Multiverse

Can someone explain in simple terms how any science discipline point to this universe spitting machine called a multiverse.  Intuitively it doesn't seem like science can because of two reasons.  First time doesn't exist before the universe, so technically it's scientifically illogical to talk of anything "before" the universe.  Second, how can physics point to anything before the universe started when the laws of physics started at the big bang

Here are 4 or 5 things to consider.  This universe is an exception to probability in many areas.  So a way to get all these exceptions in one universe is to have had many universes.  Some numbers are as high as 1 in 10**500.  BUT this requires 10**500 times more total energy.  All the universes need not have started at the time ours did. Many could have started earlier, say 1 billion years earier, then any that are less than 1 billion light years away we would see now, we see none of these.  We could get an exceptional universe if this is not the first BB, but there have been many BBs all one after the other.  If the physics changes with each bang as in evalution then we can have an exceptional universe with as few as say 25. Each BB could have been smaller then the last also.  What ever caused the extra energy for the first could have kept growing and by the 25th , ours, there was a lot more energy which can explain why we are this big.  This universe is bigger than the obversable part and thus ours seems consistant through out.

This is explained in more detail at the forum "How Time Started" here, or see the  updated one at "Physics 1st".

You are also assuming the big-bang happened the way that we think it did. There are many theories, often quantum mechanical in nature, that suppose time had no "beginning". That the big bang was merely a marked period of rapid expansion, but it could have been exponentially damped close to zero size for an infinite time before that. There also could have been the "big bounce" as some like to call it where our current universe is merely the bounce of a previously collapsing universe. 

You also assume time is a real construct, which many theories also do not assume that. So the notion of a point in causality before the big bang is not totally out of the ordinary. There are also many higher-dimensional theories that believe that our R3 existence is merely a space in a higher-dimensional space that connects the other universes. Mostly string theory deals with that idea.

So while it would be true that we cannot make predictions in a space where the laws of physics had not come to be yet, it is not necessarily true that all natural laws stop existing in any upper-dimensional space just because our timeline happened to not have begun yet, or that we had a beginning at all. However, it is hard to answer those questions until we get a complete theory of quantum gravity.

One must be a little more careful in ones reasoning. "There are many theories, often quantum mechanical in nature, that suppose time had no "beginning"."  That may be true there are those theories, but if so they are junk.  IF one can not get from here back in time an infinite amount of time, THAN time from there can not get here either. So the time period we are currently in did not come from and infinite past time period.  Therefore, OUR TIME HAD TO START.   There could have been many infinite time periods in the past,  BUT not the time period we are current in.   As I said, please try to read T#1 from Physics 1st...

Our (observable) Universe started at the Big Bang. We don't have direct knowledge of anything beyond that.

Regarding the OP, it's worth noting there are different uses of the word "Multiverse" which are entirely separate.

One use is the idea that the random aspects of QM are explained by everything that is possible happening and us seeing just one possibility. This is a vast concept, where an infinite number of Universes spring out of each one at every instant in time.

In this Multiverse, different branches can interact to some extent. Eg the two slit experiment involves two different branches of the Multiverse superposing two paths of a particle.

There is a version of quantum mechanics that simply adds every possible path and calculates the complex sum of the amplitudes, and it works fine.

A different Multiverse covers the idea that quantum gravity (specifically M-theory) might permit a vast number of different sets of laws of physics. RPaulB referred to the number 10^500. This has a solid mathematical basis. It relates to Calabi-Yau manifolds, which describe the ways tiny extra dimensions can curl up.

At least that's what they tell me. 

OK, but what I am really looking for is not a mathematical description of how, how many or even if multiverses exist.  It is philosophically how is it possible science can even predict anything (multiverse or anything else) that exists before the laws of science exist?  How can it predict anything exists when it cannot even speak of anything "before time".  Philosophically or even common sense wise, it just doesn't make sense to me. 

I understand that string theory supposedly points to it.  Intuitively though it appears logically impossible.

Your argument is totally valid. You cannot try and describe a period with no physical laws using physics. The question is weather or not the laws come into existence at the start of time, or if time is an abstraction that we have created to help describe something else that id going on.

Addressing RPaulB, it depends on how you think of time. We like to think of time as this linear thing that has a beginning and end because it is anthropomorphized to human time. However, we have known for a while that things, especially relativistically and quantum mechanically, do not always behave like expected in classical mechanics. It is kind of grandiose to assert that time definitely had a beginning when we cannot calculate what was going on back then. That would be like me asserting what is behind a closed door that I haven't actually opened before. I may be correct in the end, but that doesn't make my assertion factually based or scientific. And for all I know time did have a beginning. I just think that we cannot rule out it being infinite or the fact that things exist outside of time.

Also, I do not know what you mean by "There could have been many infinite time periods in the past,  [but] not the time period we are [currently] in." I am not sure what you mean for a period of time to be infinite in length, but our period of time is finite. Are you claiming that the period in time that we are living in has come after an infinite period in time? Because traditionally, when we refer to a period in time, we may say that the modern era was followed by the post-modern era. In that situation, the two periods of time are all existing in time still. So, are these finite current periods of time following infinite periods of time? Would that not make time infinite anyways, just not time as we necessarily know it?

dnl, then why do we even theorize about a multi-verse.  Is the only reason to avoid the fine tuning issue?

I think the multiverse is something that just is a consequence of us trying to understand certain theories like quantum gravity. For some, it is their interpretation of quantum mechanics. I, personally, find it likely that there are higher dimensions where this applies. I have not found any compelling evidence to suggest otherwise. So, I don't think someone went out with the intent to show a multiverse. It just fell out of quantum mechanics and m-theory.

How though dnl?  Can someone explain to me how it is possible for quantum mechanics or string theory to predict anything where the number of both spatial and time dimensions and all laws of physics are unknown, as they were in the pre big bang environment?  That does not seem reasonable.

OPI, you seem to be asking good questions.  So go slow now.  QM and ST are both very wrong.  QM requires a particle to interact with itself.  ST requires a space before the universe started , BB.  There are only 3 dimensions. Go read T#1 in Physics 1st.  Pre BB is good too.  There were many BBs.  why would you think there is only this one ?  There all had Pre BBs .  But each is bigger. So the problem is how and WHY did time start in the first place. 

RPaul, you seem to quote a lot of classical mechanics. Just because a theory requires that a particle intersect with itself does not make it wrong. in fact, QM is often called the theory that has stood up to the most speculation among any other theory. Just because you don't like it does not make it untrue. That is at best wishful thinking.

OP, there are a few proposals for this model. There are actually several proposal. I mentioned the big bounce, where there was an organized collapsing universe before, and when it collapsed to a sufficient size, the math in QM validates that it should start expanding.

I think that they key difference between what you are asking and what I am saying is that you say the number of spatial and time dimensions are unkown, and the laws of physics are as well. But I am arguing that they are no unknowable. So, I think that there are laws of physics that hold at that small of a time scale. So, you are correct that we cannot make predictions if we don't know the laws of physics, but I think you have the invalid premise that we cannot know the laws of physics at that time.

It is conceivable that a (many laws of physics) Multiverse hypothesis might lead to concrete predictions about the character of the Big Bang, and these predictions might be tested by observation. Another possibility is that the laws of physics are not constant on scales that we can observe. There are already claims that alpha has changed very slightly over several billion years, but it is not clear yet if this is experimental error. If it proved true, the notion of fixed laws of physics as we understand them would have to be discarded. The true laws would then be the underlying laws of unified field theory (which we don't have yet).

LOL, as I was reading your comment I thought that the Young Earth Creationists would love it if the laws of physics weren't constant, especially the speed of light.  BTW, I do understand that wasn't the gist of your statement,.

OP you started this forum.  I have said there are no multiuniverses and gave 4 or 5 reasons why.  But what is your opinion now ?

An important fact is that it is not meaningful to consider any physical constant varying unless it is dimensionless. The speed of light provides a conversion factor between distances and times. As such, it could only be considered to vary by comparison with another quantity of the same dimensions. If a speed is measured in some way relative to some standard speed, it would have to derive from other physical constants (unless that speed was itself based on the speed of light). So it is the dimensionless combinations of physical constants that are fundamental and incorporate all of the information about the nature of physics.

The Standard Model of Particle Physics contains 19 defined constants (plus either 7 or 8 more, as yet not fully defined, to explain neutrino mass). A pile more are needed for a ToE, but they could be local in nature. There is believed to be fundamentally only one M-theory, but as you know it encompasses zillions of sets of laws of physics for different configurations (if I understand correctly), and these each have a pile of constants to describe the configuration.

I didn't post a comment on your post because I tend to agree that there is no multiverse.  As a Christian not having a multiverse would support my worldview because the fine-tuning argument for a God would then be  stronger.  Allow me to put my cards on the table.

I am trying hard to take off my worldview glasses and see science as unbiased as I can.  To do this I want to understand where the idea of a multiverse came from.  I have read that the sole reason for a multiverse was atheistic scientists groping for a reason to fight Christians fine tuning principle.  I suspect that comment may have come from a Christian's worldview though.  I want to see if he is right.  

Intuitively, it seems a stretch to me that the two slit experiment really is evidence for a multiverse.  The other comments have been speculation, like it came from the science of the BB or string theory.  I doubt I could follow the math even if I saw the formulas though.  Therefore, I really wanted a philosophical answer to my post #1.  I haven't gotten it yet.  Perhaps it's because there is no one on this forum who both understands it and can explain it in terms I can understand.   

This seems like ranting to me, although I might be misreading it.  If it is, then that's the reason  I didn't initially post the religious aspects of my inquiry.  Bottom line though, the request to learn the origins of the multiverse is sincere.  Isn't anyone else curious, Christian  or not?