h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I just read a comment by Stephen Hawking. When asked, what happened before the Big Bang, he answered, that's like asking what is north of the North Pole.

The implication is: Spacetime is a fourdimensional whole. Time is fully contained in or wrapped up in space. So before there was space, there was no time either. Time came into being along with space. Thus there was no 'time' before the Big Bang.

Hawkings comparison is that we know the Earth is a sphere and that orientations like north, south, east and west, are totally bound up with its surface and constrained by its shape. Thus we can understand that there is nothing 'north' of the North Pole. Hawking implies that if we can understand this, we can understand how there was no 'before' the Big Bang.

The problem I have with his comparison is this:

We can visualise the shape of the Earth as a three-dimensional sphere. But we cannot easily visualise the four-dimensional hypersphere that is Space-time.

Furthermore, we all understand that 'north' or 'south' are not fundamental distinctions that apply to all of space; we understand that they are merely orientational directions that only apply to the sphere that is our Earth. It is only an arbitrary fact that the Earth is spinning around a stable axis, so 'causing' a distinction between North and South on it.

When we think of Time, however, it doesn't in any way seem to us that it is an arbitrary thing. Time and its distinctions don't seem to depend on some trivial fact like for instance the Universe spinning in a certain way. Time seems to be something much more fundamental. Especially: time goes from past through present to future ... or maybe one could better say, time moves backwards: the present turns into the past and the future turns into the present. There seems to be no way whatsoever to imagine time running differently than this. Einstein has changed the way we perceive time, but even in his system of relativity, Time is a sort of 'absolute' thing, and though there's no clear distinction between 'past' and 'future' it is still the case that every moment of time anywhere in the universe can clearly be indicated as 'before' or 'after' another moment in the same part of the universe. The speed of light is the maximum speed by which cause can cause effect, it is the maximum speed for conveying information and information cannot be conveyed instantaneously or backwards in time. Matter cannot travel back in time either.

Furthermore: when we think of the planet Earth, we know it is a solid body floating in space. Thus, when we say there is nothing North of the North pole, we still realise there is something 'beyond' both the North and South poles, though this 'beyond' cannot be indicated by our concepts of 'north' and 'south'. We know that 'north' and 'south' are limited to the Earth's surface, but there is a vast threedimensional space beyond the Earth's surface, where we can't use north, south, east or west to indicate directions, but still, we *can* create a threedimensional frame of reference by which any object outside of the Earth can be located.

But when we are asked to imagine the fourdimensional sphere that is the Spacetime of our Universe ... can we imagine it with *nothing* 'outside' or beyond it?

Maybe we cannot ever know what lies 'outside' it. But at the same time it is pretty much impossible (for me, at least) to imagine *nothing* being outside or beyond it. That is as difficult as imagining the Earth being the sole object in existence ... with no objects, no space, no nothing, beyond its borders.

So: when a child asks 'what is north of the North Pole', we may answer 'nothing' but then we need to explain to the child the shape of the Earth and the meaning of the term 'north', and also that there is something 'beyond' or 'even further than' the North Pole, but that it needs to be described by some different term.

So if I was a child asking what happened 'before' the Big Bang, why should I be satisfied with an explanation that doesn't tell me what lies 'beyond' or 'outside' the Universe? That asks me to imagine something I cannot: a hypersphere with nothing outside it?

Maybe the term 'before', applied to the Big Bang, is not appropriate ... like the term 'north', asking what is beyond the north pole, is not appropriate. But how would we categorise any kind of time-like or space-like dimension outside of the spacetime we know? Because... relative to such a frame of reference, there might very well have been something corresponding to 'before' the Big Bang, or 'after' the end of our Universe. Or just, 'beyond' or 'outside' the Universe we know, or anything we can ever know. Maybe we can never have concrete proof of this sort of thing... but, as a philosopher, I can conceive of such a thing, and I can conceive of it, much more easily (in fact infinitely more easily) than I can conceive of a universe that has nothing beyond or outside its own limited spacetime.