Question about direction

[bdewoody]

One thing my feeble mind has failed to grasp and that explanations have failed to explain is. Why is it that no matter which direction we look in space there are objects that are 13.7 +- billion light years away ie. objects created shortly after the Big Bang? To me its almost as if we are inside a gigantic imploding sphere and yet we are moving away from everything else out there.

To me the explanation of all the missing matter is that we can't see or detect it because it's too far away. Even using the expanding balloon analogy there are directions where you don't see back to the beginning. It just doesn't make sense to me. What does make sense if that if we are moving away from some point of origin there are objects that should be moving in the opposite direction and the light from those objects will never get here.

But if this is true then there should be some directions that we look where the space is empty and that isn't true either. The way I understand it no matter where they point a telescope if they leave it pointed there long enough distant objects will come into view. What's going on?

 

[MeteorWayne]

The Universe is far bigger than what we can see, because of how much it has expanded. No matter which direction we look, we can only see objects that are within 13.7 b LY of us. There's stuff beyond that we can not see anymore.

That doesn't explain dark matter, because dark matter is needed to explain the otion of galaxies, galaxy clusters, and gravitation lensing by both within our 13.7 bly visible bubble.

 

[SpaceTas]

Your feeling that we a looking at the inside of something larger is correct.

Here is where we need 4 Dimensions. But we can't think in 4D (maths just an extension of 3D maths) so I'll use an old analogy. Image that you are a flatlander (Great book called Flatland) or say an ant on the surface of a big balloon. You cannot see the 3rd dimension, you can only see, move and think in 2D, forward/back side to side. Now on this balloon there are glowing dots (galaxies). This balloon once started out a lot smaller: in fact a point in 2D and 3D space, and is now expanding. So to our flatlander all the glowing points are moving away from it. Of course You as a 3D being can see that going to another glowing dot, another flatlander would see the same thing; all the galaxies moving away.

The spherical geometry is just one of many possibilities. It's easiest to do an analogy. It represents a closed finite universe.But if instead of sphere our flatlaner lived in a saddle shaped universe: the whole universe just getting larger in scale. You see the same pattern of galaxies moving away from each.

Now to explain the "horizon" problem. Go back to being a flatlander on a balloon. Taking the current rate of expansion the flatland astronomers figure the universe formed in a big bang, where space-time-matter all started. For their universe is 10 billion years old (nice even number). They wonder how-come the universe looks the same every where and how-come they see galaxies on opposite sides of the sky, 9.5 billion light years away. So the galaxies are further apart than the age of the universe! Even worse they have detected a cosmic microwave background, from the hot early universe; and it is too uniform to explain the origin of superclusters of galaxies. With opposite side further apart than the age of universe there is no-way a light signal, or any other could smooth out EVERYTHING. So a theorist comes up with the idea that the universe is 3D (for us 4D) and very early on expanded near the speed of light for a short interval. This theory was given the name inflation. During inflation any lumpy-ness was stretched-out (smoothed out).

The inflation interval expansion being near the speed of light is important; because at such speeds distances do not scale linearly. The net result is that the universe is bigger than its age. The flat-landers can look back 10 billion years in every direction to a horizon in every direction.A circular patch on the balloon. We can look back to our 3D sphere in some 4D shape. The exact size of this look-back region depends on the shape (balloon, saddle, do-nut, honeycomb ...).

So now the Earthly astronomers are looking for clues to what the shape is: so far looks flat (no curve) and with the just right of total energy/mass to have it just expand forever. That leads to dark matter, dark energy but I need to cook dinner and do some data analysis ...

Recommended reading:
"The first 3 minutes" (pre-inflation description of big bang) I haven't read a good post inflation book, but there are lots of articles in astro and science magazines...keep an eye our for public lectures from unis observatories ...
Flatland.
check out books by Paul Davis.