Since the 50s, particle physicists have found ways of classifying particles intro groups, much the way Mendelev classified elements into groups via the Periodic Table. When doing this, they discover "missing" particles that fit within a certain group but were not yet known, thus giving such groupings predictive power.
Different groups have different symmetries. E8 is a group in Lie algebra. The group is "exceptional" and "simple" which is why the article is entitled tongue-in-cheekishly "Exceptionally Simple". The power and beauty of the E8 group has been known for a long time, and it's featured in many theories of physics that have tried to provide an framework for explaining the bewildered world of particles and forces that make up the universe.
What this author has done is use E8 in a new way to come up with a potential new theory that unifies all the forces and fields. This is not *strictly* a theory of everything, as there's a lot more that has to be answered, but if true it provides a geometric model that can give us insight into the underlying principles that are involved, just the way the Periodic Table does for elements.
The guy is no kook, but his theory leaves a lot to be desired. One problem is that E8 and other lie algebras and their associated symmetries have been well-studied for decades, and most all of them have run into intractable problems or incorrect predictions, so this may just be another beautiful theory that doesn't fit reality. Lisi uses a little-known method called "BRST connections" to make it all seem to work, which most physicists are unfammiliar with. Another is that his theory actually forces something physicists call as "spontaneous symmetry breaking" into the calculations to make it fit what we know to be true in the "standard model". Many people feel this is putting the cart before the horse; they would prefer a theory where the symmetry is broken in a "nautral" way and the "standard model" of the universe just naturally falls out of it. Lisi's theory doesn't really tell us WHY this is the case, it just says it is, but here's the symmetry that underlies it and which you apply it to.
Another problem is that the theory is still new and doesn't have an quantitative predictions as of yet... there's a lot of math that needs to be done, and it's not clear that such calculation *can* be done given the contraints of his theory. At issue is something known as the "Coleman-Mandula" theorem, which basically says a lot of what Lisi does in his theory doesn't work if there are subgroups in the algenbra that are equivalent to what are known as Poincare groups. Lisi says this doesn't apply to his new theory because it posits that the vacuum of spacetime doesn't have Poincare symmetry but instead is deSitter space. Well, the idea of deSitter space is well-known and has been examined in theoretical physics for decades as well, but there are a lot of problems with it. One is that the "Smatrix", which physicists love so much in making calculations in theories with Poincare symmetries, no longer works and simply becomes an approximation.
The theory also predicts a very LARGE cosmological constant, which is contrary to observation, but there are other theories that explain how this is not actually a problem, so that might not be an issue. Perhaps the largest obstacle of the theory, once the calculations can be figured out, is that it pretty much obsoletes all of String Theory in favor of something like Loop Quantum Gravity. This will make a LOT of string physicists very unhappy.
Lisi's theory will probably not be the last work in physics, but it might bring us a step closer to a real "Theory of Everything". The truth is physicists have been toying with similar geometric approaches and arrange particles in tables and trying to tie in gravity for decades now and every new theory looks great but never quite actually works out. The fact that the universe can *almost* be described via these methods probably tells us we're on the right track, but a true simple unifying description that underlies all of reality still eludes us.
You have no idea how your reply makes me feel, as I'm someone who stopped studying physics as a Freshman in college and can barely grasp the basic ideas behind the whole thing.:) But a hallmark of your theory seems to be that it's conceptually understandable even to those who don't understand all of the intricate parts.
I admit I'm still a bit skeptical... I mean, if E8 is the answer, why did none of the other E8 approaches work? But you're doing some unique things in your approach and in them may lie the answer. Almost makes me wish I had stayed in physics, but the math is just beyond me.
Hey look, my server's melting -- must of hit slashdot...
Must have! Must HAVE!
How can you write a paper revolutionizing our understanding of physics if you don't use proper grammar?!
I imagine he spent his time studying maths and physics instead of English. That is, after all, the point of specialization and university; he becomes incredibly competent in one field at the expense of another. This, of course, also explains why I have excellent karma but no life.
Hey look, my server's melting -- must of hit slashdot...
Must have! Must HAVE!
How can you write a paper revolutionizing our understanding of physics if you don't use proper grammar?!
This is precisely why he can. People who stay locked up in thinking (and therefore writing) like everybody else, can not write a paper revolutionizing anything at all.
I can't decide which is cooler: - The fact that the author posted to Slashdot. - Or the fact that he once posted to a thread called "Monkey Pays for Monkey Porn."
Another problem is that the theory is still new and doesn't have an quantitative predictions as of yet... there's a lot of math that needs to be done, and it's not clear that such calculation *can* be done given the contraints of his theory. At issue is something known as the "Coleman-Mandula" theorem, which basically says a lot of what Lisi does in his theory doesn't work if there are subgroups in the algenbra that are equivalent to what are known as Poincare groups. Lisi says this doesn't apply to his new theory because it posits that the vacuum of spacetime doesn't have Poincare symmetry but instead is deSitter space. Well, the idea of deSitter space is well-known and has been examined in theoretical physics for decades as well, but there are a lot of problems with it. One is that the "Smatrix", which physicists love so much in making calculations in theories with Poincare symmetries, no longer works and simply becomes an approximation.
Um wait a minute. Both here on Slashdot as well as over at the 'original' telegraph.co.uk article, a very important point is that Lisi's theory does makes predictions. For paticles within the energy range that the LHC will open up.
So I suppose what you're trying to say is that yet more mathematics (and mathematics given to well-known pitfalls) will need to intervene between tying together Lisi's theory and any observations that result from LHC experiments?
It does make some predictions about new particles, some new fields, and perhaps even proton decay. But actually turning the geometric model into actual predictive calculations may be problematic. And even if it can correctly predict the masses of certain particles, it may not be able to calculate various universal constants which are otherwise believed to be fundamental.
People with your gift for explaining difficult concepts with such clarity are rare. Thank you for expending the effort to make this clear to me. Your work is very much appreciated.
"The only way I can lose this election is if I'm caught in bed with a dead
girl or a live boy."
-- Louisiana governor Edwin Edwards
An attempt at a summary (Score:5, Informative)
Different groups have different symmetries. E8 is a group in Lie algebra. The group is "exceptional" and "simple" which is why the article is entitled tongue-in-cheekishly "Exceptionally Simple". The power and beauty of the E8 group has been known for a long time, and it's featured in many theories of physics that have tried to provide an framework for explaining the bewildered world of particles and forces that make up the universe.
What this author has done is use E8 in a new way to come up with a potential new theory that unifies all the forces and fields. This is not *strictly* a theory of everything, as there's a lot more that has to be answered, but if true it provides a geometric model that can give us insight into the underlying principles that are involved, just the way the Periodic Table does for elements.
The guy is no kook, but his theory leaves a lot to be desired. One problem is that E8 and other lie algebras and their associated symmetries have been well-studied for decades, and most all of them have run into intractable problems or incorrect predictions, so this may just be another beautiful theory that doesn't fit reality. Lisi uses a little-known method called "BRST connections" to make it all seem to work, which most physicists are unfammiliar with. Another is that his theory actually forces something physicists call as "spontaneous symmetry breaking" into the calculations to make it fit what we know to be true in the "standard model". Many people feel this is putting the cart before the horse; they would prefer a theory where the symmetry is broken in a "nautral" way and the "standard model" of the universe just naturally falls out of it. Lisi's theory doesn't really tell us WHY this is the case, it just says it is, but here's the symmetry that underlies it and which you apply it to.
Another problem is that the theory is still new and doesn't have an quantitative predictions as of yet... there's a lot of math that needs to be done, and it's not clear that such calculation *can* be done given the contraints of his theory. At issue is something known as the "Coleman-Mandula" theorem, which basically says a lot of what Lisi does in his theory doesn't work if there are subgroups in the algenbra that are equivalent to what are known as Poincare groups. Lisi says this doesn't apply to his new theory because it posits that the vacuum of spacetime doesn't have Poincare symmetry but instead is deSitter space. Well, the idea of deSitter space is well-known and has been examined in theoretical physics for decades as well, but there are a lot of problems with it. One is that the "Smatrix", which physicists love so much in making calculations in theories with Poincare symmetries, no longer works and simply becomes an approximation.
The theory also predicts a very LARGE cosmological constant, which is contrary to observation, but there are other theories that explain how this is not actually a problem, so that might not be an issue. Perhaps the largest obstacle of the theory, once the calculations can be figured out, is that it pretty much obsoletes all of String Theory in favor of something like Loop Quantum Gravity. This will make a LOT of string physicists very unhappy.
Lisi's theory will probably not be the last work in physics, but it might bring us a step closer to a real "Theory of Everything". The truth is physicists have been toying with similar geometric approaches and arrange particles in tables and trying to tie in gravity for decades now and every new theory looks great but never quite actually works out. The fact that the universe can *almost* be described via these methods probably tells us we're on the right track, but a true simple unifying description that underlies all of reality still eludes us.
There's a very good web summary and discussion of the theory with the author going on here:
http://backreaction.blogspot.com/2007/11/theoretically-simple-exception-of.html [blogspot.com]
Bruce
Re:An attempt at a summary (Score:5, Interesting)
-Garrett
(Yes, I'm the author of the paper. Hey look, my server's melting -- must of hit slashdot...)
Re:An attempt at a summary (Score:5, Interesting)
You have no idea how your reply makes me feel, as I'm someone who stopped studying physics as a Freshman in college and can barely grasp the basic ideas behind the whole thing.
I admit I'm still a bit skeptical... I mean, if E8 is the answer, why did none of the other E8 approaches work? But you're doing some unique things in your approach and in them may lie the answer. Almost makes me wish I had stayed in physics, but the math is just beyond me.
Good luck!
Re:An attempt at a summary (Score:5, Funny)
Re:An attempt at a summary (Score:4, Funny)
How can you write a paper revolutionizing our understanding of physics if you don't use proper grammar?!
Re: (Score:2)
Must have! Must HAVE!
How can you write a paper revolutionizing our understanding of physics if you don't use proper grammar?!
I imagine he spent his time studying maths and physics instead of English. That is, after all, the point of specialization and university; he becomes incredibly competent in one field at the expense of another. This, of course, also explains why I have excellent karma but no life.
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Re: (Score:2)
This is precisely why he can. People who stay locked up in thinking (and therefore writing) like everybody else, can not write a paper revolutionizing anything at all.
Re: (Score:2)
- The fact that the author posted to Slashdot.
- Or the fact that he once posted to a thread called "Monkey Pays for Monkey Porn."
Re: (Score:1)
Another problem is that the theory is still new and doesn't have an quantitative predictions as of yet... there's a lot of math that needs to be done, and it's not clear that such calculation *can* be done given the contraints of his theory. At issue is something known as the "Coleman-Mandula" theorem, which basically says a lot of what Lisi does in his theory doesn't work if there are subgroups in the algenbra that are equivalent to what are known as Poincare groups. Lisi says this doesn't apply to his new theory because it posits that the vacuum of spacetime doesn't have Poincare symmetry but instead is deSitter space. Well, the idea of deSitter space is well-known and has been examined in theoretical physics for decades as well, but there are a lot of problems with it. One is that the "Smatrix", which physicists love so much in making calculations in theories with Poincare symmetries, no longer works and simply becomes an approximation.
Um wait a minute. Both here on Slashdot as well as over at the 'original' telegraph.co.uk article, a very important point is that Lisi's theory does makes predictions. For paticles within the energy range that the LHC will open up.
So I suppose what you're trying to say is that yet more mathematics (and mathematics given to well-known pitfalls) will need to intervene between tying together Lisi's theory and any observations that result from LHC experiments?
If so, then elaborate.
Of course the poss
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