(September 23, 2010 at 11:10 am)Rayaan Wrote: How do you know if there are other universes at all?
I don't find that to be a good argument because maybe this is the only universe or maybe not.
We don't know if there are any, there are only reasons for suspecting that might be the case, namely due to a weird phenomenon seen in Quantum Mechanics during the double slit and other experiments. The best and most accurate understanding we have of the cause of this phenomenon at the moment comes from Richard Feynman - It's called Path integral formulation.
The theory essentially deals with the journey of a quantum structure from point A to B, and states that (because of the uncertainty principle) unlike other relativistic trajectories that can be traced as a single pathway from A to B, pathways in Quantum Mechanics are an expression of every possible path that could have been taken from A to B - of which there are an extremely large amount, with the most probable pathways occurring within a very narrow range - The combination of these pathways or 'probability amplitudes' accounts for both the motion of the particle (highly likely to be around the average of the range of amplitudes) and all of the interference that was experienced by the particle over the journey (caused by it's self) - The particle essentially took every single path at once.
If we take this principle into account and look from A to B, we see every possible journey that could happen, but the same applies looking backwards from B to A. If us here on this planet under these specific set of conditions ands values is B and the start of spacetime is A then looking back we can see that the journey from A to B has an extremely high probability amplitude (10^500 or more) This effectively means that 10^500 other occurrences happened from the very begging through to now, and we are only in one of the many many outcomes, likely one that only has a limited probability because of what we know of the goldilocks zones for universe formation, most would collapse immediately, many would expand too fast and a slight minority would have conditions such as the ones here.
M-theory is a more complete extension of this idea and it provides many more reasons for thinking that multiple-universes are the case, but this is just one of the reasons why we would expect there to be multiple universes.
M-Theory has a good change of being indicated or falsified in the coming decades, so it may not be long before we are able to know whether this idea can continue to predict experimental results into the future, or if it gets a prediction so wrong that it cannot be reconciled.
Oh, and by the way, what i just gave you in this short little post is more evidence indicating the existence of multiple universes than there ever has been indicating a God exists, just so you know.
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