[opportunity (OP)]

It's a well know analogy used by Stephen Hawking to describe what happened before the big bang.

https://www.msn.com/en-au/news/techandscience/watch-stephen-hawking-explain-what-came-before-big-bang/ar-BBJPy5h?ocid=spartanntp

Any ideas? I've heard of things going south and how bad that is, so beyond south is indescribable?

What's the code of his description knowing magnetism is bipolar (has two poles)?

Is he suggesting a potential steady state system for instance? Nothing has been said, I'm just wondering on the questions scientists may have asked him about that analogy.

[evan_au]

There are some telescopes at the South Pole, and they point away from the North pole, at stars that are more "South" than the South Pole.
https://en.wikipedia.org/wiki/Antarctica_Schmidt_telescopes

But that's not really what Steven Hawking was talking about.
He was drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime. It's not fair to point out that his 2D analogy is actually embedded in 3D space!

A point off the two-dimensional surface of the Earth can satisfy the equations of the Earth's surface (an oblate ellipsoid) if the coordinates are imaginary.

In a similar way, a time before the Big Bang could be defined if the time were imaginary.

This is somewhat similar to the way that the dimensions of time and space get twisted when extrapolated across the event horizon of a black hole.

And the early universe was definitely a black hole!
See: https://en.wikipedia.org/wiki/Black_hole_cosmology

[Bill S]

He was drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime.

Valid as this might be mathematically, it involves imaginary time.   Is there a fundamental concept of imaginary time in physics?

I fail to see how drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime solves the problem of something emerging from nothing.

[opportunity (OP)]

He was drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime. It's not fair to point out that his 2D analogy is actually embedded in 3D space!

A point off the two-dimensional surface of the Earth can satisfy the equations of the Earth's surface (an oblate ellipsoid) if the coordinates are imaginary.

In a similar way, a time before the Big Bang could be defined if the time were imaginary.

This is somewhat similar to the way that the dimensions of time and space get twisted when extrapolated across the event horizon of a black hole.

And the early universe was definitely a black hole!
See: https://en.wikipedia.org/wiki/Black_hole_cosmology

Is there a reference for this I can read by those close to his work? I'm also thinking "Imaginary time" is crucial to post-"big-bang" theoretical dynamics, not prior "big-bang"; if you could provide references there (regarding imaginary time being pre-"big-bang" dynamics) I'd be more than happy to spend time reviewing that.

Your final point, in pointing to evidence of the early universe being like a black hole, well, is that not contradictory to how black holes are meant to perform as we "perceive/calculate" them....today....? For instance, the black holes we calculate today according to your suggestion would be responsible for supplementary universes on top of our own undergoing unique if not contradictory phases of development in an otherwise homogeneous universe... as we perceive it. The only thing I can think of to support your claim about black holes is that what we perceive of black holes in the universe is that they are somehow a reflection in a greater mirror enclosing a primary-universe that we would understandably live in. And "even then" that's a stretch of theoretical imagination.

[jeffreyH]

A function describing the path into a black hole is not continuous. There is a singularity at the event horizon. This is separate from the central singularity. You can describe this path with a differential equation. Whether or not continuous solutions exist is a big question.

[jeffreyH]

If the big bang's origin was a black hole then what collapsed to form it?

[Bill S]

If the big bang's origin was a black hole then what collapsed to form it?

This would work only if something existed before the BB/Universe.  In that case, the BB would be a local event within a wider cosmos.

No prizes for guessing who has no problem with that.

[evan_au]

If the big bang's origin was a black hole then what collapsed to form it?

This would work only if something existed before the BB/Universe.

We don't know what (if anything) existed before the big bang - Stephen Hawking is exploring mathematical possibilities.

But the moment the mass of our universe existed in this universe, with a diameter thought to be around that of a melon (after the hyperinflationary period), it's density exceeded that of a black hole. This means it was a black hole, regardless of what passed before.

Our universe is separated from what came before (although the concept of time becomes a bit imaginary when you go before the Big Bang), and we don't know how to go there (although the concept of place becomes a bit imaginary when you go before the Big Bang).

This is analogous to a black hole in our universe, whose interior is separated from our universe by the event horizon. We can't see what happens inside the black hole, although in theory you could go inside a supermassive black hole (just not come back). If you try to extrapolate what happens inside a black hole, it appears that the dimensions of time and space will get warped compared to our universe - in mathematical terms, they become imaginary.

With a bit more work, this might form a neat mathematical symmetry. But at present, it is really just a speculation that some cosmologists take seriously.

[opportunity (OP)]

I did some fishing for you Evan regarding your first response. I'd read the idea somewhere but not sure where, some time ago. Luckily it turned up today in the News, what it seems you were referring to, re. 2-d space:

http://www.foxnews.com/science/2018/03/05/stephen-hawking-says-knows-what-happened-before-dawn-time.html

I've got another question though re. the big bang: do you think it's possible time operates in "reverse" in a black-hole, say underneath the 2-d manifold?

[Colin2B]

Valid as this might be mathematically, it involves imaginary time.   Is there a fundamental concept of imaginary time in physics?

As you know imaginary numbers were very much misnamed when discovered, but they do have a physical significance in many situations. In the case of imaginary time there is no physical significance needed, as used by Hawkins, it is a mathematical work around by changing the metric to a Euclidian space which is far easier to handle. If you want to imagine what has been done, it is like rotating the time axis 90 so it is still orthogonal to the 3 space dimensions but now has the same sign (using East Coast convention). It’s known as a Wick rotation if you want to look up details.

I fail to see how drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime solves the problem of something emerging from nothing.

Hawkins was interested in a slightly different issue which is whether the start of time for our universe is from a point eg like a singularity or from a smoother surface - a boundary. A Euclidian space can be modelled as if it is surface of the earth (but you have to imagine that surface is 3 space dimensions) and if you imagine the start of time as the S Pole (in some lectures he uses N Pole) with time axis pointing to N Pole and 2 of the 3 space dimensions at rt angles , then the expansion from the s pole moves up the surface of the earth as a series of time-slice circles (but in 3D). The point about starting from the s Pole is that it is a smooth curve (boundary) rather than a sharp discontinuity like the point of a cone.
Hope that makes some sense.

[opportunity (OP)]

Sure does.

I'm also wondering though if there has been any debate on the idea of time moving in "reverse" as the underlying feature of the 2-d manifold pre-big bang.

[Bill S]

We don't know what (if anything) existed before the big bang

It's the "if anything" at which I tend to balk.

So are you going to take on the questions that so many people answer, without answering?

If there were ever nothing, how could there be something now?

Can anyone provide an example of something from nothing?

[Bill S]

Hope that makes some sense.

It does, thanks.  I was obviously looking for an answer to the wrong question.