How far until nothing?

[PB666]

Regarding the universe vs. the observable universe, something's been bugging me of late. How, specifically, do we know for sure that the universe is so much bigger than the observable portion, or bigger at all?

- You say in the OP that if the CMB were near the edge of the universe, a "hole" would appear from which the radiation would fade over time. Okay. Well we haven't been around nearly long enough to be able to measure any such change. Perhaps it is fading, but since we're basically looking at a freeze-frame, we can't tell. And coincidentally... there IS a mysterious dark patch in the CMB. I'm not going to jump to conclusions here, but it could be related.

- We keep building bigger and more sensitive telescopes, but we've never looked so far into the past that we see the primordial universe. Sure, we've spotted the CMB, and distant quasars appear younger, but where is the dense, super-distorted cloud of proto-galaxies we should be seeing out there at around 13.7 billion light-years? Rather, what we see are more and more fully-formed galaxies, then... nothing at all. This could mean that the universe is enormous and the light simply hasn't arrived yet, but there's little reason we shouldn't be able to detect the light from the beginning of the universe (again, we can see the CMB, but what about light from just after that?). And perhaps our telescopes just aren't sensitive enough yet, in which case we'll find out when we find out.

The fact that beyond the visible galaxies we see nothing suggests about as strongly, given Occam's Razor, that there aren't any more and we're looking at the edge.

They call it the opaque phase or era for a reason. What is believed to have happened is that energy they poured into the late inflation phase generated immense amounts of hv and highly exotic matter and antimatter. Eventually this spread out enough that normal plasma was stable and finally to the point that normal hydrogen and helium were stable, the universe went black. Radiation is scattered by cetain forms of dense matter but not others. The type of dense gas in the early universe scatters much of the higher energy radiation causing it to be opaque to our view. It is difficult to see the first stars this is because they blue light of these stars is scattered by the dense gas that surrounds them, but there are areas of space that allowed some earliest galaxies to be seen. Thus there were 2 opaque phases the initial and the post-starformation phase.

http://www.scientificamerican.com/article/light-from-universes-first-stars-spotted-in-hubble-photos/

Edited October 7, 2015 by PB666

[YNM]

That's usually how it's presented, but the universe is, of course, 3-dimensional.... The only possible solution (to my mind) is that black holes represent an 'outlet' for the extra spacetime resulting from expansion of the center/middle regions of the universe. This could (theoretically) be shown by finding a distribution of black holes on an intergalactic scale, which is utterly impossible at the moment. Otherwise, we have to accept that some regions of spacetime are vastly more concentrated than others, or expanding more slowly.

Regardless, I don't see how it's helpful to think of a 3-dimensional structure in 2 dimensions, in order to 'make it fit' our current understanding.

It's just the same when thinking of 4-dimensional spacetime with our 3-dimensional space understanding. Minkowski spacetime is easy - you can contract the extra time dimension into informations, which is pretty much chasing you at c wrt space (AND you in the same "instance"), but start getting into robertson-walker spacetime, especially for curved cases, and you just lost account of that. Even more so for real GR implementation (robertson-walker are more or less regarded as the same, homogeneous in all site), where a shift in a few real (and even more for metric) meters can change the output a lot. This is why people simplify them down in order to grasp a bit. The maths may be there but actual grasp may not be there...

@ Darnok : That's why we have spectrometers.

@ parameciumkid : Well, for one, proto-galaxy would be faint - I mean, we even haven't found evidence for third generation star - and so requires even better telescope to capture them intact.

[PB666]

It's just the same when thinking of 4-dimensional spacetime with our 3-dimensional space understanding. Minkowski spacetime is easy - you can contract the extra time dimension into informations, which is pretty much chasing you at c wrt space (AND you in the same "instance"), but start getting into robertson-walker spacetime, especially for curved cases, and you just lost account of that. Even more so for real GR implementation (robertson-walker are more or less regarded as the same, homogeneous in all site), where a shift in a few real (and even more for metric) meters can change the output a lot. This is why people simplify them down in order to grasp a bit. The maths may be there but actual grasp may not be there...

@ Darnok : That's why we have spectrometers.

@ parameciumkid : Well, for one, proto-galaxy would be faint - I mean, we even haven't found evidence for third generation star - and so requires even better telescope to capture them intact.

There are nearly hydrogen stars in our galaxy and if you check the link http://www.scientificamerican.com/ar...hubble-photos/ this appears to be what they are referring to.

[Whirligig Girl]

I don't see the fun in speculating about tooth fairies or pink unicorns. This is on the same level.

I'd like the point out the same was said about black holes back in the day*.

But seriously, Einstein's theory of Special Relativity says you can't go faster than light. We definitely have no idea how to do it. It's handwavium, not unobtanium. We don't know how to build antimatter reactors, but we can calculate them, and thus it is unobtanium. We can't calculate faster than light travel because there are no theories to describe it. All FTL travel is handwavium.

(Disclaimer) *According to a Stephen Hawking book I read four years ago. I never existed during a time when people said black holes were like fairy tales. I've only heard of it.

Edited October 7, 2015 by GregroxMun