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Multiverse cosmology

by Otherkin
Tags: cosmology, multiverse
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marcus
#37
Nov29-11, 01:14 PM
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If you accept what Ashtekar says about the enhanced liklihood of sufficient ordinary inflation in the Loop case then the usual support for "Eternal Inflation" is flawed. There is much less reason to be interested in it, beyond inherent fantasy-appeal of the the grandiose vision.

Specifically, sufficient means 60 e-folds--to produce the observed uniformity. The usual argument is basically one of desperation: "we can't think of any normal physics mechanism for inflation to get started, and then continue 60 e-folds, and then stop!" But Ashtekar can. (Loop is comparatively mundane, you quantize and go with established cosmology. I might say it is no more than a "hop" of faith.)

Once you posit some exotic leap-of-faith mechanisms you see stuff happening like eternal inflation. Support for eternal inflation depends on not being able to think of any other way that an adequate inflation episode could have started and then turned off.

It looks to me like some of these guys with exotic brane-clash and multiverse ideas have vested interest in ignoring simple answers--which threaten the raison d'Ítre for some unnecessarily elaborate pet constructs.

You saw what happened at the end of Neil Turok's talk---we discussed this earlier. I'll get the link in case anyone else wants to check it out. It was the opening talk at a Perimeter conference he and some other people organized on "Challenges for Early Universe Cosmology"
http://pirsa.org/11070044/
Overview of the Challenges
Neil Turok
12/07/2011 - 9:00 am

The video lasts 1 hour 10 minutes and Elena's comment about the Ashtekar Sloan work starts right about 1 hour 7 minutes. You can of course drag the button to just hear the last 3 minutes. But the talk is interesting overall--especially the comments from the audience---Leonard Susskind, Sean Carroll etc etc. IIRC this starts around minute 55.

At this point Turok has his summary slide up. The challenges he identifies are:
Singularity
Tuning [in particular to get inflation which continues long enough and then turns off]
Reliance on anthropics
Measure
Several audience comments stressed challenges related to entropy: "2nd law" paradoxes.

I'm not suggesting one should take this talk as actually authoritative/representative about early universe cosmology. Neil, Lenny, Sean, Lindei, Vilenkin...etc are vocal but they are not currently writing a lot of papers or getting cited very much. I think it is a subcommunity which may be feeling a bit on the defensive at present. The interesting part is to see what arguments they have organized to justify this collection of ideas.
eloheim
#38
Dec2-11, 08:54 AM
P: 65
Aren't there some Anthropic Principle-related suggestions for the Multiverse? Like one would expect the values of any natural "constants" vital to intelligent life to be only barely deviant from typical. Basically, assuming that a universe fit for life will need to be more picky about them than otherwise, finding we live in a "1-in-a-trillion" universe when there are a "million-in-a-trillion" other ways (universes) that allow for life would make our theories on such things seem very unlikely to be true.

Does anyone have a good understanding of if we have any indications on this for our values (universe), or even any notions of what kind of values we should be looking at?
Deuterium2H
#39
Dec3-11, 02:30 AM
P: 59
Quote Quote by George Jones View Post
Please keep religious discussion, either pro or con, out of all posts in this thread, and out of all posts in the science forums at Physics Forums.
Hi George,

Not saying you don't...but I hope you are just as strong in your advice when it comes to the opposite scenario. For example, Hawking's fervent insistence that our Universe does not need or require a "Creator", is just as much a metaphysical and philosophical position (and as such, is outside the bounds of "Science) as those who posit some sort of Intelligent Creator behind it all.

In either case, we are stepping outside "Science", and what can be tested and potentially falsified. If Religion has no place in the discussion of the origin of the Universe, neither does the speculative metaphysics of a "cyclic" universe, or even a "multiverse" for that matter, IMHO.
jdm1001
#40
Dec3-11, 10:21 PM
P: 1
Sorry everyone, I had not intention to create a discussion on determining the what the un-caused, cause is. It is absolutely imperative that faith in science must be supported by observations and known facts. All I wanted to do is show how the study of the un-caused cause and the study of the unknown are rapidly merging into the one in the same.
juanrga
#41
Dec4-11, 09:19 AM
P: 476
Quote Quote by Otherkin View Post
I really know nothing whatsoever about cosmology although I find it very interesting. It seems that a lot of physicists nowadays reckon there's a multiverse. I don't particularly want there to be a multiverse. WHAT DO YOU FOLKS THINK. Also, if there was a multiverse, would the laws of physics be the same for all of the universes? And would every single possibility be actually occurring in some universe out there? Like, in one universe am I being cut into bits from the toes up without anaesthetic and then having my body regenerated by some piece of advanced technology and then being cut up again OVER AND OVER FOREVER? All the while having faeces smeared in my face?
Multiverse is a non-scientific hypothesis.
Chalnoth
#42
Dec4-11, 10:13 AM
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Quote Quote by juanrga View Post
Multiverse is a non-scientific hypothesis.
Completely and utterly false. Try again.
juanrga
#43
Dec4-11, 10:17 AM
P: 476
Quote Quote by Chalnoth View Post
Completely and utterly false. Try again.
Multiverse is a non-scientific hypothesis

http://en.wikipedia.org/wiki/Multiverse#Criticisms
Chalnoth
#44
Dec4-11, 10:21 AM
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Quote Quote by juanrga View Post
Multiverse is a non-scientific hypothesis

http://en.wikipedia.org/wiki/Multiverse#Criticisms
Noting that some people say that doesn't actually make it true. Back in here in reality, it is very much a scientific hypothesis. For example:
http://arxiv.org/abs/0901.0007
juanrga
#45
Dec5-11, 03:35 PM
P: 476
Quote Quote by Chalnoth View Post
Noting that some people say that doesn't actually make it true. Back in here in reality, it is very much a scientific hypothesis. For example:
http://arxiv.org/abs/0901.0007
My original statement remains unchanged
otherme
#46
Feb27-12, 06:45 AM
P: 1
Hi, I'm new here and don't pretend to understand very much of what's being said but physics fascinates me. Multiverse theory fascinates me. And, as with all sciences, don't you start with a postulate then go about proving or disproving that postulate. Something like multverse and M theory would be, I would imagine, very difficult to prove one way or the other. From my understanding, universes are close to, connected and sometimes intertwine each other - or so the theory goes. I should say - a theory goes, as there are so many. Like I said, I don't understand much but find it all fascinating. I feel there is something more than what we see with our eyes.
rbj
#47
Mar8-12, 11:30 PM
P: 2,251
Quote Quote by Tanelorn View Post
I agree with a Multiverse of observable universes if that is the right word. I have trouble with them having different laws of Physics,
i think the idea is that they might have different fundamental constants than our universe.

in my opinion, the concept of the Multiverse was cooked up so that the (weak) Anthropic principle would be able to explain away any teleological argument about the existence of God. if there are many, many other universes, some might be life friendly and some not. and it's an example of selection bias that we find ourselves in a universe that is life friendly.
rbj
#48
Mar8-12, 11:36 PM
P: 2,251
Quote Quote by Chalnoth View Post
Completely and utterly false. Try again.
So when you show me an experiment that will test and falsify the existence of some other universe, I'll show you an experiment that will do the same regarding God. Wanna see my God-measuring device?

Chalnoth, your belief, and that is all it is, is unscientific.
Chalnoth
#49
Mar9-12, 12:22 AM
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Quote Quote by rbj View Post
i think the idea is that they might have different fundamental constants than our universe.

in my opinion, the concept of the Multiverse was cooked up so that the (weak) Anthropic principle would be able to explain away any teleological argument about the existence of God. if there are many, many other universes, some might be life friendly and some not. and it's an example of selection bias that we find ourselves in a universe that is life friendly.
The only way you could possibly come to this conclusion would be through complete and utter ignorance of the scientific discussion surrounding the multiverse. Put simply, no god ever has or ever will come into it, because no scientist worth their salt considers a god as a reasonable hypothesis, or has done so for quite a long time. There are strong epistemological reasons for this which I won't go into, but suffice it to say that it is fundamentally impossible to make forward progress in science by using a god hypothesis (no matter which god you're talking about).

Instead, the argument has always been between two camps within the theoretical physics community. On the one side, we have physicists who think that the natural laws we observe must be derivable from some fundamental theory. This has, for much of the history of physics, been the majority view. However, recent work in developing grand-unified theories has put doubt on this view, to the point that high-energy theorists are becoming increasingly convinced that it is just not feasible. And so physicists are increasingly moving away from the idea of a fundamental theory from which everything we observe inevitably follows and towards a fundamental theory which is prolific. A prolific fundamental theory explains everything we observe by stating that many things happen, and life occurs where it can occur, with most of the universe being uninhabitable.

None of this has ever referenced any sort of god, either before or after.
Chronos
#50
Mar9-12, 01:03 AM
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Science seeks a causal relationship between properties and evolution of the universe. God is a first principle proposition and neither science or mathematics is the right tool for dealing with first principles.
skydivephil
#51
Mar9-12, 01:50 AM
P: 450
Quote Quote by rbj View Post
i think the idea is that they might have different fundamental constants than our universe.

in my opinion, the concept of the Multiverse was cooked up so that the (weak) Anthropic principle would be able to explain away any teleological argument about the existence of God. if there are many, many other universes, some might be life friendly and some not. and it's an example of selection bias that we find ourselves in a universe that is life friendly.
The history of science is not realy a question of your opinion. It is possible to go and look up things and see where certain ideas came from.
There are different definitions of the multiverse. I would sugggest the two most popular ideas are the many worlds interpretation of Qm and the inflationary multiverse.
The first was invented to deal with the problems of the Copenhagen interpretation of QM, nothing to do with anthropics. The second came from inflation. Inflation was desgined to solve one problem and one problem only, thats the magnetic monopole problem, again nothing to do with anthropics. Later it was realised it solved other problems and as the theory was developed it was argued the inevtiable consequence of inflation was a multiverse. If you would like to read about this I suggest reading Alan Guths book "The Inflationary Universe", there is also a new biography of Hugh Everett which woudl enable you to understand the motivation of the first type. They were not invented as a way of dealing with arguments for god, that just not histroically accurate at all.
pebbleanrock
#52
Mar11-12, 11:57 PM
P: 3
Quote Quote by Chronos View Post
Science seeks a causal relationship between properties and evolution of the universe. God is a first principle proposition and neither science or mathematics is the right tool for dealing with first principles.

I read a book explaining the creation of the universe. It said the universe started its journey as a tiny empty space surrounded by a sea of energy at absolute zero. The energy was in the form of straight strings before it had decayed into the circular stringed form of the particles of this universe. In describing the space /matter or energy relationship of the centre of a black hole, Einstein said it was infinity + infinity + infinity and was accused of a mistake. While a black hole has not reached this state, it does describe the sea of energy or the state the black hole energy is trying to entropize to. This is best envisaged as a super BEC [ Bohr Einstein Condensate ] where an almost infinite quanta of straight string fits into the same space. The energy, under pressure has arced into the tiny empty space and raised the temperature of the nearby sea. As this almost infinitely deep straight string area decays into circular string quantum they have their own piece of space. Part of the residue of each matter/antimatter annihilation would be 2 quanta of new space. A multitude of waves is moving through the energy sea. These differing waves of straight string then decay into different energy amounts thus producing the vast array of different particles. As well as the annihilation, other particles combine to form hydrogen and helium. The book is the Bible and seems to have been incorrectly read for thousands of years. My full essay can be found at <pebbleanrock.org>. comment?
cephron
#53
Mar12-12, 02:11 AM
P: 125
Quote Quote by pebbleanrock View Post
I read a book explaining the creation of the universe. ... The book is the Bible and seems to have been incorrectly read for thousands of years. My full essay can be found at <pebbleanrock.org>. comment?
The bible is simply not a scientific textbook. The important points made in Genesis are about who God is and what his relationship is to man and creation, not the details of the mechanistic process by which it all happened. To try to turn the Bible into a science textbook is worse than useless.

I think Chronos had it right. Science makes models to explain objective, repeatable observations. Science simply does not make any claims about God, because God doesn't interact with the world in an objective, repeatable basis.
pebbleanrock
#54
Mar12-12, 02:15 AM
P: 3
Quote Quote by cephron View Post
The bible is simply not a scientific textbook. The important points made in Genesis are about who God is and what his relationship is to man and creation, not the details of the mechanistic process by which it all happened. To try to turn the Bible into a science textbook is worse than useless.

I think Chronos had it right. Science makes models to explain objective, repeatable observations. Science simply does not make any claims about God, because God doesn't interact with the world in an objective, repeatable basis.
You do not know this . You have been told by somebody. 'circle of the earth' THEN they thought "its round." hang the earth on nothing"then they thought we're just floating there" "Write on tablet of your heart" heart transplant scientists find in 1990's that heart nerves support memory. Entropy,"the heavens will wear out like a garment" all these written 3500 years ago. Now its opened up again.


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