This indeed does place a bound on the possible existence of cosmic strings, however the description of this article seems to imply that cosmic strings have something to do with string theory. The two concepts are completely unrelated. In cosmology, cosmic strings are 1D topological defects caused by a phase change in a region of spacetime. They do not require string theory and string theory does not require them. They just happen to be two concepts in theoretical physics that used the word "string" to describe 1-dimensional entities.
I wrote a collaborative novel last year which was laid out in LaTeX. Each chapter was written by its 1-3 writers on a document I created in Google Docs. At the end, I wrote a Python script that downloaded all 23 chapters, translated them into LaTeX docs in the style that I wanted for the book layout (most of the markup I had to worry about was stuff like quotes, new paragraphs, italics, special characters, etc (it was not full of equations)), and it then called PDFLaTeX on the master document which combined them into a book. This allowed people to modify their documents online, and for me to handle the layout in parallel with the up-to-date text.
So, this allowed like 12 people to have no learning curve, but it depended on me knowing Python and LaTeX. Not sure if I answered the question. Sorry. Just use version numbers or something.
Landau and Lifshitz Classical Mechanics - concise and beautifully written. Might be stylistically appealing for someone with a background in mathematics.
Griffiths Introduction to Electromagnetism - A classic and clear introductory text. Probably his best book.
Griffiths Introduction to Quantum Mechanics - Another classic. It's also a short book. If you are looking for more Dirac notation, check out Shankar, another classic at the undergraduate level.
Reif Fundamentals of Statistical and Thermal Physics - Great and very complete introduction to statistical mechanics and thermodynamics. If you find the text daunting, you could substitute it for Schroeder.
Taylor and Wheeler Spacetime Physics - Great introduction to special relativity. You'll find a more mathematical treatment in Griffiths EM or any GR book.
-----
If you are interested in reading a bit of undergraduate-level general relativity and astrophysics as well, good books are
Hartle Gravity - An UG-level intro to General Relativity. Focuses on the physics and providing you with metrics. Fun book. Try Carroll if you want something more mathematical.
Ryden Introduction to Cosmology - Great, recent introduction to cosmology at the UG level. Will give you a lot of intuition into your later studies of cosmology.
You might want to check out a good UG-level text on stellar astrophysics as well, but there's probably more than enough on your plate, unless you're some sort of robot.
I'm a senior at Stanford now, and it seems half the CS majors are making startups and the other half have more job offers than they can say no to. On the other hand, my best friend from high school is a CS major at one of the best liberal arts schools in the country, and last I heard he was working for the park service writing tree population simulations.
It means the particles in the collider are accelerated up to 14TeV; energy is the relevant parameter in high energy physics, strangely enough. If the Higgs weighs 140 GeV for instance, we need to accelerate particles in the collider to more than that energy to produce one.
In this domain though, doubling the energy corresponds to a very small increase in speed. E = p^2/2*m is just the first order term in an expansion of E = Sqrt[m^2*c^4 + p^2*c^2], and p = m*v*(1 - v^2/c^2)^(-1/2). Thus doubling the energy corresponds to a speed difference of 0.0166415572 m/s. That's 5.5e-9 % increase in speed. One way to think of if (although technically it's not correct), the mass of the electron at 42GeV is 82,000 times it's rest mass, and the velocity increase needed to increase its energy is tiny in such as high energy domain.
First, this is not a permanent problem. It does not take long for an abandoned LEO satellite to decay, fall into the atmosphere, and burn up.
Second, imagine about 1000 cars on a surface slightly larger than the earth (not even addressing that LEO satellites are in a pretty wide variation of altitudes). Now image these 1000 cars just driving around the earth in random directions. Collisions seem unlikely.
To be precise, is we put the satellites all at 7000km from the earth's center, we have an area A = 6 million km^2. Now, give them roughly the area (actually circumference in 2D) of lets say a bus (to be generous), that be sigma = 6e-2 km. Thus, that gives us a mean free path of l = (1000*sigma/A)^-1 = 10,000,000 km. At a LEO orbital velocity of 7.8 km/s, that would be a collision every 14 days. And if we bumped it up to the full 3D problem, that'd be another couple orders of magnitude.
Ron Fedkiw at Stanford also has a lot of very impressive demonstrations of liquids, smoke, fire, cloth, rigid bodies, elasticity, and fracturing. The videos are definitely worth checking out: http://graphics.stanford.edu/~fedkiw/
I especially like the water being poured into the glass. It's nearly photo realistic.
While the LHC will be looking for the effects of supersymmetry, the Higgs boson, and extra dimensions, among other effects that would be consistent with string theory, the LHC will never end up definitively testing string theory. That is, the number one problem with string theory in its current young form is that it is not really falsifiable, especially in the energy domains currently possible in modern colliders (including the LHC). That is, there are many SUSY theories that predict supersymmetry, not just string theory, thus discovering it would not prove string theory at all. On the other hand, if supersymmetry isn't observed, string theorists may just argue the collisions were not high enough in energy.
The same arguments apply to all of the barely fleshed out predictions in string theory. In that sense, string theory is barely a kosher physical theory. This isn't to say the LHC isn't a huge deal. No matter what they find with the LHC, it'll be exciting. Many physicists are very confident that it'll give us new insight into candidates for dark matter, and certainly confirmation of supersymmetry and the Higgs would be monumental.
I'm a physics student at Stanford, and I've never heard of this guy ever. The department site says he's a visiting scholar. Maybe I'll be able to track him down. Although, I tend to be skeptical of people who communicate their theories exclusively to the public through their websites. I'm open to alternative theoriers of gravity, but I'll be more inclined to listen to this when I see it in a journal.
Slashdot Mirror
...between a mathematician and a pizza? A pizza can feed a family of four.
This indeed does place a bound on the possible existence of cosmic strings, however the description of this article seems to imply that cosmic strings have something to do with string theory. The two concepts are completely unrelated. In cosmology, cosmic strings are 1D topological defects caused by a phase change in a region of spacetime. They do not require string theory and string theory does not require them. They just happen to be two concepts in theoretical physics that used the word "string" to describe 1-dimensional entities.
I wrote a collaborative novel last year which was laid out in LaTeX. Each chapter was written by its 1-3 writers on a document I created in Google Docs. At the end, I wrote a Python script that downloaded all 23 chapters, translated them into LaTeX docs in the style that I wanted for the book layout (most of the markup I had to worry about was stuff like quotes, new paragraphs, italics, special characters, etc (it was not full of equations)), and it then called PDFLaTeX on the master document which combined them into a book. This allowed people to modify their documents online, and for me to handle the layout in parallel with the up-to-date text.
So, this allowed like 12 people to have no learning curve, but it depended on me knowing Python and LaTeX. Not sure if I answered the question. Sorry. Just use version numbers or something.
Landau and Lifshitz Classical Mechanics - concise and beautifully written. Might be stylistically appealing for someone with a background in mathematics.
Griffiths Introduction to Electromagnetism - A classic and clear introductory text. Probably his best book.
Griffiths Introduction to Quantum Mechanics - Another classic. It's also a short book. If you are looking for more Dirac notation, check out Shankar, another classic at the undergraduate level.
Reif Fundamentals of Statistical and Thermal Physics - Great and very complete introduction to statistical mechanics and thermodynamics. If you find the text daunting, you could substitute it for Schroeder.
Taylor and Wheeler Spacetime Physics - Great introduction to special relativity. You'll find a more mathematical treatment in Griffiths EM or any GR book.
-----
If you are interested in reading a bit of undergraduate-level general relativity and astrophysics as well, good books are
Hartle Gravity - An UG-level intro to General Relativity. Focuses on the physics and providing you with metrics. Fun book. Try Carroll if you want something more mathematical.
Ryden Introduction to Cosmology - Great, recent introduction to cosmology at the UG level. Will give you a lot of intuition into your later studies of cosmology.
You might want to check out a good UG-level text on stellar astrophysics as well, but there's probably more than enough on your plate, unless you're some sort of robot.
Some tips: http://thesingularityblog.blogspot.com/
The best electronics book there is.
I'm a senior at Stanford now, and it seems half the CS majors are making startups and the other half have more job offers than they can say no to. On the other hand, my best friend from high school is a CS major at one of the best liberal arts schools in the country, and last I heard he was working for the park service writing tree population simulations.
Whatever you do, don't blink near the heart or brain.
www.megalaser.com
It means the particles in the collider are accelerated up to 14TeV; energy is the relevant parameter in high energy physics, strangely enough. If the Higgs weighs 140 GeV for instance, we need to accelerate particles in the collider to more than that energy to produce one.
...bullets. Also, is it really a surprise that you can kill cancer by obliterating it with antimatter? It's not made of special cancer baryons.
In this domain though, doubling the energy corresponds to a very small increase in speed. E = p^2/2*m is just the first order term in an expansion of E = Sqrt[m^2*c^4 + p^2*c^2], and p = m*v*(1 - v^2/c^2)^(-1/2). Thus doubling the energy corresponds to a speed difference of 0.0166415572 m/s. That's 5.5e-9 % increase in speed. One way to think of if (although technically it's not correct), the mass of the electron at 42GeV is 82,000 times it's rest mass, and the velocity increase needed to increase its energy is tiny in such as high energy domain.
First, this is not a permanent problem. It does not take long for an abandoned LEO satellite to decay, fall into the atmosphere, and burn up. Second, imagine about 1000 cars on a surface slightly larger than the earth (not even addressing that LEO satellites are in a pretty wide variation of altitudes). Now image these 1000 cars just driving around the earth in random directions. Collisions seem unlikely. To be precise, is we put the satellites all at 7000km from the earth's center, we have an area A = 6 million km^2. Now, give them roughly the area (actually circumference in 2D) of lets say a bus (to be generous), that be sigma = 6e-2 km. Thus, that gives us a mean free path of l = (1000*sigma/A)^-1 = 10,000,000 km. At a LEO orbital velocity of 7.8 km/s, that would be a collision every 14 days. And if we bumped it up to the full 3D problem, that'd be another couple orders of magnitude.
Ron Fedkiw at Stanford also has a lot of very impressive demonstrations of liquids, smoke, fire, cloth, rigid bodies, elasticity, and fracturing. The videos are definitely worth checking out: http://graphics.stanford.edu/~fedkiw/ I especially like the water being poured into the glass. It's nearly photo realistic.
While the LHC will be looking for the effects of supersymmetry, the Higgs boson, and extra dimensions, among other effects that would be consistent with string theory, the LHC will never end up definitively testing string theory. That is, the number one problem with string theory in its current young form is that it is not really falsifiable, especially in the energy domains currently possible in modern colliders (including the LHC). That is, there are many SUSY theories that predict supersymmetry, not just string theory, thus discovering it would not prove string theory at all. On the other hand, if supersymmetry isn't observed, string theorists may just argue the collisions were not high enough in energy. The same arguments apply to all of the barely fleshed out predictions in string theory. In that sense, string theory is barely a kosher physical theory. This isn't to say the LHC isn't a huge deal. No matter what they find with the LHC, it'll be exciting. Many physicists are very confident that it'll give us new insight into candidates for dark matter, and certainly confirmation of supersymmetry and the Higgs would be monumental.
I'm a physics student at Stanford, and I've never heard of this guy ever. The department site says he's a visiting scholar. Maybe I'll be able to track him down. Although, I tend to be skeptical of people who communicate their theories exclusively to the public through their websites. I'm open to alternative theoriers of gravity, but I'll be more inclined to listen to this when I see it in a journal.