Freethought & Rationalism Archive

strubenuff · 07-19-2002, 04:41 PM

I didn't see any posts on this, and this forum seemed the perfect place to debate theoretical physics. What are your opinions on string theory (M-theory, now)? Any hardcore believers? Illogical bs otherwise bright and talented people are wasting their time on? Was the "discovery/necessity" of gravity/gravitons truly revolutionary? Was it even a step forward from our previous position? Are there 10, 11, 26, or 27 dimensions? Are all the curled up dimensions those of space, or are unknown dimensions of time hidden from us as well? Ect. Just wondering...

Answerer · 07-19-2002, 04:55 PM

Well, personally, I regard string theories as a product of 'mathematical fantasy'. Until the theory is being solved mathematically or there is evidence to support its predictions. I wouldn't take it very seriously.

Ron Singh · 07-19-2002, 05:52 PM

WEll one of the emerging equations out of the String Theory is Einstein's equation E=MC^2 I beleive. This should at least raise some brows. I don't think that we can empirically be certain of the theory until we can probe planck energies and actually check out these strings and such.

Friar Bellows · 07-19-2002, 06:08 PM

How many of us actually understand string theory enough to be able to have a "take" on it? I'd be interested to know. I certainly don't. Hell, I find the special theory of relativity to be daunting enough!

Steven S · 07-19-2002, 07:50 PM

Quote:

Originally posted by Ron Singh:
I don't think that we can empirically be certain of the theory until we can probe planck energies and actually check out these strings and such.

Actually, cosmology is where many theorists think ST might have a chance of being tested but I wouldn't make any bets that they will find any evidence anytime soon. But ask me more about this in about five years after I've had a chance to read and absorb Polchinski's big book.
SS

fando · 07-19-2002, 11:55 PM

Part of the reason we aren't hearing more about superstring theory is that the field is relatively new. It's very difficult for the lay audience, nay even a moderately well educated undergraduate in physics, to keep up with the rate of developments in the field. Heck, it's no longer even about strings, but membranes! It would be accurate to call the new focus Membrane theory, or M-theory for short.

eh · 07-20-2002, 06:18 AM

The theory formerly known as superstrings is an elegant theory, but lacks any real evidence as of yet. But, there are a few experiments over the next five years that could potentially give us that evidence.

It will take a lot of evidence to convince me there are all those extra dimensions out there.

Bill · 07-20-2002, 03:32 PM

The absolute, no holds barred, best book on string theory is Brian Greene's <a href="http://www.secweb.org/bookstore/bookdetail.asp?BookID=186" target="_blank">The Elegant Universe</a>.

I am predisposed towards believing that the current researchers into string theory are headed in the right direction, at least. In my essay, <a href="http://www.infidels.org/library/modern/bill_schultz/crsc.html" target="_blank">At the Intersection of "Metaphysical Naturalism" and "Intelligent Design"</a> I note, in passing, that the idea of additional dimensions of space, with the extra dimensions "rolled up" in some way, is almost as old as Einstein's theory of relativity itself. As I write in my essay:

Quote:

The key fact is that other dimensions of space must exist. In his Theory of Relativity, Einstein predicted that space would be warped around stars, and we�ve measured that to be true. If three-dimensional space is warped, it has to be warped through one or more extra dimensions over and above the three we naturally sense. Einstein tried to assert the spatial warping occurred through the time dimension. But that assertion has seemed to be flawed almost from the beginning because time is inherently measured in non-spatial units of dimension.

In 1919 an obscure mathematician by the name of Theodor Kaluza wrote Einstein about his Theory of Relativity. His basic assertion was that:

Instead of thinking of a four-dimensional universe, with time as the fourth dimension, Kaluza wrote, one should think of a five-dimensional universe, having four dimensions of space and one of time. He then proceeded to write down Einstein�s field equations in five dimensions, showing that not only is gravity included in these, but also Maxwell�s theory of light. With one bold stroke -adding a fifth dimension - Kaluza united the forces of gravity and electromagnetism in one equation.

. . .

This method of unifying gravity and electromagnetism was too much even for Einstein, however, and he never really paid it serious attention, though he did endorse the publication of Kaluza�s paper. With the development of quantum mechanics and the discovery of two more basic forces of nature, in the 1920s and 1930s, the weak nuclear force and strong nuclear force, the Kaluza-Klein theory died a quiet death. [footnote omitted]

Decades later, around 1968, physicists developed a new theory of a super-small basic particle called a "string." Unfortunately, mathematical analysis showed that these basic particles vibrated in 26 dimensions (25 of space and 1 of time). This was so disconcerting, that string theory was basically abandoned until about 1984 when the use of "super-symmetry" allowed the number of dimensions to be reduced to 10 (9 of space and one of time). At this point, physicists "resurrected the Kaluza-Klein theory. If space could consist of five dimensions, with the fifth dimension curled up, why couldn�t it consist of ten dimensions, with four space-time dimensions stretched out, and six space dimensions curled up? Ed Witten soon proved several new topological theories to help work with these ten-dimensional strings."[footnote omitted] Of course, there is no guarantee "string theory" will prove to be part of the final answer to quantum mechanics. However, at this moment in time, it remains as the leading theory which physicists everywhere are pursuing with great vigor.

The real problem with string theory is that we don't have the actual theory, and it does not appear that we will have the actual theory any time soon. What we do have are some rough approximations of what some particular pieces of the eventual theory ought to sort-of look like. The actual string theory is so incredibly complex that nobody has even begun to write the whole thing down. And in fact, it cannot even be proven that it is even possible to write the whole thing down.

However, none of these difficulties mean that string theory is not true. The universe contains many orders of magnitude of information more than could ever be represented, even if we used every single iota of matter and energy available to us within the universe (and every conceivable data compression algorithm to boot). So, if the ultimate string theory does prove to be way too complex for any human to ever write down, that (again) will not operate as a disproof of the theory. We will probably still continue to attempt to approximate what we can use from the theory.

==========

OK, now on to direct answers: <ol type="1">[*]Yes, this forum is the perfect place to debate theoretical physics. We do it all the time here. If you didn't find any relevant posts, it was merely because you didn't go far enough back into the archives.[*]My opinion of string theory is that it appears promising.[*]I'm not personally a "hardcore" believer, but I do side with those who would assert that its the best thing going at the present point in time (and it still needs to prove itself before I will become a "hardcore" believer).[*]I don't believe it is a waste of time by any means. Even failed research projects can produce highly valuable results (remember pennicillian?).[*]I don't know much about what you are referring to with your comments on gravity and/or gravitons. What we really need is a good theory of quantum gravity. So far, string theory offers the most promising road to that discovery.[*]I presume that all significant discoveries are "a step forward" even if the discovery is negative (i.e., we prove that X does not work).[*]Strings still vibrate over time in 26 spatial dimensions, for 27 dimensions, total. Are all of those dimensions real? Probably not. On the other hand, maybe 27 is an extremely small subset of all possible space/time dimensions. Who knows? The answer of 10 (9 space and 1 time) is what most current string theorists work with because they have employed the mathmatical process known as "supersymmetry" to get rid of the necessity of any additional dimensions, at least for the purposes of calculating results using the current approximations of string theory.[*]String theory does not presently postulate any extra dimensions of time. Whether or not any actually exist is somewhat of an open question. My personal opinion is that they do not exist because I rather believe that Einstein made somewhat of an error in attempting to force time to behave like a dimension of space. But again, that is my own personal opinion.[/list=a]So, there you have it; my own personal opinions (or "take" if you will) on string theory. Read and enjoy!

== Bill

Tim Thompson · 07-25-2002, 04:23 PM

Friar Bellows: How many of us actually understand string theory enough to be able to have a "take" on it?

I suspect this pretty much covers most, though perhaps not all, of the readers here. I've been trying to teach myself string theory, but it's slow going. I have <a href="http://theory.itp.ucsb.edu/~joep/bigbook.html" target="_blank">Joe's Big Book of String</a> (the 2-volume set by <a href="http://theory.itp.ucsb.edu/~joep/" target="_blank">Joe Polchinski</a>), but it really does require more preperation in quantum field theory than I think the book lets on (Polchinski claims to give you all the prep you need, but I respectfully disagree, at least in my case).

I agree with Bill that <a href="http://www.secweb.org/bookstore/bookdetail.asp?BookID=186" target="_blank">The Elegant Universe</a> is as clear a description of string theory as you are going to get, for an "lay" or "popular" level readers. Physicists & mathematicians will want more, but even for them, it's a good place to start (that's what I did).

My "take" on string theory is that it's very promising, and probably the direction that mathematical cosmology will go in for quite a while. But I also think that anyone who is willing to be a "hard core believer" in anything regarding cosmology is probably jumping the gun, to say the least. I suspect the only "hard core believers" in string theory are the few mathematicians & physicists who are actually deeply involved in constructing & investigating strings.

I think it's tremendously interesting, and worth the effort to understand. I think it is the most promising of the many mathematical directions for cosmology.

So here's a bunch of links. The webpages comprehensible, for the most part, except maybe Witten's lecture. The "technical pepers" are just that, non math-geeks may not want to download 250 pages, but you never know. Some have prose around the math that can be followed, even without the math. Unless you know your stuff, you might want to at least read Elegant Universe first.

Going away for a couple weeks vacation, and just wanted to leave something you all could remember me by!

Webpages
<a href="http://www.superstringtheory.com/index.html" target="_blank">The "Official" String Theory Website</a>
<a href="http://www.sukidog.com/jpierre/strings/" target="_blank">online Introduction to String Theory</a>
<a href="http://www.damtp.cam.ac.uk/user/gr/public/qg_ss.html" target="_blank">M-theory, the theory formerly known as Strings</a>
<a href="http://online.itp.ucsb.edu/online/plecture/witten/" target="_blank">Duality, Spacetime and Quantum Mechanics</a> (online lecture by Ed Witten)
technical Papers & Reviews
<a href="http://xxx.lanl.gov/abs/gr-qc/0205036" target="_blank">Introduction to branes and M-theory for relativists and cosmologists</a>
<a href="http://xxx.lanl.gov/abs/hep-th/0110055" target="_blank">Strings, Branes and Extra Dimensions</a> (238 pages)
<a href="http://xxx.lanl.gov/abs/hep-th/0207130" target="_blank">The Pre-Big Bang Scenario in String Cosmology</a> (250 pages)
<a href="http://xxx.lanl.gov/abs/hep-th/0202060" target="_blank">String inspired braneworld cosmology</a>
<a href="http://xxx.lanl.gov/abs/hep-th/0107176" target="_blank">Inflation and String Cosmology</a>
<a href="http://xxx.lanl.gov/abs/hep-th/0103156" target="_blank">The Promise of String Cosmology</a>

Dr Rick · 07-25-2002, 04:49 PM

Awesome, Tim; thanks for the links.
Rick

07-19-2002, 04:41 PM	#1
strubenuff Junior Member Join Date: Oct 2001 Location: NY Posts: 96	What's your take on String Theory? I didn't see any posts on this, and this forum seemed the perfect place to debate theoretical physics. What are your opinions on string theory (M-theory, now)? Any hardcore believers? Illogical bs otherwise bright and talented people are wasting their time on? Was the "discovery/necessity" of gravity/gravitons truly revolutionary? Was it even a step forward from our previous position? Are there 10, 11, 26, or 27 dimensions? Are all the curled up dimensions those of space, or are unknown dimensions of time hidden from us as well? Ect. Just wondering...

07-25-2002, 04:23 PM	#9
Tim Thompson Regular Member Join Date: Sep 2000 Location: Pasadena, CA, USA Posts: 455	Friar Bellows: How many of us actually understand string theory enough to be able to have a "take" on it? I suspect this pretty much covers most, though perhaps not all, of the readers here. I've been trying to teach myself string theory, but it's slow going. I have <a href="http://theory.itp.ucsb.edu/~joep/bigbook.html" target="_blank">Joe's Big Book of String</a> (the 2-volume set by <a href="http://theory.itp.ucsb.edu/~joep/" target="_blank">Joe Polchinski</a>), but it really does require more preperation in quantum field theory than I think the book lets on (Polchinski claims to give you all the prep you need, but I respectfully disagree, at least in my case). I agree with Bill that <a href="http://www.secweb.org/bookstore/bookdetail.asp?BookID=186" target="_blank">The Elegant Universe</a> is as clear a description of string theory as you are going to get, for an "lay" or "popular" level readers. Physicists & mathematicians will want more, but even for them, it's a good place to start (that's what I did). My "take" on string theory is that it's very promising, and probably the direction that mathematical cosmology will go in for quite a while. But I also think that anyone who is willing to be a "hard core believer" in anything regarding cosmology is probably jumping the gun, to say the least. I suspect the only "hard core believers" in string theory are the few mathematicians & physicists who are actually deeply involved in constructing & investigating strings. I think it's tremendously interesting, and worth the effort to understand. I think it is the most promising of the many mathematical directions for cosmology. So here's a bunch of links. The webpages comprehensible, for the most part, except maybe Witten's lecture. The "technical pepers" are just that, non math-geeks may not want to download 250 pages, but you never know. Some have prose around the math that can be followed, even without the math. Unless you know your stuff, you might want to at least read Elegant Universe first. Going away for a couple weeks vacation, and just wanted to leave something you all could remember me by! Webpages <a href="http://www.superstringtheory.com/index.html" target="_blank">The "Official" String Theory Website</a> <a href="http://www.sukidog.com/jpierre/strings/" target="_blank">online Introduction to String Theory</a> <a href="http://www.damtp.cam.ac.uk/user/gr/public/qg_ss.html" target="_blank">M-theory, the theory formerly known as Strings</a> <a href="http://online.itp.ucsb.edu/online/plecture/witten/" target="_blank">Duality, Spacetime and Quantum Mechanics</a> (online lecture by Ed Witten) technical Papers & Reviews <a href="http://xxx.lanl.gov/abs/gr-qc/0205036" target="_blank">Introduction to branes and M-theory for relativists and cosmologists</a> <a href="http://xxx.lanl.gov/abs/hep-th/0110055" target="_blank">Strings, Branes and Extra Dimensions</a> (238 pages) <a href="http://xxx.lanl.gov/abs/hep-th/0207130" target="_blank">The Pre-Big Bang Scenario in String Cosmology</a> (250 pages) <a href="http://xxx.lanl.gov/abs/hep-th/0202060" target="_blank">String inspired braneworld cosmology</a> <a href="http://xxx.lanl.gov/abs/hep-th/0107176" target="_blank">Inflation and String Cosmology</a> <a href="http://xxx.lanl.gov/abs/hep-th/0103156" target="_blank">The Promise of String Cosmology</a>

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07-19-2002, 04:55 PM	#2
Answerer Veteran Member Join Date: Feb 2002 Location: Singapore Posts: 3,956	Well, personally, I regard string theories as a product of 'mathematical fantasy'. Until the theory is being solved mathematically or there is evidence to support its predictions. I wouldn't take it very seriously.

07-19-2002, 05:52 PM	#3
Ron Singh Regular Member Join Date: Feb 2002 Location: Fremont, CA Posts: 163	WEll one of the emerging equations out of the String Theory is Einstein's equation E=MC^2 I beleive. This should at least raise some brows. I don't think that we can empirically be certain of the theory until we can probe planck energies and actually check out these strings and such.

07-19-2002, 06:08 PM	#4
Friar Bellows Veteran Member Join Date: Apr 2001 Location: arse-end of the world Posts: 2,305	How many of us actually understand string theory enough to be able to have a "take" on it? I'd be interested to know. I certainly don't. Hell, I find the special theory of relativity to be daunting enough!

07-19-2002, 11:55 PM	#6
fando Veteran Member Join Date: Sep 2001 Location: Los Angeles Area Posts: 1,372	Part of the reason we aren't hearing more about superstring theory is that the field is relatively new. It's very difficult for the lay audience, nay even a moderately well educated undergraduate in physics, to keep up with the rate of developments in the field. Heck, it's no longer even about strings, but membranes! It would be accurate to call the new focus Membrane theory, or M-theory for short.

07-20-2002, 06:18 AM	#7
eh Senior Member Join Date: Sep 2000 Location: Canada Posts: 624	The theory formerly known as superstrings is an elegant theory, but lacks any real evidence as of yet. But, there are a few experiments over the next five years that could potentially give us that evidence. It will take a lot of evidence to convince me there are all those extra dimensions out there.

07-25-2002, 04:49 PM	#10
Dr Rick Veteran Member Join Date: Jul 2000 Location: USA Posts: 5,393	Awesome, Tim; thanks for the links. Rick

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