It's not 10^500 outcomes. It's 10^500 vacuum states that all might potentially describe our universe. Therefore, it cannot satisfy constraints that are in gross violation of the universe we observe. Furthermore, it is hoped that there is additional physics at work, some principle that cuts the vacua to just one- ours. It is possible that such a principle could have cosmological implications that might be testable with our abilities (but this is entirely speculation).
It does predict gravity. It is a theory that says nothing about gravity from the onset, and then upon quantization requires the existence of a spin-two vector boson at the massless level. This couples to the stress energy tensor, and hence you have gravity.
There are not a gazillion possible ways of interpreting string theory. There are no free parameters to tweak. Most physicists do not call string theory bullshit, because that would be grossly illogical. A correct theory of the universe could not care less whether or not technology of this generation is capable of testing it. And finally, postulate is not something that a theory makes.
No, it is not so easy. Anomalies did not have to cancel and Green and Schwarz found. Lorentz invariance did not have to be possible in any number of dimensions, let alone only one (which is, by the way, another testable prediction being checked now at the University of Washington). What they cannot describe for want of space in the pop science books is the notion of mathematical consistency. Many times string theory needed a certain mathematical fact to be true in order to be internally consistent. The math does not care about string theory; it is either consistent or it is not. But every time it has turned out to be correct. Also, you are confusing the landscape of potential vacua which may be like our universe with theoretical flexibility. It is not so. The landscape is something to be studied, but it does not say that string theory can predict anything, nor is it something where each of the 10^500 vacua must be individually disqualified in order to reject string theory, as you implied.
The reasons you stick with strings rather than ditching it for something more convenient are plentiful beyond the obvious fact that the true nature of the universe does not care what you can or cannot build. There is something called the renormalization group which says that any good quantum theory of gravity should look like the standard model that we have rigorously tested for forty years at energy scales we can reach. There is no particular reason to expect that any unified theory will make new predictions at our energy scale. It might happen, and it might happen with strings, but no matter what you do a quantum theory of gravity should always naturally live around the planck scale. Think of it this way: if you told Stokes about quantum mechanics and he pointed out that it could not realistically be used to describe fluid motion, this would not change the fact that it is a correct theory. We are just lucky that we can reach the energy scales of quantum mechanics.
It is science because it does make predictions. It predicts gravity, gauge theory, supersymmetry, and extra dimensions, most of which sound exotic but are actually easier to test than the general expected predictions such as string scattering amplitudes. Extra dimensions, if they are large enough, may be testible in the next few years. So is supersymmetry.
It really is saying something that the best thing we've got has survived 30 years of scrutiny. I think it does say it's better than nothing, and when you've got something good, simply abandoning it to try and find something else that better fits your equipment isn't a good idea. Not to mention that it is very difficult to simply generate a new theory of quantum gravity. There are a few other contenders, but they suffer from much bigger flaws than string theory.
Also, a lot of people (many thousands, roughly) do understand string theory. It's just that they all coincidentally have Ph.D.s in the subject.
That is not true. It predicts gravity and it predicts gauge theory. It is not just mathematics because mathematics does not presume to explain anything physical- this is the very essence of string theory, to explain the most poorly understood corner of physics. There is no question that it is physics. The only intelligent question is whether or not we should be looking for other ideas. But even this is somewhat poorly stated, because one cannot just sit down and come up with a unified theory. You have to be motivated by some previous idea. And guess what? This is really hard. If someone had a good new idea, they would publish it.
Also, the topics I listed should not be confused with "nuances." They are the basis for the theory. It's not elitism, it's fact, and if it sounds short or glib it's because it's intellectually insulting that you are not the first person to treat string theorists in this manner.
I am a string theorist. I would write my own rebuttal to Peter Woit, who is well known in the community for being very vocal about his opinions, but it has already been welldone (these are blog posts by Sean Carroll at Chicago/Caltech).
I'm all for public education on all topics of physics, including string theory, but this is an unfortunate case of a little bit of knowledge being dangerous for armchair physicists. In order to properly understand string theory requires understanding conformal field theory, supersymmetry and supergravity, Riemann surfaces, Kaluza-Klein theory, and so on, just to name a few of the introductory ideas. I don't think it's too unreasonable to assume that most of Peter Woit's audience has not studied any of these. But without studying string theory, I don't think it's possible to judge whether or not the things string theorists find compelling are in fact sufficiently exciting to warrant the attention it receives from them. For my part, I think they are.
On second thought I shouldn't say no success. There have been successes in computing special, less physical cases, for example in treating the stars as frictionless dustballs not possessing magnetic fields. But these features are very important in determining the rotation structure of stellar fluids, and are probably essential in modeling the physically correct binary merger. The general problem remains to be solved, and the goal is to figure out what physical processes produce gravitational waves, so that we know what to be looking for experimentally.
Here are some visualizations of previous merger simulations: 1 2
Actually this is a pretty tough problem to solve. The computation was attempted by several leading numerical relativity institutions some years ago, but met with no success. The professor I work for is currently building up a code that will hopefully someday be able to handle the binary collision problem.
One of the major problems is that programs crash pretty quickly when the evolution develops a singularity. A good method for avoiding this is called excision, where the singularity is removed from the grid and replaced with boundary conditions. This was recently implemented in my advisor's group and applied to the binary neutron star problem. At the end of the evolution, a black hole forms, so it doesn't seem like there are too many steps before a full black hole collision is possible.
He is more of a literary device than an important piece of the epic. In the books, having this kind of completion makes the story seem more real, but in a movie, it is awkward and out of place. We have seen his reign broken in TTT, so it would be little more than the tossing of a bone to the book readers to see anything more of him onscreen. The real enemy is far greater and more interesting, and the journey ends perfectly well without him.
I like the presidential IQ stuff that keeps getting spread around, particularly when Clinton is listed at something in the 180s and Bush is exactly half. The man may be dumb as carpet but the fact that CNN will actually air the listing says something disturbing too, I think.
Re:I'd only point out that. . .
on
Tai Chi Robots
·
· Score: 1
I practice Chen and Yang styles of taiji. I weigh 155 lbs and hold my own against untrained fighters in the ~190lbs range and trained tkd fighters of over 200lbs. This is not because my style is better. It is because I have studied the form as a fluid instead of a discrete set of responses to specific attacks. Laoshr teaches a holistic approach to combat that generates a combination of balance and reflex; when sparring, I do not respond in a set way, but a way that "feels" right. While this is painfully unscientific, it works because one's opponent is either wasting time thinking frantically about "moves" (tkd), or fighting by a feeling (untrained) which is less developed than my own.
By the way, taiji does not traditionally employ a belt system.
I'd be real impressed if one of you could effectively argue how a duplicate story has so injustly wronged you so as to demand this sort of wanton, sociopathic outrage. What's more ridiculous than a few duplicate stories is a bunch of duplicate children screaming at mommy for serving the same lunchtime sandwich two days in a row. I'm sure you all work hard and are model citizens in need of fresh news quarter-hourly, but if you don't have anything worthwhile to say, then be a man and shut it.
Absolutely. Interactions and decays are governed by probabilities, where the only constraints on the results are conservation laws such as charge and angular momentum. I can't support anything on just how probable any decay is, so consider that an extrapolation, but I can give an example of a specific decay. The W boson decays into (or is produced by collision of) an antilepton and a neutrino, or an antineutrino and a lepton (total net charge must be plus or minus 1). I checked lanl for something moderately understandable and didn't find much ("Schwinger-Dyson Analysis of Dynamical Symmetry Breaking on a Brane with Bulk Yang-Mills Theory", "Charmless Exclusive Baryonic B Decays"); however, this is more common and semi-popularized physics so you might try just general googling for particle decay and collision production charts.
My focus isn't particle physics, but maybe I can offer a correction for your approach. In #2 you presuppose that antimatter and matter are produced in equal amounts; actually, nature seems to favor production of matter over the anti counterpart. Look up CP violation for more on this. So at the Big Bang, all the antimatter annihilated with much of the matter, but since there was an imbalance in the initial production, there was still some matter left over. This is the stuff you and I are made of.
As far as difficulty in production, it happens that most of the particle-pair interactions that decay into antimatter particles only occur at very high energies compared to what our accelerators can achieve, and even then at low probabilities. Then there is the matter of containment. Current methods involve redirection with magnetic fields or trapping with lasers, both of which are extremely difficult and therefore expensive.
As usual, the big problem with this bit of physics is the funding. Going out on a limb, particularly in longterm scientifics, is not promoted as a safe or particularly clever business strategy. This leads to what is not exactly the most logical method of pursuing progress, but I digress in my bias.
An interesting factor that is often ignored is the time it takes CFCs to ascend to the upper atmosphere. Most of those produced during the world's peak output have not even made it to the point where they would do any damage yet. To generalize, it may be healing now, but in the next ten years the sum total of the industrial 1980's may rip the scab right off.
P
Ha. I did CS for a year, and decided that learning about the universe is slightly more useful than memorizing swap rules for red-black trees. No offense, Jason. I do dig Chicago.
That is why it is interesting. I suspect it is not the best arrangement, and therefore exploring why it happened as it did can lead to a better understanding of what is right/wrong in the scientific community. Always room for improvement.
Interesting pick of universities that are getting the cash. Compare that list to Usnews' 2003 ranking of CS grad schools:
1. Carnegie Mellon University (PA)
Massachusetts Institute of Technology
Stanford University (CA)
University of California-Berkeley
5. University of Illinois-Urbana-Champaign
Interesting pick of universities that are getting the cash. Compare that list to Usnews' 2003 ranking of CS grad schools:
1. Carnegie Mellon University (PA)
Massachusetts Institute of Technology
Stanford University (CA)
University of California-Berkeley
5. University of Illinois-Urbana-Champaign
See for yourself @ http://www.usnews.com/usnews/edu/grad/rankings/phd sci/brief/com_brief.php
I've got no original suggestions, but I did want to say thanks to all you who responded for restoring a bit of misplaced faith in the good that can come out of geekdom. Hope it sticks around.
Fermi problems cover virtually any area of physics and serve to train the most fundamental part of being a physicist- the ability to think as one. From simple things, like the average energy imparted to your forehead by a single raindrop, to calculating the strength of a nuclear explosion from the drift of paper shreds, Fermi problems emphasize efficiency of logic and intuition to understand the natural universe.
Slashdot Mirror
It's not 10^500 outcomes. It's 10^500 vacuum states that all might potentially describe our universe. Therefore, it cannot satisfy constraints that are in gross violation of the universe we observe. Furthermore, it is hoped that there is additional physics at work, some principle that cuts the vacua to just one- ours. It is possible that such a principle could have cosmological implications that might be testable with our abilities (but this is entirely speculation).
It does predict gravity. It is a theory that says nothing about gravity from the onset, and then upon quantization requires the existence of a spin-two vector boson at the massless level. This couples to the stress energy tensor, and hence you have gravity.
There are not a gazillion possible ways of interpreting string theory. There are no free parameters to tweak. Most physicists do not call string theory bullshit, because that would be grossly illogical. A correct theory of the universe could not care less whether or not technology of this generation is capable of testing it. And finally, postulate is not something that a theory makes.
No, it is not so easy. Anomalies did not have to cancel and Green and Schwarz found. Lorentz invariance did not have to be possible in any number of dimensions, let alone only one (which is, by the way, another testable prediction being checked now at the University of Washington). What they cannot describe for want of space in the pop science books is the notion of mathematical consistency. Many times string theory needed a certain mathematical fact to be true in order to be internally consistent. The math does not care about string theory; it is either consistent or it is not. But every time it has turned out to be correct. Also, you are confusing the landscape of potential vacua which may be like our universe with theoretical flexibility. It is not so. The landscape is something to be studied, but it does not say that string theory can predict anything, nor is it something where each of the 10^500 vacua must be individually disqualified in order to reject string theory, as you implied.
The reasons you stick with strings rather than ditching it for something more convenient are plentiful beyond the obvious fact that the true nature of the universe does not care what you can or cannot build. There is something called the renormalization group which says that any good quantum theory of gravity should look like the standard model that we have rigorously tested for forty years at energy scales we can reach. There is no particular reason to expect that any unified theory will make new predictions at our energy scale. It might happen, and it might happen with strings, but no matter what you do a quantum theory of gravity should always naturally live around the planck scale. Think of it this way: if you told Stokes about quantum mechanics and he pointed out that it could not realistically be used to describe fluid motion, this would not change the fact that it is a correct theory. We are just lucky that we can reach the energy scales of quantum mechanics.
It is science because it does make predictions. It predicts gravity, gauge theory, supersymmetry, and extra dimensions, most of which sound exotic but are actually easier to test than the general expected predictions such as string scattering amplitudes. Extra dimensions, if they are large enough, may be testible in the next few years. So is supersymmetry.
It really is saying something that the best thing we've got has survived 30 years of scrutiny. I think it does say it's better than nothing, and when you've got something good, simply abandoning it to try and find something else that better fits your equipment isn't a good idea. Not to mention that it is very difficult to simply generate a new theory of quantum gravity. There are a few other contenders, but they suffer from much bigger flaws than string theory.
Also, a lot of people (many thousands, roughly) do understand string theory. It's just that they all coincidentally have Ph.D.s in the subject.
That is not true. It predicts gravity and it predicts gauge theory. It is not just mathematics because mathematics does not presume to explain anything physical- this is the very essence of string theory, to explain the most poorly understood corner of physics. There is no question that it is physics. The only intelligent question is whether or not we should be looking for other ideas. But even this is somewhat poorly stated, because one cannot just sit down and come up with a unified theory. You have to be motivated by some previous idea. And guess what? This is really hard. If someone had a good new idea, they would publish it.
Also, the topics I listed should not be confused with "nuances." They are the basis for the theory. It's not elitism, it's fact, and if it sounds short or glib it's because it's intellectually insulting that you are not the first person to treat string theorists in this manner.
I am a string theorist. I would write my own rebuttal to Peter Woit, who is well known in the community for being very vocal about his opinions, but it has already been well done (these are blog posts by Sean Carroll at Chicago/Caltech).
I'm all for public education on all topics of physics, including string theory, but this is an unfortunate case of a little bit of knowledge being dangerous for armchair physicists. In order to properly understand string theory requires understanding conformal field theory, supersymmetry and supergravity, Riemann surfaces, Kaluza-Klein theory, and so on, just to name a few of the introductory ideas. I don't think it's too unreasonable to assume that most of Peter Woit's audience has not studied any of these. But without studying string theory, I don't think it's possible to judge whether or not the things string theorists find compelling are in fact sufficiently exciting to warrant the attention it receives from them. For my part, I think they are.
On second thought I shouldn't say no success. There have been successes in computing special, less physical cases, for example in treating the stars as frictionless dustballs not possessing magnetic fields. But these features are very important in determining the rotation structure of stellar fluids, and are probably essential in modeling the physically correct binary merger. The general problem remains to be solved, and the goal is to figure out what physical processes produce gravitational waves, so that we know what to be looking for experimentally.
Here are some visualizations of previous merger simulations:
1
2
Actually this is a pretty tough problem to solve. The computation was attempted by several leading numerical relativity institutions some years ago, but met with no success. The professor I work for is currently building up a code that will hopefully someday be able to handle the binary collision problem.
One of the major problems is that programs crash pretty quickly when the evolution develops a singularity. A good method for avoiding this is called excision, where the singularity is removed from the grid and replaced with boundary conditions. This was recently implemented in my advisor's group and applied to the binary neutron star problem. At the end of the evolution, a black hole forms, so it doesn't seem like there are too many steps before a full black hole collision is possible.
He is more of a literary device than an important piece of the epic. In the books, having this kind of completion makes the story seem more real, but in a movie, it is awkward and out of place. We have seen his reign broken in TTT, so it would be little more than the tossing of a bone to the book readers to see anything more of him onscreen. The real enemy is far greater and more interesting, and the journey ends perfectly well without him.
I like the presidential IQ stuff that keeps getting spread around, particularly when Clinton is listed at something in the 180s and Bush is exactly half. The man may be dumb as carpet but the fact that CNN will actually air the listing says something disturbing too, I think.
I practice Chen and Yang styles of taiji. I weigh 155 lbs and hold my own against untrained fighters in the ~190lbs range and trained tkd fighters of over 200lbs. This is not because my style is better. It is because I have studied the form as a fluid instead of a discrete set of responses to specific attacks. Laoshr teaches a holistic approach to combat that generates a combination of balance and reflex; when sparring, I do not respond in a set way, but a way that "feels" right. While this is painfully unscientific, it works because one's opponent is either wasting time thinking frantically about "moves" (tkd), or fighting by a feeling (untrained) which is less developed than my own.
By the way, taiji does not traditionally employ a belt system.
I'd be real impressed if one of you could effectively argue how a duplicate story has so injustly wronged you so as to demand this sort of wanton, sociopathic outrage. What's more ridiculous than a few duplicate stories is a bunch of duplicate children screaming at mommy for serving the same lunchtime sandwich two days in a row. I'm sure you all work hard and are model citizens in need of fresh news quarter-hourly, but if you don't have anything worthwhile to say, then be a man and shut it.
Patrick
Absolutely. Interactions and decays are governed by probabilities, where the only constraints on the results are conservation laws such as charge and angular momentum. I can't support anything on just how probable any decay is, so consider that an extrapolation, but I can give an example of a specific decay. The W boson decays into (or is produced by collision of) an antilepton and a neutrino, or an antineutrino and a lepton (total net charge must be plus or minus 1). I checked lanl for something moderately understandable and didn't find much ("Schwinger-Dyson Analysis of Dynamical Symmetry Breaking on a Brane with Bulk Yang-Mills Theory", "Charmless Exclusive Baryonic B Decays"); however, this is more common and semi-popularized physics so you might try just general googling for particle decay and collision production charts.
My focus isn't particle physics, but maybe I can offer a correction for your approach. In #2 you presuppose that antimatter and matter are produced in equal amounts; actually, nature seems to favor production of matter over the anti counterpart. Look up CP violation for more on this. So at the Big Bang, all the antimatter annihilated with much of the matter, but since there was an imbalance in the initial production, there was still some matter left over. This is the stuff you and I are made of.
As far as difficulty in production, it happens that most of the particle-pair interactions that decay into antimatter particles only occur at very high energies compared to what our accelerators can achieve, and even then at low probabilities. Then there is the matter of containment. Current methods involve redirection with magnetic fields or trapping with lasers, both of which are extremely difficult and therefore expensive.
As usual, the big problem with this bit of physics is the funding. Going out on a limb, particularly in longterm scientifics, is not promoted as a safe or particularly clever business strategy. This leads to what is not exactly the most logical method of pursuing progress, but I digress in my bias.
An interesting factor that is often ignored is the time it takes CFCs to ascend to the upper atmosphere. Most of those produced during the world's peak output have not even made it to the point where they would do any damage yet. To generalize, it may be healing now, but in the next ten years the sum total of the industrial 1980's may rip the scab right off.
P
Fortunately, with friction, a k*v drag term will slow it to a measly 180mph or so. Which will still kill you dead.
That's a lovely thing about physics. You can do the calculations with a spherical cow and you'll still get the same result.
P
Ha. I did CS for a year, and decided that learning about the universe is slightly more useful than memorizing swap rules for red-black trees. No offense, Jason. I do dig Chicago.
That is why it is interesting. I suspect it is not the best arrangement, and therefore exploring why it happened as it did can lead to a better understanding of what is right/wrong in the scientific community. Always room for improvement.
forgot to preview. here it is more legibly:
d sci/brief/com_brief.php
Interesting pick of universities that are getting the cash. Compare that list to Usnews' 2003 ranking of CS grad schools:
1. Carnegie Mellon University (PA)
Massachusetts Institute of Technology
Stanford University (CA)
University of California-Berkeley
5. University of Illinois-Urbana-Champaign
See for yourself @
http://www.usnews.com/usnews/edu/grad/rankings/ph
Interesting pick of universities that are getting the cash. Compare that list to Usnews' 2003 ranking of CS grad schools: 1. Carnegie Mellon University (PA) Massachusetts Institute of Technology Stanford University (CA) University of California-Berkeley 5. University of Illinois-Urbana-Champaign See for yourself @ http://www.usnews.com/usnews/edu/grad/rankings/phd sci/brief/com_brief.php
I've got no original suggestions, but I did want to say thanks to all you who responded for restoring a bit of misplaced faith in the good that can come out of geekdom. Hope it sticks around.
Fermi problems cover virtually any area of physics and serve to train the most fundamental part of being a physicist- the ability to think as one. From simple things, like the average energy imparted to your forehead by a single raindrop, to calculating the strength of a nuclear explosion from the drift of paper shreds, Fermi problems emphasize efficiency of logic and intuition to understand the natural universe.
Pretty sure it's actually "Those who can do more, teach."
Kathleen Fent submits a "Should I Marry CmdrTaco" to Ask Slashdot.