Center of our galaxy and the universe

[arthwollipot]

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

Einstein's Universe by Nigel Calder is pretty good. A Brief History of Nearly Everything by Bill Bryson is also a good catch. It has a pretty good summary of cosmology. If you want to get a little deeper, The Elegant Universe by Brian Greene explains it all very well, within the framework of string theory. But that might not be your cup of tea.

 

[~enigma~]

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.

Reader's digest version of Edwin Abbot's Flatland

 

[MG1962]

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.

Simply breath takingly stunning, thank you for sharing. Some have been around for a while, some I've never seen before

 

[quarky]

The center exists in a different time. Yet, even then, pre-bang, it wasn't really a center, because there was no non-center to define it.

 

[tomwaits]

The center of the universe is t=0. Too bad, you missed it.

 

[Jeff Corey]

http://www.youtube.com/watch?v=buqtdpuZxvk&feature=channel_page

 

[godless dave]

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?

Yes. It's in the past. In this analogy, anything inside the sphere is in the past.

 

[arthwollipot]

It has been mentioned before, but it's worth mentioning again - since at the time of the big bang, every location was on top of every other location, the centre of the universe is everywhere.

 

[DC]

im very good in 2D and 3D. but not with an aditional Dimension
I had already huge problems when i learned that Time is not a constant

i imagen the Universe as a collection of planets and suns and gas clouds etc.

like when you trow a million golfballs in to the air, and while they are still in air, they have a center.

but i guess im wrong. that darn time is messing up my understanding of space

 

[sol invictus]

im very good in 2D and 3D. but not with an aditional Dimension

You don't need 4D or curved spacetime to understand this:

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 directly away from the origin 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 explosion, 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).

 

[DC]

my problem is in Time.
when we talk about a center of a City for example, we dont mind how big the city was 40 years ago. we talk about now. and we can define pretty exactly where the center is.

i think the same about the universe. could we take a picture from above the whole universe and from the front and from the side. we could define where the center of the universe is at the time the pictures was taken.

the point of origin is everywhere, because at the start all the points was on one point.

But i guess i totaly missunderstand it once again i better get to lurking

 

[sol invictus]

my problem is in Time.
when we talk about a center of a City for example, we dont mind how big the city was 40 years ago. we talk about now.

Same for the universe - not a problem.

i think the same about the universe. could we take a picture from above the whole universe and from the front and from the side. we could define where the center of the universe is at the time the pictures was taken.

What if the universe is infinitely big? Maybe we should start from that - where is the center of an infinite perfectly flat and uniform plane?

the point of origin is everywhere, because at the start all the points was on one point.

That's not the reason. The reason is that every point is identical (on average) to every other point, so there is no way to pick one and call it the center. Forget about the past - we can discuss this at one time.

 

[DC]

Same for the universe - not a problem.



What if the universe is infinitely big? Maybe we should start from that - where is the center of an infinite perfectly flat and uniform plane?



That's not the reason. The reason is that every point is identical (on average) to every other point, so there is no way to pick one and call it the center. Forget about the past - we can discuss this at one time.

well then i have an infinite problem taking my pictures to find the center

but atleast now i get the ball surface analogy

alsong we dont know which and if there are the outmost Planets we can indeed not find a center nor know if there is a center.

thanks that helped i think

 

[asmodean]

Einstein's Universe by Nigel Calder is pretty good. A Brief History of Nearly Everything by Bill Bryson is also a good catch. It has a pretty good summary of cosmology. If you want to get a little deeper, The Elegant Universe by Brian Greene explains it all very well, within the framework of string theory. But that might not be your cup of tea.

I'd say Simn Singhs "Big Bang" is quite decent. A lot of history before leading p to the formulaton of BB, but ay shed some light.

Otherwise, Kip Thornes "Black Holes and Time Warps: Einstein's Outrageous Legacy" while mostly focusing on black holes contains a bit of useful info as I recall it.

Hawkings "A brief history of the Universe" may alose contain some nuggets.

Beware, there will be much talking about bowling balls on rubber sheets.

 

[asmodean]

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.

Others have most likely already given explanations for this, but yeah. You see the ballon as a 2D surface embedded in 3D space and use the 3D-space as your model of the universe. But, we're not embedded like that, and the 2D-surface is all the room dimensions there are.

The third room coordinate could perhaps be thought of as a time axis, the balooon expands in time (as we see t, grow in volume) and in space (the surface expands). The "center of the sphere" would then be our 2D universe at t=0, and the inflated baloon would be our universe at t=now. Obviously there's no spatial centre for our 2D universe, and as we sit in one of our dots on the surface we will see all the other dots speed away from us. Of course, anyone else sitting on another dot, will likewise see all other dots speed away from them.

No one will see the dots speed away from the 3D center, except as more grey hairand a endency toramble about the good old days.

 

[roger]

Here's another, more intuitive way to think about it.

Imagine you have a spaceship that can go arbitrarily fast. A google^google lightyears in a nanosecond and far more. Take off from here. What happens? Do you hit a boundary? Are you stopped at some point? Do you loop around to the starting point or just keep going forever?

If you don't hit a boundary, how would there be a center in the space you have explored?

This is just a drawn out version of Sol's infinite plane question. It doesn't matter too much if the span is infinite, or curves back on itself like a balloon. You never stop, you never reach a boundary, and I've yet to see a mathamatical description of "center" that does not involve measuring from a boundary.

 

[Bell]

Thanks for all the feedback. I find it indeed hard to think outside the 3D box, but it slowly starts to make sence to me how to look at the universe. But I need to read up on that some more (I'll check out those recommended books).

I allways thought that the universe expanded 3 dimensional, away from it's point of origin (the Big Bang) and so the universe was finite. It also puzzled me what then was outside our universe.

 

[~enigma~]

Thanks for all the feedback. I find it indeed hard to think outside the 3D box, but it slowly starts to make sence to me how to look at the universe. But I need to read up on that some more (I'll check out those recommended books).

I allways thought that the universe expanded 3 dimensional, away from it's point of origin (the Big Bang) and so the universe was finite. It also puzzled me what then was outside our universe.

The same point Roger made above can be used to show that there is no "outside" the universe either. So just like saying the center is everywhere, we can say "outside" everywhere or IOW THE UNIVERSE IS EXPANDING INTO ITSELF.

 

[fishbob]

The center of the universe is t=0. Too bad, you missed it.

My understanding - correct me if I am wrong:
Go outside with your camera pointed any direction in 3D space, and you are looking back towards t=0. The light getting here now left those stars at t + 'a bit', so as you look at objects that are more distant, 'a bit' gets smaller, and you are getting closer to t=0.

Jeff Corey: Hubble-icious.

 

[DC]

how would there be a center in the space you have explored?

its in the middle of the parts you have explored already

but i get what you mean.

most accept that it is infinite. i have troubles with that.