If something is out there, you shall never see it.
It is very difficult to imagine the Universe in creation, at least as we observe it at present. There are many hypotheses trying to describe this creation. The mostly accepted is the Big Bang (BB) theory. Let me try to describe my own imagination of the Universe creation phenomenon.
Let think that vast empty space existed before the BB occurred. This presumption needs one or more highly energetic space, may be flat-like "Branes". Never mind, something was there before BB, but it wasn't matter nor an electromagnetic field. It was only space, and there was a lot of it. I am not sure what happened, but some assumptions predict Branes collided in some point.It is supposed to trigger the BB and creation of our Universe (1).
Now, in place of this collision, unusual phenomena occur. Mysterious space Brane energy (you may call it the dark energy (2) burst in the form of electromagnetic field creation. This inflationary expanding space, was filled with extremely heavy, bright and hot light, the photon epoch (3). After expansion of this field, the universe became transparent and the cosmic microwave background radiation was created and then structure formation took place, elemental particles and matter in the form of stars, planets, galaxies, black holes and others were formed (4). Let assume that all this exploding Universe expands all the time since Branes collision 13.8 milliard years ago.
As the consequence of described above phenomena, the electromagnetic field was created and which may be observed as the cosmic microwave background radiation. In effect we are able to observe all material objects that exist within our observable Universe. We cannot see things that may exist beyond the borders of this electromagnetic field sphere that frames our observable universe. If you may imagine yourself to somehow walk beyond this frame and light a torch into your face, you cannot see this light because without an electromagnetic field that light cannot propagate through space. One cannot see through this space which does not have an electromagnetic field in it. Such empty space I propose to call the "Zweinstein Space" (ZS), and if something is out there, you shall never see it.
It is possible that fragments of ZS may exists also within our observable Universe. As the electromagnetic field is energetic, accordingly to the Einstein equation it may have mass, so will gravitate towards masses of galaxies and their clusters, creating halloes around them (can it be the dark matter?) and living huge empty voids in between. Such a place called the Local Void (150 million light years in diameter) (5, 6, 7) exists not far away from us. So, an electromagnetic field may not be present or is very week in such places. These voids may not be transparent to light and electromagnetic radiation may be propagated through detours, around these voids. In effects some lensing may be visible and be mistaken for gravitational lensing (8, 9, 10) caused by elusive and invisible dark matter.
When one ventures into such a void, similarly to being outside our visible Universe, shall never see any light of stars and galaxies since electromagnetic waves cannot be propagated in this environment. The only information that may come, may be delivered by gravitational waves.
One may imagine, that in future, gravitational waves shall play a role for investigating this elusive invisible Universe that may exist beyond and within our observable Universe.
(1) Musser, George; Minkel, JR (2002-02-11)."A Recycled Universe: Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase". Scientific American Inc. Retrieved2008-05-03.
(2) Davis Tamara M.; Gen Relativ Gravit (1014) 46:1731 "Cosmological constraints on dark energy.
(3) Allday, Jonathan (2002). Quarks, Leptons and the Big Bang (Second ed.). Institute of Physics Publishing.ISBN 978-0-7503-0806-9.
(4)A Brief History of Time is based on the scientific paper J. B. Hartle; S. W. Hawking (1983). "Wave function of the Universe".Physical Review D 28 (12): 2960.Bibcode:1983PhRvD..28.2960H.doi:10.1103/PhysRevD.28.2960.
(5)NAME LOCAL VOID -- Underdense region of the Universe". SIMBAD. Retrieved21 December 2014.
(6) Nakanishi, Kouichiro; Takata, Tadafumi; Yamada, Toru; Takeuchi, Tsutomu T.; Shiroya, Ryuichi; Miyazawa, Morio; Watanabe, Shigeo; Saito, Mamoru (1997)."Search and Redshift Survey for IRAS Galaxies behind the Milky Way and Structure of the Local Void" (PDF). Astrophysical Journal Supplement 112: 245.Bibcode:1997ApJS..112..245N.doi:10.1086/313039
(7) Univ. of Hawaii Institute for Astronomy (12 June 2007)."Milky Way moving away from void". astronomy.com. Retrieved2008-10-13.
(8) Drakeford, Jason; Corum, Jonathan; Overbye, Dennis (March 5, 2015)."Einstein’s Telescope - video (02:32)".New York Times. RetrievedDecember 27, 2015.
(9)Blandford & Narayan; Narayan, R (1992). "Cosmological applications of gravitational lensing". Annual Review of Astronomy and Astrophysics 30 (1): 311–358.Bibcode:1992ARA&A..30..311B.doi:10.1146/annurev.aa.30.090192.001523.
(10) Matthias Bartelmann and Peter Schneider (2000-08-17)."Weak Gravitational Lensing" (PDF).
