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Old Dec 9th 2016, 09:02 AM   #1
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Question How is it possible for parallel worlds to collide?

Hi there.

I'm new here and this is my first post. I'm interested in physics and cosmology, but I have very limited knowledge. In fact I just follow the news and read articles and watch movies (e.g. the fabric of cosmos).

After watching the fabric of cosmos by Brain Greene, a problem emerged in my mind and it has remained there for a few months. I read and searched a lot, but I couldn't find the answer.

What I can't understand is this:
If each parallel universe has its own physical laws and spacetime, then how is it possible for such universes to "collide" as some theories imply? I mean, it is stupid (in my eyes) to say some parallel universe is just on "the right side" of our universe, and it is moving in some specific speed towards our universe, and it will crash ours in some specific "moment" in time... I mean, what time? which space? how are these defined in terms of different universes?????? (really puzzled!)

I know the subject of parallel universes is just something theories predict and it is not proven yet. But the same theories talk about such collisions and I really can't understand how it is possible to talk about such collisions while every universe has its own local spacetime and probably a universal spacetime is undefined.

Unfortunately my math and physics knowledge is very limited, so only an explanation of Brian Greene's type is understandable for me...

Thanks in advance
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Old Dec 9th 2016, 03:29 PM   #2
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Originally Posted by Koohyar View Post
Hi there.

I'm new here and this is my first post. I'm interested in physics and cosmology, but I have very limited knowledge. In fact I just follow the news and read articles and watch movies (e.g. the fabric of cosmos).

After watching the fabric of cosmos by Brain Greene, a problem emerged in my mind and it has remained there for a few months. I read and searched a lot, but I couldn't find the answer.

What I can't understand is this:
If each parallel universe has its own physical laws and spacetime, then how is it possible for such universes to "collide" as some theories imply? I mean, it is stupid (in my eyes) to say some parallel universe is just on "the right side" of our universe, and it is moving in some specific speed towards our universe, and it will crash ours in some specific "moment" in time... I mean, what time? which space? how are these defined in terms of different universes?????? (really puzzled!)

I know the subject of parallel universes is just something theories predict and it is not proven yet. But the same theories talk about such collisions and I really can't understand how it is possible to talk about such collisions while every universe has its own local spacetime and probably a universal spacetime is undefined.

Unfortunately my math and physics knowledge is very limited, so only an explanation of Brian Greene's type is understandable for me...

Thanks in advance
Think of a bunch of universes in a multiverse. We can think of two universes as being like a sheet of paper (or in terms of M-Theory, a "brane.") stacked on top of each other but not touching in general. You can imagine that there are "waves" on each sheet that might be large enough to intersect with the other sheet. That's one way two universes might interact. I don't if we can say that one universe "moves" toward another. I mean they are separated but in order to have lasted as long as this one has I wouldn't think that the speed of sheets toward each other would be that large.

Does that help?

-Dan
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Old Dec 10th 2016, 09:54 AM   #3
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There are several arguments in physics that independently point toward a multiverse solution.
However it is not at all clear if any, all, or none, of these arguments are correct.
It may be that the several multiverse descriptions they are pointing toward are different views of the same underlying reality, or it may be they are all simply mistaken.

Regarding M-Branes, I also have difficulty wrapping my imagination around it,
I have just enough Maths to accept that there could be higher dimensional topological descriptions of the type they propose,
But to actually understand it, no chance...

Regarding the "time" in the description I think that is a misinterpretation of the causal dimension, in other words the dimension through which one event causes an effect to another.
In our everyday lives we are so used to having time as our causal dimension we naturally think that something moving and effecting something else must be acting through time,
however in the multi-dimensional M-Brane world, the causal dimension is not the same as our everyday time dimension.
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Old Dec 12th 2016, 11:29 AM   #4
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Thanks a lot for your attention.

I know the topic of multiverse is merely theoretical and it isn't proven to be correct yet. But considering the subject is demonstrated in mathematical terms, I suppose there is a "mathematical" explanation on how such a relation is possible. Unfortunately I have to be looking for a non-mathematical explanation.

Hearing that "time" is not what we conceive in our daily life, I'm trying to understand how such relations are possible without a usual arrow of time as we are used to.

You can imagine that there are "waves" on each sheet that might be large enough to intersect with the other sheet.
What I can't understand is the relation between the universes. The place where the waves are not intersecting is supposed to be "empty (free of waves)". And some "time" passes and "then" an intersection happens.

Some "time" passes? Or not? Are the interactions between universes "timeless" (or not understandable through our experience of time)? If they can't be considered to be happening one after the other (no specific arrow of time) then what makes them "appear" to be happening one by one? Why there isn't any interaction at this moment? What if one happens e.g. half an hour later? "Half an hour later" doesn't apply to the so-called interactions, or does it?

Of course I don't expect anyone to answer all the questions I mentioned, but I was trying to show you what makes me puzzled.

however in the multi-dimensional M-Brane world, the causal dimension is not the same as our everyday time dimension.
This is exactly what puzzles me. Of course it is not like the dimension we perceive, but I'm trying to understand how the dimension really is.

As a side note, in the movie "the fabric of cosmos" Brian Greene uses a bread as an analogy for the multiverse in inflation theory. Well, in that analogy some universes are here, the others are there. Some in the right side, some in the left side. But I suppose an exact "position" of a universe in the multiverse is meaningless. Because universes are not objects sitting on a table called multiverse. In fact they are complex geometric structures which they each have their own "local" space-time. These are what I have understood about the subject in a math-less manner...

And, if in the inflation theory the so-called big-bang is happening again and again, and if the first moment of big-bang is a singularity with "timeless-spaceless" features, I then suppose the whole multiverse is made up of the "timeless-spaceless material" which the big-bang is made of.

I mean, those regions in the multiverse where an inflation has not yet happened (and the phrase "has not yet happened is puzzling me as well) have probably the same features as the first moment of big-bang when the bang has not yet happened and the so-called space-time has not yet been created (a space-time local to our universe).

What is puzzling me is that, in such a structure where time and space "has not yet been created", how can we talk about inflations "which are happening again and again here and there", while the concepts space and time have not yet been defined.

What I personally think is that this is only an analogy and the multiverse is beyond time and the inflations are not happening again and again, but they all "are" happened beyond what we call time, and in fact the structure of such a multiverse is not really changing through time, but time is an illusion local to a single universe and is a feature definable "only after" a specific bang.

I am puzzled and I don't have a source to make sure if I'm on the right track or I'm terribly wrong. I hope what puzzles me can be solved through the verbal answers you and other members provide.

Thanks again
Sorry for the long post

Last edited by Koohyar; Dec 12th 2016 at 11:39 AM.
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Old Dec 12th 2016, 02:11 PM   #5
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Originally Posted by Koohyar View Post
Thanks a lot for your attention.

I know the topic of multiverse is merely theoretical and it isn't proven to be correct yet. But considering the subject is demonstrated in mathematical terms, I suppose there is a "mathematical" explanation on how such a relation is possible. Unfortunately I have to be looking for a non-mathematical explanation.

Hearing that "time" is not what we conceive in our daily life, I'm trying to understand how such relations are possible without a usual arrow of time as we are used to.



What I can't understand is the relation between the universes. The place where the waves are not intersecting is supposed to be "empty (free of waves)". And some "time" passes and "then" an intersection happens.

Some "time" passes? Or not? Are the interactions between universes "timeless" (or not understandable through our experience of time)? If they can't be considered to be happening one after the other (no specific arrow of time) then what makes them "appear" to be happening one by one? Why there isn't any interaction at this moment? What if one happens e.g. half an hour later? "Half an hour later" doesn't apply to the so-called interactions, or does it?

Of course I don't expect anyone to answer all the questions I mentioned, but I was trying to show you what makes me puzzled.



This is exactly what puzzles me. Of course it is not like the dimension we perceive, but I'm trying to understand how the dimension really is.

As a side note, in the movie "the fabric of cosmos" Brian Greene uses a bread as an analogy for the multiverse in inflation theory. Well, in that analogy some universes are here, the others are there. Some in the right side, some in the left side. But I suppose an exact "position" of a universe in the multiverse is meaningless. Because universes are not objects sitting on a table called multiverse. In fact they are complex geometric structures which they each have their own "local" space-time. These are what I have understood about the subject in a math-less manner...

And, if in the inflation theory the so-called big-bang is happening again and again, and if the first moment of big-bang is a singularity with "timeless-spaceless" features, I then suppose the whole multiverse is made up of the "timeless-spaceless material" which the big-bang is made of.

I mean, those regions in the multiverse where an inflation has not yet happened (and the phrase "has not yet happened is puzzling me as well) have probably the same features as the first moment of big-bang when the bang has not yet happened and the so-called space-time has not yet been created (a space-time local to our universe).

What is puzzling me is that, in such a structure where time and space "has not yet been created", how can we talk about inflations "which are happening again and again here and there", while the concepts space and time have not yet been defined.

What I personally think is that this is only an analogy and the multiverse is beyond time and the inflations are not happening again and again, but they all "are" happened beyond what we call time, and in fact the structure of such a multiverse is not really changing through time, but time is an illusion local to a single universe and is a feature definable "only after" a specific bang.

I am puzzled and I don't have a source to make sure if I'm on the right track or I'm terribly wrong. I hope what puzzles me can be solved through the verbal answers you and other members provide.

Thanks again
Sorry for the long post
I don't know much about M-Theory beyond the basics so I can't answer your questions in detail, though I suspect you'll get other responses to this which should help you.

I can only make educated guesses here. The multiverse (according to M-Theory) has a number of universes that are "stacked." If the number of dimensions in the universes is 11 (10 space + 1 time) then the multiverse is at least 12 dimensional. In this 12D space the universes are "flat." (Think of a stack of paper in 3D...the extra dimensions make the paper flat instead of the 2D world that exists on them.) What is that extra dimension between the universe? Just some kind of extra 1D space.

Now comes the tricky part: the universes may be in motion with respect to this extra dimension. We can't know if this is true because this extra dimension is outside our 11. We can't measure anything in that direction, though we may speculate it Mathematically. So two universes may run into each other.

Another possibility of motion is that the universe may be "waving" in the direction of the extra dimension, like ripples on a lake. If I'm not mistaken (don't quote me on this) the ripples are caused by gravitational waves spreading through our 11D universe. (According to some gravity is not restricted to our 11 dimensions.)

However it may happen if two universes intersect it is possible that there is a huge energy surge. It is possible that such a surge is responsible for big bang events.

Of course this is all speculation.

-Dan
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Old Dec 13th 2016, 04:08 AM   #6
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I personally don't particularly like the M-Theory of island brane universes floating about in some kind of rather undefined dimensional realm.
The way I have heard the theory described, separates out the individual branes in a way I find unconvincing.

If we look at our "familiar" time and space;
Space used to be considered as a 3D brane moving through time,
Einstein showed that it has to be considered as a 4D brane with space and time inextricably entwined.
I would not expect it to be different for higher order branes.

It may be a problem with the description rather than the theory, but I am currently sceptical...
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Old Dec 13th 2016, 10:11 AM   #7
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Originally Posted by Woody View Post
I personally don't particularly like the M-Theory of island brane universes floating about in some kind of rather undefined dimensional realm.
The way I have heard the theory described, separates out the individual branes in a way I find unconvincing.

If we look at our "familiar" time and space;
Space used to be considered as a 3D brane moving through time,
Einstein showed that it has to be considered as a 4D brane with space and time inextricably entwined.
I would not expect it to be different for higher order branes.

It may be a problem with the description rather than the theory, but I am currently sceptical...
I'm not too keen on it myself but when superstring theory is derived there are something like four different possible theories that could exist. Someone (I'm too lazy to look it up) made the observation that if we have an extra dimension then all the versions essentially describe the same thing, just with different regions of application. (Such as a long wavelength, short wavelength, etc. approximations.) The resulting theory is called M-theory and possibly predicts a multiverse spreading into this extra dimension.

As there is no actual evidence for superstrings I'm also skeptical. On the other hand it seemed to be a good "background" as it were to discuss the OP's question, nothing more.

-Dan
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Old Dec 15th 2016, 06:10 AM   #8
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long sentence!

I am quite happy with the depiction of alternative solutions to string theory being realized in alternative universes, and that these alternate universes can be envisaged as existing within a higher dimensional realm where the additional dimensions encapsulate the variations in various parameters that define the a-priori assumptions that have to be made to produce string theory solutions in each of the alternate universes.
However,
If the additional dimensions are measures of the differences between the universes, how can the branes constituting these universes move with respect to each other, let alone collide?
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Old Dec 22nd 2016, 07:37 PM   #9
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Thanks a lot

I'm glad the question bothering my mind has caused me to join this forum.

I'm still confused about the subject. Does physics have a straightforward answer to the question provided here? Are the "colliding" universes only a too early speculation which don't have a strong root in the theories? Or the mathematical definition of the collisions between universes in the not-so-easy-to-define dimension is already there and what makes the subject so puzzling is caused by our minds clinging to the ordinary "classical" world we are used to?

If the additional dimensions are measures of the differences between the universes, how can the branes constituting these universes move with respect to each other, let alone collide?
And all this is going to take place in a dimension free from the time and space we are used to. How?!

Last edited by Koohyar; Dec 22nd 2016 at 07:41 PM.
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Old Dec 26th 2016, 05:00 AM   #10
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I have found none the "lay-man" explanations I have seen of this idea particularly convincing.
This may be due to the over-simplification inherent in producing a "lay-man" explanation rather than any real problem with the theory.
But some ideas just give you that gut feeling of rightness, and others don't.
For me personally, this one don't.
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