Understanding the 4-Dimensional Universe Expansion: A Philosopher's Perspective

[ronald_dai]

I am a philosopher with little bakcground knowledge in physics. The GRB news brought me here. Thanks to the help from Marcus and DaleSwanson, now I know much better about the universe expansion. I am not as good at math as most of you here are, but my hobby is drawing a big picture whenever I learn something new. I have drawn a picture about this universe expansion as follows and welcome any criticism or comments from you:


Our universe locates in a 4-dimensional spacetime sector and started from a BIG BANG with a total mass M, after the BIG BANG, the universe started to expand "OUTWARD" in the 4-dimensional spacetime under its own inertia...

Since each part of the 4-dimensional body is moving "OUTWARD", there are different relative receding velocities between different parts. This is just like when a 3-d ball explodes, while all exploded pieces flying outward, there are relative velocities between them...

Even though, the "OUTWARD" velocity of every celestial object is smaller than the speed of light, due to the great size of this 4-dimensional body, the relative receding velocities between different celestial bodies could be greater than the speed of light...

Based on this understanding, we could imagine that the size of the 3-dimensional surface of this 4-dimensional body should grow at a 2/3 power law if the size of the 4-dimensional body is increasing linearly with time (if the volume of a 3-dimensional body grows linearly with time, the radius should grow at a 1/2 power law, therefore, we might imagine that the size of this 3-d surface should grow at a 2/3 power law)...

Based on some astronomic observational data, in order to have the momentum as calculated by scientists so far, the Universe should contain some extra Mass which is called Dark Mass, otherwise the universe might not have such a big momentum...

At least up to this moment, the universe is still expanding "OUTWARD" under its own initial exploding momentum, but no body knows yet whether the expansion would stop someday and start to contract...
...

That's the whole picture I have drawn from what I have learned since yesterday...There is one major unclear point to me: If the universe is a 3-d spatial body, then I could clearly know the meaning of "OUTWARD", and I would know the universe would be a sphere, but with time as one dimension, it is hard for me to think about the meaning of "OUTWARD" and I guess the universe body might not be a 4-dimensional sphere, right? ...Besides, if I am right with the big picture, then we should be able to calculate the total volume of the universe as long as we know the total Mass M, right?

Welcome any criticism and comments...thanks

 

[ronald_dai]

I like to add some discussion to the above picture I draw, which might sound very trivial to physicists here but a bit confusing for a non-physicist like me.

1) Considering the fact that the expanding space could stretch out the wave length of the photons traveling within, we should say that when the 3-dimensional surface is running away from the original 4-dimensinal spacetime "center" it does not just leave EMPTY space between each other, but is actually stretching the space out PHYSICALLY...obviously we cannot say that the stretching out of the wave length was because the photon "feels" the departure of the 3-dimensional surface bodies...Therefore, there should be some REAL underlining physical meaning of the space stretch...

we might view this issue from 2 angles: a) the running away 3-dimensional surface is physically stretching something physically meaningful which we are calling as SPACETIME; or b) the physically meaningful SPACETIME is stretching itself and the running away of the surface is the result of the stretching out

2) based on the new GRB news, 12.2 bln years ago, i.e. about 1.5 bln years after the BIG BANG, some celestial object was 4.6 bln ly away from the Earth spot, which gives a receding velocity of more than double of the light speed...since I am poor at math so that I don't know how could a 4-dimensional running away create this great receding velocity if each part was running away at a slower than light-speed velocity (even though there was no earth, but some real thing might be even farther from that GRB at that time)...maybe it was because we need to calculate the velocity in 4-dimensional terms?...or maybe we need to assume that the space stretching is not caused by the running away surface but the is the reason for the running away of the 3-dimensional surface?

Welcome any help on this...thanks Ron