PDA

View Full Version : accelerated expansion



parenthesis
2003-Jun-10, 03:10 AM
This is for the mathematicians among you:

I still balk at the idea of "dark energy" and other exotic forces to push the Universe apart, if this should become well established mainstream astronomy that the rate of expansion of the Universe is indeed increasing.

So here is a suggestion, but I have not a clue whether the math is working: :roll: What if the overall space of the Universe is four dimensional (not in the Einsteinan sense, but strictly geometrical, as a kind of super cube or hyper sphere without an outer edge)?

I believe to remember that in this case Newton's gravity constant would require a different value to hold it all together. But since it is, what it is, it is doing its thing only in our cosmic vicinity where space flattens out to the familiar Euclidian three directions. :wink:

So only when we scale up we get into the fourth dimension and a Universe where the objects roll apart. How is this for a brain teaser? :)

I believe it all comes down to a mathematical model, which would make predictions on changes in the acceleration rate, perhaps even energy flux and a million other things I can't even think about. But math is my weakness. :cry:

michael

wedgebert
2003-Jun-10, 03:20 AM
Hmm, I think this belongs in the "Against the Mainstream" board. But here's my thoughts.

First off, the universe cannot have four geometic dimesions and still exist as it does today. You cannot form stable orbits in 4d space, and so the galaxies and galaxy clusters we see all around us (including our own) could never have formed. The stars would have long since either collided or shot off on their own.

I find no problem with the concept of dark energy. Gravity is just a force, so it's perfectly conceivable that there is some sort of counter-force. Who knows, maybe one day we'll even find complements to the Weak and Strong forces as well.

parenthesis
2003-Jun-10, 03:39 AM
That was quick.

I have no intention of being "against mainstream," I just prefer the simpler solution to the more complicated. I know and agree that there can be no stabile orbits in four dimensional space - I said so myself, when I mentioned Newton's gravitational constant.

However my idea is that we live locally by and large in a Euclidian three dimensional space and the fourth dimension comes only into place when we scale up the size. My question is, whether this is mathematically possible. If yes, then I have a defensible hypothesis. If not, not.

As for the formation of galaxies and orbiting objects in the early history after the bang (no worries, I am conservative) the transition period from a realtively small four dimensional manifold to a flat three dimensional Newton space under a four dimensional horizon may actually be helpful.

Thanks for responding
michael

wedgebert
2003-Jun-10, 04:18 AM
Maybe I'm just not sure what you're saying.

Are you saying that just our section becomes 3-dimensional when you decrease the scale, or that any section of space becomes 3d if you look at a small (galactically speaking) area?


I still think this would be impossible. If nothing else then observations of distant objects would show some sort of distortion from the 4th dimesion.

parenthesis
2003-Jun-10, 04:47 AM
You understand me perfectly! And of course any odd region on the "smaller" scale is flattening out to 3 D space, not just ours. Only when we approach the observational horizon things should look a bit weird. (As they apparently do given the data for supernovae that triggered the realization that our Universe is accelerating the expansion speed.)

michael