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Author Topic:   Cosmology 101
Alasdair
Member (Idle past 5749 days)
Posts: 143
Joined: 05-13-2005


Message 31 of 79 (472312)
06-21-2008 5:45 PM
Reply to: Message 30 by Agobot
06-21-2008 5:38 PM


Re: Multiverse
How are pentagon shaped puddles relevant to anything?
The point is that obviously the constants and conditions of the universe appear "finely tuned" to our life. That's because the sort of life that came about is the kind that would do well under these constants - otherwise it would just die wouldn't it?
The puddle shapes itself to the hole it is in - not the hole to the puddle.

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AZPaul3
Member
Posts: 8513
From: Phoenix
Joined: 11-06-2006
Member Rating: 5.3


Message 32 of 79 (472320)
06-21-2008 6:05 PM


Back to The OP
Since this is Cosmology 101 not Personality 101 let's try to get back to the OP.
cavediver or Son Goku: If it's too early for this depth of discussion please say so, but the OP specifically asked for points on inflation.
One slant on the mechanism includes a scalar field energy difference (kinetic v potential) exerting negative pressure with GR saying under such negative pressure gravity becomes a repulsive force. Another hypothesis posits a scalar field of inflatons or a combination of Higgs fields (?)
Can either of you enlighten us on these hypotheses?

Replies to this message:
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Agobot
Member (Idle past 5529 days)
Posts: 786
Joined: 12-16-2007


Message 33 of 79 (472321)
06-21-2008 6:05 PM


A couple of days ago I watched on National Geographic some scientist claim that there would be no life on Earth if the Moon wasn't there to keep the axis of the earth rock steady with its gravitational pull. Had it been not for the Moon, we'd have a widely varying temperatures due to the constant axis shift. The chance for life to occur naturally is so slim, that we either have:
1. An extremely large number of other planets rotating around suns(AFAIK so far we have found just a few) and thus multiplying the chance that at least one planet could support life or...
2. There are other universes stemming from Big Bangs
Edited by Agobot, : No reason given.

Replies to this message:
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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 34 of 79 (472330)
06-21-2008 6:42 PM
Reply to: Message 27 by Force
06-21-2008 4:04 PM


Re: It's light.
Cavediver,
the milkyway galaxy is our galaxy.
Wow, you'd have thought that as a cosmologist, I might have known that...

This message is a reply to:
 Message 27 by Force, posted 06-21-2008 4:04 PM Force has not replied

  
Force
Inactive Member


Message 35 of 79 (472331)
06-21-2008 6:46 PM
Reply to: Message 33 by Agobot
06-21-2008 6:05 PM


agobot,
so, are you saying that if the conditions were different than we see in our universe that life, not life as we know it, but life would not be?

Thanks

This message is a reply to:
 Message 33 by Agobot, posted 06-21-2008 6:05 PM Agobot has not replied

  
Force
Inactive Member


Message 36 of 79 (472333)
06-21-2008 6:49 PM


INFLATION
Greetings,
azpaul3 writes:
Since this is Cosmology 101 not Personality 101 let's try to get back to the OP.
cavediver or Son Goku: If it's too early for this depth of discussion please say so, but the OP specifically asked for points on inflation.
One slant on the mechanism includes a scalar field energy difference (kinetic v potential) exerting negative pressure with GR saying under such negative pressure gravity becomes a repulsive force. Another hypothesis posits a scalar field of inflatons or a combination of Higgs fields (?)
Can either of you enlighten us on these hypotheses?
Anyone?
http://EvC Forum: Cosmology 101 -->EvC Forum: Cosmology 101
Edited by Force, : edit

Thanks

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 37 of 79 (472336)
06-21-2008 7:39 PM
Reply to: Message 32 by AZPaul3
06-21-2008 6:05 PM


Re: Back to The OP
Can either of you enlighten us on these hypotheses?
Scalar fields have been part of space-time physics since GR was first published 93 years ago. Einstein's Cosmological Constant (CC) is effectively a trivial scalar field. The template for Inflation, the exponentially expanding de-Sitter space-time discovered a few years after GR was puclished, is driven by the CC. True scalar fields became a serious consideration in Kaluza Klein theories (1920s) and later in Brans-Dicke theory around 1960. In the 70s and 80s, scalar fields were scattered throughout Supergravity, and then onwards in all flavours of string theory and now M-theory. There is nothing new about scalar fields
For a scalar field to drive an inflationary period of the Universe is trivial. However, to get the precise type of inflation that is consistent with observation requires a bit more care, and will probably involved a mixture of competing scalar fields. For those of us who have worked with supergravity and string theory, the scalar fields needed for inflation are not the ones we normally considered of old (wrong sign), but that has now been shown not to be a problem.
There's a good chance we will see our first evidence of a scalar field in action as the LHC starts delivering results - the Higgs field.

This message is a reply to:
 Message 32 by AZPaul3, posted 06-21-2008 6:05 PM AZPaul3 has not replied

Replies to this message:
 Message 43 by Force, posted 06-22-2008 11:54 AM cavediver has replied

  
Taz
Member (Idle past 3291 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 38 of 79 (472341)
06-21-2008 8:12 PM
Reply to: Message 15 by Agobot
06-21-2008 1:57 PM


Re: Multiverse
Agobot writes:
The strentgh of the fundamental forces in the universe(force of gravity, speed of light, strong nuclear force, weak nuclear force, proton mass, etc.) is so finely tuned(to support life?), that the only good explanation for the existence of these finely tuned conditions besides god, would be a multiverse and multiple big bangs giving rise to multiple universes.
Since the universe is so finely tuned to support life, would you like to go up into space in a space shuttle and then take a little flying lesson outside in space without a space suit? I hear that there is an increasing interest to send some people to Mars. Would you like to volunteer to be the first man on Mars while not wearing a life-support suit?
Your statement there is false in so many ways... I don't even know where to begin. Everything about the universe is AGAINST life as we know it. The Earth is only a tiny oasis in an infinitely vast desert.
But don't mind me. If you really want to prove your statement to the rest of us, an action is worth more than a thousand words. Just sign up to be an astronaut and demonstrate to us just how hospitable the universe is to our form of life.

I'm trying to see things your way, but I can't put my head that far up my ass.

This message is a reply to:
 Message 15 by Agobot, posted 06-21-2008 1:57 PM Agobot has replied

Replies to this message:
 Message 39 by Agobot, posted 06-22-2008 3:07 AM Taz has replied
 Message 40 by cavediver, posted 06-22-2008 6:38 AM Taz has replied

  
Agobot
Member (Idle past 5529 days)
Posts: 786
Joined: 12-16-2007


Message 39 of 79 (472397)
06-22-2008 3:07 AM
Reply to: Message 38 by Taz
06-21-2008 8:12 PM


Re: Multiverse
Taz writes:
Since the universe is so finely tuned to support life, would you like to go up into space in a space shuttle and then take a little flying lesson outside in space without a space suit? I hear that there is an increasing interest to send some people to Mars. Would you like to volunteer to be the first man on Mars while not wearing a life-support suit?
Your statement there is false in so many ways... I don't even know where to begin. Everything about the universe is AGAINST life as we know it. The Earth is only a tiny oasis in an infinitely vast desert.
But don't mind me. If you really want to prove your statement to the rest of us, an action is worth more than a thousand words. Just sign up to be an astronaut and demonstrate to us just how hospitable the universe is to our form of life.
Hehe. I obviously meant to say to support life on Earth. I never said there's life on other planets(I couldn't know that). And I said "life as we know it"(hint here on Earth - hehe). So on to the question - how do you know there's life outside of earth? Care to present your evidence? Care to dress your space suit and take us to where alien life might be?

This message is a reply to:
 Message 38 by Taz, posted 06-21-2008 8:12 PM Taz has replied

Replies to this message:
 Message 42 by Force, posted 06-22-2008 11:06 AM Agobot has not replied
 Message 49 by Taz, posted 06-22-2008 2:38 PM Agobot has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 40 of 79 (472408)
06-22-2008 6:38 AM
Reply to: Message 38 by Taz
06-21-2008 8:12 PM


Re: Multiverse
Everything about the universe is AGAINST life as we know it.
Nonsense. Everything about the Universe is precisely what is required to enable life on at least one planet. To build up sufficient odds of life taking hold on a suitable planet/body, it appears that you require a Universe of this size, age, density, etc. To claim that the Universe is hostile or against life is simply missing the comsological "evolutionary" process that has brought us to this point. It is like claiming the utter hostily of the Earth to life, as life can only occur in a thin biosphere (even allowing for extremophiles) compared to the immense volume present. The immense volume is *required* to generate a viable biosphere. Or the inappropriateness of a Saturn V launch vehicle for manned space-flight, given how little of it is given over to human occupancy. And don't make the mistake of thinking I'm talking about design - this is simply about required precursors.
There is nothing mystical, magical, or religious in pointing out that the Universe is utterly perfect for our existence. It's just good old weak anthropic tautology.
Moving on to Rahvin's point:
If the Earth existed in isolation, in a Ptolemaic cosmology, then there really would be a "fine-tuning" argument for a creator - but we now realise that we live in a "multiverse" of countless planets around countless stars in countless galaxies. These planets allow for innumerable plays at the game of life, and by simple anthropic reasoning, we find ourselves on one of the lucky winning planets.
Now sure, tweak around with some of the fundamental constants and you may find in our local vicinity of the "Universal" parameter-space that there are some other possibilities that allow for elements with similar capabilities to carbon/silicon. There may even be far superior element sets that give rise to universes that are teaming with life compared to ours. But most modifications in the parameter-space are going to give not just useless elements, but no elements at all.
We're not looking at the Universe as a whole as being finely-tuned for life, it is finely-tuned for some resemblence of "normal" existence - for structure, for planets (or similar), for stars (or similar), and for a reasonable time-scale. Universes that exist for between 1ms and 1Myrs are not going to be much use, whatever structure they may contain. Likewise, universes that live forever by expanding so quickly that individual quanta become causally isolated after a few 10^-30 seconds are not going to be particularly useful for life!
It is difficult to have a rigorous measure on these things, but from all of our playing at building models of universes, there appears to be 10^(large number) more universes that are utterly hopeless at producing life compared to those that even get close to producing some form of structure.
Some of the parameters may well have natural methods of arriving at their "finely-tuned" values - such as the critical density of the Universe. Inflation naturally generates this precise value. But others (such as the Cosmological Constant) seem to be so far from the values that we would expect, and are intimately tied with our existence (as in, any kind of life, plants, stars, etc.) And even inflation seems to require a precise set of circumstances, and so is possibly not as "natural" as we once hoped.
The obvious answer is that just as the coarse high-level parameters relevant for life (mass of planet, distance from star, type of star, age of star, presence of moon, absence of nearby stellar unpleasantness, presence of Jupiter-type, etc, etc) are played out across the Universe, guaranteeing our existence somewhere (maybe as heptapodal gralfinches on Tau Ceti IV) - the fundamental parameters of our Universe are played out over a much larger scale. This is has been the direction that our research has pushed us for some time now - supergravity, string theory, eternal and chaotic inflation, ekpyrotic universes, and now the Landscape of modern string theory/M-theory. We are not short of multiverse theories! And for a long time, we have regarded them as a possible saving explanation for the otherwise apparent fine-tuning of our Universe that allows for "stuff" to exist, never mind life.

This message is a reply to:
 Message 38 by Taz, posted 06-21-2008 8:12 PM Taz has replied

Replies to this message:
 Message 50 by Taz, posted 06-22-2008 2:41 PM cavediver has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 41 of 79 (472409)
06-22-2008 6:40 AM
Reply to: Message 20 by Rahvin
06-21-2008 2:14 PM


Re: Multiverse
Sorry Rahvin, I made a large reply to your post but it ended up being tacked on to the end of a reply to Taz. Please see message 40 for the details.

This message is a reply to:
 Message 20 by Rahvin, posted 06-21-2008 2:14 PM Rahvin has not replied

  
Force
Inactive Member


Message 42 of 79 (472426)
06-22-2008 11:06 AM
Reply to: Message 39 by Agobot
06-22-2008 3:07 AM


Re: Multiverse
Agobot,
"HEY WHAT ABOUT MY QUESTION?"
http://EvC Forum: Cosmology 101 -->EvC Forum: Cosmology 101
Edited by Force, : LINK ERR

Thanks

This message is a reply to:
 Message 39 by Agobot, posted 06-22-2008 3:07 AM Agobot has not replied

  
Force
Inactive Member


Message 43 of 79 (472429)
06-22-2008 11:54 AM
Reply to: Message 37 by cavediver
06-21-2008 7:39 PM


Re: Back to The OP
cavediver,
Scalar fields have been part of space-time physics since GR was first published 93 years ago. Einstein's Cosmological Constant (CC) is effectively a trivial scalar field. The template for Inflation, the exponentially expanding de-Sitter space-time discovered a few years after GR was puclished, is driven by the CC. True scalar fields became a serious consideration in Kaluza Klein theories (1920s) and later in Brans-Dicke theory around 1960. In the 70s and 80s, scalar fields were scattered throughout Supergravity, and then onwards in all flavours of string theory and now M-theory. There is nothing new about scalar fields
For a scalar field to drive an inflationary period of the Universe is trivial. However, to get the precise type of inflation that is consistent with observation requires a bit more care, and will probably involved a mixture of competing scalar fields. For those of us who have worked with supergravity and string theory, the scalar fields needed for inflation are not the ones we normally considered of old (wrong sign), but that has now been shown not to be a problem.
There's a good chance we will see our first evidence of a scalar field in action as the LHC starts delivering results - the Higgs field.
So, is a "scaler field" a force of positive or negetive energy that spans the entire universe in a particular frequency?
I just wanted to provide a link on LHC:
http://www.uslhc.us/What_is_the_LHC
Edited by Force, : link

Thanks

This message is a reply to:
 Message 37 by cavediver, posted 06-21-2008 7:39 PM cavediver has replied

Replies to this message:
 Message 44 by cavediver, posted 06-22-2008 12:45 PM Force has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 44 of 79 (472432)
06-22-2008 12:45 PM
Reply to: Message 43 by Force
06-22-2008 11:54 AM


Re: Back to The OP
So, is a "scaler field" a force of positive or negetive energy that spans the entire universe in a particular frequency?
Effectively, yes. They can appear as a negative energy or a positive energy in their effect upon the Universe, in terms of causing an expansion or contraction. Noramlly a field will fluctuate over all of time and space so there would be no particular overall frequency, but scalar fields in particular do have a habit of becoming "frozen out" at particular values, so in effect they are of a particular frequency.

This message is a reply to:
 Message 43 by Force, posted 06-22-2008 11:54 AM Force has replied

Replies to this message:
 Message 45 by Force, posted 06-22-2008 12:47 PM cavediver has replied

  
Force
Inactive Member


Message 45 of 79 (472434)
06-22-2008 12:47 PM
Reply to: Message 44 by cavediver
06-22-2008 12:45 PM


Re: Back to The OP
cavediver,
Are scaler fields a complete inference or is there evidence that they exist?

Thanks

This message is a reply to:
 Message 44 by cavediver, posted 06-22-2008 12:45 PM cavediver has replied

Replies to this message:
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