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Current Thoughts in String Theory
DrLudicrous writes "The NYTimes is running a nice little synopsis of the current ideas in string theory. Apparently, there is still quite a bit of disagreement about how to interpret the various theories, with some string theorists supporting a semi-deterministic worldview a la Einstein (God does not play dice), while others believe our universe is just one possibility among many, with respect to various physical parameters."
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This site is maintained by a professor and has a great book on string theory. http://www.mkaku.org/
You are correct in stating that we lack the energy to test string theory -- According to Hawking, one estimate of the (theoritcal) grand unification energy would be a thousand million million million GeV. Further, he goes on to say that it would take something the size of a solar system to produce this. So you're right, we can't do it.
BUT, there could very well be places that do have this necessary energy and could be observed to exhibit traits that we can measure and confirm theories with. This has been how most of the more recent unification theories have been confirmed -- either by measuring very small things with very fine equipment or measuring very large things in space.
To make laws that man cannot, and will not obey, serves to bring all law into contempt.
--E.C. Stanton
Bollocks. Einstein's relativity could be readily tested at the time by measuring the bending of the light by Sun's gravity. That's exactly what made them so strong and actually respected by the experimentalists.
To an experimentalist a theory is just hot air until it can be tested in practise.
BOO! TERRO
For anyone curious about string theory, I would highly recommend Brian Greene's "The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory". He uses excellent writing style and plain, easy to follow examples to illustrate difficult concepts, and rather than going through lots of math and derivations, reserves that type of thing for the endnotes. It makes for a very approachable book that is particularly good for someone trying to learn new concepts rather than the struggle with the gory details of theoretical physics equations.
Funny, scientific american ran a better article with the same concepts, but didn't mention strings once:
1 ED D-B48A-1E90-8EA5809EC5880000
http://www.sciam.com/article.cfm?articleID=000F
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Except that the theories at least have to be consistent with all current observations - and there are a quite a few observations which simply do not match with the old-times Standard Model, so we know we need better theories. After all, relativity could not be (or at least was not) tested either when it was proposed.
Also, a theory created now that predicts observations which can only be made in the future can still tell us which observations we have to make to validate or invalidate it and like theories.
If your universe expands forever, then the energy unit per unit of volume approaches zero as your energy gets spread out. Eventually, if the universe expands forever, the universe becomes colder and colder. From a thermodynamics point of view, colder == less energy. The energy is still all there and still a constant. But it's spread so thin that it appears to be zero.
The conclusion at the time was that General Relativity was confirmed, because the likelihood of measurement or equipment error seemed to have been greater with the result consistent with Newtonian gravity.
So, to play a little mind game with her, I asked her how she knew the earth was a sphere.
If she was a little more up on her knowledge of the ancient history of science, she would have described the famous experiment of Eratosthenes where he simply used two sticks and a measuring stick to not only figure out that the planet was round, but also come up with an accurate estimate of it's circumfrence.
GMD
watch this
All long time readers of the rec.humor newgroups will recognize "the string joke". Apparently it was submitted so many times that it became a cliche for the "already heard joke", to the point that whenever somebody submitted what was thought to be an old joke, people would reply simply with the phrase "I'm afraid not". Ah, those were the good ol' days...
"Freedom means freedom for everybody" -- Dick Cheney
And the point of QM is that such "relationships" fail miserably when subjected to small distances, energies, single particles, etc.
Random outcome of dice is just a concept to help us deal with extremely complicated situations.
Not necessarily. I'll assume you're not really familiar with all the implications of the uncertainty principle, but the problem is that it's actually impossible to gather the information required to make the predictions even if you had the correct parametric forms for all the phenomena. Case in point: what happens if I precisely determine the position and momentum of a particle (your die, if you will)? Well, for a very small particle, I have to use light with a very small wavelength to get sufficient accuracy with regard to position. Unfortunately, short wavelengt == very energetic, so that photon just knocked the crap out of our particle. I knew where it was before I disturbed the system, but I know knothing of it's momentum.
The concept here is that of conjugate (ie, non-simultaneously-knowable) variables. Position and momentum are a pair. Energy and time are another. Basically, the way to check is if the QM operators for two measurements are commutative. If they're not, you can't know the two properties to arbitrart precision.
So it's not just about computational power or inferior instruments. It's actually impossible to gain this information, no matter what.
-Looking for a job as a materials chemist or multivariat
Some other good physics books that don't focus on String Theory that I also thought were very readable:
For Dark Matter and Dark Energy- Quintessence by Lawrence Krauss (who also wrote the Physics of Star Trek)
For Quantum Computing- Minds, Machines and the Multiverse by Julian Brown
The sending of this message pretty much inconveniences everyone involved.
http://www.sciam.com/article.cfm?articleID=000F1ED D-B48A-1E90-8EA5809EC5880000
I know more about string and particle theory than 99% of the population, which means I'm still a comparative dumbass on the subject in relation to people who really know what they're talking about.
However, here's a spiffy chart of the current "standard model" to help people get up to speed. Especially helpful for those who don't normally deal with Mesons and Antibayrons on a regular basis...
Lawrence Person (lawrencepersonh@gmailh.com (remove all "h"s to mail)
http://www.lawrenceperson.com/
The NY Times article mentions that Nova is doing an string theory episode this fall (Oct 28,2003 and Nov 4, 2003) based on Brian Greene's book The Elegant Universe. Turns out the homepage for this episode is already online with plenty of interviews and animations.
Einstein's General Theory of Relativity provided an explanation for the motion of the perihelion of Mercury's orbit. Further, it correctly predicted the magnitude of this motion--all of about 43 seconds of arc per century. It's a small motion, but it had been observed, measured, and puzzled at by astronomers in the nineteenth century.
Aside: Many people cite the 1919 eclipse observations made by the Royal Astronomical Society (also mentioned in the link above) as a further early proof of relativity. Though this is the most popular early 'proof', it is tainted with uncertainties. More recent work suggests that the precision of the RAS' instruments was insufficient for the task--the good agreement with theory was likely largely coincidence. Indeed, contradictory results from later eclipses and other groups did follow in succeeding decades. (Measurements with modern instruments have, of course, borne out relativity.)
~Idarubicin
He's referring to: The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory by Brian Greene.
No, that was from measuring the mass of the Higgs boson. You're also assuming that the Earth is a Type-13 planet in it's final stages.
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The best book I've ever seen for explaining special relativistic motion is Relativity Visualized by Lewis Caroll Epstein. It explains relativity via graphics and illustrations, and do it yourself excercises. While the math is there if you're interested, you don't have to understand the math in order to understand the content.
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It does matter, because if you build rocketships based on the ficticious one, they will not go anywhere.
You may also be interested in reading about loop quantum gravity, an alternative theory of everything. I' not expert, better refer to this reference that I looked up.
Not really. Quantum computers can be (very loosely) described as similar number crunching to digital computers with massive parallelization capabilities - they can basically run a given problem with every possible input at once, and figure out which is the correct. Quantum computers running with traditional algorithms will be just as slow as normal computers, probably even slower, because by the time we have decent quantum computers, conventional computers will have advanced way beyond quantum in terms of conventional measurements like clock speed or bits processed.
A Minesweeper clone that doesn't suck
Loop quantum gravity is not an alternative theory of everything. It is an alternate theory of quantum gravity; it does not attempt to be a "theory of everything". (i.e., it treats only gravity, not the other forces, and does not attempt to unify gravity with them.)
Not only are there those three states for a single qubit, but the infinite amount of values in between. Anything of the form a|0> + b|1> where a^2 + b^2 = 1. "a" and "b" can be complex.
Also with quantum computers, you have entanglement between qubits, something classical computers shouldn't have.
Physics: Making the universe open source.
"Before" the Big Bang, we don't know. In fact, the phrase "before" the Big Bang isn't really well defined, since as best we understand the working of things right now, there is no "time" at all prior to the Big Bang, since time is a property of (and temporal dimension of) our Universe. So in what stuff, place or location did the Big Bang occur? Why was all that matter compressed into one point? Was it caused by some irregularity in some higher order somethingness? Did the Universe have to come into existence, or not? Did it have to take a certain form or not? Some of these questions are properly the domain of philosophy at this point, but all of them are questions that physicists would love to be able to analyze, if there were any data available. Unfortunately, barring radical new discoveries, we're just not likely to answer most of those questions anytime soon. But that certainly doesn't mean that physics is bollocks - you just have to understand that most of modern physics seeks to describe and model predictable behaviors of the universe, rather than to explain them. If you want answers to "how", physics is pretty good at giving them. If you want answers to "why", physics sucks - every "why" just produces another question that you need to ask "why to.
For example, I can say an electric generator works because of the electromagnetic force, and that the electromagnetic force produces an r^2 force between particles with a property we call charge. Why? Well, particles with charge exchange virtual photons which results in this force. Why? Err... well... because QED says so? It all breaks down after a while. Four years as a physics major led me to a deep, deep depression when I realized physics just couldn't provide the kind of Einsteinian "why" answers I was looking for. The great physicists of the first half of this century came into a rapidly growing field where it was reasonable to think we'd have it all solved soon. I came into a sluggish, sick field filled with unsatisfied, unhappy scientists. Ugh. Glad I got myself out of there. Rant off.
As another replier also mentioned, loop quantum gravity is nota theory of everything. It is an attempt to do quantum gravity, that is the quantum version of the generally accepted of general relativity. Now at this point I should warn you that i am a string theorist, so loop quantum gravity is not my thing, but:
Loop quantum gravity has never been proven to predict the same things as ordinary general relativity to my knowledge. That is, the limit in which loop quantum gravity should reduce to general relativity is (in four dimensions) calculationally not under (analytic) control (read: some handwaiving is involved). That said, there is no fundamental reason loop quantum gravity shouldn't work....
While we are on the subject, there is one other way of doing 'quantum gravity' apart from loop quantum gravity and string theory: that is canonical quantum gravity. Here the philosophy is that the reason we cannot make sense of quantum gravity up to now is that we simply haven't found the right way to calculate (read 'regularize' for those in the know).One way of dealing with this problem is to brute force the problem: put it on a computer. This seems to work just fine (in three dimensions).
String theory: To Infinity And Beyond!