In popular science (SciPop) the reason why we can detect a distant brightness is because opposing forces, the solar wind pushing out and interstellar forces pushing in, cause glowing Hydrogen to accumulate, like foam on a beach.
The third heaven is the dome or firmament, which is a sea of glass. It's a rigid crystalline sphere on the edge of space which formed in response to the creation of gravity on the second day.
Most of the space between the firmament and Earth is the cosmos or observable universe. There's something very odd about the cosmos: there's a disconnect between what we can see vs. what we believe about it.
Part of the space between the firmament and Earth is the area in contact with the Earth that we call the atmosphere, or sky. This is where the birds fly. It's referred to as the open firmament.
How do we know that the next life is constructed from a series of elements which we have no earthly counterparts for? It's not possible to make gold pure enough that it becomes transparent like glass.
In the particle trinity which we deduced from the first two verses of Genesis, the Holy Spirit is Omega, Oxygen. However, the Holy Spirit can't be just any Oxygen, or everyone would be filled with the Holy Spirit all the time.
Given that the apostle Paul specifically refers to something called the third heaven it's not a stretch to conclude that there must also be a first and a second heaven. We need to know what they are.
SciPop is finally getting up to speed on the idea that there's a sphere of rigid crystal on the edge of space: the firmament.
The Lord Jesus refers to Himself as the Alpha and the Omega. There's more than one way to understand this, but it's possible to use deduction to ascertain which is the correct one.
There won't be a temple in the New Jerusalem because there won't be any need for a symbolic representation of God. His glory will be the light we see for the rest of forever.