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Author Topic: A Question About Gravity, Dark Matter, The Universe [...& More]  (Read 2855 times)

Offline stuffski

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Before I start; My scientific background beyond basic [public, at that] high school level is pretty much non-existent. I am however casually interested in all aspects of astronomy, physics, mathematics etc. So in lieu of trying to sound in any way competent I’ll just ask this as it is in my mind – no fancy words [largely because they haven’t found their way in]

My question is about the concept of our universe. Why do we believe our universe is alone? Is there a possibility that universes can exist in the same relationship as stars to a galaxy so that ours is just one of billions separated by unimaginably large distances but at the same time held together by a universal force of gravity.

The distances being so large we have no way of physically seeing these other universes as ours is only 14bn years old and the distances would be in the trillions of light years (for example).

If so then may this at all explain some of all of this invisible mass in our universe (i.e. that it is not mass but an external effect of gravity). Now I’ve read material which states that the distribution of this dark matter is quite closely aligned with the distribution of visible matter (due to the effects of bending light if I remember) – which of course may discount the above completely but I still wonder if it is a possibility?

What are your thoughts on this? I hope I've managed to vaguely explain what I'm talking about!


Offline Soul Surfer

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in general it is not assumed that our universe is alone.  The presence of other universes at a great distance would not have any significant effects on our universe so theories of this nature cannot be related to the effects anbd observation of dark matter

Offline Bikerman

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Some simple sums indicate that 'extra universes' cannot be responsible for the expansion of our own universe. Expansion appears to be fairly homogeneous (ie 'even') whereas an external attractive force would presumably obey the inverse square law and be much greater at the 'boundaries'. Expansion seems to be a property of spacetime, rather than an external 'force'. Now, whether it is an inherent and 'fixed' property of empty space (cosmological constant, zero point energy etc) or it is a scalar field (quintessence), well, that is another story :-)

Offline DoctorBeaver

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It is theoretically possible that areas of our own universe could inflate to form other universes that grow & evolve totally separately from ours.

There are also "multiverse" theories. Some of these conjecture separate bubble-like universes in a higher-dimensional spacetime, others that each universe is located on a "brane" (short for membrane) in this higher-dimensional "bulk".

I have seen it theorised that the Big Bang was the result of 2 of these branes coming together (although in that case there would have been no initial singularity whence the Big Bang could originate). This would not be the same as an external force causing the expansion. Both branes, hence both universes, would have to pre-exist although not necessarily in any state that we would recognise. If both of the branes were even slightly curved then they would come together like 2 balloons being pressed against one another, it would not happen all at once. The isotropy (evenness) we see in our universe is the area where the 2 branes have already coalesced. Beyond that area, anything is possible. It could be that even fundamental physical laws are different and that the particles & forces we see in our universe today are the result of this coalescence.
« Last Edit: 25/11/2008 16:48:18 by DoctorBeaver »

Offline stuffski

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Thanks everyone for your points and comments.

I have seen the membrane theory and I find it very interesting.

Thanks again, I'm sure it won't be my last question!

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