Multiple universes: Nothing more than philosophising?

[phinds]

Yes, I do not aid this parallel universe idea, you bring up a very good point, but others do believe in it, that is why people believe in multiverses, that is the point of this thread. If you go to my second reply, I used the term might be.

Fair enough

 

[Orien Rigney]

The universe could be above us, I think this wording would explain it.
"let's say that our universe is a sheet of paper. We live our entire life on this sheet of paper, but directly above us there could be a parallel universe, hovering right over us, perhaps inches, centimeters away and objects in this parallel universe would be invisible. Light travels beneath the universe, so we never see this other galaxy. But gravity, gravity goes between universes because gravity is nothing but the bending of space, so if the space between two sheets of paper is bent slightly gravity then moves across. This other galaxy in another universe would be invisible, yet it would have mass. That's exactly what dark matter is. Dark matter is massive—it has gravity—but it's invisible." (Michio Kaku,2011)

Scanning down and seeing this topic made me want to jump in with my ignorance and both feet, if I may? The sheet of paper thing? If we are part of a multi-universe system as some think, I find it difficult to understand the concept do to the fact that from earth, we can see in all directions over 13 billion light years. Also, if the sheet of paper theory is correct, at an estimated speed of over 2 million miles per hour and ever increasing in velocity, our universe is bound to encounter another of its multi-verse neighbors sooner or later.

 

[phinds]

..., at an estimated speed of over 2 million miles per hour and ever increasing in velocity, our universe ...

Huh? Where did you get that number? What do you think it represents?

 

[Quds Akbar]

Scanning down and seeing this topic made me want to jump in with my ignorance and both feet, if I may? The sheet of paper thing? If we are part of a multi-universe system as some think, I find it difficult to understand the concept do to the fact that from earth, we can see in all directions over 13 billion light years. Also, if the sheet of paper theory is correct, at an estimated speed of over 2 million miles per hour and ever increasing in velocity, our universe is bound to encounter another of its multi-verse neighbors sooner or later.

Think of it as a universe above us.

 

[Chronos]

The notion of gravity influencing our universe by leaking from 'nearby' parallel universes emerged from string theory. The hypothesis goes like this - parallel universes reside on branes [short for membranes], which are manifolds embedded in a higher dimension called the bulk. Branes conform to the holographic principle in the sense of being lower dimension objects embedded in a higher dimension, the bulk. At least part of the motivation for this idea was to explain why gravity is so weak compared to the other fundamental force of nature. Despite its noble intent, brane theory has never achieved wild popularity because it has not resulted in predictions that cannot be reproduced by simpler theories; and we all know the bias science has for simple explanations - i.e., Occam's Razor.

 

[Orien Rigney]

Huh? Where did you get that number? What do you think it represents?

Got to admit, the 2 milion mph requires several annotations to come up with that figure, but it was one without par secs or metric units.
Look at this link.

Huh? Where did you get that number? What do you think it represents?

 

[phinds]

Got to admit, the 2 milion mph requires several annotations to come up with that figure, but it was one without par secs or metric units.

Numbers like that are not particularly meaningful and certainly have nothing to do with the expansion rate of the universe which is WAY more significant than how fast we are moving relative to other objects or the CMB and even that concept is not meaningful in terms of a multiverse or encountering another brane.

 

[Czcibor]

I am not by any stretch of the imagination a multiverse fan, but I think you're being a bit unfair. The multiverse theories try answer two questions:

1. Why did inflation start and why did it stop?
2. Why do we see the sorts of apparent fine-tunings of various parameters?

I don't think there are any alternatives to either of these, although there are ideas that attempt to partially answer #2 - for instance, the small Higgs mass can be explained by supersymmetry. I would instead say that the evidence is entirely circumstantial.

I am aware of one-sided multiverse tests: for example, if there were an early universe collision between multiverse bubbles, it would leave evidence in the polarization of the CMB. If there were a collision between multiverse bubbles, that would mean they exist. If there were no collision, that doesn't mean they don't.

For question 2. I think that many religious people would give you a quite consistent answer that so far is as empirically testable as multiverse hypothesis. ;)

I think about a bit different approach - why not just say that multiverse hypothesis is just one of possible interpretation of quantum theory? Because I think that with so abstract concepts there is a problem that to what extend that you can get an ability to calculate or predict something, but without actually understanding what is going on.

 

[rootone]

For question 2, I believe the anthropic principle is as good an explanation as is multiple universes .
Observations of the physical Universe must be compatible with the conscious and sapient life that observes it.
If things were otherwise we could not exist and observations could not be made.

 

[Chronos]

The anthropic principle is useless, save for ruling out the impossible. Obviously, any observation that infers existence of the observer is impossible implies either the observation, or underlying basis for that inference is incorrect.

 

[rootone]

I do agree that the anthropic principle, while it must be true, it is essentially a philosophical position that can't be used to draw scientific conclusions.
I think the multiple universes proposal also is a philosophical position that can't be used to draw scientific conclusions..
If anything it is inferior as a philosophical proposal since unlike the anthropic principal it is not self evidently true.

 

[Ken G]

To me, the issue is not so much "is there a multiverse," or even, "is the existence of a multiverse a scientifically testable model," because it is probably too soon to make much of a judgement on either of those issues (it might be hard for a long time, it's hard to say). The interesting issue that we can address right now is, "what is a scientific explanation." When someone says the multiverse "explains" why the constants are finely tuned, or "explains" why inflation stopped at just the right moment to generate a universe like ours, what does that mean? Surely it must mean a lot more than "it gives us a sense of understanding to hold that there is a multiverse", because as has been pointed out, it also gives many people a sense of understanding to say "god did it," but we can all agree that isn't a scientific explanation. Yet when people like Carroll and Weinberg talk about multiverses, I don't see them gaining much more than that same basic sense of understanding, that feeling like it makes sense somehow-- but that isn't science, not by itself. So falsifiability has come up, and the need to make predictions-- we can agree that is important to be able to call something a scientific explanation. But I'd say the most important thing Popper said about science is that it must make "risky predictions", which basically means, it has to be possible that some idea is wrong, it cannot be so flexible that it can accommodate any result. This is what bothers me about the multiverse idea-- the very thing that defines it makes it questionable as science, it's extreme flexibility. So what I want to know is, does the multiverse concept "explain" anything in our particular universe that it could not also "explain" in any other completely different universe, but just wouldn't seem important or necessary for?

Let me put the question this way. Imagine there "really is" a multiverse, whatever that means. So most of the universes are generic, and have no need for the multiverse concept because they don't exhibit fine tuning. Is that not somewhat ironic-- it is a theory that only the rare universe would even need to invoke in the first place. Imagine a situation like that applied to fortunes in a fortune cookie-- most people find them to be very generic and not saying anything particularly tailored to their own lives, yet every once in awhile someone gets one that seems perfectly suited to some situation they are in. Would it be valid for those few who see some import in the fortune to regard fortunes as predictive because they work so well in those special cases? Do we ever let the special cases do the scientific explanations?