If the Multiverse is correct why don't they appear inside our own?

  • #27
Vanadium 50
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I understand the concepts that have been proffered
No, you really don't. You say "multiverse" when (and it took some time to sort this out) you really mean "eternal inflation".

I believe Sabine Hossenfelder is a highly respected physicist - don't shoot the messenger!
Not so much as you think. She's more famous as a blogger. In the last five years her papers have received 75 citations, of which 10 were self citations. To compare, I am not even a theorist, but have written a couple of theory papers. The least-cited single paper of mine has 115 cites, of which 3 are self-cites.

This thread's goalposts keep moving. The original question was "If the Multiverse is correct why don't they appear inside our own?" and now it's "Is there any evidence that there is more than one universe?" and "Is there any way of testing any hypotheses which postulate the existence of multiple universes?"

To answer your second set of questions, you have to define "universe" and discuss if and how it differs from "region on our universe that we have not observed and will never observe". To answer your original question, "for the same reason rocks roll spontaneously downhill but not uphill."

It is starting to sound, though, that you are not asking questions so much as pushing a position. I do not recommend it, seeing as how by your own admission you are not an expert in the physics."
 
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  • #28
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I understand the concepts that have been proffered but not the mathematics that supports them.
So you don't understand the concepts. Understanding concepts (especially when it comes to such and advanced topics like the ones you try to discuss) means mainly understanding the maths behind them.

Q1 Is there any evidence that there is more than one universe?
Of course not, but that is not what you were initially asking. You asked some questions, got some lengthy replies pointing out your misunderstanings, and then you ignored it, restated again your wrong understanding as if nothing happened and then changed the subject. Is that a way to learn? Is that a way to discuss?
 
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  • #29
The root of the word 'discuss' is the same as the roots of the words 'percuss' and 'concuss' and means literally hitting each other with words. I prefer 'converse' which means to turn together in dialogue. In a short space of time I have noticed a tendency to attack questions and questioners when what they (certainly in this case) are asking is quite obvious although lacking in technicality.
Where are the Aliens? is a valid question and so is where are the other universes?
The term universe here applies to the cosmos we inhabit and observe and know very little about. The term multiverse here means more than one of these. Is it probable that there is more than one of these grand objects of perception we generally refer to as a universe? The answer to this ought to be yes on the assumption that the initial conditions from which our universe spawned was the simplest of states devoid of entropy. The initial conditions here are those that we would encounter were we to reverse time to the moment just before the big bang. Whenever I see models of multiverse theories they postulate an infinite number of bubble like universes that never intersect. The mathematics behind why they never actually intersect seems compelling to a non mathematician - with one fundamental flaw which is that these bubble universes have the same point of origin as though there would be one giant bubble making machine that was fixed. In answer to the question 'what is the centre of the cosmos' the answer is here and here and there; in fact everywhere because prior to spacetime there were no co-ordinates therefore any point of origin is pervasive. So any bubble making mechanism would be creating universes in all directions at the same time and therefore they would have to intersect. Maybe this is true and the interference pattern created by an infinite number of universes from an infinite number of points collapses into this one single universe.
 
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  • #30
Vanadium 50
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Being told one is wrong when one says a wrong thing is not an attack.
Argument by repetition is not much of an argument.
Further discussion is pointless.
 
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  • #31
Ok, I agree that further discussion is pointless! But I don't agree with your use of the word 'wrong'. My profession is a teacher and physics is a lifelong interest (but obviously not what I teach!). If one of my learners asks me a question I try to check that I understand what it is they actually want to know then I try and answer to the best of my ability. I would never, ever, tell them that they are ignorant or that their question is wrong. On this forum and in this relationship I am the learner and you are the teacher(s). I would like to know why we do not see any evidence of other universes. What I am being told is that I don't know what I am talking about - which is quite true and precisely why I am asking questions. Can anyone point me to an explanation given here that might help me understand? I am afraid I haven't found this foray the least bit helpful so I will have to take my obtuseness elsewhere.
 
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  • #32
Ibix
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If one of my learners asks me a question I try to check that I understand what it is they actually want to know then I try and answer to the best of my ability.
You'll note that you were asked several times for a reference to which model you were talking about, precisely because we didn't know which one you wanted to know about. That you don't seem to know which one it is and are unwilling to provide a reference to whatever you've been reading so that we can find out for ourselves is a huge part of the reason you are running into resistance - you aren't helping us to help you.
I would like to know why we do not see any evidence of other universes.
I think you have this backwards, basically. Anything we can see is part of the universe, by definition. If you want to posit other universes, then, they must be regions that are somehow disjoint from our universe. My understanding is that different models achieve that in different ways. Eternal inflation, which V50 thinks is the model you are talking about, achieves it (if I understand correctly) by having the spaces between bubble universes growing faster than the bubble universes. Bubble universes cannot form inside others because the interiors of the bubbles are true vacuum not false vacuum and can never overlap if they don't overlap initially, so we can never see another universe.

One point to take into account is that, observationally, we do not see new universes forming. Any theory that posits other universes must therefore provide a mechanism by which we don't see them, otherwise it would be immediately dismissed unless all scientists discussing them were total idiots. Thus you dismissing multiverse theories in general on the grounds that we don't see other universes is somewhat disrespectful.

Again - different models have different mechanisms for explaining why we don't see other universes. Unless you are willing to specify a model, or tell us what you've been reading that prompted the question, you are unlikely to receive a specific answer.
 
  • #33
PeterDonis
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I understand the concepts that have been proffered but not the mathematics that supports them.
Then you need to go learn the math. Consulting a cosmology textbook (Liddle seems to be a good one) would be a good start.

PeterDonis tells me that space within our own universe is a complete vacuum (which I did not accept)
Since you admit you don't understand the math, you have no valid basis on which to either accept or to not accept what I said. What you should be doing is learning the math, so you can make a valid judgment.

then I am told that everywhere in our universe if full of the fundamental fields
Which is perfectly consistent with what I said about empty space in our present universe. Go read what I said in post #8 again about the empty space in our current universe. Notice the word "fields" in it, and what I said about them.
 
  • #34
PeterDonis
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What I am seeking to do is eliminate the Multiverse theories from my cosmological enquires by way of reason.
You can't eliminate hypotheses by way of reason alone unless they are logically inconsistent. Multiverse theories are not. You might not like them (and you would find plenty of physicists to agree with you), but you can't rule them out on purely logical grounds. That's why criticisms of such hypotheses by physicists don't attempt to rule them out on logical grounds; they criticize them based on lack of evidence.

Can anyone point me to an explanation given here that might help me understand?
You've already said you don't understand the math involved, and without that you won't be able to understand anything we have said in this thread in response to your questions. So, as I said in my previous post, you need to go learn the math.

Trying to understand physics without understanding the math is generally not a good idea. As Richard Feynman said, "If you want to understand Nature, you must learn the language She speaks in".
 
  • #35
PeterDonis
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I agree that further discussion is pointless!
Then you agree that this thread can be closed. So it's closed.
 

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