinite 4D curved space-time, but we only perceive it in 3D. The balloon analogy is perfect to try to understand this. The surface of the balloon has no centre, and no preferred vantage point - all points on the surface are the same.

If I take this balloon analogy literaly, I asume all the stars, all the planets, are positioned on a spehrical plane (like putting dots on a balloon with a pen). But surely that sphere has a center?

Once again, I imagine space to be spherical, expanding from the point of the big bang. And between the edge of space and the center, are all the stars and planets and whatnots.

I would like to get recommendations for books that would, in layman terms, explain the universe as it is understood today.

 

[sol invictus]

Circles and other spherical shapes have centers (generally defined as equally distant from all points on the circumference or surface). An ellipse has two foci and a center as it can be considered a circle viewed at an oblique but the foci are more related to the defined center of a circle where the sum of the distances from a point on the ellipse to each focus remains constant. Even oddly shaped masses have centers of gravity, curves do not necessarily have a center unless of course they are part of a circle or sphere (as far as I can recall).

None of those things are like the universe. The universe is observed to be homogeneous and isotropic, like the surface of a sphere, hyperboloid, or infinite plane (only in 3 dimensions). None of those surfaces have centers - every point is identical in every way to every other point - and neither do their 3D analogues.

If you want another example, imagine an explosion which took place in infinite 3D space (forget about the expansion of space, relativity, curvature and all that). Suppose this explosion has the characteristic that, starting from a given origin, the exploding stuff a distance d from that point in any direction is moving away from it at speed H*d, where H is a constant (with dimensions of 1/time). That means a time 1/H ago, all that stuff was piled on top of the origin. Sure sounds like that origin is the center of the space, right?

Wrong.

Pick a different point to be the origin, and go to a reference frame that's moving with the stuff there. What's the rule for how fast things are moving with respect to that point in the new frame? Well, the stuff at the original origin is moving away from it at speed H*d. And you can quickly check that the stuff at every other point is moving directly away from it according to exactly the same rule as the first point!

So, for every point there's a choice of reference frame in which that point is the center of the universe, and the exploding stuff is isotropic around it. In other words, this explosion is homogeneous and isotropic (and is what's called an open universe in cosmology).

 

[RecoveringYuppy]

If I take this balloon analogy literaly, I asume all the stars, all the planets, are positioned on a spehrical plane (like putting dots on a balloon with a pen).

Yes, dots on a ballon, exactly right (but not sure what you mean by "spherical plane", I'll just assume you mean the surface of the balloon)

But surely that sphere has a center?

Yes, but as you just described, that center is not part of the current universe since the current universe is on the surface of the sphere.

Once again, I imagine space to be spherical, expanding from the point of the big bang.

The "point" of the big bang doesn't exist any more and every point in the current universe was in that point way back when and all current points have equal claim to that point.

And between the edge of space and the center, are all the stars and planets and whatnots.

No, the stars and planets are on the surface of that (hyper)sphere. All the "stuff" you imagine to be in the center of that sphere isn't "stuff". In some sense the interior (and the exterior for that matter) of the sphere can be viewed as other points in time, not other points in the current universe (someone more knowledgable can probably critique that idea)

 

[Jeff Corey]

Courtesy of the Bad Astronomers and friends, right about here http://www.boston.com/bigpicture/2008/12/hubble_space_telescope_advent.html?status=complete
Not really, but they were cool pictures.

 

[roger]

Bell, imagine you live on the balloon, and are a 2D creature. You cannot look up, above the balloon's surface, nor can you look below it. Furthermore, you cannot conceive of up and down, except as a mathmatical construct. As a 3D person, if I tell you there is a 4th dimension with a direction twizle, can you look, or even imagine, looking twizle? Of course not. It's outside your keen. For the 2D person, down is just as imaginary.

So, as a 2D person, you post on JREF, where is the center of the universe? I would like to walk to it. Surely you see any answer we gave you in that 2D world would not make any intuitive sense to you, and that there is no way to walk to the center. In exactly the same way, you cannot understand center about this 3D universe, and there is no way you can fly a spaceship to the center. It's just impossible. No matter how much that 2D creature walks around the balloon he will not get to the "center" of the 3D balloon. Likewise, in this 3D world there is no direction you can point, no place you can get to, that would be considered the center of the universe.