“Yes, they are.”
No. Theories are developed, not proposed.
Below is a generalized sequence of steps taken to establish a scientific theory:
Choose and define the natural phenomenon that you want to figure out and explain.
Collect information (data) about this phenomena by going where the phenomena occur and making observations. Or, try to replicate this phenomena by means of a test (experiment) under controlled conditions (usually in a laboratory) that eliminates interference’s from environmental conditions.
After collecting a lot of data, look for patterns in the data.
Attempt to explain these patterns by making a provisional explanation, called a hypothesis.
Test the hypothesis by collecting more data to see if the hypothesis continues to show the assumed pattern. If the data does not support the hypothesis, it must be changed, or rejected in favor of a better one. In collecting data, one must NOT ignore data that contradicts the hypothesis in favor of only supportive data. (That is called “cherry-picking” and is commonly used by pseudo-scientists attempting to scam people unfamiliar with the scientific method. A good example of this fraud is shown by the so-called “creationists,” who start out with a pre-conceived conclusion - a geologically young, 6,000 year old earth, and then cherry-pick only evidence that supports their views, while ignoring or rejecting overwhelming evidence of a much older earth.)
If a refined hypothesis survives all attacks on it and is the best existing explanation for a particular phenomenon, it is then elevated to the status of a theory.
A theory is subject to modification and even rejection if there is overwhelming evidence that disproves it and/or supports another, better theory. Therefore, a theory is not an eternal or perpetual truth.
Yes yes I know all that.
What happens when the experiments to confirm the hypothesis can’t be performed?
BBT has had a run, future data will modify it or subsume it or return to validate it. Only time will tell.