Time in the Very Early Universe

[IM Egdall]

Just read Hawking and Mllodinow's new book The Grand Design. Very interesting. Although I thought it was way too short, and didn't go into concepts in nearly enough detail. For example, it says that per general relativity:

 

Due to the immense density of the very early universe and thus its stupendous spacetime curvature, time was a 4th dimension of space! As the universe expanded (and its density and spacetime curvature became less), tIme itself was formed out of this 4th space dimension . So based on this, there was no time before the big bang.

 

Can anyone tell me something about how this works? I have read that inside a black hole, time and space switch roles due to the intense spacetime curavture, but this is the first time I've read about time becoming space in the very early universe. How?

[Spyman]

If we model the expansion of the Universe backwards over time with General Relativity, then we end up with an infinite density at the ignition time of the Big Bang.

 

But this Singularity is commonly thought to signal the breakdown of General Relativity in this application.

[IM Egdall]

If we model the expansion of the Universe backwards over time with General Relativity, then we end up with an infinite density at the ignition time of the Big Bang.

 

But this Singularity is commonly thought to signal the breakdown of General Relativity in this application.

 

 

Yes, I understand that general relativity breaks down at time zero. But when going backwards towards the big bang does time (per Hawking) become a 4th dimension of space? And how?

Edited November 16, 2010 by I ME

[Spyman]

What I tried to say was that if the Universe gets compressed to high enough density then it can also be mathematically treated as a Black Hole.

 

Here is one simple answer of how spacetime works in a Black Hole:

 

The Question

 

(Submitted August 08, 1997)

 

What is the volume of a black hole?

 

The Answer

 

Our intuitive sense of volume breaks down in the strong gravitational region in a black hole. So while the "size" of a black hole is given by the radius of its event horizon, it's volume is not determined by the usual 4/3*pi*r³. Instead, relativity makes it more complicated than that. As you pass the event horizon, the spatial direction 'inwards' becomes 'towards the future'-- you WILL reach the center, it's as inevitable as next Monday. The direction outsiders think of as their future becomes a spatial dimension once you are inside. The volume of a black hole, therefore, is its surface area times the length of time the hole exists (using the speed of light to convert from seconds to meters). Since a black hole last practically forever, the black hole's volume is almost infinite. (This is also a way of explaining the fact that you can pour stuff into a black hole forever and never fill it up. Another reason why black holes never fill up is that the radius of the event horizon increases as the mass of the black hole increases.)

 

David Palmer and Jim Lochner

 

for Ask an Astrophysicist

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970808.html

 

 

And here is a much more complicated answer with math: The Volume Inside a Black Hole

[IM Egdall]

What I tried to say was that if the Universe gets compressed to high enough density then it can also be mathematically treated as a Black Hole.

 

Here is one simple answer of how spacetime works in a Black Hole:

 

 

Thank you for the explanation and links. So very close to time zero of the big bang, the time co-ordinate became a space co-ordinate. like inside a black hole, Thus per general relativity, there is no time "before" the big bang. However, since general relativity breaks down at time zero, there may be something more going on here. A quantum gravity theory may some day give us a more definitive answer. (Hope I got this right.)

[Spyman]

Seem correct to me, this is what Wikipedia says:

 

Planck epoch

"In physical cosmology, the Planck epoch (or Planck era), named after Max Planck, is the earliest period of time in the history of the universe, from zero to approximately 10−43 seconds (Planck time), during which, it is believed, quantum effects of gravity were significant. One could also say that it is the earliest moment in time, as the Planck time is perhaps the shortest possible interval of time, and the Planck epoch lasted only this brief instant.

...

If quantum effects are ignored, the universe starts from a singularity with an infinite density. This conclusion could change when quantum gravity is taken into account. String theory and Loop quantum gravity are leading candidates for a theory of unification, which have yielded meaningful insights already, but work in Noncommutative geometry and other fields also holds promise for our understanding of the very beginning."

http://en.wikipedia.org/wiki/Planck_epoch