Exploring the Universe with General Relativity Theory

[Pietro]

As we know for general relativity theory we live in a universe with (at
least) 4 dimensions, 3 directions and time. If we think that time must be
in 90° with other dimensions we can imagine the universe as a hypersphere
with time as radius. Make it easier and simpler and cut one dimension (not
time) and we have a universe that is an expanding sphere. (all we can see
is in the surface of the sphere).
This view can lead to a bunch of conclusions, some interesting, some wierd:
1) First of all, time passes because of universe expansion. If axpansions
cease then time stops.
2) If the sphere is not perfect, the time since born of the universe could
be not the same in different parts of the universe.
3) In the case of a big crunch, there must be and end in a singularity,
because no matter the shape of the universe, when a region reach the center
of the sphere time stops for that region.
4) There is no sense to talk about "rapid" or "slow" expansion of the
universe because point 1.
5) It is fun to think about different possibilities of deformations in the
sphere surface that leads to extrange phenomena in time and space behavior.
Sorry about my english, I am not native english speaker.
What do you think? :yuck:
Regards

 

[marcus]

...
5) It is fun to think about different possibilities of deformations in the
sphere surface that leads to extrange phenomena in time and space behavior.
Sorry about my english, I am not native english speaker.
What do you think? :yuck:
Regards

I agree with point 5), this does sound like fun.
I think your english is OK

Look at Carlo Rovelli's homepage:
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html
He is a world expert on certain questions about space and time.

If you live in Italy you could do me a favor
which is to find out if a new book by rovelli is available at
either the book store or the public library (biblioteca publica).
this new book exists only in Italian and it is called

Che cos' e lo spazio? Che cos' e il tempo?

there is a link about this book on the homepage, that tells who
the publisher is. I think the publisher is Di Renzo. It costs about 8 Euro.

I am curious to know if this is a good book and if it is available now.

(he also has a new, bigger, more expensive book in English but I am not
asking about that.)

 

[Pietro]

Sorry, I do not live in Italy, I am far away in the southern hemisphere.
I live in Argentina

 

[RAD4921]

I suggest to you a book by physicist Julian Barbour called "The End of Time"
The question if time even exist is a philosophical question that goes back before the birht of Christ. Time can be defined as the measurement of bodies in motion or an observation of change. In either case, time is psychic in origin.

 

[Garth]

Your suggestion of a model of the hyper-spherical universe with radial time is very intriguing and has been the basis of my research for many years. However there are two refinements that have to be made. Time is not just at 90° to the other dimensions, it is also 'imaginary' in the mathematical sense. In the metrics of special and general relativity the coefficient of the time coordinate is multiplied by the square root of minus one relative to the other three space dimensions. If you think about it if time is a dimension then it is intuitively obvious that it is not exactly the same as the other space dimensions; according to Einstein it bears the same mathematical relationship to them as the imaginary numbers do to the real, and that makes a lot of sense. The second refinement is the problem in imagining this expanding model. To see it expand we have to observe it over a period of - 'time'! Yet surely time has been already accounted for as the radius of the model? Once we step outside our normal experience of time and think about space-time then we are 'playing God' and observing all of time past-present-future as a 'block'. Perhaps we are then in another, a second, time dimension? Rather than an expanding bubble perhaps the model is one of an onion with many concentric shells. You may like to read the short section "A novel representation of space-time geometry" in my last paper "Self Creation Cosmology An Alternative Gravitational Theory", which can be found at http://arxiv.org/abs/gr-qc/0405094 .