>> ^offsetSammy:

Here's something I have never understood about Feynman diagrams, and I hope someone can explain it to me.
A Feynman diagram represents one possible way that two particles can interact, and from a single diagram you can work out the probability of that event occuring. But wouldn't there be an infinite number of ways an interaction could play out, and therefore an infinite number of diagrams? How do you know which one to draw?


It depends exactly what you mean. For an electron-positron annihilation/scatter, there are a couple of basic diagrams as he showed in the film. These are called "second order diagrams", indicating that there are two vertices. You can add in extra loops and vertices in the middle of the diagram to create third, fourth etc. orders, but each one contributes a very quickly decreasing amount towards the whole picture. I'm no physicist, but I think after the fourth or fifth order they're pretty much just ignored.

If you mean there are an infinite number of "things that can happen" for each input, then no; it's very limited by the rules of the diagram (mostly based around conservation rules - charge, momentum etc.). Drawing out the diagram, twisting it around and swapping the joins and vertices is a very good way of determining what the possible outcomes are.

Your video, Quantum Field Theory Made Easy! - Feynman Diagrams, has made it into the Top 15 New Videos listing. Congratulations on your achievement. For your contribution you have been awarded 1 Power Point.

>> ^spawnflagger:

I like the concept, but I cannot upvote it, because it has BLEEP-ing nothing to do with mother-BLEEP-ing quantum mechanics. It charges via magnetic induction, and you need a special battery/adapter on the device to do the charging.
The question is - will you pay $$$ for the mat and adapters, just so you don't have to plug a charge cable in?
It might be popular in the future if it becomes an open standard and all cell phones/etc have the charging circuits built in.


Oh I dunno... I think you can call it quantum mechanics, just like you can say an auto accident killed someone because of quantum mechanics, pauli exclusion principle quantum field theories etc. You sure as hell could come up with a quantum description for the electromagnetic interactions here right?

Now you're being condescending. "It gets the information and knows to fall" is nonsensical handwavy shite that doesn't really explain anything to a layman.

>> ^Ornthoron:

>> ^budzos:
>> ^Peroxide:
"It" doesn't "get" any information...

I found this really damn irritating, too. Why must so many physics explanations ascribe will/consciousness to the objects in question? It comes off as condescending to me, like the physicist feels as though he's talking to a child.

Calm down, it's only a visualization technique. It's the way most physicists actually think about the problem too, even though the actual physical processes are far more complicated. The reason we do that is because it is easier, and it works.
Physics, with all the underlying jumping and jittering of atoms and molecules, is hard. Most physics phenomena are impossible to describe starting from the underlying quantum field theory. That's why we describe the world using other concepts such as temperature, pressure, and elasticity. They explain the world at higher level in the hierarchy, but that doesn't make them any less real. In the same vein, propagation of information is a useful concept for explaining many phenomena, but that doesn't mean we ascribe any consciousness to the object in question.

>> ^budzos:

>> ^Peroxide:
"It" doesn't "get" any information...

I found this really damn irritating, too. Why must so many physics explanations ascribe will/consciousness to the objects in question? It comes off as condescending to me, like the physicist feels as though he's talking to a child.


Calm down, it's only a visualization technique. It's the way most physicists actually think about the problem too, even though the actual physical processes are far more complicated. The reason we do that is because it is easier, and it works.

Physics, with all the underlying jumping and jittering of atoms and molecules, is hard. Most physics phenomena are impossible to describe starting from the underlying quantum field theory. That's why we describe the world using other concepts such as temperature, pressure, and elasticity. They explain the world at higher level in the hierarchy, but that doesn't make them any less real. In the same vein, propagation of information is a useful concept for explaining many phenomena, but that doesn't mean we ascribe any consciousness to the object in question.

Small google sample. That's just about changes during youth to old age.

Your ability to "grab" data becomes slower as you age. I was pondering aloud if it would cause a sense of "time going by faster" then when you compare your memory to the "time that went by" on a typical childhood day, etc...

My main wonderment is over the interface the body uses in particular to take input then decides what is a: not real, b: is real. I know most of that will be data comparison, I want to know what element of the mind was able to start that in the first place. I was wondering aloud if it might be humans' input interface is *very* hard-handed and exact, then compared to an Elephant's system? Could it be dreams? That was the only other question I was asking above. L0cky covered the rest.

I have also seen mental illness in my time. It has also given me extreme patience for anyone as I know reality is a troublesome thing. Our unique ability to communicate across that void is the biggest mystery to solve; to heal, to push innovation; and perhaps spread it one day (if we dare, or even think we should have that right). Besides a Unified Field Theory...

If someone knows anymore go at it. I just need links because I'll want to read it all.

>> ^MycroftHomlz:
next time you eat peanut M&Ms spin one like a top it should flip up so it spinning on its skinny axis... and there you have why I became a physicist. For years that boggled my mind and was a frequent party trick. I didn't solve it until my first year as a graduate student in Classical Mechanics.
Man I miss that professor. Half of me wishes I could get him to tape his lectures. They were so clear. Seriously, it was amazing. He could have taught a monkey quantum field theory. I had him as an undergrad and hated it. He made things so incredibly clear that they were boring.
It wasn't until I learned hard things that appreciated a teacher who explained things 3 different ways and only focused on a couple topics.


SO? Tell us why it works!

next time you eat peanut M&Ms spin one like a top it should flip up so it spinning on its skinny axis... and there you have why I became a physicist. For years that boggled my mind and was a frequent party trick. I didn't solve it until my first year as a graduate student in Classical Mechanics.

Man I miss that professor. Half of me wishes I could get him to tape his lectures. They were so clear. Seriously, it was amazing. He could have taught a monkey quantum field theory. I had him as an undergrad and hated it. He made things so incredibly clear that they were boring.

It wasn't until I learned hard things that appreciated a teacher who explained things 3 different ways and only focused on a couple topics.

The Dirac equation is a pretty incredible step in physics. Dirac made a huge leap from standard quantum mechanics to modern day field theory.

Dirac tried to rectify quantum mechanics with relativity and in the process proved that negative energy - i.e. antiparticles - had to exist. But there was still a major problem. The Dirac Equation didn't take into account electrodynamics. A great question here is how can macroscopic electrodynamic fields be justified for point particles like fermions and bosons... The answer is that the are understood as spin, torque, and charge. QED was the next big step. But it all started with the elegant and simple dirac equation.

Let us put in a correct perspective quantum string theory for TOE. Firstly it is important to remark that a full understanding of what is really Quantum Mechanics is far to be completely understood in its foundational aspects ,althougth its huge operational-quantitative success.For instance, even in the usual non relativistic quantum mechanics , certainly the notion of electronic orbitals in N-electron atomic physics appears to be a mathematical suitable approximation for the full N-electron atomic wave function.On the other hand in Quantum Field Theory , this ad-hoc choice of what is free and what is interaction is not so "ad-hoc", at least in the QFT (perturbative) scattering sector: free in and out fields are primary objects producing physically observables free N-particles (lorentz invariant!) wave functions-so perturbation is building around them and carrying with the formalism all notions of renormalizations , dispersions relations etc.. .Now quantum strings : Strings are supossedly observable for us mainly through scattering among its excitations by means of an already fixed sigma-model two-dimensional quantum dynamics taking place in the somewhat ficticious purely two dimensional string parameter space-time, where are operating two scales of interaction : one is entirely ruled by the intrinsic string topological genera and other governed by the extrinsic space-time coupling constant , namely : The Regge Slope parameter. So string theory for TOE is a proposal for pure S-Matrix "Heisenbergnian" on-shell "theory" for all particles scattering in Nature (including gravitons). Now the theory's "granus salis" (points not completely grasped-at least for this reader !): Back ground fields are fixed extrinsic classical field configurations fully determined by the imposition of conformal invariance for any genera (which certainly does not affects the intrinsic 2d UV-theories'behavior,but affects its IR intrinsic behavior as a 2d QFT) and at any order in the Regge Slope coupling (all these conformal invariance phenomena quite specific to Polyakov's action proposal , possibly not for a Nambu-Goto string action reformulation of TOE).And at the same time , they are expected to be Schwinger sources (even quite non linear) for the string excitations and to be functionally differentiated in the string path-integral later .Another point is related to Kaluza-Klein Theories -It appears that quantum geometrical theories appear to be trivial QFT theories when used to describe scattering in space-time extrinsic manifolds of higher dimensionality (lambda four scalar QFT is expected to be trivial for D strictly greater than four!). As a conclusion : at most Strings are useful theoretical labs for a fully understanding of what really is Quantum Mechanics (SchrodingerX HeisenbergXEinsteinXNelson) , if there are no experimental tests for its predictions .By the way,space-time supersymmetry still remains solely as a theoretical lab in Particle Physics, nothing more!.

Well , it appears to me that string theory is a interesting attempt to "quantize" the space-time manifold (added with suitable supersymmetric structures ).Everything in higher dimensions become reduced to two-dimensional quantum field path integral models "living"on the string chart manifold (the intrinsic two-dimensional "string space-time").However , people impose dipheomorffism invariance on this intrinsic string parameter "space-time" which unfortunatelly get mixed with 2D conformal invariance , when one uses the sigma model Polyakov' action to assign "energy" for these "quantum -fluctuating extrinsic /observable higher dimension space-time process (quite different from the more geometrical Nambu-Goto string action ).In order to solve this problem one thus impose full sigma model conformal invariance by restricting that all strings Schwinger sources (the string higher dimensional field back grounds-including the own extrinsic space time manifold dimension!)to lead to a vanishing beta function for the sigma model Polyakov action at any perturbative order of the new universal coupling constant-the String length scale/Regge parameter.This produces an apparently well defined (?,and about the infrared 2D cut-off remotion on the perturbative Feynman calculationson the intrinsic string space-time ?) 2D Field theory for the extrinsic space-time quantum energy action, besides of fixing the string Schwinger sources to satisfy the usual Einstein-Maxwell-etc field equations at one loop and the extrinsic space-time dimension and the classical manifold topology of the extrinsic space-time to be fixed, when one has supersymmetry (Spin manifold space time structures,etc..).At this point , one has an apparently well defined quantum -mechanical framework to evaluate numerically scattering amplitudes (including quantum gravity!-the old dream ) to compare with the experimental results.That is the problem on this new quantum-mechanical framework : as far as I know nothing has been matched with the usual qed,qcd,etc results!(anomalous particle magnetic momentum, deduction of the asymptotic freedom in QCD ,The Higgs mechanism on the weak sector ,etc.

>> ^MycroftHomlz:
>> ^charliem:
<insert mammoth rebuke here>


Foot-in-mouth syndrome n)
Characterized by incoherent rambling and spewing of thought stream without regards to the contents of the message.

By "they", I was referring to scientists working purely for exploration research purposes. None of those achievements could be possible without a basic understanding of the underlying principles of how the laws of physics, which govern their operation, work.

They didn't start out with an idea to create an imaging machine without a foundation of understanding field theory, maxwells equations, EM theory etc.

Somewhere down the line, it had taken an exploratory researcher the time and grant money to figure out those basic laws. Without which, we wouldn't have anywhere near the amount of amazing tech available to us today.

Any argument that says "bah, its only theoretical, it cant benefit us at all" and uses it as an excuse to cut/reduce funding, needs their heads examined.

What exactly is your beef with quantum field theory?

Initially, I had a similar reaction as Bidouleroux to how the question was framed - too many open variables to assess the situation. But I think that's part of it. There's always going to be unknown factors. Who knows - the fat guy could be the key to a lasting peace settlement between Palestinians and Jews, or maybe has the solution for a true Unified Field Theory. That's the point - you can't know these things in advance.

Ultimately, I agree with Kuga. It's homicide in both cases - someone dies as a direct result of your actions. It's kind of like the difference between strangling someone vs. shooting them (killing with your hands vs. pulling a lever). The question for me comes down to your personal belief structure. Most people will apply the "utilitarian" approach, i.e., saving the lives of 4 people is better than causing the death of 1. But again, most people can only take that so far, and struggle with becoming more "directly" involved.

(side note - I put this in the science channel because I was under the impression that the study used fmri to show the areas of the brain active in answering each situation (cingulate cortex?). This may not be the case. I'm still looking for references to this, but if anyone feels this doesn't belong in science in the mean time, go ahead and knock it out.)

The most significant thing about this theory is that it makes predictions. Several of these predictions will be experimentally tested next year at the large hardron collider.

When I first saw this in Focus magazine a few weeks ago, it struck me that it is in fact a periodic table of the quantum world, and this is exactly how Lisi describes it. It has already predicted quantum particles with properies which have later been found, just as the periodic table did. It also neatly ties them all up together, along with all the interactions and force carrying particles.

The fact that it is consistent with existing quantum field theory and the standard quantum model - is exactly the point of a unified theory. Any candidate for a unified field theory must be consistent with both special relativity and the quantum standard model.