As I have stated previously, the Big Bang theory only focused on the cosmology of the Observable Universe.
And to date, what is observable is right up to sky survey made by several space missions that mapped out the Cosmic Microwave Background Radiation (CMBR):
- Cosmic Background Explorer (COBE), 1989 - 1993
- Wilkinson Microwave Anisotropy Probe (WMAP), 2001 - 2010
- Planck (Planck Surveyor), 2009 - 2013, ESA mission
The Planck has instruments that have higher resolution & sensitivity than that of WMAP’s instruments, so the CMBR images and data are more accurate. Below, is the CMBR map by ESA’s Planck:
View attachment 96071
According to the 2013 data release of the Planck, the Universe is 13.798±0.037 billion-years-old, at the above image occurred during the start of the Recombination Epoch, when the Universe was about 370,000 years old.
The Recombination Epoch was time when the nuclei of ionized elements were bonded with electrons for the first time, thereby atoms became electrically neutral. This caused 2 things:
- the Universe, or more precisely “space” became transparent for the first time (prior to that the Universe was opaque, because the universe was just hot plasma),
- and the bonding caused photons (light) decoupled and traveled freely through space (whereas before photons were scattered due to Universe being hot opaque plasma).
When the Universe was hot plasma, and all atoms were completely ionized (no electrons attached to these early atoms), as I stated the universe was opaque, thereby acting like Event Horizon, where no technology could observe beyond the CMBR. This make it difficult to observe the Universe prior to the Recombination Epoch, however the CMBR do provide some details as to what happened before this epoch, that astrophysicists can summarise as to how early atom, smaller particles formed, and when the cosmic inflation occurred.
As how to your question -
“Can you confirm, you do believe the universe is expanding, yes?”
The answer is yes.
Since you don’t understand the balloon analogy, I won’t use here.
The Universe is expanding, because of the earlier predictions made by Alexander Friedmann (1922) & Georges Lemaître (1927) use the FLRW Metric on Einstein’s Field Equations (hence it is renamed Friedmann Equations when using this metric), and Lemaître’s prediction of the Redshift.
The Redshift is the distance measurement of the distant galaxies or other objects, based on the visible light spectrum. The more distant the galaxy, the more the wavelength of the object will appear towards the red end of the EM spectrum. That‘s indication the object (eg galaxy) is moving away from the Observer, hence the indication that these objects also moving away from each other, and the Universe is expanding.
Edwin Hubble made the discovery in 1929, so it was the earliest evidence for the expanding universe model. The Friedmann equations and the Redshift together formed the Hubble’s Law, that not only the Universe is expanding, it also appeared to be isotopic.
Ever since 1929, many observatories have been using the Redshift Survey to map all astronomical objects, eg stars, galaxies, galactic clusters, quasars, etc. Examples, 2dF Galaxy Redshift Survey, Sloan Digital Sky Survey, DEEP2 Redshift Survey, etc; each of these observatories have made over 100,000 redshift measurements. The Hubble & JWST also make such measurements.