The thing about scientific theories is that there is no point about believing them or not. They work anyway.

You see, a scientific theory is an explanation of a phenomenon in nature, based on and supported by evidence, and with predictive properties which you can use or test against future evidence. They are also provisional, and can be amended or replaced by a better theory which explains the same things as the old, but better and/or more.

What you can do is to either accept them and use them or not accept them and then try to test them until they break and you have to find a new better theory. Do that thing breaking and finding well, and you may have to go to Stockholm to receive a gold medal and a million bucks from the King of Sweden.

Don't you think that the universe suddenly appearing out of nowhere is a bit strange?

That’s actually not what Big Bang cosmology states. It says that the universe was incredibly hot and dense at one point in the distant past, and now it is cold and empty. It explains how that happened, what happened in between, and it bases this on stuff which we can see and measure – including the afterglow of that hot and dense state in the past.

What it does not say is that the universe began from nowhere.

The longer explanation is that Big Bang cosmology in large part is based on the Friedmann-Lemaître-Robertson-Walker metric, named after four guys who independently discovered that if Einstein’s general relativity was true, then the universe cannot be stable and must in fact expand. That means that distances are longer in the future, and shorter in the past. The number describing how much longer or shorter is called the “scale factor”.

If you extrapolate backwards, you reach a point where the scale factor is zero, meaning that distances are zero. This is the infamous “singularity” in Big Bang cosmology. But that has its own problems, for instance that conditions are so extreme that the force of gravity must unite with the other three fundamental forces, electromagnetism and strong and weak nuclear force.

And here is the problem: while quantum mechanics can handle the unification of the other three, you need to combine the physics of gravity – general relativity – with the physics of the other three – quantum mechanics into a Theory of Everything. And, uh, we don’t know how to do that. As a result, we do not know anything about what happened in the first trillionth of a trillionth of a trillionth of a second (the point in time where you have to rely on a Theory of Everything to describe what happens), including whether that first trillionth of a trillionth of a trillionth of a second was actually that long, or even if there was a singularity. So Big Bang cosmology kinda ends at that time, and therefore does not say that the universe suddenly appeared out of nowhere.

Scientists have been trying to find out plausible hypotheses of what could have happened in the earliest moments of the universe and where the universe came from. Possible answers include a phase-shift of this universe, an earlier universe, or indeed nothing. As far as we know, neither of those hypotheses actually violates physics as we know it. But they cannot test those hypotheses, so they remain hypotheses, and are not part of Big Bang cosmology.

So Big Bang cosmology does emphatically not say that the universe appeared out of nowhere.

That said, how the universe started probably was strange. Quite a lot of physics is really weird, and cosmology is no exception.

Do you know who claims that the universe appeared out of nowhere?

Creationists

Yep, creatio ex nihilo – “creation out of nothing” – is Creation dogma and doctrine.

FatherOfJesus:
The thing about scientific theories is that there is no point about believing them or not. They work anyway.

You see, a scientific theory is an explanation of a phenomenon in nature, based on and supported by evidence, and with predictive properties which you can use or test against future evidence. They are also provisional, and can be amended or replaced by a better theory which explains the same things as the old, but better and/or more.

What you can do is to either accept them and use them or not accept them and then try to test them until they break and you have to find a new better theory. Do that thing breaking and finding well, and you may have to go to Stockholm to receive a gold medal and a million bucks from the King of Sweden.

Don't you think that the universe suddenly appearing out of nowhere is a bit strange?

That’s actually not what Big Bang cosmology states. It says that the universe was incredibly hot and dense at one point in the distant past, and now it is cold and empty. It explains how that happened, what happened in between, and it bases this on stuff which we can see and measure – including the afterglow of that hot and dense state in the past.

What it does not say is that the universe began from nowhere.

The longer explanation is that Big Bang cosmology in large part is based on the Friedmann-Lemaître-Robertson-Walker metric, named after four guys who independently discovered that if Einstein’s general relativity was true, then the universe cannot be stable and must in fact expand. That means that distances are longer in the future, and shorter in the past. The number describing how much longer or shorter is called the “scale factor”.

If you extrapolate backwards, you reach a point where the scale factor is zero, meaning that distances are zero. This is the infamous “singularity” in Big Bang cosmology. But that has its own problems, for instance that conditions are so extreme that the force of gravity must unite with the other three fundamental forces, electromagnetism and strong and weak nuclear force.

And here is the problem: while quantum mechanics can handle the unification of the other three, you need to combine the physics of gravity – general relativity – with the physics of the other three – quantum mechanics into a Theory of Everything. And, uh, we don’t know how to do that. As a result, we do not know anything about what happened in the first trillionth of a trillionth of a trillionth of a second (the point in time where you have to rely on a Theory of Everything to describe what happens), including whether that first trillionth of a trillionth of a trillionth of a second was actually that long, or even if there was a singularity. So Big Bang cosmology kinda ends at that time, and therefore does not say that the universe suddenly appeared out of nowhere.

Scientists have been trying to find out plausible hypotheses of what could have happened in the earliest moments of the universe and where the universe came from. Possible answers include a phase-shift of this universe, an earlier universe, or indeed nothing. As far as we know, neither of those hypotheses actually violates physics as we know it. But they cannot test those hypotheses, so they remain hypotheses, and are not part of Big Bang cosmology.

So Big Bang cosmology does emphatically not say that the universe appeared out of nowhere.

That said, how the universe started probably was strange. Quite a lot of physics is really weird, and cosmology is no exception.

Do you know who claims that the universe appeared out of nowhere?

Creationists

Yep, creatio ex nihilo – “creation out of nothing” – is Creation dogma and doctrine.

Thump's Up!
I love this explanation of Big Bang Theory!