[Lynda (OP)]

Does anyone else believe in parallel universes?     I do not believe we are in the only universe - there must be loads of them out there!     

Apparently, a parallel universe occupies approximately the same space as we do.    Could explain ghosts - when they appear "from the other side"?    I have seen a ghost of my parents' late dog a few years ago - then approximately three years later I saw the ghost of a friend who had died nine years previously.

Both ghosts looked exactly like they did in life and just appeared briefly when I was concentrating on something completely different.

[Kryptid]

I'd say that it is more likely that what you saw was some kind of trick of the mind instead of visitors from a parallel universe. When my brother broke up with his girlfriend, he said that he kept seeing her in different places out of the corner of his eye. Also, it has been found that certain kinds of infrasound can create feelings of fear and cause you to see grayish blobs that aren't really there. You can't hear infrasound, so you wouldn't know if it was present or not. Perhaps some combination of these two phenomena can explain many ghost sightings.

[Soul Surfer]

Lynda.  You have to remember that absolutely everything that you "see" is a model of "reality" manufactured by your senses and exists only in yor mind.  It is quite therefore possible for images from your own memory to be put into this model. Normally your brain avoids doing this and you can tell the difference betweem the images of a daydream and reality but sometimes this barrier slips.  It has absolutely nothing to do with other universes.

[lyner]

Does anyone else believe in parallel universes?     I do not believe we are in the only universe - there must be loads of them out there!     

. . . . or IN there?

[another_someone]

To use the phrase 'parallel universe' is one thing, but to define it is another.

Generally, our universe (and thus by inference, all parallel universes) are subject to various conservation laws that require that all interactions within the universe conserve various properties (primarily, but not limited to, energy) within a single universe.  This implies that energy cannot flow between universes, for that would violate the conservation of energy within any given universe.

If you see light travelling between one universe and another, since light is a form of energy, then it must violate the conservation of energy in each of the two universes between which the light flows.  Since light is also an electromagnetic wave, it would imply that electric fields of all sorts would flow between the two universes, and so would mean matter cannot exist in the same locality in the two universes, since the electric fields associated with that matter would be mutually repulsive (in the same way as it is in either one of the separate universes).

Thus, anything you can see must be regarded as being within our own universe, and subject to the laws of our universe.  Ofcourse, light can be bent, and as we know with mirages, where we believe we see things may not be where the thing actually is (or, as Soul Surfer has mentioned, it may not be there at all), but it cannot be in a parallel universe, for you could not see what was in a parallel universe.

[graham.d]

Well, I don't wish to be picky but ...

Conservation of energy would not prevent an equal exchange of energy or an exchange of particles (like photons). I don't think this argument would preclude information transport between parallel universes. There are probably other issues that would prevent such communications but this is all so hypothetical given that this is all speculative at this time.

[another_someone]

Well, I don't wish to be picky but ...

Go ahead - be picky []

Conservation of energy would not prevent an equal exchange of energy or an exchange of particles (like photons).

Yes, but in a local context, there is still a violation of the conservation of energy.  The creation of a photon in this universe is a consequence of energy in this universe, and the direction and energy of that photon depends of the nature of the incident that caused it.

If an incident occurs in this universe, and the photon from that incident disappears from this universe but appears in another universe, at least with regard to that local interaction, there is a loss of energy.  That elsewhere, there may be a counterbalancing incident where the other universe loses a photon to us may balance the whole universe, but still violates the laws of conservation locally for each local situation.

[LeeE]

You really need an unabiguous definition of 'universe' before you can discuss universes pleural:)  Heh - you should also be aware of the difference between multiple universes and parallel universes.  Implicit in the concept of parallel universes is an alignment or similarity between different universes whereas multiple universes need have nothing in common.  For example, the idea of bifuricating universes that form with each quantum event would lead to parallel universes where everything follows the same laws of physics and were identical until the quantum events that split them off.  A non-parallel universe could be anything, including things we have no way of describing.  I suppose that parallel universes are a subset of multiple universes.

Now if you understand the concept of universe to be the sum total of everything then there can't be multiple universes because they too are part of a single 'everything'

On the other hand, if you apply limits to 'our' universe, such as confining it to four dimensions, it's easy to imagine that many other universes could exist that do not occupy that same set of dimensions.  The Space and Time we exist in appears to have been created at the Big-Bang, meaning that the BB created not just the contents of our universe, in terms of the matter and energy, but also the environment within which it all exists, so it's possible to imagine that other Big-Bangs have created their own environments with their own set of dimensions, which may or may not be four-dimensional.

Another alternative is that our four-dimensional universe exists within a five or more dimensional universe, in which case, our universe, from our point of view, having zero size in the fifth dimension, would in turn allow for many of our four-dimensional universes to be placed side-by-side.  This scenario would seem to allow anything that existed in five dimensions to intersect every four dimensional universe that existed within the 'parent' five-dimensional universe.

This might seem to be a good candidate for ghosts but on the other hand, there'd be no reason for such apparitions to behave so inconsitantly.  While in some reported cases a ghost behaves rationally and with intent, in many others the ghosts just appear to be doing random things, quite without purpose.  If ghosts were a phenomenom independent of the observer we'd know much more about their behaviour and characteristics than we do but our current level of understanding is that we're still speculating about their existance, which amounts to no progress at all.

Just as with UFOs, ghosts would be a lot more credible if they behaved more rationally.  (DNA's take on the behaviour of alien/UFO visitors is the only one I've heard that makes any sense:)