I If all of spacetime was created with the Big Bang....

[rumborak]

...why do people like Stephen Hawking talk about things/events "before" the Big Bang? If time (as part of spacetime) was created with this event, it also marks the point in time that had no "before", doesn't it?

 

[Drakkith]

It's believed that the big bang singularity, which is what leads people to say that spacetime was "created" in the big bang, is simply an artifact of our incomplete knowledge of physics at the extreme energy and density scales of the very early universe. It's a bit like predicting that the EM force becomes infinite as you approach the center of an atom. Before the advent of quantum physics we had no idea why the force did not become infinite, even though our theories predicted it would. Now we know better. Same for the big bang. That's why physicists like to talk about things that happened before the big bang. They know that our theories and models are likely incorrect and are continuing the search for better and more accurate theories.

 

[sophiecentaur]

That's why physicists like to talk about things that happened before the big bang.

Caveat - only Physicists who know what they're talking about. Common clods like you and me need to be very careful about that.

 

[PeterDonis]

why do people like Stephen Hawking talk about things/events "before" the Big Bang?

Because they're using the term "Big Bang" properly, to refer, not to an "initial singularity" in idealized models that we know don't correctly describe the very, very early universe, but to the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. We don't know for sure what preceded that state, but the current best hypothesis is that it was preceded by an era of inflation.

 

[rumborak]

Well ... but doesn't that usage imply the assumption that normal physics prevailed during that process, i.e. that spacetime was "intact" enough to give a notion of a "before"? It's probably a good assumption ("barring contrary evidence, assume everything stays the same"), but at the same time the event is so outside of normal physics operation that it's not (I would think).

 

[Jetro]

What would you call the "time" before space-time?

 

[PeterDonis]

doesn't that usage imply the assumption that normal physics prevailed during that process, i.e. that spacetime was "intact" enough to give a notion of a "before"?

If you mean, is there spacetime "before" the Big Bang when that term is used properly, yes, there is. As I said, we don't know for sure what occupies the spacetime before the Big Bang, but our best current hypothesis is that it was an era of inflation.

 

[PeterDonis]

What would you call the "time" before space-time?

There is no such thing.

 

[rumborak]

There is no such thing.

Disregarding the Big Bang event for a moment, I find that topic incredibly interesting from a standpoint of causality. At least to me, causality implies the requirement of time. So, if it is nonsensical to ask "what was before spacetime", then isn't nonsensical to ask "what casued/created spacetime"?
(Totally aware that I am straddling philosophical/religious considerations here, I just find the thought that millenia of questioning might eventually be answered by "it's a stupid/nonsensical question", somewhat amusing)