Why the multiverse makes no sense to me

[Mlesnita Daniel]

So, basically, multiverse make sense because we can't imagine our universe standing in nothing(or being everything that just expands itself).

If we take this principle, we should have a multi-multiverse, a multi-multi-multiverse and so on. (When the chain ends?).

Is it more evidence to support "multiverse theory", or it is just an idea?

 

[phinds]

So, basically, multiverse make sense because we can't imagine our universe standing in nothing(or being everything that just expands itself).

No, that's a personal opinion on your part and is not widely shared. The consensus among cosmologists is that it IS everything and it IS expanding but not "into" anything.

If we take this principle, we should have a multi-multiverse, a multi-multi-multiverse and so on. (When the chain ends?).

Is it more evidence to support "multiverse theory", or it is just an idea?

Since your question is based on a false premise, there is no answer.

 

[Mlesnita Daniel]

No, that's a personal opinion on your part and is not widely shared. The consensus among cosmologists is that it IS everything and it IS expanding but not "into" anything.

It is everything the universe or the multiverse?

 

[Nik_2213]

One rather whimsical reply could be that the 'universe' we see is but one shard from a supra-cosmic 'fender bender'.

Just bang the branes together...
;-))

 

[phinds]

It is everything the universe or the multiverse?

Well, if you believe in the multiverse (which most of us, I think, don't), then "everything" is a bit fuzzy. The consensus is that the universe we live in is all there is, and in any event it's really totally irrelevant since even if the multiverse exists, it's all causally disconnect from us and cannot be seen, felt, or detected in any way so it might as well not exist as far as we are concerned.

 

[Bandersnatch]

multiverse

You used this term without defining what exactly is it that you mean by it. It might seem obvious to you (it's the multiverse, duh), but depending on the definition the answers to 'does the multiverse exist' can range from 'obviously', to 'possibly', to 'it's a matter of personal opinion', to 'probably not'.

 

[Mlesnita Daniel]

You used this term without defining what exactly is it that you mean by it. It might seem obvious to you (it's the multiverse, duh), but depending on the definition the answers to 'does the multiverse exist' can range from 'obviously', to 'possibly', to 'it's a matter of personal opinion', to 'probably not'.

Wait are there more definitions for it? :)

I thought this is the only one "The multiverse is a hypothetical group of multiple universes including the universe in which humans live. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, the physical laws and the constants that describe them.".

 

[Bandersnatch]

Right. This already narrows it down, since we know you don't mean the many-worlds interpretation of quantum mechanics.

So let's look at this definition. It talks about the multiverse comprising of multiple 'universes', and also being 'everything that exists: the entirety of space, time, matter, energy, the physical laws and the constants that describe them'.
Taking the same source for our definitions (i.e. Wikipedia), we look up 'universe', and we see that it's: 'all of space and time[a] and their contents'.
This should give one a pause, since it's contradictory - everything that is cannot be a part of something else. They appear to be describing the exact same thing.

So if we want to talk about the multiverse, we need a different definition of what this sub-component called 'universe' is. For example:
1. Each observable universe (this one is stretching it, but for the sake of argument let's keep it).
2. Each currently non-overlapping observable universe.
3. Each causally separated patch of space (=observable universes that will never overlap).
4. Each patch in inflating space that stopped inflating and undergoes regular expansion.
All of these are just from the standard model of cosmology (with inflation). More definitions are possible if one's thinking about some other cosmologies, branes or whatnot, that I know little about and will not comment on here. The point is, the list is not exhaustive. (I can see now that the Wiki article talks about those in some more detail)

In each of those four cases, an argument can be made that each one describes universes that are in one way or another separate, and together form something that could be called a multiverse. Each next case is just the previous one, but that has been more restricted. So 2 is a special case of 1, 3 is a special case of 2, and 4 of 3.

As we go towards 4, the distinction between separate universes becomes less trivial, while our confidence that those other universes (and by extension, the multiverse) exist becomes less solid. But, we always have some good reasons to suppose their existence, and the choice to favour one definition over another is to a large extent arbitrary.
Furthermore, even if you pick the most restricted definition (4), and which is probably the most often referred to as multiverse of the four, you're not talking about there being some 'nothing' outside our universe (as defined). You're basically just saying that the universe is in some sense larger than what you see, so you need to update your old definition of 'everything that exists' to be more inclusive.

 

[Bandersnatch]

and in any event it's really totally irrelevant since even if the multiverse exists, it's all causally disconnect from us and cannot be seen, felt, or detected in any way so it might as well not exist as far as we are concerned.

Oh my, I hope Alan Guth can't see your hurtful comment!

 

[rootone]

I think this mainly a discussion about semantics; the meaning of words.
Personally I am happy with the definition of 'Universe' being "everything there is", including bits we cannot observe.
In the past, the concept of 'The World' was similar, but now we tend to routinely consider other planets and moons to be worlds, in their own right.
None of this however makes any difference to actual physical reality.

 

[pinball1970]

Oh my, I
hope Alan Guth can't see your hurtful comment!

From what I have read inflationary theory indicated the multiverse scenario?

Discoveries of Gravity waves and small differences in the CMBR support inflationary theory and therefore the multiverse?

My sources I suspect are mainly from pop science books so this is an opportunity for me to ditch some misconceptions hopefully.