Freethought & Rationalism Archive

luvluv · 10-04-2002, 04:55 PM

I read Lee Smolin's book (3 Roads to Quantum Gravity) which was centered mostly around loop quantum gravity. He seemed to be very pessimistic about the idea that a theory of quantum gravity would be able to overcome the anthropic argument. He even resorted to outlining a cosmic evolution scenario involving black holes "giving birth" to other universes as a means by which the laws of our own universe became so (seemingly) fine-tuned. He said that there were several consistent ways of describing a GUT for universes with one and two dimensions of space, and so there is no reason to assume there may not be more than one internally consistent equation to describe our world with 3 dimensions of space. He seems to believe that even if a theory of QG were to be found, there would still be unknown constants, pre-existing laws of nature, that are injected into the system, seemingly without explanation. I am almost finished with Brian Greene's the Elegant Universe, and while he seems a little more optimistic than Nolin (I gather because string theory is having more succes than LQG?) he still periodically admits that there is no reason to believe that there even is a single theory which will unify everything, and seems to admit that even if a system is fully internally consistent and ends with no infinities, it may still be wrong.

When I first started reading these physics books, I was told by many that the work of physicists in the arena of quantum gravity would totally eliminate the anthropic arguments. The books I am reading seem to suggest this is not the case. Unless I am misreading somewhere, quantum gravity will not answer all the anthropic coincidences. Some laws of nature just are, and no one knows why they are. So, will QG really solve the anthropic question? Or is this notion simply philosophy riding the coattails of science?

Nat · 10-04-2002, 05:38 PM

Indeed quantum gravity will most definitely not answer everything - all it will do is hopefully link gravity with the remaining fundamental force(s) (they are all linked through QED and QCD). We still won't likely be that close to "figuring it all out."

String Theory, however, has a potential to go quite a ways beyond QG and explain more of the structure of the Universe than anything previously, showing more of the constants we consider to be fundamental are likely contigent upon deeper structure. It won't, however, necessarily show why this deeper structure is the way that it is.

The old antropic principle and the related fine-tuning arguments aren't going away that easily, despite the fact that they are fallacious because they equate ignorance with knowledge. Unfortunately, ignorance may be unavoidable - I highly doubt we will ever be able to answer all the questions of physics.

Cheers

WinAce · 10-04-2002, 09:29 PM

What I don't get about the argument is that they require an intelligent being *possibly more fine-tuned than the universe* to arbitrarily exist without any explanation whatsoever before they can *explain the fine-tuning of the universe*.

Hey, come on--postulating an unexplained Borg Cube in an asteroid field to "explain" a 747 in a junkyard isn't really the best example of rational thinking.

Personally, I find the existence of *anything* existing for no real reason quite strange--but adding a magical entity to it only worsens the situation beyond the "head will explode in 5...4...3..." boundary.

eh · 10-05-2002, 06:49 AM

No, quantum gravity will not solve everything. But it will, however, allow us to explain what the big bang was, and put a cap on wild AP speculations. It may turn out that this universe is the only one possible, or it might indeed be one of thousands, or millions. But without having such a theory, the strong AP is mere speculation, and is an argument with a foundation built on sand.

luvluv · 10-05-2002, 02:57 PM

Side note:

1) How in the world do the strings get the energy to vibrate? If I understand correctly they are at the Planck tension, which is supposedly enourmously tense. Where in the world do the strings get the energy to vibrate these enormous tensions.

2) Why don't string vibrations ever slow down? What happens if they do?

fando · 10-05-2002, 10:51 PM

Answer questions by asking more detailed questions.

Quote:

Where in the world do the strings get the energy to vibrate these enormous tensions.

Remember, they're very small.

Quote:

Why don't string vibrations ever slow down? What happens if they do?[/QB]

Why does a guitar string attenuate when plucked? What would be the analogous reason for strings? Remember that strings (now membranes) are hypothesized to be the smallest things there are.

luvluv · 10-08-2002, 10:15 PM

But is there any actual theory for what makes them vibrate? Granted their small, but they should be subject to inertia like everything else.

Nat · 10-08-2002, 10:20 PM

"Granted their small, but they should be subject to inertia like everything else. "

Umm, why?

Inertia is not a very well understood concept, but most ideas milling about (Higg's Field and such) would not have any effect on anywhere near a Planck length level.

atrahasis · 10-09-2002, 05:58 AM

Quote:

Whatever can be done will be done

luvluv · 10-10-2002, 02:15 PM

Okay, Nat, but if I understand correctly the energy bands (or whatever strings are made of) have a supposedly enormous tension, greater than, say, a bar of steel. Even if a thing with such a tension is small, wouldn't it need to get energy from somewhere to vibrate? And wouldn't it slow down?

And why do they only vibrate at the rates which produce the handful of elementary particles? If inertia and all the other laws don't apply, couldn't they perhaps vibrate with infinite speed? Why isn't there an infinite number of elementary particles, if there is no law or process governing how or why the strings vibrate?

I'm not asking anybody HERE to answer the question, I would just like to be pointed to answers to the question.

10-04-2002, 04:55 PM	#1
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	Will Quantum Gravity solve everything? I read Lee Smolin's book (3 Roads to Quantum Gravity) which was centered mostly around loop quantum gravity. He seemed to be very pessimistic about the idea that a theory of quantum gravity would be able to overcome the anthropic argument. He even resorted to outlining a cosmic evolution scenario involving black holes "giving birth" to other universes as a means by which the laws of our own universe became so (seemingly) fine-tuned. He said that there were several consistent ways of describing a GUT for universes with one and two dimensions of space, and so there is no reason to assume there may not be more than one internally consistent equation to describe our world with 3 dimensions of space. He seems to believe that even if a theory of QG were to be found, there would still be unknown constants, pre-existing laws of nature, that are injected into the system, seemingly without explanation. I am almost finished with Brian Greene's the Elegant Universe, and while he seems a little more optimistic than Nolin (I gather because string theory is having more succes than LQG?) he still periodically admits that there is no reason to believe that there even is a single theory which will unify everything, and seems to admit that even if a system is fully internally consistent and ends with no infinities, it may still be wrong. When I first started reading these physics books, I was told by many that the work of physicists in the arena of quantum gravity would totally eliminate the anthropic arguments. The books I am reading seem to suggest this is not the case. Unless I am misreading somewhere, quantum gravity will not answer all the anthropic coincidences. Some laws of nature just are, and no one knows why they are. So, will QG really solve the anthropic question? Or is this notion simply philosophy riding the coattails of science?

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10-04-2002, 05:38 PM	#2
Nat Regular Member Join Date: May 2002 Location: USA Posts: 100	Indeed quantum gravity will most definitely not answer everything - all it will do is hopefully link gravity with the remaining fundamental force(s) (they are all linked through QED and QCD). We still won't likely be that close to "figuring it all out." String Theory, however, has a potential to go quite a ways beyond QG and explain more of the structure of the Universe than anything previously, showing more of the constants we consider to be fundamental are likely contigent upon deeper structure. It won't, however, necessarily show why this deeper structure is the way that it is. The old antropic principle and the related fine-tuning arguments aren't going away that easily, despite the fact that they are fallacious because they equate ignorance with knowledge. Unfortunately, ignorance may be unavoidable - I highly doubt we will ever be able to answer all the questions of physics. Cheers

10-04-2002, 09:29 PM	#3
WinAce Beloved Deceased Join Date: Feb 2002 Location: Carrboro, NC Posts: 1,539	What I don't get about the argument is that they require an intelligent being possibly more fine-tuned than the universe to arbitrarily exist without any explanation whatsoever before they can explain the fine-tuning of the universe. Hey, come on--postulating an unexplained Borg Cube in an asteroid field to "explain" a 747 in a junkyard isn't really the best example of rational thinking. Personally, I find the existence of anything existing for no real reason quite strange--but adding a magical entity to it only worsens the situation beyond the "head will explode in 5...4...3..." boundary.

10-05-2002, 06:49 AM	#4
eh Senior Member Join Date: Sep 2000 Location: Canada Posts: 624	No, quantum gravity will not solve everything. But it will, however, allow us to explain what the big bang was, and put a cap on wild AP speculations. It may turn out that this universe is the only one possible, or it might indeed be one of thousands, or millions. But without having such a theory, the strong AP is mere speculation, and is an argument with a foundation built on sand.

10-05-2002, 02:57 PM	#5
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	Side note: 1) How in the world do the strings get the energy to vibrate? If I understand correctly they are at the Planck tension, which is supposedly enourmously tense. Where in the world do the strings get the energy to vibrate these enormous tensions. 2) Why don't string vibrations ever slow down? What happens if they do?

10-08-2002, 10:15 PM	#7
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	But is there any actual theory for what makes them vibrate? Granted their small, but they should be subject to inertia like everything else.

10-08-2002, 10:20 PM	#8
Nat Regular Member Join Date: May 2002 Location: USA Posts: 100	"Granted their small, but they should be subject to inertia like everything else. " Umm, why? Inertia is not a very well understood concept, but most ideas milling about (Higg's Field and such) would not have any effect on anywhere near a Planck length level.

10-10-2002, 02:15 PM	#10
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	Okay, Nat, but if I understand correctly the energy bands (or whatever strings are made of) have a supposedly enormous tension, greater than, say, a bar of steel. Even if a thing with such a tension is small, wouldn't it need to get energy from somewhere to vibrate? And wouldn't it slow down? And why do they only vibrate at the rates which produce the handful of elementary particles? If inertia and all the other laws don't apply, couldn't they perhaps vibrate with infinite speed? Why isn't there an infinite number of elementary particles, if there is no law or process governing how or why the strings vibrate? I'm not asking anybody HERE to answer the question, I would just like to be pointed to answers to the question.

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